Model Test And 3D Numerical Simulation Analysis On The Excavation Of Expansive Soil Tunnel

With the development of infrastructure construction,tunnel plays an significant effect on transport facility.However,the geologic conditions are complex in many parts of our country,the expansive rock and soil which causes destruction on tunnel structure is often found during the construction of tunnel.It is mainly cause that we realize the insufficiency of knowledge on swelling-shrinkage mechanism of expansive soil and its engineering characteristics,because surrounding rock of tunnel has expansive force and easily soften under the condition of water,the surrounding rock will generate large deformation and even destruction which will bring loss to construction project during excavation of tunnel.Thus,this thesis mainly rely on the example of Yihe’s highway expansive soil tunnel project in the Guangxi province of China.The key points of surrounding rock stress during the process of excavation were monitored by physical model experiment,and the software FLAC3 D was used to conduct the three-dimensional numerical simulation of tunnel construction under the three excavation methods(the whole section method,bench method,CRD method).The deformation and stress variation law of surrounding rock in expansive soil tunnel were observed during the rainy season construction.The main results and conclusions of this thesis are as follows:1)The basic physical and mechanical properties of expansive soil and the relationship between shear strength of expansive soil and the water content were studied by indoor basic experiment,it can be concluded from research that the cohesion and internal friction angle of expansive soil decreases with the increase of water content.2)The study of model test shows that the stress variation of surrounding rock in vault and arched bottom is larger than that of surrounding rock in arched waist during the tunnel excavation,and the stress of surrounding rock appears sharp decline when the tunnel is excavated to the observation surface;the stress release rate of surrounding rock near the tunnel decreases gradually with the increase of distance,the stress release speed is also slow down gradually,and this phenomenon is mainly manifested in two times the diameter of tunnel range.3)The study of numerical simulation shows that the deformation of tunnel surrounding rock which appears settlement in the area of vault,bump in the area of arched bottom and convergence to the center in the area both sides of tunnel under the three excavation methods;the deformations of surrounding rock stress both are symmetrical along the vertical tunnel,the vertical stress concentration is mainly reflected on both sides of the tunnel,horizontal compression zone formed in the area of vault and arched bottom;the stress and deformation of surrounding rock appear shapely change when tunnel surface is nearly twice as far as the back and front of observation surface,in this phase,the stability of surrounding rock is worst,and need to take timely measures to support.Comparing the results of three excavation methods,it can be concluded that full section construction causes apparently deformation than that of other methods in the area of vault and arched bottom,it is uneasy to control the increase of deformation and stress.However,CRD method has a minimum disturb effect on surrounding rock and is the best of all excavation program on the rainy season construction of tunnel with expansive soil.4)The result shows that the stress variation of surrounding rock are similar under the two method including model test results and data simulation results.It was found that the concludes which can be used basic on stability of similarly surrounding rock are reasonable.