Model tests on earth pressure and settlement of shield tunnel crossing adjacent underground retaining structures

To study the influences on the earth pressure and ground settlement when the shield tunnel passes through the adjacent underground retaining structures, a self-designed test device is developed, and 15 model tests are carried out taking into account the ratios of tunnel depth to width, side limit width and excavation distance. In the tests, the stratum loss is simulated using the trapdoor settlement. The earth pressures of retaining structures are measured using 18 cantilever load gauges. The particle image velocimetry technique is used to measure the surface settlement. The variations of earth pressure and distribution of surface settlement during excavation under lateral confinement conditions are analyzed. The results show that the earth pressure at the bottom of retaining wall decreases sharply and then increases at a turning point with a certain height when the shield tunnel passes through the adjacent underground retaining structures. The smaller the ratio of depth to width of tunnel, the larger the decrement of the earth pressure at the bottom and the higher the turning point, and the larger the maximum displacement of surface settlement. The larger the ratio of tunnel depth to lateral limit width, the larger the reduction range of earth pressure, and the larger the maximum ground settlement. The greater the ratio of tunnel depth to distance, the greater the influences on earth pressure of retaining structures, and the greater the maximum ground settlement. Two correction coefficients, the maximum surface subsidence C₁and the correction coefficient of settlement trough C₂, are introduced, and the Peck’s settlement prediction equation is modified. The predictions show good agreement with the measured values of model tests.