Physical and Mechanical Performance of Frozen Rocks and Soil in Different Regions

Junhao Chen,Lexiao Wang,Zhaoming Yao,Yanjun Shen

doi:10.1155/2020/8867414

Abstract

The artificial freezing method is extensively used in the reinforcement of engineering strata in various regions for shaft excavation and subway connection channels. In this study, representative rock and soil strata from different regions were subjected to low-temperature physical and mechanical performance tests. The results show that, compared with Cretaceous and Jurassic rock and soil strata, deep topsoil and shallow coastal topsoil have high water content, low thermal conductivities, high frost heave rates, and high freezing temperatures. In addition, the results show that, as the curing temperature decreases, the uniaxial compressive strengths and elastic moduli of deep topsoil and shallow coastal topsoil increase almost linearly. The strength of the sandy soil strata is the highest, followed by the cohesive soil strata, and the strength of the mucky soil and the calcareous clay is the lowest. The strength of the frozen wall and the waterproof requirements must both be taken into account in the freezing design. Deep Cretaceous and Jurassic rocks can have high strength of more than 5 MPa under normal temperature conditions. An increase in the uniaxial compressive strength and elastic modulus with decreasing curing temperature is mainly manifested within the range from the normal temperature to −10°C. The strength can reach more than 10 MPa at −10°C, and only the strength requirements of the frozen wall need to be considered in the freezing design. At low temperatures, deep topsoil and shallow coastal topsoil are dominated by the form of compression failure. The average failure strain at −10°C is typically greater than 5%. When excavating the strata, it is essential to pay attention to the effect of creep. The failure strain of deep Cretaceous and Jurassic rocks is between 1% and 2%, and the breaking and sudden collapse of surrounding rocks should be prevented.

Highlights

Academic Editor: Yanjun Shen e artificial freezing method is extensively used in the reinforcement of engineering strata in various regions for shaft excavation and subway connection channels
In the cases of the mucky soil and calcareous clay, when the temperature decreased from −5°C to −10°C, the strength increased by 68.16% and 76.74%, respectively, whereas when the temperature decreased from −10°C to −15°C, the strength increased by only 45.85% and 41.12%, respectively
By means of laboratory tests of frozen rock and soil samples from the eastern, central, and northwestern regions of China, the differences in the physical and mechanical performance of the different rock and soil strata in the different regions at low temperatures were examined. e main conclusions are as follows: (1) e thermal conductivities of the different strata were found to differ. e thermal conductivities of the mucky soil and calcareous clay in the topsoil strata were relatively low, and the development rate of the frozen wall temperature field was relatively slow, whereas the thermal conductivity of the rock strata was high, and the frozen wall temperature field developed relatively quickly, which is conducive to freezing

Summary

Test Plan

(2) e mechanical performance test performed was a uniaxial compressive strength test conducted under various temperature conditions, in accordance with the coal industry standard “Physical and Mechanical Performances of Artificial Frozen Soil Test” (MT/ T593-2011). Samples were cured for 48 h at temperatures of −5°C, −10°C, and −15°C and subjected to uniaxial compressive strength testing using a WDT-100 frozen soil testing machine at a strain rate of 1.0%/ min. Because the rock strata in the D6–D9 group exhibited a certain selfstability under normal temperature conditions, the uniaxial compressive strength of the samples in this group was tested under normal temperature conditions. E uniaxial compressive strength and elastic modulus are calculated from the test measurements, and the average values for three samples were taken as the final results for each group. E uniaxial compressive strength of frozen rocks and soil (σ) can be calculated as follows:.

D2 D3 D4 D5 D6 D7 D8 D9

Results of Low-Temperature Mechanical Performance Tests

Conclusions