ABSTRACT: Based on the theory of the limit equilibrium method of slope stability analysis, this article studied the infinite slicing calculate theory under the circumstance that the loess slope sliding-plane does not cross the slope foot. Through the formula derivation, the analytic formula of the sliding torque Mr, and resisting moment Mf were calculated, and then it was concluded that the safety factor K is function of the smooth arc radius R, the sliding body string angle a and angle of slope plane distance Δl. We simplified the process of searching the most dangerous sliding surface on genetic evolution method reasonably and effectively. On the basis of concept of replication, hybridization, variation, competition and selection in biological genetic evolution steps, in the process of the most dangerous sliding surface search, change the two-way variation for one-way and increase mutant genes of the slope angle of plane distance. While other factors remain unchanged and only one of the factors changes, the minimum safety factor was computed under the restrictive condition and its applicability was determined. After changing another factor and repeating the searching process, the minimum safety factor and the corresponding value of various factors were figured out finally. Realizing search on the most dangerous sliding-plane does not cross slope foot. Also, we used FORTRAN software program to complete the compilation of the search procedures. The engineering examples have confirmed that this method is feasible and safe. This paper has important value of reference to improve the loess slope stability analysis theory.
At present, the theory of the limit equilibrium method is the main approach to analyse slope stability. However, it simplifies the boundary conditions of the landslide.
Different assumptions lead to various theory of limit equilibrium method of slope stability analysis.
The common theories are Bishop, Janbu, Spencer, Morgenstern-Prince and so on.
For various limit equilibrium methods stand for different hypothesis, they make remarkable effect on results and precision.
At the same time, these methods have complete and meticulous theoretical derivation. Because the methods themselves make some simplifying assumptions. Thus some unavoidable limitations and the final results are often different from the engineering practice, which may leads to low precision of results because we can only rely on the experience of slopes. In view of that, particularly on loess areas, it's eager to make an intensive study of each past theory to draw more precise limit equilibrium methods of slope stability analysis to guide the project. Moreover, it could reduce disasters of engineering to secure the safety of people's life and wealth.
Peng, C. (University of Science and Technology Beijing) | Guo, Q. S. (University of Science and Technology Beijing) | Zhang, Z. C. (University of Science and Technology Beijing) | Zhao, L. (University of Science and Technology Beijing) | Yan, Z. X. (University of Science and Technology Beijing)
ABSTRACT: With the increase of the slope height in open-pit mines, the contradiction between the mining safety and stripping quantity becomes progressively serious. According to the analysis and calculation, the original slope angle in Gaocun Iron mine is conservative. After engineering geological investigation and rock mechanical tests, three optimization schemes were proposed. FLAC3D numerical simulation software was used to analyze the slope stability by several indexes such as displacement and plastic zone. In addition, the safety factors were obtained according to the limit equilibrium method by Geo-slope software. Eventually, the final slope angle of the mine was determined. It showed that the optimized slope angle is improved by 3° compared with that of the former design on the whole, and the slope stability well meets the requirement of production.
There are a growing number of metal mines carrying on deep mining in our country, and the design of open pit slopes faces a dilemma in that situation: When the slope angle is too big, the steep slope will cause instability and failure, which is not conducive to the normal production of the mine; In contrast, the small angle will increase the stripped amount and the production costs significantly. To solve this problem, slope angle must be optimized on the premise of mining safety (Heok & Bray 1981, Duncan & Christopher 2005).
Gaocun pit of Nanshan Mining Co., Ltd., is a large open pit mine, whose ore production has reached 7 million tons per year with the total mining and stripping of 18 million tons. After entering the second phase of open pit mining, the north-south length of the stope expands from 780 m to 1500 m, and the east-west width expends from 575 m to 820 m. The highest level of open pit mining is up to +90 m and the bottom elevation is down to-186m. Under the conditions of high and steep slope mining, with mining depth increases, the contradiction between security and economic production is gradually highlighted. Therefore, slope design must be optimized to ensure the production safety and increase economic efficiency.
Joint inversion of PP and PS reflection data has been hindered by the difficult task of registration or correlation of PP and PS events. It can perhaps be achieved by registering the events during inversion but the resulting algorithm is generally computationally intensive. In this paper, we propose a stochastic inversion of PP and PS data which have been registered to the same PP time scale using a new interval velocity analysis technique. The prestack PP and PS wave joint stochastic inversion is achieved by using the PP and PS wave angle gathers using a very fast simulated annealing (VFSA) algorithm. The objective function attempts to match both PP and PS data; the starting models are drawn from fractional Gaussian distribution constructed from interpolated well logs. The proposed method has been applied to synthetic and real data; the inverted results from synthetic data inversion compare very well with model data, and inverted results for real data inversion are consistent with seismic data and log data. These also show that the proposed method has a higher accuracy for estimating rock physics parameters while it circumvents the horizon registration problem in the data interpretation. We also estimate uncertainty in our estimated results from multiple VFSA derived models.
In Montel and Lambare´ (2011), we put in evidence the pitfalls when using angle domain common-image gathers (ADCIGs) for velocity model building and the ways to solve for them. Using non-linear slope tomography, we show here through a complex synthetic example the critical role of a good understanding of the kinematic observed in the ADCIGs. We show what happens when handling things the “wrong” and the “right” way to get a good quantitative idea of the improvement we can expect from an accurate theoretical analysis of the kinematics of ADCIGs.
Angle domain common image gathers are recommended in Kirchhoff and reverse time migration for velocity model building in complex area. For these both approaches there is a general agreement that the tomographic ray pairs are fully defined by the reflection and azimuth angle information and the reflection dip and that if the velocity model is correctly updated down to a given horizon, it is not necessary to shoot the tomographic ray pairs upwards through this horizon. We show here through examples and a theoretical analysis that these both statements have to be mitigated when the common image gathers exhibit a significant residual move out on. We also show how to accurately compute the tomographic ray pairs allowing then for an accurate angle domain migration velocity analysis.
Angle-domain common image gather is a powerful tool for migration velocity updating and AVA analysis. We present a method to compute the angle gather from the wavefields reconstructed by either acoustic or isotropic elastic RTM. A slowness-based method is employed to decompose both source and receiver wavefields into superposition of local plane waves along different directions. For elastic RTM, P- and S- modes are separated simultaneously with the plane wave decomposition. Local image matrix (LIM), which is a collection of angle-domain partial images, is constructed by cross-correlating the decomposed plane wave components from both source and receiver sides. Finally, the angle gather is obtained by sorting the energy in LIM. Numerical examples show that the technique can successfully extract angle gathers for both acoustic and isotropic elastic medium.
Due to the diversity of measuring geometry, the wavefields from 3D3C vertical seismic profile (VSP) are often complex, and therefore wavefield separation is very important in the processing of VSP data. In this abstract, we analyzed the theory of polarizing filtering with floating coordinate system (PFFCS) and applied it to 3D3C VSP field dataset. We reviewed the methods of computing polarizing angle and described the algorithm of PFFCS. The polarizing angles of reflected wave computed by PFFCS vary with the traces and reflection layers. Depending on the direction of the concentrated reflected wave from the reflection point, the coordinate system is established. We set up the processing workflow according to characteristics of the field VSP dataset, effectively separated and obtained the all kinds of wavefield. Compared to the conventional polarizing filter, the PFFCS gives a better result for this field data.
Microseismic event locations are increasingly used as input parameters for additional calculations, e.g. stimulated reservoir volume (SRV), moment tensor inversions. Uncertainties in the event locations often have a direct effect on the derived parameters and therefore it is important to quantify the location uncertainty. Although companies generally report location uncertainties in form of error bars, often along Cartesian coordinates, the calculation of these error bars and their interpretation is not standardized and sometimes obscure. By assigning each point in the localization grid a probability for the event location based on the available input data it is possible to use input from very different sources, e.g. traveltime residuals, hodogram analysis, velocity model uncertainties, and combine them in a probability grid. The distribution of the overall probability can then be used to define the uncertainty space based on the desired level of accuracy, e.g. the 95% confidence uncertainty space will be larger than the 90% confidence space. This method has the advantage that very different types of uncertainty, e.g. sensor position, can be included in the calculation and that an interpretation of the uncertainty space in terms of confidence is possible. The derived uncertainty space clearly represents the space where the event is with 90%, 95% or any other degree of probability.
Gerritsen, Sijmen (Shell Global Solutions International) | Roozemond, Leen (Shell Global Solutions International) | van Daalen, Diederik (Shell Global Solutions International) | Bakker, Peter (Shell Global Solutions International)
Wave-equation (WE)-based residual moveout (RMO) inversion for migration velocity analysis aims to update model parameters related to the seismic wave velocity using WE migration common image gathers (WEMCIGs) as input. Here we explain how to use RMO, picked on subsurface angle gathers (a type of WEMCIG), for velocity model building through angle domain sensitivity kernels. We show how to compute finite bandwidth sensitivity kernels that relate the depth shift of the image to a local change of the velocity. These sensitivity kernels replace ray-traced Fre´chet coefficients in conventional reflection tomography. In this way we can formulate the inverse problem that finds the velocity model by minimizing RMO without having to rely on ray-tracing, while keeping a lot of the inversion functionality of the conventional model building implementation in place. We show how to use RMO inversion in the subsurface angle domain for sub salt model building using the Sigsbee2A synthetic 2D model. We find that in such a complex setting combining subsurface angle gathers with angle-domain sensitivity kernels allows for WE-based RMO inversion in areas where the ray-based methods break down.
Migrated gathers are a key input for velocity model building and for subsurface characterization. Kinematic information is used for velocity model updates, and amplitude and phase attributes are used for the derivation of material properties. Conventional gathers are two dimensional: a vertical axis that is either time, time migrated or depth, and a horizontal axis that can be offset, or angle in the depth migrated domain. With wide azimuth acquisition the gathers are 3D by nature. The additional horizontal axis is the azimuth angle. The importance of the azimuthal information for short wavelength velocity determination has been demonstrated theoretically (Bartana et. al., 2009). The nai¨ve way of describing the 3D gathers is by a set of azimuth sectors, where the offsets or angles are binned at each azimuthal sector. In other words, the separation for azimuth sectors treats the 3D gather as a set of multi 2D gathers. In this work we show a different approach, in which the azimuthal information is represented in a continuous manner for the purpose of delay analysis. The method for representing the 3D angle gather and the delay analysis performed in this domain are described. The method is demonstrated on a synthetic example and on field data.