Study on engineering-hydrogeological problems of hydroelectric project

Engineering-hydrogeological problems arise from the interaction between engineering activities and geological environment, in which rock-soil mass and groundwater are especially important constituents. However, up-to-date research on them is relatively dispersive and simple due to their complexity and lack of comprehensive and systematic study methods. Starting from geological analysis of mechanism to geological model based on geological regularities, the paper predicts the tendency of geological evolvement and puts forward proper measures to solve problems. In this paper, elevated water-sensitive structure in rock-soil mass, which mainly causes engineering hydrogeological problems, and problems in hydropower is discussed based on unique construction in Chinese Western hydropower projects. Engineering hydrogeological problems are reservoir induced earthquakes leakage from reservoir bottom in karst, stability of high slope at reservoir banks, sliding of dam foundation and dam abutment, and confined water at key positions which are introduced and determined by using water-sensitive factors(or structure) according to special hydrogeological conditions.

Extraction and imaging of indicator elements for non-destructive,in-situ,fast identification of adverse geology in tunnels

The lag in quantitative methods and detection techniques for geologic information has resulted in time-consuming and human-experienced geologic analysis in tunnels.Geochemical indicators of rocks can be used to identify adverse geology and to explain the intrinsic causes of damage to normal rocks.This study proposes a method to identify adverse geology by extracting and imaging the indicator elements.The mapping relationship between rock components and geologic bodies is quickly determined by indicator element extraction based on factor analysis,and then the data are gridded for image output.The location and size of the target adverse geology are visually identified through the distribution images of the indicator elements,thus reducing data dimensions and analysis time.A non-destructive,in-situ and fast element detection technique in tunnels was adopted to speed up the process of geology identification.The accuracy of the detection was validated by comparing field and laboratory test results.This study further confirms and refines the previous research,and the results provide references for geological,mining and underground projects.

Total loads modeling and geological adaptability analysis for mixed soil-rock tunnel boring machines

Rock-soil interface mixed ground(RSI)is often encountered in tunnel construction.The excavation loads of tunnel boring machines(TBMs)are controlled by the interaction characteristics between TBM and rock/soil layers.The different properties of rock and soil cause the varying interaction range and stress distribution.Currently,there have been several studies available to estimate excavation loads under RSI,and the conclusion is that the total loads increase with increasing the rock layer proportion in the excavation face.However,the previous studies cannot take the difference of rock/soil properties into account,except for the calculation of cutters loads.Therefore,the interaction characteristics between RSI and TBM is unclear.This paper analyzes the interaction characteristics between TBM’s main components and complex geological conditions(e.g.,layered soil,layered rock,and RSI condition).A model is proposed to calculate the total thrust and total torque assuming quasi-static equilibrium of the tunneling equipment.The rationality and applicability of the model are discussed and verified by two typical projects.Furthermore,the geological adaptability is discussed in terms of the excavation difficulty and the matching relationship between total torque and total thrust.The results indicate that when the rock layer proportion in the excavation face increases,the reduction of overall extrusion and friction loads is 1.5 times higher than the increase of disc cutters breaking load.The total loads and the ratio of the total torque to total thrust decrease approximately linearly.There is a power function relationship between the excavation difficulty index and the penetration depth.The results of this study provide an important reference for the total loads design of equipment propulsion systems and the parameter adjustment during tunnel construction.

Research on the relationship between geophysical structural features and earthquakes in Mid-Yunnan and the surrounding area

In this study, we analyzed the gravity and, magnetic characteristics, and the occurrence of a fault zone and discussed the relationships between the two locations. The results reveal that the subsurface structures strikes are different compared with those in the research region. In other words, the geophysical advantageous directions from the gravity and magnetic anomalies are not the same as those caused by the surface structures. The local horizontal gradient results from the gravity and magnetic anomalies show that the majority of earthquakes occur along an intense fault zone, which is a zone of abrupt gravity and negative magnetic change, where the shapes match very well. From the distribution of earthquakes in this area, we find that it has experienced more than 11 earthquake events with magnitude larger than Ms7.0. In addition, water development sites such as Jinshajiang, Lancangjiang, and the Red River and Pearl River watersheds have been hit ten times by earthquakes of this magnitude. It is observed that strong earthquakes occur frequently in the Holocene active fault zone.

3D Seismic Attributes for Structural Analysis in Compressional Context: A Case Study from Western Sichuan Basin

Compressional region usually forms complex thrust faults system, which is difficult to identify using traditional migration profiles. The successful application of three-dimensional（3D） seismic attributes analysis greatly reduces the difficulty, and improves the accuracy and efficiency of seismic interpretation and structural analysis. In this paper, we took Qiongxi area in the compressional region of western Sichuan as an example, using two 3D seismic attributes, coherence and instantaneous phase, to identify fault assemblages and variations both vertically and laterally. The results show that the study area mainly consists of NS-, NE- and NEE-trending faults. The NS-trending faults are the largest and have a component of sinistral slip controlling the formation of NEE-trending faults, while the NE-trending faults are intermediate in scale, formed earlier and were cut by the NS-trending faults. Our results demonstrate that using seismic attributes for structural analysis have the following advantages：（1） more details of major fault zones,（2） highlighting minor faults which are hardly traced in seismic migration cube, and（3） easier acquisition of accurate fault systems. The application of seismic attributes provides a new idea for deciphering fine and complicated structures, and will significantly contribute to the development of objective and precise geological interpretation in the future.

A Fast Evaluation and Research Method for Exploration Potential of Oversea Basins

Oversea hydrocarbon exploration always faces some problems,such as multiple basin types,different exploration prospects,various exploration degrees,diverse data quantities and geological recognitions.This paper focuses on overseas basins with different exploration degrees and offers a new evaluation system and research method for fast evaluation and risk analysis on hydrocarbon potential.Based on the theory of probability,this new evaluation system evaluates each parameter and core accumulation factor with comprehensive and quantitative assignment,to accelerate geological evaluation.In addition,this paper suggests that source rock evaluation should be the core criterion in screening evaluation of poorexplored basins,and also proposes that both the exploration potential and geological recognition should drive the evaluation for basins with high exploration degrees.This new system and method,which is an effective system for fast basin evaluation,is suggested to be used in oversea evaluation and decision-making objectively,scientifically and efficiently.