Advanced Materials Research Vols. 594-597

Abstract: Fracture persistence is an essential parameter to evaluate the stability of rock mass. In the present paper，a projection method based on fracture network modeling was employed to study the three-dimension(3D) fracture persistence of abutment rock mass in Wudongde dam site. Fracture data from an exploration tunnel was used to generate a fracture network model. Subsequently in the fracture network, numbers of projection planes with different positions and different attitudes were set. A computer program was written to calculate 3D fracture persistence. The scale effect on persistence is discussed. The distribution characteristic of persistence values was analyzed. Also the change of lateral persistence with directions was studied. The following conclusions were drawn from the study：(1)The horizontal persistence values do not have a noticeable scale effect, while the effect of size on the lateral persistence is significant;(2)The lateral persistence values conform to a normal distribution with a mean value of 3.9;(3)The persistence value varies with the direction of projection plane. The steep dip angle corresponds to a low persistence value. A maximum value is obtained when the trend and dip angle of the projection plane are 175°and 65°.

Abstract: Encasing a cylindrical granular column with tensile resistant material is proven an effective practice to improve granular column strength. Laboratory triaxial compression tests were conducted on encased granular columns to study the tensile resistant material reinforcing effects. This study explores the behavior of geosynthetic-encased sand columns using a converted approach to reduce laborious efforts. The encased column behavior is simulated by applying persistently increased chamber pressure to unreinforced sand column specimens. Three column specimen diameters, 5, 7 and 10 cm, were employed to study the scale effect. The test results indicate that the converted approach simulates larger diameter encased column well.

Abstract: The correlation of the load history in the nonlinear large deformation mechanical design method is discussed. Then the different schemes of support construction process which are used to control the nonlinear large deformation of the east wing main haulage roadway in -1000m level of a certain coal mine are simulated by the program of 3D finite difference. The results show that the deformation results, the displacement distribution characteristics and the stress concentration degree of surrounding rock are significantly different due to the different construction sequence. After plastic large deformation occurs in deep soft rock ,the mechanical response characteristics of the surrounding rock closely related to the entire loading history. And different construction sequence will produce different deformation control effect. Therefore, the use of large deformation mechanical design method for the supporting design of deep soft rock is necessary, then based on the proposing of the mechanical countermeasures the best construction process is determined, and the optimization of support parameters must be for this process.

Abstract: The loose-fractured rock mass of Badong formation exposed stratum in New Fengjie county is a typical unsteadiness rock group, possessing unique formation and evolution mechanism of rock mass structure and engineering properties. This paper mainly aiming at the influencing factors such as the tectonic action, formation lithology, the effect of water and so on, analyzes and researches the causes and evolution mechanism of the loose-fractured rock mass of Badong formation in New Fengjie county.

Abstract: The general soft soil widely exists in coastal, riverside and lakeside areas. Large area along the Yangtze River in Anhui Province is also the distribution of soft soil. The existence of soft soil has some degree effect on the project construction. According to the laboratory tests, the basic properties of the soft soil in these areas were researched. Based on test results, and compared with the soft soil of other areas, results show that the soft soil of Anhui along the Yangtze River has its own special nature. It include that, compared with other areas soft soil, the soil void ratio and compression coefficient are a little smaller; the consolidation coefficient, permeability coefficient and shear strength parameters are a little bigger; the silt content is above normal. The results and further understanding of soft soil basic nature may have certain guiding significance to construction projects along the Yangtze River region.

Abstract: Engineering dewatering not only makes soil release gravity water, increasing soil self-weight stress, but also lead to seepage occur along the two sides of waterproof curtain driven by water head difference inside and outside the pit, forming a hydrodynamic pressure, which are the main reasons causing ground settlement. In this paper, the equation of groundwater level drawdown funnel curve firstly is deduced, then we investigate the total effective stress increments of foundation pit soil with seepage works alone as well as both gravity drainage and seepage effect work together, and obtained the formulas for soil effective stress increment calculation. Studies show that the shape of soil settlement cross-section is closely related to the characters of water drawdown funnel curve.

Abstract: Engineering dewatering has been widely used to improve soil characteristics currently, whereas dewatering always bring about soil settlement around the pumping well inevitably, which may be the largest defect of dewatering. In this paper, several possible factors leading to soil subsidence are explored, then the change of soil stress under the action of dewatering drainage during phreatic aquifer well pumping are investigated. From the two aspects that may be encountered during dewatering in confined aquifer: only pressure lowering effect as well as simultaneous function of both pressure relief and dewatering drainage, we study the change of soil stress state around foundation pit. The conclusions obtained through this research will contribute much to the calculation of soil settlement caused by dewatering, also beneficial to seek the settlement control measures.

Abstract: Combined composite foundation has been widely used in actual projects, but its working behaviors need to be studied further. By establishing finite element model, the effect of the core pile was researched. Analysis shows that, the diameter and the length of core pile affect the bearing capacity of combined composite foundation significantly. There is an optimal value of the length and the diameter of core pile, which can make the foundation generate maximum carrying capacity. With the increase of core pile length, the depth of neutral point increased.

Abstract: Load transmission characteristics and rules of pile foundation’s soil-pile system have become one of the basic research contents for pile foundation researchers. Given the different geological and constructive conditions, the load-bearing features of pile foundations in different places have their own rules. Hence, research on the features of load transmission in different places has turned out to be an important project facing all the pile foundation researchers. The Xigeda-rock group is widely spread in Xichang-Panzhihua area in Sichuan Province. This rock stratum is a kind of extremely soft rock, with the nature of argillization, softening, hydrating and cracking with water. According to the static load test data from the pile test in Xinjiu of Panzhihua, this thesis obtained the load-settlement curve with displacement coordinate transformation method. And it is then compared with the actually measured load-settlement curve. Ultimately, the model and value range for parameters of axial load transmission function for cast-in-place pile in Xigeda-rock stratum is proposed.

Abstract: Because of the existence of high stress in the surrounding rock of deep roadway, the physical and mechanical properties of the surrounding rock to change, and the surrounding rock stress distribution is very different from the shallow, so the way of shallow roadway support is not suitable for deep roadway. Deep soft-rock roadway support is a complex systems engineering, it should consider the different geological conditions, roadway scope of application, construction technology conditions, construction period and the cost and other factors to determine the optimal combined support program, if the special geological conditions encountered in the construction, it should be timely to improve the supporting program to meet the construction safety and ensure the quality. This paper is based on the characteristics of deep roadway support, sums up the combined support form in the project, researches and analyzes the combined support technology, and explores how to use suitable combined support form in deep roadway.