Advanced Materials Research Vols. 168-170

Abstract: Taking the design of composite soil-nailing in deep foundation pit in complex surroundings for example, the paper discusses numerical analysis of soil-nailing using FLAC, a general analysis program of geotechnical engineering, used to predict the displacement and interior force in soil-nailing. Furthermore, a comparison about the interior force in soil nails between the numerical analysis and the traditional methods is made. The measurements show that the numerical analysis is more accurate than traditional methods. The conclusion is drawn that by contrast with the deficiency of traditional methods, more satisfactory results can be got from numerical analysis on composite soil-nailing using the program of FLAC.

Abstract: Considering the heterogeneous characteristics of rock at mesoscopic level, the damage propagation constitutive relation and evolution equation of freeze-thaw and loaded rock were established by using the theory of macro phenomenological damage mechanics and the generalized theory of strain equality. The evolutionary mechanisms of micro-structural damage and materials mechanical properties for the loaded rock were discussed under freeze-thaw condition, verified by experimental results of the freeze-thaw cycle and compression test of rock. It is shown that the freeze-thaw and loaded damage model can represent the complicated relations among the freeze-thaw, load and the damage inside the rock, reveal the coupling failure mechanism of macroscopic rock under the freeze-thaw and load from the micro-damage evolution. The combined effect of freeze-thaw and load exacerbates the total damage of rock with obvious nonlinear properties, but the coupling effect weakens the total damage. The lithology and initial damage state of the freeze-thaw and loaded rock in engineering structures in cold regions determine the weights of influence factors to mechanical properties, including environmental factor, loading factor and the coupling effects, so the rock performances different damage mechanical characteristic.

Abstract: For the construction of the proposed Qinghai-Tibet Express Highway in warm and ice-rich permafrost regions, it will be necessary to utilize the new technique of cooling the ground temperature by the coarsely crushed rock layer with a low fines content, instead of the traditional measures taken to increase simply thermal resistances, so as to protect from damage to highway embankment due to thaw settlement. The vibrating loads such as wheel load and tamping load may cause the breakage and abrasion of the matrix grains in the coarsely crushed rock layer. This results in decreasing of grain size and increasing of fines content in the crushed rock layer, thus decreasing the porosity of crushed rock layer. The smaller porosity of crushed rock layer may weaken the cooling effect of buoyancy-driven natural convection of the pore air in the crushed rock layer of the highway embankment, thus resulting in instability and failure of the embankment structure in permafrost regions. Under these conditions, the influence of vibrating load on the grain size distribution of the coarsely crushed rock layer has to be investigated experimentally. In the present study, laboratory experiments on the grain size variation of the coarsely crushed rock layer under vertically vibrating loads were carried out. The test results show that the vibrating load can cause the breakage and abrasion of the matrix grains in the coarsely crushed rock layer and the shapes of coarely crushed rock grain tend to be non-angular.

Abstract: The cohesive crack model is widely employed to the fracture analysis of concrete for mode I crack. The tension softening relationship is a very important constitutive law in the cohesive crack model. The determination methods of tension softening relationship of concrete are introduced in this paper which are direct tension methods, J-integral method and inverse analysis method. Meanwhile, those simplified softening curves including linear form and nonlinear form are summarized.

Abstract: Mechanical behavior and bearing capacity of ordinary concrete filled steel tubular short column (NCSSC) and ceramsite concrete filled steel tubular short column (CCSSC) subjected to fire load are experimentally investigated. Effect of the parameters, such as the maximum value of fire temperatures, fire duration on the strength and ductility of the two types of specimens were especially discussed. The test results show that both of the specimens of NCSSC and CCSSC after fire have higher bearing capacity and better ductility, there was no descent segment in load-displacement curves of the most specimens after the fire load was subjected, and even the case that bearing load increased again after descent segment arose. It was concluded that the maximum response temperature of specimens and fire duration time has great effect on the axial bearing capacity of concrete-filled steel tubular short columns subjected to fire, and there is a turning point of temperature for the influence.

Abstract: Compared with ordinary concrete composite floor, profiled sheet-ceramsite concrete composite floor(PSCCF) has the advantages of lighter weight and higher strength, and its resistant fire characteristics is better than ordinary concrete composite floor for stability of characteristics of ceramsite under high temperature. For study of the characteristics of the floor after fire, the experimental research on bearing capacity of the profiled sheet-ceramsite concrete composite floor after fire and the floor not subjected to fire load are further carried out at indoor temperature here. Based on the experimental results, effect of the fire on post-fire bearing capacity of the profiled sheet-ceramsite concrete composite floor is discussed, and the failure phenomenon and mechanism are analyzed. It is shown that he failure form of the profiled sheet-ceramsite concrete composite floor after fire has great change compared with the floor not subjected to fire load, but the bearing capacity of it is still higher.

Abstract: Vacuum freeze drying method is applied to prepare samples for SEM from one-dimensional consolidation clay which suffered different pressures from original remolded state. And then simple and synthetical micro-structure parameters of SEM photos obtained from some section are studied to uncover relation between mechanics properties and micro-structure. The results tell us that the first principal component approximately linear increases with consolidation pressure. It is distinct that the synthetical parameters are superior to the simple parameters in construction soil mechanics relation because the former can reflect the whole micro-structure qualities, but the latter can not.

Abstract: Simulating traffic loading, the high liquid limit clay specimens and the low liquid limit clay specimens of the Pearl River delta are engaged in cyclic triaxial tests under one-way cyclic loading respectively. The influence of axial stress, confining stress and plasticity index are taken into account. A critical dynamic stress ratio of saturated soft clay under one-way cyclic loading and the variations of axis strain and pore pressure with number of cycles were obtained. The conclusions are helpful to compute the settlement of saturated soft foundation under traffic loading after work.

Abstract: To the inclined rectangle plate subjected to forces acting longitudinally and laterally, the analytical solution of deflection, stress and inner force, considering the influence of inner force in central surface on the bending of the plate, were given by using the theory of plate and energy method. In accordance with the characteristics of structural form of rock layers in horizontal section top coal sublevel caving for the mining steep seam, deflected deformation rules of the roof and evolution path along influencing factors were discussed, the critical technical parameter of horizontal section top coal sublevel caving was got, and engineering technique measures to control strata movement were given. It is shown that, the deflected deformation and inner force are related to plate material, geometrical properties and inclined angle of the plate with obvious nonlinear properties. Then the reasonable range of horizontal section altitude of top coal sublevel caving is between 20m and 30m. The severest area of strata movement is in the central of mined-out area along mining, the upper part of subsidence area must be filled to reduce the length of hanging roof and retard the movement of overlying strata, further control the ground subsidence.

Abstract: A modified version of an existing drying shrinkage model developed by the authors is proposed which incorporates the influence of the aggregate on the process of shrinking. Whereas it is traditionally thought that the aggregate restrains the deformation of the cement paste and hence the shrinkage of the concrete, in this paper, the effect of aggregate on shrinkage is better represented by considering the effect of the aggregate on moisture diffusion. It is suggested that the presence of the aggregate modifies the diffusion of moisture which governs the moisture loss and hence the drying of concrete. Also, as the volume fraction of the aggregate in a normal concrete is about 75% or more, the shrinkage of the cement paste is ‘diluted’ by the aggregate in the concrete. Taking into account these effects, this new diffusion based shrinkage model has been proposed. To assess the accuracy of the new model the shrinkage of two concrete mixes is predicted and compared with the measured shrinkage of these mixes. Comparisons are also drawn with the shrinkage predicted using the Model Code 1990 (MC90). It was observed that the new model proposed here predicts the shrinkage of the concrete mixes more accurately than the MC90 model, particularly at early ages.