# Study on Seismic Reduction Measures of a Diaphrag Wall--Underground Structure System
## 2 Underground Structure-Isolation Layer-Diaphragm Wall System  
As the crucial seismic component of the subway station, the collapse of the central column and top plate occurs when the top plate is damaged and loses its vertical bearing capacity, leading to the complete transfer of overlying earth pressure onto the central column. To enhance the seismic resistance of the top plate, this paper proposes a vibration absorption technique by introducing a segmented isolation layer between the side wall and the diaphragm wall, on the premise that the horizontal deformation transfer function of the diaphragm wall and the side wall is ensured and the lateral deformation of the structure is basically unchanged. The seismic measures relax the rotation constraint of the diaphragm wall on the side wall, thus reducing the seismic response at the connection of top plate and the side wall. The purpose of this measure is to reduce the seismic internal force of the top plate and improve the overall seismic capacity of the station structure.  
A segmented isolation layer is implemented between the side wall of the station structure and the diaphragm wall. The segmented isolation layer is mainly composed of two parts. The rigid isolation layer connected with the plate and partial wall structure. The rest parts are the flexible isolation layer. The system composed of the diaphragm wall and the station structure is shown in Figure 1a. The structural design of the segmented isolation layer measures is shown in Figure 1b. The three sections of the rigid isolation layer are connected with the station top plate, middle plate and bottom plate, respectively, to ensure the horizontal deformation transmission function of the underground diaphragm wall and side wall. The purpose is to keep the lateral deformation of the structure basically unchanged, so as to avoid the adverse situation that the deformation between the isolation layers of the station structure increases significantly due to the overall outsourcing of the flexible isolation layer. The rigidity of the flexible isolation layer is relatively small. When an earthquake is approaching, the top and bottom side walls can be allowed to have bending deformation within the safe range and reasonably distribute the internal forces of key structural members such as plates and side walls. The rigid isolation layer and the diaphragm wall can be consolidated into a whole through shear bolts, as shown in Figure 1c. Along the longitudinal direction of the diaphragm wall, the bolts connect the segmented rigid isolation layer into a whole through reserved bolt holes. The lower surface of the bottom rigid isolation layer is at the same horizontal elevation as the lower surface of the station bottom plate. Similarly, the upper surface of the top rigid isolation layer and the middle rigid isolation layer are flush with the upper surface of the station top plate and the station middle plate, respectively. The inner surface of the isolation layer is pasted with a waterproof layer. If groundwater seeps from the joint of the ground connecting wall, the waterproof layer can be effectively isolated. The flexible isolation layer is protected by the diaphragm wall, the rigid isolation layer and the station side wall, which avoids the possibility of erosion in direct contact with the soil and is conducive to extending its service life. The shear bolts connect the diaphragm wall, rigid isolation layer and station structure into a whole through the reserved bolt holes arranged on the left and right of the rigid isolation layer. The thickness of the rigid isolation layer along the depth direction of the diaphragm wall is the sum of the plate thickness and the plate support thickness.