Summary of Ph.D thesis: A study on the embankment caculation method reinforced by geotextile in the construction of highway in Vet Nam

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Reasons for Ph.D thesis A study on the embankment caculation method reinforced by geotextile in the construction of highway in Vet Nam: to complete calculation methodology for problem embankment using geotextiles in the construction of highways.

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Nội dung Text: Summary of Ph.D thesis: A study on the embankment caculation method reinforced by geotextile in the construction of highway in Vet Nam

-i- MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATION Hao Huynh Ngoc A STUDY ON THE EMBANKMENT CACULATION METHOD REINFORCED BY GEOTEXTILE IN THE CONSTRUCTION OF HIGHWAY IN VIETNAM Major: Construction of hightway and street Code: 62.58.30.01 SUMMARY OF Ph.D THESIS Hanoi, June 2014
- ii - This thesis was completed at the university of transport and communication Supervisors: Prof. PhD Phung Vu Dinh PhD Sy Vu Duc Examiner 1: Prof, Dr.Sc Quang Nguyen Van Hanoi Architectural University Examiner 2: Prof, PhD Chuong Do Ba National University of Civil Engineering Examiner 3: Ass.Prof, Dr.Sc Can Nguyen Van Hanoi University of Mining and Geology This thesis is defended at the university of transport and communication on ... h, ........., 2014. Thesis can be found at: 1. National Library 2. Library of the university of transport and communication
- iii - Publications 1. Hao Huynh Ngoc MS, Phung Vu Dinh Prof.PhD (2009), “Several designing measures using geotextiles in order to stabilize weak soil in the constructing of road and dam, dike”. Bridge and Road Magazine, No. Nov-2009, Page 8-11. 2. Quang Tran Dinh PhD, Hao Huynh Ngoc MS (2011), “Study of the improvement for fabrication and construction of prestressed I beam l = 42m with continous thermo slad based on the construction of Hoa xuan brigde- Danang city“, The Transport and communications magazine, No. Aug-2011, ISSN 0866-7012, Page 26-29. 3. Hao Huynh Ngoc MS, Phung Vu Dinh Prof.PhD (2013), “Probability of instability of backfill construction from design perspective“, Bridge and Road Magazine, No. Aug-2013, ISSN 1859-459X, Page 19-22. 4. Hao Huynh Ngoc MS, Phung Vu Dinh Prof.PhD (2013),“The stability caculation model of embankment (highways, dikes, dams) reinforced by geotextile thanks to the finite element method and mention pull behaviors of geotextile and relationship between stresses and strains of the contact elements between embankment and geotextile“, Bridge and Road Magazine, No. Nov-2013, ISSN 1859-459X, Page 8-11. 5. Hao Huynh Ngoc MS, Vu Duc Sy PhD, Phung Vu Dinh Prof.PhD (2014), “Slide curve analysis results of slope stabilization by finite element method (HNH_RESS software) in comparison with analytic method “, Bridge and Road Magazine, No. Jan and Feb-2014, ISSN 1859-459X, Page 38-41.
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-1- INTRODUCTION 1 - Introduction to the study: Along with the strong growth in the application of new materials technology in the world , Vietnam’s also very interested in the study of materials using in geotextile reinforced embankment works roads , dikes and dams . So that, the research methods completing for calculating results for reliability problems embankment reinforced by geotextile in the construction of roads in Vietnam becomes necessary . Within the scope of this study , the author used the finite element method - numerical method has several advantages in the present time to apply the construction algorithm , based on the programming software suit Vietnam and the conditions for a number of research results stability problems , stress - state deformation embankment , proposed making calculations and charts used in utility design . 2 - Reasons for choosing topic : To complete calculation methodology for problem embankment using geotextiles in the construction of highways 3 - Purpose : Develop computational models roadbed embankment reinforced by geotextile , contribute to improve the calculation method actually worked closely with the material and the ability to predict an instability correctly in order to bring high efficiency , ensure technical requirements designed embankment geotextile reinforcement 4 - Research Subjects : The land cover using geotextile in road works background 5 - Scope of the Study : Selection , calculation model building problem embankment geotextile reinforcement . Construction algorithms and computer programs using the finite element method . Look at the problem embankment geotextile reinforcement . 6 - The meaning of scientific and practical subjects : geotextiles is a new material made from synthetic polymer materials or products related to the polymer through different manufacturing technologies together. Since the 70s of last century geotextile fabric was born in the western world . Due to the interesting properties of geotextile Vietnam should have quickly been used to enhance reinforcement load capacity and stability for the construction, especially the building embankments in road and bridge construction and irrigation ... The early years of the '90s - last century, geotextiles are widely used in many countries such as France , the Netherlands , the U.S. and Japan , particularly in Southeast Asian countries like Thailand , Philippines , Indonesia , Malaysia , ... in our country , geotextile be put to use building the road since 1993 and more using widely. According to a study by experts at home and abroad show geotextile used in the construction of high embankment of earth or embankments on soft soils are effective economic and technical, easy simple in construction, reduced costs from 15-20%, increase quality of use, the life of the facility . Thus the complete study methodology , embankment design using geotextile reinforcement is needed to serve the practical requirements in the integration and
-2- implementation of industrialization and modernization development of the country CHAPTER 1 OVERVIEW ABOUT USING AND CALCULATION METHODS OF GEOTEXTILE REINFORCEMENT EMBANKMENT 1.1 . The study used calculations and embankment geotextile reinforcement at home and abroad 1.1.1.Historical development and use of geotextile . 1.1.1.1 . Introduction : geotextile appear first Bidium trade name in the 60s of the last century in France, but has not been noticed and used very little. Since 1975, the geotextile is more complete study of water from the development phase, calculation methods and construction technology. Geotextile is used for rapid reinforcement enhance the load capacity and stability of the construction work in general and especially the ground up for work in the construction of roads and irrigation. In the 80s of the last century geotextile is widely used in many countries such as France , the Netherlands , the U.S. , Japan , China , India , South Korea , especially in Southeast Asia : Thailand , the Philippines , Indonesia , Malaysia,Brunei... In 1993 our country geotextile was first used in the project to upgrade Highway 5 (Ha Noi - Hai Phong ) by the Design Consultant Company KEI - Japanese design with over 500,000 m2 of geotextile is to effectively handle embankment on soft ground . And from 1995 till now, geotextiles have been used a lot with different functions in various projects such as road construction project to upgrade National Highway 1, QL10, QL18, NH3, highway 51, QL32, QL38, QL39 and in construction projects like highways : highways Ho Chi Minh City - Trung Luong , Thang Long Boulevard ( away from Lang Hoa Lac ) , high speed Hanoi - Hai Phong Expressway Gie - Ninh Binh , Noi Bai - Lao Cai Highway Long Thanh - Dau Giay Expressway and Ben Luc - Long Thanh ... 1.1.1.2. Classification of geotextile [14] , [28] , [29] , [30] Based on the fabrication technology , geotextiles are classified into two types : woven geotextile and silk geotechical kind of non-woven . Some evaluation criteria geotextile : Appendix 1 : Table 1.3 introduces the main physical and mechanical by application of geotextiles ; Table 1.4 specifications polyfelt TS nonwovens ; Table 1.5 and Table 1.6 non-woven geotextile HD - Vietnam [ 50 ] . 1.1.1.3 The function of geotextile [13] , [14] , [27] , [31] , [34] , [35] , [36] , [38] , [44], [56], [58], [61], [62], [63], [66], [68] . 1 . functional separation between the layers of material together ( separation ) Geotextile separation layer is made between the buffer layer of sand and mud below , separated between subgrade below ( subbase ) and the bottom layer of pavement covered with sand on top . 2 . Functional soft soil reinforcement (reinforcement) For high embankments on soft ground , it reaches a certain height sliding platform will emerge - the whole
-3- block sliding , sliding local slope should therefore use geotextile TECHNICAL reinforcement . Geotextile can also be used in case of reinforced soil need not weak but the background causeway . 3 . Geotextile reinforcement retaining wall (wall soft key) to increase the ability to land up tall retaining wall , or steep to 900 degrees , people use geotextile wall build certainly unsatisfactory medium height wall covering , durability and use landscaping aesthetics but cheaper from 25 % to half of the reinforced concrete wall [14] , [19] , [34] , [44] , [45] . 4 . Function filtering , drainage behind the retaining wall ( drainage ) ( or a system of underground drainage embankment works on traffic , irrigation ... ) , was previously used as filter bed material particle counter - with a grading of certain materials . For the first time in Vietnam , the filtering function , drainage was used in the retaining wall of the path to the bridge on National Road 1 , Tan Thinh , Hanoi - Lang Son . 5 . Geotextile to function absorbent They lowered groundwater levels using geotextile wrap small aggregate materials for drainage , underground drainage pipe wrap before sanding , enveloping material macadam when no drainage tube , which take the form of crushed stone material cut trapezoidal openings no drainage pipe , make waterproof layer functions to lower groundwater levels . 6 . Protection, erosion control embankment dykes and dams and roof slope erosion Geotextile is used for erosion control function [ 31 ] , protecting eroded slopes not to damage the roadbed , the ditch along the road , slope erosion control line , dikes , dams , bottom of the canal , filling the polder areas , riverine lake embankment , slope areas upstream and downstream river , especially through space segment of river basin narrow bridge ... eg erosion in the upper and downstream of the bridge : Phu Dong bridge ( over the river road) , Nhu Nguyet bridge ( over the river bridge ) , Suong Giang bridge ( over the River Trade) on National Highway 1, Hanoi - Lang Son . 7 . Geotextile tubes geotechnical work (Geosolution SI) [35] Geotextile tubes used are diverse with many different forms : people unfortunately get into geotextile tubes and fill with sand , lined shore erosion protection levees , buildings along the coast sea . 1.1.1.4 The construction projects have used geotextiles in Vietnam 1 . With geotextile separation layer functions as project to upgrade Highway 5 in the year 1993-1994 , expanding the old road surface by 20 meters on the main embankment . It separates the function of geotextile , road systems in urban areas Trung Hoa - Nhan Chinh (Hanoi) , before spreading the layer of macadam people to spread a layer of geotextile Specifications for separating the sand embankment that separates below the mixed layer between the sand and stone chips easily lead to unstable surface . With this function geotextile was also used in the upgrade of Highway 5 , National Highway 1 , QL10 , QL18 and some highways such as
-4- Highway District. Ho Chi Minh City - Trung Luong ; Gie - Ninh Binh , Noi Bai - Lao Cai , Ha Noi - Hai Phong , Ha Noi - Thai Nguyen ... Also geotextile is used in landfills to make division between land and the class rubbish such as landfill bottom liner Tam Tan (Cu Chi , Ho Chi Minh City , 2011) , landfill Bo Trach district (Quang Binh) , landfill Nhon district (Binh Dinh) , Hung Yen city landfill ... 2 . Geotextile reinforcement function embankment on soft soil : In the years 2000- 2003 , before the construction of embankments online Troi - Vu Oai [ 40 ] , grade III Delta (Quang Ninh) , chaired set design was used 2 , 3 layers of geotextile separation layer by doing medium duty reinforcement for embankment on soft soil . Also in 2002, on National Highway 1 bypass the city of Vinh [ 39 ] design chair used as geotextile separation layer between the soft soil at a depth of 80cm and digging up sand poured on . Then continue to use 3 more geotextile layers , each layer separated by 40cm to reinforcement training background ( 80cm ) and section 4 ÷ 5 m high embankment . Two works have exploited so far ( 2013 ) is more than 10 years , very good quality . This is the process of using geotextiles to handle embankment on soft soil for the first time in Vietnam , simple construction , reduced construction costs . Two works make a good premise for the use of geotextiles for reinforcement of soft soil embankment on many other road construction projects such as highways , Ho Chi Minh City - Trung Luong , Gie - Ninh Binh, Ha Noi - Thai Nguyen, Noi Bai - Lao Cai,… . 3 . Geotextile for erosion control functions When slope embankment built to protect the coastline of Bai Chay - Quang Ninh , geotextiles are used to spread on the embankment slope surface , then place over the stones deck form concrete brick cement to prevent erosion of the dam due to heavy pressure waves . Also geotextile was also used to protect , reinforced slope reservoirs such as reservoir park Lao Cai city center ( designed in 2000 by the Department of Transportation as an investor in Lao Cai ) , two lakes Regulators at the National Conference Center - Hanoi, designed by the German Advisory also used as geotextile layer of protection against erosion . National Highway 1 Improvement Project paragraph Hanoi - Lang Son PMU18 represented by the investor , in the period leading to the Phu Dong Bridge ( River road) , As for the Moon ( The River ) , Xuong Giang Bridge ( River Trade) , one also used geotextile layer to protect against river erosion in the upper two side roofs - three downstream of the bridge . 4 . Geotextile material is used instead of filter layer upside down on National Highway 1 bridge , Tan Thinh - town ( Lang Giang , Bac Giang ) section between Tan Thinh bridge and railway bridge ( the old National Road 1 ) length of 80m people built construction of reinforced concrete retaining walls with a height H = 7.2 m in 1998 . At the bottom of the side walls of poured gravel embankment was then coated with a layer that geotextile before covering background material to replace the filter bed to the opposite wall at the foot drainage .
-5- 1.1.2 The calculation method geotextile reinforcement embankment: The analytic methods reinforced embankment calculated to assess stability using limit equilibrium methods ( force or torque ) and is accompanied by is the use of partial coefficients, respectively [15], [63] . 1.1.2.1 Methods of analytical calculations have reinforced embankment on soft ground [ 2 ] , [ 3 ] , [ 7 ] , [ 9 ] , [ 15 ] , [ 16 ] , [ 17 ] , [ 21 ] , [ 32 ] , [ 33 ] , [ 35 ] , [37] : Reinforcement is placed in the internal ground and even in body embankment , to prevent damage due to shear through the embankment itself or in shear zones soft soil . 1 . Locally stable [7] , [15] , [32] , [33] : Check the local stability of the embankment slope under the following inequality : (1.1) H : height embankment ; Ls : length of horizontal side slope (the slope foot width) ; φ'cv : friction angle of embankment materials at large deformation effective stress conditions ; fms : partial material factor applied to φ'cv tg ( fms = 1 ) . 2 . Stable circular slide (sliding surface analysis method) : analysis of sliding surface method is used most commonly in circular sliding stability calculations for embankment using reinforced embankment placed at the bottom . The torque caused by the land sliding and load MD as : (1.2) MRS torque by keeping the land : Torque remains enhanced by keeping MRR : (1.4) in which: ffs is the partial load factor of unit weight of soil ; wi : the weight of soil column i ; bi : the ith soil column width ; αi : angle tangential bottom soil column with the ith lateral Rd : radius circular slip ; fms : partial material factor applied to tgφ'cv ; φ'cv : friction angle at the base construction material in large deformation effective stress conditions ; ui : pore-water pressure effects on the ith sliding piece Troj traction required for 1 meter long embankment at each point along the bottom of the embankment j is defined as : (1.5) Among them : YJ ¬ arm is in the vertical direction of the torque to the dangerous sliding surface at the center point on the bottom of the embankment j ; MRRj : largest holding torque by strengthening core at point j on the bottom of embankment ; MDJ : maximum torque slip at the bottom of the embankment j (human factor has been) ; MRSj : keeping the largest torque generated by the soil at the bottom of the embankment point j (human factor has been) . 1.1.2.2 Method of computation analysis on reinforced soil embankment good natural 1 . Where the external stability of one or more results to sabotage occurs, treatment options may ways , such as reducing roof slope embankment , increasing the width column layout , using quality packing material good quality , enhanced by the foundation soil reinforcement measures , counter pressure pad ,
-6- packing material used is lightweight , reinforced combinations in various high level , more layout drainage system to reduce pressure pore water pressure , or combined treatment options in [15] , [32] . 2 . Internal stability [ 15] , [32] , [33] , [35] , [57] , [53] , [63] The method of calculating reinforced embankment on the basis of gender balance method and use the term partial coefficients corresponding to limit state are calculated . Includes : a. Method two wedge blocks ( slip surfaces kinked shape ) [12] , [15] Driving forces synthesis ( synthetic human disturbance ) in the case of a slope no more subject to external load is calculated as : ( 1.7 ) Among them : the human Rh disturbing synthesis of 1m length along the slope ; ffs is the partial factor applied to the unit weight of the soil , K is the ratio of stress ( pressure ) horizontal and vertical stress ; ɣ is the unit weight of the soil ; H is the height of embankment . To pull off being reinforced , reinforced distance vertically is determined from the expression: (1.8) Among them : Svj gap remains vertical in slope at j ; Tj is the greatest traction in the 1 m core length in slope at j ; ffs the partial load factor applied to the weight unit volume of soil , hj is the height of the embankment on the slope j ; fq is the partial load factor applied to the external load , ws is the external load due to static load ( evenly distributed on the surface at structure [ 15 , p . 10 ] ) . Paragraph anchor Lej not happen to slip reinforcement is determined from the limit state vandalism , anchor length remains satisfied [ 15 , p . 118 ] . (1.9) Among them : Lej is reinforced anchor length minimum calculated at j ; fp : partial factor control remains pulled slip phenomenon , fn : partial coefficient control works damaged due cause ; fms : partial factor applied to tgφ'p and c ' , ws : external load , α ' : interaction coefficient indicates the relationship between power and ground anchor reinforced with tgφ'p ; φ'p : corner resistance biggest cut of fill materials ; αbc ' : stickiness factor denotes an anchor link between soil health - reinforced with c ' c ' : effective cohesion of the packing material . Comment crease sliding surface method - The method of calculating " wedge block two " not consider the effects of horizontal thrust due to the inclination of the upper surface created ( only considering the vertical force is the weight soil ) . " Block wedge two part " is a general form of the limit equilibrium method . This method has the advantage of simplicity , the present destructive potential can determine the approximate gradually in a wide range . In addition, this method is also easy to set up a loop calculation program on your computer. Crease sliding surface method is used in
-7- case of ground sandwiched between soft soil [12] , occurred sliding surface will follow the crease sliding surface soft soil layer , this case Fsmin safety factor is determined principle of sliding block fragmentation , applied to heterogeneous soil types ( sandwiched weak soil layer ) . b . The method for calculating fragmentation circular slip surfaces [12] , [15] , [32] , [33] , [35] , [49] , [65] , [63] The assumptions for the fragmented approach to circular slip surface properties of the reinforced embankment interaction forces between the fragments are ignored because of the complex remains influential to the power and presence of sliding soil core makes little disturbed . In addition, the method also assumes interaction force between the core is ignored and the core layer are horizontal ; remains only to be considered at the position sliding surface intersects with assumptions at each piece separately ; torque to keep the combined effects of soil aggregate and not less than slipping torque caused by the weight of soil ( with interest calculated torque rotary sliding blocks ) . Thus equilibrium conditions need to satisfy to solve the problem : (1.10) Where: MD sliding torque caused by the weight of the soil itself and external load ; MRS : torque due to a shear strength of the soil ; MRR : holding torque due to the presence of aggregates in slope ( 1.11 ) Where: Tj is the greatest traction in core in slope at j ; yj : j distance to the center core layer sliding Y axis ; ffs : partial factor applied to the unit weight of the soil ; fq : partial factor applied to the external load , Wi : weight of the ith soil column ; Wsi : external load acting on the piece i c ' : unit cohesion of fill materials identified in effective stress conditions , ui : pore water pressure exerted on the sliding surface in pieces i ; φ'p : maximum shear angle of fill materials ; fms : the partial material factor applied to tgφ'p and c ' ; : adjust the torque coefficient ( limit state damage taken by 1.25 , limit state obtained by using 1.0 ) . In length it remains to be determined not undermining slip occurs remains is : (1.14) Lej is reinforced anchor length at least j in slope ; fp : partial coefficient to control the core is pulled slip phenomenon , fn : partial coefficient to control the economic consequences caused by damaged buildings cause ; fms : partial factor applied to tgφ'p and c ' , ws : external load ( due to static load ) , α ' : interaction coefficients indicate the relationship between power and ground anchor reinforced with tgφ ' p ; φ'p : maximum shear angle of fill materials ; αbc ' : stickiness coefficient indicates the relationship between soil anchor strength - reinforced with c ' c ' : effective cohesion of the packing material . Slip circle method was developed by [48] : K. Terzaghi , AV Bishop ; G.B. Janbu ; A.A. Nichiprovich ; Theory Method humidity . Comment circular slide fragmentation methods : Method assuming stable sliding
-8- surface with a radius R , are commonly used calculations to figure out the most dangerous slip with a safety factor Fsmin . Slip circle method can calculate the slope stability is generally different shapes , suitable only for homogeneous soil . Essence reinforcing factors to be considered tensile strength Tmax . c . Some other computational methods for reinforced embankments based on equilibrium torque or force . i . The method combined stress calculations [15] , [32] , [33] The destructive method combined stress calculations , is determined on the basis of combined stress theory and the method of analysis according to Mohr interest . In the final analysis , this method is somewhat more complex but potentially better analysis can be reviewed by the local variation of stress . ii . The method calculates the logarithmic spiral slip surface [15] This method , assuming slip surfaces logarithmic spiral has simplified the calculations , can be directly determined torque causing imbalance . Holding torque ( due to the presence of aggregates in slope MRR ) must be greater than the torque cause imbalance (M0), ie, M ≥ M0 . Among them : MRR is the torque due to a presence of aggregates in slope , Mo : torque imbalance caused by slope (1.15) Where: Tj is local tension of the fabric at j ; YJ : the core layer j distance to the center of the Y -axis slide . (1.16) ffs is the partial factor for the unit weight of the soil ; fq : partial coefficients for external load ; wi : ith soil column weight ; Wsi : external load acting on the piece i ; ui : Pore water pressure effect on the ith sliding piece ; : torque correction factor . The length of the anchor reinforcement is also determined by the formula (1.14) iii . Gravity method cohesion (Rankin) [15] , [35] , [63] This method of calculation applied retaining wall is adjusted to calculate the slope remains the case . In calculating principle applies two wedge blocks but adjusted to determine how lateral pressure of the soil and the connecting points of greatest traction corresponding to the tilt of the structure . Comment analytic methods . The analytical method based on limit equilibrium , embankment stability analysis using assumed sliding surface : circular , with every crease ... assumed sliding surface found a corresponding safety factor . So should identify numerous slip surfaces with values different safety factor . Therefore, the ability to find the most dangerous sliding surface with safety factor hardly accurate fit . Circular sliding surface method is mainly applied to homogeneous background ; kinked slip surface applied to multi-layered backgrounds , different physical properties . The
-9- analytical method applied in the case of computational geometry embankment sections normal , relatively simple . Not yet reviewed analytical methods to elastic modulus ( E ) of land , land cover , and reinforcement material stiffness ( EA ) of the reinforcement material in the background . 1.1.2.3 Numerical methods and computational software 1 . Method extreme Gauss principle and finite difference [8] extreme method Gauss principle by GS . Prof. Ha Huy Cuong proposed , Hoang Dinh Dam authors consider the problem in the absence of reinforcement layout and software problems have reinforced horizontal . This problem is multi-layered elastic system , relations between state suat_bien application form on the basis of elastic theory for the case of plane strain problem . In the case of reinforced embankment , to determine the state of stress - deformation of the embankment below the horizontal reinforcing effects of vehicle weight ( distributed on a circle with a radius defined ) is asymmetric problem axis , Hoang Dinh Dam authors have used finite difference methods to calculate . 2 . Basis of a calculation software program . a. Geo.Slope Software ( Canada ) [10] , [11] , [12] , [20] , [22] Stability calculations : Theoretical Foundations of stability calculation in the program Geo.Slope balance of power and torque to balance safety factor based on the theory of general limit equilibrium ( General Limit Equilibrium - GLE ) . As of stress , deformation : finite element method is applied in this problem based on stability problems limit equilibrium . Variables , the factor of safety obtained from using limit equilibrium methods . Thus , the factor of safety (Fs) is calculated by finite element software is regarded as a stable factor in Slope / w , is defined as the ratio of the total jet cutting along the sliding surface ( ΣSr ) to the total shear stress along the slip surface that (ΣSm) : b . Plaxis software (Netherlands) In the stability analysis and slope deformation problem embankment using geotextile , see Plaxis model stress-strain relationship of geotextile and contact elements between geotextiles for ground assuming ideal elastic plastic Mohr - Coulomb as picture 1:27 Finite element method determines stability safety factor method decreased c - φ read as follows : tani ci su ,i (1.19) F    tanr s cr su ,r Among them : , and is the friction angle , unit cohesion and undrained cohesion of the ground ; , and is the friction angle , cohesion and unit cohesion was not impaired drainage of land background . The decline in value is calculated as
- 10 - follows   arctan  tani  ;   cr  ci and r 3 1  Fs  Fs su ,i su ,r  (1.20) Fs c . Software phase2 ( Canada ) phase2 2sin 2c cos  software calculates stability analysis and slope 1-sin 3 1-sin E excavation constructed by FEM method , find 1 the safety factor method decreased by c - φ . Phase2 Plaxis see similar stress-strain relationship of geotextile and contact elements with geotextile ground is linear Mohr - Coulomb model in Figure 1.27 Comments calculation methods : The software presented above are considered in calculating the drag system behavior of geotextile and contact elements geotextile with elastoplastic ground is ideal , the standard linear Mohr - Coulomb vandalism. In fact , this relationship is complex includes several different stages according to Robert M.Koerner model is presented in the next chapter . Therefore, in calculating not realistically describe the material work . Compared to other analytical methods mainly solved the problem of slope normal shaped , circular slip surfaces , kinked hypothesis , based on the limit equilibrium calculations taking into account the intensity geotextile ART but not considering the elastic modulus (E) of land , the reinforcement material and stiffness (EA) of the reinforcement material , the finite element method to calculate all kinds slope different shapes , which consists of multiple layers embankment complex nature , the safety factor is defined as unique and single sliding surface based on the consideration transferred in the element node . On the other hand , the finite element method also include many factors affect the elastic modulus of the ground , elastic modulus , hardness of structural reinforcement material in the soil ; Compared with organic difference method limit approximation problem by differential equations , applicable only basic rectangular in shape with a simple relationship , while finite element methods solve approximation results by word solution of the problem , the background can be applied to any geometric shape and have complex boundary problem in discrete relationships . From the comparison presented above shows the finite element method has several advantages compared to other methods . 1.2 These issues exist which thesis research will focus . 1 . The calculation methodology slope stability embankment with or without reinforcement geotextile materials , commonly used analytical methods according calculate equilibrium limit based on the assumption sliding circular , sliding surface kinked hypothesis . However, numerous studies around the world show that the slip surface is not sliding round and should be studied by the proposed calculation methods [15] , [57] , [60] . 2 . Calculations embankment stabilization geotextile reinforcement method
- 11 - analysis considering only the intensity of the geotextile (Tmax) without considering the stiffness of geotextile (characterized by elastic modulus eg) . 3 . Relationship stress - deformation of the geotextile is a complex non-linear path . Therefore need to develop computational models suitable for materials which have ties pull this complex behavior . 4 . Tension Tmax values of geotextile -reinforced embankment should be studied to determine the calculated value at each point (location) of the layer of geotextile -reinforced embankment reaching the limit state intensity . 5 . The study determined the effect of hardness (EAg) geotextile to the safety factor embankment stability . 6 . The study reinforced embankment geotextile on : the number of necessary geotextile use , embankment slope coefficient , strength and stiffness of geotextile reinforcement affect safety fine the embankment , should be studied computation . From the experimental results calculated to draw the graph using geotextile , serving for quick reference in the preliminary design work embankment geotextile reinforcement . 1.3 Objectives of the study : Select models and algorithms built computer program problem embankment geotextile reinforcement by finite element method . From this set , solve real-world problems in construction of reinforced embankments and suggest that problems exist thesis focused research . 1.4 Contents of Applications Research geotextiles in the construction and computational models embankment geotextile reinforcement in the world and Vietnam . Computer model stability problem , embankment reinforcement permeability of geotextiles by the finite element method . Compared with other programs , other software in the world and Vietnam to establish algorithms and computational software program for research . 1.5 Research Methodology : Based on the construction of computational models using the finite element method , established algorithms and software programs compare with the calculation methods and programs in and outside the country, solving accounting and proposed outcomes achieved . Selection and calculation model building problem embankment reinforcement geotextile material is presented in the next chapter . CHAPTER 2 COMPUTATIONAL MODELS OF GEOTEXTILE REINFORCED EMBANKMENT PROBLEM . 2.1 Purpose and requirements . 2.1.1 Purpose : Selection , calculation model built using reinforced embankment soft materials describes geotechnical realistic work of structural materials in the system " soil - core " FEM method study the parameters affecting the stability analysis and stress states - deformation of reinforced embankment 2.1.2 Requirement calculation model towards working closely with the actual materials in structural system " + core land " was modeled and selection of materials characteristic landforms, such that proper reinforcement case .
- 12 - 2.2 Properties of Geotextile [42] , [62] , [63] . 2.2.1 Some properties of the concept of geotextile [62] , [63] Within the scope of this thesis , the hardness is not used in accordance with the concept of bending stiffness hardness concept here is understood as : ( EA / L ) is the stiffness of the unit element bearing axial bar , model chemical element geotextile in finite element problems . And so EA is called the element stiffness geotextile , unit is kN . 2.2.2 Road relations stress - deformation of the geotextile According to the model of Robert M.Koerner in " Designing with Geosynthetics " , 5th Edition, (USA, 2005) [63] , depending on the geotextile fabricating various relationships that last curve behavior quite complex . Some types of geotextile typical path ties stress - deformation characteristic is shown in figure 2.1 . According to Robert M.Koerner , stress-strain relations of contact elements with geotextile ground in a laboratory slide relations includes several phases : phase nonlinear , 0 - 1 , increasing stress and deformation continued slow growth , the period re- durable (hardened) - paragraphs 1-2 , to increased stress and deformation increases , and the softening phase - paragraphs 2-3 , to reduce stress and increase distortion. That relationship is shown in Figure 2.2 2.2.3 Some examples of determining mechanical properties of geotextiles [63] 2.3 Modeling the problem: FEM method in the Plaxis program , Pharse2 are considered stress - related deformation of the geotextile pull is ideal elastoplastic Mohr - Coulomb modeled (Figure 1.27) . That is the road slope - related stress as linear distortion (this slope is characterized by elastic modulus geotextiles) . Then , when the state of intensity , the geotextile will be destroyed immediately . However, according to Robert M. Koerner model of the stress - deformation of the geotextile is a non-linear path consists of several stages (Figure 2.1) . So depending on the degree of deformation of the geotextile that the stress state will be different . The following section will build computer model problem embankment geotextile reinforcement by finite element method . In particular , the specific relationship stress - deformation of the geotextile is built in a
- 13 - nonlinear model of Robert M. Koerner . 2.3.1 Some assumptions : Assumptions ground up n type, the background is one or more natural soils , each soil layer uniformity . Soft geotextile reinforcement placed in a soil layer or between two layers of soil . Minutes embankment slope m1 , m2 , ... mn . View the soil is elastoplastic multi-layered system , each layer is characterized by elastic modulus Es , Poisson's ratio ν and intensity characteristics as unit cohesion c , friction angle  . View reinforced elastic plastic material resistant traction only , not pressurized , which is characterized by (Eg) elastic modulus, hardness Eag and tensile strength Tmax. 2.3.2 Develop computational models stability problem of reinforcing soft embankment according to the finite element method [23] 2.3.2.1 The basic equations of the theory of elasticity [1], [24] According to Hooke's law , the relationship between the stress-strain response by  x   y   z   1 x  E  1  y   y   x   z   the formula: E  (2.2)  z   z   x   y   1 E  2 1    xy   xy E 2 1    yz   yz E 2 1     zx   zx E 2.3.2.3 The safety factor method decreased c - φ The safety factor is calculated as the ratio of the actual resistance and the minimum resistance as follows : (2.20) or (2:21) Among them : , and is the friction angle , unit cohesion and undrained cohesion of the ground ; , and is the friction angle , cohesion and unit cohesion was not impaired drainage of land background . The decline in value is r  arctan  tani  : cr  ci and su ,r  su ,i (2.22)    SF  SF SF Comment calculations by the finite element method taking into account many factors characteristic of the ground and reinforcing materials such as elastic modulus ground ; strength , elastic modulus , hardness reinforcement material . Finite element method to find stability safety factor in the decline of the iterative solution c - φ . In the next chapter will focus on building research program algorithm and FEM
- 14 - calculation method to calculate math embankment reinforced by geotextile . In particular , the program will build computer algorithm analysis according to the relational model stresses - deformation of the geotextile by Robert M.Koerner . This model has not been built in algorithm programs around the world as : Geo.Slope ; Plaxis or Pharse2 . This is close to the actual model of the kind of work geotextile material which is related stress - deformation complex is given in Robert M.Koerner Designing with Geosynthetics , 5th Edition [63] in 2005 previously in this document and in the 1986 version does not have version 1990 or have incomplete model stresses - deformation of materials geotextile. CHAPTER 3 THE PROGRAM ALGORITHM AND SOFTWARE TO ANALYSE GEOTEXTILE REINFORCEMENT EMBANKMENT BY FINITE ELEMENT METHOD 3.1 Develop algorithms . 3.1.1 triangular plate element [18], [24] . A flat block structure can be divided into three nodes triangular element . Each displacement element has six degrees of freedom located at the nodes . The buttons are numbered 1 , 2 , 3 in the opposite direction clockwise . The matrix elements of the triangle is given by the general equation is rewritten as follows : k e   B  E  B  dV   h  B   E  B  d   Ah  B   E  B  (3.2) T T T e 3.1.2 Element level parametric triangular plates [18] , [24] , [64] Coordinates any point in the element coordinates interpolated from nodes: . n n  Nie  1 , x   xi Nie , and y   yi Nie ( 3.4 ) displacements at any point in the n i 1 i 1 i 1 n element displacements are interpolated according to the button : ux   u xi Nie , i 1 n u y   u yi Nie (3.5) i 1 The form function of triangular plate element 3 knots written as class parameter N1  1 ; N2  2 ; N3  3  1  1  2 (3.6) The form function of triangular plate elements are nodes 6: N1  1  21  1 ; N2  2  22  1 ; N3  3  23  1 ; N4  412 ; N5  423 ; N6  431 Stiffness matrix of triangular plate element written in the local coordinate system 1 11 is: K e   B T  E  B  dV  h     B   E  B  J d  2 d 1 ( 3:13 ) T 0 0 The integral in Eq (3:13) can be done by using numerical integration are:
- 15 - 1 11 n   f  ,   d d 1 2 2 1  0.5Wi f 1i , 2i  (3:14) 0 0 i 1 3.1.3 Mohr - Coulomb model [ 33 ] , [ 54 ] , [ 59 ] , [ 64 ] Mohr - Coulomb model is the first model included the effects of stress on the intensity of the ground . The damage occurs when the stress states followed , normal stress on any plane of material that satisfies the equation:    tan   c Mohr - Coulomb model can be written as a function of stress components main (with the convention that compressive stress is negative ) as follows (Chen and Mizuno, 1990) [54] : 1 1  1   3    1   3  sin   c cos  (3:16) 2 2 3.1.4 Contact Element . 3.1.4.1 Contact element theory [26] , [48] Contact element is used to describe the phenomenon of slip between two materials with large differences in hardness . For example, the contact between geotextile and soil. Stress often limited slip largest by plastic Mohr - Coulomb criteria. Contact elements is characterized by normal stress and tangential stress, and these two components is related to the normal deformation and shear strain as follows : .    kn 0    (3:26) Where: k 0 (327)       D n 0    0 ks      ks   D is called the elastic matrix , and kn; ks is the normal stiffness and tangential 1 Stiffness matrix of contact elements : K   B T  D B  t J d (3.28)  1 Among them : [B] is a matrix relationship between deformation and displacement ; [D] is the elastic matrix as above , is the determinant of Jacobi matrix and t is the thickness of the element .  u yt  u yb  Deformation of the element :    t    (3:33)       u xt  u xb   t    In that matrix deformation displacement relations in expression ( 3:28 ) takes the following-form:  B   1   N1 0  N2 0 N3 0 N4 0 (3:35) t 0   N1 0  N2 0 N3 0 N4   3.1.4.2 The nonlinear model of contact between the land and VDKT : stress-strain relationship of the contact elements are often assumed to be ideal elastic plastic Mohr - Coulomb . However, the actual behavior of the contact between the geotextile and soil includes several stages as non-linear , re durable and soft goods . Therefore , depending on the degree of contact between deformation and geotextile - soil that stress exposure status is different in construction algorithm
- 16 - calculates loop characteristic way relationship stress - deformation characterized the relationship as shown in Figure 2.2 . 3.1.5 Geotextile Element . 3.1.5.1 Theory of Computation Element VDKT : VDKT element is modeled with bar elements have the characteristic stiffness elastic is pulled . FEM method , displacements at any point within the element can be approximated by the first two buttons of the displacement element is : uz  N1u x1  N2u x 2 (3:36) 3.1.5.2 The nonlinear model of the geotextile element: Conduct of the nonlinear geotextile element quite complex . Can model the nonlinear behavior of the line segment , based on the degree of deformation geotextile that can determine the corresponding stress . The relationship of this behavior is shown in Figure 2.1 3.1.6 Nonlinear Analysis [24] When analyzing structures under nonlinear material models or nonlinear geometry , stiffness matrix or load vector depends on the displacement . Typically , the problem is nonlinear solution based on the linear approximation of . Currently, two methods are the most widely used Newton - Raphson and Newton - Raphson improvement . 3.1.7 General block diagram program . 3.2 Construction program features : 3.2.1 Introduction to computer interface program hnh_ress V 1:00 Program Name : hnh_ress V 1:00 ( HNH_ Reinforced Embankment Stability Software - Software calculates reinforced embankment stability ) . Figure 3.12 Declaring relationship stress – Figure 3.13 Declare hardness (EAG) based strain of the geotextile on stress-deformation path of geotextile Fg 3.14 Trails approximately sliding surface Fg 3.15 Approximately the ellipse running through the most extensive deformation and circle slide 3.2.2 Introduction hnh_ress V1.00 computer program