Jianbin Li

A new method of replacing soft soil with lightweight foam concrete (lightweight foam concrete replacement method, LFCRM) is carried out to treat deep soft foundation under the low-filled embankment. Two-dimensional models with different thicknesses of replacement are established by the finite element platform (MIDAS/GTS). Moreover, the deformation and stress distribution law of treated foundation is analyzed by numerical simulation with different models. The results are as follows: (1) LFCRM can offset part of dead load; (2) the transverse distribution of settlement presents an “arc” shape; (3) the replacement made of lightweight foam concrete can spread stress well; (4) increase of replacement thickness will cause the necking of the additional stress “bubble”; (5) initial excess pore water pressure is related to the additional stress, and its dissipation path is deduced; (6) preliminary analysis indicates the feasibility of LFCRM for treating deep soft foundation with the low-filled embankment.

Aiming at the problem of deformation of adjacent masonry structures caused by the surrounding soil disturbance in the construction of twin shield tunnels, taking the spatial variability of soil parameters as the breakthrough point and the surface deformation mode as the basis, a program is compiled to search the position of characteristic points of the settlement curve, and a safety assessment method of masonry buildings above twin tunnels based on the random field theory is obtained. According to the reliability theory, the concept of the potential damage zone is defined. The probability that the maximum tensile strain of the building exceeds the allowable ultimate tensile strain is not less than 5% in the potential damage zone. The assessment method mentioned above, together with the Monte Carlo simulation, is used to evaluate the safety of buildings and the range of potential damage zones induced by twin tunneling with different relative locations and different construction sequences, taking into account configurations and construction sequences of twin tunnels, the scales of fluctuation of elastic modulus of the soil, and the size of the building. The research results show that, in the parallel and overlapping twin tunnels, the randomness of the surface deformation mode caused by construction increases with the decrease of the transverse scales of fluctuation or the increase of the vertical scales of fluctuation. In overlapping and shoulder-mounted twin tunnels, the effect of the construction sequence on the safety of buildings is the opposite. When the overlying tunnel is excavated first in shoulder-mounted condition, the safety of buildings is more excellent. Considering the effect of the spatial variability of parameters, the probability of higher damage levels in the buildings is significantly increased. The greater the scales of fluctuation, the greater the damage probability. The potential damage zones of the buildings will be expanded, and the safety distance of the buildings will be wider than the deterministic analysis result by 1.5∼2.5 m.