Search

Three-dimensional (3D) roughness of the rock discontinuity plays a controlling function on the rock mass stability of excavation face during deep buried tunnel construction, which can be predicted based on the discontinuity outcrop from excavation face. However, there exist some disturbing factors such as dust and debris which affect the non-contact measurement accuracy on the outcrop information under construction environment. In this study, a new method to predict three-dimensional roughness of rock discontinuity (JRC 3d) based on the limited outcrop and drilling test information from the rock mass of excavation face is proposed. Two-dimensional roughness of rock discontinuity (JRC 2d) is derived based on different asperity orders firstly. The first-order profile roughness is calculated by combining drilling test result, and the second-order profile roughness is predicted on establishing the statistical relationship between the geometrical parameter of the outcrop and the entire profile. Based on the prediction of JRC 2d , JRC 3d is characterized probabilistically with the improved Bayesian theory where the bootstrap method is used to deal with the difficulty of obtaining μ and σ of the prior distribution because the sample size is limited. A rock tunnel engineering in southwest China is taken as the engineering application, and the relative errors of the predicting JRC 3d are lower than 11 %. Finally, the effect of outcrop width on the predicting JRC 3d results is investigated. For Barton standard profiles, the statistical parameters of the first k climbing angles of the second-order roughness profiles are calculated to estimate the appropriate outcrop width as 16 mm. A rock discontinuity is generated to study the effect of discontinuity size on the predicting JRC 3d , and the relative error of the predicting JRC 3d is lower than 12 %, thereby validating the method applicability across a broad spectrum of discontinuity sizes, ranging from small to large. • A new method of predicting JRC 3d is proposed considering insufficient outcrop information during the tunnel construction. • The second-order roughness is derived by studying the geometrical parameters of the outcrop and entire profile. • JRC 2d and JRC 3d are predicted based on two asperity orders and the improved Bayesian theory respectively. • The sensitivities of the influencing factors which are the outcrop width and discontinuity size are analyzed. [ABSTRACT FROM AUTHOR]

Research on rock slopes has attracted considerable attention in the fields of infrastructure construction and disaster prevention. The search for an efficient and reliable method for discontinuity collection is an important task for various studies of jointed rock slope. Capturing high-precision and complete rock exposure images based on unmanned aerial vehicle (UAV) multi-angle and nap-of-the-object photogrammetry technology is proposed to realize the construction of a millimeter-level 3D point cloud for the high and steep slope. This study develops a new automatic methodology for discontinuity identification and interpretation. A Delaunay triangulation network is created for connecting adjacent points in the point cloud to calculate normal vectors and search for neighbor points efficiently. Combined with the modified region-growing algorithm, an automatic procedure which identifies discontinuities and acquires geometrical parameters efficiently and accurately is established. The proposed approach is applied to the high-steep rock slope on the northern bank of the Sequ Grand Bridge in the Changdu area of Tibet. Compared with the results from the manual survey, the proposed method is more reliable and exhibits high accuracy for discontinuity identification and interpretation on rock exposure. [ABSTRACT FROM AUTHOR]

The shear strength of rock discontinuities is known to be scale dependent, and past research has revealed that both positive and negative scale effects could be observed. It is far from trivial to predict the occurrence of the scale effect and, to date, there is still no consensus on how to satisfactorily predict the shear strength of large discontinuities. A new stochastic approach was proposed and validated at laboratory scale by the authors. The approach consists of (1) using the information available from visible traces to create synthetic surfaces via a random field model and (2) estimating the shear strength of each one of the synthetic surfaces in order to obtain a distribution of shear strength and a mean shear strength. This paper presents the first application of this new approach to a large discontinuity that was surveyed with a resolution of 1 mm and an accuracy in the order of 150–230 µm in the Pilkington reserve of Newcastle, Australia. The paper first confirms that a scale effect does exist for the surface tested, before demonstrating that the new stochastic approach produces a strength envelope that is very close to the deterministic failure criterion of the whole surface. The key conclusion of this research is that there is enough information on visible traces, if surveyed accurately, to obtain an estimate of the shear strength of the discontinuity. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]

The slip shear failure along rock discontinuities is one of the predominant failure modes of landslides. To simulate impact shear loads during landslide and rockburst, an experimental method is presented to achieve the dynamic shear load in a direct shear testing configuration. The dynamic loading system is derived from the SHPB methodology and can provide high shear velocities around 1–10 m/s. Dynamic direct shear experiments on rough rock discontinuities are conducted by using a dynamic shear apparatus combined with a high-speed digital camera. The effects of shear velocity and normal stress on the slip displacement, slip velocity and slip acceleration of rough rock discontinuities are analyzed using a two-dimensional digital image correlation (DIC) technique. It is observed that the rate of the slip is linearly proportional to the shear velocity and decreases with the increasing normal stress. Using the DIC method, the strain at failing asperities is calculated as a function of the shear velocity and the normal stress. The micro-structural characteristics of the shear zone formed in the slip failure is examined to understand the slip failure mode. Moreover, the dynamic viscous is added to the static Barton's shear strength criterion and the damage evolution occurred at the asperities due to the dynamic loading is introduced by means of a damage control parameter D. Thereafter, a dynamic failure criterion is developed by considering both surface roughness and dynamic loading. The failure model can provide a good prediction of the experimental data, indicating that the proposed models can describe well the dynamic shear process of rock discontinuities under high velocity impact. [ABSTRACT FROM AUTHOR]