Applied Mechanics and Materials Vols. 353-356

Abstract: Unconfined compressive strength tests of soil with different cement dosage of stabilization have been conducted to determine the optimum cement stabilizing dosage. And, the shear strength and deformation of the geocell reinforced cement soil have been investigated through a serial of direct shear tests and plate-loading tests. The results show that there is a significant improvement on shear strength and modulus of the soil by reinforcement. Moreover, FEM has been used to simulate and analyze the performance of abutment with geocell reinforced cement soil backfill. And the comparison of the computing results to field testing results has been carried out. The research results indicate that: the abutment with wedge-shape geocell reinforced cement soil backfill has remarkable effect on decreasing the differential settlement on bridge-embankment transition section. The gradient of settlement along the longitudinal direction of bridge-embankment gets much more smooth-going and less.

Abstract: Some subgrade of high-speed railway in operation occurred abnormal settlement,so need to reinforcement, however, the reinforcement measures and these mechanism have got little attention. Numerical analysis method was adopted to study the mechanism and effects of the grounting and churning pile which was used to reinforce soft soil subgrade a high-speed railway Results shows that the settlement and lateral deformation not symmetrical distribution but got larger along the inclined derection of stratum, reinforcement by grouting can decrease the settlement and the transverse differential deformation by improving the properties of soil, which can decrease the viod ratio and increase the compression modulus; reinforcement by churning pile which can increase the stability of embankment on soft soil subgrade. The result could provide theoretical guidance for reinforcement of soft soil subgrade of high speed railway in operation.

Abstract: In order to real time monitor and analyze the rock fracturing due to continuous construction and consolidation at the left slope of Jinping I hydropower station, southwest of China, a microseismic monitoring system was conducted and an optimal design for the sensor arrays was investigated. The sensor array was designed on the basis of P method and Powell algorithm. The artificial fixed blasting tests were applied to adjust the positioning accuracy of the monitoring system. The results show that the location error of seismic source is less than 12 m in the scope of the sensor array, which demonstrates the monitoring system has high positioning g accuracy. The contour of source location shows that the location errors near the main tunnels at the left bank slope is below 6 m. Signals from 689 microseismic events with moment magnitude ranging from -2.1 to -0.2 were recorded during the first year monitoring period from June 15, 2009. The spatial distribution of microseismicity can identify and delineate the potential failure at the left bank slope, which provides some references for the future excavation and consolidation of the hydropower station.

Abstract: Directed against the special nature conditions in loess donga, topography and geomorphology, meteorology, foundation soil and subgrade section type, pavement design and construction, drainage facilities design, construction and maintenance and other reasons caused drainage damages were analyzed. Combined with current maintenance specifications, subgrade drainage maintenance technology after construction and damage prevention measures of loess donga are brought forward.

Abstract: This study fitted the measured loading-settlement curve of half-screwed pilewith least square model solution of difference form of integrated exponential functional model, and predict ultimate bearing capacity of half-screwed pile according to the fitted curve of maximum curvature point. Combined with practical engineering research, the study explored the feasibility, rationality and limitations of predicting the half-screwed single pile ultimate bearing capacity with least square model solution of difference form of integrated exponential functional model, and provided the theoretical basis for the popularization and application of the half-screwed pile.

Abstract: Based on the detection principle of ground penetrating radar, the feasibility of detecting breaking rock zone of roadway surrounding rock with ground penetrating radar is analysed. In the case of detecting breaking rock zone of roadway surrounding rock in Huafeng Colliery, the method of radar detection and image analysis is suggested. The results show that using ground penetrating radar to detect breaking rock zone of roadway surrounding rock can achieve good result, so it provides a new technical way for the field detection.

Abstract: Joint spacing is one of the significant factors affecting the rock fragmentation by TBM cutters. Based on laboratory test, the effect of joint spacing on the fragmentation modes and penetration under TBM disc cutters is studied. In the test, two kinds of concrete with different strengths are adopted to simulate rock sample. The joint spacing varies from 50mm, 80mm, 200mm and the intact samples are also tested for comparison. Firstly, four kinds of fragmentation modes for single-set jointed rock are found: (1) the crack initiates from the joint plane and propagates to free surface, to form fragmentation chipping. (2) The side crack and median crack initiate beneath the crushed zone and propagate to joint plane to produce chipping. (3) In the rock block indirectly indented by cutter, the crack initiates from the joint plane and propagates to adjacent joint plane to produce chipping. (4) Normal fragmentation mode. Basically, the first two kinds are generally for jointed rock, while the other two kinds are respectively for the jointed rock with small and large joint spacing. Secondly, from the viewpoint of the fragmentation modes, the effect of joint spacing on tunnel face stability is investigated and then compared with field data of Jinping II Hydropower Station. Finally, it is shown that highest penetration rate can be achieved with the joint spacing of 50-80mm, and moreover, joint spacing gives more notable effect on fragmentation of the rock with higher strength.

Abstract: In view of the shortage of using classical earth pressure theories to calculating passive earth pressure of cohesive soil on retaining wall under complex conditions. Based on the planar slip surface and the back of retaining wall was inclined and rough assumption, the calculation model of passive earth pressure of cohesive backfill under uniformly distrubuted loads was presented, in which the upper bound limit analysis was adopted. Meanwhile it was proven that the prevailing classical Rankine’s earth pressure theory was a special example simlified under the condition of its assumptions. For it’s difficult to determine the angle of slip surface , a relatively simple method for calculating the angle was proposed by example. And the influence of angle of wall back , friction angle of the interface between soil and retaining wall, cohesion force and internal friction angle of backfill soil to planar sliding surface and passive earth pressure were analyzed. Some good calculation results were achieved, these analysis can provide useful reference for the design of retaining wall.

Abstract: The composition of the energy in the process of material deformation and failure and the relationship between energy and strength were summarized; the features, essences and main problems of the energy release rate theory, the three-shear energy theory and the net shear strain energy density theory were illustrated. It is pointed out that the roles of distortion strain energy, volumetric strain energy and dissipated energy are not identical, especially distortion strain energy and volumetric strain energy must be separately processed. The three-shear energy theory and the net shear strain energy density theory can properly deal with the problems, and also well reflect the intermediate principal stress effect. The above research results can provide references for further discussions.

Abstract: To investigate the effect of foundation slope on stability of embankment upon the slope in permafrost area, 3 groups of model tests with different foundation slope are designed using the mechanical similarity based on geotechnical centrifuge modeling, when the freezing-thawing depth of the embankment reaches the greatest. The results show that: (1) The foundation slope has effect on the stability of the embankment. The deformation mainly concentrates on the soil layers above the freezing-thawing interface, and the deformation mutation point takes place at the freezing-thawing interface. (2) According to fracture characteristics and failure severity of the embankment, failure modes can be divided into the cracking failure in shallow layer and in deep layer. (3) The cause of unstable failure is the deficiency of shear resistance strength of the weak belt, the soil layers above the freezing-thawing interface slips along the freezing-thawing interface under gravity load. (4) Under the experimental conditions, the critical value of the foundation slope influencing on the stability of the embankment is about 1:6 when the height of the slope embankment is 5.0 m.