Guo Xing Chen

The Mechanical Behaviors of the Embankment Filled with EPS Composite Soil

EPS composite soil is a new kind of lightweight soil. As the fill material for the embankment, it has enormous advantages. Based on a known case, a finite element model was established, and its efficiency and rationality were verified. The established model was used to analyze the mechanical behaviors of the embankment considering EPS composite soil and the conventional soil. It was concluded that EPS composite soil can effectively reduce the settlement, soil pressure and excess pore water pressure and so as to improve the safety of the ground. It will have widespread applications.

Modified Singh-Mitchell Creep Model for EPS Composite Soil

EPS composite soil is a new kind of lightweight fill material. Its engineering properties have been widely studied. However, the creep behavior has not been well investigated. In this study, triaxial undrained creep test is conducted on EPS composite soil regarding various confining pressures. Based on the testing results, a modified Singh-Mitchell creep model is established for EPS composite soil considering the influence of the deviator stress on the parameter m. Compared with the original Singh-Mitchell model, the modified creep model can well describe the creep behavior of EPS composite soil. It can provide references for engineers to design the project using EPS composite soil.

Studies on Damage Distinguishing of Underground Tunnel Structure Based on BP Neural Network

With the expansion and development of scale of construction on metro engineering, the damage diagnosis and the safety evaluation on underground engineering structure have become vital problems to be solved. This paper raised an idea to distinguish underground engineering structure based on BP neural network: define change rate of curvature of structure, and recognize it as the input scalar of BP neural network, using a reducing unit elastic modulus method to simulate damage location and damage degree, through various set of underground structure extent of damage, recognize the first four order curvature structure change rate as input of BP neural network. The results show that the method using BP neural network can identify the damage degree of underground engineering structure accurately and can solve the damage identification problem of underground engineering structure conveniently and effectively.

3D Simulation of Mechanised Excavation in Brittle Rock

During the excavation by TBM of the Aicha Exploratory Tunnel along the Brenner Base Tunnel in Italy, in hard brittle granitic rocks, an instability phenomenon occurred at chainage 6+151. The left-hand sidewall lining partially collapsed for a length of approximately 60m. This led to a stoppage of the TBM lasting about 4 months. With the reconstruction of the geological model, a sub-vertical fault, not forecast at the design stage, was identified parallel to the direction of the excavation. In this paper, a three-dimensional (3D) model, which simulates the complex interaction between the rock mass, the TBM and its system components, and the tunnel support, is presented. The model accounts for the main machine components: shields, cutterhead, grippers, pea gravel and lining. The brittle failure of a thin granite diaphragm between the fault zone and the tunnel wall is reproduced and the results are discussed in terms of failure zone and horizontal displacements.

Analysis of Seismic Response Influence of High Rise Building Nearby Subway Station in Soft Site

A two-dimensional finite element model for soil-subway station- high rise building was created based on the representative soft soil site along the Nanjing subway to study the nonlinear dynamic interaction among three parts. The influence of two-layer and three-stride island-type subway station was explored on the seismic response of nearby high rise building. The results showed that the natural frequency of high rise building was reduced apparently because of the existence of soft soil. The displacement angle between the layers of high rise buildings and right swing relative horizontal displacement amplitude between top and bottom was increased when the subway station was located at the left of the high rise building. In the same time, the shear force of the beam end and the moment amplitude on the middle span of the first and second floor of high rise building, the shear force of the column end on the fist layer, the shear and moment amplitude of the middle column end and right side column end on underground layer were all increased, and the increase proportion is even up to 30% on certain areas, which could weaken the seismic performance of high rise building.

Spatial Effect Analysis on Shaking Table Tests of Subway Station Structure in Liquefiable Ground

Based on the test data of shaking table tests of subway station structure in liquefiable ground under both near-field and far-field earthquakes, the spatial effects of dynamic pore water pressure (PWP)and peak ground acceleration (PGA)of liquefiable ground as well as peak strain response of the subway station structure are analyzed. The results show that there exists time-lag phenomenon of dynamic PWP ratio of each measuring point on different observation planes. The characteristic of input ground motion has a noticeable influence on the spatial effect of dynamic PWP ratio. The PWP ratio obtained on the major observation plane presents to be larger than that on the minor one when under far-field Songpan wave. Meanwhile, the peak acceleration of measuring points on both major and minor planes increase with the growing peak acceleration of earthquake. The law of PGA and frequency spectral character of measuring points on different observation planes or at different depth varies with each other, and there present remarkable spatial effect. The peak strain of central cylinders at the top and middle floors on the major plane appear larger than that on the minor planes. However, the peak strain of central cylinders at the bottom floor are more remarkable than that of the top and middle floors, There are sharp contrasts among the peak strain responses in different spatial positions of the station structure.

Influence of Ground Structure on the Seismic Response of Underground Subway Station in Soft Site

This paper selected representative soft site along the subway lines and created two-dimensional overall finite element analysis model about nonlinear dynamic interaction among soil, underground subway station, and ground structure based on Nanjing underground subway station. It explored the seismic response influence of neighboring high-rise structure on the two-layer and three-span island-type underground subway stations. The results showed that the structure near the subway station had a significant constraint effect on the deformation of subway station which is oriented to the structure, and the influence of deformation of subway station which is backward to the structure is related to vibration characteristics of the soil-underground structure interaction system. The influence of neighboring ground structure on the strain stress response of subway station is useful in most part of important nodes. However, this influence is disadvantageous in the outer part of connections of side walls and plates and middle plate-interior column connections.

Seismic Response Characteristics of Deep Soft Site with Depth under Far-Field Ground Motion of Great Earthquake

Considering the dynamic nonlinear characteristics of soil by equivalent linear method, one-dimensional wave models were established to study the seismic effects along depth of deep soft sites under far-field ground motions of great earthquake. The results show that the magnified effect of acceleration response spectrum of each layer present more outstanding under far-field ground motions than under Suzhou artificial waves, with the increasing of bedrock peak ground acceleration, there is probability that the peak of long-period component of acceleration response spectrum appears higher than that of the short-period within 15m depth, which may adversely affect the long-period building structures. However, the reduction coefficient of peak ground acceleration (PGA) along depth according to the three levels of earthquake fortification standard was relatively higher when inputting far-field ground motions of great earthquake. As the curve fitted by Longjun Xu et al. based on records collected California Strong Motion Instrumentation Program geotechnical arrays of the United States and Hosokura Mine arrays of Japan, is not suitable for Suzhou area, suited quantitative formula about reduction coefficient curve of PGA with depth in deep soft site is given. Besides, maximum shear strain at the depth of approximately 15m and 40m present to be greatly changed when inputting far-field ground motions of great earthquake, with the growth of inputting bedrock peak ground acceleration, the layer in the depth of about 15m comes to be the most unfavorable position of shear deformation.

Spatial Effect Analysis on Shaking Table Tests of Subway Station Structure in Soft Ground

Based on the test data of shaking table tests of subway station structure in soft ground under both near-field and far-field earthquakes, the spatial effects of peak ground acceleration (PGA) of soft ground as well as peak strain response of the subway station structure are analyzed. The results show that the peak acceleration of measuring points on both major and minor planes increases with the growing peak acceleration of earthquake. The law of PGA and frequency spectral character of measuring points on different observation planes or at different depth varies with each other, and there presents remarkable spatial effect. The peak strain of central cylinders on the major plane appears larger than that on the minor planes. There are sharp contrasts among the peak strain responses in different spatial positions of the station structure.

Comparative Testing on Ground Surface Vibration Caused by CRH Trains Running on Viaduct and Embankment

Based on the measurement of the vertical velocity of ground surface vibration caused by CRH trains running on viaduct and embankment of Hu-Ning Intercity Railway, the characteristics and propagation attenuation rules of the ground surface vibration of two routes are analyzed. The result shows that the main frequency of ground surface vibration caused by the CRH trains running is less than 80Hz, which belongs to low frequency vibration. The number of carriages has little effect on ground surface vibration intensity. The effect of train speed for 153km/h to 201km/h on ground surface vibration intensity has no obvious difference. With the increased distance between the ground surface and the track, the main frequency of ground surface vibration on viaduct decreases, and the attenuation curve of peak value of ground surface vibration velocity becomes smoother. However, the main frequency of ground surface vibration on embankment is nearly unchanged and the attenuation curve of peak value of ground surface vibration velocity has several rebound regions of the vibration. Ground surface vibration intensity of viaduct is higher than that of embankment. The drainage trench built beside the embankment has vibration isolation effect on ground surface vibration.