Huang Run-qiu

Geo-engineering lessons learned from the 2008 Wenchuan earthquake in Sichuan and their significance to reconstruction

The 2008 Wenchuan earthquake in Sichuan of China was the result of quake-triggering along an active several hundred-kilometer-long fault. The subsequent landslides and debris flow geohazards are dominating factors in planning post-disaster recovery and rebuilding. This paper presents recommendations for coping with large-scale geohazards and disasters. It is essential to establish a national emergency management system for huge scale catastrophe and earthquake precursor identification. Town construction must be kept away from active faults, especially to improve town safety in areas with high risk of seismic and geological hazards, and it is important to improve geohazard investigation and remediation for mountain areas that have become loosened by earthquake activity. Geological factors must be better understood to reduce direct and secondary risks and effects of earthquakes. Site selections for public relocation require clear and informed analysis of geological and social risk reduction, so that relocation, infrastructure reconstruction, and commemorative relic-sites can be protected.

Application of Three-Dimensional Laser Scanning and Surveying in Geological Investigation of High Rock Slope

Abstract The appearance of 3D laser scanning technology is one of the most important technology revolutions in surveying and mapping field. It can be widely used in many interrelated fields, such as engineering constructions and 3D measurements, owing to its prominent characteristics of the high efficiency and high precision. At present its application is still in the initial state, and it is quite rarely used in China, especially in geotechnical engineering and geological engineering fields. Starting with a general introduction of 3D laser scanning technology, this article studies how to apply the technology to high rock slope investigations. By way of a case study, principles and methods of quick slope documentation and occurrence measurement of discontinuities are discussed and analyzed. Analysis results show that the application of 3D laser scanning technology to geotechnical and geological engineering has a great prospect and value.

Cyclic load testing of pre-stressed rock anchors for slope stabilization

The objective of this research was to assess the characteristics of seismic induced damage and the deformation patterns of pre-stressed cement-grouted cables that are used for rock slope stabilization projects subjected to quasi-static cyclic loading. The experimental configuration includes the installation of 15 pre-stressed cables in a slope model made of concrete blocks (theoretically rigid rock mass) on top of a pre-existing sliding surface. The study showed that: (i) The pre-stressed cables exhibited great seismic performance. Rapid displacement of the model blocks was observed after the complete loss of the initial pre-stress load under continued applied cyclic loads and exceedance of the state of equilibrium, which implies the higher the initial pre-stress load, the better the seismic performance of the rock anchor; (ii) The failure of the pre-stressed cables was due to fracture at the connection of the tendons and cable heads under cyclic loading. The sequence of failure had a distinct pattern. Failure was first observed at the upper row of cables, which experienced the most severe damage, including the ejection of cable heads. No evidence of de-bonding was observed during the cyclic loading; (iii) The stress distribution of the bond length for pre-stressed cables was highly non-uniform. High stress concentrations were observed at both the fixed end and the free end of the bond length both before and immediately after the state of equilibrium is exceeded. The results obtained can be used to evaluate the overall performance of pre-stressed rock anchors subject to seismic loading and their potential as rockfall prevention and stabilization measures.

Engineering geological classification of the structural planes for hydroelectric projects in Emeishan Basalts

The scale and characteristics of rock mass are important indexes of the rock mass structural plane classification. This paper firstly analyzes the spatial distribution characteristics, the structural plane types (original structural plane, tectonic structural plane and hypergenic structural plane) and the associated features of the Emeishan basalts and then studies the classification schemes of the built hydropower structure planes of different rock areas (the east district, the central district and the west district) in the Emeishan basalt distribution area, Southwest China. Based on the analysis and comparison of the scale and the engineering geological characteristics of the typical structure planes in the basalt hydroelectric Stations, the types o f structural planes are used in the first order classification. The secondary order classification is made by considering the impact factors of rock mass quality, e.g., the state of the structural planes, infilling, joint opening, extending length, the grade of weathering and strength. The engineering geological classification for Emeishan basalt is proposed. Because there are no evidences of a large structure presenting in study area, the first-order (I) controlling structural planes do not appear in the classification, there only appear II, III, IV and V grade structural planes influencing the rock-mass quality. According to the different rock-block types in bedding fault zone, the second-grade (II) structural planes consisted of bedding fault zone is further classified into II1, II2 and II3. The third-grade (III) structural planes constructed by intraformational faulted zones are not subdivided. According to the different characteristics of intrusion, alteration and weathering unloading structural planes, the IV grade structure plane is divided into IV1, IV2 and IV3. According to the development characteristics of joints and fractures, the V grade structure plane is divided into fracture V1 and columnar joint V2. In all, the structural planes are classified into four groups with nine subsets. The research proposes the engineering geological classification of the structural plane for the hydropower project in the Emishan basalts, and the result of the study has a potential application in similar regions.

The formation and evolution of the Qiaojia pull-apart basin, North Xiaojiang Fault Zone, Southwest China

Sedimentary sequences with drastic thickening over short distances have been observed in Qiaojia County, Yunnan Province, Southwest China. These are related to a pull-apart basin controlled by the Xiaojiang strike-slip fault. Our field investigations include determining the surface characteristics of the Qiaojia basin which consists of three terrace sequences and a series of alluvial fans. Several drill holes were used to reveal the internal structure of the basin. The results suggest that the basinal sediments are over 300 m thick. From bottom to top, they can be classified into five different units. We inferred that the units of lacustrine sediments are deposited in a paleo-lake which was formed by a paleo-landslide. Accelerator mass spectrometry radiocarbon dating (AMS 14C dating) was used to estimate the ages of the terrace and lacustrine sediments. We use the results to infer that the paleo-lake has existed about 15,000 years and that the Qiaojia basin was uplifted at an average rate of 3.3 mm/a. Furthermore, we then model the evolution process of the basin and interpreted 6 phases of development.

Influence of the characteristics of fault gouge on the stability of a borehole wall

How to find more effective way to stabilize the borehole wall in the fault gouge section is the key technical challenge to control the stability of the borehole wall in the Wenchuan fault gouge section during the process of core drilling. Here we try to describe the characters of deep fault gouge in fracture zones from the undisturbed fault gouge samples which are obtained during the core drilling. The X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF) and Scanning Electron Microscope (SEM) provided the detailed information of the fault gouge’s microscopic characteristics on the density, moisture content, expansibility, dispersity, permeability, tensile strength and other main physical-mechanical properties. Based on these systematic experimental studies above and analysis of the fault gouge instability mechanism, a new technical procedure to stabilize the borehole wall is proposed — a low water and a low loss low permeability drilling fluid system that consists of 4% clay + 0.5% CMC-HV + 2% S-1 + 3% sulfonated asphalt + 1% SMC + 0.5% X-1 + 0.5% T type lubricant + barite for core drilling in fault gouge sections.

Solutions for stability of anchored earth slopes subjected to seismic loading

The limit analysis approach is paid more attention to in the stability analysis of slopes subjected to seismic loading. However, the solutions obtained from the approaches are in general limited to a designated slope or the same kind of slopes. It seems that a wide applicability of the solutions in their present form is rather difficult. Based on the kinematic theorem and the assumption of combined log-spiral rotational failure mechanism, the integral formulation for expressing the rate of external work rate due to soil weight and seismic loading is derived under the framework of pseudo-static method considering the complex geometrical configurations and the multilayer soils in slopes with multi-row anchors. Further, the work-energy balance equation is established, and the analytical expressions for the global factors of safety (FS) and the yield acceleration coefficient of anchored slopes are obtained by using the strength reduction technique combined with the optimization method. Moreover, the permanent displacement with Newmarks method is also solved. Several representative examples are employed to validate the analytical solutions, and some comparisons of the FSs and the corresponding critical sliding surfaces obtained by various methods are also made. The results show that the analytical approach can yield the high-accuracy solutions and is widely applicable to the seismic stability analysis of complex slopes with multi-row anchors. Finally, a practical case is analyzed using the proposed approach. ©2016, Editorial Office of Chinese Journal of Geotechnical Engineering. All right reserved.

Earthquake Damage Zone GIS Modelling: A Modulation Between Co-Seismic Deformation and Landslide Susceptibility

In mountainous regions, earthquake events are typical of naturally-occurring multiple hazards and are frequently the trigger for cascade effects which range from the destruction of the initial shock, to extensive and complex slope failures in the immediate, short and very long-term. The conventional seismic intensity zonation method cannot adequately characterise both the current damage level and long-term geohazards, while detailed information is critical in guiding post-disaster mitigation and regional development. In studying the most severely damaged Beichuan area by the Mw7.9 Wenchuan earthquake, we proceeded with a qualitative numerical method for earthquake damage zone mapping which is novel in its integration of the multi-variable GIS modelling of geohazard susceptibility with co-seismic deformation via a modulation. This new model, we call it earthquake damage, characterise not only the destruction immediately after an earthquake but also the potential for future damage as the consequences of the earthquake.