Shear Strength Of Discontinuities Research Articles

Rock Slope Stability Study for Yujian River Dam Site Based on Kinematic Analyses

Lithological information, rock mass fracture data and discontinuity shear strength obtained through field investigations have been used in conducting kinematic analyses for the rock slopes that exist in the Yujian River dam site to evaluate the stability of the slopes. Results given in the paper can be considered as conservative because of several conservative assumptions used in the analyses. Dam site slopes seem quite stable up to 40º dip angle. Out of the three basic failure modes, possible wedge sliding seems to be the most likely one followed up with possible plane sliding as the second. Irrespective of the considered slope regions, slope dip direction ranges 270-315º and 200-210º seem to be the worst cases for possible instability of slopes in the dam site. Regional slopes in the dam site can be ranked with respect to safety from the lowest to highest in the following order: R-c-1, R-e-2, R-c-2, R-d-1, R-b, R-a, R-d-2 and R-e-1. Note that the dam site slopes are currently stable and the existing slope angles agree well with the results obtained from the rock slope stability analyses.

Rock Slope Stability Study for Yujian River Dam Site Based on Kinematic Analyses

Lithological information, rock mass fracture data and discontinuity shear strength obtained through field investigations have been used in conducting kinematic analyses for the rock slopes that exist in the Yujian River dam site to evaluate the stability of the slopes. Results given in the paper can be considered as conservative because of several conservative assumptions used in the analyses. Dam site slopes seem quite stable up to 40º dip angle. Out of the three basic failure modes, possible wedge sliding seems to be the most likely one followed up with possible plane sliding as the second. Irrespective of the considered slope regions, slope dip direction ranges 270-315º and 200-210º seem to be the worst cases for possible instability of slopes in the dam site. Regional slopes in the dam site can be ranked with respect to safety from the lowest to highest in the following order: R-c-1, R-e-2, R-c-2, R-d-1, R-b, R-a, R-d-2 and R-e-1. Note that the dam site slopes are currently stable and the existing slope angles agree well with the results obtained from the rock slope stability analyses.

Shearing Mechanical Properties of Structural Planes of a Regular Tooth Rock

Abstract Mechanical properties of discontinuities are different from those of a whole rock. In particular, shear strength of a discontinuity is closely related to its morphological characteristics. Study on mechanical behavior and its failure mechanism of jointed rocks under shear stresses is of great theoretical significance. This paper presents a fundamental research on mechanical properties of the regular jugged discontinuity under various normal stresses. The strength and roughness of discontinuity under shear stress are investigated by analysis of the shear test data. An empirical formula between slope ratio and roughness coefficient of discontinuity are proposed to calculate shear stiffness, and an empirical formula is finally established to evaluate shear strength of discontinuity.

Evaluation of rock slope stability for Yujian River dam site by kinematic and block theory analyses

Lithological information, rock mass fracture data and discontinuity shear strength obtained through field investigations have been used to conduct kinematic and block theory analyses for the rock slopes that exist in the dam site to evaluate the stability of the slopes. The analyses were performed using mean discontinuity set orientations for each rock mass region under gravitational loading to calculate the maximum safe slope angles (MSSA) for different cut slope directions. Results show that final MSSAs obtained from kinematic analysis are less than or equal to that obtained from block theory analysis. The following conclusions have been made based on the block theory analysis results, which are closer to the reality: (1) The final MSSA range between 30° and 47°, 44° and 70°, 47° and 69° for cut slope dip directions of 20–30°, 105–210°, and 270–355°, respectively; (2) For cut slope dip directions of 20–30°, 200–210° and 275–315°, wide ranges of values have been obtained for the final MSSA reflecting the influence of variability of fracture orientations on MSSA; (3) Apart from the region R-d-1 for slope dip directions in the range 20–30°, rest of the regions at the dam site seem to be stable for slope angles less than 40°. Detailed comparisons are given between the kinematic and block theory analyses covering both the theoretical concepts and application results. Also a brief comparison is included between the laboratory and in situ discontinuity shear strength results.

Study on the Mechanical Properties of Discontinuity under Shearing

The mechanical properties of discontinuity are different from those of a whole rock. And the shear strength of discontinuity is closely related to its morphological characteristics. The study of the mechanism of failure of jointed rock mass under shear stress is to reveal its mechanical behavior and its mechanism of failure. This paper presents a fundamental research in the mechanical properties of the regular jugged discontinuity under various normal stresses in the shear test. And it describes the mechanical properties of the regular jugged discontinuity under shear stress and their principal regularities. The strength and roughness of discontinuity under shear stress are investigated by the analysis of the data obtained. And this paper study the calculation of shear stiffness of discontinuity and proposed an empirical formula between the slope ratio and roughness coefficient of discontinuity. Also the changing regularity of the parameters of the shear strength of discontinuity under shear stress is investigated, and an empirical formula is developed to evaluate the shear strength of discontinuity in this paper.

Study on the Mechanical Properties of Discontinuity under Shearing

This paper presents a fundamental research in the mechanical properties of the regular jagged discontinuity under various normal stresses in the shear test. The mechanical properties of the regular jagged discontinuity under shear stress and their principal regularities are described. The strength and roughness of discontinuity under shear stress are investigated by the analysis of the data obtained. The calculation of shear stiffness of discontinuity and an empirical formula between the slope angle and roughness coefficient of discontinuity are proposed. The changing regularity of the parameters of the shear strength of discontinuity under shear stress is investigated, and an empirical formula is established to evaluate the shear strength of discontinuity.

A probabilistic model for the assessment of uncertainties in the shear strength of rock discontinuities

Discontinuity shear strength plays a critical role in many problems encountered in rock engineering, especially in the design of rock slopes. Since its precise estimation is generally not possible, it is crucial that the errors and uncertainties associated with its estimate be quantified and reflected in the design procedure. In this study, the uncertainties underlying discontinuity shear strength are thoroughly examined and an uncertainty analysis model is developed for the estimation of in situ discontinuity shear strength with a special emphasis on rock slopes. An extensive literature survey on shear behavior of unfilled rock discontinuities has been carried out and the necessary data for the quantification of uncertainties are extracted from this survey. These uncertainties stem from the discrepancies between laboratory-measured and in situ discontinuity shear strength values, as well as from the inherent variability of shear strength within a rock medium. The main causes of discrepancies, namely, scale, anisotropy and water saturation are considered. For each source of discrepancy a correction factor, treated as a random variable, is assigned and guidelines for the quantification of the statistical parameters of these correction factors are presented within the framework of the proposed uncertainty analysis model. The proposed uncertainty model provides an analytical tool for the systematic treatment of uncertainties involved in the estimation of the in situ value of peak friction angle from the laboratory test results.

Time-dependent Effect of Drilling Fluids On Fernie Shales

Abstract This paper investigates the time-dependent effect of drilling fluids on the shear strength properties of Fernie Formation shales. Direct shear tests were conducted on samples that were split along their bedding planes and soaked in four different drilling fluids systems for varying periods of time: oil based mud, gel chem, TAME and PHPA. Distilled water was used as a base line fluid in this study. The shear tests were conducted at a normal stress range of 0 – 1 MPa. For each fluid, five samples were tested, four of which had their natural rough surface, whereas, the surface of one was artificially smoothened. The test results show that both TAME and PHPA fluids increase the angle of shearing resistance of the smoothened shale samples indicating that these may be absorbed into the shales, at least at the surface. The distilled water, oil based and gel chem muds have no effect on the angle of shearing resistance of smooth shale samples, whereas, the angle of shearing resistance of the rough samples decreased. The angle of shearing resistance of the rough samples in the TAME fluid showed both increases and decreases, whereas rough samples in the PHPA fluid had a general increase in the angle of shearing resistance with period of soaking. Introduction Shales from the Cretaceous and Jurassic periods are found at depths of thousands of metres in the Rocky Mountain Foothills region of British Columbia and Alberta, Canada. In undisturbed conditions, these shales exist in equilibrium under high in situ stresses. However, when drilled for oil and gas, these shales tend to become unstable in boreholes(1,2,3). This loss in stability is due to the mechanical stresses induced while drilling as well as the physico-chemical effects of the drilling fluids. The relative contribution of each of the two effects in causing instability is not well understood in some brittle shales like the Fernie Formation. Mechanical stresses are caused by the excavation of the wellbore, whereas some physico-chemical effects are the result of capillary action due to absorption of the fluid and interaction between the constituents of the rock and that of the fluid(4). To our knowledge, the physico-chemical effects of the various drilling fluids on Fernie Formation shales have not been studied in the laboratory. Hence, a study was initiated to determine the shear strength parameters of Fernie shales along pre-failed bedding planes when exposed to different drilling fluids for varying periods of time. The time-dependent effect of the fluid on the shear strength properties of the shales was examined by conducting direct shear tests on samples soaked in the fluid for periods of one, seven and 28 days. There are several different parameters that affect the shear resistance of natural rock discontinuities. The surface roughness and interlocking of protrusions (asperities) are considered major obstacles in objectively determining rock discontinuity shear strength. The problems are compounded by the apparent effects of fluid induced lubrication including softening of asperities, fluid composition, rock mineral content, base frictional properties and normal stress levels.

Scale effect evaluation on natural discontinuity shear strength : Giani, G P; Ferrero, A M; Passarello, G; Reinaudo, L Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3–5 June 1992P456–462. Publ California: Lawrence Berkeley Laboratory, 1992

Scale effect evaluation on natural discontinuity shear strength : Giani, G P; Ferrero, A M; Passarello, G; Reinaudo, L Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3–5 June 1992P456–462. Publ California: Lawrence Berkeley Laboratory, 1992

The effect of frictional fill thickness on the shear strength of rock discontinuities

The results of a series of direct shear tests on models of a sandstone discontinuity of mean roughness amplitude 7 mm and filled with different thicknesses of dry pulverised fuel ash (PFA) are reported. Peak shear strength is shown to decrease with increasing fill thickness ( f), expressed as a ratio to discontinuity mean roughness amplitude ( a), and approaches a minimum when f a is between 1.25 and 1.5, depending upon the normal stress. Residual strength decreases less markedly with increasing f a ratio and tends towards a constant value when f a > 1.0 . For layers of fill thicker than the discontinuity mean roughness amplitude, failure planes may develop partly through the fill and partly along the interface. When f a > 0.8 , the peak shear strength of the discontinuity is less than that of the fill but higher than that of the rock-fill interface. Expressions for prediction of peak and residual friction coefficients for a filled discontinuity are derived from the experimental results: μ = μ min + (μ max − μ min) n and n = [1 − 1/ c( f a )] m where μ = frictional coefficient (%) μ max is that for the clean discontinuity, μ min is the minimum for the system, f a is the ratio of fill thickness to asperity height and c and m are experimentally derived constants.

Another approach to discontinuity shear strength assessments, based on investigations of bore cores : van Staveren, M T Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990V1, P775–782. Publ Rotterdam: A A Balkema, 1990

Another approach to discontinuity shear strength assessments, based on investigations of bore cores : van Staveren, M T Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990V1, P775–782. Publ Rotterdam: A A Balkema, 1990

Algorithm for predicting the effect of variable normal stiffness on shear strength of discontinuities

Algorithm for predicting the effect of variable normal stiffness on shear strength of discontinuities

Quantification of power law indices for discontinuity shear strength prediction : Denby, B; Scoble, M J In: Rock Mechanics in Productivity and Protection (Proceedings of the Twenty-Fifth Symposium on Rock Mechanics, Evanston, Illinois, 25–27 June 1984P475–482. Publ New York: AIME, 1984

Quantification of power law indices for discontinuity shear strength prediction : Denby, B; Scoble, M J In: Rock Mechanics in Productivity and Protection (Proceedings of the Twenty-Fifth Symposium on Rock Mechanics, Evanston, Illinois, 25–27 June 1984P475–482. Publ New York: AIME, 1984

Reliability engineering approach to the design of rock slope and cavern in fractured rock : Nishimatsu, Y; Okubo, S Proc 5th Congress of the International Society for Rock Mechanics, Melbourne, 10–15 April 1983V1, PB29–B32. Publ Rotterdam: A. A. Balkema, 1983

Taking into account the statistical distribution of spacing and shear strength of the discontinuity in rock mass, a theoretical formula is given on the probability of failure of rock structure in fractured rock. The statistical distribution of the shear strength of discontinuity is discussed on the basis of the result of direct shear tests of rock samples. As an example of the application of the theory to the design of rock structure, the stability of a rock slope is evaluated as a function of spacing and shear strength of discontinuity as well as of the height and the gradient of the rock slope. The number of the covering abstract of the congress is TRIS no. 385148. (TRRL)

On the Structural Study of a Wide-beam Tanker

In this report authors carried out structural study on a wide-beam tanker with DW 400, 000 T. L/B ratio of this vessel is five, whereas that of conventional tankers is about six.Main items of the study are as followings : -(1) Selection of structural systemComparative study for probable three structural systems are carried out from strengthwise and constructionwise view-points. Finally, structural system with center line bulkhead is selected.(2) Longitudinal strengthWave bending moment and shearing force on this type of vessel are relatively smaller than those on conventional tankers.(3) Transverse strengthTransverse strength for structure selected under (1) is checked by using 3-D frame analysis method.(4) Shear strength of hull girder in way of engine roomAt the fore end of engine room center line bulkhaed terminates and in view of such structural discontinuity shear strength is checked by replacing the structure with a beam element model. As a result it proved that the shear strength of this part is enough.(5) Reaction force from supporting blocks imposed to hull during constructionIn view of fairly big canti-lever type stern construction, reaction force from supporting blocks are feared to become a big amount and calculation of this reaction force is carried out. In result the force is found to be below allowable limit but to secure sufficient allowance, development of suitable method to support the weight of stern construction is desired.Through these studies authors reached the conclusion that the main problems pertaining to the structural design of this type of vessel have almost been solved and construction of this vessel is possible.