UNITED STATES BUREAU OF MINES

UNITED STATES DEPARTMENT OF THE INTERIOR

RI 9573 REPORT OF INVESTIGATIONS/1995

Transport of Total Tailings Paste Backfill:

Results of Full-Scale Pipe Test Loop

Pumping Tests

By C. C. Clark, J. D. Vickery, and R. R. Backer
U.S. Department of the Interior

Mission Statement

As the Nation’s principal conservation agency, the Department of the

Interior has responsibility for most of our nationally-owned public

lands and natural resources. This includes fostering sound use of our

land and water resources; protecting our fish, wildlife, and biological

diversity; preserving the environmental and cultural values of our

national parks and historical places; and providing for the enjoyment

of life through outdoor recreation. The Department assesses our

energy and mineral resources and works to ensure that their

development is in the best interests of all our people by encouraging

stewardship and citizen participation in their care. The Department

also has a major responsibility for American Indian reservation

communities and for people who live in island territories under U.S.

administration.

Cover: Total Tailings paste backfill full-scale pipe test loop.
Report of Investigations 9573

Transport of Total Tailings Paste Backfill:

Results of Full-Scale Pipe Test Loop

Pumping Tests

By C. C. Clark, J. D. Vickery, and R. R. Backer 

UNITED STATES DEPARTMENT OF THE INTERIOR

Bruce Babbitt, Secretary

BUREAU OF MINES

Rhea Lydia Graham, Director
International Standard Serial Number

ISSN 1066-5552
CONTENTS

Page

Abstract ...................................................................................... 1

Introduction .................................................................................... 2

Engineered support ............................................................................. 2

Waste reduction ............................................................................... 3

Use of paste backfill ............................................................................ 3

Paste backfill transport tests ......................................................................... 3

Pipe test loop ................................................................................. 3

Test mixes ................................................................................... 3

Pumping tests ................................................................................ 3

Paste backfill ................................................................................... 8

Slump ...................................................................................... 8

Slurry concentration ............................................................................ 9

Particle size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Addition of cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Pipe diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Flow rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Vertical flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Appendix A.—Pipe test loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Appendix B.—Material properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Appendix C.—Terms and equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

ILLUSTRATIONS

1. Particle-size distribution of uncemented and cemented total tailings ........................................ 4

2. Strength of coarse and fine cemented total tailings ..................................................... 5

3. Pipe test loop configuration and pressure monitoring locations ............................................ 6

4. Pressure gradients for uncemented and cemented total tailings paste backfill .................................. 8

5. Summary of test results for total tailings paste backfill .................................................. 9

6. Pressure gradients for total tailings paste backfill at different slumps ........................................ 9

7. Slurry concentrations for coarse and fine total tailings paste backfill at different slumps . . . . . . . . . . . . . . . . . . . . . . . . . . 11

8. Consistency of total tailings paste backfill at different slumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

9. Volume relationships for coarse and fine total tailings at different slumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

10. Pressure gradients for coarse and fine total tailings paste backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

11. Decrease in slump over time for cemented total tailings paste backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

12. Pressure gradients for uncemented and cemented coarse total tailings paste backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

13. Pressure gradients for uncemented and cemented fine total tailings paste backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

14. Transport distance for total tailings paste backfill through pipelines of different diameters . . . . . . . . . . . . . . . . . . . . . . . . 15

15. Pressure gradients through pipelines of different diameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

16. Pressure gradients for total tailings paste backfill through horizontal and vertical 154-mm-diam pipe . . . . . . . . . . . . . . . . . 16

17. Transport distance for total tailings paste backfill at different column heights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

18. System pressure and transport distance for total tailings paste backfill at different column heights . . . . . . . . . . . . . . . . . . . 17

A-1. Flow rates for total tailings paste backfill at different slurry concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

A-2. Flow velocities of water through different pipe diameters at different flow rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

A-3. Positive-displacement pump mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

A-4. Electronic pressure transducer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

A-5. Data from strip chart recorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

A-6. Conveyor system used to load dry total tailings into ready-mix truck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

A-7. Transferring total tailings paste backfill from ready-mix truck to pump hopper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
ii

ILLUSTRATIONS

C-1. Horizontal and vertical flow paths and pressure gradients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

TABLES

1. Paste backfill mixes ........................................................................... 4

2. Comparison of test results for total tailings paste backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

A-1. Flow rates of total tailings paste backfill at different slurry concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

A-2. Velocity through different pipe diameters at different flow rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

A-3. Equipment list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

A-4. Description of monitoring system on pipe test loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

B-1. Particle-size distribution of cemented and uncemented total tailings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

B-2. Volume relationships of total tailings paste backfill at different slumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

B-3. Average unconfined compressive strength of total tailings paste backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

B-4. Slurry concentration of total tailings paste backfill at different slumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

C-1. Water content of bunker-stored tailings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

C-2. Weight-volume data for total tailings paste backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

C-3. Results of pumping tests with horizontal sections only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

C-4. Results of pumping tests using 154-mm-diam pipe with vertical and horizontal sections . . . . . . . . . . . . . . . . . . . . . . . . . . 31

C-5. Combined test results for total tailings paste backfill at flow rate of 29 m /h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3

C-6. Pressure gradients for water and mix 6 at various pipe diameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

C-7. Transport distance of total tailings paste backfill through 154-mm-diam pipe at different column heights at flow

rate of 29 m /h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3

C-8. System pressure of total tailings paste backfill through different pipe diameters at different columnheights at flow 

rate of 29 m /h, mix 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

Metric Units

cm centimeter m /h cubic meter per hour 3

deg degree m /min cubic meter per minute 3

g gram min minute

h hour mm millimeter

kg kilogram m/m meter per meter

kg/m kilogram per cubic meter MPa megapascal 3

km kilometer m/s meter per second

kPa kilopascal m/s meter per second squared 2

kPa/m kilopascal per meter pct percent

kW kilowatt t metric ton

L liter t/d metric ton per day

m meter t/h metric ton per hour

m cubic meter EC degree Celsius 3

U.S. Customary Units

ft foot lbf pound of force

ft cubic foot lb/ft pound per cubic foot 3 3

ft foot to the 4th power mi mile 4

ft /min cubic foot per minute psi pound per square inch 3

ft/s foot per second psi/ft pound per square inch per foot

gal gallon st short ton

hp horsepower yd cubic yard 3

in inch yd /h cubic yard per hour 3

lb pound EF degree Fahrenheit

Reference to specific products does not imply endorsement by the U.S. Bureau of Mines.
Mechanical engineer, Spokane Research Center, U.S. Bureau of Mines, Spokane, WA. 1

Mining engineer, Kennecott Mining Co., Salt Lake City, UT. 2

Supervisory mining engineer, Spokane Research Center, U.S. Bureau of Mines, Spokane, WA. 3

TRANSPORT OF TOTAL TAILINGS PASTE BACKFILL: RESULTS

 OF FULL-SCALE PIPE TEST LOOP PUMPING TESTS

By C. C. Clark, J. D. Vickery, and R. R. Backer 1 2 3

ABSTRACT

This report presents the results of tests conducted by the U.S. Bureau of Mines to determine the transport

characteristics of highly concentrated paste backfill mixes made from dewatered total mine tailings. The slurry

concentrations of the mixes were all above 78 pct by weight with slumps ranging from 6.4 to 16.5 cm (2.5 to 6.5

in). Laboratory material property tests and full-scale pumping tests were conducted using pipe diameters of 102,

128, and 154 mm (4, 5, and 6 in) and a positive-displacement pump. The results indicated that the tested backfill

mixes can be successfully transported as a stiff paste and identified the influence of and the interaction among the

various mix and system variables.
2

INTRODUCTION

ENGINEERED SUPPORT factors limit the structural strength that can be obtained at low

The U.S. Bureau of Mines (USBM) has been active in mine content and void ratio (Landriault, 1987). There are also

waste management research for over 25 years. The goal of this additional costs associated with pumping excess water to the

research is to ensure that mine wastes are disposed of in a safe and surface; maintaining clogged bulkheads, ditches, and sumps; and

environmentally benign manner. As part of its program in mine repairing wear on pump components caused by the flushed

waste disposal technology, the USBM initiated projects to cement.

investigate the transport characteristics of high-concentration paste In recent years, low-water-content, high-concentration paste

backfill formulated from total tailings. The results are described backfills have been developed to reduce the problems associated

in this Report of Investigations (RI). with high-water-content slurry backfills. This type of fill

Many of the underground mines in the United States contain provides better support and a safer working environment than

ore pillars that have been, and are being, left in place for mine does slurry sandfill because the excess water is eliminated, which

stability. The use of engineered backfill having predictable allows greater strengths to be achieved and minimizes

structural properties may allow these valuable pillars to be maintenance costs (Brackebusch, 1992).

recovered. Among the reported advantages of backfilling The term "paste" refers to a class of backfills that have low

mined-out areas with engineered fill are the cost-effective use of water contents; high densities (>75 pct by weight); and

mine waste, provision of uniform structural support, consistency, transport, and deposition properties different from

improvements in overall air quality, reductions in ventilation and those of traditional low-concentration slurries or other types of

refrigeration costs, and increased flexibility in mining technique high-concentration backfill (Aref and others, 1992; Putzmeister

because mining can take place above or below the fill (Cuerten, Thomsen, 1987, 1989a, 1989b; Verkerk and Marcus, 1988).

1983; DeJongh and Morris, 1988; McKinstry and Laukkanen, Paste backfill has a homogenous appearance and a consistency

1989; Udd, 1989). that produces a measurable slump. The grain-size distribution of

Underground mining methods that incorporate backfill as a the backfill is such that, when placed, the fill is free standing and

primary support system are common in other parts of the world. the contained water does not tend to be released. When tranMany of these mines use an engineered sandfill. While aiding in sported through pipes, no minimum carrying velocity is required,

the support of mine structures, this type of fill requires special and uncemented pastes can generally be remobilized if left

processing, transport, and placement techniques (Crandall, 1993; stationary for many hours. The pressure gradients developed

Kramers and others, 1989; Nicholson and Wayment, 1964). The when high-concentration paste is transported are greater than

sandfill is composed of partially classified tailings and water with those for low-concentration slurries.

added cement and is transported through boreholes and steel The material used to make a paste fill is usually waste products

pipes using centrifugal pumps or gravity flow at slurry from milling. Portland cement and other cementatious materials

concentrations up to 75 pct by weight. are commonly added to the backfill to increase support potential

While simplifying transport, the use of large amounts of water (Barrett, 1973; Thomas, 1973; Weaver and Luka, 1970). The

causes many problems. The fill must be dewatered after it is advantages of using this type of fill are that it allows complete

placed so it will consolidate, a process which causes entrained fine filling of stopes to the back, significantly increases strength gain

material (fines) and cement to be flushed out along with the large rates for cemented fills, reduces void ratios in placed fills, lowers 4

volumes of excess water. This reduces the strength of the placed cement requirements for a given strength, and reduces the amount

fill and deposits fines and cement in the lower workings, creating of fine material requiring surface disposal (Aref and Hassani,

hazards for workers and increasing the need for maintenance of 1987; Robinsky, 1975; Verkerk and Marcus, 1988). Mining

workings and equipment. These firms in South Africa, Germany, and Canada (Lerche and

The terms coarse and fine are arbitrary and relative to the tailings grinds 4

being compared. The percentage of material passing screen sizes of 0.074,

0.044, and 0.020 mm (0.0029, 0.0017, and 0.00146 in) is also used as a

reference point, because materials of these sizes are missing from traditional

classified sand-type tailings (Boldt and others, 1989; Brackebusch, 1992;

Lidkea and Landriault, 1993; Vickery and Boldt, 1989). Material of minus

0.074 mm (200 mesh) is referred to as fines; material of minus 0.044 mm (325

mesh) is referred to as slimes.

costs, since load- bearing capacity of the fill depends on cement

5

Renetzeder, 1984; Landriault and Goard, 1987; Verkerk, 1983)

have reported success in developing new methods to batch,

transport, and place paste backfill.

Slump is a measure of the drop in height a material undergoes when it is 5

released from a cone-shaped slip mold. It is more fully described in the section

"Slump."
3

WASTE REDUCTION from that ore. This puts greater demands on a mine's tailings

The disposal of mill tailings has become a significant concentration slurry backfill.

economic factor in domestic mine operations. Traditionally, the The result is that more attention is being paid to the

method of disposal was by impounding the waste material on the development and use of highly concentrated paste backfill as a

surface. Dams were constructed out of the coarse sand fraction of mine support system. This type of backfill is formulated from

the mill tailings, and the fines were discharged behind the dams. dewatered total tailings.

Operating costs were low (Soderberg and Busch, 1977). Such The technology for transporting engineered highimpoundments were not only unsightly, but recent evaluations concentration paste backfill made from tailings, additives, and

have indicated that many such structures could be unsafe during water is just emerging in the United States (Boldt and others,

periods of heavy rain or during high winds, thus creating 1989; Brackebusch, 1992; Crandall, 1993; Putzmeister Thomsen,

environmental and safety hazards as well as aesthetic liabilities to 1989b; Vickery and Boldt, 1989). A principal requirement in

society (Khuntia and Pradhan, 1987; Vick, 1983). As a designing a pipeline delivery system is determining the transport,

consequence, strict state and federal regulations now govern the or flow, properties of the material. These transport properties are

construction and abandonment of tailings impoundments. The a function of mix composition and system variables, some of

expense associated with compliance, in the form of permitting, which are relatively fixed because of the quantity of backfill

construction of subsurface drainage systems and elaborate needed and the desired load-bearing characteristics of the placed

spillways, dust control, monitoring equipment, water treatment, fill. It is, therefore, of great importance to be able to optimize

etc., has had a major effect on the average cost of waste disposal flow conditions when given a particular set of variables (Gilchrist,

using impoundments (Sauermann, 1983; Verkerk and Marcus, 1988). This task is made difficult because of the wide variability

1988). in materials that can be used and the effect on transportability this

USE OF PASTE BACKFILL achieve the desired goals. The development of techniques for

Economic demands are forcing mines to recover as much ore particular paste backfill will change when mix and system

as possible from underground workings. At the same time, mill variables are altered is needed if this technology is to be used by

operators are producing more finely ground tailings U.S. mining firms.

in an effort to extract greater percentages of minerals

disposal system and leaves less coarse sand available for low6

variability produces. Thus, significant effort is required to

logically determining how the transport characteristics of a

PASTE BACKFILL TRANSPORT TESTS

PIPE TEST LOOP concentrations from 81 to 78 pct by weight. Two different mill

A fully instrumented pipe test loop (PTL) was constructed by coarse tailings and two using fine tailings. Descriptions of the

personnel at the USBM's Spokane Research Center (SRC) to tailings and physical property tests are found in appendix B.

determine the transport characteristics of high-concentration paste Tailings concentrations were varied from 94 to 100 pct of the

backfill. The PTL is an instrumented, closed-circuit pipeline solids weight. Cement was added in concentrations of 4 and

system powered by a diesel engine positive-displacement pump. 6 pct of the tailings weight. Strength tests on similar backfill

The design and operation of the PTL are described in detail in mixes formulated from coarse and fine total tailings, cement, and

appendix A. Test loops of this type provide essential engineering water indicated that 28-day unconfined compressive strengths

data (flow rate, pressure loss per unit length of pipe, shutdown between 379 and 868 kPa (55 and 126 psi) can be obtained with

and restart capabilities, and power consumption) needed to design these cement concentrations (figure 2) (Boldt and others, 1989,

full-scale pipelines. The USBM's PTL measures the gauge p. 13).

pressure associated with the flow of material through the pipeline

at distinct points along its length. PUMPING TESTS

TEST MIXES Pumping tests were conducted on the six backfill mixes using

Six high-concentration paste backfill mixes were developed

and batched (table 1). The slump of the mixes was varied from

11.4 to 17.8 cm (4.5 to 7 in) with corresponding slurry

grinds (figure 1) were used: four mixes were batched using

the PTL. Mixes 1 and 5 were tested using a 62-kW

Total tailings include the full range of particle sizes from tailings produced 6

by a mill, typically from 0.001 to 0.6 mm (0.00004 to 0.024 in).
4

Figure 1

Table 1.—Paste backfill mixes1

Mix Tailings Cement Cr Gs Slump, cm

Ct St Gt Cc Sc pct Gc w/c Beg. End2 Diff.

Coarse tailings:

 1 . . . . . . . . . . . . . . . . . . . . . . . . . . 80 100 2.8 0 0 0 3.15 0 81.3 2.06 11.4 NC NC

 2 . . . . . . . . . . . . . . . . . . . . . . . . . . 80 100 2.8 0 0 0 3.15 0 80.7 2.06 16.5 NC NC

 3 . . . . . . . . . . . . . . . . . . . . . . . . . . 77 96 2.8 3.2 3.8 4 3.15 6 79.6 2.06 17.8 15.4 -2.4

 4 . . . . . . . . . . . . . . . . . . . . . . . . . . 75 94 2.8 4.8 5.7 6 3.15 4 79.5 2.07 17.1 12.7 -4.4

Fine tailings:

 5 . . . . . . . . . . . . . . . . . . . . . . . . . . 80 100 2.7 0 0 0 3.15 0 79.6 2.01 11.4 NC NC

 6 . . . . . . . . . . . . . . . . . . . . . . . . . . 75 94 2.7 4.8 5.7 6 3.15 4 78.1 2.03 11.4 6.4 -5.0

C Concentration of tailings as a perc Concentration of solids as a entage of total slurry weight. C percentage of total slurry weight. t r

S Concentration of tailings as a percentage of dry solids weight. G Specific gravity of slurry. t s

G Specific gravity of tailings. w/c Water-cement ratio. t

C Concentration of cement as a percentage of total slurry weight. Beg. Beginning. c

S Concentration of cement as a percentage of dry solids weight. Diff. Difference. c

G Specific gravity of cement. NC No change. c

Initial mix batching was to 20 pct water, after which water was added to adjust mix to indicated slump. 1

Slump was changed to these values by end of pumping test. 2
5

 Figure 2

Particle-size distribution of uncemented and cemented total tailings.

(83-hp) pump and the pipe loop configuration shown in fig- (240-hp) unit for the remaining tests. Mixes 2 and 6 were tested

ure 3. Because of difficulties in obtaining sufficient pressure, the using the pipe loop shown in figure 3C, while mixes 3 and 4

first pump was replaced with a more powerful 180-kW were tested using the pipe loop shown in figure 3D.

 Strength of course and fine cemented total tailings.
6

Figure 3

Pipe test loop configurations and pressure monitoring locations. A, Mix 5; and B, mix 1.
7

Figure 3-Continued

Pipe test loop configuration and pressure monitoring locations. C, mixes 2 and 6; D, mixes 3 and 4.
8

Figure 4

PASTE BACKFILL

Pressure gradient was calculated to determine the transport

characteristics resulting from different combinations of mix

and system variables. The influence of each variable on

transportability was determined by comparing the difference

in pressure gradient among mixes that shared similar

characteristics. Pressure gradient determines the system operating

pressure required for pump specification and provides a good

indication of how easily material will flow through pipes. The

pressure gradient as a function of flow rate for each combination

of mix and pipe size tested is shown in figure 4. A composite of

the test results is shown in figure 5. The terms and equations

used to reduce the pressure gradient data are described in

appendix C.

SLUMP

Slump is a measure of the drop in height a material undergoes

when it is released from a cone-shaped slip mold. Determination

of slump provides a way of characterizing a material's consistency

that can be related to transportability. Although pastes batched

from dissimilar materials at the same slump will not flow in the

same manner, comparisons can be made between mixes batched

from similar materials at different slumps. A low-slump mix will

flow less easily than a high-slump mix even if both are batched

from the same material. A comparison of the pumping test results

for mix 1 and mix 2 (figure 6) shows a substantial difference in

pressure gradient associated with the 5-cm (2-in) change in slump.

For a flow rate of approximately 25 m /h (32 yd /h), the pressure 3 3

gradient changes from 28 to 6 kPa/m7 (1.2 to 0.3 psi/ft). This

corresponds to a 78-pct decrease in pressure gradient for a

 5-cm (2-in) increase in slump.

The effect on transportability produced by changes in mix

variables can be determined by noting changes in slump.

Changes in a specific mix will be manifested as changes in

pressure gradient. This leads to the question as to whether the

transportability of an untested mix can be determined from the

material properties of its constituents and its slump without

actually subjecting it to a pumping test. In short, if pressure

gradient data produced from pumping tests exist for a particular

mix, can the transportability of another untested mix be

determined by comparing its proportion of these variables with

the tested mix. The mixes are compared factor to factor in table

2. Note that in all cases, the mix with the smaller slump has Pressure gradients for uncemented and cemented total

tailings paste backfill. A, 102-mm-diam pipe; B, 128-mmdiam pipe; C, 154-mm-diam pipe.
9

Figure 5

Figure 6

Summary of test results for total tailings paste backfill at flow rate of 25 m /h through 154-mm-diam pipe. 3

a greater pressure gradient—this is the most significant result of

the investigation.7

SLURRY CONCENTRATION

Slurry concentration is the ratio of the weight of the solids in

a mix to the weight of the total mix (water and solids). Slurry

concentration is often used to compare the composition of mixes,

particularly when batching. Although slurry concentration does

not provide a direct indication of a material's consistency, in some

cases it can be correlated to slump, which does.

Although the following method was not used, it represents one of the most 7

practical means of achieving the same mix consistency from batch to batch.

Consistency can be measured by monitoring the electrical power used by a

motor turning the paddles of a mixer. Batching is accomplished by carefully

weighing the dry mix constituents into a container. The mixer is started and

water is added until the power required by the motor corresponds to the target

power for the mix consistency desired (Brackebusch, 1992; Lidkea and

Landriault, 1993). Using this arrangement requires only that slump be correlated to consistency and consistency be correlated to power. It is also possible

to predict what pressure gradient a mix will produce based on power once a correlation has been established between slump and pressure loss (figure 5). Pressure gradients for total tailings paste backfill at diferent

slumps through 154-mm-diam pipe.
10

Table 2.—Comparison of test results for total tailings paste backfill1

Variable First mix Second mix Difference

COMPARISON 1

Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 2-1 

Tailings grind ........................ Coarse Coarse NAp 

Slump, cm .......................... 11.4 <16.5 5.1 

Slurry concentration ................... 81.3 >80.5 -0.8 

d , mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 0.109 0.109 0 

dP/dL, kPa/m ........................ 28.1 >6.1 -22.0 

COMPARISON 2 

Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 4-2 

Tailings grind ........................ Coarse Coarse NAp 

Slump, cm .......................... 16.5 >12.7 -3.8 

Slurry concentration ................... 80.5 >80.4 -0.1 

d , mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 0.109 >0.100 -0.009 

dP/dL, kPa/m ........................ 6.1 <23.4 17.3 

COMPARISON 3 

Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6 6-5 

Tailings grind ........................ Fine Fine NAp 

Slump, cm .......................... 11.4 >6.4 -5.0 

Slurry concentration ................... 79.2 <79.5 0.3 

d , mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 0.055 >0.049 -0.006 

dP/dL, kPa/m ........................ 15.3 <18.0 2.71 

COMPARISON 4 

Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 4-1 

Tailings grind ........................ Coarse Coarse NAp 

Slump, cm .......................... 11.4 <12.7 1.3 

Slurry concentration ................... 81.3 >80.4 -0.9 

d , mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 0.109 >0.100 -0.009 

dP/dL, kPa/m ........................ 28.1 >23.4 -4.7 

COMPARISON 5

Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 3-2 

Tailings grind ........................ Coarse Coarse NAp 

Slump, cm .......................... 16.5 >15.4 -1.1 

Slurry concentration ................... 80.5 >80.0 -0.5 

d , mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 0.109 >0.103 -0.006 

dP/dL, kPa/m ........................ 6.1 <11.3 5.2 

COMPARISON 6 

Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4 4-3 

Tailings grind ........................ Coarse Coarse NAp 

Slump, cm .......................... 15.4 >12.7 -2.7 

Slurry concentration ................... 80.0 <80.4 -0.4 

d , mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 0.103 >0.100 -0.003 

dP/dL, kPa/m ........................ 11.3 <23.4 12.1 

COMPARISON 7 

Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 3-1 

Tailings grind ........................ Coarse Coarse NAp 

Slump, cm .......................... 11.4 <15.4 4.0 

Slurry concentration ................... 81.3 >80.0 -1.3 

d , mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 0.109 >0.103 -0.006 

dP/dL, kPa/m ........................ 28.1 >11.3 -16.8 

COMPARISON 8

Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 5-1 

Tailings grind ........................ Coarse Fine NAp 

Slump, cm .......................... 11.4 11.4 0 

Slurry concentration ................... 81.3 >79.2 -2.1 

d , mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 0.1 >0.055 -0.054 

dP/dL, kPa/m ........................ 28.1 >15.3 -12.9 

 dP/dL Pressure gradient.

 NAp Not applicable.

 Flow rate for all comparisons was 25 m /h through 154-mm-diam pipe. 1 3
11

 Note.—Bolded numbers indicate the most significant factor for determining which mix will have a

greater pressure gradient.
12

Figure 7

Figure 8

In these tests, slurry concentration was correlated to slump using with a repeatable consistency and, therefore, consistent transport

a series of mixes in which water was added in small increments. characteristics from batch to batch. When batching by weight, it

Slumps corresponding to the slurry concentrations were plotted was impossible to control slurry concentration within ±1 pct. For

on a graph to produce relational curves in which slump decreased these reasons, mixing by slurry concentration is not

as slurry concentration increased (figure 7). It should be noted recommended.

that since the specific gravity of a material contributes to slurry

concentration, pastes with identical particle-size distributions but

different specific gravities will have different slurry concentrations

at the same slump.

It was difficult to correlate slump with a particular slurry

concentration because large changes in slump (consistency)

corresponded to very minor changes in slurry concentration (in

the range of 78 to 81 pct by weight). A comparison of mix 3 at

slurry concentrations of approximately 79 and 81 pct by weight

(figure 8) shows a large difference in slump, from 27 to 13 cm

(10.5 to 5 in). Obviously, at these two slurry concentrations, this

mix has different transport properties. A comparison of mix 1

and mix 2 (table 2) shows that slumps for these two mixes correspond to slurry densities of 81.3 and 80.5 pct by weight,

respectively, which represents a 45-pct increase in slump for a 1-

pct decrease in slurry concentration. This characteristic made

trying to correlate slurry concentration to pressure gradient

impossible. For example, comparing pressure gradients for mix

1 and mix 2 with changes in slurry concentration shows a 78-pct

reduction in pressure gradient for a 1-pct decrease in slurry

concentration.

Using slurry concentration as a basis for mixing a batch was

also very difficult in terms of producing a material

Slurry concentrations for coarse and fine total tailings paste

backfill at different slumps.

PARTICLE SIZE

The particle-size distribution curve shows the range of particle

sizes present in a tailings sample and the type of

Consistency of total tailings paste backfill at different slumps.

A, 27-cm slump; B, 13-cm slump.
13

Figure 9

Figure 10

distribution of these particles. The diameter corresponding to 50 pumps for pumping high-pressure, high-slump mixes is not

pct (d ), finer by weight, in the particle-size distribution curve recommended. 50

(figure 1) was used to identify differences among the tailings A comparison of the pumping test results for these mixes

used. D is often used to characterize the particle-size distribution through 154-mm (6-in) diam pipe (figure 10) shows that 50

of tailings grinds and, as such, provides a reference point for although the mixes were batched to the same slump,

comparing tailings (Sauermann, 1982; Verkerk and Marcus,

1988). The two tailings used in this investigation have a d of 50

0.109 (coarse tailings) and 0.055 mm (fine tailings) (140 and 270

mesh).

The relative proportions of fines and slimes present in the

mixes have a significant influence on consistency. A threshold

amount of fines and slimes, i.e., an amount that exceeds the pore

volume of the large-sized particles, is required to present enough

wetted surface area to trap the mix water in the paste matrix and

prevent segregation of the particles and release of water, known

as bleeding. It has been suggested that 15 pct, finer by weight,

minus 0.020-mm (0.00079-in) material is sufficient to prevent

bleeding (Brackebusch, 1992; Lidkea and Landriault, 1993). If

sufficient amounts of fines and slimes are not present in the

material, then water is released and a "sand-pack" forms in the

pipeline if mix transport is stopped and restarted.

If there is an excess of fines and slimes in the mix in relation

to the amount of water, then the increased wetted area presented

by the fines and slimes leaves less free water, which then causes

the formation of a more dense carrying medium with a higher

resistance to flow (Verkerk and Marcus, 1988, p. 232).

A comparison of the grain-size distribution for mix 1 and mix

5 (table 2) shows that while the mixes were batched to the same

slump, differences in d particle size were substantial, i.e., 50

diameters of 0.109 and 0.055 mm (140 and 270 mesh),

respectively. The fine tailings [minus 0.074 mm (200 mesh) and

minus 0.044 mm (325 mesh)], finer by weight, particle-size

fractions are also greater than those of the coarse tailings. Because

the finer material contains more particles per unit volume, there

is more surface area to come into contact with water.

Comparisons of void ratio, porosity, and degree of saturation

of the coarse and fine tailings mixes also show differences in

surface area available for wetting. Fine tailings have a higher

void ratio and porosity at nearly the same degree of saturation as

coarse tailings. Thus, more water is required to wet the finer

tailings, resulting in lower slurry concentrations for a given slump

(figure 9). The degree of saturation indicates how much air is entrained in the mixes of lower slump. The air makes the mixes

slightly compressible, which tends to dampen pressure surges

(pressure surges are a consequence of the design of the positivedisplacement pump). These surges were observed during

pumping because the high-slump pastes caused tremendous

hammering and resultant pressure spikes in the pipeline when the

positive- displacement pump was used. Because of this, the use

of twin-cylinder positive-displacement 

Volume relationships for ciarse and fine total tailings at

different slumps.

Pressure gradients for coarse and fine total tailings paste

backfill through 154-mm-diam pipe.
14

Figure 11

there was a substantial difference in pressure gradient between the A comparison of the reduction in slump over time for the mixes

two mixes, even though the pressure gradients were very similar (figure 11) shows that the decrease in slump was related to the

in slope and the relative difference in pressure gradient was initial slump of the mix and the concentration of cement. Degree

constant. For a flow rate of approximately 25 m /h (33 yd /h), of agitation also influenced decreases in slump, but for the mixes 3 3

the pressure gradient changed from 28 to 15 kPa/m (1.2 to 0.7 tested, this variable was constant from mix to mix. Although

psi/ft). This corresponded to a 46-pct reduction in pressure slump can easily be increased by adding water, this practice is

gradient as a result of reducing the d by half (figure 5). In terms counterproductive to achieving high strengths with minimum 50

of fines and slimes, a 46-pct reduction in pressure gradient results cement consumption. Adding water can easily result in a mix in

from increasing the quantity of minus 0.074-mm (200 mesh) which the water-cement ratio is higher than optimal for strength.

material by 19 pct, finer by weight, and the quantity of minus In these mixes, the cement becomes overhydrated, and cured

0.044-mm (325 mesh) material by 20 pct (figure 1). strengths can be quite low for a given cement content.

During pumping tests, the mix material was observed to form The reduction in slump for cemented mixes is driven by the

a plug as it was discharged from the PTL into the pump inlet reaction between water and portland cement in the mix. When

hopper. Inspection of the cross section of this plug revealed that water is added to dry cement, an immediate and rapid reaction

fines and slimes in the mix had migrated toward the periphery of takes place, resulting in the formation of a supersaturated gel.

the plug during transport and had formed a thin layer of material The reaction then slows and a film of gel-like, microcrystalline

at the interface between the pipe annulus and the plug. This layer calcium sulphoaluminate forms around the cement particles. This

of fine material appeared to lubricate the plug and could be is followed by a period of slow reactions during which the

responsible for the 50-pct reduction in pressure gradient. This amount of hydration products gradually builds up, forming loose

phenomenon depended on there being a sufficient quantity of bonds and slowly increasing the viscosity of the mix until there

water in the mix to allow the fines and slimes to flow between the is a definite yield stress (a minimum shearing stress required to

grains of the large-sized particles (Aref and others, 1992, pp. produce flow) (Lea, 1971, pp. 256-365).

272-273; Crandall, 1993, pp. 1776-1777). The increase in viscosity results in a lower slump and,

The finer material was more transportable at a given slump. consequently, a higher pressure gradient. A comparison between

A comparison of the d lines for the mixes tested (figure 5) the pressure gradients for the uncemented and cemented coarse 50

indicates that when well-graded total tailings mixes were batched and fine tailings mixes shows the effect

by slump, the general trend was one of increasing pressure

gradient with increasing d [the orientation of the lines was 50

estimated using the two 0.109-mm (0.0043-in) data points for

mixes 1 and 4].

ADDITION OF CEMENT

Cement addition or cement content is expressed as a

percentage of tailings weight, as a percentage of solids weight, as

a percentage of total slurry weight, or as a ratio of the weight of

the water to the weight of the cement. In this investigation,

cement was added as a percentage of tailings weight. The other

expressions for cement content are included in table 1 for

comparison. 

The Type I-II portland cement used had a d diameter of 50

0.023 mm (minus 400 mesh) (figure 1). Although the particle

size of this material is smaller in diameter than tailings particles,

for the concentrations used to batch the mixes (4 and 6 pct of the

tailings weight), the particle-size distribution was changed only

slightly, as the percentage of fines and slimes increased and d50

decreased.

The slump of the cemented mixes decreased over the 3-h time

required to complete the pumping tests (table 1).

Decrease in slump over time for cemented total tailings paste

backfill. Straight lines connecting data points were drawn

for clarity and do not represent data points.
15

Figure 12

Figure 13

of this viscosity increase (figures 12 and 13). The differences in slump developed previously is still valid. Note that un-cemented

increases of pressure gradients for mixes 2, 3, and 4 and mixes 5 mix 1 has a higher pressure gradient (and lower slump) than any

and 6 would suggest that incremental additions of cement were of the cemented mixes, which confirms that pressure gradient

responsible. However, if the slump of the mixes at the time of increases as slump decreases regardless of the presence of cement.

testing is used as a basis for determining pressure gradient, the The development of yield stress within the cemented mixes

relationship between pressure gradient and also influences transportability. When the bonds between the mix

instead, flow properties can be determined using uncemented

Pressure gradients for uncemented and cemented coarse total

tailings paste backfill through 154-mm-diam pipe.

Pressure gradients for uncemented and cemented fine total

tailings paste backfill through 154-mm-diam pipe.

particles are strong enough to hold the mix together, but not

strong enough to withstand small shearing forces, the paste

exhibits a shear thinning behavior by becoming more fluid once

mobilized. Shear thinning also implies that the structure of the

paste recovers to its initial state if left standing, but considering

the hydration process, this is not possible because as time passes,

the material becomes stiffer and requires more pressure to

overcome the yield stress and initiate flow.

Because adding cement can cause slump to decrease with time

and leads to the formation of yield stress within the mix, it may

be necessary to batch the mix to the slump required at the time of

transport and placement and to ensure that the batching and filling

cycle be completed within a time frame dictated by the formation

of structures within the material. If these time elements are

known, then the transport characteristics of cemented mixes are

the same as those for uncemented mixes with respect to slump,

slurry concentration, and particle size.

These findings have important implications with respect to

system design and testing, because the correlation between cement

addition, decrease in slump over time, and formation of yield

stress over time can be established in a laboratory. It becomes

unnecessary to test cemented mixes to obtain flow properties;

mixes with the proper slump applied. This not only reduces the

amount of material necessary for testing (because the material can

be used over and over again), but also eliminates disposal,

cleanup, and machinery maintenance problems associated with

cemented mixes.

PIPE DIAMETER

A comparison of pressure gradients through pipes of different

diameters shows that increasing the pipe diameter can

significantly lower pressure gradient for a given flow rate. Note

as well that pressure gradients in different pipe diameters do not

change linearly; that is, the rate of increase in pressure gradient as

flow rate increases is greater in a 102-mm (4-in) pipe than in a

154-mm (6-in) pipe. A comparison of the maximum transport

distances for the 102-, 128-, and 154-mm (4-, 5-, and 6-in) diam

pipelines (figure 14) [using a pump outlet pressure of 6.9 MPa

(1,000 psi)] and the pressure gradients obtained for mixes 2, 3, 4,

and 6 [mixes 1 and 5 were only tested in the 154-mm (6-in) diam

pipeline] shows
16

Figure 14

Transport distance for total tailings paste backfill through

pipelines of different diameters. Initial system pressure is 6.9

Mpa. A, 102-mm-diam pipe; B, 128-mm-diam pipe; C, 154-

mm-diam pipe.

this relationship. Mix 2 had the lowest pressure gradient; a flow

rate of 25 m /h (33 yd ) through the 102-mm (4-in) diam line 3 3

produced a maximum delivery distance of 476 m (1,567 ft). By

increasing the line diameter to 154 mm (6 in), this distance

increased to 1,141 m (3,743 ft).

FLOW RATE

A comparison of pressure gradient test results shows that

pressure gradient increased with increasing flow rate for all the

mixes tested. The rate of increase was greatest for flow rates

below 15 to 20 m /h (20 to 26 yd /h), then became less as flow 3 3

rate increased (figure 4). This pseudoplastic behavior is an

important characteristic because it indicates that the flow rate of

high-concentration paste mixes can be varied considerably

without dramatically altering the pressure gradient. A comparison

between pressure gradients for mix 6, a cemented total tailings

paste backfill, and water at 25 EC (77 EF) though standard steel

pipe (figure 15) can be used to generalize the marked contrast

between this type of material and high-water-content, lowconcentration slurries that behave like water. At low flow rates,

the pressure gradient for water is also low. As flow rates increase,

the rate of increase accelerates.

The noted pseudoplasticity of pastes in the tests could be

partially explained by the possibility that the pump cylinders were

not filling completely at higher pumping rates. If the cylinders

are not completely filled, there will not necessarily be air

entrained in the mix. A vacuum would be pulled when filling the

piston, and the vacuum would collapse under positive pressure.

Changes in flow rate had the greatest influence on pressure

gradient when flow rates were below 30 m /h (39 yd /h). The 3 3

practical limit of flow rate for the mixes tested was a function of

pressure gradients for the individual mixes and the line diameter.

The maximum transport distance obtained, 1,257 m (4,124 ft),

was for mix 2 through the 154-mm (6-in) diam pipeline at a flow

rate of 12 m /h (16 yd /h). 3 3

VERTICAL FLOW

A comparison of pumping test results (figure 16) shows that

the net pressure gradient in the combined vertical section of pipe

(up plus down) was approximately equal to the pressure gradient

in the horizontal section. Thus, other than the force of gravity, no

additional forces were introduced in the vertical section. The

pressure gradient decreased by an amount equal to the force of

gravity exerted on the paste when the material was transported

vertically downward. The gravity component of the pressure

gradient was calculated to be between 20.1 and 20.6 kPa/m (0.88

and 0.91 psi/ft) depending on the unit
17

Figure 15 Figure 16

Pressure gradients through pipelines of different diameters.

A, Water; B, mix 6.

weight of the mix. The frictional component of the pressure

gradient for each mix remained the same regardless of the

orientation of the pipe.

The significance of this finding is that, by using gravity to

reduce the net pressure gradient for vertical flow, it becomes

possible to deliver material horizontally with only the pressure

generated by the standing column of material in the vertical

section of the pipeline. The pressure gradients shown in figure 16

can be used to illustrate this concept.

In this figure, the line represents a pressure gradient of 1 m of

slurry per 1 m of pipe. Pressure gradients below the line indicate

that the mix will flow under its own weight; thus, the pressure

generated by the standing column of material would be sufficient

to deliver the material. Pressure gradients above the line indicate

that the mix would have to be pumped. The

Pressure gradients for total tailings paste backfill through

horizontal and vertical 154-mm-diam pipe. A, Mix 3; B, mix

4.

intercept of the line and the pressure gradients indicates the

maximum flow rate that can be obtained by freefall in a vertical

pipe.

Because the pressure at the base of the standing column of

material available for transport is a function of the pressure

imparted by gravity and the pressure lost through functional

pressure gradient, it is possible to alter the distance the material

can be transported horizontally by making changes either in the

height of the standing column or in the diameter of the pipe. In

figure 17, there is a tremendous difference in transport distance

among the mixes at different column heights. Figure 18 shows

pressure at the bottom of the standing column as a function

of column height through different pipe diameters for mix 2.

Note that a column height of 485 m (1,591 ft) in a 154-mm
18

Figure 17 Figure 18

Transport distance for total tailings paste backfill at different

column heights through 154-mm-diam pipe at flow rate of

25 m /h. 3

(6-in) diam pipe can produce the same amount of pressure [6.9

MPa (1,000 psi)] used in the previous examples for pump output 1993, p. 1775; Lidkea and Landriault, 1993, pp. 337-347), there

pressure. The 128- and 102-mm (4- and 5-in) diam pipes require are several aspects unique to the type of system discussed here.

column heights of 1,110 and 5,700 m (3,642 and 18,700 ft), (1) Care must be exercised in situations where the physical

respectively, to produce the same pressure. Since the gravity geometry of the mechanical system would allow the transported

pressure for a given column height is the same regardless of pipe material to accelerate, which can occur when the line is first filled.

diameter, the frictional difference between pipe diameters In this situation, the impact on a pipe elbow at the bottom of the

produces drastic differences in maximum transport distance. pipeline can be destructive. Such an impact can be alleviated by

Using 300 m (984 ft) as the column height, the maximum trans- first filling the line with a less-dense material, such as water, and

port distances for the 102- and 128-mm then pushing the water out of the line with the transported

(4- and 5-in) diam pipes are 19 and 133 m (62 and 436 ft), material. (2) If the feed to the vertical portion is intermittent, it is

respectively. By increasing the pipe diameter to 154 mm (6 in), necessary to vent the top of the pipe to prevent generating a

a transport distance of 710 m (2,329 ft) is attainable. vacuum. The falling plug will actually be slowed and cushioned

Although the use of a vertical column to provide system by the air trapped beneath it.

pressure is well documented (Brackebusch, 1992; Crandall,

System pressure and transport distance for total tailings paste

backfill at different column heights at flow rate of

25 m /h, mix 2. 3

CONCLUSIONS

This investigation has focused on identifying the interaction variables on pressure gradient are examined, a consistent

among mix and system variables and the transportability of relationship does emerge: That changes in mix variables affect

highly concentrated paste backfill. When pipe diameter, flow slump and slump can be related to pressure gradient (figure 5).

rate, and pipeline orientation are changed, the effects on Thus, by examining slump, it is possible to determine the gross

transportability are predictable. The same cannot be said when impact on pressure gradient that will be produced by changes in

changes are made in slurry concentration, particle size, and mix variables.

cement content. If the cumulative effects of all these
19

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Brackebusch, F. W. Basics of Paste Backfill Systems. Paper in En- Eng., Cranfield, Bedford, Engl., Paper E1, 1982, pp. 241-248.

vironmental Issues and Management of Waste in Energy and Mineral Soderberg, R. L., and R. A. Busch. Design Guide for Metal and Nonmetal

Production. Proceedings of Second International Conference, ed. by R. K. Tailings Disposal. USBM IC 8755, 1977, 136 pp.

Singhal, A. K. Mehrotra, K. Fytas, and J. L. Collins (Calgary, AB, Sept. 1-4, Thomas, E. G. A Review of Cementing Agents for Hydraulic Fill. Paper

1992). Balkema, 1992, v. 2, pp. 879-883. in Proceedings of the Jubilee Symposium on Mine Filling. Australas. Inst. Min.

Crandall, W. E. Backfilling Methods. Ch. 19.3 in Underground Mining Metall., Aug. 1973, pp. 65-75.

Methods Handbook. SME, 1993, pp. 1756-1778. Udd, J. E. Backfill Research in Canadian Mines. Paper in Innovations in

Cuerten, H. J. Pneumatic and Hydromechanical Techniques in the Gold and Mining Backfill Technology: Proceedings of the 4th International Symposium

Coal Industries in South Africa. Bulk Solids Handling, v. 3, No. 1, Mar. 1983, on Mining with Backfill, ed. by F. P. Hassani, M. J. Scoble, and T. R. Yu

pp. 105-112. (Montreal, PQ, Oct. 2-5, 1989). Balkema, 1989, pp. 3-13.

DeJongh, C. L., and A. N. Morris. Considerations in the Design and Verkerk, C. G. The Current Status of Hydraulic Backfill Techniques in

Operation of Backfill Systems for Narrow Tabular Orebodies. Paper in Backfill South Africa. Bulk Solids Handling, v. 3, No. 1, Mar., 1983, pp. 93-94.

in South African Mines. S. Afr. Inst. Min. Metall., Johannesburg, S. Afr., Spec. Verkerk, C. G. and R. D. Marcus. The Pumping Characteristics and

Pub. Ser. SP2, 1988, pp. 355-368. Rheology of Paste Fills. Paper in Backfill in South African Mines. S. Afr. Inst.

Gilchrist, I. C. R. Predicting the Values of Flow Parameters for the Design Min. Metall., Johannesburg, S. Afr., Spec. Pub. Ser. SP2, 1988, pp. 221-233.

of Pipelines Conveying Backfill Slurries. Paper in Backfill in South African Vick, S. G. Planning, Design, and Analysis of Tailings Dams. Wiley &

Mines. S. Afr. Inst. Min. Metall., Johannesburg, S. Afr., Spec. Pub. Ser. SP2, Sons, 1983, 369 pp.

1988, pp. 235-261. Vickery, J. D., and C. M. K. Boldt. Total Tailings Backfill Properties and

Glover, T. J. Pocket Reference. Sequoia Publ., Morrison, CO, 1992, pp. Pumping. Paper in Innovations in Mining Backfill Technology: Proceedings of

389-396. the 4th International Symposium on Mining with Backfill, ed. by F. P. Hassani,

Khuntia, G. S., and G. K. Pradhan. Tailings Disposal Systems Adopted in M. J. Scoble, and T. R. Yu (Montreal, PQ, Oct. 2-5, 1989). Balkema, 1989, pp.

Iron Ore Mines an Indian Overview. Bulk Solids Handling, v. 7, No. 4, Aug. 369-377.

1987, pp. 553-558. Victaulic Co. of America (Easton, PA). Victaulic Mechanical Piping

Kramers, C. P., P. M. Russell, and I. Billingsley. Hydraulic Transport of Systems. G-100E 1/83, 1981, 64 pp.

High Concentration Backfill. Paper in Innovations in Mining Backfill Weaver, W. S., and R. Luka. Laboratory Studies of Cement- Stabilized

Technology: Proceedings of the 4th International Symposium on Mining with Mine Tailings. Paper in Research and Mining Applications in Cement Stabilized

Backfill, ed. by F. P. Hassani, M. J. Scoble, and T. R. Yu (Montreal, PQ, Oct. Backfill (Proc., 72nd Ann. Gen. Meet., Toronto, ON, Apr. 1970). Can. Inst.

2-5, 1989). Balkema, 1989, pp. 387-394. Min. Metall., 1970, pp. 988-1001.

Landriault, D. Preparation and Placement of High Concentration Backfill.

Ch. in Underground Support Systems, ed. by J. E. Udd. CIM Spec. Vol. 35,

1987, pp. 99-103.

Landriault, D., and B. Goard. Research into High Density Backfill

Placement Methods by the Ontario Division of Inco Limited. CIM Bull., v. 80,

No. 897, Jan. 1987, pp. 46-50.

Lea, F. M. The Chemistry of Cement and Concrete. Chemical Publ., 1971,

700 pp.

Lerche, R., and H. Renetzeder. The Development of "Pumped Fill" at

Grund Mine. Paper pres. at Hydrotransport 9, 9th Int. Conf. on Hydraulic Trans.

of Solids in Pipes, (Rome, Italy, Oct. 17-19, 1984), 24 pp.; available from C.

Clark, Spokane Res. Cent., USBM, Spokane, WA.

Lidkea, W., and D. Landriault. Tests on Paste Fill at INCO. Paper in

Minefill 93, ed. by H. W. Glen (Johannesburg, S. Afr., Sept. 1993). S. Afr. Inst.
20

APPENDIX A.—PIPE TEST LOOP

DESIGN (65 yd /h) and a maximum pressure of 4,826 kPa (700 psi). The

The choice of materials and equipment used to construct the 0.18 by 1 m (7 by 39 in) bore-and-stroke cylinders and pistons,

PTL was based on what would typically be available to a and an S-shaped swing-tube valve. Flow rate was controlled by

commercial mining operation (Crandall, 1993; Lerche and varying the cycling speed of the pump. A continuous flow of

Renetzeder, 1984; Putzmeister-Thomsen, 1987, 1989a, 1989b). material through the delivery line was produced by sequencing

The system was designed on the premise that a mine would need the operation of the pump's two pistons with the swing tube. The

to fill a 300-m (392-yd ) void with dry solids within 7 h of an 8- swing tube allowed one cylinder to be open to the hopper on 3 3

h shift. Assuming slurry concentrations could vary from 75 to 85 the suction stroke while the other cylinder discharged material

pct by weight and the specific gravity of the solids could vary through the swing tube outlet. At the end of piston travel, the

from 1.9 to 2.2, approximately 50 to 57 m /h (65 to 75 yd /h) of direction changed and the swing-tube shifted to discharge material 3 3

slurry would have to be transported and placed per shift (table A- from the second cylinder (figure A-3) (Putzmeister-Thomsen,

1; figure A-1). Since paste backfill does not require a critical 1987, 1989b).

carrying velocity to remain in suspension, the velocity in the After two pump tests were completed, it was determined that

system pipeline was minimized to less than 2 m/s (6.6 ft/s) to the power output of the pump could not meet the desired pipe

reduce wear. The relationship between flow rate and velocity for loop flow rate requirements, and the pump was replaced with a

selected standard steel pipe diameters is given in table A-2 and more powerful one. Although similar in design to the first pump,

shown in figure A-2. Pipes with diameters of 102, 128, and 154 the second pump was powered by a 180-kW (240-hp) diesel

mm (4, 5, and 6 in) were selected on the basis of satisfactory engine. This pump had a maximum output of 74 m /h (97 yd /h)

combinations of adequate flow rate and low velocity. A list of and a maximum pressure of 8,687 kPa (1,260 psi). The pump

the equipment used to construct the PTL is given in table A-3. consisted of a 0.40-m (0.52-yd ) receiving hopper, two 0.18 by

PUMP SELECTION elephant-trunk-shaped swing-tube valve.

A trailer-mounted, positive-displacement concrete pump was PIPE SYSTEM

used to pump the paste backfill mixture through the pipe loop

circuit. The first pump used was powered by a 62-kW (83-hp) The pipe loop used to test mix 5 consisted of 129 m (423 ft)

diesel engine with a maximum output of 50 m /h of 154-mm (6-in) diam pipe arranged in a horizontal loop, 3

3

pump consisted of a 0.40-m (0.52-yd ) receiving hopper, two 3 3

3 3

3 3

2.1 m (7 by 83 in) bore-and-stroke cylinders and pistons, and an

Table A-1.—Flow rates of total tailings paste backfill at different slurry concentrations 

Slurry Solids Slurry

concentration, h h Specific m3 m /3 t/h t/d Specific m3 m /3 t/h

pct gravity gravity

75 . . . . . . . . . . . . . . . . . . . . . . 2.7 300 43 116 810 1.89 400 57 108

85 . . . . . . . . . . . . . . . . . . . . . . 2.8 300 43 120 840 2.20 353 50 111

Table A-2.—Velocity through different pipe diameters at different flow

rates, meters per second

Flow rate, Pipe diameter, mm

m /h3

102 128 154 

50 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.70 1.08 0.75

51 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.73 1.10 0.76

52 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.77 1.12 0.78

53 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.80 1.14 0.79

54 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.84 1.17 0.81

55 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.87 1.19 0.82

56 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.90 1.21 0.84

57 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.94 1.23 0.85

58 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.97 1.25 0.86

59 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.01 1.27 0.88

60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.04 1.30 0.89
21

Table A-3.—Equipment list

Item Manufacturer Model Specifications

Concrete pump:

Thompson ......... TTS 2065 Trailer-mounted, positive-displacement pump powered by

62-kW (83-hp) diesel engine with a maximum output of

50 m /h (65 yd /h) and a maximum pressure of 4,826 kPa 3 3

(700 psi). Pump consists of 0.40-m (0.52-yd ) receiving 3 3

hopper, two 0.18 × 1 m (7 × 39 in) bore and stroke cylinders

and pistons, and S-shaped swing-tube valve.

Putzmeister ........ 2100S Trailer-mounted, positive-displacement pump powered by 

180-kW (240-hp) diesel engine with a maximum output

of 74 m /h (97 yd /h) and a maximum pressure of 8,687 kPa 3 3

(1,260 psi). Pump consists of 0.40-m (0.52-yd ) receiving 3 3

hopper, two 0.18 × 2.1 m (7 × 83 in) bore and stroke cylinders and pistons, and elephant-trunk-shaped swing-tube

valve.

Pipeline:

 Sections . . . . . . . . . . . . . . . NA . . . . . . . . . . . . . . . . Schedule 40 ASTM A-53 standard steel pipe.

 Couplings .............. Victaulic ........... Style 77 Grooved end.

 Elbows ................ Victaulic ........... Style 100 Grooved end, long radius, each elbow has 3-m (10-ft) 

straight pipe equivalent length. 1

Recorder ................ Chessell . . . . . . . . . . . 320 Six-channel strip chart.

Pressure transmitter:

 Mix 1 .................. Bailey ............. KA14111-10k 0-4.13 MPa (0-600 psi), locations 1, 2.

 Mix 2 .................. Bristol-Babcock ..... 2408-15B-621-110 0-5.17 MPa (0-750 psi), locations 3, 4.

Bristol-Babcock ..... 2408-15B-621-110 0-4.13 MPa (0-600 psi), locations 5, 6.

Bailey ............. KA14111-10k 0-6.89 MPa (0-1,000 psi), location 7.

Bailey ............. KA14111-10k 0-1.17 MPa (0-200 psi), location 9.

 Mix 3, 4 ................ Bailey ............. KA14111-10k 0-5.17 MPa (0-750 psi), locations 3, 4.

Bristol-Babcock ..... 2408-10B-611 0-4.13 MPa (0-600 psi), locations 5, 6.

Bristol-Babcock ..... 2408-10B-711 0-6.89 MPa (0-1,000 psi), location 7.

Bailey ............. KA12111-10k 0-1.17 MPa (0-200 psi), location 8.

Bristol-Babcock ..... 2408-10B-711 0-6.89 MPa (0-1000 psi), location 9.

 Mix 5 .................. Bailey ............. KA14111-10k 0-4.13 MPa (0-600 psi), locations 1, 2.

Bailey ............. KA121111-10k 0-1.38 MPa (0-200 psi), location 3.

 Mix 6 .................. Bristol-Babcock ..... 2408-15B-621-110 0-5.17 MPa (0-750 psi), location 3.

Bristol-Babcock ..... 2408-15B-621-110 0-4.11 MPa (0-600 psi), location 4.

Bristol-Babcock ..... 2408-10B-611 0-3.45 MPa (0-500 psi), location 5.

Bristol-Babcock ..... 2408-15B-621-110 0-1.38 MPa (0-200 psi), location 6.

Pressure sensor, mixes 1-6 Hildebrandt . . . . . . . . . J-4 Diaphram seal, locations-all.

1, pp. 19-22. Victaulic, 198 1

as shown in figure 3A. To test mix 1, the pipe loop length was the line and cause extremely high wear. That is, a leak permits

increased to 148 m (486 ft) (figure 3B). To test mixes 6 and 2, fines and water to pass through the mix matrix, abrading the area

the pipe loop length was reduced to 118 m (387 ft), and 102- and around the leak and leaving a coarse sand pack in the pipe.

128-mm (4- and 5-in) diam sections were added (figure 3C). To

test mixes 4 and 3, the pipe loop length was increased to 172 m MONITORING SYSTEM

(564 ft); the loop was changed by adding a 20-m (66-ft) vertical

section with 7-m (20-ft) horizontal legs of 154-mm (6-in) diam The performance of the pipe test loop was monitored using

pipe to the existing 118 m (387 ft) of horizontal loop (figure 3D). two six-channel strip chart recorders. The chart recorder allowed

This section was installed to evaluate the vertical flow the operator to determine visually when steady-state conditions

characteristics of the mixes. A lateral pipe with removable cap were achieved after changing test parameters. Visual inspection

was installed near the pump discharge point. This pipe was used was necessary because line pressures fluctuated very rapidly as a

to introduce water and air into the loop. function of the twin-cylinder pump and were very difficult to

All of the test loop configurations were fabricated using 6-m capture with point readings unless the sampling rate was

(20-ft) lengths of grooved-end, standard steel pipe. The pipes extremely high. And, if the sampling rate were increased, the

were connected with grooved-end couplings and elbows with large amount of data generated would make it extremely difficult

long radii (Victaulic, 1981). The pipe sections were assembled todistinguish changes in system performance as a test was being

with tight connections to prevent line leaks, which can block r u n . S t r i p c h a r t recorders
22

Figure A-1 Figure A-2

Figure A-3

Flow rates for total tailings paste backfill at different slurry

concentrations assuming placement of dry solids at 43 m3/h. Flow velocities of water through different pipe diameters at

different flow rates.

Positive-displacement pump mechanism.
23

Figure A-4

Table A-4.—Description of monitoring system on pipe test loop

Mix1 Length

of pipe loop,2

m

Location of

transducers

(figure 3)

Distance between transducers, m

Additions

5 . . . 129 1, 2 55 None.

2, 3 56 None.

1 . . . 148 1, 2 64 None.

6 . . . 118 3, 4 15 128-mm section.

5, 6 15 102-mm section.

8, 9 12 Three elbows.3

2 . . . 118 3, 4 15 128-mm section.

5, 6 15 102-mm section.

7, 9 42 Three elbows.4

3 . . 172 3, 4 15 128-mm section.

5, 6 15 102-mm section.

7, 8 42 154-mm-diam,

 20-m-long ver-

 tical section;

 one elbow.5

4 . . . 172 8, 9 53 154-mm-diam,

 20-m-long ver-

 tical section;

 four elbows.6

 in order tested. Mixes are listed 1

 All original pipe was 154 mm in diameter. 2

 Each elbow had a length equivalent to a 3-m-long straight section, for 3

an adjusted length of 21 m between transducer locations 8 and 9.

 The adjusted length between transducer locations 7 and 9 was 51 m. 4

 The adjusted length between transducer locations 7 and 8 was 45 m. 5

 The adjusted length between transducer locations 8 and 9 was 65 m. 6

were selected because they permit continuous real-time inspection

of system performance, which is not possible with point-reading

collection systems.

Pipeline gauge pressure was measured using electronic

pressure transducers. The transducers were composed of pressure

transmitters mounted to large oil-filled diaphragm seals of the

type pictured in figure A-4. Figure A-5A shows a continuous

pressure trace taken by the strip chart recorder. An analysis of a

typical pressure pulse is shown in figure A-5B. Pressures were

determined by taking the average peak pressure for each

transducer. The cycling rate of the pump was determined by

counting the spikes in the pressure readout from the strip chart.

Table A-4 describes the monitoring system setup on the pipe

test loop for each mix tested.

Electronic pressure transducer. cement was added in an amount equal to a percentage ofthe

ADDITIONAL EQUIPMENT

Additional equipment for conducting the pumping tests

included various drain and discharge valves; several 208-L (55-

gal) barrels; a small 0.20-m (0.25-yd ) capacity front-end loader; 3 3

a 1.5-t (1.65-st) capacity forklift with a barrel attachment; a 0-to816-kg (0- to 1,800-lb) floor scale; a 25-m /h (33-yd /h) capacity 3 3

loading conveyor; a 7.1-m / -min (250-ft /min), 827-kPa (120- 3 3

psi) air compressor; and a 7-m3

(9-yd ), high-discharge, ready-mix truck. 3

TEST PROCEDURE

The PTL required between 3 and 4 m (4 and 5 yd ) of paste 3 3

mix for each pumping test. A ready-mix concrete truck was

rented to mix and transport the paste mixes. Each test was started

by filling the barrels with tailings using a small front-end loader.

These barrels were then weighed. The water content of the

bunker-stored tailings was used to determine the weight of the

tailings. The tailings were transferred from the barrels to the

loading conveyor with a forklift and loaded onto the concrete

truck (figure A-6). Commercially available Type I-II portland

tailings weight and mixed in for several
24

Figure A-5

Data from strip chart recorder. A, Continuous pressure trace; B, analysis of pressure pulse.

minutes. Tap water was added until the mixture reached the pipe loop was clear of debris, and it provided a lubricating film

target slump. The mixture was transported to the pumping to prevent the test material from drying out when the pipe loop

facility 16 km (10 mi) away. was loaded.

Before the truck arrived at the pumping facility, the pipe loop Once the truck arrived at the pump site, the mix slump was

was filled with water, which was circulated through the loop for rechecked and adjusted by adding water until it reached the target

several minutes. A foam-rubber plug was inserted into the loop consistency. This was necessary for all mixes because the slump

through the lateral pipe, and the compressor was connected to the would decrease during transport, which probably indicated that

cap using a 31.75-mm (1.25-in) diam air line with quick-connect relatively dry tailings require a significant amount of time and

end fittings. A three-way valve allowed water to be diverted from agitation to become completely saturated. The transfer of the mix

the main pipeline through an inclined pipe. Compressed air was to the pump hopper was then begun (figure A-7). After the

used to force the plug and water around the test loop and push the pump hopper was nearly filled with mix, the pump was started,

water out the line and onto the ground. This water-flushing mix was replenished using the truck discharge chute until the

served several purposes: it served as a check for mechanical PTL was full, and paste was discharged on the return of the loop

problems, it ensured that the i n t o t h e h o p p e r .
25

Figure A-6 Figure A-7

Conveyor system used to load dry total tailings into ready-mix

truck.

The progress of the test material through the loop was monitored main pipeline through an inclined pipe and back into the readyby tapping the pipe with a hammer and noting the sound. mix truck to be transported back to SRC for disposal or reuse.

Blockages in the pipe could also be detected using this technique. The uncemented tailings were mixed with a larger quantity of

The pump was run for several minutes to be certain that the paste unused material and reused on later tests of cemented tailings.

was homogeneous. Large fluctuations in peak line pressure Particle-size degradation was investigated and determined to be

served as a good indicator that the paste was not of consistent insignificant with the tailings used for testing. A foam-rubber ball

thickness throughout the pipeline. was then inserted into the line through the lateral pipe.

The transport tests consisted of pumping the mixes through Compressed air was introduced to force the ball around the test

the pipe loop at six flow rates while collecting pressure data from loop and push the paste out the discharge section into the readythe transducers. Data were collected for 10 to 15 min at each mix truck. This process was repeated several times. Then, two

flow rate to ensure that line pressures had stabilized. balls with approximately 0.25 m (1 ft) of water trapped between

The pipeline was emptied and cleaned at the end of each test. them were inserted into the line and circulated to clean out the test

A three-way valve was used to divert material from the loop.

Transferring total tailings paste backfill from ready-mix truck

to pump hopper.
26

Table B-1.—Particle-size distribution of cemented

and uncemented total tailings

Particle size, pct,

Constituent Cement, d , 50 finer by weight

 pct mm 0.074

 mm

 0.044

 mm

Coarse tailings:

 Lower limit of U.S.

 metal mine tailings. NAp 0.117 38 24

Mix 1, 2 .............

0

0.109 38 26

Mix 3 ...............

4

0.103 40.2 28.2

Mix 4 ...............

6

0.100 41.3 29.2

Fine tailings: 

 Upper limit of U.S.

 metal mine tailings. NAp 0.028 81 65

Mix 5 ...............

0

0.055 57 46

Mix 6 ...............

6

0.049 59.2 48

Portland cement,

 Type I-II. 0.024 94 80

NAp Not applicable.

Table B-2.—Volume relationships of total tailings paste

backfill at different slumps

Volume relation, cm Void ratio Porosity Degree of

saturation

Mix 1, coarse tailings:

 5.1 . . . . . . . . . . . . . . . . . . . . 0.682 0.406 0.849

 8 ...................... 0.703 0.413 0.883

 13 . . . . . . . . . . . . . . . . . . . . . 0.723 0.420 0.919

 20.3 ................... 0.739 0.425 0.958

Mix 5, fine tailings:

 5.1 . . . . . . . . . . . . . . . . . . . . 0.740 0.425 0.850

 7.3 . . . . . . . . . . . . . . . . . . . . 0.756 0.431 0.884

 9.5 . . . . . . . . . . . . . . . . . . . . 0.767 0.434 0.900

 14.6 ................... 0.772 0.436 0.922

 15.2 ................... 0.793 0.442 0.927

APPENDIX B.—MATERIAL PROPERTIES

DESCRIPTION OF TAILINGS strength values used to establish initial mix cement concentraThe tailings used in the investigation were obtained from two prepared 76.2- by 154-mm (3- by 6.06-in) samples of the same

underground metal mines with different mill grinds. The coarser tailings material (table B-3; figure 2).

tailings came from a silver mine and the finer tailings came from

a copper-silver mine (figure 1). Bulk samples of the coarser

tailings were obtained directly from the mine's batch plant storage

facility, loaded into a dump truck, and transported to the USBM

laboratory at SRC. These tailings had been slightly classified by

the mine as part of its backfilling operation to facilitate handling

by conventional means.

Bulk samples of the finer tailings (unclassified) were collected

directly from the mine's tailings pond delivery line as a 40-pct-byweight slurry. The barrels were then sealed and transported to

SRC, where they were deposited in individual bunkers. In the

bunkers, the tailings were spread and periodically mixed and

respread to aid drying until they reached an as-stored moisture

content of approximately 8.5 pct. These tailings were then used

in the investigation.

PHYSICAL PROPERTY TESTS

Laboratory tests were conducted to determine the physical

properties of the tailings and backfill mixes. Particle- size

analyses were performed on the tailings according to American

Society for Testing Materials (ASTM) standard D422-63 (1991b)

using dry U.S. standard sieves for the particles above 0.074 mm

(200 mesh). The minus 0.074 mm (minus 200 mesh) fraction

was tested with a particle-size analyzer that operated on the

principle of Stokes' law and utilized X-ray absorption.

The data from the particle-size analyses (table B-1) were

combined with published data on particle sizes for cement and

other tailings and plotted. Figure 1 and table B-1 show the

particle-size distribution curves for the tailings, cement, and mix

combinations. The particle-size distribution shows that these

tailings fall within the range of grain sizes for most domestic

metal mine tailings (Vick, 1983). Weight-volume relationships

were also determined for the uncemented coarse and fine total

tailings and water at different slumps (table B-2; figure 9). The

fine tailings have greater void ratios and porosities than the coarse

tailings at nearly the same degree of saturation.

The particle-size distribution curve for Type I-II portland

cement shows that the cement is considerably finer (d = 0.024 50

mm) than either of the tailings. This is consistent with most

present-day Type I-II portland cements, which average around 95

pct, finer by weight, than 0.088 mm (170 mesh) (Lea, 1971, p. The specific gravity of the tailings ranged from 2.7 to 2.8

372). The effect of adding cement to either fine or coarse tailings (table 1). These values are typical for domestic metal mine

is to decrease the d particle size. The 50 compressive tailings (Vick, 1983). The specific gravity of the cement used

tions were obtained from published results of tests on laboratorywas 3.15 (Glover, 1992). The calculated specific gravity for the

coarse tailings mixes ranged from 2.06 to 2.07 and for the fine

tailings paste backfill mixes from 2.01 to 2.03.
27

Table B-3.—Average unconfined compressive

strength of total tailings paste

backfill, kilopascals

Compressive

Cement, pct Slump, strength, kPa

cm 7 day 28 day

Coarse tailings:

 4 . . . . . . . . . . . . . 19 496 586

 6 . . . . . . . . . . . . . 16 572 868

Fine tailings:

 4 . . . . . . . . . . . . . 18 269 379

 6 . . . . . . . . . . . . . 18 434 689

Table B-4.—Slurry concentration of total tailings paste

backfill at different slumps, percent

Mix Cement, Slump, cm

 pct 5 8 11 14 17 20 

Coarse tailings:

 1, 2 . . . . . . . . 0 83.0 82.0 81.4 80.9 80.4 80.0

 3 .......... 4 82.8 81.8 80.9 80.3 79.7 79.2

 4 .......... 6 82.2 81.4 80.7 80.2 79.6 79.0

Fine tailings:

 5 .......... 0 80.9 79.9 79.2 78.8 78.3 77.8

 6 .......... 6 80.2 78.8 78.1 77.5 77.0 76.0

Slump was determined according to ASTM standard

C143-90a (1991a) using a 31.75-cm (12.5-in) slump cone tester.

The relationship between slump and slurry concentration was

determined by preparing a series of mixes with slurry densities

between 74 and 84 pct by weight. The slump corresponding to

each slurry concentration was then measured. Specific gravity

was determined according to ASTM standard D854-58 (1991c).

The relationship between slump and slurry concentration

shows that large changes in slump corresponded to small

changes in slurry concentration (table B-4; figure 7). The

slump of cemented paste backfill decreased over time as a

function of initial slump and cement concentration (table 1; figure

11). Mix 6, with the lowest initial slump [11.4 cm (4.5 in)] and

the highest cement concentration (6 pct), decreased in slump to

6.4 cm (2.5 in), which was the largest amount of decrease among

the three mixes. Mix 4, with an initial slump of 17.1 cm (6.7 in)

and 6-pct cement content, had the next largest decrease in slump,

to 12.7 cm (5 in). Mix 3, with an initial slump of 17.8 cm (7.0

in) and 4-pct cement content, had the least amount of decrease in

slump, to 15.4 cm (6.0 in).
28

Table C-1.—Water content of bunker-stored tailings

Weight, g Water Water 

Sample Sample Oven-dried Water content, concentra-

 sample pct tion by 

weight, pct

1 ...... 152.0 139.1 12.9 9.3 8.5

2 ...... 146.6 134.5 12.1 9.0 8.3

3 ...... 153.3 140.5 12.8 9.1 8.4

4 ...... 121.6 109.7 11.9 10.8 9.8

5 ...... 130.3 120.3 10.0 8.3 7.7

6 ...... 218.6 205.2 13.4 6.5 6.1

7 ...... 223.3 210.4 12.9 6.1 5.8

Average 8.5 7.8

APPENDIX C.—TERMS AND EQUATIONS

WEIGHT-VOLUME S = weight of additive ÷ weight of solids, 

Mixes were batched using the percentage values from table 1 S = concentration of tailings as a percentage of

and a target volume of material. The weight of this volume of dry solids weight, 

material was determined from the calculated specific gravity of the

slurry. The weight-volume relationships used throughout this and S = concentration of cement as a percentage of

investigation were determined using the following equations and dry solids weight.

data from tables 1, C-1, C-2, C-3, and C-4. So that the text

would be easier to follow, measurements are given in metric only. Specific Gravity of Slurry

Concentration

Concentration as a percentage of the total slurry weight, C, is

the ratio of the weight of constituent material to the weight of Specific Gravity of Solids

solids and water. Therefore, 

C = weight of constituent ÷ (weight of solids + concentration of the tailings as a percentage of the dry weight of

weight of water), the solids multiplied by the specific gravity of the tailings plus the

C = concentration of water as a percentage of the solids multiplied by the specific gravity of cement. Therefore, w

total slurry weight, 

C = concentration of solids as a percentage of r

total slurry weight, where G = specific gravity of solids,

C = concentration of tailings as a percentage of S = concentration of tailings as a percentage of t

total slurry weight, dry solids weight,

and C = concentration of cement as a percentage of G = specific gravity of tailings, c

total slurry weight. 

Concentration as a percentage of the dry solids weight, S, is

the ratio of the weight of the additive to the weight of solids in and G = specific gravity of cement.

the mix. Therefore, 

t

c

The specific gravity of slurry is the inverse sum of the

concentration of water as a percentage of the total slurry weight

and the ratio of the concentration of solids as a percentage of total

slurry weight to the specific gravity of the solids. Therefore, 

G = (C + C /G ) , s w s r

-1

where G = specific gravity of slurry, s

C = concentration of water as a percentage of w

total slurry weight,

C = concentration of solids as a percentage of r

total slurry weight,

and G = specific gravity of solids. r

The specific gravity of solids is the sum of the products of the

concentration of the cement as a percentage of the dry weight of

G = (S × G ) + (S × G ), r t t c c

r

t

t

S = concentration of cement as a percentage of c

dry solids weight,

c
29
30
31
32
32

EXAMPLE

Test mix 3 is used as input for the following example, where

C = 0.2, C = 0.77, and cement = 4 pct of tailings weight. w t

Thus,

S = 1.0/1.04 = 0.96, t

S = 0.04/1.04 = 0.038, c

and C = 0.80 × 0.04 = 0.032. c

G = (0.77 × 2.8) + (0.032 × 3.15) = 2.81 r

 0.802

or G = (0.96 × 2.8) + (0.038 × 3.15) = 2.81, r

and G = 0.2 + 0.77 + 0.032 = 2.06. s

-1  2.81 

Therefore, for a 4.85 m batch, 3

target weight is 4.85 m × 2.06 × 1,000 kg/m 3 3

= 10,000 kg, 

weight of water is 0.2 × 10,000 kg = 2,000 kg, 

weight of dry solids is 10,000 kg - 2,000 kg = 

8,000 kg,

and weight of cement is 0.04 × 8,000 kg = 320 kg.

NOTE: Calculated slurry C differs from the value

shown in table 1 because water was added to adjust the

slump during batching, thus changing the target weight

value of the water. The slurry C was determined from figure

7, which shows the relationship between slurry concentration

and slump as determined from laboratory tests. The slurry C

for a 17.8-cm slump = 79.6.

Water-Cement Ratio

The water-cement ratio, w/c, is the ratio of the weight of the

water to the weight of the cement. Therefore, w/c = weight of

water ÷ weight of cement.

Continuing with the example described above, w/c

= 2,000/320 kg = 6.25.

Addition of Water

Water addition is expressed in two ways: as a percentage

of the solids weight (water content), which is used by civil

and geotechnical engineers, and as a percentage of the

total slurry weight (water, concentration by weight), which is

used by metallurgical engineers. 

Water Content

Water content as calculated by civil and geotechnical engineers

is the ratio of the weight of the water to the weight of the solids

given a unit volume of material. Therefore, water content =

weight of water per unit volume ÷ weight of solids per unit

volume.

Water content for the bunker-stored tailings was determined

by taking samples of the tailings from different locations within

the storage bunker and then averaging the values. The water

contents of individual tailings samples were determined by

subtracting the oven-dried weight of each sample from the

original stored weight and dividing this value by the oven-dried

weight. For example, the water content of tailings sample 1

(table C-1) was 12.9 ÷ 139.1 g = 9.3 pct.

The water content for the bunker-stored tailings was

determined by averaging the water content values of seven

individual samples, so that (9.3 + 9 + 9.1 + 10.8 + 8.3 + 6.5 +

6.1) ÷ 7 = 8.5 pct.

Because the stored tailings contained water, when batching,

additional tailings samples were added to compensate for the

weight lost to water. The water content of the tailings and the

weight of the dry tailings were used to determine the amount of

additional stored tailings and water needed for the mix.

The weight of the stored tailings needed to batch the mix was

determined by multiplying the dry tailings weight by 1 and the

water content, so that weight of stored tailings = weight of dry

tailings × (1 + water content), or 8,000 kg × (1 + 0.085) = 8,680

kg.

The amount of additional water needed for batching the mix

was determined by subtracting the weight of the water contained

in the stored tailings samples from the original weight of the

water needed for the mix, or 2,000 kg - (8,680 kg - 8,000 kg) =

1,860 kg.

Water, Concentration by Weight

 Water, concentration by weight, as used by metallurgical

engineers, is calculated as the ratio of the weight of the water to

the weight of the total sample given a unit volume of material.

Therefor, water, concentration by weight = weight of water per

unit volume ÷ total slurry weight per unit volume.

Water, concentration by weight, for the bunker-stored tailings

was determined by taking samples of tailings from different

locations within the storage bunker and then averaging the

values. The water, concentration by weight,

of individual tailings samples was determined by subtracting the oven-dried weight of each sample from the original stored

weight, and dividing this value by the original stored
33

EXAMPLE

Using data from table C-2 for mix 3, sample 1, 

V = 0.00049 m + 0.0028 m = 0.00329 m , v

3 3 3

V = 0.0047 m + 0.00017 m = 0.00487 m , r

3 3 3

and e = 0.00329/0.00487 m = 0.68. 3

EXAMPLE

Using calculations from the previous example,

n = 0.00329/0.0081 m = 0.41 3

and S = 0.0028/0.00329 m = 0.85. 3

weight. For example, the water, concentration by weight, of

tailings sample 1 (table C-1) was 12.9 g ÷ 152.0 g = 8.5 pct.

The water, concentration by weight, of the bunker-stored

tailings was determined by averaging the values of water,

concentration by weight, of seven individual samples, so that (8.5

+ 8.3 + 8.4 + 9.8 + 7.7 + 6.1 + 5.8) ÷ 7 = 7.8 pct.

Because the stored tailings contained water, when batching,

additional tailings samples were added to compensate for the

weight lost to water. The water, concentration by weight, of the

tailings and the weight of the dry tailings were used to determine

the amount of additional stored tailings and water needed for the

mix. Porosity and Degree of Saturation

The weight of the stored tailings needed to batch the mix was

determined by dividing the dry tailings weight by 1 minus the Porosity is the ratio of the volume of voids to the total volume

water, concentration by weight, so that weight of stored tailings per unit volume, or 

= weight of dry tailings ÷ (1 - water, concentration by weight), or

8,000 kg ÷ (1 - 0.078) = 8,680 kg. n = V /V, 

The amount of additional water needed for batching the mix

was determined by subtracting the weight of the water contained where n = porosity, 

in the stored tailings samples from the original weight of the

water needed for the mix, or 2,000 kg - (8,680 kg - 8,000 kg) = V = volume of voids, 

1,860 kg.

Void Ratio

The void ratio is the ratio of the volume of voids to the of voids per unit volume, or 

volume of solids per unit volume. The equation is given as 

e = V /V , v s

where e = void ratio, 

V = volume of voids occupied by air and water, v

and V = volume of solids. and V = volume of voids. r

V , which is the sum of the volume of air and the volume of v

water per unit volume, is determined as 

V = V + V , v a w

where V = volume of air a

and V = volume of water. w

V , which is the sum of the volume of tailings and the volume r

of cement per unit volume, is determined as 

V = V + V , r t c

where V = volume of tailings t

and V = volume of cement. c

v

v

and V = total volume. 

Degree of saturation is the ratio of volume of water to volume

S = V /V , w v

where S = degree of saturation, 

V = volume of water, w

v

PRESSURE GRADIENT

Pressure exerted on the walls of the pipeline by material being

transported was measured using transducer pairs mounted in the

pipeline. Differential pressure was determined by calculating the

difference between upstream and down-stream pressure

measurements. The pressure gradient as a function of flow rate,

pipe size, and mix combination is shown 
34

EXAMPLE

Using mix 3 at a rate of 3.l strokes per minute

through 154-mm-diam pipe (table C-3),

L = 42 m + adj 3 m = 45 m

and dP/dL = (1.32 MPa - 0.82 MPa)/45m

= 11 kPa/m.

EXAMPLE

Using the unit weight for mix 3 (table 1),

dP/dL = 2,060 kg/m × 9.81 m/s grav

3 2

= 20.2 kPa/m.

Figure C-1

in figure 4. Pressure gradient relationships are determined from The locations of the transducers in the pipeline and the

the ratio of the differential pressure difference to the pipe length

between the transducer pairs according to the following

equations.

dP/dL = (P - P )/L , in out adj

where dP/dL = differential pressure ÷ differential

length = pressure gradient,

P = pressure at upstream transducer, in

P = pressure at downstream transducer, out

and L = adjusted length between upstream and adj

downstream transducers.

L is calculated according to the equation adj

L = L + L , adj in-out fit

where L = sum of length between upstream and in-out

downstream transducers 

and L = equivalent length of additional pipe fit

resulting from line fittings. 

distance between pairs were changed for each of the six loop tests,

as shown in figure 3.

The vertical component of the pressure gradient was obtained

by multiplying the unit weight of the mixes by acceleration due

to gravity (9.81 m/s ). Thus, 2 1

dP/dL = unit weight × g , grav a

where dP/dL = vertical component of pressure grav

gradient

and g = gravity. a

The pressure gradient for vertical up or vertical down transport

is obtained by adding or subtracting the vertical component plus

the frictional component of the pressure gradient. The frictional

component of the pressure gradient is the resistance present

regardless of the orientation of the pipe (table C-4 and figure C1). 

Therefore,

In the U.S. customary system, the unit weight must first be converted to an 1

equivalent force in slugs. Therefore, unit weight = 129 lb/ft ÷ 32.2 lb " ft/lbf 3

" s = 3.88 lbf " s /lb " ft , so that dP/dL = 3.88 lbf " s /lb " ft × 32.2 ft/s ÷ 144 2 2 4 2 4 2

grav

in /ft = 0.90 psi/ft. 2 2

Horizontal and vertical flow paths and pressure gradients.
35

EXAMPLE

Using mix 3,

dP/dL = 20.2 kPa/ vert-up m + 12 kPa/m

= 32 kPa/m 

and dP/dL = -20.2 kPa/ vert-down m + 12 kPa/m

= -8 kPa/m. 

EXAMPLE

Using data from table C-3 for mix 3 at a rate of 3.1 strokes

per minute,

Q = 3.1 strokes per minute × 60 min/h 

× 0.0521 m per stroke 3

= 10 m /h. 3

Table C-5.—Combined test results for total tailings paste

backfill at flow rate of 29 m /h3

Slump, Pressure gra- Slurry con- Particle

Mix cm dient (dP/dL) centration, size, 

kPa m/m pct mm 

Fine tailings: 

 6 . . . . . . . . . . . 6 18.0 0.92 80 0.05

 5,1 . . . . . . . . . 11 15.3 0.78 79 0.06

Coarse tailings: 

 5,1 . . . . . . . . . 11 28.1 1.43 81 0.109

 4 . . . . . . . . . . . 13 21.2 1.08 80 0.100

 3 . . . . . . . . . . . 15 10.3 0.52 80 0.103

 2 . . . . . . . . . . . 17 6.1 0.31 80 0.109

dP/dL = ±dP/dL + dP/dL , The equation for the volumetric displacement of the grav vert up and down

where dP/dL = frictional component of vert up and down

pressure gradient  V = L m × B × (D m) /4, 

pressure gradient for

horizontal transport. where L = stroke length of Putzmeister pump

The following example shows the calculations involved in

determining the vertical up and vertical down pressure gradients and D = diameter of pump cylinders. 

(table C-4).

Flow Rate

Flow rate is a function of pump speed and displacement and

is determined by taking the product of the stroke rate per minute Table C-5 lists the test results used to obtain figure 5 and is

and multiplying this figure by the volumetric displacement of the based on data from tables B-1, B-4, and C-3. Mixes are

pump cylinders. Thus, compared factor by factor in table 2. The most significant factor

Q = N × V , is shown in bold. Pressure gradients for water and test mix 6 at p

where Q = flow rate, and 16. 

N = number of strokes per minute,

and V = volumetric displacement, cubic meters per p

stroke. 

It was assumed that 100 pct of the material in each stroke was

actually delivered because the material fed directly into the

pumping cylinders and no air pockets were observed at the pump

discharge point. 

The equation for the volumetric displacement of the

Thompson TTS 2065 pump is 

V = L m × B × (D m) /4, TTS 2065 TTS 2065 TTS 2065

2

where L = stroke length of Thompson pump TTS 2065

cylinder Horizontal Transport Distance

and D = diameter of cylinders. The horizontal transport distance generated by a standing TTS 2065

Therefore, V = 1 m × B × (0.1778 m) /4 = 0.0248 m per gradient into the pressure at the bottom of the standing column. TTS 2065

2 3

stroke. Thus, 

Putzmeister 2100S pump is 

2100S 2100S 2100S

2

2100S

cylinder 

2100S

Therefore, V = 2.1 m × B × (0.1778 m) /4 = 0.0521 m per 2100S

2 3

stroke. 

for determining which mix will have a greater pressure gradient

different flow rates are given in table C-6 and shown in figures 15

column of material is obtained by dividing the frictional pressure
36

EXAMPLE

For mix 2 (tables 1 and C-7), where column height is 300

m, pipe diameter is 154 mm, and flow rate is 29 m /h, 3

P = 300 m × 9.81 m/s grav

2

× 2,060 kg/m = 6.1 MPa, 3

P = 300 m × 6 kPa/m dP/dL

= 1.8 MPa, 

P = 6.1 MPa - 1.8 MPa bottom

= 4,263 kPa, 

and transport distance = 4,263 MPa ÷ 6 kPa/m

= 710 m.

Table C-6.—Pressure gradients for water and mix 6 at various pipe diameters

Flow rate (Q), 102 mm 128 mm 154 mm

m /3 h v, m/s dP/dL, kPa/m v, m/s dP/dL, kPa/m v, m/s dP/dL, kPa/m

WATER (25 EC)

10 . . . . . . . . . . . . . . 0.34 0.011 0.22 0.004 0.15 0.001

15 . . . . . . . . . . . . . . 0.51 0.025 0.32 0.008 0.22 0.003

20 . . . . . . . . . . . . . . 0.68 0.045 0.43 0.014 0.30 0.006

25 . . . . . . . . . . . . . . 0.85 0.070 0.54 0.022 0.37 0.009

30 . . . . . . . . . . . . . . 1.02 0.101 0.65 0.032 0.45 0.013

35 . . . . . . . . . . . . . . 1.19 0.137 0.76 0.044 0.52 0.017

40 . . . . . . . . . . . . . . 1.36 0.179 0.86 0.057 0.60 0.023

45 . . . . . . . . . . . . . . 1.53 0.226 0.97 0.073 0.67 0.029

50 . . . . . . . . . . . . . . 1.70 0.280 1.08 0.090 0.75 0.036

MIX 6

10 . . . . . . . . . . . . . . 0.34 18 0.22 17 0.15 13

15 . . . . . . . . . . . . . . 0.51 24 0.32 23 0.22 15

20 . . . . . . . . . . . . . . 0.68 27 0.43 26 0.30 17

25 . . . . . . . . . . . . . . 0.85 30 0.54 27 0.37 17

30 . . . . . . . . . . . . . . 1.02 33 0.65 28 0.45 19

35 . . . . . . . . . . . . . . 1.19 36 0.76 29 0.52 21

40 . . . . . . . . . . . . . . 1.36 39 0.86 30 0.60 22

45 . . . . . . . . . . . . . . 1.53 41 0.97 31 0.67 24

50 . . . . . . . . . . . . . . 1.70 42 1.08 35 0.75 25

dP/dL Pressure gradient.

v Velocity.

transport distance = P ÷ dP/dL, bottom

where P = pressure at bottom of a standing bottom

column

and dP/dL = pressure gradient.

The pressure at the bottom of a standing column is obtained

by taking the difference between the pressure imparted by gravity

and pressure lost through frictional pressure gradient, so that

P = P - P , bottom grav dP/dL

where P = column height × g × unit weight grav a

and P = column height × dP/dL. dP/dL

The following example shows the calculations involved in

determining system pressure and transport distance as given in

tables C-7 and C-8.
37

Table C-7.—Transport distance of total tailings paste backfill

through 154-mm-diam pipe at different column heights

at flow rate of 29 m /h, meters 3 1

Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6

Column height, m:

 0 ................... 0 0 0 0 0 0

 100 . . . . . . . . . . . . . . . . . -28 237 84 -12 31 10

 200 . . . . . . . . . . . . . . . . . -56 474 167 -23 63 19

 300 . . . . . . . . . . . . . . . . . -83 710 251 -35 94 29

 400 . . . . . . . . . . . . . . . . . -111 947 335 -47 126 38

 500 . . . . . . . . . . . . . . . . . -139 1,184 419 -59 157 48

 600 . . . . . . . . . . . . . . . . . -167 1,421 502 -70 189 57

 700 . . . . . . . . . . . . . . . . . -195 1,658 586 -82 220 67

 800 . . . . . . . . . . . . . . . . . -223 1,894 670 -94 252 76

 900 . . . . . . . . . . . . . . . . . -250 2,131 753 -105 283 86

 1,000 ............... -278 2,368 837 -117 315 95

dP/dL, kPa/m . . . . . . . . . . . 28 6 11 23 15 18

dP/dL Pressure gradient.

Negative numbers indicate no flow. 1

Table C-8.—System pressure of total tailings paste backfill through different pipe diameters

at different column heights and flow rate of 29 m /h, mix 2 3

 Column P , grav 102 mm1 128 mm2 154 mm3

height, m MPa P , bottom

 MPa dist., m MPa dist., m MPa dist., m

Transport P , bottom Transport P , bottom Transport

1 . . . . . . . . . . . . 0.020 0 0.06 0.006 0.40 0.014 2.0

10 . . . . . . . . . . . 0.20 0.012 0.64 0.062 4.0 0.14 24

20 . . . . . . . . . . . 0.40 0.024 1.3 0.120 9.0 0.28 47

30 . . . . . . . . . . . 0.61 0.036 1.9 0.190 13 0.43 71

40 . . . . . . . . . . . 0.81 0.048 2.5 0.250 18 0.57 95

50 . . . . . . . . . . . 1.0 0.060 3.2 0.310 22 0.71 118

60 . . . . . . . . . . . 1.2 0.073 3.8 0.370 27 0.85 142

70 . . . . . . . . . . . 1.4 0.085 4.5 0.430 31 0.99 166

80 . . . . . . . . . . . 1.6 0.097 5.1 0.500 35 1.1 189

90 . . . . . . . . . . . 1.8 0.11 5.7 0.560 40 1.3 213

100 . . . . . . . . . . 2.0 0.12 6.4 0.620 44 1.4 237

200 . . . . . . . . . . 4.0 0.20 13 1.2 89 2.8 474

300 . . . . . . . . . . 6.1 0.40 19 1.9 133 4.3 710

400 . . . . . . . . . . 8.1 0.50 25 2.5 177 5.7 947

500 . . . . . . . . . . 10 0.60 32 3.1 222 7.1 1,184

600 . . . . . . . . . . 12 0.70 38 3.7 266 8.5 1,421

700 . . . . . . . . . . 14 0.80 45 4.3 310 10 1,658

800 . . . . . . . . . . 16 1.00 51 5.0 355 11 1,894

900 . . . . . . . . . . 18 1.10 57 5.6 399 13 2,131

1,000 . . . . . . . . 20 1.20 64 6.2 443 14 2,368

2,000 . . . . . . . . 40 2.0 127 12 887 28 4,736

3,000 . . . . . . . . 61 4.0 191 19 1,330 43 7,104

4,000 . . . . . . . . 81 5.0 254 25 1,774 57 9,472

5,000 . . . . . . . . 101 6.0 318 31 2,217 71 11,841

6,000 . . . . . . . . 121 7.0 382 37 2,661 85 14,209

7,000 . . . . . . . . 141 8.0 445 43 3,104 99 16,577

8,000 . . . . . . . . 162 10 509 50 3,548 114 18,945

9,000 . . . . . . . . 182 11 572 56 3,991 128 21,313

10,000 . . . . . . . 202 12 636 62 4,435 142 23,681

P = Column height × gra vity × unit weight. grav

P = Pressure at bottom of standing column. bottom

Pressure gradient (dP/dL) = 19 kPa/m. dP/dL = 14 kPa/m. dP/dL = 6 kPa/m. 1 2 3

INT.BU.OF MINES,PGH.,PA 30159