Automated becker hammer drill bounce chamber energy monitor

A system and method for providing analysis and evaluation of penetration test data for modifying Becker Hammer drill programs while in progress by measuring the bounce chamber pressure of a diesel hammer. The system comprises a pressure transducer connected to the bounce chamber for sensing the bounce chamber pressure, a data logger for monitoring the pressure transducer, storage means, a control module and a keyboard having a display screen to enable user control of the data logger, a telephone modem, and a series of instructions for controlling the schedule, pressure transducer measurement, control module signal monitoring, computation of data, and data storage operations of the data logger.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to novel data gathering and sampling in 
connection with in-situ soil testing and analysis. More particularly, the 
invention concerns a method and apparatus for providing analysis and 
evaluation of Becker Penetration Test Data more accurately and timely to 
be used immediately to modify drilling programs while in progress. 
2. Discussion of the Prior Art 
In the past, it has been common practice to extract soil samples and make 
laboratory measurements of data concerning the characteristics of a soil 
bed on the recovered samples. While some arrangements have exhibited at 
least a degree of utility in the gathering of data in connection with soil 
mechanics analysis, room for significant improvement remains. 
There are many cases in engineering practice where it is necessary to 
determine the engineering characteristics of gravelly and course-grained 
soils. Desirably, this would be done in-situ, since the properties of 
cohesionless soils are known to be influenced significantly by sample 
disturbance. However, standard methods of in-situ exploration developed 
for sands, such as the Standard Penetration Test (PST), the Cone 
Penetration Test (CPT), the self-boring pressuremeter, etc. give erroneous 
results in gravels because the soil particles are large compared to the 
dimensions of the test equipment. Furthermore, determining soil properties 
by laboratory testing is hampered by the fact that it is virtually 
impossible to take undisturbed samples of gravelly soils, except by 
in-situ freezing techniques, and these are enormously expensive. 
In consequence, the engineering properties of gravels are more customarily 
determined by constructing test pits to extract samples for grain size 
distribution tests and for determining the in-situ density or relative 
density of the gravelly soil. Representative samples are then prepared in 
the laboratory to the same density as that of the field deposits and used 
to determine engineering properties such as strength, deformation, and 
compressibility characteristics. Alternately, the engineering properties 
of the deposit are assessed on the basis of judgment, based on a knowledge 
of the grain distribution and the density of the deposit. Only 
occasionally has in-situ testing been attempted or used for engineering 
property determinations of gravelly soils. 
In many cases the above procedures have provided useful data for design 
studies. However, care must be exercised to insure that all relevant 
factors influencing the interpretation of the test data obtained from the 
reconstituted samples are considered in the final evaluation of 
properties. This involves consideration of changes in density, if it is 
necessary to change the gradation by scalping or adopting a parallel 
gradation curve for preparation of laboratory test specimens, and in some 
cases, consideration of other effects such as "aging", which is likely to 
change the properties of any cohesionless soil over a long period of time. 
In recent years, it has been found necessary to explore other properties of 
gravelly deposits, in addition to the conventional determinations of 
strength, deformation and compressibility characteristics. These include 
the response of gravelly deposits to cyclic loading, which may be induced 
by earthquake shaking or water action. It is only recently that the need 
for such studies and determination has been recognized. Some years ago it 
was the conventional wisdom of the goetechnical engineering profession, 
for example, that gravelly soils were not susceptible to large increases 
in pore water pressure, leading possibly to liquifaction, under the 
effects of earthquake shaking. It was generally believed that gravelly 
soils, because of their high permeability, would be able to dissipate pore 
pressures virtually as fast as they could be generated by earthquake 
shaking, and thus were not vulnerable to liquefaction during earthquakes. 
Clearly, this depends on the nature of the soil (sandy gravels for 
example, may not be significantly more pervious than sands); pore pressure 
dissipation also depends on the boundary drainage conditions since a 
gravel is not freedraining if it is underlain and overlain by relatively 
impervious layers of other soils. 
The concept that gravels were not vulnerable to liquifaction was also 
fostered by the better field performance of foundations on gravel, as 
compared with sands, in earthquakes such as the Alaska earthquake of 1964, 
and by laboratory tests, conducted under cyclic loading conditions, which 
showed that significantly higher stresses were required, even under 
undrained cyclic loading conditions, to induce high pore water pressures 
in gravelly soils than in sands. It has since been recognized that the 
higher laboratory strengths were due mainly to the effects of membrane 
compliance, and that when laboratory test results are corrected for this 
effect, the cyclic loading resistance of gravels is not very different 
from that for sands. 
Finally, and more importantly, there have been a number of cases in recent 
years where liquifaction of gravelly deposits has been observed to occur, 
with associated effects, during earthquakes. These events have prompted a 
review of earlier earthquake performance of gravelly soils and several 
cases of earthquake-induced liquifaction in gravelly soils are now 
recognized to have occurred. 
In a number of these cases, the generation of soil "blows" at the ground 
surface showed that particles up to one inch size had been carried upward 
by flowing water, or that sand was washed out of sandy gravel deposits to 
form sand boils at the surface. 
Recognition of these effects has led to a renewed interest in the 
liquifaction characteristics of gravelly soils and in methods of field 
exploration which can lead to meaningful determinations of their in-situ 
characteristics. Since the nature of gravelly soils is likely to involve 
many of the same problems in geotechnical investigations as sands, i.e., 
significant variability within relatively short distances and significant 
changes in properties due to sample disturbance, it has seemed desirable 
to explore the possibility of exploring the properties of gravelly soils 
using procedures which have proved successful for sandy soils; that is by 
the use of some type of penetration test which can be performed rapidly, 
at a number of locations in a deposit, to provide a representative index 
of overall characteristics. Clearly such a test would need to be much 
larger in scale than the relatively small-scale SPT or CPT tests used 
widely for investigating the liquefaction resistance and other properties 
of sands. In fact, a large scale version of either of these tests would 
seem to provide a useful basis for investigating the characteristics of 
gravelly soils. An added advantage of such an approach is that a 
large-scale version of, say, the SPT test should be just as applicable in 
sands as the conventional SPT test and thus it should be possible to 
correlate the results of the test results with the extensive body of field 
performance data, such as liquifaction resistance and compressibility, 
through the development of correlations between the different test 
procedures. This would provide a direct basis for evaluating the field 
behavior of gravelly soils. 
Fortunately, such a large-scale type of penetration test already exists in 
the form of the Becker Penetration Test, developed in Canada in the later 
1950's and now widely used for exploring the characteristics of deposits 
containing gravel and cobble-size particles. 
Present methods and apparatus for measuring the ability of a soil bed to 
support a structure are limited in several ways. First, there are no known 
methods or apparatus that measure the dynamic loading characteristics of a 
soil bed as a function of time. Moreover, present methods and apparatus 
utilize short displacement, cyclic, linear penetration techniques that 
penetrate a soil bed at a constant rate and do not measure the dynamic 
loading characteristics of the soil. 
One prior art device is shown in U.S. Pat. No. 5,339,679 to Ingram et al 
discloses a self-contained apparatus for determining the static and 
dynamic loading characteristics of a soil bed. In operation, a drill 
string presses the apparatus into a soil bed at an uncontrolled rate 
resulting in a variable penetration rate. The apparatus has a 
self-contained data acquisition system that measures and records, as a 
function of time, the force exerted on the sampling apparatus and the 
depth of penetration as the drill string presses the sampling apparatus 
into the soil bed. Data is provided that enables the user to determine the 
static soil characteristics (e.g., shear strength and stress-strain 
characteristics) and the dynamic loading characteristics of the soil bed. 
U.S. Pat. No. 4,542,639 to Cawley et al discloses apparatus and method for 
testing structures by impact. The structure is struck by an impacter 
associated with a force transducer, the output of which is related to the 
force which the transducer experiences on impact and encompasses a 
frequency range including the lowest frequencies (typically approaching 
zero frequency) which that force contains to any substantial degree. A 
test spectrum of the force including that full range of frequencies is 
produced by a Fourier transformer in a form suitable for automatic 
comparison, and is than compared with a reference spectrum typical of 
impact with a reference structure, and a signal is produced indicating fit 
or lack of fit between the test and reference spectra. 
U.S. Pat. No. 5,048,320 to Mitsuhashi et al and U.S. Pat. No. 5,195,364 to 
Dehe et al disclose methods and apparatus for testing the hardness of 
objects or structures using non-destructive impact to an object to be 
inspected. 
The problems enumerated in the foregoing are not exhaustive but rather are 
among many which tend to impair the effectiveness of previously known 
testing devices and data gathering systems. 
SUMMARY OF THE INVENTION 
The present invention addresses the problems described above by providing a 
method and apparatus for providing analysis and evaluation of Becker 
Penetration Test Data more accurately and timely to be used to modify 
drilling programs while in progress. The data logger monitors the bounce 
chamber pressure by use of a pressure transducer connected in line with, 
and adjacent to, the monitoring gauge. Locating the pressure transducer 
adjacent to the monitoring gauge ensures that the recorded pressure is the 
same as the visually monitored pressure and that any effect of hose length 
is the same for both automated and manual monitoring. Since the bounce 
chamber pressure is cyclical, and the primary interest is the peak 
pressure for each hammer blow, the data logger repeatedly measures the 
transducer pressure, selects the peak pressure for each hammerblow, and 
stores the peak pressure along with the date and time of each blow in the 
data logger memory.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The Becker Hammer Drill, shown in FIG. 2, was developed by Becker Drills 
during the late 1950's as a method for rapidly penetrating deposits of 
gravels and cobbles. The method consists of driving a double-walled casing 
into the ground with a double-acting diesel pile hammer. During driving, 
air is forced down the annulus of the casing system to the drive bit as 
shown in FIGS. 2A and 2B. Soil particles entering the bit (FIG. 2B) are 
then transported up the inner casing (FIG. 2B) to the surface (FIG. 2A) by 
the air flow and they are then collected in a cyclone as illustrated in 
FIG. 2. 
The diesel hammer used on Becker drill rigs is rated at a maximum energy of 
8100 foot-pounds per blow. This type of pile hammer is closed off at the 
top and part of its energy during driving is developed by the compression 
of air in the top of the hammer cylinder during the travel of the ram 
during each cycle. By measuring the pressure of this trapped air pressure 
(bounce chamber pressure), in bounce chamber 23, an estimate of the 
driving energy can be obtained for each blow. Correlations between 
potential hammer energy and bounce chamber pressure have been developed by 
the manufacturer. 
The hammer frame is mounted on rollers or wear blocks which move along 
guides on the drill rig mast. Delivering 92 blows per minute, it is not 
unusual for the hammer to achieve penetration rates of about 100 feet per 
hour. On completion of each sounding, the casing is gripped with tapered 
slips and raised by hydraulic grips. It usually requires about 60 minutes 
to withdraw 100 feet of casing from the ground. 
The double walled casing is composed of two heavy pipes arranged 
concentrically (FIG. 2B). The inner pipe floats inside the outer pipe, 
separation being provided by neoprene cushions, and only the outer pipe 
absorbs the direct impact of the hammer. The casing is provided in 8 to 10 
foot lengths, and segments are connected with threaded joints in the outer 
pipe. An "O" ring seal is used on one end of each inner pipe segment to 
avoid leaks between the outer and inner pipes. 
The Becker Penetration Test consists basically of counting the number of 
hammer blows required to drive the casing one foot into the ground. By 
counting blows for each foot of penetration, a more or less continuous 
record of penetration resistance can be obtained for an entire soil 
profile. This test was originally called the "Becker Denseness Test" and 
was developed in Canada by using a plugged 8-tooth crowd-out bit with 
5.5-inch O.D. casing. The plugged bit was employed because it was found 
that open-bit soundings in saturated sands often gave erratic results. 
Over the years, however, Becker penetration testing has employed both open 
and plugged bits together with both 5.5-inch and 6.6-inch O.D. casing 
sizes. 
On a number of investigations, the Becker Penetration Test has often been 
used for the purpose of obtaining equivalent Standard Penetration Test 
(SPT) blowcounts and using correlations between SPT resistance and field 
behavior to predict performance. During the last 13 years, several 
correlations between Becker blowcounts and (SPT) blowcounts have been 
developed. The great variability of Becker-SPT correlations is due in 
large measure to the fact that the different studies often employed 
different Becker and SPT procedures and equipment, as well as different 
methods of data interpretation. 
The studies do indicate that the penetration resistance measured by the 
Becker Drill procedure has the potential for development as an index of 
soil penetrability and that if tests were performed under suitably 
standardized conditions, a useful correlation between SPT and the Becker 
Test blowcounts could be developed. 
Use of the automated Becker Hammer Bounce Chamber Pressure Monitor of the 
invention, designated by the numeral 10, to monitor bounce chamber 
pressure for the Becker Penetration Test was initially performed to 
improve the quality of data obtained during a typical test, and to enable 
test data to be evaluated at the test site enabling the test program to be 
altered if required. Prior to use of the automated monitor 10, an observer 
was required to count the number of hammer blows for each one foot 
interval of casing penetration, and observe the monitoring gauge to record 
the average peak pressure for all of the hammer blows in that interval. 
Monotony, high blowcounts, or variances in pressure within each interval 
often resulted in errors in recording the data. Furthermore, the recorded 
data required additional handling to enable input into the computer 
programs for analysis. Use of the monitor 10 eliminated these problems by 
recording bounce chamber 23 pressure for each hammer blow, and computing 
an average bounce chamber 23 pressure and standard deviation for each one 
foot interval. Recorded data is immediately available for analysis and is 
in a format suitable for input into computer programs for further 
analysis. 
The monitor 10 consists of a pressure transducer 11, quick connect manifold 
12, data logger 13, storage devices 15 and 16 weatherproof control module 
17, indicator lamp 18, keyboard 19, and telephone modem 20. The components 
of the monitor 10 are housed in a weatherproof storage case 21 and powered 
by a battery 14. The Becker Hammer bounce chamber 23 is connected to the 
monitor 10 through socket 25, plug 26, through hose 24 to "Tee" 12 with 
quick connect couplings. Pressure transducer 11 is connected from the 
"Tee" 12 through weatherproof connectors 22 to the data logger 13. 
In a preferred embodiment, the pressure transducer 11 had a range of 0-50 
psi, with an output of 4-20 mA. Transducer 11 was a model 27-142-1050 
manufactured by Keller PSI, Hampton, Va. 23666. Data logger 13 was a model 
CR10, storage modules 15, 16 were models SM192 and SM716, keyboard display 
19 was a model CR10KD, telephone modem 20, was a model DC112. Additional 
components (not shown) are power supply, model BK; optically isolated 
RS-232 interface, model SC32A; 9 pin peripheral to RS-232 interface, model 
SC 532; data logger 13 support software, model PC 208; and cables model 
SC12. All of these units were supplied by Campbell Scientific, Inc., 
Logan, Utah. Control pod 17 was fabricated from a Woodhead Pushbutton 
Station, Model 4023, manufactured by Daniel Woodhead, Co., Aurora, Colo. 
Enclosure 21 was a model 827, manufactured by Underwater Kinetics, San 
Marco, Calif. The connectors were supplied by Newark Electronics of 
Denver, Colo., or Warren Fluid Power, of Denver, Colo. 
The monitor 10 is controlled by a program containing a series of 
instructions which control the schedule, pressure transducer 11 
measurement, control module signal monitoring, computation of data, and 
data storage operations of the data logger 13. The program is described in 
Appendix I to the specification. The data logger 13 monitors the bounce 
chamber 23 pressure by use of a pressure transducer 11, connected in line 
with, and adjacent to the monitoring gauge 27. Locating the pressure 
transducer 11 adjacent to the monitoring gauge 27 ensures that the 
recorded pressure is the same as the visually monitored pressure and that 
any effect of hose 24 length is the same for both automated and manual 
monitoring. Since the bounce chamber 23 pressure is cyclical and we are 
interested in the peak pressure for each hammer blow, the data logger 13 
repeatedly measures the transducer 11 pressure, selects the peak pressure 
for each hammer blow. and stores the peak pressure along with the date and 
time of each blow in the data logger 13 memory 15 and 16. 
The operator is required to depress a switch on the keyboard 19 or control 
module 17 to signal the data logger 13 for each one foot of casing 
penetration. This signal causes the data logger 13 to compute the 
blowcount, and the average and standard deviation of the pressure peaks 
for the previous foot of penetration. This penetration, as well as the 
date, time, and depth of penetration is stored in the data logger 13 
memory. The operator is also required to depress a switch on the keyboard 
19, or control module 17 to signal the data logger 13 to indicate the 
completion of a drill hole. 
The data logger 13 monitors the pressure transducer 11 signal sixty four 
times per second. At a Becker Hammer rate of ninety two blows per minute, 
the pressure is measured about forty two times per blow, and thus the 
accuracy of the measured pressure is expected to be less than the 
estimated 0.5 psi accuracy of visual observations. The data logger 13 is a 
battery powered, programmable controller in a small, rugged, sealed module 
which enables scheduled measurement of the pressure transducer 11, 
monitoring and recording of user input control signals via the control 
module 17 and keyboard 19, mathematical computations based upon the 
measurements and control signals, and storage of recorded and computed 
data. 
The pressure transducer 11 has a range of 0-50 PSI, with an output of 4-20 
MA. The quick connect manifold has quick connect fittings for instant 
installation of the pressure transducer 11 in the manual bounce chamber 
pressure gauge supply hose 24. 
The storage devices 15, and 16 are small, sealed modules which expand the 
random access memory of the data logger 13 and retain that memory with 
internal battery power 14 separate from the data logger 13. 
The weatherproof control module 17 contains waterproof control switches 
with large pushbuttons to enable user control of the data logger 13 
functions. An indicator lamp 18 is provided on the wiring panel of the 
data logger 13 to indicate the on/off status of the data logger 13. 
The keyboard 19 is a series of pushbutton switches and a display screen to 
enable user control of the data logger 13 and user monitoring of the 
status of the data logger 13 and collected data. The telephone modem 20 is 
a device enabling transfer of data and programming and control of the data 
logger 13 via telephone by using a personal computer. 
The weatherproof storage case 21 is a suitcase-type box, which houses all 
of the monitor's components, and is fitted with external connectors for 
the pressure transducer 11 and weatherproof control module 17 to enable 
use in rainy or inclement weather. 
SYSTEM OPERATION 
The data logger 13 is controlled by user controlled flags which can be set 
and cleared by using the keyboard 19, control module 17, or an external 
personal computer. User controlled flags enable the user to start or stop 
operation of the data logger 13. When operating, the data logger 13 
monitors the pressure transducer 11 signal 64 times per second, converts 
the signal to pressure (PSI), compares each reading to the previous 
reading, and retains the highest reading. When the pressure decreases 
below 5 psi following a reading greater than 5 psi, the retained highest 
reading is considered to be the peak pressure for the cycle or pulse and 
is stored with an identification code indicating that the data pertains to 
a peak pressure data point, the julian day, hour, minute, and seconds. The 
completed cycle increments a counter called blow/foot, and zeros out the 
previous peak pressure reading. Operation continues indefinitely until 
stopped by the user. 
A second user controlled flag signals the data logger 13 to indicate 
completion of a one foot interval of penetration by the Becker Hammer 
Drill. This signal causes the data logger 13 to increment a counter called 
a foot counter, and to compute the average and standard deviation of all 
peak pressure readings since the last time the flag was turned on by the 
user. The computed data is stored with an identification code indicating 
that the data pertains to completion of a one foot interval of 
penetration, along with the julian day, hour, minute, seconds, and battery 
voltage, and the blows/foot counter is zeroed out. Then the flag is 
automatically reset. 
A third user controlled flag signals the data logger 13 to indicate 
completion of the drill hole. This signal causes the data logger 13 to 
zero the foot counter and the blows/foot counter, and to store an 
identification code indicating that the data pertains to the completion of 
a drill hole, the julian day, hour, minute, and seconds. Then the flag is 
automatically reset. 
All stored data is retained in the data logger in two separate areas until 
it overwrites itself, or until the power is interrupted. The data is 
separated as follows: One area includes only the data recorded for each 
foot of penetration, and consists of the identification code, the julian 
day, hour, minute and seconds, standard deviation of the pressure peaks in 
psi, average pressure of the pressure peaks in psi, number of blows per 
foot for the completed foot of penetration interval, and foot counter 
value indicating depth of penetration. The second area includes an 
identification code, the julian day, hour, minute, and seconds, and peak 
pressure for every completed pressure cycle, foot counter value indicating 
depth of penetration, and battery voltage. The identification code is 
unique depending upon the type of data, whether pressure data for each 
completed pressure cycle, foot counter increment or completion of drill 
hole signal. 
All data from one area is transferred automatically to the first storage 
device and from the other area to the second storage device. Data in the 
storage devices are retained by internal battery power even when the 
devices are removed from the data logger 13 enabling transport of the 
devices while the data logger 13 continues to operate. Data in the storage 
devices can be examined or transferred to a personal computer for import 
into spreadsheet programs for analysis. 
It will be appreciated that the method and apparatus for determining the 
dynamic characteristics of a soil bed by penetrating a soil bed at a 
variable penetration rate and measuring the force and displacement of the 
of the sampling device as a function of time of the present invention, 
provide certain significant advantages. The principal utility of the 
invention would be in-situ soil testing and analysis. The general field of 
application in geotechnical engineering, in-situ testing. The invention 
would be used by both federal and public agencies and private entities 
utilizing the Becker Hammer Drill to determine penetration resistance of 
soils. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims, the invention may be 
practiced otherwise than as specifically described.