Advanced Materials Research Vols. 168-170

Abstract: The evaluation of the correct stability factor of tunnel is a critical element in the various design and construction phases of a tunnel excavated in difficult geotechnical conditions. An innovative, and well-applied, procedure for optimize the construction phase management is described in this article. The starting point of this procedure involves the verification of the results of numerical methods obtained from referenced analytical methods. In the first step of the procedure the results obtained through the analytical method are verified by means of a numerical method in order to evaluate the practical consequences in terms of development of deformations and plastic zone. In this manner, the assumed design risk is evaluated for the different methods and the solution that gives the best correspondence with numerical simulation is selected. Finally, residual uncertainties and parametric variations are incorporated in the analysis and Monte Carlo simulation is used to calculate the statistical distribution of the face-stabilizing pressure and the design value is selected on the basis of an acceptable probability of failure.

Abstract: Energy saving and low carbon footprint are becoming key issues in recent architectural design. It's necessary to develop new materials and new building forms for this purpose. After introducing some famous model projects appling ETFT air pillows, this paper lists major physical properties of this new product and puts forward some design measures such as passive solar heating, great span structure system, natural lighting and cavity ventilation for energy saving and low carbon footprint buildings.

Abstract: In order to study high strength and other characteristics of high strength concrete, scanning electron microscopy and mercury pressure method were used to analysis the surface morphology, organization, structure, composition and fractal features of C100 high strength concrete materials in terms of the microscopic mechanism, and the material strengthen mechanism and the causes of failure were revealed. The results shows that, as the adequate hydration and particle hydrates increase in C100 concrete, more gel-like mesh or wrinkles are generated, and there is a strong bonding effect between fine particles. As the use of mixing composites material in C100 high strength concrete, the density of the material is improved and the proportion of harmful hole is lowed, and its mechanical properties and durability are all improved. When concrete is damaged, cracks increase and coalescence show an increase of fractal value.

Abstract: In this paper a 3D FEM model is established to simulate the dayuliang tunnel which is located in the gob area. The vertical and horizontal surface displacements of gob area are obtained in different simulation condition. By these calculated results the character and key region of gob surface subsidence is analyzed. The warning line of subsidence basin is determined. In order to control tunnel structural’s stability its deformation and stress character are also researched to determine stress concentration and important supporting position. These analysis results provide a scientific basis and technical guidance for the tunnel construction in gob area.

Abstract: For judging the security of pile foundation, the loading static test is popularly used in engineering. Some conditions could confine this method to estimate the ultimately loading according with objectivity, for example the high loading bearing pile foundation, the especial condition of static test, over length pile, etc.. So the strength reduction method (SRM) is put research this question in the basis of the ultimate loading capacity theory of pile foundation and the limit analysis of FEM. The judging condition and the safety storage factor (SSF) of SRM were built. The judging condition have three item, (1) the inflexion lies on F-s curve, and the bottom of F-s curve is parallel to the s axis; (2) the point of V type appear on F-Qu curve, so the previous reduction factor of this inflexion of F-s curve and the point of V type of F-Qu curve is SSF on the loading condition of pile head; (3) the equivalent plastic strain connected in soils around pile shaft and pile end. This method was used to analyze and estimate the ultimately loading of the large diameter pile, and its error of SRM to the static loading test and the increment loading method of FEM (ILM) are less 5%. So it shown that SRM may be used to attempt in engineering for judging the security of pile foundation and computing the ultimately loading.

Abstract: Weak intercalated rock plays an important role in the stability of engineering rock mass. It controls the mechanism of deformation and breakage of rocks. Systematic numerical tests have been carried out to study the stability of surrounding rock mass with different distributions of weak intercalated rock has been analyzed by the FEM software ABAQUS. All of the numerical modelings are plain-strain type with elasto-plastic constitutive law and Drucker-Prager failure criterion. Some quantificational results about the influence of weak intercalated rock are summarized, especially the influence on the deformation, stress of surrounding rocks and plastic zone. Because of weak intercalated rock, the stress of surrounding rock appears the character of discontinuity. In addition, the distribution of plastic zone is also affected. When weak intercalated rocks exist in vault, spandrel and bottom, the situation of surrounding rock is comparatively unfavorable. These results have a certain role in guiding significance to the site selection and layout, the majorization of supporting system and the construction of tunnel of the same kind.

Abstract: Testing the overlength pile in urban subway engineering is the key for quality control. Because of the limitations of urban construction sites, it is difficult to achieve efficient results with the normal testing method. Optical fiber measuring technique has gradually replaced the application of the traditional strainometer in geotechnical engineering testing as a result of the unique advantages it offers. In this study, first, the principles underlying the optical fiber measuring technique are introduced and its application in pile foundation testing in subway engineering is discussed. Then, combined with engineering practice, the optical fiber measuring technique is employed to study the law of development of strain in the overlength pile with the loading process under the action of vertical load. Finally, some meaningful conclusions are arrived at and reference foundations are provided for the optimized design of the same kind of engineering.

Abstract: The initial crack propagation directions of branched cracks under tension are investigated. In this study, the material is assumed to be brittle and deformed linear elastically. The elastic stress fields and stress intensity factors are obtained by using finite element analysis method. Various parameters which including the lengths, the directions and the locations of branched cracks are investigated to study their effects on the crack initiation angles. Three kinds of crack propagation criteria are employed to obtain the crack initiation angles. The effects of crack propagation directions due to the use of different crack initiation criteria are studied and discussed in details.

Abstract: The passive evaporative cooling roof in building is an important passive thermal insulation technology with the development of green roof, spraying water roof and storing water roof. For its complexity of heat and moisture transfer process only some sample experiments could be done on some controlling conditions. In this paper on the basis of analyzing the unsteady heat transfer model with the first boundary conditions and by using the integral method based on the concept of thermal boundary layer the critical penetration time, the critical penetration thickness and the temperature attenuation ratio are calculated and analyzed for different materials with different thickness. The research results show that the critical penetration time is gradually attenuated with the increasing of thermal diffusivity. The critical penetration time of being researched materials is lower than one hour when the thickness of materials is 0.1 meter, when the thickness of materials is 0.2 meter the critical penetration time is between 46.83 and 214.55 minutes, when the thickness is 0.3 meter the time is between 105.36 and 482.73 minutes. The sandy soil has the maximal critical penetration time and the critical penetration thickness in all analyzed materials, and the loose sawdust has the minimum critical penetration time and the maximal critical penetration thickness. On the side of temperature attenuation ratio the different material thickness has different attenuation law.

Abstract: The deterioration on sulfate attack was investigated both in physical crystallization and the chemical erosion. Specimens that suffered long-term immersion and dry-wet cycles in saturated sodium sulfate solution are compared to trace the physical attack. And the chemical erosion was conducted by comparing specimens which have been suffered long-term immersion in saturated sodium sulfate solution and saturated limestone solution. In the investigation, the non-destructive detecting indexes, such as the ultrasonic velocity, and the dynamic modulus of elasticity were measured. The permeability, the porosity and mechanical strength at 28-day age were measured. The flexural/compressive strength was measured after 90 wet-dry cycles. And then all the specimens were cut into cubes to take the measure of compressive strength. Based on the experiments, feasibility of various parameters, such permeability, relative dynamic modulus of elasticity, ultrasonic velocity and relative flexural/compressive strength, were investigated to evaluate the concrete deterioration. The results indicate that there is a close relationship between the deterioration by sulfate attack and concrete permeability, so the reduction of permeability is effective in promoting the resistance. The index of the resistance expressed by the dynamic modulus of elasticity ratio is comparable to that expressed by the relative flexural strength. A novel method was suggested in evaluating concrete by sulfate attack, namely, combined with some mechanical tests, the parameter of relative dynamic modulus of elasticity can be used to evaluate the deterioration; the permeability denoted as the amount of transporting charges within 6 hours can be used to evaluate the properties to sulfate attack.