Model Test Study on Interaction Between Shield-Cobble Strata-Existing Tunnels During Under-crossing Process

Taking a field project as the background, a test model with single cobble strata and two existing tunnels was designed. Then, a test of shield under-crossing the existing horseshoe and rectangular tunnels in the cobble strata was conducted based on the self-developed platform of the EPB shield. Physical quantities, including motive power of the shield as well as the weight of the discharged soil, the surface settlement of the test model, the strain of the existing tunnels, and the earth pressure acting on the existing tunnels, were measured during the test process. The influence of the existing tunnel on the shield advancing was clarified through the changes of motive power of the shield and the amount of soil discharged. Based on the change of the amount of soil discharged, the reason for the collapse of the cobble soil around the existing tunnel was explained. Based on the measured surface settlement and the variation of earth pressure acting on the existing tunnel, the interaction mechanism between the existing tunnel and cobble soil was revealed.