Direct Shear Box Test

Topics: Soil mechanics, Geotechnical engineering, Shear strength Pages: 3 (516 words) Published: January 12, 2013
Direct Shear Box Test

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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