To investigate the stability of a soil-rock-mixture (SRM) slope subjected to sequential excavation, two modifications are made to the numerical manifold method (NMM). One modification is the ...implementation of sequential excavation algorithms including an algorithm to find the excavated manifold elements and an algorithm named as “manifold element birth and death” to remove the excavated manifold elements in the excavation simulation. The other modification is the implementation of an improved shear strength reduction technique to evaluate the stability of a slope, as well as to obtain the factor of safety (FOS). In this technique, apart from the shear strength parameters, the Poisson's ratio υ is also adjusted for the purpose of eliminating the spurious plastic deformation that may happen in the deep areas of the slope. Two criterions including the NC criterion (Non-convergence criterion) and DPZ criterion (The criterion based on the distribution of plastic zones) are used to define the critical equilibrium state of the slope. With the improved NMM, three numerical examples including a homogeneous slope under one step of excavation, a slope under three steps of excavation and a SRM slope under two steps of excavation are solved. The simulation results show that: (1) the improved NMM is able to accurately simulate the excavation process of slopes, and predict the FOSs of slopes; (2) the FOSs based on the NC criterion are usually greater than or equal to those based on the DPZ criterion; (3) it is very difficult to form a slipping surface passing from the toe of the SRM slope to the top of the SRM slope; (4) rock blocks have some positive effects on the stability of a SRM slope.
•The NMM is used to simulate sequential excavation of a soil-rock-mixture (SRM) slope.•The sequential excavation algorithms are proposed to simulate the process of sequential excavation.•An improved shear strength reduction technique is adopted and implemented into the NMM.•Results obtained from NC criterion and DPZ criterion are compared.•The advantages of the NMM in discretization and accuracy are demonstrated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Hydraulic fracturing is widely used in the exploitation of unconventional gas (such as shale gas).Thus, the study of hydraulic fracturing is of particular importance for petroleum industry. The ...combined finite-discrete element method (FDEM) proposed by Munjiza is an innovative numerical technique to capture progressive damage and failure processes in rock. However, it cannot model the fracturing process of rock driven by hydraulic pressure. In this study, we present a coupled hydro-mechanical model based on FDEM for the simulation of hydraulic fracturing in complex fracture geometries, where an algorithm for updating hydraulic fracture network is proposed. The algorithm can carry out connectivity searches for arbitrarily complex fracture networks. Then, we develop a new combined finite-discrete element method numerical code (Y-flow) for the simulation of hydraulic fracturing. Finally, several verification examples are given, and the simulation results agree well with the analytical or experimental results, indicating that the newly developed numerical code can capture hydraulic fracturing process correctly and effectively.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•An improved NMM with multiple layers of mathematical cover systems is proposed for the soil-rock-mixture(SRM) slopes.•An improved shear strength reduction technique is adopted and implemented into ...the improved NMM.•The FOSs based on the NC criterion is greater than those based on the DPZ criterion for SRM slopes.•The advantages of the improved NMM in discretization and accuracy are demonstrated.
In order to carry out stability analysis of soil-rock-mixture(SRM) slopes, an improved numerical manifold method (NMM) with multiple layers of mathematical cover systems is proposed. For SRM problems, the computational cost of the improved NMM is smaller than that of the traditional NMM. Besides, an improved shear strength reduction technique(ISSRT) which can eliminate spurious plastic deformation of the slopes is implemented. Based on the improved NMM with multiple layers of mathematical cover systems, the stability of three slopes, namely, a homogeneous slope and two SRM slopes with different contents of rock blocks is analyzed. The numerical results about the three slopes indicate that: 1) the proposed numerical model can obtain the FOS of a slope with high accuracy; 2) the bigger the content of rock blocks, the larger the FOS of the SRM slope will be; 3) due to the existence of rock blocks, the failure mode of a SRM slope is different from that of a homogeneous soil slope.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
An improved numerical manifold method (INMM) with multiple layers of mathematical cover (MC) systems is employed for a sequential excavation analysis of SRM (soil-rock-mixture) slopes. For the ...purpose of obtaining the FOS (factor of safety) of a SRM slope, an enhanced SSRT (shear strength reduction technique) is used in the INMM. Furthermore, two algorithms, i.e., an algorithm to identify the excavated MEs (manifold elements) and an algorithm to remove the excavated MEs, are incorporated into the INMM to study the effects of excavation of the SRM slopes. With the INMM, two examples, including a soil slope and two SRM slopes subjected to sequential excavation construction, are investigated. The simulation results show that 1) the excavation processes, as well as the FOSs of the slopes, can be accurately predicted with the INMM; 2) the higher the content of rock blocks, the larger the FOS of the SRM slope will be; and 3) the FOSs assessed from the INMM are the same as those from the traditional NMM (TNMM), but the memory consumption and computational cost of the INMM are smaller.
•An improved NMM (INMM) is proposed for the sequential excavation analysis of the SRM slopes.•The excavation algorithms are implemented to simulate the sequential excavation processes.•The improved shear strength reduction technique is adopted and implemented into the INMM.•Compared to the traditional NMM, computational cost of the INMM is smaller.•The advantages of the INMM in discretization and accuracy are demonstrated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To increase the total power output of the Three Gorges Hydropower Station and generate greater economic benefits, it is necessary to reduce the time required for the water level of the Three Gorges ...Reservoir to drop, i.e., to increase the rate at which the water level drops. A rapid drop in the reservoir water level might result in a significant change in the reservoir bank environment, which can destabilize landslides that extend into the water, reactivate old landslide masses and form new landslide masses in the reservoir region. A typical slope that extends to the water in the Three Gorges Reservoir region was selected for study. We studied the geologic conditions of a selected landslide mass and developed an expression for the hydrodynamic pressure under the effects of groundwater within the slope area and an expression for the normal stress on a sliding surface under the effect of hydrodynamic pressures. In addition, the evolution of the stability of the slope (submerged to various depths) under the effects of the lowering of the reservoir level is investigated based on a strictly global analysis: (a) safety factor decreases about 14% as the reservoir level drops with rate of 0.6m/d and about 16% with rate of 1.2m/d at the fall of reservoir water level 30.0m; (b) an increase in the drawdown rate of the Three Gorges Reservoir from 0.6m/d to 1.2m/d is unfavourable for the stability of the slope that extends into the water, but the extent of the decrease in safety factors resulting from this increase in rate is not significant.
•Expression of the normal stress on sliding surface in condition of hydrodynamic pressures is deduced.•Evolution of the selected slope stability in Three Gorges reservoir is investigated.•Effects of drawdown rates on the stability of the slope are studied in details.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Based on the incremental method of elastic-plastic mechanics and bilinear projection operators, by combining the strength reduction method with the φ-ν inequality, this paper proposes a virtual ...element method strength reduction technique for slope stability analysis. The deformations of a homogeneous slope and heterogeneous slope are solved under different strength reduction factors, and the mesh dependency problem of the method is discussed. Numerical examples verify the correctness and effectiveness of the proposed method. The results demonstrate that due to the differences in the physical and mechanical properties of soil and rocks, stress becomes concentrated in the contact zone between soil and rocks, and thus, the plastic zone surrounds the rocks. Therefore, it is difficult to form regular connections in a plastic zone, such as a soil slope. This method can be used to analyse the stability of a stony soil slope and to study the effects of particle size, rock content, rock density, and rock spatial distribution on the mechanical behaviour of stony soil slopes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Previous studies suggested that the Qianjiangping landslide was caused by the combined effect of rainfall and reservoir water after the first water storage of the Three Gorges Reservoir. The ...Sanmendong landslide with a length of 830m, an area of 2.49×105m2, an average thickness of 22m and a volume of 5.48×105m3, which is located by the Qinggan river, a tributary of the Yangtze River, is only 4km away from another famous landslide along the same river: the Qianjiangping landslide. Based on the experimental data of mechanical parameters of the landslide and displacement monitoring, a nonlinear mapping relationship between mechanical parameters of the failure mass and the displacement of landslide were established by using genetic algorithms by means of uniform design, numerical calculation and artificial neural networks. The mechanical parameters of the failure mass are obtained by the global minimization of the deviation between the calculated displacements and the monitored displacements. On this basis, the deformation mechanism of the Sanmendong landslide under the combined effect of rainfall and reservoir water level fluctuations was analyzed in detail. The results indicated that the increase of displacement of Sanmendong landslide can be primarily attributed to the combined result of reservoir water level fluctuation and rainfall.
•Determination of mechanical parameters of the Sanmendong landslide was conducted.•Deformation mechanism of the Sanmendong landslide was analyzed.•The combined effect of water level flunctuations and rainfall of the reservoir was addressed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The PU (partition-of-unity) based FE-RPIM QUAD4 (4-node quadrilateral) element was proposed for statics problems. In this element, hybrid shape functions are constructed through multiplying QUAD4 ...shape function with radial point interpolation method (RPIM). In the present work, the FE-RPIM QUAD4 element is further applied for structural dynamics. Numerical examples regarding to free and forced vibration analyses are presented. The numerical results show that: (1) If CMM (consistent mass matrix) is employed, the FE-RPIM QUAD4 element has better performance than QUAD4 element under both regular and distorted meshes; (2) The DLMM (diagonally lumped mass matrix) can supersede the CMM in the context of the FE-RPIM QUAD4 element even for the scheme of implicit time integration.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The Huangtupo riverside slope, which extends an area of 1.35 × 10
6
m
2
and has a total volume of 6.934 × 10
7
m
3
, is one of the most noted large-scale landslides with great concern about the ...safety of immigrants in the Three Gorges reservoir area of China. During the normal operation, the reservoir water level fluctuates periodically. Water level fluctuation will soften the strength of the geologic materials on the banks, induce underground water fluctuation, and in turn affect the slope stability. On the basis of the thorough engineering geological survey, the analysis of engineering geological conditions and deformation mechanism is conducted primarily. Then, the Huangtupo landslide is divided into four minor landslides, all of which have typical three-dimensional characteristics. To these landslides, a three-dimensional rigorous limit equilibrium method is proposed, which can accommodate failure surfaces of any shape, and satisfies all the equilibrium conditions. In terms of the strength parameters of geologic materials, the stability evolution of the four minor landslides at the Huangtupo landslide under periodical water level fluctuation is investigated in detail. From the results, the 3D safety factors turned out to be somewhat bigger than the 2D results even though they displayed the same trends. The differences between 2D and 3D results are about 2.92–6.11 %. The maximum reduction in safety factors with the rapid down of water level is 0.11. It is suggested that the safety margin of the two minor landslides near the riverside is insufficient and might become instable under periodical water level fluctuation.
In Miyi County of Sichuan Province of China, landslides are the most common type of waste dump failure, resulting from poorly compacted waste rock dump on weak soil. A waste dump failure on a soft, ...gently dipping foundation is examined in terms of the geological conditions, failure characteristics, movement processes and deposit forms, including the long run-out feature of the landslide. The waste dump failure and the subsequent deformation to the foundation are caused by an increase in pore water pressure and developed through the soft foundation underlying the heavy waste. The landslide run-out distance is influenced by the liquefiable silty clay layer. In this study, the landslide was triggered by the heavy load of waste rocks on top of a soft foundation of low-bearing capacity. The increased pore pressure in the foundation could not be released, which caused deformation of the foundation and triggered a landslide. The stability evolution is also researched in this study. In this study area: (1) the landslide mass is accelerated by the liquefaction of the saturated and water-rich silty clay layer, and the plastic deformation of the foundation caused by the collapsed waste dump; (2) the shear strength is strongly influenced by the water content; (3) when a waste dump is constructed on top of a water-sensitive gently dipping ground, it is important to provide drainage to dissipate pore water pressure; and (4) considering low factors of safety during heavy rains, secondary landslide is possible in the event of heavy rain and earthquake, indicating that heavy rainfall is the leading cause of the waste dump failure.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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