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
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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