Borehole Shear Test Research Articles

Shear Strength of Prestressed Cohesive Soils

The results of an experimental investigation to determine the effects of preloading on the Mohr-Coulomb failure envelopes of cohesive soils are described. In situ shear tests using the Borehole Shear Test (BST) were performed on a number of natural soil deposits. Initially, conventional stage tests were conducted to obtain the failure envelope. Subsequent tests were conducted by consolidating to a higher normal stress than was used in the shear phase of the test. Results are evaluated by examining the relative increase in shearing resistance between the original failure envelope and the prestressed failure envelope. By defining the Preloading Stress Ratio (PSR) as the ratio of the normal stress where shear strength comparisons are being made to the preloading stress, the relationship between relative strength increase and PSR could be determined. The data indicate that this increase may be described as a power function of the form y = axb, where a and b are regression coefficients which indicate the rate ...

Criterion of failure for design of rock mass structures as determined by borehole shear tests : Panek, L A Proc 4th Congress International Society for Rock Mechanics, Montreux, 2–8 Sept 1979, Vol 2, P509–515. Publ Rotterdam, A A Balkema, 1979

Criterion of failure for design of rock mass structures as determined by borehole shear tests : Panek, L A Proc 4th Congress International Society for Rock Mechanics, Montreux, 2–8 Sept 1979, Vol 2, P509–515. Publ Rotterdam, A A Balkema, 1979

Borehole Shear Test for Stiff Soil

The Iowa Borehole Shear Test (BST) is a rapid, direct shear test performed on the walls of borehole in soil. The test measures in-situ soil shear strength by failing the soil along the circumference of the hole. Sharply ridged, diametrically opposed shear plates are expanded by gas pressure to apply a normal stress against sides of the hole. A shearing stress is then applied by pulling the plates axially along the hole while maintaining a constant normal stress until failure occurs. By repeating the test with different values of normal stress, a series of shearing stress values are obtained from which a Mohr-Coulomb failure envelope is drawn. Allowing time for drainage between successive points permits interpretation of results on a consolidated-drained basis.

Slope Angles in Friable Loess

Maximum stable heights of steep, friable loess slopes of western Iowa and western Tennessee were found to relate to the soil density and shear strength in accord with the sliding-wedge method of analysis. Shear strength was determined in situ with the borehole shear test, which allows a rapid field determination of the Mohr-Coulomb failure envelope. Tests at six sites in Iowa showed no consistent difference between horizontal versus vertical shear strength, except that horizontal strength was more variable. The frequently cited vertical cleavage of loess appears to be a result of tension in the surface layer in accord with Rankine theory and is not unique to loess. Vertical slab or cleavage failure should result in an average slope angle of about 77°, which coincides with an observed modal frequency in western Iowa loess. Failure of a 77° cut in shear should then result in an average slope of 51° dependent in part on the angle of internal friction, ; the 51° angle also coincides with an observed mode. A third observed modal frequency around 38° is attributed to the angle of repose of failed loess, and lower slope angles must relate to other mechanisms. The internal-friction angle, , of friable loess is fairly constant (20°-30°), and the cohesion, c, can be estimated by measuring the maximum heights of steep loess cuts.