Yu-Yong Jiao

Numerical investigation of joint effect on shock wave propagation in jointed rock masses

To investigate the joint effect on shock wave propagation and attenuation in jointed rock masses, a small-scale field explosion test is analyzed numerically by using the three-dimensional discrete element method (3D DEM) and the three-dimensional finite difference method (3D FDM). Results show that rock joints act as a kind of filter through which only low frequency shock waves are allowed to pass. This indicates that high frequency shock waves do no harm to far-field structures when they have to travel across joint sets with specific spacing. Results also reveal that the orientation of the joint sets can remarkably affect the amplitude and frequency composition of shock waves. Furthermore, as a discontinuous numerical method, 3D DEM can capture the main features of shock waves, and most importantly, it can simulate the 3D effect of rock joints. It can be concluded that in modelling 3D shock wave propagation and attenuation in jointed rock masses, 3D DEM has unique advantages over 2D modeling, 3D FDM, and even field testing.

A relationship-based and object-oriented software for monitoring management during geotechnical excavation

Abstract The efficient management of monitoring data is necessary for large geotechnical engineering projects. The development of an information management, prediction and warning software system for geotechnical monitoring is presented in this study. Seven categories of property objects that describe the hierarchical relationships among the monitoring objects, as well as two objects that represent and manage the construction progress, are proposed based on the requirements of geotechnical monitoring, data flow and the monitoring objectives of the site. The corresponding data structure and database were established using the object-oriented method in the Visual C++ environment. The software integrated various types of information and document management schemes, including data input and processing, CAD drawing visualisation, data modelling and prediction, as well as an early warning function. The applied case studies indicate that the software system is highly flexible and reliable and can be widely applied to monitor the sites of various geotechnical construction projects, such as tunnels, underground caverns, slopes and foundation pits.

Material Weakening of Slip Zone Soils Induced by Water Level Fluctuation in the Ancient Landslides of Three Gorges Reservoir

This experimental study investigated the effect of repeated wetting and drying on the reduction of slip zone soils taken from the Huangtupo landslide in the Three Gorges Reservoir, China. The variation process of the physical property and substance composition of the slip zone soils under the wetting-drying cycles was studied through liquid and plastic limit test and X-ray diffraction test. The results indicate that (1) the shearing strength of the slip zone soil dramatically decreased after one wetting-drying cycle and then gradually decreased until reaching a relatively stable state at the fourth cycle; (2) the plasticity index of the slip zone soil varied with increasing number of cycles and a variation process opposite to that of the strength value was observed; and (3) the clay mineral content in the slip zone soil increased and the calcite and quartz contents relatively decreased with increasing number of cycles. The variations in the plasticity index of the slip zone soil, as well as the increase in its clay mineral content, play important roles in the strength reduction. The results of this study provide a foundation for revealing the deformation and damage mechanism of landslides in reservoir banks.

A New Apparatus for Testing the Bearing Capacity of Calcareous Sand in Laboratory

Calcareous sand, widely spread on coral reefs in Nansha Islands, South China Sea, will be used as backfill material in oceanic engineering, but its engineering property is still elusive. Its difficult and extremely costly to conduct in-situ plate load tests to investigate the bearing capacities of calcareous soils foundation because the coral reefs are too far from the mainland and located in tidal zone. In order to study the bearing capacity and deformation behavior of calcareous soils, the authors designed an apparatus to carry out laboratory tests. The apparatus has the advantages as listed: (1) estimating the bearing capacity and deformation of soil foundation; (2) measuring the soil pressures and settlements at diffirent depths; (3) investigating the load transmission depth. Test results of calcareous sand indicate that the apparatus is suitable to test the engineering behavior of soil in laboratory.

Numerical and experimental investigation on the stability of slopes threatened by earthquakes

This paper presents a methodology for evaluating the safety of slopes threatened by strong earthquakes. Based on the theory of modal analysis, the proposed approach analyzes the seismic landslide spectrum, including the calculation of the landslide intrinsic frequency and the investigation of the resonance effect. The concept and the solution of the resonance index (RI) of the seismic landslide are also proposed. By using the VC++ computer language, corresponding dynamic finite element program, namely Analysis of Seismic Landslide Spectrum (ASLS), is developed. To verify the proposed method, three examples are presented: a fixed-end beam, a specially designed landslide vibration experiment, and the largest landslide triggered by the 2008 Wenchuan earthquake. The obtained numerical and experimental results show that the proposed method can effectively evaluate the safety of seismic landslides. It is suggested that the resonance phenomenon of landslides should be considered in the landslide treatment and the seismic design.

A discontinuous numerical model to simulate rock failure process

Due to the difficulty of the classical fracture mechanics in dealing with multicrack coalescence, the simulation of jointed rock failure has remained a worldwide problem since the middle of the last century. Through a nearly 10-year effort, we have developed a novel but simple discontinuum-based approach, namely DDARF (discontinuous deformation analysis for rock failure), to simulate the progressive failure process of jointed rock mass. In the proposed method, by adopting the FE adaptive mesh generation technique—the advanced front method, the computational model of triangular DDA block system is automatically established. Also, the randomly distributed mechanical parameters statistically satisfying Weibull’s law are assigned to the blocks to simulate the heterogeneity of rock mass. In the generating process of the block system, numerous artificial joints come into being. These artificial joints provide the potential paths along which the cracks generate and propagate. The two blocks beside an artificial joint are glued together through adhesive algorithm, and if the glue is invalid, the artificial joint will break and turn into a real crack. In this way, the rock fragmentation process can be simulated. The results of several verification examples indicate that the DDARF method can simulate the whole process of rock fragmentation, and is suitable for cases of intact rock, rock mass with non-penetrative joints, and even blocky rock.

Mechanism of the Mudstone Tunnel Failures Induced by Expansive Clay Minerals

Expansive clay minerals can be a serious threat to underground rock structure because of their swelling behavior when absorbing water. Roof and wall collapse as well as large deformation were observed in Xiaotun Coal Mine, Guizhou Province, China. This paper studies the characteristics of expansive clays in order to understand the mechanism of the mudstone tunnel failures in the mine. The physical and mechanical properties of the tunnel surrounding rock samples, including mudstone, silty mudstone, argillaceous siltstone and fine sandstone were determined. X-ray diffraction analysis was conducted to determine the mineralogical composition while the scanning electron microscope was used to examine the internal structure of the different samples. The results indicate that the illite–smectite and the montmorillonite are the main minerals composing the rock samples. A series of micro-cracks and pores occur in the samples which suggest a good hydraulic conductivity. The results indicate that the mudstone has poorer mechanical properties in comparison to the fine sandstone. Also, the Flac3D numerical simulations were conducted and it was shown that the large deformations were consistent with the field observation due to weak mechanical properties of the surrounding rock under seepage action especially with the increase of water head and porosity. It is concluded that internal structure and mechanical strength of the mudstone is weakened by the illite–smectite and the montmorillonite mineral content as well as the combined action of underground water causing physical disintegration.

Prediction of tunneling hazardous geological zones using the active seismic approach

This paper presents a seismic method and a newly developed device to predict the hazardous geological zones ahead of a tunnel face. The equipment used to predict hazardous geological zones consists of three components: the seismic source, the acquisition unit, and the data processing unit. The following features enable this device to be a valuable tool in predicting hazardous geological zones: the precise trigger time detection; the application of semi-liquid couplant, which improves geophone coupling with the surrounding rock; the filtering of the prominent tunnel acoustic wave interference; and a software package of information on hazardous geological zones. Through extensive detection exercises of hazardous geological zones in the excavations of nearly 100 tunnel projects in China, it has been demonstrated that this device can satisfactorily predict hazardous geological zones, such as faults, water-bearing zones, karst caverns, etc., within 150 m in front of the tunnel faces.

Discontinuous deformation analysis and numerical manifold method

This Special Issue of the Geomechanics and Geoengineering journal is a collection of selected papers from the 10th International Conference on Analysis of Discontinuous Deformation (ICADD 10) held in Honolulu, Hawaii, USA, in December 2011, which focus on the recent development and practical application of discontinuous deformation analysis (DDA) and numerical manifold method (NMM). The DDA and NMM are numerical methods, specifically developed for geomechanics to handle the discontinuous material response, which have been widely applied in geoengineering such as stability analysis of tunnels and slopes, rock fall analyses and earthquake engineering. Since the pioneering work of Dr. Genhua Shi on DDA in 1985, there have been many advances to enrich its abilities for handling deformable blocks, cracking propagation, nonlinearity analysis, etc. The eight papers selected for this special issue cover interesting practical applications of DDA and NMM, e.g. the stability analysis of slopes and tunnels using DDA by Shi, the earthquake response analysis and maintenance of ancient world heritage masonry structures in UNESCO activities by Ohnishi et al. and the rockfall analysis using 3D DDA with GIS supported by Zheng et al. Useful computational algorithms such as fast contact detection based on the hashing method for the NMM and crack propagation enrichment of the DDA are also presented. In summary, this Special Issue is a valuable collection which can reflect the latest application and theoretical developments of DDA and NMM. It would be useful for researchers who are interested in discontinuous numerical methods and its engineering application. The Guest Editors wish to acknowledge the authors preparing these papers by extending their conference papers and the reviewers for maintaining a high standard of assessment for these papers.

Generating Irregular Models for 3D Spherical-Particle-Based Numerical Methods

The realistic representation of an irregular geological body is essential to the construction of a particle simulation model. A three-dimensional (3D) sphere generator for an irregular model (SGIM), which is based on the platform of Microsoft Foundation Classes (MFC) in VC