Advanced Materials Research Vols. 368-373

Abstract: Construction of large-section tunnel leads to changing of rock stress and comes about complicated stress-path, which causes continuously redistribution of rock stress with changing of stress path, leads expansion and change of plastic zone and brings relaxation-are avariation between left guide hole and right guide hole. The paper firstly introduced the construction situation of four-lane tunnel, and then analyzed its developments of design and construction at present. Relying on Dragon Head Mountain expressway tunnel with eight-lane and two way in Guangzhou, analyzed and discussed stress path, rock relaxation area effect on large-section tunnel by using site measured data from multi-displacement meter and numerical calculation result of rock relaxation area in different excavations. At the same time, verified the rational range of rock relaxation-area of large-section four- lane tunnel, which made the rock load of large-section tunnel to be studied further.

Abstract: This study examines the performance of a deep metro excavation constructed by top-down technique in Shanghai clay deposits. The monitoring items included deflections of diaphragm walls, vertical movements of steel columns, and axial forces of the struts. Based on analysis of the field measurements, some interesting findings were obtained, which will be useful for both practitioners and researchers.

Abstract: Related to the actual project in the new Qi Daoliang tunnel between Lanzhou and Lintao highway, select 300-meter calculation range along the tunnel vertically including fault-rupture zone and effect fault-rupture zone, utilize 8 -node, 6-plane block element to scatter the calculating range, at the same time, use the deduced 8 -node, three dimensional jointed element to imitate the transformation gap of the tunnel lining, employ three-dimensional elasto-plastic static finite element program to analyze stress and transformation state of surrounding rock and lining in different construction stages of the new Qi Daoliang tunnel. Through the analysis and comparison of the calculation result of the three conditions: not placing transformation gap through, placing one transformation gap in the middle of the fault-rupture zone, placing two transformation gaps in the beginning and the end of the fault-rupture zone etc, we can get the following points: ①The gallery transformation in the fault-rupture zone and the plastic area in the surrounding rock are obviously bigger than the non-fault-rupture zone. ②Owing to the effect of fault-rupture zone, the increasing range of internal force of the initial support and twice lining is about 10% to 30%. ③Placing the transformation gap in the fault-rupture zone can obviously play a role in releasing lining internal force and transformation energy in the surrounding rock. ④In the start and end changing point of fault-rupture zone, the transformation gap should be placed in the tunnel lining.

Abstract: The necessity to carry out study of the influence of metro works on tree growth in their vicinity is explained in the present paper. A preliminary analysis of how various engineering measures in different construction methods influence the growing conditions of trees is conducted. It is pointed out that to reduce the influence of metro works on the growth of trees involves two knowledge aspects: the necessary conditions and basic requirements in the growth habit of trees and how the underground growing environment is changed by metro works. A research perspective is put forward, which is to adopt the combination of the mechanism analysis, physical model test and numerical simulation in the study of the influence of metro works on the underground growing environment of trees.

Abstract: Shrinkage induced tensile force was observed in a 264m long reinforced concrete struts through field monitoring during a foundation excavation in Shanghai, China. In the construction period, shrinkage occurring in latter cast concrete induces a tensile force to the former part of long Reinforced Concrete strut. Inclinometer installed in retaining wall also shows that the tensile force produced by shrinkage tends to pull the diaphragm wall, which makes an enlargement to the deflection under earth pressure. This paper describes the layout of retaining structure, ground conditions, excavation procedures, and monitoring installation. Monitoring data shows that concrete shrinkage in the super-long RC strut will produce tension to the supporting structure. The influence of concrete shrinkage and relative controlling strategy are suggested in the end.

Abstract: Cyclic triaxial tests were carried out for remodeled saturated clayey sands with the clay content varying in a relatively wide range from 0% to 40%. In the tests, saturated uniformity clayey sands were obtained by pre-freezing method, i.e. immersing samples in pure water for 12 hours under vacuum, and then, freezing the sample to -15°C for 6 hours. Experimental results indicate that the lowest liquefaction resistance in mixtures occurs when clay contents is of the order of 15%. The ratio of liquefaction shear stresses of the specimens obtained using pre-freezing method are larger than those obtained with the traditional deposit-in-water method.

Abstract: The conventional triaxial compression(CTC), triaxial compression(TC) and reduce triaxial compression(RTC) of ordinary loess in Xi，an Ba He was conducted with GDS stress path tests and the strength behavior and deformation capacity of loess was studied. The experimental results showed that the larger the initial moisture content, the smaller the shear strength. The strength characteristic of loess varied under different stress path. Relationships between σ and ε was strain hardening model. The peak strength of CTC is larger than that of TC and the peak strength of RTC was smaller.

Abstract: In this paper, the design of the single cuboids cavity model of cavity is on the basis of national defense works and human defense works design specifications, with which to get the distribution of blast load on the wall of typical cavity and the destroy model. In experiment, we added the mass of explosive until the construction is destroyed. Data of pressure-time curve of blast load and acceleration-time curve of the structure wall vibration are used to analyze the distribution of blast load and the destruction form of structure, and to be the basis of further research on other kinds of underground cavity.

Abstract: Duncan—Chang constitutive model is widely used for it reflecting the main property—nonlinearity of soil. In the paper, the geotechnical Duncan—Chang constitutive model is introduced into ANSYS software by using the User Programmable Features (UPFS) of ANSYS. The calculation results with eight parameters variation in Duncan—Chang model are analyzed, which has much wider reference value for geotechnical engineering problems. The relative solution methods provide important reference for other constitutive models to be introduced into and analyzed in ANSYS program.

Abstract: Ground motion is closely related with subsoil properties. Under dynamic loading, subsoil tends to soften. Using a 1D model to simulate horizontal stratum, the correlation between ground motion and subsoil softening is investigated. Subsoil softening mainly influences ground motion, especially for long period components. Response spectrum intensity relative changing rate is proposed as an index for evaluating the influence of subsoil softening on ground motion. Response spectrum intensity relative changing rate keeps constant when shear wave velocity ratio v’/v0 is greater than 0.2 but increases dramatically with decreasing v’/v0 when v’/v0 is smaller than 0.2. Comparing to subsoil nonlinearity, subsoil liquefaction greatly increases long-period component energy which affects long period structures such as high rising buildings, long span structures