Zongqing Zhou

An Attribute Synthetic Evaluation System for Risk Assessment of Floor Water Inrush in Coal Mines

An attribute synthetic evaluation system was combined with attribute mathematical theory and the analytic hierarchy process (AHP) to evaluate the risk of floor water inrush in coal mines. The evaluation indices of floor water inrush were divided into continuous variable indices, which were quantitatively graded according to floor water inrush risk and discrete variable indices, which were qualitatively graded by expert opinion. Single index attribute measurement functions were constructed to calculate the membership degree of the continuous variable indices. The membership degree of the discrete variable indices were evaluated using expert opinion eliciting techniques, such as the Delphi method. The contribution weighting of the evaluation indices were rationally distributed by the AHP. A confidence criterion was applied to discern the risk of floor water inrush. These results were compared with those from a secondary fuzzy comprehensive evaluation; the results from the present method agrees well with field-observed results. This approach provides a referential methodology for engineers to systematically assess and manage risk of floor water inrush in coal mines.ZusammenfassungEin attributsynthetisches Bewertungssystem wurde mit attributmathematischer Theorie und dem analytischen Hierarchieprozess kombiniert, um das Risiko von Liegendwassereinbrüchen im Kohlenbergbau zu bemessen. Kennziffern für Liegendwassereinbrüche wurden in kontinuierliche Variable, welche quantitativ nach dem Liegendwassereinbruchsrisiko klassiert wurden, und in diskrete Variable unterteilt. Die Letztgenannten wurden nach Expertenbefragung gestaffelt. Funktionen einzelner Indexattributmessungen wurden erstellt, um den Grad der Gruppenzugehörigkeit der Kennziffern kontinuierlicher Variabler zu berechnen. Der Grad der Gruppenzugehörigkeit der Kennziffern diskreter Variabler wurde mittels Techniken der Expertenbefragung evaluiert, wie etwa der Delphimethode. Die Gewichtung des Anteils der Bemessungskennziffern wurde mit dem analytischen Hierarchieprozess rational verteilt. Ein Konfidenzkriterium wurde angewandt, um das Risiko eines Liegendwassereinbruches zu erkennen. Die Ergebnisse wurden mit jenen verglichen, welche mittels sekundärer ganzheitlicher Fuzzy-Bewertung erstellt wurden; die Ergebnisse der vorgestellten Methode stimmt mit Feldbeobachtungen überein. Dieses Vorgehen stellt Ingenieuren eine Referenzmethode zur Verfügung, um das Risiko von Liegendwassereinbrüchen im Kohlenbergbau systematisch einzuschätzen und handzuhaben.ResumenUn sistema de evaluación sintética de atributos se combinó con la teoría matemáticas de atributos y el proceso analítico jerárquico (AHP) para evaluar el riesgo de irrupción de agua desde el piso en minas de carbón. Los índices de evaluación de irrupción de agua fueron divididos en índices variables continuos que fueron graduados cuantitativamente de acuerdo al riesgo de irrupción de agua desde el piso e índices variables discretos, que fueron graduados cualitativamente por opinión experta. Se construyeron funciones de medición de índices de atributos para calcular el grado de pertenencia de los índices variables continuos. El grado de pertenencia de los índices de variable discreta fue evaluado usando técnicas de opinión experta como por ejemplo, el método Delfos. El peso de la contribución de los índices de evaluación, fue racionalmente distribuido por el AHP. Un criterio de confidencia fue aplicado para discernir el riesgo de irrupción de agua. Estos resultados fueron comparados con aquellos obtenidos con una evaluación integral difusa; los resultados del método presentado aquí coinciden bien con los resultados observados en el campo. Esta aproximación proporciona una metodología referencial para ingenieros para relevar y manejar sistemáticamente el riesgo de irrupción de agua desde el suelo en minas de carbón.摘要基于属性数学理论和层次分析方法,提出了一种用于评价煤矿底板突水风险的属性综合评价系统。首先,将底板突水评价指标划分为连续型和离散型两类,连续型变量指标根据底板突水风险进行定量分级,离散型变量指标依据专家意见进行定性分级。其次,通过构建单指标属性测度函数,计算得到连续型变量指标的隶属度,并采用德尔菲法获得离散型变量指标的隶属度。然后,采用层次分析法构造判断矩阵来确定评价指标的权重,应用置信度准则确定底板突水的风险等级。最后,将本方法与二次模糊综合评价法的评价结果作对比分析,本方法评价结果与现场结果具有较好的一致性,为煤矿底板突水风险评估与管理提供了一种有效指导方法。

Risk assessment of water inrush in karst tunnels and software development

Water inrush makes time extended, instruments destructed, and casualty increased, which is the biggest threat for safe construction of tunnels in karst areas. A software system for risk assessment of water inrush was established with considering eight risk factors, including groundwater level, unfavorable geology, formation lithology, topography, strata inclination, excavation, advanced geological prediction, and monitoring. In the present software system, fuzzy mathematics and Analytical Hierarchy Process (AHP) were used to quantitatively describe the risk levels for each factor. The influence degree of each factor to water inrush was assigned an objective weight and a subjective weight, and the proportion of the two weights in the risk assessment was defined as weight distribution. The objective weights of the risk factors were obtained from more than 100 water inrush instances in karst tunnels, whereas the weight distribution was totally derived from expert field assessment and subjective weights were determined by using AHP in the risk assessment. Two case studies of karst tunnels were applied to check the reliability of the proposed software system, and the comparisons between the software assessment and practical excavation yield good consistency. Therefore, the software system can appropriately be used in practice to forecast water inrush in karst tunnels.

Hazard-based evaluation model of water inrush disaster sources in karst tunnels and its engineering application

Water inrush is one of the typical geological hazards that may occur during tunnel construction in a karst area. In this paper, a potential model is established based on attribute mathematics, to assess the risk of water inrush. First, the CaCO3 content of regional strong karst, thickness of the regional strong karst layer, groundwater recharge area, discharge of groundwater, average temperature characteristic, groundwater level, groundwater cycle characteristic, surface karst morphology, fault structure, fold structure, and monoclinal structure are chosen as evaluation indexes of water inrush based on the principles of scientificity, rationality, operability, and representativeness. Second, the objective weight calculation formula is used to calculate the weights of the evaluation indices, and attribute measurement functions of each evaluation index are constructed to reckon the attribute measurement of a single index and synthetic attribute measurement. Lately, the identification and classification of water and mud inrush hazard in tunnels have been performed using a confidence criterion. In this paper, hazard level is graded as one of four types. The hazard-based assessment methodology is applied to the construction site of the Jigongling Tunnel along the entire Fanba Expressway route, and the findings are compared against the site’s actual situation. The results of the engineering practice show that the evaluation result is consistent with the actual construction situation; thus, the method can provide scientific guidance for tunnel construction units.

Application of the comprehensive forecast system for water-bearing structures in a karst tunnel: a case study

While tunneling in karst terrains, engineers may encounter unpredictable well-developed karst conduits, which frequently lead to water inrush accidents. Geological processes significantly affect the varieties and characteristics of water-bearing structures. Therefore, a comprehensive system for water-bearing structure prediction is first put forward, and then the geological and hydrogeological engineering conditions of the Yuelongmen tunnel in Southwest China are analyzed. To accurately predict the geometric characteristics of water-bearing structures and their spatial relationship with the tunnel face, the transient electromagnetic method (TEM) and ground-penetrating radar (GPR) were comprehensively applied. Then, the induced polarization method (IP) was utilized separately to detect the three-dimensional position and spatial distribution pattern of the water-rich area. According to the comprehensive forecast conclusion, targeted boreholes were drilled, which were selected to verify the water-bearing structure in the survey area. The drilling and detection results matched. Furthermore, the curtain grouting method was adopted for the treatment of the water-rich area. By establishing a comprehensive prediction technology system with the principle of “from qualitative analysis to quantitative identification, from structure locating to the water-bearing structure discrimination, as well as from far and near,” this comprehensive prediction system was successfully put into practice in the karst tunnel in Sichuan; it can play a guiding role in similar projects.

Field, experimental, and numerical investigation of a rockfall above a tunnel portal in southwestern China

Combining the results of detailed field investigation, laboratory tests, and numerical simulations, this paper studies the rockfall problem above a tunnel portal. The mechanism of potential rock instability was analyzed, and model tests were conducted based on geological conditions and described in detail, so as to study the restitution coefficients used in programs simulating rockfall trajectory. Improvements in the tests were made in terms of experimental techniques and creative similar materials. A newly developed test bench was built by steel frames and can be assembled or disassembled at will according to requirement of model size. An innovative block-release device was adopted and controlled by computer to change the release position of block. During the model construction, the slope and blocks were fabricated with similar materials developed through quantities of mixing proportion tests. Then experiments were conducted with varied shape, mass, and release height of blocks to clarify their effect on restitution coefficients. Results indicate that restitution coefficients are apparently related to these factors and their values decrease when block mass and releasing height increase. Restitution coefficients of the wedge block are larger than those of a sphere or cuboid block. Subsequently, numerical simulations adopting the calibrated parameters were performed, and the velocities, bounce heights, and kinetic energies of rockfall along the slope profiles were obtained. Based on the research, this paper provides a useful reference for practical remediation design.

Analysis on the Precursor Information of Water Inrush in Karst Tunnels: A True Triaxial Model Test Study

Water inrush in karst tunnels usually results in casualties, equipment damage, project delays and other serious consequences. An important measure to ensure the safety of tunnel construction is to provide accurate prediction of water inrush during tunnel excavation. To study the stability of the surrounding rock under effect of a water-bearing cave in front of the tunnel face, a true triaxial geomechanical model test was carried out based on the engineering background of the Xiema Tunnel in Chongqing Province. The response regularities of multivariate physical information of the surrounding rock during rock failure and water inrush were obtained by monitoring the displacement, stress and seepage pressure of different monitoring sections. The results show that some internal connections exist among the kinds of physical information. When the tunnel face was adjacent to the disaster source, the change of displacement and stress was in a decreasing trend, and the seepage pressure increased first and then decreased during the tunnel excavation. In addition, by fusion analysis, the sensitivity priority of precursor information for a rock failure and water inrush disaster in karst tunnels was summarized as stress, displacement and seepage pressure. Finally, the theoretical basis of the prediction of water inrush in karst tunnels had been established, which proved the feasibility of predicting disasters according to the precursor information.

Numerical Analysis of Surrounding Rock Stability in Super-Large Section Tunnel Based on Hydro-Mechanical Coupling Model

The groundwater seepage has an important effect on the stability of tunnel surrounding rock. Considering the effect of seepage, a hydro-mechanical coupling mathematical model is developed based on stress deformation equation of rock mass, flow equation of porous media and relation equation of hydro-mechanical coupling. In connection with the leakage situation of Jiangshuiquan Tunnel with super-large section, a geometry model of tunnel construction is built by COMSOL software platform. Furthermore, the hydro-mechanical coupling model is embedded in the PDE module of the software for numerical simulating the construction process of super-large section tunnel. Consequently, the surrounding rock displacement deformation under is discussed and verified by the data measured in field. Besides, the distribution characteristics of surrounding rock stress, seepage pressure and velocity are deeply analyzed. Results indicate that the displacement calculated by hydro-mechanical coupling model is well consistent with the site monitoring data and is greatly more than that of uncoupling model. After tunnel excavation, stress concentration phenomenon occurs around the cavern, especially at the arch foot part of the outer side wall, so the parts should be viewed as the key supporting part. The groundwater flows into the cavern and the surrounding pore water pressure is unloaded. A large hydraulic gradient occurs in the vault of the tunnel, prone to incur major engineering accidents; while the hydraulic gradient at vault is relatively small and usually has little harmful to engineering safety. The conclusion may provide guidelines for similar tunnel engineering construction.

Design of a Displacement Monitoring System Based on Optical Grating and Numerical Verification in Geomechanical Model Test of Water Leakage of Tunnel

The displacement monitoring of surrounding rock is necessary in geomechanical model test. However, traditional monitoring technology is difficult to meet the needs of displacement monitoring in small geological model tests. To solve the problems mentioned above, the authors developed a multi-point displacement monitoring system based on optical grating including multi-point extensometer, grating scale and multi-channel data acquisition system. Firstly, 3D anchor head with six barbs is designed and connected to the grating ruler by the steel wire, which proved to be rather sensitive to the rock deformation. Additionally, the displacement data collected can be transformed into electrical signal, which can be obtained by multi-channel acquisition system. Finally, the system was used in the model test of tunnel water leakage. The designed anchors were pre-embedded in some key monitoring points around the section in order to investigate measurement of displacements in the lining during the loading of geostress and hydraulic pressure. Afterward, FLAC3D, the finite-difference method, is adopted to simulate the whole process of physical model test and to compare with the experimental results. The results show that the experimental data was in good agreement with the numerical simulation results. In conclusion, the multi-point displacement monitoring system based on optical grating has higher precision and can be widely used in the physical model test of geotechnical engineering.

Numerical Investigation to Influence of Perforation Angle on Hydraulic Fracturing Process

Considering the heterogeneous characteristics of rock in a meso-scale, a flow–stress–damage coupling model was created based on the finite element method firstly. Then the hydraulic fracturing process of the heterogeneity rockmass under different perforation angles were investigated by the RFPA2D-flow software. The numerical simulation results show that the maximum principle stress controls the fracture propagation direction no matter how perforation angle changes. With the increase of the perforation angle, a turning fracture becomes more obvious and the turning distance bigger. The best perforation angle area is from 0° to 30°. Above results are of some significance to hydraulic fracturing tests and engineering practice.

A New Advance Classification Method for Surrounding Rock in Tunnels Based on the Set-Pair Analysis and Tunnel Seismic Prediction System

An advance optimized classification method is proposed to accurately predict the surrounding rock classification based on set pair analysis (SPA) and tunnel seismic prediction (TSP). Several factors that greatly affect rock mass classification are selected as evaluation indices of SPA based on analysis of TSP data. Evaluation indices are divided into five grades according to its response characteristics of seismic wave field, and their membership functions are proposed by using frequency statistical method. Entropy weight method is adopted to determine the weights of evaluation indices, and a SPA model is established for optimized classification of surrounding rock. Engineering application of Shimenya Tunnel of Yi-Ba Highway is taken as a case study, and proved that the evaluation indices are easy to obtain and the evaluation results are accurate and reliable. The SPA–TSP method can be further used for other tunnel engineering.