Study on Mechanical Behavior of Jurassic Frozen Sandstone in Western China Based on NMR Porosity

Maoyan Ma,Shiliang Xu,Jian Lin,Yishun Huang,Guangyong Cao

doi:10.1155/2020/2936932

Maoyan Ma, Shiliang Xu + Show 3 more

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https://doi.org/10.1155/2020/2936932

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Abstract

Study of frozen rock mechanical properties is necessary for safe application of the artificial ground freezing method in excavation of Chinese western water-rich soft rock layers. Triaxial compression tests and NMR test for samples from the western Jurassic sandstone were performed to investigate rock mechanical properties affected by low temperature and confining pressure. The results show mechanical parameters such as peak strength, cohesion, internal friction angle, residual strength, and elasticity modulus increased with the decreasing temperature under stable pressure, and the above parameters increased with the increasing confining pressure at a certain temperature. In particular, the growth rate of the rock strength would decline when the temperature was below −10°C in this study. Strength attenuation coefficients increased with the decreasing temperature, which indicated higher brittleness, whereas plastic characters got more obvious with the increasing confining pressure at a stable temperature. Furthermore, during the first two freezing stages, porosity decreased sharply with obvious increase of pore (crack) ice content, while porosity varied little at the third stage, which was the reason for the growth rate of rock strength declining with continuous low temperature from microcosmic point of view.

Highlights

During the “ irteenth Five-Year Plan” period, China will reduce the total coal production of eastern, central, and northeastern areas and promote the base construction of western coal fields gradually
Taking the Jurassic sandstone in Western China as an example, rock strength and deformation characteristics as well as the influencing mechanism of confining pressure and temperature were analyzed by the triaxial compression test and NMR test under different conditions
The above parameters increased with the confining pressure at a specified temperature. e increment appeared to be especially obvious at subzero temperature, while the strength growth rate declined at colder temperature

Summary

Introduction

During the “ irteenth Five-Year Plan” period, China will reduce the total coal production of eastern, central, and northeastern areas and promote the base construction of western coal fields gradually. Coal beds mainly distributed in Jurassic and Cretaceous water-rich soft rock layers are weakly cemented. Water-rich soft rock layers are ready to hydrolyze with sharply dropped strength when exposed to hydrodynamic erosion. Erefore, artificial ground freezing method is still the key method used in the mine construction of Western China. Rocks show mechanical properties which are different from those at normal temperature and mechanical properties at low temperature are the basic data of freeze sinking, so the mechanical properties of the frozen soft rock in Jurassic and Cretaceous layers in Western China are important to guide effectively the design and construction of frozen wells of western mines. It is critical to the safety of other cold area engineering construction. erefore, more and more attention has been paid to the mechanical properties of frozen rocks

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