Advanced Materials Research Vols. 639-640

Abstract: In order to study the deformation characteristics of red clay deep foundation pit, the horizontal displacement of lateral wall and the subsidence of surrounding surface were analysed in the step-by-step excavation of red clay deep foundation pit in the construction process. Using finite element software and D-P model, the numerical simulation of a deep foundation project was done. On this basis of differentiated models, the deformation characteristics of different support schemes were further analysed. This study indicates that the spacing of anchor bolt affects the deformation most, followed by the length of anchor bolt and pre-stress. The result shows that selecting a rational scheme for design and construction according to special conditions is important, which can not only guarantee the foundation pit safety, but also save the engineering cost．

Abstract: The PCA (principal component analysis method) of statistical mathematics theory is used to establish the evaluating model of zone subway structural form. Aiming at the complexity, ambiguity and lack of reasonable evaluating methods of the subway structural performance, the model selected the leading indicator which affecting the structures of subways and having the aid of using Matlab mathematical tools to evaluate comprehensively the functional and structural performance of them. The analysis showed that it’s feasible to use PCA to evaluate the zone subway structural performance, which can objectively reflect the strength of the evaluation index’s influence on the comprehensive evaluation value and it has some practical value and referential significance.

Abstract: The dissipating of pore water pressure caused by pile sinking is one of the main factors resulting in time effect of ultimate bearing capacity of pile.The pore water pressure is monitored at each observing point during pile sinking and after that. With the pore pressure plan embedded in advance, by means of spot test in the process of pile sinking, under this geological conditions of the pile foundation by referring to the second phase project of the free port logistics processing zone in Dongjiang, Tianjin.The change law of the distribution and dissipation of excess pore water pressure with time, depth, radial distance and permeability coefficient of soil was also discussed. It’s found that the excess pore water pressure attenuates approximately linearly with the increase of the distance from the pile heart and the scope influenced is around 10d. As the numerical simulation accord with the test results effectively, promote the results then get the change rule of pile bearing capacity with time.The formula of pile bearing capacity about time effect in dredge fill was deduced for engineering reference.The effect of soil internal friction angle on the ultimate bearing capacity of pile was discussed. Numerical simulation shows that the ultimate bearing capacity of pipe pile increases over time and keeps stable after 20d.The ultimate limit bearing capacity is 1473kN with increase of 12.3%, the time when it reaches the stable state is in accord with the excess pore water pressure dissipation monitored at each observing point. The larger the internal frictional angle of soil becomes, the more the ultimate bearing capacity is. The angle exceeding 20°,the bearing capacity would not increase as internal frictional angle of soil increases.

Abstract: This paper presents an optimum design model for the bracing structure，Based on a foundation pit project as an example, five different design schemes by the optimization and selection, to clarify the combined support scheme in practical engineering applications and conducted technical and economic analysis, by monitoring the results and use results to prove its feasibility, a number of similar projects come to a certain reference value of the conclusions for similar reference works.The Optimum calculation results of the example shows the optimum design could produce obvious economic results when it used in the design for the bracing structure of foundation pit.

Abstract: It is used as an example that the composite foundation with long-short-piles is used in liquefied soil under a high-rise building .By using the finite element method, the effects of short pile replacement ratio, long pile replacement ratio, raft thickness on side friction of the pile are discussed respectively. The results show that: Short pile replacement ratio changes have an effect on side friction of the long pile from 4m to 15m. With long pile replacement ratio increasing, negative friction and positive friction of the long pile decreases gradually. With the raft thickness increasing, negative friction and positive friction of the long pile decreases gradually. Otherwise, the distance of side friction of the long pile comes up to zero increase gradually. These conclusions are provided as references for future optimum design.

Abstract: According to the Biot wave theory and the complex function combined with multi coordinate method, seismic wave dynamic response of underground holes in the half space saturated soil is studied. Given P wave on two circular holes of the dynamic stress concentration factor of the numerical results, the distribution situations of the dynamic stress concentration factors are discussed with the variation of the hole spacing, incidence angle and the dimensionless wave number. The results show that, the effect of the underground hole spacing to the interaction effects of the holes is obvious. When the hole spacing reaches up to 6 times the radius of the hole, the peak value of the dynamic stress concentration factor decreases obviously, and the peripheral distribution of offset is weakened. With increasing of the incident angle, the hole peripheral stress concentration coefficient showed the trend of first increasing then decreasing, distribution also occurs at certain angle deflection. In low frequency waves, the hole stress peak value will influence mutually more, while in the high frequency input, interaction between holes will reduce.

Abstract: It is of significance to determinate the consolidation state of soil for evaluation of deformation and strength of foundation soil. The consolidation state of red clay is determined through laboratory experiments combined with static cone penetration tests. The results show that the law of consolidation history of red clay is opposite to other soils. The static point resistance obtained from cone penetration test decreases linearly with soil depth increasing. The over-consolidate rate of different soil layer gotten by laboratory experiments also decreases linearly with soil depth increasing. The slopes of two linear regress curves are similar. The change of static point resistance can be used to estimate over-consolidate rate of red clay at different depth.

Abstract: A series of loading - unloading consolidation creep experiments had been carried out on Nanning unsaturated expansive soils. Lots of loading - unloading creep curves under different stress levels were obtained. Through the various stages of creep deformation analyzed, it was concluded that the creep deformation of expansive soil contained elastic deformation, viscoelastic deformation and plastic deformation of components. Then model components in constitutive model of expansive soils were discussed. The rheological model of the seven components was proposed, which can describe unsaturated expansive soil elastic - viscous - plastic behavior. According to the experimental datum, all parameters of this model under different stresses were determined by the inverse analysis method. It is showed that the values of numerical calculated using this model agree well with those obtained by the creep tests. The conclusions provide a reliable theoretical basis for the rheological model of expansive soils to further study.

Abstract: Speed control of longitudinal ventilation systems in road tunnels is being combined with typical model predictive control (MPC) strategies which may bring huge energy saving potential to the system. Theoretical analysis of the inertia effect is presented based on the energy equation of one dimensional incompressible unsteady flow, step response model is chosen to describe the dynamic behaviors of the system. The results show that the effect of jet speed change on CO concentration is nonlinear within fan’s economical working range and the settling time of CO level has similar change trend with that of the flow field but is a little longer. The system settling time is longer when jet speed decreases than it increases and is related to the change extent of jet speed. The effect of traffic intensity on CO concentration can be regarded as linear disturbance to the system output. These results may provide useful indexes to control the tunnel ventilation system more economically and lay foundation for the application of predictive control strategy in the system.

Abstract: It is shown that liquefaction induced uplift is one of the most typical disasters for underground structures in liquefiable zone. Though a lot of researches were conducted to investigate the uplift phenomenon of underground structures in the past years, further studies need to be carried out to discover its mechanism because the seismic responses were correlated with many factors. In the paper, a fully coupled dynamic analysis was performed to investigate the dynamic responses of underground structure in layered saturated ground. The soils were simulated by a cyclic mobility constitutive model, which adopted some important concepts such as stress induced anisotropy, subloading yield surface, and superloading yield surface. It was verified that the constitutive model can perfectly describe the dynamic character of both liquefiable sand and non-liquefiable clay. Simulated results were obtained for excess pore water pressure and deformation of soil deposit and uplift of underground structure. Special emphasis was given to discuss the influence of soil consolidation history on the seismic responses of underground structure. Simulation indicated that with the occurrence of liquefaction, soils at lateral sides of underground structure flowed toward the bottom of the structure, which led to the uplift of structure. Results also showed that the excess pore water pressure ratio of liquefiable soil decreased with the increasing of soil pre-consolidation pressure. Then the liquefied zones diminished, and the uplift of underground structure reduced.