盾构始发化学加固范围

A Numerical Simulation Study on the Chemical

Reinforcement Area at Shield Start Shaft

Zeng Hui

School of Civil Engineering and Architecture

Wuyi University

Jiangmen, Guangdong, China

wyunjfu@

Hu Jun Yang Ping College of Civil Engineering Nanjing Forestry University Nanjing, China

hj7140477@

Abstract—When the ends of shield tunnel in soft soil regions are reinforced in a chemical manner, it is vital to solve some urgent key problems, such as determining the range of shield start shaft which requires reinforcement, the reinforcement time of various reinforcement techniques. Frequently-adopted methods to reinforce the soil at the shield tunnel ends were summarized in this paper first, then by combining the case of shield launching project (exclusive of aquifer) of Fenhu Road Station’s west end in Suzhou Subway, ADINA program was applied here to conduct simulation analysis of different reinforcement areas at shield start shaft under the most unfavorable construction condition—removal of the sealed door. The research indicates: a) Frequently-adopted methods to reinforce shield tunnel ends include deep mixing method, high pressurized jet grouting, artificial freezing and precipitation technique, etc. Soil reinforcement may adopt one method or combination of many methods; b) According to the numerical simulation, when longitudinal reinforcement length reaches 3mm, the soil shall move towards the working well in the tunneling direction of shield tunnel, the maximum displacement occurs in the center of exposed tunnel face, up to 12.92mm. Surface soil above the sealed door becomes deformed most, settling by approximately 3. 0mm and soil within the strong reinforcement area is stressed in designed strength range; c) At the shield start shaft which is exclusive of aquifer, if the longitudinal reinforcement length reaches 3m, requirements in both strength and deformation can be met, and it is considerably safe; d) Most of the shield tunnel ends in Suzhou Subway are distributed in rich water-bearing layer (especially water-bearing sand layer), therefore, the longitudinal reinforcement length is usually designed to be 9m.

Keywords-shield launching; Suzhou Subway; reinforcement area; numerical simulation

I.I NTRODUCTION

Shield launching is a stage of frequent accident in shield tunnel construction, having great construction risk. Reasonable selection of the method to consolidate the soil of tunnel ends is a quite important step to ensure the smooth process of shield tunnel starting construction[1]. Frequently-used methods of reinforcing shield tunnel ends include deep-mixing method, high pressurized jet grouting, SMW technique, artificial freezing, grouting, prime concrete pile method and precipitation technique, etc. Soil reinforcement may adopt one technique or combination of various techniques. Reinforcement methods may fall into the following two categories:

(1) Chemical reinforcement (high pressurized jet grouting, deep mixing, grouting and prime concrete pile method, etc.)

(2) Physical reinforcement (freezing and precipitation technique, etc.)

In the soft soil region, when adopting chemical methods to reinforce shield tunnel ends, it is vital to solve some urgent key problems, such as determining the range of tunnel ends which require reinforcement, the reinforcement time of various reinforcement techniques. The range of shield tunnel ends requiring reinforcement is determined according to two aspects: first, longitudinal reinforcement length towards the tunnel; second, transversal reinforcement length of shield tunnel. At present, there are a lot of controversies with regard to reinforcement area at shield start shaft and no consensus has been reached over the years[2][3][4].

II.E NGINEERING S ITUATIONS

Fenhu Road Station is the third station of Line 1 of Suzhou Subway, heading from the west to the east. The station is located west of Fenhu Road, in line with Zhuyuan Road, with an east-west layout. Top slab and bottom slab of Fenhu Road Station’s west end are both located in ⑤soft-plastic silty clay layer, that’s to say, the tunnel only needs to pass through ⑤soft-plastic silty clay layer. According to the geotechnical test of the soil taken from Suzhou [5][6], physical and mechanical parameters of soil in this station’s west end are shown in TABLE I.