Tài liệu hạn chế xem trước, để xem đầy đủ mời bạn chọn Tải xuống
1
/ 27 trang
THÔNG TIN TÀI LIỆU
Nội dung
MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT THUYLOI UNIVERSITY NGUYỄN MAI CHI RESEARCH FOR SCREW ANCHOR WITH APPLICATION TO STRENGTHEN COMPONENT REVETMENTS OF CANAL LINING Major: Geotechnical Engineering Major Code: 9580211 SUMMARY OF DOCTORAL THESIS HA NOI, 2021 The work was completed in Thuyloi University Supervisor 1: Prof, Dr Trịnh Minh Thụ Supervisor 2: Prof, Dr Nguyễn Chiến Reviewer 1: Assoc Prof Dr Nguyen Van Hoang Reviewer 2: Assoc Prof Dr Nguyen Duc Manh Reviewer 3: Assoc Prof Dr Nguyen Huy Phuong The thesis will be defended at the Thuyloi University at 14/ 01/2022 Can be Referenced: - National Library - Library of Thuyloi University INTRODUCTION The necessary of research The work is to strengthen canal in which there is a protection slope as a concrete, placed concrete blocks or grouted rock (rigid canal) These protections have heavy weight, when applied on soft soil then usually appear subsidence, crack on the surface, erosion of concrete or open joint the space has developed between the two revetments which may initiate further damage When the space becomes to large, subsoil material may be transported through the joint or grass will grow at joint lead to prevent flow in the canal In addition, the construction of concrete slope protection, placed concrete blocks or grouted rock are usually taken much time Especialy, during fully irrigation condition, the quality of slope protection canal will be difficult checked Since, the study: “Research for screw anchor with application to strengthen component revetments of canal lining”, for the purpose of proposal a new solution to protec of slope canal so that to make good the mistake of existing slope protection canal as mentioned above, and to achieve good technical condition, fine arts, save time and easy during installation process, and long-time effect Acordingly, the study has necessity, scientific meaning and reality Aim of the study The purpose of research is to find out a scientific, economical, modernistic solution and apposite to Vietnamese farm condition In order to strengthen component revetments of slope protection canal Objectives and scope of the study 3.1 Objectives of the study The objectives of the study is screw anchor with application to strengthen component revetments of slope protection canal 3.2 Scope of the study - Revetments of canal slope protection - The soil at field site test will be selected 2nd group in TCVN 4253-2021, standard of hydraulic engineering foundation, which are cohesive soils with plastic state, semi-plastic state - The material such as polyme or composite, has not researched yet The research content (1) Overview of canal slope protection in Vietnam and the world, review existing technical mistakes and point out the problem which will be solved in the study (2) Study on the basical theory of earth anchor To propose the basic theory for estimating of the pulled out bearing capacity of screw anchor on the canal slope (3) The testing for pulled out bearing capacity equation of screw anchor on the earth slope in the laboratory and field Establishment the pulled out bearing capacity equation of screw anchor on the canal slope and proposal condition of application (4) To find out a new structural revetments including screw anchor and light material revetment plates for canal slope protection with application to case study Research approach and methods 5.1 Approaches Systems approach: A comprehensive view of solving problem for upgrade of canal slope protection as well as basic theory, design procedure, installation and mainternance Inheritance approach: Inheritance of previous research results on screw anchor, proposal to expand with applications Modern approach: Proposal a new structural canal slope protection with innovation of material and radically new technical solution 5.2 Research methods: - Theory method: Analysis of earth anchor theory, principle for design - Experimential method: Testing for pulled-out bearing capacity of screw anchor on big sample in the laboratory and field test at study sites - Expert method: Contributions of scientistes and experts for the study Scientific and practical significance 6.1 Scientific significance Establishment a scientific basis and calculation method to apply for screw anchor, using to strengthen component revetments of canal slope protection, estimating for pulled-out bearing capacity of screw anchor on the earth slope with an equation The screw anchor with its structure including plate revetment, cable connection which can be used to strengthen for existing canal revetments or replace traditional material by modern light material as a polyme or composite 6.2 Practical significance The screw anchor with application to strengthen component revetments of canal lining can be used as a effective solution in soft soil foundation, especially saturated cohesive soil is popular soil in typical deltas of Vietnam The screw anchor is installed in the soil, then connected it to revetments The pulled-out force bearing of screw anchor will keep more stable of revetments This feature is to lead for options of application which are reducible weight of concrete or stone, using HDPE Geomemberane, or prefabricated (formatting shape) of composite revetments plate This solution will bring canal slope protection closer to natural slope and still fully required technical condition and the beauty of lining Thesis structure In addition to the Introduction and Conclusion, the thesis includes main chapters as follows: Chapter 1: Overview of canal slope protection and application of screw anchor to strengthen of component revetments for slope protection Chapter 2: Theoretical background of earth anchors and research methods for using screw anchors to strengthen component revetments of slope protection Chapter 3: Testing for pulled-out bearing capacity of screw anchor on earth slope Chapter 4: Application of research results- A case study CHAPTER OVERVIEW OF CANAL LINING AND APPLICATION OF SCREW ANCHOR TO STRENGTHEN OF COMPONENT REVETMENTS FOR SLOPE PROTECTION 1.1 Overview of canal slope protection in Vietnam, on the world and shortcoming of existing protections 1.1.1 1.1.1.1 Types of canal lining in Vietnam Orriginal canal slope (Earth canal slope) Grass is usually grown on canal slope with simple structure protection and easily installation However, this type of canal is impacted by rain, wave or animal then the banks frequently eroded and it was necessary to make stronger bank protection 1.1.1.2 Grouted rock or stone masonry of slope protection Grouted rock or stone masonry is a popular type of lining in Vietnam This type of lining is suitable when canal is constructed on stiff soil Lining of stone masonry can be applied in areas where suitable materials, such as stone is available – The construction of this type is relatively slow and the cost of labour is the major expense 1.1.1.3 Precast cement concrete slab Canal lining with prefabricated cement concrete slabs is more suitable at places where cheap labour, aggregate and transport are easily available – This type of lining is preferred over the insitu concrete lining because of better control over mixing, moulding and curing which can be achieved in a controlled casting yard Dimention of precast slabs may around 600 x 600 x 80 mm and beton vary from M150 to M250 Disadvantage of this type are easily cracked, open at joint lead to grass will grow or lose soil 1.1.1.4 Insitu concrete lining without casing Insitu concrete lining without casing is quite easily but It is not quality because of lower control during work… 1.1.1.5 Insitu concrete lining with moving casing Concrete lining is rammed in dense moutar, flat of canal slope and beauty However, It is difficult to move casing machine in narrow space The equipment is expensive and complex 1.1.1.6 Insitu concrete lining without casing and constructed using canal paver machine Insitu concrete lining without casing and constructed using canal paver machine with paddles to distribute concrete moutar Advantage of this equipment is to make dense cement moutar and also flat of canal slope and beauty But this equipment is suitable when constructed in large work and it is not flexible for all kind of canal 1.1.1.7 Neoweb material lining Neoweb is a three-dimensional cellular confinement system in ahoneycombed structure When filled with granular infill, a new composite geosynthetic entity is created from the complex interaction of cells, geometry and soil on three planes, ideal for soil confinement, stabilization and reinforcement solutions and now there is an application to canal lining How ever this technical solution is suitable on good soil foundation only 1.1.2 Types of lining on the world 1.1.2.1 Steel (or concrete) sheet piling bank protection 1.1.2.2 Reinforced Concrete of lining 1.1.2.3 Insitu Concrete bank protection 1.1.2.4 Insitu Concrete lining with special equipment of construction 1.1.2.5 Exposed Membrane Lining 1.1.2.6 Concrete filled Mattresses lining 1.1.3 Summary shortcoming of existing protection of canal slope 1.1.3.1 Subsidence or instability slope 1.1.3.2 Small moving between Components of revetment or seperate 1.1.3.3 Damage of concrete lining a) Shortcoming of precast cement concrete slab b) Shortcoming of in-situ concrete 1.1.3.4 Grass grows on the concrete lining cause low velocity in the canal 1.1.3.5 In-comprehensive in lining to make canal low efficient 1.1.4 Comment and assessment on current protective structure of canal Concrete, concrete slab or stone lining are typical lining materials for canals in Vietnam Those structures often have high weight and when constructing or installing in weak soil formation they often lead to settlement, surface cracking or forming large gaps within structure elements The canal slopes therefore affect the aesthetics and technical requirements of the canal Additionally, the construction of protective structures for canal slope using concrete or stone lining is time consuming and often results in difficulties for verification of construction quality It is noted that the construction process is implemented in a short time to satisfy the requirement of irrigated water, the construction quality therefore could be impacted Dealing with those above technical shortcomings, this research thus approaches the technology in reducing the weight of protectional structures for canal slops Taking advantages of anchorage and ease in installation, the author introduces the application of torsion anchor in fixing light-weight structures to protect canal slopes 1.2 Overview of screw anchors with application to civil engineering 1.2.1 Introduction 1.2.1.1 General information 1.2.1.2 Typical applications 1.2.2 Research on screw anchors on the world Screw anchors had studied since 1950, there were many publications, books on experimental at laboratory and field The theorytical background was almostly formed with estimating equations of pulled-out bearing capacity of screw anchors Typical researches are Trô-phi-men-cốp (1965), I-Rô-Đốp (1968), Tran Vo Nhiem (1971), Das B.M (1983), Ghaly (1991), These researches had a same interest which is the depth of screw anchors in order to get the most effective for anchoring 1.2.3 Research on screw anchors in Việt Nam Prof Nguyen Cong Man (1983) studied on limit analysis method to make an equation of screw anchor The typical of the research is to transfer from static analysyses to dynamic analysises for establishing pulled-out bearing capcacity of screw anchor Hoàng Việt Hùng (2012) had developed the problem of Prof Man with application to seadike slope protection 1.2.4 Remarks on the application and research on screw anchors The overview of screw anchors shows that the screw anchors have good uplift capacity, easily installation without noise and viberation, not deep installation and can be placed by both handdle or machine At the present, screw anchors has been used in many forms of structure engineering, so that the screw anchor is applied for canal lining which is a feasible solution With the good anchoring of screw anchor and light material of plate revetment are conneted by tensile cab to become a fully structure with reality of application 1.3 Technical issue and research approaches The general approach for canal protection issue worldwide is technology innovation including advanced construction technology, or changes in material technology for slope protection As mentioned in section 1.1.4 about disadvantages of current protection solutions for canal slope, this research proposes an advanced solution to overcome above shortcomings using torsion anchor This technology will fix the protective structures for canal slope by reducing the structure weight or replacing protective structure from traditional material such as concrete or stone lining to plastic or fiber composite Screw anchor using for reinforcing the stability of protection structure for canal slope often has moderate dimension The anchor is installed on the slope, it is therefore necessary to analyze and obtain formulas in determining the pull-out bearing capacity of torsion anchor to take full advantages of torsion anchor and ease in installation Recently, in situ experiments about pulling screw anchor are often implemented on the horizonal surface, while studies on installing and pulling screw anchor on slope are not carried out This research focuses on the experiment about anchoring capacity of screw anchor on slope especially on weak-cohesion soil (type II in TCVN 4253-2021 – cohesive soil in plastic state, quasi-plastic or softplastic) 1.4 Conclusion chapter The project: “Research for screw anchor with application to strengthen component revetments of canal lining” with the purposes of analyzing and finding new technology solutions to deal with technical shortcomings for canalslope protection is and has scientific and reality meanings In conclusion, with the technical solution in reducing the weight of protection structure of slope or replacing protective material for canal slope, the stability requirement for the protective structure is quite important The application of CHƯƠNG EXPERIMENTAL STUDY ON UPLIFT CAPACITY OF SCREW ANCHORS ON CANAL SLOPE AND ESTABLISHING OF ULTIMATE TENSILE CAPACITY EQUATION 3.1 Introduction 3.1.1 General concepts 3.1.2 Contents of Experimental Study 3.1.3 Selected parameters of screw anchors for testing In this study, the diameter of screw anchors is inherited from previous research [30], D=8cm to D=14 cm, the reasons were showed in full thesis The screw anchors with D=8cm, D=10cm, D=12cm and D=14cm were designed with corresponding inter-helix (Lx) Lx=1,2D, Lx=1,6D, Lx=2D, Lx=2,4D There are 16 types of screw anchors for experimental study on canal slope (m=1) at field site The results test had selected Lx=1,2D, Lx=1,6D, Lx=2D which were easily installed, additional selected anchor with Lx=2D is better in direction of installation on the canal slope The screw anchors with inter-helix Lx=2,4D is difficult in installation So, the screw anchor with Lx=2D is selected for experimental study in field site 3.1.4 3.2 Selected embedment ratio in series testing Tensile testing of screw anchors on model soil in laboratory 3.2.1 Aims 3.2.2 The testing Equipments 3.2.3 Testing Procedures 3.2.4 Physical Properties of soil model (big soil sample) in Laboratory 3.2.5 Construction process of model soil in laboratory 3.2.6 Testing circumtances 3.2.7 Results test in laboratory 3.2.8 Assessment for testing results 11 Results testing of ultimate screw anchors tensile capacity with embedments ratio on slope ratio m=1 and m=1,5 of soil model in laboratory were summed up at Fig 3.25 The result testing shows that the embedment ratio crictical is H/D=8, when screw anchor is istalled at H/D=8 then ultimate tensile capacity of screw anchor is fully effective The same remarks were given in B.M Das (1983) … I-Rô-Đốp (1968), B.M Das (1978) also studied on embedment ratio (H/D) of screw anchors and gave conclusions When embedment ratio (H/D=6), the screw anchors is moderately effective of uplift resistance When embedment ratio H/D=8, the screw anchors is fully effective of uplift resistance In case embedment ratio H/D>8, uplift resistance of screw anchor is slightly increase so that the embedment ratio of (H/D=8) is critical value The results test in laboratory will help cut-down ineffective testing at field so that field test will work for cases with embedment ratio critical (H/D=8) and screw anchor with inter-helix (Lx=2D) using for revetments of canal slope protection 3.3 3.3.1 The testing of ultimate screw anchors tensile capacity at field Aims The testing of ultimate screw anchors tensile capacity at field for precise pullout bearing capacity equation of screw anchor, improve of installed procedure for screw anchor on canal slope 3.3.2 Introduction of field site for testing The project of reformation Dong Coi river to become a drainage canal for area of 1612 (ha) during rainy season In adition, a segment of Dong Coi old river was dredged to become a regulable lake of Luylau culture zone, Ho town, Thuanthanh district The field site for testing is construction site of project The testing duration is from 17/05/2018 to 29/05/2018 3.3.3 Geology Engineering In the construction site of project has three mainly soil layers: 12 Bảng 3.1: Physical Properties of soil Symbol l Unit Moister content W % Unit Weight Dry Unit Weight Particle Unit Weight Void No Properties of soil Layer 2A Layer 2B Layer 35,64 37,54 23,02 kN/m 17,3 17,3 18,7 d kN/m3 12,7 12,6 15,2 s kN/m3 27,1 26,9 26,8 n % 53,0 53,2 43,5 Saturated G % 86,9 88,9 80,2 Void ratio eo 1,129 1,137 0,770 Liquit Limit LL % 43,3 40,8 25,1 Plastic limit PL % 27,0 26,8 19,1 10 Plastic Index PI % 16,3 14,0 6,0 10 Liquid Index LI 0,47 0,77 0,68 11 Friction of angle độ 12 Cohesion c 13 Compresion Factor a1-2 14 Permeability Factor 3.3.4 k 13 12' 11 05' 15058' kN/m2 19,5 15,2 12,2 m2/kN 0,039e-2 0,048e-2 cm/s 2,61x10 -5 5,10x10 0,030e-2 -5 1,07x10-4 Testing Procedure 3.3.4.1 Equipment for testing 3.3.4.2 Testing Cases 3.3.4.3 Testing steps The tensile load is increased by steps until rearched top load capacity and followed ASTM Designation D3689-1990 [48] The duration of testing and remaining tensile load are followed BS 8081:1989 [49] 3.3.5 Result Test 3.3.5.1 Results test for ultimate tensile capacity of screw anchor in Clayer soil hard-plastic state (Layer 2A) a) Uplift capacity of screw anchor on slope ratio m=1,0 b) Uplift capacity of screw anchor on slope ratio m=1,5 13 3.3.5.2 Results test for ultimate tensile capacity of screw anchor in Clayer soil soft-plastic state (Layer 2B) c) Uplift capacity of screw anchor on slope ratio m=1,0 d) Uplift capacity of screw anchor on slope ratio m=1,5 3.3.5.3 Results test for ultimate tensile capacity of screw anchor in Sandy soil soft-plastic state (Layer 3) e) Uplift capacity of screw anchor on slope ratio m=1,0 f) 3.3.6 Uplift capacity of screw anchor on slope ratio m=1,5 Assessment of field testing Table 3.2: Uplift capacity of screw anchors on the slope canal (kN) Types of soil 3.4 Slope Ratio m=1 Slope Ratio m= 1.5 (%) Difference Clayer soil, hard-plastic state (Layer 2A) Screw anchor NMK8 6,55 6,21 5,19 Screw anchor NMK14 21,96 20,54 6,47 Clayer soil soft-plastic state (Layer 2B) Screw anchor NMK8 5,10 4,83 5,29 Screw anchor NMK14 17,72 16,71 5,70 Sandy soil soft-plastic state (Layer 3) Screw anchor NMK8 4,65 4,42 4,95 Screw anchor NMK14 17,23 16,18 6,09 Establishing equation of untimate uplift capacity screw anchor with application on the canal slope 3.4.1 General principle In this sudy, the shape of failure surface, in the processing screw anchor is pullout of soil, is analysed and selected From area of failure surface and shear strength of soil around helix, the equation of ultimate uplift capacity will be given This equation will be checked with field test for correction 3.4.2 3.4.2.1 Establishing equation Analysises of embedment ratio and shape of failure surface For establishing equation of ultimate uplift capacity, the anchors type was proposed by author, the embedment ratio H/D=8 was selected In this case, the 14 shape of failure surface around helix is a sphere with diameter 2D in which D is diameter of helix 3.4.2.2 Establishing equation Fig 3.41 shows the shape of failure surface around helix is a sphere with diameter 2D during pullout screw anchor, because the screw anchor has inter-helix Lx=2D h so that the inter-helix will change the dimension of sphere H D 2.D Fig 3.41: The shape of failure surface around helix in case H/D=8 The equation of ultimate uplift capacity of screw anchor on the canal slope: ( 3.1) Pgh 4 (D) ( i hi )tg C Where: Pgh - ultimate uplift capacity of screw anchor (kN); correctional factor; D diameter of helix (m); angle of canal slope; , C friction angle and cohesion of soil at helix; hi heigh of soil layers above helix (vertical dimension), h is sum of hi and H is deep installation of screw anchor The line H is perpendicular to the line of canal slope H cos Determination of correctional factor h hi 3.5 15 Correctional factor () was determined by field test of ultimate uplift capacity of screw anchor From equation 3.1, factor () can be disposed to become equation (3.2) if you know Pgh : Pghhc xxD (3.2) ( h )tg C i i hc In order to determine the correction factor , Pgh value was selected about 0,95𝑃𝑔ℎ at field test so that the calculated value is smaller than real value From result field test of ultimate uplift capacity of screw anchor Pgh in soil layer (2A), soil layer (2B), soil layer (3), we have corresponding values, the mean value using for all soil can be used 1,80 Review of ultimate uplift capacity of screw anchor Pgh when using 1,80 in equation (3.1) for all kind of soils The review results show that equation (3.1) is smaller than Pgh of Pgh at field site about 3,4% to 8,0% Hence, correction factor 1,80 in equation (3.1) is faithful in case inter-helix Lx=2D of screw anchor 3.6 Conclusion chapter Results test in laboratory show that the uplift capacity of screw anchor on slope depend on dense of soil (); slope ratio (m); embedment ratio (H/D) The ultimate uplift capacity value of screw anchors, which were pulled-out on slope ratio m=1,0, are bigger than values of screw anchor on slope ratio m=1,5 about 5,0% to 6,5% Results test in laboratory also express that the critical embedment ratio is H=8D, if H/D>8, the uplift capacity of screw anchor is slightly increase In case H/D