SPECIAL REPORT 97-14

Ripping Frozen Ground with

an Attachment for Dozers

Paul V. Sellmann and Dale R. Hill June 1997
Abstract: Ripping of hard and frozen ground is commonly done by using crawler tractors with rear-mounted

rippers that are usually a permanent part of the machine. Ripping is an attractive alternative to other methods of breaking a hard surface layer that restricts

excavation, since it utilizes existing equipment and

personnel, and a tractor that can be used for the

excavation project. A simple ripper attachment for use

on the blade of a dozer was used to determine if this

easily installed tool could provide some ripping capaHow to get copies of CRREL technical publications:

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bility when machines with rear-mounted rippers are

not available. This ripper attachment was used in a

range of frozen soils that could not be excavated with

a dozer, and was used on tractors ranging in size from

small commercial dozers to a large military dozer with

a suspension system. In all cases, at the sites used,

the ripper attachment provided the machines with some

ripping capability. The ripper was also easy to install,

with no modifications required to the tractors or the

rippers.
Special Report 97-14

Ripping Frozen Ground with

an Attachment for Dozers

Paul V. Sellmann and Dale R. Hill June 1997

Prepared for

OFFICE OF THE CHIEF OF ENGINEERS

Approved for public release; distribution is unlimited.

US Army Corps

of Engineers

Cold Regions Research &

Engineering Laboratory

®®

Cold Regions Research &

Engineering Laboratory
PREFACE

This report was prepared by Paul V. Sellmann, Consultant, Applied Research

Division, and MAJ Dale R. Hill, Deputy Commander, U.S. Army Cold Regions

Research and Engineering Laboratory. Funding for this work was provided by the

Office of the Chief of Engineers through DA Project 4A762784AT42, Work Unit CSC06, Excavation in Frozen Materials.

Technical review of this report was provided by Herbert Ueda and Wayne

Tobiasson, both project engineers associated with CRREL. Appreciation is expressed

to the GH Hensley Co. for providing product literature covering moldboard rippers.

The contents of this report are not to be used for advertising or promotional

purposes. Citation of brand names does not constitute an official endorsement or

approval of the use of such commercial products.

ii
CONTENTS

Page

Preface ........................................................................................................................ ii

Introduction ............................................................................................................... 1

Objective ................................................................................................................ 1

Background ........................................................................................................... 1

Tractor-mounted rippers ......................................................................................... 2

Rear-mounted rippers ......................................................................................... 2

Dozer back-rippers .............................................................................................. 2

Removable ripper attachment for dozers ......................................................... 2

Excavating hard and frozen ground ...................................................................... 5

Observations of work using the ripper attachment............................................. 6

Dozers .................................................................................................................... 6

Excavation sites .................................................................................................... 6

Rippers on commercial tractors ......................................................................... 8

Ripping with the John Deere 750 ....................................................................... 8

Ripping with the John Deere 550 ....................................................................... 9

Ripping with the CEV ......................................................................................... 10

Ripper on the Caterpillar D7 .............................................................................. 13

Conclusions and recommendations ....................................................................... 13

Literature cited .......................................................................................................... 14

Abstract .................................................................................................................... 16

ILLUSTRATIONS

Figure

1. Idealized view of linkages commonly used for attachment and

adjustment of rear-mounted rippers ..................................................... 2

2. Back-rippers attached to the rear of a dozer blade for ripping

and scarifying ........................................................................................... 2

3. Ripper attachment for use on moldboards of dozers ............................... 3

4. Distribution of permafrost and seasonally frozen ground in the

Northern Hemisphere ............................................................................. 4

5. Effect of freezing and subsequent cooling on the unconfined

compressive strength of concrete and earth materials ....................... 5

6. Ripper attached to the dozer blade of an Army CEV ............................... 6

7. John Deere 750 fitted with a moldboard ripper ........................................ 7

8. John Deere 550 with blade tilted to use its corner as a slide to limit

depth of cut and control ripping depth ................................................ 8

iii
9. John Deere 550 ripping the frozen surface of the test site ....................... 9

10. Ripper attachment on the blade of the CEV .............................................. 10

11. Ripper shown at full penetration in asphalt pavement with the

blade sliding along the pavement surface............................................ 11

12. Ripping seasonally frozen ground to the total depth of 14 in. (36 cm)

with the CEV ............................................................................................ 12

13. Dozer blade, ripper, and simple skid used to control depth of cut,

independent of CEV suspension ........................................................... 12

14. GH Hensley 1000-HL ripper attached to the outer part of the

blade on an Army Caterpillar D7 tractor ............................................. 13

TABLES

Table

1. Machine and ripper specifications .............................................................. 6

Figure Page

iv
INTRODUCTION

Objective

A ripper attachment was mounted on the dozer

blades of commercial crawler tractors and on a

military dozer (the M728 Combat Engineer Vehicle, CEV) in an attempt to improve performance

for work in hard and frozen soil when more conventional rear-mounted rippers are not available.

The tractors were selected to help predict the ripping performance of smaller military and commercial dozers, and that of a military dozer with a

suspension system. This was done for a better

understanding of how a blade-mounted ripper

could be used for combat engineering operations

during the winter, such as construction of fighting positions and denial structures. Observations

were made at several sites with a range of ground

conditions, including sites with seasonal frost

greater than 2 ft (0.6 m) thick. Some of these observations were made during military exercises

and during field demonstrations.

Background

Combat engineers have a number of missions

that require excavation, including constructing

fighting positions for combat vehicles, constructing obstacles, and maintaining and constructing

roadways, runways, and other facilities in all terrain and weather. The difficulty of these missions

significantly increases when construction is in

hard and frozen ground. Reduced availability of

the D7 tractor with a rear-mounted ripper and

poor performance in hard ground of other available equipment further complicate this problem.

Dozers that lack ripping capability are usually

restricted to operating in ground that is not highly

compacted or bonded by ice or some chemical

cement. Rippers greatly expand the capability of

tractors, providing a means to break up and

disagregate hard surface materials, preparing an

area for more rapid excavation by conventional

methods. In some quarry and mining operations,

large ripper-equipped tractors are used in coal

and rock, eliminating the need for drilling and

blasting. Russian experiments with a ripper

mounted on a modified military T-34 tractor indicated that ripping hard ground was 15 times less

expensive than drilling and blasting (Zelenin et

al. 1985). Some manufacturers of crawler tractors

equipped for ripping provide data on ripability

of materials to aid estimates of ripper performance

and productivity (Nichols 1976, Caterpillar 1989),

which helps to allow cost comparisons with other

alternatives, such as drilling and blasting. Ripping is an appealing concept for military operations because a minimum amount of equipment

and manpower is required.

Rippers on dozers are commonly rear-mounted

on a hydraulically operated linkage that is usually a permanent accessory to the tractor. This

report discusses a less common ripper attachment

used on the blades of crawler tractors. This device

can be rapidly installed on most tractors that have

a conventional dozer blade to provide some ripping capability. It can be easily transported to the

field and installed with no modifications. For some

tasks it can also be more versatile and less restricted by its location than a rear-mounted ripper. When mounted on part of the blade that is

visible to the operator, it can be used to hook and

remove rocks, barriers, and debris from the

ground, and to trench for burying cables or small

utility lines.

Ripping Frozen Ground with

an Attachment for Dozers

PAUL V. SELLMANN AND DALE R. HILL
TRACTOR-MOUNTED RIPPERS

Rear-mounted rippers

Crawler tractors have been fitted with a variety of ripping schemes, as mentioned in the following discussion. Rear-mounted rippers are often fitted on modern crawler tractors and are

specifically designed by the manufacturer to

match machine characteristics. They are made for

a large range of tractor sizes with various ripper

configurations and linkage designs for depth control and adjustment. This type of ripper provides

the greatest penetration and highest productivity. Penetration depth using rippers on very large

machines can be as great as 4 to 5 ft (1.2 to 1.5 m)

and range from 10 to 30 in. (0.25 to 0.75 m) on

machines of the D7 class and smaller.

Rippers are hydraulically controlled through

their linkage systems, with radial and parallelogram attachments common. The radial system in

Figure 1a is an idealized version of a ripper used

on the Russian T-34 tractor. Ripper tooth angles

change with depth with the radial system. The

parallelogram attachment (Fig. 1b) has the advantage of maintaining the same ripper angle at

all depth settings. A single ripper is usually used

to concentrate forces when ripping is difficult or

when deep penetration is needed. Multiple ripper arrangements are often used on large tractors

and when ripping is less difficult. Increased productivity and performance in hard ground and

rock is possible with new hybrid rippers that create high ripping forces at the ripper tooth using a

hydraulically powered impact system.

Dozer back-rippers

Back-rippers are attached to the rear of a dozer

blade in a manner that allows them to swing down

into place for use when a tractor reverses. They

rip and scarify a surface so that on a following

forward pass loosened material can be moved

with the blade. These rippers do not interfere

when dozing, since forward motion causes them

to swing to the rear from their upper connection

and drag along the ground as shown in Figure 2.

When not in use they can be moved up and secured. These small blade-mounted rippers are installed on the Caterpillar DEUCE, and are also

fitted on the Army D7 bulldozer. Ripping with

this type of ripper is also discussed in FM 5-434

(U.S. Army 1992).

Removable ripper

attachment for dozers

A less common commercial ripper attachment

is available for use on the moldboards of dozers

(moldboard refers to the curved metal plate that

makes up most of the blade on a dozer, snow, or

land plow; it is a continuation of the cutting edge

Figure 1. Idealized view of linkages commonly used for

attachment and adjustment of rear-mounted rippers.

Variants of these attachments have additional control

for adjusting the angle of the ripper tooth.

a. Radial.

b. Parallelogram.

Figure 2. Back-rippers attached to the rear of a dozer

blade for ripping and scarifying.

2
* Personal communication with GH Hensley Co.

and is used to direct the material being displaced).

The attachment was introduced around 1947* and

is still available in several sizes for use on a large

range of bulldozers, depending on blade size, tractor power, and weight. The length of these rippers also increases with tractor size and weight,

with a maximum penetration depth of 2 ft (61 cm)

for the largest model. Attachment is not difficult.

The top of the ripper is secured with an adjustable yoke that clamps at the top of the dozer

blade, and the bottom is engaged by placing the

lower part of the blade into a notch in the ripper

shank. This notch is constructed to distribute

forces to the lower part of the blade and cutting

edge. Figure 3 shows all the components of the

ripper, including the replaceable ripper tooth or

wear point. Rippers for smaller tractors can be

easily installed by two people since they can be

put on one component at a time. On the smallest

model, the largest and heaviest component is the

ripper shank, which weighs 112 lb (51 kg). The

total weight of the Hensley rippers varies from

Figure 3. Ripper attachment for use on moldboards of

dozers (used with permission of the GH Hensley Co.).

4” Pin with Cotter

Sleeve

Shank

Adjusting Nut

Adjusting Bolt

Yoke

6” Pin with Cotter

Wear Collar

Pin

Wear Point

Figure 2 (cont'd).

3
Figure 4. Distribution of permafrost and seasonally frozen ground in the Northern Hemisphere (after Bates and Bilello 1966). Note the B line for the

southern limit of seasonal frost as defined in the illustration.

4
about 170 to 870 lb (77 to 395 kg). The smallest

model has 11 in. (28 cm) of penetration and, for

our observations, was attached to the blade of a

John Deere 550 dozer.

Quantitative performance information for

blade-mounted rippers is not readily available,

compared to the large background of experience

and information on the more common rearmounted rippers. However, if it is assumed that

dozer blade penetration force and rear-mounted

ripper penetration force are similar for most

crawler tractors, it may then be possible to make

some performance predictions for the less common blade-mounted attachment. It is interesting

to note that data for the D7H indicate that down

force on the cutting edge of the dozer blade is

approximately 21,000 lbf* (93 kN), which is very

close to the penetration force developed for a rearmounted parallelogram ripper on this tractor.

Horizontal force should also be similar when considering either a front- or rear-mounted tool, both

having similar configurations.

EXCAVATING HARD

AND FROZEN GROUND

A variety of hard ground conditions cause problems for conventional, unassisted dozers. These

commonly include frozen ground, dense overconsolidated sediments, weak rock, coral, and

desert caliche. Seasonally frozen ground causes

significant problems because it is very common

and because freezing greatly increases the strength

of the ground surface, often preventing penetration with conventional tools. Seasonal frost is

widespread in the Northern Hemisphere, and can

be several feet thick. The southern limit of substantial frost penetration, where frost depth is

about 12 in. (30.5 cm) once in every 10 years, is

shown in Figure 4 (Bates and Bilello 1966); however, south of this limit seasonal frost can be thick

enough to frequently hinder excavation.

Soil and rock significantly increase in strength

with freezing (Fig. 5), with more than an order of

magnitude increase common for most soils

(Sellmann 1989). The strength of frozen soils continues to increase with cooling at temperatures

normally encountered during winter. Frozen soils’

strengths can approach those of unfrozen chemically bonded materials, such as weak rock and

concrete. Therefore, excavation problems are

caused by even thin layers of frozen ground.

Soil strength depends on several factors, including moisture content, grain size, and ground

temperature. For purposes of excavation, frozen

soils can be grouped into two general categories

based on their grain size: 1) fine-grained soils that

include various mixtures of silt, clay, organic material, and ice, and 2) coarse-grained soils consisting primarily of sand and gravel, with aggregates

ranging from small pebbles to large cobbles. Of

these the frozen fine-grained soils usually are most

easily ripped and cut, and tend to be more ductile

compared to the more brittle and abrasive coarsegrained material. The high strength and often large

particle size and abrasive nature of the coarsegrained material make excavation difficult to impossible for small machines. Machines that can

generate high tool forces, and have large teeth

compared to aggregate size, have the best chance

* Personal communication with Caterpillar, Inc., 1994. of working the coarse material.

Figure 5. Effect of freezing and subsequent cooling on

the unconfined compressive strength of concrete and

earth materials: soil, rock, and ice (from Sellmann

1989).

5
OBSERVATIONS OF WORK USING

THE RIPPER ATTACHMENT

Dozers

To determine if this type of ripper might have

military applications, rippers were acquired that

would fit on a large military dozer and on two

commercial dozers selected to represent smaller

commercial and military tractors. The military

tractor was an Army Combat Engineer Vehicle

(CEV), constructed on the M-60 tank chassis with

modifications to armament and addition of a lifting boom and hydraulically operated dozer blade.

It was selected because it is unable to excavate in

hard or frozen ground. It also represents a type of

softly suspended tractor, based on fighting machine chassis, that has suspension characteristics

that may affect ripper performance and control.

This tractor with a ripper attachment is shown in

Figure 6.

The smaller commercial tractors were used to

gain an understanding of ripping characteristics

and limits in frozen ground and of the potential

performance of proposed military tractors. The

John Deere 550 and 750 used are shown in Figures

7 and 8 with ripper attachments. General information on the tractors and rippers is given in Table 1.

The ACE (Armored Combat Earthmover) was

not considered for mounting a ripper attachment

because of aspects of blade geometry, construction, and ground clearance of the blade.

Excavation sites

Observations were made at several locations

with different soil types and frost conditions. Sites

free of frost, but with hard ground, were also

used. Frost thickness varied from approximately

4 in. (10 cm) to greater than 2 ft (60 cm). Soils

included a frozen loamy soil in a natural setting

with a sod cover, a dense frozen silty sand with

local zones containing clay and scattered gravel

at an old borrow pit, and a more rocky soil that

contained some very coarse gravel. Frost greater

than 2 ft (60 cm) thick occurred at two of the sites,

and the ground at these locations was well frozen

and strong.

The objective was to learn more about ripping

performance and characteristics, taking into consideration tractor size, traction, tractor suspension (rigid versus sprung), ripping depth, and

machine control during ripping. Attempts to tiltdoze with the corners of the commercial tractor

blades were used to help assess ground strength

and as a comparison for judging ripper effectiveFigure 6. Ripper attached to the dozer blade of an Army

Combat Engineer Vehicle (CEV).

Table 1. Machine and ripper specifications.

Weight Power

Tractors (lb) (kg) (hp) (kW)

CEV* 114,000 65,300 750 559

JD550 20,000 9,000 90 67

JD750 29,000 13,150 110 82

D7 Cat. 45,000 20,400 200 149

Weight† Penetration

Ripper (lb) (kg) (in.) (cm)

750-H 170 77 11 28

1000-HL 305 138 14 36

* The CEV is several tons heavier than the D9 Cat. and has

twice the power.

† Total weight. The ripper attachment consists of three

components. The individual parts were handled by two

people for installation and transport.

6
a. Ripping frozen ground.

Figure 7. John Deere 750 fitted with a moldboard ripper.

b. Close-up of fractured material produced after one pass.

7
ness. The observations were made during field

demonstrations, and during runs planned for observing ripping characteristics. The observations

in frozen ground were made at sites in northern

New England. The CEV was used at the site with

the strongest and most difficult ground conditions.

Rippers on commercial tractors

The GH Hensley model 750-H and 1000-HL

rippers were used on the John Deere tractors. The

1000-HL ripper was attached to the center of the

blade on the John Deere 750 without difficulty in

about 5 to 10 minutes. The 750-H used on the

John Deere 550 could not be installed on the center of the blade because controls on the rear of the

blade interfered with the attachment yoke. Also,

this ripper’s standard yoke was not long enough

to solidly engage the back of the blade. The 750-H

was securely attached to the 550 blade by placing

it just off center and using the longer yoke from

the larger 1000-HL ripper. The lighter weight of

the 750-H ripper also made installation easier. As

mentioned, the ripper was installed in pieces to

reduce the weight of the equipment handled. The

ripper shank was first positioned on the blade,

then the sleeve, followed by the yoke.

The 550 tractor was selected to help predict the

potential ripping capability of the smaller military machines, such as the DEUCE, being tested

by the Army. Caterpillar indicated that the down

pressure on the blade edge of the DEUCE is approximately 7900 lbf (35 kN), which is similar to

the John Deere 550 and some Caterpillar D4 and

D5 tractors. The 750-H provided an indication of

ripping performance of machines larger than the

550, but smaller than the D7 tractors used by the

Army (Table 1).

Ripping with the John Deere 750

At the borrow pit, the seasonal frost was just

over 2 ft (60 cm) thick. The surface and this layer

were well frozen. Note in Figure 8 that the track

grousers do not penetrate the surface and only

mark the ground on high areas and in the turns.

We initially tried to penetrate the frozen ground

by tilt dozing (no ripper) with the corner of the

blade. Tilt-dozing passes did not penetrate and

only smoothed and polished the ground surface.

With the 1000-HL ripper attached, continual

forward progress could be made when passes

were less than full ripping depth. At this site 5 to

6 in. (13 to 15 cm) was routinely ripped (Fig. 7a).

Figure 8. John Deere 550 with blade tilted to use its corner as a slide to limit depth of cut and control

ripping depth.

8
A close-up of the fractured material is shown in

Figure 7b. Attempts to immediately go to full

depth (14 in. [36 cm]) usually stopped the tractor

and caused it to lose traction. The best performance was obtained when three to four passes

were made to rip a single starting slot to full

depth. This cut to full depth along a 60-ft (18-m)

excavation took less than 5 minutes. Parallel offset passes were then made with less effort, with

material failing to the prior cut; however, multiple passes (usually two or three) were still required for full penetration. The tractor and blade

were stable and the ripper did not noticeably pull

down the blade or the front of the tractor. Generally, forward travel was not smooth, and usually

would slow when the ripper caught, loaded, and

failed a slab. Occasionally, when the track slipped,

lifting the blade would help fail the ground and

restore forward motion. Failure of the frozen

ground was often accompanied by a noticeable

bang as the ground fractured and the blade unloaded. Forward progress was also restored by

reversing and starting again, ripping at a shallower

depth. At this site 10 to 14 passes were required to

rip the frost to a depth of 14 in. (36 cm) over a

swath approximately the width of the blade.

Ripping with the John Deere 550

The John Deere 550 with the model 750-H ripper attachment also effectively ripped frozen

ground at the barrow pit. During these observations, ripping performance was improved with

less catching and much better control over the

ripping depth. The depth of cut was controlled by

tilting the blade and using its corner as a skid.

This prevented the ripper from pulling down the

front of the tractor, which increased the depth of

cut and occasionally stalled forward progress. The

ripper was mounted just left of center on the blade,

as shown in Figure 8, with the right corner placed

on the ground and used as a skid. With this control, a 3- to 4-in. (8- to 10-cm) depth of cut could

be maintained at a uniform forward rate. On an

average it took 45 seconds to make a 50-ft-long

(15-m) pass, ripping to this depth. It took approximately 10 minutes to rip an 11-in. (28-cm)

frost layer in a 10- × 50-ft (3- × 15-m) area, which

is about half of the area required for construction

of some vehicle fighting positions. The 550 is

shown ripping at this site and some of the large

slabs produced can be seen in Figure 9.

During these observations the ground was flat,

well frozen, and free of snow and ice. Traction

9

Figure 9. John Deere 550 ripping the frozen surface of the test site; total ripping depth is approximately

1 ft (30 cm).
was good, with the grousers only rarely slipping

on the frozen soil surface. Although the effect of

having the ripper slightly off-center on the 550

was not substantial, it occasionally caused the

tractor to crab when ripping resistance was great.

Ripping with the CEV

The model 1000-HL ripper used on the John

Deere 750 was also attached to the dozer blade on

the Combat Engineer Vehicle (Fig. 10). A larger

ripper model would have fit on this machine for

greater ripping depth and a closer match with

machine power; however, the greater weight of a

larger ripper would have been much more difficult to handle and installation would have required mechanical assistance. This model was selected because it fit the CEV blade, it could be

handled in pieces without mechanical assistance,

the 14-in. (36-cm) penetration depth matched our

requirements, and, if mechanical problems occurred, damage to the ripper was preferred to

damage to the machine. The tool also appears to

have value for general engineering tasks, such as

moving obstacles. Use in a range of site conditions demonstrated its value for ripping hard,

compacted soils and asphalt pavement.

The CEV was used at two sites with seasonally

frozen soils: an undisturbed site with thin frost (4

to 5 in. [10 to 13 cm]) and a sod cover, and an area

with a frost layer greater than 14 in. (36 cm) consisting of gravely material with sufficient fines

and moisture to form very strong well-bonded

ground. Both sites also had a thin snow cover

(approximately 1 in. [3 cm]). A thin snow cover

over smooth frozen ground can provide poor traction for the CEV fitted with rubber road pads.

The thin frost layer was easily ripped. The ripper was lowered to full depth as the machine

advanced and the cutting edge of the dozer slid

over the frozen surface. A narrow groove was

produced that appeared very similar to the ones

made ripping asphalt pavement at the engineer

Figure 10. Ripper attachment on the blade of the Combat Engineer Vehicle (CEV). This ripper is the same model

that was used on the John Deere 750.

10
school (Fig. 11). At no time was ripping resistance

great enough to cause track slip or any significant

motion in the suspension of the machine. Ripping

this thin frost seemed effortless.

In contrast, ripping at the site with thick frost

was noticeably different, with much greater resistance to ripper advance. Ripping to the depth of

the ripper (14 in. [36 cm]) usually required three

passes. Ripping forces were also great enough to

affect traction and cause significant interaction

with the suspension. As with the commercial tractors, the best performance was obtained when

passes were made parallel to a cut ripped to full

depth, which provides an additional free face for

material failure. The large size of the frozen blocks

produced can be seen in Figure 12. Since ripping

to full depth required successive passes, it was

necessary to hold the blade in a position that

would permit incremental penetration.

Initial penetration was not difficult, and Figure

12 shows the CEV starting a pass while holding

the blade in a position that would allow 6 to 8 in.

(15 to 20 cm) of penetration. Very little down

pressure on the blade was required to reach the

planned depth. In hard ground, maintaining the

depth was a problem, since tooth configuration

and variations in material properties tended to

cause large fluctuations in the vertical force required to control the ripper. The ripper would

tend to grab and pull into the ground, loading the

suspension system. This would result in the ripper cutting a deeper groove, which could slow

forward progress and occasionally stop the machine. Attempts to respond by pulling up the blade

only compressed the suspension further until sufficient vertical force was available to pull the ripper up, out of the ground; sometimes the ripper

jumped to a position above the ground surface

when the suspension unloaded. It was not possible to fine tune the depth of cut as it was with

the commercial tractors that have no suspension

system. However, careful teamwork between the

operator and the spotter on the ground and good

operating technique can reduce this problem and

maintain productive ripping.

A technique that worked well was based on

responding to changes in forward progress. Once

the operator sensed that forward progress was

Figure 11. Ripper shown at full penetration in asphalt pavement with the blade sliding along the pavement

surface. The slots cut during the previous passes are similar to those produced in thin seasonal frost.

11
Figure 12. Ripping seasonally frozen ground to the total depth of 14 in. (36 cm) with the CEV. Ripping to this

depth (i.e., the length of the ripper below the blade) required multiple passes along the same path.

Figure 13. Dozer blade, ripper, and simple skid used to control depth of cut,

independent of CEV suspension.

12
slowing because of increased ripping resistance, instead of making a

blade adjustment, it was best to stop,

reverse, and let the suspension unload, then advance again, essentially

starting over with a shallow cut. In

hard ground productivity was greatest with successive shallow cuts

compared to fewer deep cuts.

Since the blade of the CEV can

not be tilted, this means of controlling depth of cut and reducing the

influence of the suspension was not

available. However, to see if overall

performance could be improved

with better control of ripping depth,

a skid was used on the blade to make

depth of cut independent of the suspension. This was done in a very

expedient manner. A section of railroad tie, approximately 3 ft (90 cm)

long, was used as a skid and placed

under the blade like a ski. The front

was cut with a ramp, and a shallow

notch in the top engaged the blade

(Fig. 13). The blade was lowered into

the notch, limiting penetration to

about 8 in. (20 cm). Passes made with

the skid were noticeably different

from those made when depth was

controlled by blade adjustments

alone. With the skid, forward

progress was smooth with no stalling and loss of traction.

Considering the poor traction

usually attributed to the CEV when

it is operated on packed snow with

road pads, we found that performance was good. Traction was lost

only a few times, and on those occasions it usually could be anticipated. Ripping was resumed by reversing the machine for a new start

at a shallower depth.

Ripper on the Caterpillar D7

The model 1000-HL can also be attached (fully

extended) to the outer part of the 7-S dozer blade

used on some Army D7 tractors (Fig. 14). The

ripper was used to rip compacted gravel and asphalt pavement; no frozen ground was available

at the time. However, with the tractor’s weight,

power, and blade control, good ripping performance in frozen ground would be expected.

CONCLUSIONS AND

RECOMMENDATIONS

The moldboard ripper attached to the blades

of commercial and military dozers provided a

rapid, low cost means of developing a ripping

capability. The rippers were easily attached in the

field in less than 10 minutes with no modification

required to the tractor or the ripper. At our sites

the ripper attachment provided the dozers a means

of ripping hard and frozen ground.

Figure 14. GH Hensley 1000-HL ripper attached to the outer part of

the blade on an Army Caterpillar D7 tractor. This model was also

used on the CEV and John Deere 750.

13
We observed no significant difficulty with ripping, given the ground conditions that existed at

the time of testing, which included some hard,

well-frozen soils. Ripping performance can vary

greatly, depending on the strength properties of

the frozen ground, which is controlled by the soil

type, moisture content, and ground temperature.

Much less than ideal traction was available at the

sites since grouser penetration was not possible.

However, after a few passes with the ripper, traction should have improved.

Full penetration (14 in. [36 cm]) of the large

ripper in one pass was not possible when frost

thickness approached this depth. Asphalt pavement and a seasonal frost layer, both varying from

3 to 5 in. (8 to 13 cm) thick, were ripped by the

CEV with little noticeable resistance to both initial penetration and forward progress. In both

cases the ripper was placed at full depth and

the dozer blade was allowed to slide on the

surface.

Multiple passes were required to rip to the full

depth of the rippers when frost thickness was

greater than about 6 in. (15 cm). The depth of

penetration for a single pass uninterrupted by

stalling and catching was similar for the JD750

and the CEV using the model 1000-HL ripper and

ranged from 4 to 8 in. (10 to 20 cm); however, soil

properties were a little more difficult at the CEV

site. Three to four passes were required to make

the first cut to the depth of 14 in. (36 cm). The

suspension on the CEV made maintaining optimum depth of cut and smooth forward progress

a difficult task. Depth control was more easily

regulated with the JD750 and JD550, since the

machines were more rigid and tilt-blading could

be used to control depth of cut.

The more limited control over ripping depth

with the CEV did not prevent it from ripping. It

required a technique to minimize the effect of the

suspension system. This involved stopping forward progress as soon as the front of the machine

started to drop and forward progress began to

slow. Starting again by reversing a short distance

to free the ripper, then advancing while slowly

lowering the ripper to a depth that allowed smooth

forward progress was quite effective. Also, it is

important for an operator to work closely with a

spotter on the ground for better control of depth

of cut and spacing of the paths to be ripped. A

number of shallower cuts can be made faster than

a few deeper ones.

A ripping depth of several inches was easily

controlled with the JD550 and 750-H ripper by

tilting the blade and letting the corner act as a

slide to limit the depth of cut. Forward progress

was smooth using this technique and overall productivity of the JD550 using the smaller 750-H

ripper was similar to that of the JD750 with the

larger 1000-HL ripper. Smoother and uninterrupted ripping was also possible with the CEV

when depth of cut was controlled by using a skid

under the blade, which eliminated the influence

of the suspension.

For some tasks a blade-mounted ripper can be

more versatile than a rear-mounted ripper. With

slightly better visibility for the operator, it can be

more easily used to remove barriers, rocks,

stumps, and other obstacles; however, it can not

be expected to have the performance of a rugged

rear-mounted ripper that is designed for production ripping.

The rippers fit well on all of the machines, and

neither the rippers nor machines were damaged

during these observation. Once the rippers were

adequately tightened, they were stable on the

blades and moved only slightly.

LITERATURE CITED

Bates, R.E., and M.A. Bilello (1966) Defining the

cold regions of the Northern Hemisphere. USA

Cold Regions Research and Engineering Laboratory, Technical Report 178.

Blaisdell, G.L., E.J. Chamberlain, and M. Mellor

(1987) Evaluation of the cold regions aspect of

mobility and hardening of the mobile test bed at

Malmstrom Air Force Base. Report for U.S. Air

Force Ballistic Missile Office—Small ICBM Program. USA Cold Regions Research and Engineering Laboratory, Internal Report 1004.

Caterpillar Inc. (1989) Caterpillar performance

handbook. Peoria, Illinois.

Haynes, F.D. (1978) Effect of temperature on

strength of snow-ice. USA Cold Regions Research

and Engineering Laboratory, CRREL Report

78-27.

Mellor, M. (1972) Strength and deformability of

rocks at low temperatures. USA Cold Regions

Research and Engineering Laboratory, Research

Report 294.

Monfore, G.E., and A.E. Lentz (1962) Physical

properties of concrete at very low temperatures.

14
Journal of the Portland Cement Association (PCA),

Research and Development Laboratory, p. 33–39.

Nichols, H.L. Jr. (1976) Moving the Earth—The

Workbook of Excavation. Greenwich, Connecticut:

North Castle Books.

U.S. Army (1992) Earthmoving operations, FM

5-434.

Sellmann, P.V. (1972) Geology and properties of

materials exposed in the USA CRREL Permafrost

Tunnel. USA Cold Regions Research and Engineering Laboratory, Special Report 177.

Sellmann, P.V. (1989) Strength of soils and rocks

at low temperatures. Cold Regions Science and Technology, 17: 189–190.

Zelenin, A.N., V.I. Balovnev, and I.P. Kerov

(1985) Machines for Moving the Earth (translated

from Russian). New Delhi: Amerind Publishing

Co., Pvt. Ltd.

15
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Ripping Frozen Ground with an Attachment for Dozers PE: 7.627.84

PR: 4A762784AT42

TA: CS

WU: C06

Paul V. Sellmann and Dale R. Hill

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 97-14

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24

Bulldozers Moldboard ripper Ripping frozen ground

Cold regions Ripper attachment

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

Ripping of hard and frozen ground is commonly done by using crawler tractors with rear-mounted rippers that

are usually a permanent part of the machine. Ripping is an attractive alternative to other methods of breaking a

hard surface layer that restricts excavation, since it utilizes existing equipment and personnel, and a tractor that

can be used for the excavation project. A simple ripper attachment for use on the blade of a dozer was used to

determine if this easily installed tool could provide some ripping capability when machines with rear-mounted

rippers are not available. This ripper attachment was used in a range of frozen soils that could not be excavated

with a dozer, and was used on tractors ranging in size from small commercial dozers to a large military dozer with

a suspension system. In all cases, at the sites used, the ripper attachment provided the machines with some ripping

capability. The ripper was also easy to install, with no modifications required to the tractors or the rippers.