Carbonate sands can be crushed under low confining pressure to achieve high compressibility. So particle crushing has significant influence on characteristics of strength and deformation. Carbonate sand of Sabkha layer in the middle east was made of deposition of shell fragments and it was consisted of porous particles containing inner void.
Generally, the soil structure begin to be destroyed at yield stress, so the porewater pressure and the settlement are increased rapidly. The carbonate sands of the Sabkha layer in the Middle East have very low shear strength. Therefore, instant settlement and time-dependent secondary settlement occur when inner voids are exposed, in the case of particle crushing.
The consolidation tests are conducted to investigate the soil particle crushing stress for understanding the secondary compression characteristics of carbonate sandy sabkha soil caused by particle crushing under a high confining stress. The rate of secondary crushing compression () is introduced instead of the rate of secondary compression to define the characteristic of the particle crushing compression settlement(). Void ratio () and settlement () in particle crushing are used as a reference point of secondary behavior, and the ratio of primary compression index () to secondary crushing compression (), value was changed from 0.0105 to 0.0187. When comparing with quartz sands, secondary compression settlement of sabkha is very large due to particle crushing. And this is not usually observed in quartz sand. It is observed that as the depth of sabkha layer is deep, the and are increased under the same stress level.
In carbonate sand, if particle fracture happens, the inner voids are exposed and porewater pressure can be decreased under yield stress which is different to compare with quartz sand. Porewater pressure can be determined as the sum of excess porewater pressure due to increase of relative density, inner void expose of particle under particle fracture stress and rearrangement of fractured particle fragments. The porewater pressure can be negative value in case of greater amount of inner void expose, so if particle fracturing is bigger, the porewater pressure value is smaller. The negative value zone of porewater pressure from Triaxial test result means particle fracture effect is bigger than outer void decrease effect and the particle fracture effect dominant zone size was 1.46∼3.46% from Triaxial test result of Sabkha layer.
The unusual shear strength graphes of carbonate sands resulted from the degrees of particle-precrushing. And for the range at > of ()- diagram, the negative(-) excess porewater pressures were happened, if the axial pressure makes the particle-crushing which induces the exposes of inner voids. Also, value was decreased after particle-crushing. It was concluded the unusual characteristics of carbonate sands were induced from the particle-crushing. Also, from the triaxial tests, the degrees of particle precrushing made the different types of excess porewater pressures.
We analyzed settlement of the Sabkha layer under a large-scale foundation by hydrotesting, and compared the field test results with the results of laboratory tests. With ongoing particle crushing, we observed the following stress-strain behaviors: strain-hardening (Sabkha GL-1.5 m), strain-perfect (Sabkha GL-7.0 m), and strain-softening (Sabkha GL-7.5 m). General shear failure occurred most frequently in dense sand and firm ground. Although the stress-strain behavior of Sabkha layer carbonate sand that of strain-softening, the particle crushing strength was low compared with the strain-hardening and strain-perfect behaviors. The stress-strain behaviors differ between carbonate sand and quartz sand. If the relative density of quartz sand is increased, the shear strength is also increased. Continuous secondary compression settlement occurred during the hydrotests, after the dissipation of porewater pressure. Particle crushing strength is relatively low in the Sabkha layer and its stress-strain behavior is strain-softening or strain-perfect. The particle crushing effect is dominant factor affecting foundation settlement in the Sabkha layer.