Advanced Materials Research Vols. 368-373

Abstract: The Identification of rock constitutive model is a typical nonlinear system problem; introduction of the intelligent methods has greatly stimulated the research. In this paper, genetic algorithm , BP neural network and genetic programming are used in the identification of constitutive model ,the capacity of three intelligent methods in the model identification is compared ,whose results show that genetic algorithm can largely reduce the probability of trapping into localized optimum solution by means of its global searching ability ,however , because its pre-assumption of constitutive model has already lead to some error ,its fitting results are not so good . BP neural network and genetic programming need not pre-assume the structure of constitutive model ,the nonlinear mapping expressions between stress and strain are obtained by self-organization and self-learning .But ,the determination of BP neural network structure is experience-depending and time-consuming . In addition, genetic programming need not define its structure, so long as the functional set and terminal set are chosen, after series of genetic operations, the nonlinear relations between variables are outputted, therefore, the operation of genetic programming is simple which realize the visualization of the constitutive equations.

Abstract: There are many effective researches about tunnel at home and abroad, because the complexity of design and construction for Y-shape tunnel, in public there is no research about it yet, with the background of nanliang-tunnel which merge two single-beam into a two-lane tunnel as Y-shape. This paper obtains the rock mass mechanics parameters on the basis of nonlinear Hoek-Brown criterion first, and has a numerical simulation according the tunnel construction with FLAC-3D. we arrange many monitor sections in this model and discuss the law of deformation and failure in different section, at last have a comprehensive analysis of displacement, stress, plastic zone of different sites which caused by tunnel construction and discover that: with the distance of two single tunnels decreased, the interaction caused by the merging increase together with the compressive stress, tensile stress. The displacements of surrounding rock increase corresponding, the amplitude of variation is up to 44.8%, After the two-lane tunnel is 15m long, the stress and displacements redistribution of surrounding rock become stable.

Abstract: Coal mining often results in settlement of tower foundation and stress change of tower. The influence of tunnel construction on above tower is similar to the influence of coal mining on above tower. Therefore, it is necessary to analyze the settlement of tower foundation and stress of tower. Some reinforcement measures have been taken to the foundation of tower before tunnel construction. The settlement of tower foundation and stress of tower is analyzed by ABAQUS finite element software. The analyses show that the settlement of tower foundation and stress of tower are within the range of the allowable, during tunnel construction. These show that the safety of the tower can be guaranteed after reinforcement.

Abstract: Aiming at medium distance transportation of excavated spoil and constructional components in the tunnelling process, this paper combines with a water-conveyance tunnel engineering and analyzes the influence factors that affect the construction efficiency of earth pressure balance shield(EPB shield), and then works out an available scheme based on that the transport link should well match with shield tunnelling. The field condition indicates that the equipment lectotype, marshaling and transport organization in this scheme guarantee the transport capacity and continuity for tunnelling, which ensures construction progress. The idea in this design can provide similar engineering with reference.

Abstract: A coupled numerical simulation of a river-crossing shield tunnel excavation in saturated soft clay with high groundwater has been performed using a three-dimensional finite difference model, which takes into account variation of soil permeability with stress, anisotropy of permeability, reduction effect of joints on segment bending stiffness and the hardening process of synchronized grouting material. Groundwater seepage conditions around the tunnel, bending moment, axial forces and strength safety factor of tunnel segment as well as deep soil displacement during tunnel diving are investigated numerically. The analyses provide valuable information concerning the mechanical behavior of tunnel segment and hydrological field in soil around tunnel during advancing. The result also is benefited to control groundwater for river-crossing tunnel in soft clay under high water table.

Abstract: A localized high hydraulic conductivity zone with high water pressure is denoted as a hazardous zone. This study focuses on the 3D coupled mechanical and hydraulic analysis of the effect of a front hazardous zone on shield tunnelling. The tunnelling process is modelled by a step-by-step excavation. And a series of three-dimensional coupled mechanical and hydraulic analysis are performed to estimate the distribution of the TSR of the ground ahead of the tunnel face. The result show that the tunnelling directly influences on the distribution of the pore water pressure and the TSR. The maximum influence range of the hazardous zone on the face stability is within 4 times the R value. And the high water pressure can induce a failure of the ground at the tunnel face by itself in conjunction with a poor ground condition.

Abstract: Measure the test points of the natural frequencies, the Fourier amplitude spectrum, power spectrum and other parameters by enter different types and frequencies of seismic waves and the stimulation of white noise in the pile shaking table test and seismic wave propagation in the model pipe. Analysis of the transfer law of seismic waves in the pipe pile-pile cap-superstructure lead to the dynamic characteristics result of the test point. Besides, the thesis studies the dynamic characteristics and dynamic response of the pipe pile-pile cap-superstructure under the action of earthquake and the propagation law of seismic waves in the system of the pipe pile-pile cap-superstructure.

Abstract: The main objective of adding piles to a raft is sometimes for settlement control. In design, the number of piles for reduce settlements under work load to a tolerable limit is usually small. This often results in a high stress in piles that may impede the application of this foundation due to the limits on raft stress or pile stress in practice. An alternative is to install a cushion between piles and raft. In this paper, the performance of disconnected settlement-reducing piles is studied. Based on some simplifications, a mechanical model of pile penetration into cushion and a calculation method of pile-soil interaction are respectively formulated. In consideration of stress-deformation coordination of pile-soil-cushion, a calculation method of pile-soil stress ratio is presented. Optimization design of disconnected settlement-reducing piles can be performed with this method.

Abstract: Filling replacement combined with dynamic compaction is a very effective method to preprocess the soft soil to obtain larger bearing capacity. That not only has remarkable effect to improve soil bearing capacity, but also has some advantages, such as quick construction, simple equipment, low cost and so on. And that is appropriate for large area ground treatment engineering. The purpose of ensuring the reinforcement effect and saving the project cost, and providing references for the similar projects can be achieved through the test study on effective reinforcement depth of dynamic compaction and filling replacement.

Abstract: Based on indoor compression test material of high liquid limit clay about Ji-He expressway,analyzed the relationship among compression modulus,compression coefficient,cuts modulus and resilience modulus of high liquid limit clay of the Yellow River alluvial plain with its moisture content and dry unit weight,and their changing rules.The results show that in a certain dry unit weight condition,free expansion ratio of high liquid limit clay is decreasing with the increasing of natural moisture content, however, in a certain moisture content condition,the free expansion ratio is increasing with increase of the dry unit weight.Compression modulus decreases along with the rising of moisture content,while increases to gether with the increasing of the dry unit weight.The compression coefficient increases with moisture content,while decreases together with the increasing of the dry unit weight.Cuts modulus reduces when moisture content goes up,certain as moisture content is, it is going to magnify along with the increasing of dry unit weight,when both dry unit weight and moisture content are constant,cuts modulus will increase with the pressure.In certain dry unit weight conditions, the resilience modulus decreases as the moisture content increases,by contrast in certain moisture content conditions,the resilience modulus increases with the increasing of the dry unit weight.