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The geotechnical behavior of cohesionless soils is governed by field conditions. Such soils exist in two distinct forms, namely: disintegrated, such as fresh sediments under no overburden and/or no suction, and intact, such as old deposits with overburden and/or suction. The main contribution of this research was the successful capture of field conditions in laboratory samples, and the determination of shear strength under saturated and dried states. Results indicated that disintegrated samples possess identical soil behavior under both saturation states. Shear stiffness and peak shear increased with increasing normal stress, and no clear failure peaks were observed, similar to loose soils. Both samples showed an initial contraction followed by dilation at low normal stresses and mostly contraction at high normal stresses. Apparent cohesion was non-existent, and the friction angle measured 44.5° in the saturated state and 48° in the dried state. The intact sample exhibited behavior similar to the disintegrated sample when saturated. Under the dried state, clear failure peaks followed by residual shear were observed, similar to dense soils. Soil response was primarily dilative at low normal stresses and largely contractive under high normal stresses. Apparent cohesion was zero, and friction angle was 42° in the saturated state and changed to 91 kPa and 36°, respectively, in the dried state. Finally, structural cohesion increased with normal stress, and the friction angle due to suction was between 0.05° and 0.02°.

Deformation behavior and bearing capacity of geogrid-reinforced sand were investigated through experimental study. Series of cyclic and monotonic loading tests were performed by using a large container, a rectangular footing and two geogrid types: triangular and biaxial. Footing orientation was considered as a parameter to examine the directional confinement effect of the geogrid. Test results showed that this effect was obvious on the development of permanent deformation and on the ultimate bearing capacity of reinforced sand. However, this influence became smaller on the ultimate bearing capacity if a stiffer geogrid was used for reinforcement. Significant reduction in permanent deformation and beneficial improvement in bearing capacity were observed in all geogrid-reinforced tests.

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The deformation potential of geogrid-reinforced aggregate layer was investigated through laboratory large scale model tests. The influence of the aggregate layer thickness was mainly considered together with reinforcement depth. Cyclic pressures were applied with increasing the amplitude after every 500 cycles. Under low pressure amplitude, the rate of surface deformation reached a stable stage with increasing load cycles, regardless of reinforcement condition. This rate was more progressive with load cycles under high pressure amplitude, which was more obvious in unreinforced case. Surface deformation was considerably resulted from lateral flow in thick aggregate layer, and from subgrade deformation in case of thin aggregate layer, especially for the reinforced case. The contribution of subgrade deformation was small on surface deformation in thick aggregate layer, while it was significant in thin layer. The effective reinforcement condition was achieved when geogrid was placed at the middle of layer.