Model Experiments And Theoretical Calculations For The Interactions Between Shallow Tunnel Excavations And Pre-existing Building Foundation Loads

The interaction between shallow tunnel excavation and the foundation load of existed buildings is studied by model tests, theoretical analysis and numerical simulation. The specific contents and the main results of this paper are as follows:(1) An experimental model system, a pile foundation load model, a box foundation load, a shallow tunnel excavation model and an associated support model, together with plane strain model test system for measuring pile foundation load, box foundation load soil pressure, ground settlement, and support strain were set up. The plane strain model test system is built in order to study the influence on the effect of excavation and supporting internal force of the pre-existing building foundation load.①A series of model tests according to the different ground loss verify that the settling tank of surface and ground meets normal probability distribution and analyze the relationship of the maximum settlement and the width coefficient of settling tank between the surface and the ground.③Experiments were conducted to study the influences on soil pressure redistributions, soil set, ground settlements, and internal forces of the tunnel support caused by a nearby shallow tunnel excavation under the condition of various horizontal and vertical pre-existing pile foundation loads. Meanwhile, the model test process and different working conditions were simulated via the software. The results are as follows: For pile foundation loads of different length, fixed magnitude and horizontal position, the ratio of pile length and tunnel buried depth is the same, it causes a most great influence on the effect of tunnel excavation; For file foundation loads of fixed magnitude and length, The influence degree of the tunnel increased with the decrease of the relative horizontal distance between the center of pile foundation loads and the tunnel axis. If the ratio of horizontal distance between the center of pile foundation loads and the tunnel axis and tunnel diameter is from0.5to4, influence on the excavation effects is larger.③A series of experiments and numerical simulation of tunnel excavation are carried out under the box foundation loads. The results are as follows:when the horizontal distances are the same but box foundation with different buried depth, the influence degree of box foundation of tunnel increases with the depth of the box foundation. If the bottom depth of embedment more than the tunnel vault, the influence degree of the box foundation load on tunnel decreases with the depth increasing. If box foundation embedment depth is same but different horizontal distance, the impact on the tunnel with the edge of box foundation levels increase with the decrease of the distance to the tunnel axis. When the edge of box foundation and the tunnel axis horizontal distance and the diameter of tunnel ratio is between0.5～4, the effect of box foundation on tunnel excavation is bigger.(2) The mathematical expressions of predicting the ground settlement of shallow tunnels with the changes of construction parameters and time are put forward. The time function model is established in combination with the solution of Sagaseta. The computational expressions of the ground deformation induced by full face excavation, bench excavation and segment excavation are derived by simplified models. The excavation parameters of speed, step spacing and the characteristics of surface subsidence under the effect of velocity coefficient surface subsidence are analyzed by analytical calculation.(3) The concept of formation Load-bearing area of building foundation load is put forward, displacement field of formation of the pile foundation load and the box foundation load is deduced in this paper. The displacement solution of Verruijt-Booker without initial stress is applied to analyze characteristics of formation Load-bearing areas of pile foundation load or box foundation load under the influence of different tunnel excavation. The characteristics of Load-bearing formation areas of building foundation load under the influence of difference of the horizontal distance of tunnel and building foundation load, tunnel depth, the radius of tunnel excavation and the progress of tunnel excavation are analyzed by numerical calculation. The results are as followed:the shape and scope of formation bearing areas of building foundation in excavation direction, horizontal direction and vertical direction would vitiate by changing the parameters of the tunnel construction and the variation law is important to guild the design and construction of tunnels.