工程地质条件对爆破坝体块度的影响

定向爆破法直接筑坝,成本低,见效快,但处理坝体的渗漏问题较复杂,而坝体内破碎岩块块度级配对坝体渗漏特性的影响最大。本文主要结合柴石滩野外大型爆破试验的资料,通过分析破碎岩块的表面特征(即岩块表面的新鲜破裂面比例与岩块粒径的对应关系),以及爆破破岩作用机制,详细讨论了各种工程地质条件对爆破块度的影响关系,并推断出影响爆堆内细粒级含量的主要工程地质因素是岩石的力学强度,而不是裂隙发育程度,裂隙发育程度仅对爆堆块体级配关系起重要影响。最后还讨论了岩体结构对爆块形状的影响,认为厚层状或完整块状结构的岩体,易爆碎成三维相近的多面体爆块,而爆块越接近圆粒状,爆堆密实性越好,针、片状爆块堆积密实性最差。

A modified Hoek-Brown failure criterion considering the damage to reservoir bank slope rocks under water saturation-dehydration circulation

After water is impounded in a reservoir, rock mass in the hydro-fluctuation belt of the reservoir bank slope is subject to water saturation- dehydration circulation （WSDC）. To quantify the rate of change of rock mechanical properties, samples from the Longtan dam area were measured with uniaxial compression tests after different numbers （1, 5, 10, 15, and 20） of simulated WSDC cycles. Based on the curves derived from these tests, a modified Hock- Brown failure criterion was proposed, in which a new parameter was introduced to model the cumulative damage to rocks after WSDC. A case of an engineering application was analyzed, and the results showed that the modified Hock-Brown failure criterion is useful. Under similar WSDC-influenced engineering and geological conditions, rock mass strength parameters required for analysis and evaluation of rock slope stability can be estimated according to this modified Hoek-Brown failure criterion.

A review of the geomechanics aspects of a double fatality coal burst at Austar Colliery in NSW,Australia in April 2014

A coal burst occurred on 15 April, 2014 at the Austar Coal Mine, located west of Newcastle, NSW,Australia. The burst resulted in fatal injuries to two men working as part of the mining crew at the development face. At the time, a continuous miner was being used to mine a longwall development gate road through heavily structured coal, at a depth of approximately 550 m. A number of pre-cursor bumps had occurred on previous shifts, emanating from the coal ribs of the roadway, in proximity to the coal face.This paper reviews the geological, geotechnical and mining conditions and circumstances leading up to the coal burst event; and presents and discusses the available evidence and possible interpretations relating to the geomechanical behaviour mechanisms that may have been critical factors in this incident. The paper also discusses some key technical and operational considerations of ground support systems and mining practices and strategies needed for operating in such conditions in the future.

Support technology for mine roadways in extreme weakly cemented strata and its application

For the engineering geology conditions of bad mine roadway roof and floor lithology in extremely weak cemented strata, the best section shape of the roadway is determined from the study of tunnel surrounding rock displacement, plastic zone and stress distribution in rectangular, circle arch and arch wall sections, respectively. Based on the mining depth and thickness of the coal seam, roadway support technology solutions with different buried depth and thickness of coal seam are proposed. Support schemes are amended and optimized in time through monitoring data of the deformation of roadway, roof separation, l-beam bracket, bolt and anchor cable force to ensure the long-term stability and security of the roadway surrounding rock and support structure. The monitoring results show that mine roadway support schemes for different buried depth and section can be adapted to the characteristics of ground pressure and deformation of the surrounding rock in different depth well, effectively control the roadway surrounding rock deformation and the floor heave and guarantee the safety of construction and basic stability of surrounding rock and support structure.

Development of fractures in soft rock surrounding a roadway and their control

As the excavation of roadway, new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks. Eventually, fracture zone and bed separation are formed in rocks because of the developed fractures. Therefore, mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway. The surrounding rocks of main haulage road- way in a certain coal mine is so broken and loose that the supporting is very difficult. Based on compre- hensive anal[ysis of the engineering geological conditions, a sight instrument was used to observe the fractures of internal surrounding rocks, Four indices, i.e., the width of fracture zone W, the number of fractures n, the width of fractures d and rock fracture designation RFD, are put forward to evaluate the fracture dewelopment. According to the evolution rules of the soft rock roadway from this paper, control principles by stages and by regions are presented through the research. At the same time, the best time of grouting reinforcement is determined on the basis of fracture saturation. Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.

Applications of Pre-Geological Prediction in Tunnel Construction

Pre-geological prediction (PGP) is defined as the prediction of engineering geologic condition and hy-drogeological condition certain distance ahead of the working face. The purpose of this paper is to introduce mainlygeologic survey before and in excavation, to clarify their emphasis on PGP. At the same time, the technique is appliedto an engineering case, the longest highway tunnel in Gansu province. Data of geological survey of outside tunnels,sound wave detection, and geologic sketch for both tunnel face and sidewalls within the tunnel are analyzed. Afteranalyzing these data, long-term pre-geological prediction forecasting basic geological conditions of fault 4 such aslithology, scope, location, etc., and short-term and more accurate pre-geological prediction are reported.

Geometrical and Geotechnical Characteristics of Landslides in Korea under Various Geological Conditions

The goal of this study is to determine the geometrical and geotechnical characteristics of landslides under various geological conditions using detailed field surveys, laboratory soil tests and precipitation records. Three study areas are selected to consider different rocks, including gneiss in Jangheung, granite in Sangju and sedimentary rocks in Pohang, South Korea. Many landslides have occurred in these three areas during the rainy season.Precipitation records indicate that landslides occurring in the gneiss area of Jangheung and granite area of Sangju may be influenced by the hourly rainfall intensity rather than cumulative rainfall.However, landslides occurring in the sedimentary rock area of Pohang may be influenced by hourly rainfall intensity and cumulative rainfall. To investigate the factors that influence these types of landslides, a detailed landslide survey was performed and a series of laboratory soil tests were conducted.According to the detailed field survey, most landslides occurred on the flanks of mountain slopes, and the slope inclination where they occurred mostly ranged from 26 to 30 degrees, regardless of the geological conditions. The landslide in the gneiss area of Jangheung is larger than the landslides in the granite area of Sangju and sedimentary rock area of Pohang.Particularly, the landslide in the sedimentary rock area is shorter and shallower than the landslides in the gneiss and granite areas. Thus, the shape and size of the landslide are clearly related to the geological conditions. According to the integrated soil property and landslide occurrence analyses results, the average dry unit weight of the soils from the landslide sites is smaller than that of the soils obtained from the nonlandslide site. The average coefficient of permeability of soils obtained from the landslide sites is greater than that of soils obtained from the non-landslide sites with the same geology. These results indicate that the soils from the landslide sites are more poorly graded or looser than the soils from the non-landslide sites.

Developing a risk assessment system for gas tunnel disasters in China

Gas disasters always restrict the tunnel constructions in mountain area, which becomes a major geological barrier against the development of underground engineering. China is rich in coal resources and has a large amount of gas with a wide range of distribution. However, China experienced not only adverse effects on coal mining but also gas disasters in underground engineering construction, such as tunnels and chambers. With the increased number of tunnels passing through coal-bearing strata, the incidence of gas accidents is also rising. Therefore, the significance of preventing and mitigating gas disasters should be emphasized, and an effective risk assessment method for gas disasters should be established. On the basis of research on over 100 gas tunnels in China, a relatively ideal gas disaster risk assessment method and system for tunnels are established through the following measures. Firstly, geo-environmental conditions and gas situations were analyzed during construction. Secondly, qualitative analysis was combined with quantitative analysis. Finally, the influencing factors of gas disasters, including geological conditions, gas,and human factors, were investigated. The gas tunnel risk assessment system includes three levels:(1) the grading assessment of a gas tunnel during the planning stage,(2) the risk assessment of gas tunnel construction during the design and construction stages,(3) the gas tunnel outburst risk assessment during the coal uncovering stage. This system was applied to the dynamic assessment of gas disaster during the construction of the Zipingpu tunnel of Dujiangyan–Wenchuan Highway(in Sichuan, Southwest China). The assessment results were consistent with the actual excavation, which verified the rationality and feasibility of the system. The developed system was believed to be back-up and applied for risk assessment of gas disaster in the underground engineering construction.

Risk assessment study on bridge foundation in deep overlying stratum

Based on the analysis about the hydrogeological conditions and engineering geological conditions, this paper makes analysis on the possible risks of the deep overlying stratum foundation and establishes the risk evaluation index system during the foundation operating period. Such methods as analytic hierarchy process （AHP） , Delphi method and fuzzy comprehensive evaluation method are adopted to make the quantitative analysis on the risk factors and establish the risk judgment model. According to the actual engineering of Taizhou Bridge, the paper evaluates the risk of the foundation during the operating period at the condition of deep overlying stratum. The evaluation results can provide the reference for the risk management of the bridge foundation durin~ the ooerating period.

Crucial problems on security assessment of a building site adjacent to an excavated high slope

The subject of this work is the assessment on the stability of an excavated high slope in order to insure the security of the building site adjacent to the slope, which is frequently encountered in town construction in mountainous areas due to terrain limit. On the base of some typical engineering cases in Chongqing, several crucial problems on security assessment of building site adjacent to an excavated high slope, including the natural geological conditions and man-destroyed degree, engineering environment, potential failure pattern of the high slope, calculation parameters and analysis methods, are roundly discussed. It is demonstrated that the conclusion of security assessment can be determined according to the aspects above-mentioned, and the security assessment is one of the fundamental data to insure the safety of the related construction, site and buildings.

Engineering geological conditions and features of geologic hazards in Wudongde reservoir of Jinshajiang River valley

There is a great difference between the distribution and evolvement characteristics of slope geological hazard in the same geographical location and climatic conditions,taking the similar structural-genetic connection in Wudongde reservoir area of Jinshajiang River valley for example. In all engineering geological conditions,the chronologic age and attitude of strata,and the lithologic association factors control the distributions and evolvement characteristics of slope geological hazard in the studied area. The study shows that the slopes in geological evolution are in different stages. The conclusion helps to understand the types and the intensity of geological disasters.