Applied Mechanics and Materials Vols. 170-173

Abstract: The damage process is accompanied by the acoustic emission (AE) for brittle materials such as rocks. An AE experimental research was investigated based on different loading velocity, moisture content and rock structure. The research shows that Increasing loading velocity makes the duration of obvious AE longer, average AE rate improved, the strain values of obvious AE decreased; More moisture content delays the time of obvious AE, reduces the values of AE, increases the strain values of obvious AE; inferior structure rock has little AE, and appears discretely; The main reason of AE difference is the different rock structure.

Abstract: The long-short-piled raft foundation is an unusual type of building base. This kind of foundation is usually applied for pile foundation reinforcement of existing buildings when shortage of bearing capacity of piles occurs. The bearing capacity of pile foundation is improved and less settlement is expected. Since this method has so many obvious advantages, it is recommended in the reinforcement design of piled raft foundation of an existing building in Tianjin. Longer reinforced concrete bored piles are adopted as the supplementary ones. The bearing capacity of this kind of piled raft foundation was studied. The settlement was also analyzed with the National standard method together with the finite element numerical method. According to the study, the bearing capacity of piled raft foundation is enhanced effectively after adding piles. Also, the results show that the total settlement and differential settlement during the construction is in control respectively.

Abstract: m-method is a widely used method for pile-soil interaction analysis. The main shortcoming of traditional m-method is ignoring the non-linear of soil. The actual relationship between the m and the displacement of pile (y) caused by loads is non-linear; however, it is unreasonable to used a linear curve and a fixed value of m during the calculation. Two methods for getting the m-y curve based on the p-y curve and the NL method are given. Linear spring is used and the m is dynamic modified based on the m-y curve by iteration. A test problem of a large-diameter monopile for offshore wind turbine is given and the dynamic modification of m of the full-range, the shallow and the deep-seated soil are carried out. It reveals that the dynamic modification of m by iteration made it possible to consider the non-linear of soil; the difference between the traditional m-method and the p-y curve method or NL method is caused by the way that using one and fixed m value and it is reasonable to use the non-linear m-y curve obtained by in-situ test; the lateral load-bearing capacity of the pile is influenced mainly by the soil between the mud-line and the depth of 3~5D (pile diameter), so that the dynamic modification of the m can be carried out for this part of soil to raise efficiency.

Abstract: The flexible pile and the rigid pile, the gravel pile and CFG pile are arranged in a group as compound piles, which utilize their merits and avoid their shortcomings. Based on the study of the existing calculation methods for the bearing capacity of multi-pile composite foundation, the working behavior of loaded multi-pile composite foundation and the general influence of different construction methods to the bearing capacity of the soil are considered. The coefficient of the bearing capacity exertion of master piles, the coefficient of the bearing capacity exertion of minor piles, the coefficient of the bearing capacity exertion of the soil between piles and the coefficient of the bearing capacity improvement of the soil are introduced. The new step-by-step calculation method for the bearing capacity of multi-pile composite foundation is put forward. Through designed a high-rise frame structure with multi-type-pile composite foundation, the results show that the multi-type-pile composite foundation is more whole and possess stronger capacity of load transfer compared with single-type-pile composite foundation. It can satisfy the requirements of load bearing capacity and deformation under special foundation conditions.

Abstract: Permeability of pore air is one of the main basic characters of unsaturated soil. Measuring it accurately is important in anti-seepage design. In this paper, a new kind of device was invented that could test permeability of pore air of unsaturated soil in situ quickly and accurately. With this apparatus, the relationship of air permeability coefficient with various dry densities and saturation of ground soils were obtained in a reservoir. Compared with routine indoor test, field test can decrease the disturbance to the soil and the result is more accurately.

Abstract: The major instable modes of the gravity retaining and protecting structure for foundation pit are overturning and slipping. Because of the stability of these geotechnical problems is affected by many uncertain factors, the stability analysis of them should be involved in the scope of the fuzzy and random event. Therefore, based on the theory of probability and fuzzy mathematics, the random and fuzzy characteristics were took into account, the calculating model of the fuzzy reliability of the gravity retaining and protecting structure for foundation pit was established. Through an engineering example’s calculating analysis of its overturning and slipping instable modes, the fuzzy instable probability and reliable index are calculated, some relevant conclusions are acquired via comparing with the traditional safety-coefficient method, and the feasibility of the fuzzy reliability method is testified.

Abstract: Experiment of thermal shock was conducted by laser on cylinder head of graphite cast iron. Infrared pyrometers were mounted on the top of the workbench to sample the transient surface temperatures. The high resolution CCD camera was employed to sample transient images of the cylinder head. Microstructure of thermal shocking specimen was characterized by scanning electron microscopy (SEM) and optical microscope (OM). Mechanical properties of thermal fatigue specimen were evaluated by hardness. Results show that microstructure and hardness are not obviously changed, which mean that cylinder head of graphite cast iron has performance stabilization within the rang of thermal shocking temperature.

Abstract: The effect of anisotropy of friction angle in natural deposited soil on the stability of soil slopes was studied in this paper. Stability analysis was performed on a uniform soil slope with anisotropic friction angle. Spencer’s method was used, and the variation of friction angle was assumed to be linear to the change of direction of the slip surface. It was shown that 7-10 percent of change in safety factor might achieve within a 10m-highed anisotropic soil slope. It was also found from the analysis that that frictional anisotropy had no obvious effect on the location of critical slip surface.

Abstract: The polypropylene bar shell bolting shotcrete and support system was studied on the basis of the analysis of the mechanics principle of shell structures. The technique feature is a kind of specially three-dimensional bar-mat reinforcement instead of three-dimensional bar-mat. It has very high mechanical property and was applied in difficult drift without profiled bar, anchor bolt, grouting and so on. The model experiment was done by relying on the industrial test on the broken laneway of Xishan Coal Power Company. The distortion, destruct shape, developmental rule of the supporting system were examined while the stress and strain distributing rule and also the ultimate load were obtained. The application showed that without reducing the carrying capacity of supporting the case, and heavy metal stent compared to the steel supporting the form of reduced consumption and the amount of concrete rebound, and has good flexibility, is all excellent soft rock drift Jean pressure retaining structure, and has good prospects for widespread application.

Abstract: Take 3 coal repeated mining of Luxi colliery as research background, overburden strata rupture development rules in repeated mining of thick coal seam were studied by using the methods of field measurement. The results indicate that the height of overburden crack belt reduced along with the increase of goaf development time; the crack belt height of upper layer is 34.73m, the ratio of crack height and mining thickness is 15.1, the crack belt height of lower layer increased to 41.51m, but the increased trend declined, the ratio is only 12.14, the development height after up-layer was excavated is 83.6% of the height after two coalface were excavated. The results have important guiding sense for predicting overburden rupture rules in the similar mining conditions and improving the upper limit.