Applied Mechanics and Materials Vols. 90-93

Abstract: Rail traffic greatly alleviates the pressures of urban traffic, but it also has many negative effects, such as vibration and noise, which bring many inconveniences on the production and people’s daily life. Through the tests of railway vibration, we have got a number of ground vibration signals, and we analyze the basic frequency and peak speed of the vibration by dimensional analysis and wavelet packet analysis as the straight-line distance between the test point and track centerline changes, understanding the propagation of the vibration caused by rail and providing a basis for future research on vibration control of rail traffic.

Abstract: This study investigated the effects of different active filler types and contents on the mechanical properties of foamed bitumen treated materials under laboratory conditions. Four different active fillers were tested namely Portland cement, hydrated lime, quicklime and fly ash, at varying concentration of 0%, 1%, 3% and 5%. To evaluate the effects of the additional active fillers, samples were prepared under laboratory conditions and tested using indirect tensile strength, indirect tensile resilient modulus and unconfined compressive strength tests. Based upon our findings, all active filler types except fly ash contributed in improving the strength of foamed bitumen mixtures at different levels. Cement, regardless of adding contents, always provided the highest mechanical performance compared with the other two counterparts: hydrated lime and quicklime. Fly ash was deliberated to be precluded because fly ash on its own did not affect any mechanical strength of foamed bitumen mixes instead it acted as a mineral filler to modify aggregate gradation. The addition of active filler content should be limited within 3% in terms of strength gain and potential cracking prevent when mixing with 4% foamed bitumen content and locally sourced raw materials for base course.

Abstract: Numerical simulation analysis of the deformation characteristics in the construction process of subgrade are conducted. Based on the different filling unit weight and roadbed elastic modulus conditions, the main research is that vertical settlement of roadbed center and the horizontal lateral displacement of road slope toe change with the increase of the depth of filling. It is believed that the lightweight filling should be selected or the roadbed elastic modulus will be enhanced as much as possible under the condition that satisfies various standard, which can improve the settlement deformation of highway.

Abstract: To research and analyze the neutral point distribution of rigid pile composite foundation on collapsible loess ground in high speed railway, the centrifuge model tests are used to imitate pile raft composite foundation and pile net composite foundation in different pile spacing based on the experimental study at home and abroad. The research results show that the movement of negative skin friction and the position of neutral point which is drop conspicuously with larger pile spacing are a continuous changing process in composite foundation. In the pile spacing 2D,4D,6D of pile raft composite foundation, the stable range of neutral point position are 0.25(the pile length ratio), 0.59,0.63 separately in post-construction stage. In the pile spacing 2D(no pile-cap),4D(no pile-cap),4D(pile-cap),6D(pile-cap) of pile net composite foundation, the stable range of neutral point position are 0.37to0.43(the pile length ratio),0.50,0.80,0.81separately in post-construction stage. The pile-cap setting has more influence on Neutral point distribution. Suggestions are given that the waterproof and drainage measures in foundation must be considered when setting up composite foundation on collapsible loess.

Abstract: In order to study the influence of mining-induced fractures field on gas drainage,the paper adopts software of numerical simulation COMSOL Multiphysics to simulate gas drainage of coal seam under the condition of high-strength underground mining. The main aspects can be seen as the following: (1) In the case without considering the fractures, gas drainage in single hole, the gas pressure distribution showed a funnel-type distribution in space along the drainage holes around. (2) The orientation and direction of fractures play a major role on the flow field of gas. In the region that exits fractures, the distribution of gas pressure has a clear fluctuation and adjustment.(3) The numerical simulation of coal seam gas drainage that considered the fracture of coal mining, was closer to the true gas flow.

Abstract: The enclosure pile is extensively used as retaining structure in the foundation pit excavation. And it is always combined with other reinforcement measures. So it is unreasonable to a certain degree that the enclosure pile is analyzed as cantilever structure. Taken the deep foundation pit of a subway station in Hefei for instance, the effect of other reinforcement measures on restrained conditions of enclosure piles in the paper was taken into account. And the behavior of enclosure pile under various restrained conditions was analyzed. Based on that, some helpful suggestions for practical retaining structure of foundation pit were put forward.

Abstract: According to character of resident building and engineering geological condition, method of digging and watering along horizontal direction is put forward, and used for building’s rectification. Namely soil of horizontal hole is digged under one-floor ground and watered in superior subsidence side. Then subsidence is come into existence, and subsidence speed is controlled, the inclined building is forced to reverse step by step. Combining engineering examples, influence factors of building’s rectification are analyzed by numerical simulation method, which includes hole spacing, hole diameter and hole depth, and influence law of relative settlement is obtained.

Abstract: The research of rock deformation and breaking has important scientific significance and engineering significance. Deformation is a long process, while the breaking happens in a monent relatively. In this paper the rock uniaxial compression test was simulated by using PFC2D. The complete curve of stress-strain was devided into six stages: compaction stage, elastic deformation stage, plastic sclerosis stage, plastic softening stage, breaking stage and breaking residual stage. It was found that the deformation localization generated the formation and extension of the cracks. When there were enough cracks, the specimen began to damage. Only a few crack bands evolved to breaking bands. The specimen’s breaking was mainly caused by indirect tension, supplemented by shear.

Abstract: Numerical simulation is one of main methods for tunnel surrounding rock stability analysis. By now, there hasn’t be unanimous view on that what kind of yield criterion is adopted for different surrounding rock class and different buried depth. Mohr-Coulomb yield criterion is always adopted abroad, Drucker-Prager yield criterion is always adopted in China, moreover, the principles are different when adopting D-P yield criterion at home and abroad. Based on introducing the Mohr-Coulomb yield criterion and D-P yield criterions, this paper uses the M-C exterior angle point of circle criteria, which is popular in the international arena for the D-P yield criterion, and finds parameters of geotechnical material for D-P yield criterions through the parameter transformation. Combining with 3D elastic-plastic finite element simulation of the tunnel construction process, with the tunnel buried by soft and weak surrounding rock (V class) at shallow (15m) and deep (550m), this paper analyzes the impact of the M-C and D-P yield criterions on surrounding rock’s displacement, stress, strain effects, and proposes the appropriate yield criterion for the simulation of shallow and deep soft and weak rock tunnel construction and for tunnel surrounding rock stability analysis.

Abstract: In order to analysis force characteristics and changes of the anchor tension during the process of filling soil of the pull cantilever retaining wall, a model test is designed for research. The test mainly monitors basal earth pressure, lateral earth pressure of the retaining wall, anchor shaft force, lateral displacement of the retaining wall.