Zhenhao Xu

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.

Application of comprehensive prediction method of water inrush hazards induced by unfavourable geological body in high risk karst tunnel: a case study

ABSTRACT While tunnelling in karst terrains, karst fissure water may endanger the safety of tunnel engineering and cause geological disasters such as water inrush. To ensure the safety of tunnel construction, in investigation stage, engineering geological and hydrogeological conditions of Jigongling Tunnel was analysed firstly. In design stage, a reasonable prediction method combining with optimization principle was selected to calculate the water inflow according to the geological and hydrogeological conditions analysed in the investigation stage. Then the advanced geological prediction was divided into different classes based on the water inflow. To make an accurate prediction, tunnel seismic prediction method, transient electromagnetic method, induced polarization method and advanced geological drilling were comprehensively applied in construction stage. This method combined with geology analysis, water inflow calculation and classification of advanced geological prediction is successfully applied in the Jigongling Tunnel of Fanba Expressway, and has provided a reference for the similar engineering constructions.

Escape route analysis after water inrush from the working face during submarine tunnel excavation

ABSTRACT More and more deep-seated long submarine tunnels are under construction, which greatly promotes the development of tunneling technology. The complex geological conditions and frequent geological disasters have become great challenges during submarine tunnel excavation. Among them, casualties and economic losses caused by water inrush are on the top levels in all kinds of tunnel geological disasters. Escape routes after water inrush from the working face during submarine tunnel excavation are investigated and optimized in the present study. Numerical simulations are performed using the FLUENT software to probe water flow characteristics after inrush. Two common cases of water inrush during double-line submarine tunnel excavation are researched. The variation rules of velocity and pressure in the tunnels after inrush are analyzed and discussed. The optimized escape routes are achieved. Finally, the water movement laws after inrush from the working face under different excavation situations are further discussed by comparing the two case studies. Water inrush of high velocity occurs on one working face of the double-line submarine tunnel, and the research results are as follows: (1) The velocity close to the tunnel side wall is the minimum, while it is the maximum in the middle position. (2) The pressure changes greatly at the intersection area of the cross passage and the tunnels. (3) The velocity and pressure nearby the working face without water inrush are both small. (4) The velocity at the high location of the cross passage is relatively small.

A possible prediction method to determine the top concealed karst cave based on displacement monitoring during tunnel construction

The existence of concealed karst caves can cause major displacement and even large deformation of surrounding rock during karst tunnel excavation. As such, these concealed caves pose a large threat to the stability of surrounding rock and represent major hidden threats to safe tunnel construction. Here we report on our investigation of a possible method to predict the top of a concealed karst cave based on displacement monitoring during tunnel construction. Displacement laws of monitoring sections were analyzed and compared to a case study without karst caves after the tunnel was excavated once. Numerical calculation was carried out to verify the proposed method. The impacts of a number of factors were studied by taking into account the effects of displacement fields, such as tunnel depth, the surrounding rock grade, the size of the karst cave, the distance between the tunnel and the karst cave and the depth–span ratio of the karst cave, on the stability of surrounding rock in tunnels. Compared with the case study without karst caves, the surrounding rock deformation affected by the top karst cave during tunnel excavation is discussed, and simulation results were found to be consistent with those predicted by the proposed method. These research results can provide a new concepts for comprehensive forecasting techniques of the concealed karst cave.

Attribute recognition model for risk assessment of water inrush

An attribute recognition model of water inrush risk evaluation is established based on attribute mathematic theory and software is developed for risk assessment in a tunnel. In our model, the entropy weight method is applied to analyze the weights of evaluation indexes. Considering karst hydrologic and engineering geological conditions of a tunnel under construction, eight major influencing factors of water inrush (formation lithology, unfavorable geology, groundwater level, attitude of rocks, contact zone of dissolvable and insoluble rocks, layer and interlayer fissures, catchment ability and surrounding rock mass classification) are selected as the evaluation indexes, and an index system of water inrush risk assessment is constituted. The tunnel is divided into 26 sections, and 340 evaluation objects are selected from these 26 sections in order to construct a judgment matrix. The water inrush risk of the whole tunnel is evaluated by using the proposed software. The results indicate that the attribute recognition model of water inrush risk evaluation is scientific and reasonable and that the software is convenient for use in calculations and is easy to master.

Risk assessment of water inrush in karst tunnels excavation based on normal cloud model

Water inrush in karst tunnels is a dynamic process in which internal and external factors are involved. The evaluation of this process is fuzzy, complex, and uncertain. In the current research, few articles give full consideration to the fuzziness and randomness of the water inrush evaluation with useful dynamic feedback. A new assessment method has been proposed for the water inrush evaluation based on a combination of the weighting method and normal cloud model. Specifically, an evaluation index system is forged and each index is quantitatively classified into four grades. A synthetic weighted algorithm combining the analytic hierarchy process, entropy method, and statistical methods is proposed to assign the index weight rationally. Based on the cloud generator algorithm, three numerical characteristics are calculated and a sufficient number of cloud droplets are generated. The membership degree of each index belonging to each grade is constructed and the integrated certain grades are determined. In this paper, the multi-factor normal cloud assessment method is applied to the risk assessment of the Qiyueshan tunnel. The assessment result of the risk grade is accurate, that is, the water inrush risk of different samples at the same risk grade can be reflected in figures. The results not only show high consistency with other assessment methods but are also in good agreement with the excavation results. The proposed cloud model method demonstrates good practical reference for risk assessment of tunnel construction in karst areas and can be applied to tunneling, mining, and other engineering practices in the future.

Numerical analysis of gas-liquid two-phase flow after water inrush from the working face during tunnel excavation in a karst region

Increasingly, deep tunnels are under construction, which greatly promotes the development of tunnelling technology. Complex geological conditions and frequent geological disasters have become great challenges during tunnel excavation. Among them, casualties and economic losses caused by water inrush are on the top levels in all types of tunnel geological disasters. In the present study, numerical simulation of the gas-liquid two-phase flow is carried out by using the FLUENT software to probe water flow characteristics after water inrush. Three common cases of water inrush from the working face during double-line tunnel excavation are researched. The variation rules of velocity, pressure and water volume fraction in the tunnels after water inrush are analyzed. The water movement laws under the conditions of different excavation situations and different water inrush positions are further discussed by comparing the three case studies. When water inrush occurs on the left tunnel working face, the following conclusions are drawn: (1) The velocity is smaller at the lower location of the left and right tunnels. In the width direction of the cross passage, the velocity is smaller on the left and right sides of the section, and in the height direction, the velocity is smaller on the upper end and lower end of the cross passage. (2) The pressure decreases gradually with the increase of height in the left tunnel and the cross passage. In the vicinity of the cross passage, the pressure on one side of the left and right tunnels close to the cross passage is the minimum, and then it gradually increases towards the other side. (3) The water volume fraction decreases gradually with the increase of height. (4) The velocity, pressure and water volume fraction changes greatly at the intersection of the cross passage and tunnels. In addition, the velocity nearby the working face without water inrush is very small.

Flow Catastrophe Evolution Laws of Nonlinear Seepage for Water Inrush Induced by Conductive Fault

Geological defects, such as conductive faults, karst conduits, fracture zones and so on, often lead to serious water inrush disaster, because they frequently become potential water inrush passage especially when large water bearing structure exists. This will cause high construction risks of water inrush. Water inrush process is the catastrophe evolution process of flow state for conductive fault. The initial stage of the catastrophe evolution process is the water seepage in confined aquifer, which then develops into rapid flow in the fault. The last stage manifests as conduit flow in the tunnel. Brinkman equation has been adopted for the seepage characteristic description of karst water in fault. Based on the conservation of mass and pressure balance, Darcy equation and Naier-Stokess equation are respectively used to characterize the flow in confined aquifer and tunnel. The variation characteristics of velocity, pressure and discharge on different position of the fault have been analyzed. In addition, the permeability effect of water inrush on different faults has been modeled. It has been found that risk of water inrush becomes higher for obvious pressure relief resulting from increasing permeability.