Abstract
When shield tunnelling is in a water‐rich sand stratum with poor bearing capacity, instability is easily generated, and even ground collapses may occur. The variation of pore water pressure in a water‐rich sand stratum during shield tunnelling was analyzed based on a large‐scale cross‐river shield tunnel in China, which was also investigated by a three‐dimensional fluid‐solid coupling finite element model. The results show that the influence range of the pore water pressure in front of the excavation face is approximately 2.0 times the excavation diameter and 1.5 times on both sides of the shield. The tunnelling steps would cause obvious variation in the pore water pressure and lead to great disturbance to the surrounding fine sand stratum. The quality of filter cake and the set of support pressure imposes an important impact on the nonlinear variation in the pore pressure, which could cause great disturbance to the stratum. To ensure the safety of the subsequent tunnelling in the fine sand layer, effective treatment should be taken.
Highlights
With the rapid urban development, how to quickly cross the river and to link the two sides of a city have become the main concerns for modern society. e utilization of cross-river shield tunnel obviously is an inevitable choice for its excellent tunnelling speed, lower environmental impact, and safety
When shield tunnelling in water-rich sand strata, the variation in the pore water pressure in the soil will influence the state of the soil stress and change the physical and mechanical properties of the soil
Based on laboratory tests and engineering experience, the main engineering properties of the fine sand soil are summarized as follows: e in situ fine sand is slightly medium dense. ere is a certain amount of clay particles in the sandy soil, but the cohesive force is very low. e stability and bearing capacity of soil are mainly maintained by the friction between particles, and the internal friction angle is between 30 and 32. e composition of the soil particles is uniform, and 75.1% of the particles are less than 5 mm in diameter
Summary
With the rapid urban development, how to quickly cross the river and to link the two sides of a city have become the main concerns for modern society. e utilization of cross-river shield tunnel obviously is an inevitable choice for its excellent tunnelling speed, lower environmental impact, and safety. When shield tunnelling in water-rich sand strata, the variation in the pore water pressure in the soil will influence the state of the soil stress and change the physical and mechanical properties of the soil. Research on the pore water pressure responses caused by shield tunnelling mainly includes field monitoring, theoretical analysis, and numerical simulation. Yasuhiko and Hirotaka [12] reproduced the liquefaction process of sand soil based on the discrete element method, taking into account the dynamic change in pore water pressure and found that the effective average stress of sandy soil was inversely proportional to the initial porosity at the steady state. Based on a cross-river highway shield tunnel in China, both the field test and numerical simulation on pore water pressure during shield tunnelling were carried out, and the responses of the pore water pressure in a waterrich fine sand stratum were analyzed. Based on laboratory tests and engineering experience, the main engineering properties of the fine sand soil are summarized as follows: e in situ fine sand is slightly medium dense. ere is a certain amount of clay particles in the sandy soil, but the cohesive force is very low (approximately 5–10 kPa). e stability and bearing capacity of soil are mainly maintained by the friction between particles, and the internal friction angle is between 30 and 32. e composition of the soil particles is uniform, and 75.1% of the particles are less than 5 mm in diameter
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