oa Civil Engineer in South Africa - Laboratory ko testing of cohesionless soil
The value of the coefficient of earth pressure at rest, ko and the stress-strain characteristic of soils at rest condition are important engineering considerations in the solution to problems involving pressure on stiff retaining structures, soil pressure on buried structures, and stability of excavations or settlement of large fills. The lateral soil pressure ring, a new instrument, which allows laboratory determination of the lateral soil pressure response to vertical loading without lateral strain and with limited lateral strain, is introduced in this paper. A series of tests performed on uniform and poorly graded sand specimens is described.
Test results show that ko is affected by the particle size, particle size distribution, stress history, overconsolidation ratio, the level of vertical pressure and the lateral strain. The elastic parameters of the material were also determined using the lateral soil pressure ring. Some comparative triaxial ko tests were performed using Bishop and Henkel's ko belt and it was found that when the vertical stress was low the ring yielded higher ko values and when the vertical pressure increased both methods yielded similar ko values.
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