Effect of dry-wet cycles on the mechanical properties of earthen archaeological site under low stresses

In order to analyze the influence law and mechanism of dry-wet circulation on the mechanical properties of earthen archaeological site, the dry-wet circulation test was carried out by using the self-made stratified sampling test device. The test lasted as long as 15 months. The samples which were prepared for microscopic test and triaxial drainage shear test under low stress conditions were from the soil column after a certain number of dry and wet cycles. Triaxial drainage shear test results show that the strain softening characteristics are enhanced significantly when the soil experiences the first dry-wet circulation. As the number of dry-wet cycles continues to increase, the strain softening decreases gradually on the whole. The cohesion c and deformation modulus E0 also increase significantly after one cycle, and then gradually decrease. The strength and deformation parameters of soil show the law of nonmonotonic change under the action of dry-wet circulation. It was suggested that mechanical parameters of dry-wet circulation after stabilization under low stress level should be used for the shallow damage restoration project in earthen archaeological sites. Combined with the mercury injection test results, It was concluded that the main reason of the nonmonotonic change law is that the volume of intra-aggregate pore decreases after one cycle and then the volumes of intra-aggregate, intragranular pores and intergranular pores increase at the later stage of circulation. The dry-wet circulation effect of silt mechanical properties may be mainly controlled by the uniform shrinkage and local failure of clay "three-dimensional grid structure" in silt, which is essentially different from that of clay. The research can provide technical basis and theoretical support for the preventive protection and reinforcement of earthen archaeological site. © 2019, Science Press. All right reserved.