Direct Shear Box Test
Prepared by Seah (7/10/02)
Soil Sample Requirements:
• Test Material: Sand (or Clay)
• Size: 50 mm to 63.5 mm in diameter, 20 mm in Height
Equipment Check:
• Balance loading arm
• Fix moment arm ratio: 1:10
• Align Dial Gauge
Sample Preparation and Equipment Setup (for Sand):
1. Prepare dry uniform sand for testing.
2. Release the four (4) lifting screws from touching the lower box.
3. Assemble the box by tightening the two (2) central screws to fix the lower box.
4. Place the base plate and lower porous stone in the lower box.
5. Rain the sand through a plastic cup with holes, keep a distance of 15 cm from
the surface of the sample.
a. For loose sand, enlarge the holes so that the sand can fall at a fast rate
b. For dense sand, rain the sand slowly to achieve high density.
6. Ensure that the sand is rained uniformly to form flat surface. Vacuuming with
fix distance from the top of the box can be used to ensure the surface is
horizontal.
7. Weigh the sample along with the box.
8. Place the top porous stone and top cap - Refer to Figure 1.
9. Release the lower two (2) pins in the sample bath.
10. Move the box to the loading frame.
11. Lock the lower two (2) pins in the sample bath.
12. Align the loading piston and turn the piston until it touches the top cap (note
that the loading arm will be lifted upwards).
13. Lock the piston by turning the nut downwards.
14. Lower the dial gauge so that it just touches the top of the piston.
15. The test is ready.
1
Consolidation:
1. Place the load required on the hanger to achieve required vertical stress. At
each increment, record the dial gauge reading at time.
2. Once the vertical consolidation stress is reached, then the sample is ready to be
sheared.
Shearing:
1. Reset the horizontal proving ring to zero by turning the end knot.
2. Connect the horizontal dial gauge.
3. Turn the four (4) lifting screws until they touch the lower box.
4. Turn the two (2) central screws anti-clockwise by quarter of a turn.
5. Turn the lifting screws clockwise by quarter of a turn.
6. Remove the central screws from the lower box.
7. Set the shearing rate (Sand: 0.2mm per minute).
8. Start the motor, measure the vertical displacement, horizontal displacement
and horizontal load.
9. Shear sample until a horizontal displacement of 5 mm is reached.
Disassemble Equipment:
1. Drive the motor back until initial horizontal position is reached.
2. Release the lifting screws from touching the lower box.
3. Reassemble the box by tightening the central screws to fix the lower box.
4. Remove the lifting screws.
5. Tighten the central screws.
6. Dismantle the piston and vertical dial gauge.
7. Release the lower two (2) pins in the sample bath.
8. Lift the box out of the bath.
9. Remove the sample from the box.
10. Weigh the sample.
Results:
1. Plot compression curve
2. Plot shear stress versus horizontal displacement.
3. Plot vertical displacement versus horizontal displacement.
2
Control Panel
Dial Gauge
(Vertical Displacement)
Direct Shear Sample
Dial Gauge
(Horizontal Diaplacement)
Proving Ring
Direct Shear Sample
(horizontal Load)
Hanger Top Cap
Porous Stone
Load Soil Sample
Dead Weight
(Vertical Load)
Horizontal Load
Bearing Plate
Results of Direct Shear Test Typical Values of φ and φcv
for Granular Soils
Note : τm = Peak Shear Stress Type of Soil φ, Deg φcv, Deg
τcv = Ultimate Shear Stress σ'τ
m3 Sand : round grains
Loose 28 to 30
Medium
σ'τ 30 to 35 26 to 30
m2 σ'τ Dense 35 to 38
cv3
Sand : angular grains
σ'τ Loose 30 to 35
m1 σ'τ Medium 35 to 40 30 to 35
cv2
Dense 40 to 45
σ'τ Sandy Gravel
φ φcv cv1 34 to 48 33 to 36
C'
Effective Normal Stress, σ'
Figure 1 Direct Shear Box Equipment
