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Nội dung Text: Summary of doctor thesis of engineerin: Research of earth embankment stability on natural ground MINISTRY OF EDUCATION TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS Do Thang RESEARCH OF EARTH EMBANKMENT STABILITY ON NATURAL GROUND Major: Highway Engineering Code: 62.58.02.05.01 SUMMARY OF DOCTOR THESIS OF ENGINEERING Hanoi 2014WORK TO BE COMPLETED IN LIST OF PUBLISHED WORKS UNIVERSITY OF TRANSPORT AND COMMUNICATIONS 1. Do Thang (2013). “Stress field in soil is obtained by using the theory of elastic and the theory of min (max)”. Vietnam Bridge and Road Magazine. 102013. pp. 30 33. SUPERVISORS: 2. Do Thang (2013). “Research of stability for vertical slope by limit 1: Prof. Dr Ha Huy Cuong analysis method”. Review of Ministry of Construction of VietNam. (Military University of Science and Technology) 11 2013. pp. 103 104. 2: PhD Vu Duc Sy 3. Do Thang (2014). “New method research earth embankment stability (University of Transport and Communications) on natural ground”. Review of Ministry of Construction of VietNam. 62014. Reviewers 1: Prof. Dr Nguyen Xuan Truc (National University of Civil Engineering) Reviewers 2: Prof. Dr Nguyen Van Quang (Hanoi Architectural University) Reviewers 3: Prof. PhD Nguyen Truong Tien (Vietnam Society Soil Mechnical and Geotechnical Engineering) The thesis is defended to the Council assessing doctoral dissertation at the case level: University of Transport and Communications at ….h… ……, 2014. Thesis can be found in the library: 1. National Library VietNam 2. University Library of Transport and Communications
MINISTRY OF EDUCATION & TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS Do Thang RESEARCH OF EARTH EMBANKMENT STABILITY ON NATURAL GROUND Major: Highway Engineering Code: 62.58.02.05.01 SUMMARY OF DOCTOR THESIS OF ENGINEERING Hanoi - 2014 WORK TO BE COMPLETED IN UNIVERSITY OF TRANSPORT AND COMMUNICATIONS SUPERVISORS: 1: Prof. Dr Ha Huy Cuong (Military University of Science and Technology) 2: PhD Vu Duc Sy (University of Transport and Communications) Reviewers 1: Prof. Dr Nguyen Xuan Truc (National University of Civil Engineering) Reviewers 2: Prof. Dr Nguyen Van Quang (Hanoi Architectural University) Reviewers 3: Prof. PhD Nguyen Truong Tien (Vietnam Society Soil Mechnical and Geotechnical Engineering) The thesis is defended to the Council assessing doctoral dissertation at the case level: University of Transport and Communications at ….h…' ……, 2014. Thesis can be found in the library: 1. National Library VietNam 2. University Library of Transport and Communications LIST OF PUBLISHED WORKS 1. Do Thang (2013). “Stress field in soil is obtained by using the theory of elastic and the theory of min ( max )”. Vietnam Bridge and Road Magazine. 10/2013. pp. 30 - 33. 2. Do Thang (2013). “Research of stability for vertical slope by limit analysis method”. Review of Ministry of Construction of VietNam. 11/ 2013. pp. 103 - 104. 3. Do Thang (2014). “New method research earth embankment stability on natural ground”. Review of Ministry of Construction of VietNam. 6/2014. 1 INTRODUCTION 1. The reason of selecting project Subgrade is an important part of highway. To ensure the stability of subgrade is a prerequisite to ensure the stability of the pavement structure. Research methodology stable subgrade is widely used in today's designs is limited equilibrium methods. Basic equations of this method consists of two balance equations (plane stress problem) and Mohr- Coulomb yield condition. However, the limit equilibrium method is not consider the phenomenon volume change of soil when using the yield condition Mohr- Coulomb. On the other hand, the basic equations above do not allow determining the stress state in the yield imperfections, ie not consider the stress state of the entire soil mass. Therefore, in the thesis "research of earth embankment stability on natural ground" is presented below, using theoretical min ( max ), author can apply directly limit theorem to study the stability of the overall soil mass and stability of the embankment on natural ground. 2. Purposes of the research Building a new method (method directly applicable limit theorem) evaluate soil stabilization in accordance with the actual working of the soil environment, the study contributes to the development of stable subgrade . Applying the above method to build a computer program, set the tables and nomogram helps engineers quickly determine the height and slope of embankment limited. In addition, using the lower limit theorems of the theory of limit analysis tells us that the stress distribution in the soil mass before ruin and slip surfaces occur in soil mass, freely given variables appropriate enhance soil stabilization when necessary. 3. Subjects and scope of the research Research subjects: The earth embankment on natural ground. Scope of the research: The research of the stability problem of earth embankment on natural background consider in the case of plane problems. 2 4. Scientific meanings and pratice of the project Soil is not so elastic material in plane problems, two balance equations are not sufficient to determine the three components of stress. Author used more conditions min ( max ) to have enough equations determine the stress state in the entire soil mass and directly applicable limit theorem for stability studies and natural embankment and foundation. In the thesis presents the various stability problems: limited intensity of the ground under load horizontally forward hard (Prandtl problem), block slope of dry sand , steep tomorrow so natural on under Business Use of the external ear and self-weight, trapezoidal embankment on so natural under the effect of self-weight. Since the study was able to draw conclusions and explanations and quantitative following: - The yield condition Mohr- Coulomb said materials with internal friction greater the bigger the load capacity. However, for embankment construction materials such as soil, sand, shred lascivious the material has a large capacity unit new headquarters is the material guarantee a better slope stabilization. Practices embankment construction in our country attest to that. - Slip surface appears on the sliding surface slope and embankment surface when external load effects. - When study the stability of embankment only consider self weight of the soil does not appear on the slip surface on slope and embankment surface. - Depending on the intensity (c, ) patch material to natural ground which happens all cases Disruptive packing material intensity the greater the height of the dam increasingly limited so large, increasingly large talus slope . When embankment intensity (c, ) equal to or less than the natural ground intensity it takes only appear at the foot sliding embankment slopes, embankments When intense than natural background is ingrained into the sliding surface nature. - The calculation and comparison shows embankment height limit under the author’s method approximates the heights rebate under sliding surface methods (using a safety factor greater than 1). This is explained by the method of sliding surface gives the upper limit of the height of the embankment . 3 Author has developed a computer program, set the tables and nomogram helps engineers quickly determine the height and slope of embankment limited . Also, from the graph contours plastic flow rate will determine the net slip surfaces should be able to come up with measures for reinforcing appropriate place to raise the roadbed stability when needed 5. Layout of thesis The thesis includes the following sections and chapters: - Introduction - Chapter 1: Overview of research of earth embankment stability on natural ground - Chapter 2: Facility theory to research stabilize earth embankment stability on natural ground - Chapter 3: Fundamental problem about limit load and slope stability - Chapter 4: Research of stability of soil mass with vertical slope - Chapter 5: New method to research stability problem of the earth embankment on natural ground - Conclusions and Recommendations - The appendix 6. New contributions of the thesis 1- Different from traditional methods of soil mechanics, author uses theory min ( max ) to be able to directly apply the method limit analysis to research earth embankment stability on natural ground (not given stress state or shape of slip line). Use the lower bound theorem of the theory of limit analysis gives us the stress distribution in the soil before failure and found slip line field, that we can take appropriate measures to improve stability when needed. 2- Different from traditional methods is research methods separate slope and bearing capacity of the natural, author built overall stability problem of the embankment so natural to be able to study the impact between them. 3- The soil stability problems presented in the thesis is correct on mechanics, mathematics and strict new. In terms of mathematical is that the non-linear programming problem because constraining is the yield 4 condition Mohr- Coulomb. The solution method is a method of finite difference and to optimize the use of available content, author programmed on Matlab's software to solve. Difference schemes for the solution of the thesis results with high accuracy, such as Flamant problem with some, limited slope angle of internal friction materials that do not intend to use ice internal friction angle of the material, load within the limits of medium to steep tomorrow theoretical formula (this result is also new), etc 4- Research methods stability problem of the earth embankment on natural ground is presented in the thesis in a new method. Author has developed a computer program, set the tables and nomogram helps engineers quickly determine the height and slope of embankment limited. Also, from the diagram contours plastic flow capabilities will determine the slip line field should be given the appropriate measures for reinforcing the right position to raise the embankment stability when required. Chapter 1 OVERVIEW OF RESEARCH OF EARTH EMBANKMENT STABILITY ON NATURAL GROUND This chapter presents the research of earth embankment stability on natural ground has been applied in Vietnam and countries around the world. Next, the authors analyze strengths and weaknesses and the existence of that approach. Finally presentation objectives and content of the research thesis. 1.1. Analysis of related research in the country and abroad 1.1.1. The unstable form embankment on natural ground According roads design standards TCVN 4054-2005 [7] and its foundation to ensure stability, maintaining the geometric size, have sufficient strength to withstand the impact of vehicle and load factors nature during use. Therefore, the embankment must not be phenomena such as slope sliding, sliding part up on the slopes, slip surfacing, embankment subsidence on soft soil 1.1.2. Research methodology stable subgrade Soil material is complicated, we do not know the full range of mechanical and physical characteristics of it. However, soil samples studied in the laboratory experiments and pressure plate at the scene 5 showed that the land can be considered as ideal materials comply wizened the yield condition Mohr- Coulomb [34] to be able to use limit equilibrium method or the more general theorem of limit analysis to study the stability of the soil mass. So, in this section, before the introduction of the research methodology stable ground, the author presents the basic contact ideal plastic materials. 1.1.2.1. The basic contact of elastic perfectly plastic material There are many different mathematical models to establish the relationship between stress and deformation of plastic material. So far, the researchers have agreed to use the model determines the speed plastic deformation according to the following equation [35], [36],[40], [41]: (1.9) where: is a scalar proportionality factor; ≥ 0 if f = k and ' f = 0 (k is a yield limit); = 0 if f < k or f = k and ' f < 0. Relation (1.9) shows the dimensions of the plastic deformation of the surface normals coincide with the construction of flexible plastic surface in stress coordinates. So the formula (1.9) is called the normal rules, also known as associated flow rule, regarded dimensional plastic deformation rate coincides with the gradient of the plastic flow function. It is possible that the plastic problem is complex because flexible nonlinear properties. However, designers are often interested in power limit, or limit load of the structure, ie the capacity to cause structural damage. In that case use "limit analysis" is a simple method that designers are interested in [25], [33], [34], [48]. The foundation of this approach are two definitions and the following theorem: Definition 1: An equilibrium system, or a statically admissible field of stresses is a distribution of stresses that satisfies the following conditions: a. It satisfies the conditions of equilibrium in each point of the body, b. It satisfies the boundary conditions for the stresses, c. The yield condition is not exceeded in any point of the body. ij ij p ij )(f 6 Lower bound theorem: The true failure load is larger than the load corresponding to an equilibrium system. Definition 2: A mechanism, or a kinematically admissible field of displacements is a distribution of displacements and deformations that satisfies the following conditions: a. The displacement field is compatible, i.e. no gaps or overlaps are produced in the body (sliding of one part along another part is allowed), b. It satisfies the boundary conditions for the displacements, c. Wherever deformations occur the stresses satisfy the yield condition. Remark: From the definition 2 we can see the structure or hard state, or plastic (hard plastic systems). Upper bound theorem: The true failure load is smaller than the load corresponding to a mechanism, if that load is determined using the virtual work principle. From the definitions and theorem of limit analysis we see: lower bound - the stress balance; upper bound - only determine the stresses in the yield point. The upper bound indicates the same flow as ranges or chute should be to determine the load limit, the upper bound can not be used separately but must use the lower bound. Correct answers when the upper bound equal the lower bound. 1.1.2.2. Method of subgrade stability research Method of subgrade stability research (Bearing capacity of natural ground and slope stability) in plane stress problem is the method to solution following system of equations: (1.14) where: x , y , xy , yx is the stress state at a point in the soil; is the angle of internal friction; c is the cohesion. cos.csin 2 0 xy 0 yx yx max xyy yx x 7 Third equation of the system (1.14) is the yield condition Mohr- Coulomb written as stress component. 1.1.2.3. Bearing capacity of natural ground Prandtl (1920) was the first to solve the equations analytically for the case of problem on the ice when the foundation could not land at the weight. The load limit is determined from the lower limit theorems and limit theorems on the results can be considered equal to the Prandtl solution is the correct solution of the limit analysis method. Novotortsev (1938 ) address the general problem when the work load versus vertical oblique angle. In addition, there are several methods of calculating load limits other sliding surface is determined from the limit equilibrium methods such as Terzaghi method, Berezansev, Vesic, Ebdokimov, Meyerhof, Hansen,… Exact mathematical solution to the problem is an important consideration volumetric weight of the ground is very complex. Therefore , many methods approximate solutions have been developed . Sokolovski (1965 ) provide numerical solution methods based on approximation by finite difference . Actual construction and experimental models have shown that the soil mass destruction , the soil mass of the state of damage at the same time that place is still in stable equilibrium [24]. 1.1.2.4. Research methodology slope stability a. Method assumes the slip surface Actually common method used classic W.Fellenius fragmentation and auditing methods to Bishop slope stability assumption soil on the slope instability will slip round cylindrical slip surface. Bishop method takes into account the effect of horizontal thrust from both sides of the sliding slice (not to the point of interest of the two horizontal forces put it). In addition to the above two methods is very much the way fragmentation methods such as: Janbu method, Morgenstern-Price, Spencer, American engineers association, or methods based on general limit equilibrium theory GLE, the method takes into account the forces between the pieces to reflect most closely the actual interaction between the slice 8 b. Method assumed stress field To determine the height limit of a vertical slope according to the lower bound theorem, WF Chen [33], [34] has assumed stress field in three regions correspond to two equilibrium equations. Conduct Mohr circle for each area and get points to reach the foot of the steep yield limit first plastic (Mohr circle tangent to the Coulomb) when increment height of the vertical slope H. 1.2. Shortcoming issues in the research of earth embankment stability on natural ground Research methodology stable roadbed is widely used in today's designs is limit equilibrium method or methods of solving equations (1.14) includes two balance equations and yield condition Mohr-Coulomb (plane stress problem). Solve the system under stress on users to limit theorem under the assumption of stress states in each region soil mass balance equation satisfied and Mohr - Coulomb condition, so here 's how indirect. Solve the system used on the skating track on the limit theorem by writing equations in polar coordinates . However, the slope of the applied solution is very difficult to have assumed before sliding surface . Methods commonly used method today is fragmented classical and Bishop method assuming circular slip surface is cylindrical . W. F. Chen used a logarithmic spiral slip surface to calculate . Limit equilibrium method with the above two solutions , as WF Chen commented [34], is not a proper application of limit analysis method of the above theory - ideal plasticity by for not considering the volume of soil mass phenomenon altered flow situations using the yield condition Mohr- Coulomb. On the other hand, the basic equations above do not allow determining the stress state in the plastic flow imperfections, which is not considered a state of stress of the whole block of land because land is not so elastic material with two balance equation which has three hidden, so can not determine the state of stress in the soil. 1.3. Objectives and contents of the thesis research Ngo Thi Thanh Huong when researchers calculated stresses in the ground transportation works [19], under the guidance of Prof. Dr Ha Huy Cuong combined max shearing stress conditions to achieve the greatest [...]... right position to raise the embankment stability when required 2 Recommendations 1- Uses theory min (max) and limit analysis method to be able to research earth embankment stability on natural ground 2- We can use this method to research the stability of excavation 3 Further research directions Combined with the theory of consolidation to solve the two most important issues for subgrade stability and... Kmin stability or displacement limits There are these results are due the accurately diagram and directly applicable limit theorem of limit analysis methods Chapter 5 NEW METHOD TO RESEARCH STABILITY PROBLEM OF THE EARTH EMBANKMENT ON NATURAL GROUND In this chapter, using the theory min (max) and limit analysis method to research stability problem of the earth embankment on natural ground 5.1 Research. .. deformation zone and hard soil wedge below foundation similar solution of Prandtl 16 Limit load of ground approximately with a solution of Prandtl, pgh = 5,14c (difference 2,8%) This difference is due to the solution of Prandtl consider only the stress state of yield deformation zone limited to a certain range below the foundation , the author's solution allows us to identify the stress state of the... complete the research process and embankment stability and natural ground 2- The program lets solve a stable embankment and quickly determine the stress state in the embankment appear natural and ground in the different conditions on the ground geometry of the road, the mechanical and physical characteristics of the land cover and natural background Through the survey, a systematic calculation shows the... stabilization Practices embankment construction in our country attest to that 4.2- Slip surface appears on the sliding surface slope and embankment surface when external load effects 4.3- When study the stability of embankment only consider self weight of the soil does not appear on the slip surface on slope and embankment surface 4.4- Depending on the intensity (c, ) patch material to natural background... problem constructively determine stress field in the earth Finally, the method presented in accordance finite difference solution and some results to show properties can use this theory to research of earth embankment stability on natural ground 2.1 Theory min (max) Soil is the product of weathering processes on the same layer of the earth' s crust, which formed the sediments In natural conditions, soil... Research stability problem of the earth embankment on natural ground The problem arises: For width of the embankment and slope gradient, the physical properties of embankment and natural ground; asked to identify the critical height to ensure a stable embankment B nÒn 1: m m 1: H c1, 1 1 Hgh c0, 0 0 Figure 5.1 Diagram determined the critical height of embankment 21 The author's solution... gh slope of dry sand equal internal friction angle of sand We found that limited research steep angle of dry sand blocks by the way of PhD Ngo Thi Thanh Huong [19] gives us the full status of the entire mass of sand, while previously only solution is balanced review of the counterclaim on the slope From solving the problem of limited angle of sand, the author received a stable shape of the sand... CONCLUSIONS AND RECOMMENDATIONS 1 General conclusions 1- Different from traditional methods of soil mechanics, author uses theory min (max) to be able to directly apply the method limit analysis to research earth embankment stability on natural ground (not given stress state or shape of slip line) Use the lower bound theorem of the theory of limit analysis gives us the stress distribution in the soil before... Huong in his thesis on applied theory to solve the following problem : - Status subcritical stress natural soil under the effect of self-weight - Angle of slope of the critical mass of dry sand - Load capacity of the ground under the foundation tape not consider myself weight PhD Nguyen Minh Khoa in his thesis was developed to solve theoretical limit stress in the natural ground under the weight of . the embankment stability when required. Chapter 1 OVERVIEW OF RESEARCH OF EARTH EMBANKMENT STABILITY ON NATURAL GROUND This chapter presents the research of earth embankment stability on natural. stabilization when necessary. 3. Subjects and scope of the research Research subjects: The earth embankment on natural ground. Scope of the research: The research of the stability problem of earth. 4: Research of stability of soil mass with vertical slope - Chapter 5: New method to research stability problem of the earth embankment on natural ground - Conclusions and Recommendations