Shengwen Qi

Experimental Study of Ultrasonic Waves Propagating Through a Rock Mass with a Single Joint and Multiple Parallel Joints

Experiments were conducted to study the relationship between the transmission ratio (TR) and normal stress, joint roughness, joint number and frequency of incident waves, respectively, when ultrasonic waves pass across a rock mass with one joint and multiple parallel joints oriented normally. The ultrasonic waves were generated and received by pairs of piezoelectric transducers and recorded by an ultrasonic detector. The specimens were subjected to normal stress by a hydraulic jack and loading frame. The jointed rock mass was produced by superposing rock blocks in the study. Rough joints were produced by grooving notches on the planar joints formed by sawing directly. In the case of multiple parallel joints, the overall thickness of specimens was maintained while the joint number changed. Three pairs of P-wave transducers and one pair of S-wave transducers with different frequencies were, respectively, applied and all transducers emitted signals perpendicular to the joints in the experiment. The results indicate that TR increases with increasing normal stress while the increment rate decreases gradually. This is particularly so when the normal stress is high enough that TR will approximate 1 even if the rock mass has many joints. In addition, the experiments indicate that the higher the wave’s frequency, the lower its TR, and this phenomenon is gradually reduced as the normal stress increases. In response to S-waves, TR increases with increase in joint roughness; however, in response to P-waves, TR decreases gradually with increase in joint roughness. For multiple parallel joints in a fixed thickness rock mass with normally incident P-waves, TR does not always decrease with increase in the number of joints, and there is a threshold joint spacing for a certain incident wave: when the joint spacing is smaller than the threshold value, TR will increase with a decrease in joint spacing. The experimental results support similar conclusions based on analytical results drawn by Cai and Zhao (Int J Rock Mech Min Sci 37(4):661–682, 2000), Zhao et al. (Int J Rock Mech Min Sci 43(5):776–788, 2006b) and Zhu et al. (J Appl Geophys 73:283–288, 2011a).

Numerical Simulation on Seismic Response of the Filled Joint under High Amplitude Stress Waves Using Finite-Discrete Element Method (FDEM)

This paper numerically investigates the seismic response of the filled joint under high amplitude stress waves using the combined finite-discrete element method (FDEM). A thin layer of independent polygonal particles are used to simulate the joint fillings. Each particle is meshed using the Delaunay triangulation scheme and can be crushed when the load exceeds its strength. The propagation of the 1D longitude wave through a single filled joint is studied, considering the influences of the joint thickness and the characteristics of the incident wave, such as the amplitude and frequency. The results show that the filled particles under high amplitude stress waves mainly experience three deformation stages: (i) initial compaction stage; (ii) crushing stage; and (iii) crushing and compaction stage. In the initial compaction stage and crushing and compaction stage, compaction dominates the mechanical behavior of the joint, and the particle area distribution curve varies little. In these stages, the transmission coefficient increases with the increase of the amplitude, i.e., peak particle velocity (PPV), of the incident wave. On the other hand, in the crushing stage, particle crushing plays the dominant role. The particle size distribution curve changes abruptly with the PPV due to the fragments created by the crushing process. This process consumes part of wave energy and reduces the stiffness of the filled joint. The transmission coefficient decreases with increasing PPV in this stage because of the increased amount of energy consumed by crushing. Moreover, with the increase of the frequency of the incident wave, the transmission coefficient decreases and fewer particles can be crushed. Under the same incident wave, the transmission coefficient decreases when the filled thickness increases and the filled particles become more difficult to be crushed.

Numerical Studies on the Failure Process of Heterogeneous Brittle Rocks or Rock-Like Materials under Uniaxial Compression

In rocks or rock-like materials, the constituents, e.g. quartz, calcite and biotite, as well as the microdefects have considerably different mechanical properties that make such materials heterogeneous at different degrees. The failure of materials subjected to external loads is a cracking process accompanied with stress redistribution due to material heterogeneity. However, the latter cannot be observed from the experiments in laboratory directly. In this study, the cracking and stress features during uniaxial compression process are numerically studied based on a presented approach. A plastic strain dependent strength model is implemented into the continuous numerical tool—Fast Lagrangian Analysis of Continua in three Dimensions (FLAC3D), and the Gaussian statistical function is adopted to depict the heterogeneity of mechanical parameters including elastic modulus, friction angle, cohesion and tensile strength. The mean parameter μ and the coefficient of variance (hcv, the ratio of mean parameter to standard deviation) in the function are used to define the mean value and heterogeneity degree of the parameters, respectively. The results show that this numerical approach can perfectly capture the general features of brittle materials including fracturing process, AE events as well as stress-strain curves. Furthermore, the local stress disturbance is analyzed and the crack initiation stress threshold is identified based on the AE events process and stress-strain curves. It is shown that the stress concentration always appears in the undamaged elements near the boundary of damaged sites. The peak stress and crack initiation stress are both heterogeneity dependent, i.e., a linear relation exists between the two stress thresholds and hcv. The range of hcv is suggested as 0.12 to 0.21 for most rocks. The stress concentration degree is represented by a stress concentration factor and found also heterogeneity dominant. Finally, it is found that there exists a consistent tendency between the local stress difference and the AE events process.

Characteristics and mechanism of deep weathering of argillaceous limestones at Fengjie County, Three Gorges Region, Central China

The paper reports the ground conditions in the Sanmashan area where people were relocated as a consequence of the impoundment of the Three Gorges Reservoir. Examination of the geology indicates the strong calcareous rocks were not only highly fractured to considerable depths but were also decalcified in the near surface layers. A combination of the highly fractured state and decalcified nature of the material resulted in significant changes in the bedrock parameters between the northern and southern parts of the study area; the southern area having been affected by the deep down-cutting of the Yangtze River, release of stress and the development of three large landslides.RésuméL’article présente le cadre géologique de la région de Sanmashan où des personnes ont été installées en conséquence de la mise en eau du barrage des Trois-Gorges. Les études ont montré que les roches calcaires résistantes étaient non seulement fracturées à des profondeurs importantes mais aussi altérées dans les couches superficielles. La combinaison de la fracturation et de l’altération a pour résultat des changements importants des paramètres géotechniques du substratum entre le nord et le sud de la zone d’étude. Le sud de la zone a été affecté par le creusement profond du Yangtze, le relâchement des contraintes et la formation de trois grands glissements de terrain.

A Recognition and Geological Model of a Deep-Seated Ancient Landslide at a Reservoir under Construction

Forty-six ancient Tibetan star-shaped towers and a village are located on a giant slope, which would be partially flooded by a nearby reservoir currently under construction. Ground survey, boreholes, and geophysical investigations have been carried out, with results indicating that the slope consists of loose deposit with a mean thickness of approximately 80 m in addition to an overlying bedrock of micaceous schist and phyllite. Ground survey and Interferometric Synthetic Aperture Radar (InSAR) indicated that the slope is experiencing some local deformations, with the appearance of cracks and occurrence of two small landslides. Through using borehole logs with the knowledge of the regional geological background, it can be inferred that the loose deposit is a result of an ancient deep-seated translational landslide. This landslide was initiated along the weak layer of the bedding plane during the last glaciation in the late Pleistocene (Q3) period, which was due to deep incision of the Dadu River at that time. Although it has not shown a major reaction since the ancient Tibetan star-shaped towers have been built (between 200 and 1600 AD), and preliminary studies based on geological and geomorphological analyses incorporated with InSAR technology indicated that the landslide is deformable. Furthermore, these studies highlighted that the rate of deformation is gradually reducing from the head to the toe area of the landslide, with the deformation also exhibiting relationships with seasonal rainstorms. The state of the toe area is very important for stabilizing a landslide and minimizing damage. It can be expected that the coming impoundment of the reservoir will increase pore pressure of the rupture zone at the toe area, which will then reduce resistance and accelerate the deformation. Future measures for protection of the slope should be focused on toe erosion and some bank protection measures (i.e., rock armor) should be adopted in this area. Meanwhile, some long-term monitoring measures should be installed to gain a deep understanding on the stability of this important slope.

Application of cross-hole radar tomograph in karst Area

Electromagnetic wave CT, containing velocity CT and attenuation CT, is one of the effective geophysical prospecting methods to detect underground caves. The accuracy is low when applying the velocity CT and the attenuation CT separately into investigation in a karst area. This paper briefs the basic theory of electromagnetic wave CT imaging, and then mainly introduces the basic theory and applying methodology of cross-hole radar tomography for exploration in a karst area. Through numerical value simulation and practice verification, the advantage and disadvantage of the velocity CT and the attenuation CT of electromagnetic wave based on very high frequency have been studied, respectively. It has been found that the attenuation CT does better in confirming the location of karst caves, and the velocity CT is better in determining the shape of the karst caves although the whole distribution regular of the velocity CT is almost consistent with the attenuation CT.

ARMR, a new classification system for the rating of anisotropic rock masses

The engineering behavior of rock masses is strongly dependent on anisotropy, which is present at different scales, from the microscale in the intact rock due to the alignment of rock crystals (inherent anisotropy) to the macroscale in rock masses with anisotropic rock structure, characterized by distinct bedding or schistosity planes. This paper presents a new rock mass classification system, Anisotropic Rock Mass Rating (ARMR), specifically developed for the classification of anisotropic rock masses. ARMR considers the following rating parameters: (a) anisotropy strength index, RC; (b) uniaxial compressive strength of intact rock; (c) degree of structure anisotropy; (d) corrected rock quality designation (RQD); (e) condition of anisotropy surfaces; and (f) groundwater conditions. Its use is illustrated and explained by application to specific case studies in anisotropic rock masses, and the advantages and limitations of the classification system are outlined. The strength of anisotropic rock masses is determined using the modified Hoek–Brown criterion (Saroglou and Tsiambaos, Int J Rock Mech Mining Sci 45:223–234, 2008), which is extended to rock masses with the use of ARMR.

Susceptibility of Rocky Desertification Based on Analytical Hierarchy Process and Certainty Factor (AHP-CF) Method: A Case from Changshun County, Guizhou Province, SW of China

Rocky desertification induced by Karst is still serious in rocky mountainous region in SW of China although it is mitigated due to endeavor paid by Chinese government. New high technologies such as remote sensing is wildly used to investigate the development of the rock desertification, and some experiences have been reached. However the susceptibility mapping is still in a coarse stage, which largely relies on subjective experiences. A case from Changshun county, Guizhou Province, China is studied. Firstly, the influence factors of rocky desertification are analyzed and weight of each factor is evaluated based on analytical hierarchy process (AHP) method (Saaty 1977). Secondly, a mathematical model based on certainty factor (CF) is established with support of Mapgis, and the susceptibility of the area is assessed. According to natural break rule, the susceptibility is divided into four classes as extremely high, high, medium and low susceptible. The mapping result indicates that low susceptible area only accounts for about 6.61 %, which means most of the area is prone to rocky desertification. The result is verified by the investigation based on remote sensing.

In Situ Test on Dynamic Response of Single Surface Slope

An in situ explosion test on dynamic responses of one single surface slope (stepped slope) of open-pit iron mine in Miyun County, Beijing has been carried out. The slope consists of gneiss and magnetite quartzite with blocky structure and its surface is strongly disturbed due to excavation and explosion. Four explosion recorders have been used as data acquisition instruments in the experiment. Each of the recorder has two channels and can record horizontal and vertical component at the same time. Four recorders have been placed at different elevation of the slope to monitor the dynamic responses of the slope during explosion. The explosion point was located at the foot of the slope. The results indicate that peak ground velocity (PGV) and peak ground acceleration (PGA) varies with elevation changing. It can be seen that both PGV and PGA decrease gradually with elevation increasing, and then amplify at the near crest of the slope.