Coefficient of Restitution and Kinetic Energy Loss of Rockfall Impacts

Li-Ping Li,Shang-qu Sun,Shucai Li,Qian-qing Zhang,Cong Hu,Shao-shuai Shi 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.6

This paper presents the results of the coefficient of restitution and the kinetic energy loss rate obtained by lab experiment, two parameters that are crucial for rockfall impact. However, various definitions of coefficient of restitution exist and the most appropriate one is still not formed and obtained. In addition, the energy variation during the rockfall impacts has important significance in practical design. In this research, two kind shapes of blocks including plate and strip were adopted in the laboratory testing and the block material was tested before, indicating that the material has sufficient strength to prevent shattering during the impact. Furthermore, an apparatus specifically built for this study was established including a base, a slope and a releasing device. The falling testing was performed using plate and strip block while the falling height as well as the slope angle and releasing height were altered during the tests in order to estimate the effect of each parameter on the coefficients of restitution and energy loss rate. It was observed that collision reflection angle is less than impact angle for all, suggesting energy loss in collision. Impact angle decreases with increasing slope angle while there was no obvious effect of releasing height and releasing angle on impact angle. The relevant coefficient of restitution was found to decrease with impact angle, and the kinetic energy loss rate increased. Finally, the kinetic energy before and after the impact was found to significantly affect the COR and energy loss rate and the results can provide basis for mitigation measures.

Numerical investigations on stability evaluation of a jointed rock slope during excavation using an optimized DDARF method

Li, Yong,Zhou, Hao,Dong, Zhenxing,Zhu, Weishen,Li, Shucai,Wang, Shugang Techno-Press 2018 Geomechanics & engineering Vol.14 No.3

A jointed rock slope stability evaluation was simulated by a discontinuous deformation analysis numerical method to investigate the process and safety factors for different crack distributions and different overloading situations. An optimized method using Discontinuous Deformation Analysis for Rock Failure (DDARF) is presented to perform numerical investigations on the jointed rock slope stability evaluation of the Dagangshan hydropower station. During the pre-processing of establishing the numerical model, an integrated software system including AutoCAD, Screen Capture, and Excel is adopted to facilitate the implementation of the numerical model with random joint network. These optimizations during the pre-processing stage of DDARF can remarkably improve the simulation efficiency, making it possible for complex model calculation. In the numerical investigations on the jointed rock slope stability evaluations using the optimized DDARF, three calculation schemes have been taken into account in the numerical model: (I) no joint; (II) two sets of regular parallel joints; and (III) multiple sets of random joints. This model is capable of replicating the entire processes including crack initiation, propagation, formation of shear zones, and local failures, and thus is able to provide constructive suggestions to supporting schemes for the slope. Meanwhile, the overloading numerical simulations under the same three schemes have also been performed. Overloading safety factors of the three schemes are 5.68, 2.42 and 1.39, respectively, which are obtained by analyzing the displacement evolutions of key monitoring points during overloading.

Mechanical Behaviour of a Large-span Double-arch Tunnel

Shuchen Li,Chao Yuan,Xianda Feng,Shucai Li 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.7

A scaled physical model test and numerical simulations of a shallow-buried double-arch tunnel, the Great Wall Ridge Tunnel (GWRT), are performed as a first step toward a full understanding of the deformation of double-arch tunnels in shallow formations. The instrumentation of the model experiment includes high-accuracy dial gauges, miniature stress sensors, and strain gauges to record the mechanical responses of the tunnel supporting system and the surrounding rocks. The experiment strictly follows the designed excavation procedure planned for the GWRT, and the results show good agreement with those obtained from numerical simulations. We focus on the accurate approximation of the ground movement in order to ensure the safety of a neighbouring ancient relic, the Great Wall of the Qi. We also investigate the stress distributions of the surrounding rock formations and the middle wall. Based on the settlements of the ground and the plastic zone distribution, we conclude that the current design of the GWRT construction could potentially damage the neighbouring historical site.

An experimental investigation on mechanical property and anchorage effect of bolted jointed rock mass

Yong Li,Chao Li,Lei Zhang,Weishen Zhu,Shucai Li,Jian Liu 한국지질과학협의회 2017 Geosciences Journal Vol.21 No.2

Apparent discontinuities can be easily found in natural rock medium owing to the constant motion and change of the Earth’s crust, which contains large amount of discontinuous surfaces such as faults, joints, cracks and so forth. Rock bolt is one of the most effective and economical reinforcing tools in practical geotechnical engineering for a long time. This paper investigates the mechanical properties, anchorage effect, cracking, and coalescence process of intact rock-like specimens, rock-like specimens containing flaws, and bolted rock-like specimens containing flaws. A series of uniaxial compression tests, splitting tests, and biaxial compression tests are performed on these specimens. Some findings can be observed from this study. (1) The number of rock bolt(s) and the anchoring angle have a great influence on the anchorage effect of rock bolt(s). With the increasing number of rock bolt(s), the uniaxial compressive strength (UCS), the splitting peak strength (which can be converted to the tensile strength), and biaxial compressive strength (BCS) can all be improved, whose variation tendencies do not follow a linear relationship. (2) The contributions to the tensile strength for rock bolt is greater than that to the UCS for the same-type specimen. (3) In the biaxial compression tests, with the increasing of the lateral pressures, the anchorage effect of rock bolt gradually declines and the lateral pressure plays a dominant role in improving the strength of the specimen. The failure characteristics of three types of laboratory tests have also been systematically analyzed in this paper.

Experimental and numerical investigations on the shear behavior of a jointed rock mass

Yong Li,Hao Zhou,Weishen Zhu,Shucai Li,Jian Liu 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.3

The original forming process of the earth crust is companied with internal in situ stress, which gradually complicates while the earth crust evolves with geological conformation movements, leading to the generation of large amounts of faults, joints and fissures. These structural planes, to some extent, remarkably reduce the strengths of rock mass, including the shear behavior. In this paper, the authors report a physical model test on jointed rock mass under direct shear stress state and also adopt a numerical method, Discontinuous Deformation Analysis for Rock Failure (DDARF), to simulate the shear failure process, the variation of stresses and displacements of some key monitoring points. The comparative analysis demonstrates that the numerical results are favorable with those obtained in the physical model test. Therefore, it is concluded that the method of DDARF could effectively simulate the shear behavior of jointed rock mass. Furthermore, other than the original physical model test, the numerical models with echelon joints under different axial loadings are also simulated. The crack initiation, extension, coalescence, and the ultimate shear failure are totally investigated, after which the shear behavior of numerical models in different cases are comparatively analyzed.

An Extension Theoretical Model for Grouting Effect Evaluation in Sand Stratum of Metro Construction

Jiwen Bai,Shucai Li,Yujing Jiang,Rentai Liu,Zhaofeng Li,Wei Li 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.5

Water-rich sand stratum is a common geological disaster source for the metro construction in coastal cities, and grouting is the most widely-used and efficient method to improve the characteristics of tunnel-surrounding rock. The grouting effect evaluation plays a key role in guaranteeing the subsequent construction safety. However, the grouting effect evaluation is a complex problem since it involves influence factors of uncertainty and variability. In order to comprehensively and quantitatively evaluate the grouting quality and guarantee the safety of metro construction, an extension theoretical model for grouting effect evaluation in water-rich sand stratum is established. Firstly, according to the geological and engineering influence factors, rock mass strength, permeability of surrounding rock, attitude of stratum, moisture content, grouting material, and grouting technology are selected as the grouting effect evaluation indexes, which make up the evaluation index system. The dimensionless method is used to avoid the influence of the unit and order of magnitude of each index, and index weight of each factor is ascertained by entropy-information theory. Also, through the grouting information of typical waterrich sand stratum and expert experience, the grouting effect evaluation grade classification is achieved. Combining with the extension theory and measured data, the correlation degree of each evaluation grade is obtained. Finally, according to the correlation degree identification criteria, the grouting effect evaluation categories can be judged. In the engineering application, the water-rich sand stratum grouting effect in Qingdao metro is evaluated based on the proposed model. The results show that the evaluation grade agrees well with the excavation situation. The extension theoretical model provides an effective method for grouting effect evaluation in water-rich sand stratum.

A new geopolymeric grout blended completely weathered granite with blast-furnace slag

Zhang, Jian,Li, Shucai,Li, Zhaofeng,Li, Hengtian,Du, Junqi,Gao, Yifan,Liu, Chao,Qi, Yanhai,Wang, Wenlong Techno-Press 2020 Advances in concrete construction Vol.9 No.6

In order to reduce the usage of cement slurry in grouting engineering and consume the tunnel excavation waste soil, a new geopolymeric grouting material (GGM) was prepared by combine completely weathered granite (CWG) and blast-furnace slag (BFS), which can be applied to in-situ grouting treatment of completely weathered granite strata. The results showed CWG could participate in the geopolymerization process, and GGM slurry has the characteristics of short setting time, high flowability, low viscosity, high stone rate and high mechanical strength, and a design method of grouting pressure based on viscosity evolution was proposed. By adjusted the content of completely weathered granite and alkali activator concentration, the setting time of GGM were ranged from 5 to 30 minutes, the flowability was more than 23.5 cm, the stone rate was higher than 90%, the compressive strength of 28 days were 7.8-16.9 MPa, the porosity were below 30%. This provides a novel grouting treatment and utilizing excavated soil of tunnels in the similar strata.

Developing brittle transparent materials with 3D fractures and experimental study

Jing Wang,Shucai Li,Weishen Zhu,Li-Ping Li 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.2

The fracture propagation mechanism and fractured rock mass failure mechanism were important research in geotechnical engineering field. Many failures and instability in geotechnical engineering were related on fractures propagation, coalescence and interaction in rock mass under the external force. Most of the current research were limited to two-dimensional for the brittleness and transparency of three-dimensional fracture materials couldn't meet the requirements of the experiment. New materials with good transparent and brittleness were developed by authors. The making method of multi fracture specimens were established and made molds that could be reused. The tension-compression ratio of the material reached above 1/6 in normal temperature. Uniaxial and biaxial loading tests of single and double fracture specimens were carried out. Four new fractures were not found in the experiment of two-dimensional fractures such as the fin shaped crack, wrapping wing crack and petal crack and anti-wing crack. The relationship between stress and strain of the specimens were studied. The specimens with the load had experienced four stages of deformation and the process of the fracture propagation was clearly seen in each stage. The expansion characteristics of the fractured specimens were more obvious than the previous research.

Study on anchorage effect on fractured rock

Jing Wang,Shucai Li,Li-Ping Li,Weishen Zhu,Qian-qing Zhang,Shu-Guang Song 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.17 No.6

The effects of anchor on fractured specimens in splitting test are simulated by DDARF method, the results of which are compared with laboratory test results. They agree well with each other. The paper contents also use the laboratory model test. The main research objects are three kinds of specimens, namely intact specimens, jointed specimens and anchored-jointed specimens. The results showed that with the joint angle increased, the weakening effects of jointed rock mass are more obvious. At these points, the rock bolts' strengthening effects on the specimens have become more significant. There is a significant impact on the failure modes of rock mass by the joint and the anchorage.

Study on Deformation Behavior at Intersection of Adit and Major Tunnel in Railway

Hong-liang Liu,Shucai Li,Li-Ping Li,Qian-qing Zhang 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.6

Behavior of rock mass in the intersection between adit and major tunnel is a complicated three-dimensional problem, the increasing support load and additional tunnel deformation may endanger tunnel stability during construction. To understand the deformation behavior of rock mass in the intersection, a 3D numerical analysis was conducted. Comparing the monitoring data, the distribution of the plastic zone, the extrusion displacement of working face and the deformation of the sidewall in the adit and major tunnel were studied. Following analysis results, the distribution and potential influenced area of the intersection in the adit and major tunnel were analyzed. The principle of detection and reinforcement in the intersection were also discussed.