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OPERATING MANUAL
HM-381 & HM-381F Direct/Residual Shear Device
This shear device utilizes a pneumatic loading piston
for applying the vertical load to the sample. The device
is a self-contained table-top model that eliminates the
need for the numerous weights used in dead weight
systems. It has a built-in digital pressure readout (psi)
for setting the vertical load and a load cell with readout
for measuring shear forces. Consolidation and shear
displacement are measured with a analog mechanical
dial indicator. The readout can be read manually.
Applying the vertical load is accomplished by setting
the precision regulator to the required pressure per the
calibration chart. Load settings are veried on the pressure readout accurate to 0.25%. Sample loads are obtained using two pneumatic pistons. A small diameter
rolling diaphragm piston is capable of applying loads
up to 100lbs.
Maximum shear displacement is 0.8”. Travel is set with
limit switches by the operator. A stepping drive motor
and controller maintains the desired rate of strain. The
strain rate is easily set with digital thumbwheels and
is maintained within 1% by a crystal stabilized clock.
The thumbwheel settings represent direct readings in
inches per minute (0001 = .0001in/min).
CONSTRUCTION
The Direct Shear was designed for harsh lab environments with a solid base (1.25” thick) for the loading
and shear box assembly coupled with a sturdy aluminum cabinet. The upright rods are stainless steel and
the cabinet is painted with an enamel nish. The water
chamber is a Teon® - coated anodized aluminum for
corrosion resistance.
Specications
Horizontal Movement: 0.8”
Strain Rate: .0001”to .2999 in/min.
Overall Height: 22”
Length: 30”
Depth: 14.5”
Weight: 175lbs.
Electrical: 110 V 60Hz/ 220 Volts 50Hz
Model Load
Capacity
HM-381/
HM-381F
1500lbs. 90 psi 1500 lbf
INTRODUCTION
The direct shear test may be run on any type of soil
sample, but it is particularly adapted to cohesive materials. This machine can also be used to establish the
undrained shear strength of saturated, highly plastic
cohesive soils under certain conditions.
HM-381
(for HM-381F)
Air Pressure
Required
Horizontal
Shear Force
PHONE: 800-444-1508 P.O. Box 200, Lewis Center, Ohio 43035-0200
740-548-7298 E-mail: customerservice@gilsonco.com Product Web Page: www.globalgilson.com
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Rev: 10/2019
FAX: 80 0 -255- 5314
740-548-5314
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The direct shear test is normally run as a strain-controlled test. In order to obtain the effective stress parameters of any soil, excluding the most pervious
medium and ne sands, it is necessary to use a slow
rate of shearing in order for induced pore pressures
to dissipate. The remainder of this procedure presents
a discussion on the sample preparation for testing,
equipment preparation, and running direct shear machine. Refer to ASTM D3080 and/or AASHTO T 236 for
procedures and details on the test methods.
CONNECTIONS
Vertical Displacement Rod – Screws into the top platform to the right of the rear pull-down rod.
Vertical Displacement Clamping Arm – Attach to the
above rod.
Vertical Displacement Dial Gauge – Consolidation –
Attach to the clamping arm with the screw provided.
Horizontal Displacement Dial Gauge – Shear – Attach to the threaded rod on the angle bracket-top platform, right front.
Air Line – A constant supply of air is required. The air
inlet air pressure should not exceed 200 psi, nor should
it ever be less than 20 psi higher than the highest pressure setting. The connection is a ¼” Swagelok, located
in the rear of the cabinet. Insert the tubing into the tting until it bottoms out. With the nut nger tight, tighten
the tting 1 ¼ turns with a wrench. Do not over tighten.
nger tight position. One full turn will give .031” gap.
There is a line scribed on the adjusting knob for determining how much gap each screw has provided. The
screws should be turned evenly to maintain a proper
gap. At the bottom of each screw is a nylon glide which
keeps the top shear ring from dropping during the test.
PANEL CONTROLS — LOAD SETTING
Residual Shear Force LCD Readout – The digital
readout will display real time load settings and peak
load of the horizontal load cell. Use the tare button to
zero the display before starting test.
Load Regulator – A precision Fairchild regulator is
used to set and maintain the air pressure to the pistons which provides load to the sample. The regulator
is sensitive to 1/8” variations in water column. Select
the load required from the load setting table.
Note: The consolidation load pad, porous stone, and
stainless-steel ball have not been included in the load
setting calibrations.
High Load/Low Load Selector Valve – This valve
has two positions. The LOW LOAD position is used for
loads up to 100lbs depending on the model. The HIGH
LOAD position is used for loads up to 1500lbs.
Load Valve – This valve is actuated by 90-degree ro-
tation of the handle. When open it allows air to ow
from the regulator to the pistons (HIGH or LOW LOAD)
selected.
Load Cell – Connect the load cell to the support casting at the right end of the direct shear using the two
knobs. Adjust the knobs so that the load cell is as far
to the right as possible. This will allow room for assembling the water chamber and the shear rings with minimum interference. Connection is made at the rear of
the readout cabinet.
Water Chamber – Special care should be taken to
see that the four (4) roller bearings between the water
chamber and the base slide tracks are properly cleaned
and contain a slight amount of oil during and after use.
We advise using a cover over the direct shear after
use to eliminate dust from entering the precision slide
assembly. The main drive shaft should be at its home
position. This will place the sample load pad in the center of the crossarm for consolidation.
Shear Boxes (sold separately) – The shear boxes
are held together with (2) stainless steel screws. There
are also (4) screws for adjusting the gap between the
rings once consolidation has been reached. The gap
is adjusted by turning the screws clockwise from the
PANEL CONTROLS — POWER & SHEAR RATE
Power Switch – An indicator light is present when
power is turned on.
Strain Rate Selector – The strain rate is set with
thumbwheel selectors. The switches are direct reading
in inches/minute with an implied leading decimal point.
Once the rate is set and the test is started, the switch
setting is ignored until the stop switch is pressed or a
limit switch is tripped.
Limit Switches – These switches are located on the
platform behind the water chamber.
Adjustment of these switches is made by loosening the
Phillips-head screws and moving the limit switch assembly in the direction desired. The home position has
been set so that the load crossarm is in the middle of
the shear rings.
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Note: The limit of travel of the drive shaft is dependent
on the limit switch settings. Do not operate the drive
motor with the water chamber disconnected because
this will make the limit switches inoperable.
Stop Switch – Momentary push button to stop the
motor.
Direction Switch – Momentary (spring loaded) switch.
After setting the desired shear rate, moving the switch
in the desired direction will initiate movement. This
switch will then become inactive until the stop button is
pressed, or a limit switch is activated. The left position
will move the water chamber to the left. It will continue
until the water chamber activates the limit switch. At
this time, the limit indicator light will be lit. The right
switch position will move the shear box to the right until
the home limit switch is made. See above note…
Home & Limit Indicators – Used to indicate the limit
of travel of the shear box.
Fuse – 4 amp SLO BLO fuse located in the cabinet
rear.
SHEAR BOX (WATER CHAMBER) ASSEMBLY
Place the two roller slide assemblies on the tracks between the load arms. Position the rollers in the center of the tracks. Be certain the tracks on the platform,
shear box bottom and the roller assemblies are clean
and are lightly oiled. Place the shear box assembly on
the slide tracks being careful to align the limit switch
and the drive bolt connection to the slots in the shear
box.
SAMPLE PREPARATION
Once extruded, the samples should be trimmed carefully down to the internal diameter of the direct shear
rings, in a similar manner as for consolidation test samples. The object is to get at least once inch of soil sam-
ple sandwiched between a layer of lter paper and a
porous stone on either side of the sample. The porous
stones provide drainage and are used to distribute the
pressure during the test.
Place the bottom drainage plate and then a porous
stone with a lter paper into the locked shear rings.
Extrude one inch of soil sample into the shear rings.
Place another piece of lter paper and porous stone on
the top of the sample along with the top load pad.
SAMPLE SET-UP IN MACHINE
At this time, the direct shear box is held together by two
(2) nylon bolts and the soil sample would be centered
inside the rings. The shear rings with sample stones
are then carefully placed inside the direct shear water
chamber being certain the load cell shaft is connected
to the top shear ring. Tighten the two (2) shear ring
clamping knobs located on the left side of the water
chamber.
Tare the load cell by pushing the “tare” button on the
digital readout. The top crossarm should be adjusted
so that there is 1/8” gap between the cross arm and
the ball that sits on the load pad . Make sure the cross
arm is level . The upper cross arm has a displacement
indicator pin that is positioned on the load pad ball. Adjust the dial indicator or linear displacement transducer
to the top of this pin and allow for sufcient travel when
the soil sample compresses. The vertical dial indicator is positioned and set to read some arbitrary initial
reading.
CONSOLIDATION OF THE TEST SAMPLE
At this time, select a seating load per the load setting
table. Set the high/low load selector valve to “LOW”
and the load valve to “LOAD”. Adjust the pressure regulator to the desired seating load per the load setting
table. This sets the stage for the consolidation phase of
the sample with the application of the desired overburden pressure or some other normal pressure.
Turn the “LOAD” valve to the “OFF” position and adjust
the regulator to the desired normal load per the load
setting table.
The vertical dial indicator is read at this time and noted
on the data sheet. At the same time the load valve is
turned to “LOAD”, a stopwatch is started in order to
record the appropriate time deformation characteristics
of the soil sample undergoing consolidation. Consolidation data is taken at the usual time increments. The
purpose of recording the time deformation characteristics of the soil sample is to establish the rate of shear
testing of the soil. Refer ASTM D3080 or AASHTO
T 236 for computations.
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TEST PROCEDURES
The nal dial reading after consolidation is noted on
the data sheet. Adjust the shear force on the sample
by adjusting the two knurled nuts on the load cell support casting. Allow a small seating load to be exerted
on the sample. The horizontal dial indicator is then adjusted to some convenient zero point. Until this time,
the two shear rings have been held together by two (2)
screws – these screws are now removed. There are
also four (4) screws for adjusting the gap between the
rings once consolidation has been reached. The gap
is adjusted by turning the screws clockwise from the
nger tight position. One full turn will give .031” gap.
For sands of a ne to medium size, 1 ¼ of a revolution
of the adjusting screw is used. For coarser sands, 1 2/3
of a revolution is used. For ne grain soils and clays, ½
of a revolution is used. These values are not absolute
and can be altered accordingly. Initial readings are taken at this time. The screws should be turned evenly to
prevent tilting the top ring.
The test is now started at the prescribed rate of shear
by setting the shear rate selector. Unless automatically recorded, the shear and compression dial indicators
will be read at various prescribed horizontal deection
readings such as every ten divisions of the three-place
dial until failure. Usually the test is carried out past failure to determine the residual strength which may be
used in design. At this point the test is completed, the
shear loading is stopped, and the vertical load is removed.
SAMPLE REMOVAL AND CLEAN-UP
Put the motor drive in reverse (towards the home position) and stop when zero (0) load is reached on the
load cell readout. Remove the sample at this time and
inspect per ASTM or AASHTO procedures. The vertical
load is now reduced to zero (0) by adjusting the pressure regulator to zero (0) psi. The apparatus is taken
down in reverse order as assembled. The sample is
extracted and weighed in order to determine the dry
density and water content at failure. The water chamber is returned to the home position by using the drive
motor. Cover the roller bearing slide assembly to prevent dust and dirt from entering the bearings.
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