Applied Mechanics and Materials Vols. 90-93

Abstract: With full-bridge longitudinal-connected foundation plates,CRTSⅡslab track sets type ∏ terminal restricted configuration anchorage structure in the bedroad-bridge transition section,in order to transmit forces such as temperature force and braking force from foundation plate to subgrade. In connection with the deficiency of exsiting researches, through the established finite element analysis model on Type ∏ terminal restricted configuration transition section,its mechanical characteristics under the most unfavorable longitudinal load by changing the structural parameters of transition section are analyzed, focusing on the criterion that the range of maximum of longitudinal displacement is 3mm.Analysis results show that when the longitudinal force is being transmitted to the anchorage structure, the maximum stress and longitudinal displacement of main terminal restricted configuration are far less than the limit and this process has little influence on track geometrical regularity .The laying of sliding layer can ameliorate structural force and deformation. However, changing its friction coefficient has no effect. Moreover, as the soil is under elastic deformation stage, its elastic modulus presents significant effects on mechanical properties of transmit section while its internal friction angle and cohesion have no influence.

Abstract: The stability control of the overlapped tunnels system has been one of the hot issues and difficulties in tunnel and underground engineering field. According to the whole process analysis for instability evolution of the overlapped tunnels, its nonlinear dynamics characteristics are studied by the nonlinear dynamics method, including material and energy metabolism, fluctuation, thermodynamics irreversible process, correlation dimension and entropy. On this basis, combining with stability control measures such as grouting, bolt and gunite and so on, the dynamics mechanism and energy dissipation mechanism for stability control of the overlapped tunnels system are studied by synergetics and dissipative structure theory. The nonlinear dynamics evolution law of the control process is also revealed. This research is not only able to provide theoretical support for establishing optimal control model and risk control principle based the nonlinear dynamics, but also of great significance for the stability control technology of the overlapped tunnels.

Abstract: This paper explores the methods used widely in China and western world interpreting the ultimate capacity of driven piles based on axial static load tests. A database consisting of 57 prestressed high- compression-capacity concrete pipe piles, which are widely used in soft soil ground conditions for building and transportation projects in China, is built. Two methods widely used in China and western world to interpret the ultimate capacity of driven piles based on axial static load testing data, S-lg(t) curve and Davisson Offset Limit, are applied to the database. Findings indicate that both methods work well and reach almost the same estimation. Conclusions suggest that both academia and industry of China and western world should take the advantages of the methods and apply them to engineering practice.

Abstract: Abstract：On the basis of preliminary exploration, complement exploration is executed to obtain excavation seepage analysis detail parameters. According to the three-dimension finite difference method and regulating calculation method, the excavation seepage analysis of anchorage circular foundation at Huangpu bridge south and the influence of different depth rock-socketed on foundation seepage are discussed. With the experience in similar projects at home and abroad, the depth of diaphragm wall embedded in weak weathered rock is not less than 3 meters, grouting curtain wall consists of 10 meters, and the waterproof curtain outside the foundation is canceled from preliminary design. The stress, strain and water level are monitored during the excavation process, and the deformation of the supporting structure is within the control. The structure is under reasonable force and the sealing effect is obvious when the foundation is excavated. Construction practice shows that the excavation seepage analysis of anchorage circular foundation at Huangpu bridge south are consistent with engineering practice.

Abstract: There is uncertainty during analysis the stability of karst roof under pile tip. The interval numbers are used to express the calculation parameters. Secondly, the limit equilibrium analysis model of karst roof under pile tip is presented based on the present study. Thirdly, the performance function is suggested to evaluate the reliability of the stability of karst roof under pile tip. The non-probabilistic reliability analysis method for stability of karst roof under pile tip is finally founded. This method is proved to be rational and feasible by engineering case analysis.

Abstract: In order to effectively control deep roadway under mining influence, based on the typical engineering geological conditions of Dingji coalmine in Huainan mining area, we researched on the laws of stress evolution and failure mechanism of roadway influenced by working face advancing by using numerical simulation and applying field test. The results showed that the surrounding rock stress of roadway ribs increased gradually with face advancing, vertical stress peak transfer to in-depth of roadway surrounding rock, the trend of roadway surface displacement variation consistent with corresponding stress variation. An appropriate coal pillar size (105 m) was proposed. We put forward the basic ideas for surrounding rock controlling and surrounding rock reinforce technology, namely U-steel support back grouting and bolt-cable cooperative supporting. By roadway deformation, roof layer separation and borehole detecting, we found out that displacement of roadway ribs was less than 250 mm, subsidence of roof was less than 110 mm, and the roadway deformation has been effectively controlled.

Abstract: For cement-soil pile composite subgrade under rigid foundation, a three-dimensional nonlinear finite element analysis is performed to analyse critical length-diameter ratio based on deformation, which is first introduced, according to replacement ratio, pile-soil modulus ratio and the modulus ratio of substratum and reinforced area. It is found that critical length-diameter ratio of cement-soil pile under rigid foundation mainly depends on replacement ratio, the impact of pile-soil modulus ratio and the modulus ratio of substratum and reinforced area is relatively little.

Abstract: More cuttings producing in higher penetration rate of gas drilling are usually in the larger non-uniform size at the bottom and in the smaller uniform size back to the wellhead. It is indicating that cuttings in the well should be appeared in the successive breaking in the process of upward migration. According to the particle broken theories, the successive breaking phenomenon were analyzed, and given the calculating method for the probability of secondary impact crushing, and applied the breaking process matrix and the particle size distribution function to the cuttings migration crushing in the whole wellbore. The calculating results show that the cuttings in the wellbore are broken by the uneven size volumetric fracture progressively turned into the surface fracture of the uniform process, and ultimately stabilized the small size distribution.

Abstract: This paper presents a study on influence of model parameters on deformation analyses with Duncan-Chang Modified Nonlinear Stress-strain (E-B) model for an ore mining tailings located in Chengde, Hebei Province of China. How to determine and derive these parameters from the laboratory experimental results was introduced first. Findings from numerical analyses performed with Midas GTS indicate that model parameters K and n most significantly affect the vertical and horizontal deformation respectively. Based on the analysis, the accuracy and effectiveness of these parameters were discussed further. Principles of the model and the parameter derivations suggest the model and parameters work better for small strain cases, hence model parameters shall be better determined with laboratory tests with low confining pressures or using new apparatus to measure small strain behavior of soil to ensure analysis results reliable.

Abstract: Pit excavation influences the stress and deformation of adjacent underground pipelines seriously. On the base of former study, the project was analyzed with the aid of general finite element soft ABAQUS, in which the interactive action of soil with pipeline and pit protection structure were taken into account. Wall-soil friction and pipeline-soil friction contact were used. The influence on adjacent pipelines of pit excavation was analyzed. The laws of deformation and the stress were gained. The results showed that the horizontal displacement was much bigger than the vertical displacement, and the pipeline would lift at the end close to the symmetric plane and fall at the other end. The displacement would decrease with the increment of the distance between pit and pipelines. The laws of influence of the pipeline’s embedment and wall-soil friction were similar, while the latter’s influence was greater than the former’s. The influence on horizontal displacement aroused by wall-soil friction was greater. The principle tensile stress mainly aroused by the pipeline’s horizontal displacement would cause tension fracture. The sections of the pipeline around the area of the end and the middle of the pit were dangerous, which should be particularly protected.