Rock Slope Engineering.pdf (original) (raw)

A Practical Procedure for the Back Analysis of Slope Failures in Closely Jointed Rock Masses

Where closely jointed rock masses are encountered in slopes, failure can occur both through the rock mass, as a result of combination of macro and micro jointing, and through the rock substance. Determination of the strength of this category of rock mass is extraordinarily dicult since the size of representative specimens is too large for laboratory testing. This diculty can be overcome by using a non-linear rock mass failure criterion or by back analysis of such slopes to estimate the rock mass strength. In this paper, a practical procedure and a computer program are presented for the back determination of shear strength parameters mobilized in slopes cut in closely jointed rock masses which obey a non-linear failure criterion rather than a linear one. The procedure shows that the constants to derive normal stress dependent shear strength parameters of the failed rock masses can be determined by utilizing a main cross-section and without a pre-determined value of rock mass rating (RMR). Trials are made for dierent RMR m and RMR s values corresponding to various possible combinations of the constant m and s, which are used in the Hoek±Brown failure criterion, satisfying the limit equilibrium condition. It is also noted that the procedure provides a quick check for the rock mass rating obtained from the site investigations. The method is used in conjunction with the Bishop's method of analysis based on circular slip surfaces. The procedure outlined in this paper has also been satisfactorily applied to documented slope failure case histories in three open pit mines in Turkey. # 1998

Considerations on failure mechanisms of rock slopes involving toppling

IOP Conference Series: Earth and Environmental Science

Probably, the most relevant issue in stability analysis of rock slopes is the correct identification of the potentially occurring failure mechanism, which should be mechanically analyzed to assess stability, later on. Traditional rock slope stability approaches consider planar, wedge, rotational and toppling failure as potential instability mechanisms. Whereas the three first types involve sliding associated to different geometries of the unstable element or mass, toppling often involves also sliding and very complex geometries of multiple elements. In this sense, toppling should be contemplated more like a group of mechanisms than like a simple mechanism such as planar or wedge failure. Toppling could involve moreover one or many blocks. Initial studies classified toppling failure mechanisms in three groups: block, flexural and block-flexural toppling. The stability analysis of rock slopes prone to toppling involves the mechanical analysis of individual slab like blocks, which are considered to present perfect rectangular cross-section. However, the actual shape of these rock elements may not be so regular, so the influence of more realistic irregular shapes is usually not accounted for. In this article, the author will address how some geometry variations may be included in this analysis based on analytical considerations and physical models. Additionally, failure mechanisms observed in rock cuts and open pits often combine toppling with other sliding phenomena in different more or less complex manners. These combined mechanisms involving toppling will be reviewed and some case studies worked out by the author will be presented. Moreover, all along this document, considerations will be put forward regarding the nature of toppling related phenomena where small equilibrium variations may produce a release of a large mechanical energy, which can ultimately produce the destabilization of large slopes or groups of blocks. This suggests that it is wise in these cases to analyze not only the factor of safety, but also the evolution of the potential failure mechanism to understand what is happening and eventually provide sensible and reliable designs or appropriate remedial measures.

Evaluation of safety factors in discontinuous rock

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1996

Safety factors for kinematically admissible failure mechanisms in jointed rock masses have been defined with linear and nonlinear failure criteria for rock discontinuities. Data required to compute these safety factors are obtained by means of two finite element analyses of the effects of selfweight and external (structural) loading, respectively. Both types of analysis are closely linked since they share a common geometry. Joint elements are used to simulate the behaviour of rock discontinuities. If kinematically admissible mechanisms are possible under field conditions, the finite element mesh should also allow them to develop. Different aspects of the methodology have been illustrated through the safety evaluation of a 150m high arch dam and its foundation in fractured cretaceous limestone. Special attention has been paid to the modelling of a realistic geometry including three-dimensional rock blocks and discontinuities. The paper discusses the effect of initial state of stress, the evolution of safety as the external load increases and the relation between the defined safety factors. It also provides practical guidelines for conducting this type of analysis in complex situations.

The Simulation Blasting Process and Stability Study of Slope

This article studied the slope blasting process. The research is, based on the principle of conservation of energy and one assumption. The assumption is that the blasting energy is endured by some range of rock mass around the blasting point, then a part of energy is transformed into kinetic energy, finally the energy can be transferred and absorbed by fractured rock and ultimately achieving the balance. To the above process, the paper used PFC3D based on the theory of particle flow as the simulation platform and simulated the blasting process with one hole in different height, buried depth and charge weight in the slope of open-pit mine, and discuss the slope stability after blasting. Result shows that: the blasting process can be divided into three phases. The first phase, blasting impact plays a leading role; the second stage, gravity is dominating in the collapsing process; the third phase, particles slip down and are adjusted to balance in local. In the view of time, the stage is in an order of larger magnitude than its previous stage. In general, upper sandstone is stable after blasting. The lower sandstone and sandy mudstone are subject to some degree of damage but still manageable.

Stability Analysis and Failure Mechanisms of Open Pit Rock Slope

Journal of the Civil Engineering Forum

Rock mass in nature tend to be unideal, for it is heterogeneous, anisotropic and has discontinuity. The discontinuity makes anisotropic strength and stress in the rock mass, and also controls the changing of the elastic properties of rock mass. This condition results to disruptions in the rock mass strength balance, and finally drives the slopes to collapse. This study aims to determine the slope failure mechanisms in the area of case study, as well as its variations based on the Rock Mass Rating (RMR), Geological Strength Index (GSI), Slope Mass Rating (SMR), kinematic analysis, numerical analysis and monitoring approach slope movement in a coal mine slope applications. The site investigations were implemented to obtain information about slope collapse. Prior to the collapse, the slope inclination was 38° with of 94 meters height, strike slope of N 245 E and direction of slope surface of 335°. After the collapse, the slope was became 25º; and after the collapse materials were clear...