Abstract
Silty sand is highly permeable and has a large internal friction angle. To ensure the stable and efficient construction of the Earth pressure balance (EPB) shield in silt stratum, it is necessary to reduce the disturbance to the stratum during tunneling and reduce the risk of spewing and blocking during soil discharge. Thus, a new type of dense slurry‐EPB shield construction technology is proposed. Using a custom‐made test device, the consolidation tests were conducted on sand after mixing it with different amounts of slurry to study the change in the pore pressure in the mixed soil and sand stratum and analyze the stress transmission rule. In addition, slump tests were conducted on the mixed soil to study the change in the fluidity. Based on the laboratory test results, a field investigation was carried out to study the effects of the amount of slurry addition on the pore pressure in the stratum, the driving parameters, and the sand’s flowability during shield tunneling. The results show that when the amount of slurry reaches a certain value, the filter cake effect occurs. The greater the amount of slurry added during the shield tunneling, the smaller the rate of change of the pore pressure in the stratum. When the amount of BC2 slurry added reached 8 m3 per ring, the rate of change was reduced by 57%, and the slump value improved by 93%. The type of filter cake of the DS‐EPB shield was only internal filter cake during tunneling, which reduced the disturbance of the excavation face and improved the flowability of the sand. These results are of great significance to the application and promotion of DS‐EPB shields in sandy cobble strata.
Highlights
Earth pressure balance (EPB) shields are widely used in urban rail transit engineering because of their advantages; i.e., they occupy a small land area during construction, they are suitable for tunneling in most strata, and they have simple operation technology in subway and tunnel construction [1,2,3]
After the addition of the slurry, the change in the pore pressure in the silt layer during shield tunneling gradually decreased, and the addition of the slurry decreased the pore pressure in the Earth chamber, causing it to dissipate into the silt layer. is is consistent with the change in the pore pressure in the stratum when the slurry was added in the laboratory test
As can be seen from the laboratory test results, the mixed soil layer was consolidated under the application of additional stress, and when the amount of slurry in the mixed soil layer reached a certain ratio, the excess pore pressure partially converted into effective stress, and together with the remaining excess pore pressure it supported the additional stress
Summary
Earth pressure balance (EPB) shields are widely used in urban rail transit engineering because of their advantages; i.e., they occupy a small land area during construction, they are suitable for tunneling in most strata, and they have simple operation technology in subway and tunnel construction [1,2,3]. During the excavation of the EPB shield, the state of discharged soil was improved by adding conditioned materials to the Earth chamber so the soil forms a plastic fluidity. Studied the influence of the slurry density on the permeability of stratum based on the variation of pore water pressure in the stratum and deduced the formula for calculating the infiltration distance of slurry in the sandy soil. High-density slurry and silty sand are mixed in the soil cabin to stabilize the excavation surface so as to reduce the disturbance of the stratum caused by the stress change during the driving of the shield machine. E variation in the tunneling parameters and the pore pressure in the stratum were studied during actual shield tunneling, and the effects of the DS-EPB shield based on the result of the excavation surface stability control and the soil conditions were determined Soil slump tests were simultaneously conducted to analyze the impact of different slurries on the fluidity of the mixed soil. en, based on the results of the laboratory test, a field test of the dense slurry-EPB (DS-EPB) shield was carried out in a section of silty sand stratum during the construction of China’s Wuxi Metro Line 3. e variation in the tunneling parameters and the pore pressure in the stratum were studied during actual shield tunneling, and the effects of the DS-EPB shield based on the result of the excavation surface stability control and the soil conditions were determined
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