Effect of Cobble Content on the Shear Behaviour of Sand-Cobble Mixtures

Chuang Wang,Jihong Yang,Jianjun Zhou,Zhiquan Huang,Jinyu Dong,Xun Xi

doi:10.1155/2021/5554617

Abstract

The sand and cobble stratum is a kind of mechanically unstable stratum. Shield machine often encounter problems such as difficulty in excavation, cutterhead wear, and poor slag discharge of the spiral dumper while constructing in this kind of stratum. Considering the complexly and variety of the material composition and structure of this stratum, the sand and cobble stratum in China, Chengdu Subway Line 7, Chadianzi-Yipintianxia Station, was selected to conduct indoor large-scale direct shear tests to systematically study the effects of cobble content (CC) on the shear strength and shear properties of sand and cobble soil. The test results showed that the shear strength and angle of internal friction of sand and cobble soil nonlinearly increased with CC, and the shear strength and angle of internal friction slightly increased when CC was less than 40%. The shear strength and angle of internal friction of sand and cobble soil significantly increased after CC reaching 40%. The shear stress-shear displacement curve has three stages, including the elastic deformation stage, yield stage, and hardening stage. The CC had a control effect on the strength and deformation characteristics of sand and cobble soil. The shear stress-displacement curve of sand and cobble soils with CCs of 20% and 80% can be fitted as an exponential model, while the shear stress shear displacement curves of sand and cobble soils with CCs of 40% and 60% are hyperbolic. For sand and cobble soil with same CC, the larger the vertical stress is, the larger the normal displacement is.

Highlights

Sand-cobble mixture is widely distributed in the stratum, and its physical and mechanical properties are different from that of sand and intact rock mass
Sand and cobble soil distributed between Chadianzi Station and Yipintianxia Station of Chengdu Metro Line 7 is taken as the research object. rough the indoor large-scale direct shear test of sand and cobble soil with different cobble content (CC), the influence of CC on the shear strength and shear characteristics of sand and cobble soil was systematically studied. e research results can provide a reference for shield construction in sandy cobble stratum and have good engineering practical significance
Analysis of the Shear Strength of Sand and Cobble Soil. e shear strength and internal friction angle of sand and cobble soil with different CCs were obtained and are summarized in Table 1. e relationship between the shear strength and CC is shown in Figure 4, and it can be seen that the shear strength changed nonlinearly with the increase of CC, showing a consistent law. e overall trend is that with the increase of CC, shear strength gradually increased. is is similar to the conclusion of Vallejo [26] on the shear strength of soil-rock mixtures

Summary

Introduction

Sand-cobble mixture is widely distributed in the stratum, and its physical and mechanical properties are different from that of sand and intact rock mass. It has the characteristics of higher strength and uneven particle size, which make the high-speed construction and utilization of underground space face many difficulties [1,2,3]. Wu et al [14] studied the relationship between maximum dry density, optimum moisture content, and coarse particle content of sand and cobble soil through a series of laboratory tests He et al [15] and Wang et al [16] studied the dynamic characteristics of sand and cobble soil through the dynamic triaxial test. Sand and cobble soil distributed between Chadianzi Station and Yipintianxia Station of Chengdu Metro Line 7 is taken as the research object. rough the indoor large-scale direct shear test of sand and cobble soil with different CCs, the influence of CC on the shear strength and shear characteristics of sand and cobble soil was systematically studied. e research results can provide a reference for shield construction in sandy cobble stratum and have good engineering practical significance

Laboratory Direct Shear Test of Sand and Cobble Soil

Test Results

Conclusions