Mechanical Characteristics Research On Deep Sand-Weathered Rock Contact Zone

Concealed coalfield covered by thick soil layer is widely distributed in our country. Reducing the protective coal and rock pillars to improve the upper limit of mining means underground coal mining activities are closer to the deep soil-weathered rock contact zone. For many years, mining practice closing to the zone shows that: There exists instance of success in retention coal producing, accordingly, the service life of mine was extended and the production benefits was improved; At the same time, pronblems that threatening mining safety appear, such as water and sand inrush and abnormal mine pressure increase.The deep soil-weathered rock contact zone is a special engineering geological petrofabric with a feature of overall low strength and gradual mechanical properties after a long-term water-soil-rock geological interaction process, which is composed of soil, water and weathered rock and coordinating the uncoordinated deformation between the overlying soil and underlying rock mass. This article focuses on the sand-weathered rock contact zone and researches were carried out in aspects of mining disturbance and physical-mechanical properties of the zone: ①Based on the elastic-plastic finite differential calculation data, stress path of rock and soil in the weathered zone under mining disturbance was summaried and generalized in 6 kinds of triaxial test loading modes. ②Based on the proportion test of weathered rock alternative materials, composite specimens with continuity differences in intensity characteristics were made for triaxial test. ③Direct shear tests of soil-rock interface, reduced triaxial compression tests of soil-rock contact zone and swelling tests of clay minerals in in weathered zone were conducted, Mohr-Coulomb shear strength indexes of soil-rock interface or contact zone and swelling indexes of clay minerals in in weathered zone were obtained. According to the test data, 3-parameterss model considering the continuity characteristics of intensity was established. Further, intensity gradient of rock and soil in the weathered zone was quantified by continuity index of intensity and bring into the model, finally, the 3-parameterss model of soil-rock contact zone was established.