Abstract
Soil conditioning is one of the important methods to ensure tunnel face stability and excavation efficiency in Earth Pressure Balance (EPB) shield tunneling. Commonly used soil conditioning agents currently include water, foam, bentonite slurry, polymers, and other materials. At present, there is a lack of testing apparatus and experimental methods for evaluating the compressibility and shear strength of conditioned soil, as well as a lack of evaluation criteria and quantitative indicators for conditioned soil properties. This paper proposes a laboratory testing apparatus for measuring the rheological properties and compressibility of conditioned soil, which enables simultaneous compression testing and rotational shear testing, addressing the technical challenge that existing testing equipment cannot perform shear tests under multi-stage pressurization conditions. This paper applies foam and bentonite slurry to conduct soil conditioning tests on soil from a rounded gravel stratum, uses the proposed testing apparatus to measure the shear strength of conditioned soil at different rotational speeds, and obtains rheological curves and Bingham model equations for conditioned soil with different conditioning mix ratios. Based on the test results, regression analysis is performed on the consistency coefficient, yield strength, and slump using Design-expert analysis software, and the functional relationship between conditioning agent parameters and conditioned soil property parameters is obtained, along with optimal mix ratios for foam-conditioned soil and bentonite-conditioned soil. It is proposed that the slump of conditioned soil should be within 180mm-200mm, the yield shear strength should be less than 35kPa, and the consistency coefficient should be less than 10 kPa·s. The optimal soil conditioning mix ratios for rounded gravel strata obtained in this paper will provide construction guidance and theoretical support for EPB shield tunneling in rounded gravel strata.
Full Text
A Large-scale Instrument for Measuring the Rheology and Compressibility of Improved Soil
Wang Zhiguo, Zhong Yiyan, Chen Minjie
(Guangzhou Metro Engineering Consulting Co., Ltd., Guangzhou 510000, China)
Abstract
Soil conditioning is a critical method for ensuring tunnel face stability and advancing efficiency in Earth Pressure Balance (EPB) shield tunneling. Commonly used conditioners include water, foam agents, bentonite slurry, and polymers. However, there is currently a lack of testing instruments and experimental methods for evaluating the compressibility and shear strength of improved soil, as well as a deficiency in judgment criteria and quantitative indicators for improved soil properties. This paper proposes a large-scale laboratory testing instrument capable of simultaneously measuring the rheological properties and compressibility of improved soil, which solves the technical challenge that existing equipment cannot perform shear tests under multi-stage compression conditions.
The instrument was applied to soil conditioning tests on gravel stratum soil using foam agents and bentonite slurry. Shear strength of the improved soil at different rotation speeds was measured, and rheological curves together with Bingham model equations were obtained for various conditioning mix ratios. Based on the experimental results, regression analysis of the consistency coefficient, yield strength, and slump was conducted using Design-Expert software. The functional relationships between conditioner parameters and improved soil property parameters were established, and optimal mix ratios for foam-conditioned soil and bentonite-conditioned soil were determined.
The study proposes that the slump of conditioned soil should be within the range of 180–200 mm, yield shear strength should be less than 35 kPa, and consistency coefficient should be less than 10 kPa·s. The optimal soil conditioning ratios obtained for gravel stratum in this research will provide construction guidance and theoretical support for EPB shield tunneling in similar geological conditions.
Keywords: Earth Pressure Balance shield; soil conditioning; gravel stratum; foam agent; bentonite slurry