Study On The Effect Of Tunnels Construction On The Upper Key Structures In Thin-Layered Fracture Hard Rocks

The main research contents of this thesis are based on tunnels in GuiYang LongDongBao airport. This tunnel goes through the thin-layered fracture hard rocks, and many structures exist in the rocks, such as stratification and joint. The rocks tend to displace and break along structure surfaces when disturbed. Using 3DEC discrete element method, this thesis studied the effect on the ground settlement and structures by the tunnel construction. From this thesis, we can draw the following conclusions:(1) The ground settlement regularity caused by tunnels construction is affected not only by construction factors but also by surroundings, such as rock property, structures’ mechanical property and structures’distribution form, etc. The effect of structures on ground settlement is listed below:The rocks tend to displace and break along structure surfaces when disturbed, because the strength and stability of structures are much lower than stones; Different formation dip may cause different position of the ground settlement center relative to the tunnel center; In rocks with straight joints, the ground settlement may change suddenly at points of straight joints around the tunnel, whereas In rock with stagger joints, the ground settlement regularity is similar with continuous medium condition. In the lateral direction, the curve of the ground settlement can be described by the normal distribution curve, formulated by Peck formula. In the tunnels’long direction, the ground settlement can be divided into 3 parts:the early settlement region, the rapid settlement region and the convergent settlement region.(2)The displacement caused by tunnel construction, such as uniform settlement, ground inclination, the curve of the ground, horizontal displacement, etc, can cause upper structures’ distortion and stress redistribution, and affects the structures’stability, even cause structural damage or failure. The pattern of structural damage related to structures’types and position. To assure the regular service of structures, some interrelated norms of building put forward some deformation standards and stress standards. In tunnel program, we often use 30mm as ground settlement control standard, but this standard came from engineering experience and had application fields. For specific projects, we need to calculate the ground settlement control standard.(3) Based on tunnel in LongDongBao airport program, using 3DEC discrete element method, this thesis studied the effect on the viaduct and underground car park by the tunnel constructions. Usually, the closer to the settlement center, the greater of the effect on the structures foundation; relative to CRD method, the effect of double side drift method on the structures is smaller; the auxiliary methods in tunnels can obviously reduce the effect on rocks and structures. In specific programs, usually, the construction measures are determined by the engineering experience or numerical simulation or model experiment, but they need adjust in time according to the monitoring measurement results.(4) Based on tunnels in LongDongBao airport program, through calculation, this thesis proposed 25mm as the ground settlement regularity when the tunnels went through the viaduct. Based on the numerical simulation and the monitoring measurement results, the ground settlement, the structures’ deformation and stress could meet the control standards when using the designed requirements in tunnels construction.