Advanced Materials Research Vols. 594-597

Abstract: A new belled wedge pile, which can improves the friction of pile shaft, tip resistance and reduce the influence of negative skin friction, was developed. The analysis model of single belled wedge pile embedded on soft soils was built by p-y curves method via LPILE software, models of conventional belled pile, tapered pile, and uniform section pile with the same volumes were also built for comparative analyze. The performances on load deflection curves, and bending moment distributions for these four pile types were comparative analyzed and discussed. Then the parameter studies of single belled wedge pile are carried out. The results show that belled wedge pile is one of cost-effective piles, which can improve lateral bearing capacities effectively.

Abstract: According to hot research of subsidence time function at home and abroad in recent years that there are commonness of less parameters and difficult to extended reflecting surface subsidence characteristics in the dynamic process, the surface subsidence dynamic coordinates time function were proposed based on the probability integration principle, established the calculation methods of surface dynamic process, anal sized the applicability and limitations of the dynamic time function and verified some examples. The results show that the function is more accurate than the Knothe time function in analyzing the actual regularity of surface subsidence caused by underground mining, reflecting the dynamic characteristics of surface movement in real time, interoperating mining phenomenon, it is more accurate to predict dynamic ground displacement and deformation which has a certain significance value in mining design and subsidence disaster management.

Abstract: it is already confirmed that the rock mechanical characteristics under unloading condition differ from those under load condition, and the excavation process should be considered to be a typical kind of unloading mechanical behavior. As thus, a series of representative unloading tests and shear strength tests about unloading cracks are performed on hard granite samples from the underground workshop excavation zone in Dagangshan hydropower station in western China, where the surrounding rock is affected by high geo-stress. Based on the tests results, some significant theory research is made.

Abstract: Underbalance drilling has been applied to each oil field at home and abroad, due to the advantage of increasing the penetration rate substantially, protecting the reservoir effectively and reducing the drilling costs. But in respect of rock stress state characteristics near the bottom, relatively speaking, the study was rarely.Take the borehole near the bottom in underbalance drilling as the research object, analyze the influence of terrestrial stress, pore pressure and fluid column pressure on mechanics characteristic of rock in the bottom, to study the rock crushing efficiency, well deviation and hole stability of non-permeable wellbore and permeable wellbore in underbalanced drilling. The result shows that the mechanical properties of rocks near the bottom are subject to terrestrial stress, pore pressure and fluid column pressure. In non-permeable rock, the rock crushing efficiency, the penetration rate and the concentrated force of well trend to increase, the well trends to inclination. In permeable wellbore, with the permeability increasing, the rock crushing efficiency, the penetration rate and the concentrated force of well trend to decrease, the tendency of inclination becomes lower.

Abstract: During turning open-pit into underground mining, the state of slope stability is related to the relative space positional relationship between open-pit mining and underground mining. The toe area of slope is the most unfavorable area to slope stability and the outer region of slope is the most favorable area, while the central area of the slope has the most complicated effect on slope stability so that the mechanism of its influence can be understood only by the means of calculation. The slope stability coefficient decreases with the augment of underground mining geometric dimension. But it remains constant when the underground mining area is fully extracted. With the increase of mining depth, its range of influence on slope stability increases, which results in the decrease of slope stability coefficient. However, the slope stability coefficient tends to unchanged when the mining depth increases to some certain value.

Abstract: Whether the stress sensitivity in the mid-high permeability is stronger than that in the low permeability reservoir is current hot debate, aimed at this question. 14 samples are selected to calculate the permeability loss rate separately in the laboratory simulation experiment, the results show that the absolute value of loss rate of the mid-high permeability core is higher than that of low permeability core, but the relative permeability loss rate is lower than that of low permeability core, which, namely, means the low-permeability reservoir has stronger stress sensitivity. The stress sensitivity curve in the high permeability reservoirs could be classified into the type model of "gentle", while the stress sensitivity curve in the low permeability reservoir could be concluded as the "first steep then slow " mode. Hence the bottom-hole flowing pressure must be controlled reasonably in order to keep the productivity well.

Abstract: How to demonstrate the deformation and failure mode of the slope under combine surface and underground mining and evaluate its stability scientifically is one of the problems that need urgent solutions in mining engineering. First, the deformation and failure mode of the slope under simple surface mining, the deformation and failure mechanism of the overlying strata affected by underground mining and deformation mechanism of the slope under combined surface and underground mining were analyzed, then the failure mode and the stability calculation method of the slope under combined surface and underground mining was studied. The results show that the failure modes of the slope under combined surface and underground mining involve three patterns: slipping failure, subsiding failure and slipping-subsiding combined failure, that the failure modes and the stability of the slope under combined surface and underground mining be significantly affected by the underground mining positions and the influence be mainly controlled by the length of the latent slide plane of the slope and the weakening degree of the rock masses in the subsidence range. Finally, a limit equilibrium method to calculate the slope stability under combined surface and underground mining was put forward.

Abstract: It is an important way to realize mine intensive production by increasing of the coal face length. During the transformation period of mining methods about thick coal seams, the character parameters of surface movement and deformation will be provided to guarantee scientifically mining of thick coal seams in Jincheng mining area. In this paper, numerical simulation, theoretical analysis and field measurement are used for studying the influence of coal face length on surface movement and deformation in the condition of large height mining. The results show that the separated strata space range extended with the increasing of coal face length and advancing distance, the surface movement and deformation become more violent, the mining influenced range also gradually expands, and the maximum surface subsidence and horizontal displacement increases gradually in form of linear relationship. In the condition of fast mining, the duration of abscission layer reduces, and the surface movement and deformation shows obviously hysteretic and zonal characteristic.

Abstract: Expansive rock is a special gneis with problems, spread widely in our country. Currently the government is carrying on constructions of infrastructure such as railways and transfer project of south water to the north. Such defective rock can disturb the construction process: due to its extreme sensitivity to temperature, humidity and stress field, swell rock has big potential harm to the project construction; a slight change in external factors could bring great damage to the project construction. Based on the analysis of the project characteristics, The thesis gives the treatment measures of expansive rock slope. The study is quite meaningful for the stability of the expansive rock slope.

Abstract: To offer or predict the shear strength of stabilized expansive soils after cyclic wetting and drying for the slope analysis, the paper carried out direct shear test on the stabilized expansive soils after different times of cyclic wetting and drying. The test results show: The first 3-5 times of cyclic wetting and drying will cause the shear strength decreased sharply, and after about 7-9 times of cycle, the shear strength will trend to a stable value, which is about 40-60% of the normal strength before the cycles. Logarithm model can well fitted the variation of the shear strength and the times of cyclic, so the shear strength index can be predicted by using the models which was established according to the test results.