关键词: 土遗址, 干湿循环, 土柱, 强度特性, 核磁共振

Abstract: Concentrated rainfall and fluctuation of groundwater level are important factors to induce the sapping and collapse of silty soil earthen archaeological site in Central Plains. Six groups of soil column models with layered sampling function were subjected to different dry-wet cycles respectively for silty soil from earthen archaeological site at Guchengzhai in Xinmi. The samples prepared for consolidation drainage shear test, nuclear magnetic resonance (NMR) test and scanning electron microscope (SEM) test were taken from the soil column, and then the correlation between the mechanical properties and pore structure influenced by dry-wet cycles was studied. The results showed that the stress-strain curve shape of the silty soil under the influence of dry-wet cycles was related to confined stress. The shear strength and cohesion increased after the first dry-wet cycle, and then gradually decreased to be stable. The stable values were lower than those of the initial sample not experiencing dry-wet process. Also, the internal friction angle slightly changed. It was recommended that mechanical parameters of dry-wet circulation after stabilization should be used for the damage restoration project in earthen archaeological sites for areas frequently affected by water. Combined with the NMR and SEM test results, the main reason for the change of macroscopic mechanical properties was that with the increasing of dry-wet cycles, the intermediate pore volume of soil firstly decreased and then slowly increased to a steady state, while the small pore volume of soil gradually increased to a steady state. The total pore volume of soil firstly decreased and then gradually increased to a steady state due to the adjustment of the two types of pore. It is believed that the intrinsic mechanism lies in the uniform contraction of the clay “net frame” after one dry and wet cycle and the destruction of the clay “net frame” in the subsequent cycle caused by the special grain grading of silty soil.

Key words: earthen archaeological site, dry-wet cycles, soil column, strength properties, nuclear magnetic resonance