Analyzing the causes of strong seepage on xahuong dam and proposing solutions for handling

THUY LOI UNIVERSITY & UNIVERSITY OF LIEGE FACULTY OF CIVIL ENGINEERING Presented by MAI THI NGAT ANALYZING THE CAUSES OF STRONG SEEPAGE ON XAHUONG DAM AND PROPOSING SOLUTIONS FOR HANDLING Major : Sustainable Hydraulic Structures Student ID # 148ULG09 MASTER THESIS Supervisor : Dr HO SY TAM - Thuy Loi University Co-supervisor : Prof RADU SARGHIUTA - University of Liege Ha Noi, 2016 MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES REASSURANCES NAME: MAI THI NGAT Major: Sustainable Hydraulic structure Student Number: 148ULG09 I hereby declare that I am the person who conducted this master thesis under the guidance of Dr Ho Sy Tam and Prof.Radu Sarghiuta with the research topic in the thesis “Analyzing the causes of strong seepage on XaHuong dam and proposing the solution for handling” This is a new research topic which does not overlap with any dissertation before, so there is no copy of any public dissertation The contents of the thesis are presented in accordance with regulations; the data resources and materials used in research are quoted sources If there is any problem with the contents of this thesis, I would like to take full responsibility as prescribed SIGN MAI THI NGAT MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES ACKNOWLEDGEMENTS Master Thesis in major of sustainable hydraulic structure “Analyzing the causes of strong seepage on XaHuong dam and proposing the solution for handling” was completed in August, 2016 In the process of implementation of the thesis, I always get the encouragement and devoted directions from my instructors _ Dr Ho Sy Tam and Prof Radu Sarghiuta I am really grateful for their invaluable help I also would like to express our sincere thanks to all of my teachers in Sustainable Hydraulic structure Master course at Thuy Loi University, along with professors from University of Liege had imparted valuable specialized knowledge for me so that i can get this result Finally, I sincerely thank my family, my friends, and especially my classmates who had exchanged enthusiastically, contributed and encouraged me to complete this thesis Sincerely SIGN MAI THI NGAT MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES CATEGORY PREMISE 1.1 THE URGENCY OF THE PROJECT 1.2 RESEARCH OBJECTIVES 1.3 METHODOLOGY TO STUDY THE SUBJECT 1.4 RESEARCH SCOPE OF THE STUDY CHAPTER GENERAL INTRODUCTION 1.1 INTRODUCTION OF THE PROJECT 1.1.1 Location of Project area 1.1.2 Topographical and geomorphological conditions 1.1.3 Geological features 1.1.4 XaHuong reservoir 1.1.5 XaHuong Dam 10 1.1.5.1 Dam crest 10 1.1.5.2 Upstream dam slope 11 1.1.5.3 Downstream dam slope 12 1.2 SEEPAGE PROBLEM TO XAHUONG DAM 13 1.3 STUDIES ON SEEPAGE INSTABILITY THROUGH EARTH DAM 16 1.3.1 Seepage flow 16 1.3.1.1 Causes of permeability 17 1.3.1.2 Basic principle of seepage flow 18 1.3.1.3 Hydraulic gradient 19 1.3.1.4 Darcy law 19 1.3.1.5 Hydraulic conductivity 21 1.3.1.6 Basic principle of seepage line 22 1.3.1.7 Permeable basic equation 23 1.3.1.8 Planar permeable equation 24 1.3.2 Calculation of perfect anisotropy 26 MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES 1.3.2.1 Definition 26 1.3.2.2 Analysis about cause of permeability 30 CHAPTER 2: STUDY ABOUT CAUSES MAKING SEEPAGE INSTABILITY THROUGH THE BODY OF XA HUONG DAM 33 2.1 INTRODUCTION ABOUT CALCULATION SOFTWARE 33 2.1.1 Description 33 2.1.2 Steps to calculate 35 2.2 CALCULATION 40 2.2.1 Case 1: Normal working filter layer 42 2.2.2 Case 2: Clogged filter layer 44 2.2.3 Case 3: Effects of anisotropic permeability 46 2.2.4 Case 4: Effect of Anisotropy interlayer 52 CHAPTER 3: SEEPAGE TREATMENT SOLUTIONS 60 3.1 PROPOSED SOLUTION 60 3.1.1 Solution for case 3: Effect of anisotropic permeability 60 3.1.2 Solution for case 4: effect of anisotropic interlayer 64 3.2 ASSESSMENTS ABOUT RESULTS 67 CHAPTER 4: CONCLUSION & RECOMMENDATION 68 REFFERENCES 70 MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES LIST OF FIGURE Figure 1- 1: Location of XaHuong reservoir ensembles Figure 1- 2: XaHuong reservoir Figure 1- 3: Upstream view of XaHuong Dam .10 Figure 1- 4: Dam crest from the right abutment 10 Figure 1- 5: Dam crest from the left abutment .10 Figure 1- 6: Crest of parapet wall 11 Figure 1- 7: Foot of parapet wall 11 Figure 1- 8: Dam slope in the left abutment 12 Figure 1- 9: Dam slope in the right abutment .12 Figure 1- 10: Overall downstream dam slope 13 Figure 1- 11: Dam slope m = 2.5, from elevation of +83.0m to dam crest 13 Figure 1- 12: The first dam berm at elevation of +83.0 m 13 Figure 1- 13: Dam slope m = 3.0 from elevation of +71.5 to +83.0 13 Figure 1- 14: Handling the seepage of dam slope from elevation +71.5 to +83.0 15 Figure 1- 15: Concentrated rocks for seepage drainage on slope 15 Figure 1- 16: Seepage drainage on berm at elevation +71.5 .16 Figure 1- 17: Cross-section of dam .26 Figure 1- 18: Transformation for Anisotropic Conditions 28 Figure 1- 19: Effect of Anisotropy on Seepage through an Earth Dam .29 Figure 2- 1: Geoslope software interface .33 Figure 2- 2: Creating analysis properties .35 Figure 2- 3: Importing region from AutoCAD program .36 Figure 2- 4: Defining material layers 36 Figure 2- 5:Defining hydraulic boundary conditions 37 Figure 2- 6: Drawing material layers 37 Figure 2- 7: Drawing boundary conditions 38 Figure 2- 8: Solving data 38 Figure 2- 9: Displaying results .39 MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Figure 2- 10: Viewing report 39 Figure 2- 11: Drawing permeable grid and sliding center 40 Figure 2- 12: Contributed material layers 40 Figure 2- 13: Calculated diagram of seepage stability for case 42 Figure 2- 14: Seepage calculation results for case 42 Figure 2- 15: Calculated result of slope slide stability (Normal load combination) 43 Figure 2- 16: Calculated diagram of seepage stability for case 44 Figure 2- 17: Seepage calculation results for case 44 Figure 2- 18: Calculated result of slope slide stability (Normal load combination) 45 Figure 2- 19: Calculated diagram of seepage stability for case 46 Figure 2- 20: Calculated diagram of slope stability (Normal load combination) 46 Figure 2- 21: Seepage calculation results for case (ratio=7) 47 Figure 2- 22: Calculated result of slope slide stability (Normal load combination) 47 Figure 2- 23: Seepage calculation results for case 3(ratio=10) 48 Figure 2- 24: Calculated result of slope slide stability (Normal load combination) 48 Figure 2- 25: Seepage calculation results for case3(ratio=14) 49 Figure 2- 26: Calculated result of slope slide stability (Normal load combination) 49 Figure 2- 27: Seepage calculation results for case3(ratio=20) 50 Figure 2- 28: Calculated result of slope slide stability (Normal load combination) 50 Figure 2- 29: Contributed material layers 52 Figure 2- 30: Calculated diagram of seepage stability for Z=70m 53 Figure 2- 31: Seepage calculation results for Z=70m 53 Figure 2- 32: Calculated result of slope slide stability (Normal load combination) 54 Figure 2- 33: Calculated diagram for Z=80m 55 Figure 2- 34: Seepage calculation results for Z=80m 55 Figure 2- 35: Calculated result of slope slide stability (Normal load combination) 56 Figure 2- 36: Calculated diagram for Z=84m 57 Figure 2- 37: Seepage calculation results for Z=84m 57 Figure 2- 38: Calculated result of slope slide stability (Normal load combination) 58 Figure 3- 1: Contributed material layers 61 MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Figure 3- 2: Calculated diagram of seepage stability 61 Figure 3- 3: Seepage calculation result 62 Figure 3- 4: Calculated diagram of slople stability (Normal load combination) 62 Figure 3- 5: Calculated result of slope slide stability (Normal load combination) 63 Figure 3- 6: Contributed material layers 64 Figure 3- 7: Calculated diagram of seepage stability 65 Figure 3- 8: Seepage calculation result 65 Figure 3- 9: Calculated diagram of slople stability (Normal load combination) 66 Figure 3- 10: Calculated result of slope slide stability (Normal load combination) 66 MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES LIST OF TABLE Table 1: Mechanical and physical indicators of fill-soil for dam body and foundation 41 Table 2: Output data of case 51 Table 3: Output data of case 58 Table 1: Output data 67 MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES PREMISE 1.1 THE URGENCY OF THE PROJECT Earth dam is a type of dam built by the existing soils in the building region such as clay, clayed , sandy loam, sand, gravel, cobbles Earth dam has simple and stable structure, capable of highly mechanized during the construction and in most cases Earth dam is widely applied in most countries This type of dam has advantage of using local materials which are available at construction area, so it has cheaper construction costs comparing to other types of the same scale dams However, earth dam also contains many risks, easy to occur unsafe incident to dams if the designing work and construction does not guarantee the requirements such as foundation treatment, dam structure selection, appropriate material planning for fill soil of an embankment dam as well as densification ensure uniformity and tightness of each fill layer According to statistic, permeability occupies high rate in the cause of making reservoir built with local materials unsafe In our country, most of the earth dams are made of homogeneous soil When water level rise and lowered erratically, it will destabilize the slope of dam, leading to sliding, subsidence, local erosion Therefore, the calculation of stability mode for the earth dam is very important… Usually we only calculate permeability in homogeneous environments Concept of permeability of earth dams in case of homogeneous soil often not lead to significant errors comparing to fact If the dam body or the dam's waterproofing parts are constructed with materials relatively homogeneous with small value of heterogeneous coefficient then we can solve the seepage problem with homogeneous environment Moreover, beside case of normal calculation (isotropic environment), we must pay attention to the heterogeneity of the material (anisotropy of permeability) The inhomogeneous - anisotropic usually occur because of earth dam construction MaiThiNgat Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Figure 2- 35: Calculated result of slope slide stability (Normal load combination) MaiThiNgat 56 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES c) Anisotropy interlayer lied at elevation Z = 84m Figure 2- 36: Calculated diagram for Z=84m Results: Figure 2- 37: Seepage calculation results for Z=84m MaiThiNgat 57 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Figure 2- 38: Calculated result of slope slide stability (Normal load combination) Command: Table 3: Output data of case - Case q (10-5m3/s.m) Zout(m) JXYmax K Conclusion Z=70(m) 5.18 70 0.79 1.272 Unstable Z=80(m) 4.85 80 0.78 1.268 Unstable Z=84(m) 4.7 84 0.78 1.261 Unstable With the results getting from the above calculation of case 4, we see that, the seepage line in this case has been raised; the seepage line goes out the downstream slope at elevation +70 - 84m, suits with the description of the current state of infiltration occurring in XaHuong dam MaiThiNgat 58 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES - Similar with case 3, when position of interlayer increases, stability coefficient of XaHuong dam decreases - In the case anisotropy interlayer lied on elevation Z = 84m, the seepage rise very high On the other hand, we could say that anisotropic seepage is a major cause of instability for dam seepage XaHuong CONCLUSION After calculating seepage and slope stability of XaHuong Dam with cases: - Normal working filter layer - Clogged filter layer - Effects of anisotropic permeability - Effect of Anisotropy interlayer Based on monitoring data and the actual phenomenon, we can see that the factors causing seepage phenomena in the dam leading the dam not ensure both seepage and slope stability are effects of anisotropic permeability and anisotropic interlayer Whereby, anisotropic permeability with increasing ratio between Kx and Ky and increasing elevation of anisotropic interlayer will raising the seepage line , leading to the instability of XaHuong dam MaiThiNgat 59 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES CHAPTER 3: SEEPAGE TREATMENT SOLUTIONS 3.1 PROPOSED SOLUTION In chapter II, we had find out the causes making seepage instability are anisotropic permeability and anisotropic interlayer, so that in this chapter, the auther will apply waterproofing methods to decrease the effects of seepage to XaHuong Dam In both case, waterproofing method applied is drilling cement grouting – Bentonite membrance into dam body This membrance plays a important role in decreasing the seepage line and increasing stability for the dam slope  Advantage:  good waterproofing  it can be constructed when the reservoir remain a certain amount of waterso not need to drainning the reservoir  Disadvantage: Require high construction techniques As usual, drilling wall is arranged on top of the dam, near the upstream slope However, because the layer has large permeability coefficient so this wall will be arranged along the cutoff wall, leading to it was skewed towards upstream With this position, the elevation of wall crest is still lower than NWL thus we add layer of drilling on the upstream slope, connecting top of the dam with wall crest, this layer thickness is m 3.1.1 Solution for case 3: Effect of anisotropic permeability Description: - In this case of anisotropic seepage (case 3), calculating with a clogged filter layer of sand which has hydraulic conductivity k = 5.04-6 (m/s) MaiThiNgat 60 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES - In this part, we use case with ratio = 20 which making greatest influence to seepage instability (case has highest seepage line) - Taking thickness of waterproofing membrance is 5m, we have diagram to calculate permeability as follows: Figure 3- 1: Contributed material layers Figure 3- 2: Calculated diagram of seepage stability MaiThiNgat 61 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Result Figure 3- 3: Seepage calculation result Figure 3- 4: Calculated diagram of slople stability (Normal load combination) MaiThiNgat 62 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Figure 3- 5: Calculated result of slope slide stability (Normal load combination) Command: We see that, if comparing to case of anisotropic seepage (case 3, ratio =20), the seepage line is lowered significantly and the safety factor K is also increase to 1.368 So that method of waterproofing by clay drilling is quite effective in order to decrease the seepage line of XaHuong dam MaiThiNgat 63 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES 3.1.2 Solution for case 4: effect of anisotropic interlayer Description: - Inter layer layer is continuous - Assuming calculating with a clogged filter layer of sand which has hydraulic conductivity k = 5.04-6(m/s) - In this case, the dam XaHuong still has waterproofing walls by clay - Taking thickness of waterproofing wall is 5m, we have diagram to calculate permeability as follows: Figure 3- 6: Contributed material layers MaiThiNgat 64 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Figure 3- 7: Calculated diagram of seepage stability Result: Figure 3- 8: Seepage calculation result MaiThiNgat 65 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Figure 3- 9: Calculated diagram of slople stability (Normal load combination) Result: Figure 3- 10: Calculated result of slope slide stability (Normal load combination) MaiThiNgat 66 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Command: - We see that, in this case the seepage line is lowered if comparing to the case (anisotropic seepage), so we could say that method of waterproofing by clay drilling is suitable in order to decrease the seepage line of XaHuong dam 3.2 ASSESSMENTS ABOUT RESULTS Table 1: Output data Case q (10-5m3/s.m) JXYmax K Conclusion 1.1 4.308 1.43 1.368 Stable 1.2 4.2 1.411 1.358 Stable According to TCVN 8216-2009, with construction grade I, after water proofing by drilling clay layer into dam body, almost seepage line is decreased Besides, the safety factors ensure the standard requirement ( larger than [K=1.3]) and the value of gradient at outlet is still quite large in both cases (~1.4) The results of calculations show that XaHuong dam is stable MaiThiNgat 67 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES CHAPTER 4: CONCLUSION & RECOMMENDATION Conclusion: Based on the results of calculation of permeability and stability of Xa Huong dam in case of taking into account of anisotropy permeability and anisotropic interlayer , the following conclusions are drawn: - Drainage equipment in the dam body no longer work as effectively as the original design - The study shows the influence of the anisotropic degree to the permeable characteristics and the coefficient of slope stability of Xa Huong dam Calculation results show that the anisotropic ratio Ratio = Kx then the calculation results Ky consistent with seepage monitoring data - The study also examined the effects of interlayer position to the permeable characteristic and slope stability of XaHuong dam Accordingly, the position of interlayer in elevation greater than or equal the elevation of dam berm I (with the elevation of 84m) may be the cause of seepage in XaHuong dam, similar with the data observed in the field - This thesis also proposed suitable solutions for waterproofing treatment for XaHuong dam through seepage and stability calculations - Although the dam body is treated waterproofing by drilling a clay layer, the value of gradient at outlet is still quite large in both cases So that, XaHuong dam still exist factors that thread its safety MaiThiNgat 68 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES Limitations Although many cases was calculated but the study also has certain drawbacks: - The survey data is incomplete, mainly based on the data in the old design documents - Research also assumes a certain parameters of interlayer such as continuity, interlayer number, unchanged size which are not correctly reflect the reality in nature, but it also have somewhat indicated the causes - The new processing solutions base on the results of permeability and stability calculation, there are many other factors that the author has not mentioned when choosing MaiThiNgat 69 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta MASTER THESIS SUSTAINABLE HYDRAULIC STRUTURES REFFERENCES [1] Safety report of XaHuong dam [2] National Technical Regulation QCVN 04-01:2010/BNNPTNT on the composition and contents of preparing investment report, investment project, and economic and technical report of hydraulic works [3] National Technical Regulations QCVN 04-05: 2012 /BNNPTNT – Main provisions on designing for irrigation works [4] National standard TCVN 8216: 2009 – Design of compacted earth dam [5] National standard TCVN 8421: 2010: Hydraulic works – Waves and shipsinduced load and force on the works [6] The book of introduction and the design establishments of irrigation worksNguyen Van Mao [7] Current regulations, standards [8] http://people.eng.unimelb.edu.au/stsy/geomechanics_text/Ch6_SeepDam.pdf) [9] https://www.geo-slope.com/products/slope-w [10] GEO-SLOPE International Ltd, Calgary, Alberta, Canada : www.geo- slope.com) MaiThiNgat 70 Supervisor: Dr Ho Sy Tam Co-Supervisor: Prof Radu Sarghiuta