Advanced Materials Research Vols. 261-263

Abstract: Guanjiao tunnel being reconstructed is the key engineering in the 2^nd line between Xingning and Golmud. It is 32.645km long. Carbonaceous slate stratum thereinto is nearly 300m long. The rock mass was suffered tectonic movement and crushed, and its physical and mechanical properties are poor. So large deformation will occur while tunnelling under high horizontal tectonic stress. Numerical simulation along with field experiments were utilized to study the mechnical effect of tunnel section shape. Two kinds of section shapes were considered, that are horseshoe-shaped section and large curvature wall, quasi-circle-shape section. Results show that quasi-circle-shape section could effectively lessen the deformation of tunnel and minish stress concentration of support. Field experiments of different support forms were also conducted. Support forms include Grid steel frame (4×ф22mm)with 0.5m span, I 20a steel frame with 0.67m span and I 20a steel frame with 0.5m span. Pressure of surrounding rock, axial force of anchor, stress of steel frame and shotcrete under different support form were measured and analysed. Because composite lining was adopted in the tunnel, the contact pressure shared by secondary lining and stress of molded concrete under different primary support stiffness were also analysed. Results showed stress of support are rational under support form of I20a. Deformation of tunnel measured in situ under different support forms showed that support form of I20a could control deformation of surrounding rock. Synthetically considering the above and economic benefit, support form of I 20a steel frame with 0.67m span was deemed to be optimal in carbonaceous slate stratum. That could offer engineering experience to tunneling in soft rock under high tectonic stress.

Abstract: The weight and length, width and height of three directions of cuboids’ type calcareous mudstone after infiltrated with water in different period of time were measured by using electronic balance and vernier caliper. The results show that the calcareous mudstone expansion strain is proportional to volume and mass water content. Mchanical properties of calcareous mudstone were studied by uniaxial compression experiments of calcareous mudstone with different water content which carried out by using microcomputer controlled electro-hydraulic servo compression testing machine control system of YAW series. It is concluded from experiment result that calcareous mudstone is brittleness with low water content but when water content reaches saturation, calcareous mudstone presents plastic features. Based on the results above, the constitutive equation of rock considering humidity field is derived which provides important guiding significance to engineering practice.

Abstract: This paper introduces a new failure mode pattern of soil slope – the logarithmic spiral slippery fracture. A mathematical model for the logarithmic spiral slippery fracture is established, taking the anti-shear function of the soil-nailing into consideration. The shear of soil-nailing, axial force, and the safety coefficients based on the limiting equilibrium method are derived, leading to an accurate stability analysis of the strengthening of soil slope. A case study shows that the anti-shear function of the soil-nailing can be significant and should not be ignored in engineering design.

Abstract: All true tri-axial experimental apparatuses are usually applied to test the mechanics characteristics of soils under complicated stress conditions. Because of the analysis of non-rationality of three kinds of chamber framework developed in past, a new true tri-axial apparatus with a new structural chamber is recently developed by the institute of geotechnical engineering, Xi’an University of Technology. The mechanical description of a new tri-axial apparatus for soil testing is presented herein. The design of new tri-axial apparatus took into the flexibility in adjusting sample size, convenience in assembling sample and easily controlling of three normal stress conditions. The stress-controlled and strain-controlled performance of experiments can be accomplished respectively in the new true tri-axial equipment, which is of a special chamber. The special chamber includes of four cells with bursa filling liquid, being corresponding to four lateral surfaces of cubic sample respectively, separated by steel clapboards. The steel clapboards can turn freely on the horizontal plane and flex in the radial direction so as to adapt to the displacement of sample corner. Through the true tri-axial testing of remolded loess and intact loess were executed on the new true tri-axial apparatus, and the characteristics of stress-strain curves for the true tri-axial tests of remolded loess and intact loess were analyzed under different intermediate principal stresses. The characteristics of the new true tri-axial apparatus are as following: structure is simple, and operation is well-suited, and stress state is real, and strain measurement is accurate, and testing process is controlled easily.

Abstract: In current engineering practice, the effect of strength anisotropy on stability analysis of tailings dam is often ignored. This paper presents direct shear test results on a tailing sand with different angles between shear direction and bedding plane. It is found that shear strength of this soil is significantly directional dependent. The variations in peak friction angle are about 11^o, which is approximately 28.3% of the minimum value. The effect of strength anisotropy on stability of a tailings dam is also investigated. The analysis considering anisotropic strength shows a smaller factor of safety and shallower most critical slip surface as compared with isotropic strength model that is used in current engineering practice. To achieve more accurate stability analysis of tailings dams, it is suggested to take into account shear strength anisotropy of tailings soils.

Abstract: The location of phreatic line of a tailings dam is of significant importance on the stability of the tailings dam. In this study, extensive numerical analysis in ABAQUS have been performed to study the influences of loading mode and construction speed on position of the phreatic line of tailings dam in the process of construction from the existing elevation of 59 m to the final elevation of 100 m. The results show that the location of the phreatic line changes very little at the lower part of the dam; by contrast, the location of phreatic line dramatically changes at the upper part of the dam. At a certain construction speed, loading mode has negligible influence on the position of the phreatic line during the duration of one rising round for the tailings dam. The construction speed has more significant influences on the position of phreatic line in the middle term in the service duration of the tailings dam than in the later period.

Abstract: A new geometric correction method in processing close range digital photograph is presented. All the critical steps involved in the geometric correction method are briefed and discussed, including determination of Control Points (CP) on the exposure of the rock mass, projection of the 3-D CPs on the exposure of the rock mass to the projection plane, mathematically solving the transformation matrix, geometrically correcting and resampling the digital photograph. As an illustrative example, the whole process of application of the method for a specific digital photograph taken from an outcrop of rock mass is also presented. It is found that the new geometric correction method is effective and more convincing.

Abstract: Reasonable distribution of the rock fragmentation can reduce the overall cost in a mining industry. Digital image processing technique can be used to determine the rock fragmentation distribution function. This paper proposes an improved watershed segmentation method in digital image processing technique. The seven key steps in the new method are presented. Meanwhile, the detailed rock fragmentation analysis is performed on an example digital photo of fragmented rock pile taken from a practical underground mine, to further explain the mechanism of the new method. It is found that the new method can overcome the phenomenon of over-segmentation and over-lapping in digital photos, and exactly detect boundaries for every individual target in the photo.

Abstract: The in-situ stress is one of important basic data for stability evaluation, engineering design and construction of tunnels. For southwest high mountain region, the in-situ stress in the site test is very difficult. Thus, for satisfying engineering design and construction, it is necessary to back analyze the in-situ stress. The highway tunnel which locates at the 1# road of Lianghekou hydropower station is researched as the object. Based on measured displacements, the inversion model of initial earth stress is built. By comparing the calculated and measured results, the reasonable horizontal pressure parameters and the modulus of elasticity are confirmed.

Abstract: According to the actual state of the 1150 horizontal main haulageway of Tailai colliery is in the affected areas of many faults, both on the roof to floor and two sides convergences are about 1000mm,the YTJ20 strata structure detector was used to detect the strata structure character of the roadway roof, it showed the surrounding rock of 1150 horizontal main haulageway is very broken and the maximum failure depth reached to 6m; meanwhile we took 4 group of rock samples from the broken zone to carry out x diffraction, the results showed that the surrounding rock in the broken contained high expansibility rock, so measure of rock surrounding grouting reinforcement was proposed without changing the original supporting parameters. Comparative analysis of rock surrounding reinforcement effect before and after grouting was calculated by FLAC simulation soft. The result shows only supported “bolts + shotcrete layer + cables”, both the deformation speed and deformation amount are very obviously, the community of “rock-support” shows loose and breaking state; But using the combined supporting method of grouting reinforcement and “bolts + shotcrete layer + cables”, the surrounding rock deformation obtained effectively control with less stress release, the community of “rock-support” shows higher integrity degree, It can ensure the safe use of the roadway.