Influence of Clayey Soil Structure on Its Modulus of Stiffness

Disturbance of soil structure influences its density, strength and deformation properties. Among other cases soil structure could be disturbed by compacting it. It is possible to increase deformation properties of sand or gravel by compacting them. However, for clay soils deformation properties may increase if they are compacted. Differences of settlements of a building depends on the different deformation properties of the artificially placed and compacted soils beneath the foundations. Different values of stiffness modulus are used for the structural design of the buildings which are constructed on the soils with different compressibility. Coefficient of changeability of soil compression (1) was used. It may be calculated as a ratio of maximum and minimum values of deformation modulus, or according to the maximum and minimum values of coefficient of relative compressibility (3). Coefficient of the relative compressibility of soil can be calculated depending on the maximum and minimum values of tip resistence from CPT test (5). According to the coefficient of the relative compressibility we could estimate whether the soil is uniform, nonuniform or extremely non-uniform. It is important for the design of civil engineering structures. Mechanical properties of soils may be back-calculated using theoretical values of settlements and loads. Most frequently within the building layout area soils are natural and artificially compacted. For a compacted soil it is possible to draw compression curve in semi-logarithmic scale using compression curve of the same natural soil and the void ratio of the artificially placed and compacted soil. Thus we can determine compressibility of the soil with disturbed or undisturbed structure. Using parameters of soil compressibility, we can determine the coefficient of the relative compressibility, maximum and minimum values of settlement and modulus of stiffness.

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