Hui-ge Xing

A reliability analysis method for rock slope controlled by weak structural surface

Catastrophic landslides maybe occur in rock slope due to the effect of strong earthquakes or heavy rainfall. The stability of rock slope is usually controlled by different scales of weak structural surfaces, which are uncertain and randomly exist in the rock slope. According to the geological characteristics of rock slope, two typical failure modes – plane and wedge are possible. A second-order second-moment (SOSM) method is presented to calculate the reliability index and the failure probability of rock slope, which is an improvement over the first-order second-moment (FOSM) method, and performance functions are built up with the classic limit equilibrium method. The presented method is applied to analyze the failure probability of two rock slopes at the Jinping I Hydropower Station and is compared with the Monte Carlo method and the FOSM method. The computed results show that for plane failure, the reliability index and the failure probability determined by the presented method are 0.563 and 28.7%, respectively, and the reliability index and the failure probability determined by Monte Carlo method are 0.677 and 24.9%, respectively. However, for the FOSM method, the reliability index and failure probability are –0.025 and 51.0%, respectively. For both plane failure and wedge failure, the difference between the presented method and the Monte Carlo method is very small, but the failure probability of plane failure determined by FOSM method is larger than that of the other two methods. The presented method can provide a useful tool to evaluate the failure probability of rock slope.

Experimental Study of Epoxy Resin Repairing of Cracks in Fractured Rocks

Cracks in rock mass have always posed a big threat on the durability of fractured rocks in shear zone. Cracking of rock mass in shear zone is a random process, highly variable and influenced by many factors. Cracks in fractured rocks can be repaired by injection of epoxy resin in order to bond the crack and restore its structural integrity. Epoxy resins are used to repairing the shear zone at the Jinping Hydropower Station. An improved polymer grouting material is adopted and the polymerization process is determined. The polymer grouting materials is consisted of resin (component A) and hardener (component B). Polarizing microscopy (PM) tests and mechanical experiments are adopted to evaluate the filling situation of epoxy resin in rock and the mechanical properties of epoxy-repaired rock, respectively. Experimental test results show that, the cracks and pores are filled by epoxy resin, and also the crack surface are boned. The mechanical properties of epoxy-repaired rock are improved by the polymer grouting and the permeability coefficient is decreased.

Determining the Critical Slip Surface of Three-Dimensional Soil Slopes from the Stress Fields Solved Using the Finite Element Method

The slope stability problem is an important issue for the safety of human beings and structures. The stability analysis of the three-dimensional (3D) slope is essential to prevent landslides, but the most important and difficult problem is how to determine the 3D critical slip surface with the minimum factor of safety in earth slopes. Basing on the slope stress field with the finite element method, a stability analysis method is proposed to determine the critical slip surface and the corresponding safety factor of 3D soil slopes. Spherical and ellipsoidal slip surfaces are considered through the analysis. The moment equilibrium is used to compute the safety factor combined with the Mohr-Coulomb criteria and the limit equilibrium principle. Some assumptions are introduced to reduce the search range of center points and the radius of spheres or ellipsoids. The proposed method is validated by a classical 3D benchmark soil slope. Simulated results indicate that the safety factor of the benchmark slope is 2.14 using the spherical slip surface and 2.19 using the ellipsoidal slip surface, which is close to the results of previous methods. The simulated results indicate that the proposed method can be used for the stability analysis of a 3D soil slope.

Assessment of the Excavation-Damaged Zone in a Tall Rock Slope Using Acoustic Testing Method

During slope excavation, high stresses can become concentrated in the rock mass because of stress redistribution. Failure of the rock mass creates an excavation-damaged zone (EDZ) in the slope. The damage reduces the acoustic wave velocity in the rock mass. Results of field tests measuring acoustic wave velocity at the Jinping I Hydropower Station are used here to study the EDZ in a tall rock slope. Two acoustic testing methods were adopted in the field tests: single-hole acoustic testing (SAT) and cross-hole acoustic testing (CAT). The acoustic wave velocity was lower in the EDZ, and the depth of the EDZ increased with decreasing slope elevation. Statistical analysis shows that the acoustic wave velocity obtained by the SAT method is larger than that obtained by the CAT method, and the relative difference between the SAT- and CAT-derived velocities is lower for a high quality rock mass than for a low quality rock mass. The integrity ratio and severity of damage can also be determined by acoustic wave velocity test results, revealing that the integrity ratio and elastic modulus of a rock mass are reduced in the EDZ.

Two-dimensional stability analysis of a soil slope using the finite element method and the limit equilibrium principle

A slope stability analysis method using the finite element method and the limit equilibrium principle is presented in this paper to determine the critical slip surface and to calculate the minimum safety factor based on the stress field produced by a numerical simulation. This method assumes a cutting export and makes good use of geometric combination to reduce the search range during the calculation process. The proposed method was validated using two classical benchmark slopes and an engineering slope; it was also compared with other conventional limit equilibrium methods. The error between the proposed method and the limit equilibrium method was relatively small. The proposed method resolved several limitations of the traditional methods, and a comparison of the benchmark slopes showed that the proposed method exhibited good accuracy and efficiency. The proposed method can thus analyse both the stability of a natural slope and the stability of a soil slope under seismic loading conditions.

An Experimental Study on the Water-Induced Strength Reduction in Zigong Argillaceous Siltstone with Different Degree of Weathering

The water-softening property of soft rocks is a key problem in geotechnical engineering. A typical red-bed soft rock (the Zigong argillaceous siltstones) with different weathering degree is selected as an example to study the water-softening property and the influence of degree of weathering. A series of mechanical and microstructure tests are carried out to analyze the weathering characteristics and mechanism of the Zigong argillaceous siltstones. The results of mechanical experiments reveal that the water content and the weathering degree of rock specimens both have a weakening effect on the compressive and shear strengths. According to the results of present microstructure tests, the mechanical properties of the Zigong argillaceous siltstones are closely correlated with their physical properties, including internal microstructure and material composition for highly weathered rocks or moderately weathered rocks (in both natural and saturation conditions). Finally, experimental results indicate that the changes of microstructure and internal materials are two main factors that influence rock strength parameters after contacting with water and that these properties reflect the rock weathering degree. In a word, when red-bed soft rocks are encountered in geotechnical engineering, special attention should be paid to presence of water.

Experimental study on the dynamic response and stability of bedding rock slopes with weak interlayers under heavy rainfall

Rainfall-induced landslides are notable geological hazards that occur frequently in the mountainous areas of Southwest China. Heavy rainfall in the wet season often causes landslides in mountainous areas, posing a threat to the infrastructure and human safety. For rock slopes, the sliding surface often occurs along a weak interlayer which plays a key role in controlling the mechanism of slope failure during the wet season. Typical bedding rock slope in the Maoergai reservoir was taken as the prototype to determine the physical modeling test materials and parameters, and a three-layered slope model was used to simulate a rock slope with a weak interlayer. A series of laboratory tests were carried out to study the dynamic response and stability of the bedding rock slope with a weak interlayer under heavy rainfall. The experimental results showed that the shear strength of the weak interlayer decreased due to a water softening effect. The changes of pore water pressure and rainfall erosion were the two dominant dynamic factors inducing the gradual decrease of shear resistance of the weak interlayer. In addition, the limit equilibrium method (Janbu’s method) was used to analyze the stability of the slope model and investigate the relationship between shear strength and slope stability. The obtained correlation between shear parameters and the safety factor indicated that the safety factor of the slope model decreased with the softening of the weak interlayer, and its internal friction angle was the key parameter influencing slope stability.

Comparative experimental study of mechanical properties of concrete prepared by different fibres

This paper reports a comparative experimental study on the mechanical properties of concrete containing different types of fibres: polyvinyl alcohol (PVA), polypropylene (PP) and steel fibres. Compression and three-point bending tests are performed on both plain concrete and each type of fibre-reinforced concrete (FRC). The experimental results show that the presence of fibres has less of an effect on the FRCs compressive strength. The tensile strength is commonly increased by the addition of fibres, but an appropriate fibre content of PVA or PP fibres should be selected. PVA and PP fibres decrease the concretes elastic modulus, but steel fibres increase the modulus due to the steels higher Youngs modulus. The FRC containing PVA shows brittle characteristics, but the FRC containing steel or PP fibres have load-deflection curves with flattened descending paths. Flexural behaviour of the concrete is improved by addition of steel or PP fibres, but not by PVA fibres, and the concretes fracture toughness is increased by the addition of steel fibres.