Experimental Study on Permeability Characteristics of Geotubes for Seepage Analysis on Safety Assessment of Dams

Geotubes are heterogeneous structures composed of filling sand and bag material,and its pemeability characteristics are different from that of flling sand.The uncertainty of geotubes permeability characteristics results in the failure of seepage analysis of geotube dams,which restricts the safety assessment of the dams.As the basis of the study on the seepage mechanism of the geotubes,the influence of particle grading on pemeability cofficient of flling sand and sand covered with geotextiles were explored by the pemmeability tests of flling sand with different particle grading under the condition of sand covered with or without geotextiles.And the infuence of geotextiles on the permeability coefficient was analyzed by comparing permeability coefficient of sand covered with and without geotextiles.The test results show that the influence of single particle size content on permeability coe ficient is consistent under the condition of sand covered with and without geotextiles.The content of powder,fine,medium and coarse particles is linearly related to their respective permeability cofficients.And the content of powder,fine,medium particles is negatively correlated with their permeability coefficients,while the content of coarse particles is positively correlated with the permeability coefficient.But the pemeability coefficient of sand covered with geotextiles is smaller than that of flling sand under the same conditions.Finally,the parameter d2 50 Cc/Cu was selected as a variable representing the particle grading to fit the empirical formula of permeability coefficient of flling sand and sand covered with geotextiles.

Seepage analysis of Upper Gotvand Dam concerning gypsum karstification(2D and 3D approaches)

Upper Gotvand Dam is constructed on the Karun River at the south west of Iran.In this paper,2D and 3D models of the dam together with the foundation and abutments were established,and several seepage analyses were carried out.Then,the gypsum veins that are scattered throughout the foundation ground were included in the models,and the seepage pattern,considering the dissolution law of gypsum,was analyzed.It was disclosed that the discharge fluxes obtained from 2D and 3D analyses are not similar,and the discharge flux in 3D model is about four times that of the 2D model.Also,the 3D model locates the phreatic surface somewhat higher than the 2D model.This means that the 2D model estimates lower pore water pressure pattern in comparison with the 3D model.These may be attributed to the fact that with 2D model the lateral components of vectors of seepage velocity are ignored.In the current case,the rate of increase of discharge flux due to dissolution of gypsum veins was obtained to be a thirdorder function of the aperture width.In spite of the fact that the grout curtain is designed to be about 170 m deep,however,complete dissolve of gypsum will severely increase the discharge flux through the foundation ground.

Upper bound limit analysis of roof collapse in shallow tunnels with arbitrary cross sections under condition of seepage force

The analytical solutions for predicting the exact shape of collapse mechanisms in shallow tunnels with arbitrary excavation profiles were obtained by virtue of the upper bound theorem of limit analysis and variation principle according to Hoek-Brown failure criterion. The seepage force was included in the upper bound limit analysis, and it was computed from the gradient of excess pore pressure distribution. The seepage was regarded as a work rate of external force. The numerical results of roof collapse in square and circular tunnels with different rock parameters were derived and discussed, which proves to be valid in comparison with the previous work. The influences of different parameters on the shape of collapsing blocks were also discussed.

Determination of hydraulic conductivity of fractured rock masses:A case study for a rock cavern project in Singapore

In order to reduce the risk associated with water seepage in an underground rock cavern project inSingapore, a reliable hydro-geological model should be established based on the in situ investigationdata. The key challenging issue in the hydro-geological model building is how to integrate limitedgeological and hydro-geological data to determine the hydraulic conductivity of the fractured rockmasses. Based on the data obtained from different stages （feasibility investigation stage, constructionstage, and post-construction stage）, suitable models and methods are proposed to determine the hydraulicconductivities at different locations and depths, which will be used at other locations in thefuture. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Prediction of mine drainage generation potential and the prevention method of the groundwater pollution in the Gümüskoy(Kütahya)mineralization area,NW Turkey

One of the leading factors of seepage contamination is mine drainage,which creates serious ecological risks on the environment both during operation and post-mining times.In this study,experimental processes have been carried out to determine the occurrence of mine drainage in the Gümüskoy(Kütahya)mineralization area(Northwest Turkey).The prevention method for potential mine drainage occurrence has been also discussed.High enrichment was observed which are directly related to mineralization in trace element concentrations,especially in potentially toxic metals such as Ag,Cd,Mo,Ba,Bi,and Zn.Based on short-term tests,mine drainage formation has not been expected according to the p H(7.36-9.38),contact leaching,and acid-base accounting studies.However,in the long-term,acid generation potential has been expected because of weathering and oxidation in terms of rock type and mineralization in the area.Therefore,in order to prevent groundwater contamination in the event of a possible formation of mine drainage,the hydraulic conductivity of the stock area bedrock was evaluated by the in situ tests performed in the field and it was found to be moderately permeable(K=1.9×10^-6 m/s).In order to make the stock area bedrock impermeable,natural clay will be laid and compressed at the base of the stock area.When the finite elements were modeled by seepage analysis,the seepage discharge to be formed on the base rock at a depth of 5 m was determined as 3.17×10^-19 m^3/s.Since the discharge value determined in the seepage analysis after modeling is very close to zero,contamination of possible ground and surface water will be prevented.

Application of entropy-based fuzzy matter-element analysis in seepage monitoring of RCC dam

Taking account of the fuzzy results of the seepage monitoring analysis of roller compacted concrete(RCC)dam and uncertainties of the individual indicator evaluation,the fuzzy matter-element model of seepage monitoring of RCC dam analysis has been established with the use of the fuzzy matter-element analysis theory and the concept of euclid approach degree.The use of entropy theory can calculate the weighting factor through the disorder utility values of the information reflected by the data itself,which can effectively avoid the problems of weight distribution and uncertainties of subjective judgments of the seepage monitoring analysis of roller compacted concrete dam.And further the example shows that the analysis of entropy-based fuzzy matter-element analysis model of the seepage monitoring of roller compacted concrete dam is in accordance with the actual situation,which verifies the effectiveness of the method.

Study on coupled 3D seepage and stress fields of the complex channel project

Seepage is a vital reason that may bring many adverse consequences such as subsidence,inclination and fracture to the channel,and is harmful to the safety and stability of the channel.Thus,a 3D visualization model is established for the engineering geological information of the research channel section by using NURBS-TIN-BRep hybrid data structure.Coupled with the VOF(volume of fluid)method,the N-S(Navier-Stokes)equations are applied to seepage simulation of the research channel section.Then the stability of the channel is studied coupled with the seepage simulation results,to comprehensively analyze the stress and displacement conditions of the channel under the impact of different factors such as seepage and underground goafs.The results of this study illustrate that the channel seepage has great influence on its stability,especially on the displacement field:it will lead to a significant sedimentation to the foundation.Therefore,during the practical construction,it is suggested that the certain part of the channel should be reinforced and effective seepage control measures should be taken.