# Direct Shear Box Test

**Topics:**Soil mechanics, Geotechnical engineering, Shear strength

**Pages:**3 (516 words)

**Published:**January 12, 2013

Contents

Introduction

Objective

Apparatus

Description of Test

Results

Calculations

Relevance to Geotechnics

Soil Description and Conclusion

References

Introduction

Shear strength is the property that enables a material to remain in equilibrium when its surface is not level. (Smith, 2006) The direct shear test is used to determine the shear strength of soils on a predetermined failure surface. This test is used to measure the shearing resistance, undrained shear strength, and dilative and contractive tendencies in soils. (Fratta et al, 2007) The results can then be used to determine the allowable bearing capacity of foundations and stability of retaining walls, cuttings and embankments. Objective

To determine the angle of shearing resistance of a sample of sand; the test may be carried out either dry or fully saturated but not anywhere in between. Apparatus

* Motorised shear box

* Electronic balance

* Horizontal and vertical measuring gauges

* Assorted steel weights

* Lever arm attachment

* Tamper

* Proving Ring

Description of Test

Three samples of the same soil are placed into the shear box, which has two stacked squares to hold the sample. A confining stress is applied to the sample and the upper square is pulled laterally until the sample fails. The normal stress applied, the vertical displacement and proving ring are recorded at regular and frequent intervals.

Normal Stress(kPa):25,050,075,0

Sheat stress at Failure (kPa):22,439,073,0

Area = 60 * 60 = 3600mm2 = 3,6 * 10-3 m2

σ1 = 25,0/Area = 6944,45 kPa

σ2 = 50,0/Area = 13888,89 kPa

σ3= 75,0/Area = 20833,34 kPa

Τ1= 22,4/Area = 6222,23 kPa

Τ2= 39,0/Area = 10833,34 kPa

Τ3= 73,0/Area = 20277,78 kPa

ɸ‘= tan-1 (6222,23/6944,45) = 41,86°

Relevance to Geotechnical Design

The relevance of this test is to determine whether the soil will have enough shear strength to support planned construction works upon it, such...

References: Smith, I. 2006. Smith’s Elements of Soil Mechanics. 8th Ed. Blackwell Publishing

Fratta. 2007, Introduction to Soil Mechanics Laboratory Testing. CRC Press

Liu, C. Evett, J B. 2000. Soil Properties: Testing, Measurement and Evaluation. 4th Ed. Carlisle Publishers

British Standards Institute 1999. BS5930: 1999

British Standards Institute 1999. BS1377: 1999

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