Applied Mechanics and Materials Vols. 90-93

Abstract: It is important to research the existence of the top Ordovician water-resisting strata, under which the regional Ordovician karts aquifers pose great water pressure threat to the upper late Carboniferous coal seam mining. So we take the samples from JK-02 to do mercury test, SEM and microscopic identification. The results show: ① 0 ~10m of the top strata of Ordovician is made of crystal powder dolomite. Most of the pores of the strata are intercrystalline pores, intercrystalline dissolved pores, microspore as well as stylolite ,and part of which are filled by calcite and clay. Its porosity is 11.3242%; and permeability 6.2324;and diameter of volume median 66.3nm; capillary median pressure 6.88MPa; mercury withdrawal efficiency is 42.22%; maximum pore throat's diameter is 145.32μm, and effective pore volume is about 13% out of total pore volume. ②10 ~112m of the top Ordovician is mainly made of powder crystal limestone and calsilutites. The most of pores are micropore; its porosity is only 0.8409% and permeability 7.0438; and diameter of volume median 66.3nm; and capillary median pressure 5.497~34.391MPa; maximum pore throat's diameter is 0.0227～0.453μm; ③The number of pores and the porosity of the limestone are less than that of the dolomite. The limestone of the top Ordovician can serve as water-resisting layer for its lower permeability and compactness if there is no water-conducted faults.

Abstract: Compaction piles is one of the conventional methods for foundation treatment in collapsible loess, there are very few research results about soil compaction effect between piles when forming the piles. Firstly, the stress field and displacement field of soil around compaction piles are elastic-plastic analyzed on the basis of the cavity expansion theory; then a series of field and laboratory tests were performed to evaluate the treatment effect of the compaction pile composite foundation. The result shows that the collapsibility has been eliminated, all physical mechanics indexes have been improved, and soil compressibility and modulus of compressibility are also increased remarkably. It embodies the correctness of the computation theory. And the feasibility of the compaction piles composite foundation on collapsible loess area is further proved.

Abstract: The elasticity cavity swelling is investigated, and based on equivalent loading and elastic wave theory, blasting propagation model at great depth is established. Using the potential functions which is equal to different boundary conditions, a transformation rule between velocity field and stress field is given. The result shows that for the same stress condition, the particle’s velocity is smaller, the reason for which is that the factors influencing the magnitude of this difference are the propagation distance and speed. Through the stress field attenuation analyses under shock wave loading, variable attenuation of spherical wave field is r^-1at least. At the beginning of the medium’s movement, the circumferential stress is tensile stress, and then turns into compressive stress. The tensile stress may cause radial cracks. The shearing stress is the decreasing function of r/R₀in the area from seismic source to elastic wave front.

Abstract: For vibration control of long-span arch bridges under multi-support seismic excitation, this paper presents schemes of control to seismic responses of arch bridges with Magneto-Rheological dampers(MRD). In the semi-active control system of arch bridge-MRD, Linear Quadratic Gaussian (LQG)-based Sign function control algorithm is used to command MRD，and traveling wave effects on the responses of structure are considered. The Nimu arch bridge is used as a simulation example to verify the proposed control scheme. Numerical results show that traveling wave effects have no unfavorable influence on the control to response of arch bridge.

Abstract: Seismic behavior of the steel & concrete hybrid structure is studied by Sap2000, including modal analysis, response spectrum analysis and time-history analysis. Also, a simplified calculation model of the steel & concrete hybrid structure is established, and some formulae have been derived from this model, such as the natural frequency, top displacement, shear of both the core tube and the steel frame, on the basis of finite element method of bar system. Those formulae can be used to explain and approximately count the seismic response of steel & concrete hybrid structure.

Abstract: Based on liquefaction survey of 2003 Xinjiang Bachu earthquake of Ms6.8 and in-situ shear wave velocity testing data, the feasibility and applicability of five typical liquefaction evaluation methods which use shear wave velocities as criteria are presented herein. Analysis showed that none of the five liquefaction evaluation methods can provide a satisfactory result in Bachu area. The successful judging rates are only 36% to 64%. The intensity method which is employed to evaluate liquefied and non-liquefied sites in Bachu area provides only 40% successful judging rate, and the method is risky in intensity VII area and conservative in intensity IX area. The critical lines of the five methods deviate greatly from the actual lines. In intensity VII area all the five methods incorrectly misjudge. Further work has to be conducted to research on the soil properties in Bachu area and to establish the regional liquefaction evaluation method in Xinjiang.

Abstract: This paper, based on the Chongqing urban small earthquake zoning, structure of ground calculation model to analysis soil seismic response , determined the design ground motion parameters , and with the current seismic code were compared ,for the general construction projects in Chongqing provides a reference for seismic design . At the same time, it’s of importance to disaster mitigation of other cities, sustainable social and economic development.

Abstract: So far, nonlinear analyses on seismic effect of large-scale basin model have rarely been reported. Based on the explicit finite element method and 32 CPU parallel computing cluster platform of ABAQUS, a two-dimensional（2D） large-scale refined model for Fuzhou Basin is established using a nonlinear analytical method in the time domain. Both the peak ground acceleration (PGA) and acceleration response spectra of ground surface are emphatically analyzed. Meanwhile, the results by one-dimensional equivalent linearization method in frequency domain are added for the sake of contrast. The study results show that the PGA of ground surface will be obviously amplified when compared with the peak acceleration of bedrock ground motion; and the ground acceleration response spectra of Fuzhou Basin may appear a double-peak or multi-peak phenomenon. Moreover, the 2D large-scale model can reflect amplification effect of Fuzhou Basin soil to bedrock ground motion in particular periods; In addition, the acceleration responses of ground surface right above the bedrock valleys and crests appear larger than the other positions adjacent to them, these phenomenon are generally manifested as focusing effect and amplification effect, which are thought to be produced by the recently deposited soils in the basins as well as the special soil layer such as lens. In general, the PGA of ground surface obtained by 2D model present to be greater than that obtained by the one-dimensional model.

Abstract: According to the geological conditions of the Danjiangkou reservoir, the computational model was set up considering fracture zones and the changing along the depth of mechanical properties of rock. Adopting this model, the seepage field of the reservoir area was simulated for long time, which shows that: 1) The medium and small earthquakes in the reservoir area were induced mainly by reservoir water seepage since phaseⅠimpoundment; 2) A series of medium earthquake would be induced in the fracture zones of reservoir bottom and around the reservoir bank in the depth of 5km about in a month of phaseⅡ impoundment; 3) A series of small earthquakes would be induced in the fracture zones in the depth of 12km to 16km at the same period.

Abstract: For linear parametric system, like mass proportional damping case, physical parameter identification of horizontal layered soil and inversion of ground motion of bedrock are done by using the Least-squares-based hybrid inversion algorithm. For nonlinear parametric system, such as Rayleigh proportional damping case, the modified Levenberg-Marquardt (mLM) method is introduced. Since the mLM method is sensitive to the initial values of parameter, a SVD-mLM method is proposed with combination of singular value decomposition (SVD). Parameter identification of nonlinear parametric system and inversion of ground motion are performed by using the SVD-mLM-based hybrid inversion algorithm. The numerical simulation results show that the identified parameters of horizontal soil layers and inversed ground motion of bedrock have high precision, and the proposed method is useful for geotechnical engineering and robust on noise.