| With the development of economy and the construction of structures,people pay more and more attention on the stability of geotechnicalengineering. As far as water conservancy hydropower engineering isconcerned, up to the end of 20th century, there are more than 40,000 dams arebuilt. They play important parts in development of economy and society. Ourcountry has rich resources of water conservancy and water power. In order todevelop economy, almost half dams in the world are constructed in our country.Very high dams are built in recent years, such as the height of dams of ThreeGorges and Longtan is about 200 meters, and the height of first level archdams of Xiaowan, Xiluodu, and Jinping is up to 300 meters. With the increaseof the height of dams and the complexity of geological conditions, the safetyand stability of dams are more and more important. The stability exists inhydraulic structures, slopes, dam foundation, and dam abutment etc. Thefeasibility of engineering construction is directly determined by the stability ofengineering and influences invest and safety of engineering.The number of prestressed anchor cables used in water conservancyhydropower engineering is very large in our country. The costs of manyprojects are about 100 million yuan. Along with the high tide of exploitationin the west, large numbers of prestressed cables will be used in waterconservancy hydropower projects. For example, more than 1,000 prestressedanchor cables of 2,000 KN and 3,000KN will be used on the high slope ofwater conveyance system of right bank of the water conservancy engineeringin Zipingpu. Moreover, the number of prestressed cables used in Xiaowan andLongtan hydroelectric power station probably exceeds 10,000. It needs 4,000and 1,500 cables respectively for cable crane platform slope reinforcement offirst level hydroelectric power station in Jinping and underground factoryworkshops and aqueduct tunnels of the right bank of the Three Gorges Project.The technology of reinforcement with prestressed cables has become one ofthe most economical and effective methods to increase the stability andresolve complicated problems of geotechnical engineering.There are a lot of kinds of cables used in geotechnical engineering.According to different methods, cables can be divided into several types. Forexample, according to the structural types of the anchorage, cables can bedivided into OVM cables, QM cables, XM cables, and Feishi cables etc;According to the types of bodies of cables, cables can be divided into steelline cable, wire bundle cables with high strength, reinforcing steel cables;According to the service life, cables can be divided into temporary cables andpermanent cables;According to the bearing state of bond length, cables can beclassified into tensile force type, compressive force type and load dispersiontype. Meanwhile, anchor cables of load dispersion types can be divided intotensile dispersion type, compressive dispersion type, tension compression type,and shearing force type. In addition, there are observation anchor cables andremovable anchor cables. According to the current situation of technologydevelopment at home and abroad, it is not difficult for technologicalparameters of anchorage and body of the cable to meet the needs ofreinforcement technology. So for definite aims and practicability,classification according to the bearing state of bond length is widely used athome and abroad. There are two different theories of operating principle ofshotcrete-bolt supporting. One is based on the conception of structuralengineering. The basic characteristic of it is the "load-structure" mode. Ittakes the weight of probably collapsed parts from rock matrix and soil mass asload that is borne by shotcrete plus rockbolt support. The most typical theoryis hanging principle of anchor bolt supporting. The requirement of this theoryis that the length of anchor rod cut across the height of collapsed arch so as tohang collapsed rocks. Another is based on the conception of rock massengineering. The basic feature is fully utilizing self-stability and preventingdamage of rock. The main function of supporting and timely rationalconstruction steps is timely controlling deformation and displacement andimproving stress state. The major application fields of anchoring areprestressed anchoring of rock mass in underground excavation, slopereinforcement, prestressed sluice and side pier, and reinforcement of damfoundation and dam abutment.Because anchoring technology develops continuously, constructionmethods are improved and developed unceasingly. Anchor construction isvery covert and professional and the experience of builders directly influencesthe quality of construction, so the anchor construction should be undertakenby specialized contingents. The main technological processes includeconstruction organization design, drilling, making anchor, storage, set up,grouting, compressed water test, tension, and record. The technology ofdrilling, tension, and grouting is key factor of construction, so it should bepaid attention in construction.New type anchor structure refers to series of compressive force type andload dispersion type. They have more rational action mechanism, moreeffective anchoring result, better economical performance, and more extensiveapplication fields. In order to obtain anchoring mechanism of new dispersiontype anchor of compressive friction combination, simulation has been donefor compressive dispersion type anchor firstly, and then dispersion typeanchor of compressive friction combination is studied in this dissertation.Numerical calculation and analysis of compressive force dispersion typeanchor use large-scale international general software ANSYS. Deformation andmechanical condition of anchoring system are researched in this dissertation.ANSYS is based on finite element method. It transforms continuous solutionzone into a group of discrete infinite combined mutually elements, and then usesapproximate function in each unit to express fragmentary field functions thatshould be solved in the whole solving domain. Design tonnage of anchor cable is180t, and the body of cable is made up of 12 unbonded steel lines. Each anchorcable has 3 internal anchorages. The numerical simulation models ofanchoring system of unbonded prestressed anchor cable of compressivedispersion type and dispersion type anchor of compressive frictioncombination are built in the dissertation. Through the test of simulation bycomputer, for one cable under the action of anchoring force, axial stress ofmortar along the hole and the distribution rule of shear stress on the interfacebetween mortar and rock mass are obtained.Based on calculation and analysis, we get the following rules:( ⅰ ) Axial compressive stress distribution between internal anchorages andshear stress distribution on the interface between mortar and rock mass aremainly influenced by the cohesive force on the interface, but frictioncoefficient of the interface has less influence on it.(ⅱ) When the distance between two internal anchorages exceeds theminimal value, superimposition of axial stress and shear stress in the grout isnot serious, so the distribution towards be stable.(ⅲ) The ratio between elastic modulus E of grout and deformation modulus E′of rock mass has important influence on selection of distance between internalanchorages. The more E/ E′is small, the more shear distribution on theinterface between grout and rock mass is even, so the distance between twointernal anchorages can be reduced, vice versa.(ⅳ) Shear stress on the interface between grout and rock mass has a closerelation to the radius of the hole. When the radius is big, the distance betweentwo internal anchorages can be reduced, vice versa.(ⅴ)The characteristics of shear distribution at the side of friction of internalanchorage and on the contact surface between two grouts show that shearresistance force is about 62KN for 140 type internal anchorage (length of frictionsegment is 180mm, diameter of friction segment is 95mm ) that is loaded with600KN. It is about 10% of 600KN load of each internal anchorage, so design forfriction of dispersion type internal anchorage of compressive frictioncombination is reasonable. Because it can effectively disperse the load onbearing board of internal anchorage, the reliability has been enhanced.(ⅵ) Determination of distance between two internal anchoragesHow to decide distance between two internal anchorages of unbondedprestressed anchor cable of compressive friction combination dispersion typeis a concerned question of cable designers. Through the numerical simulationand analysis method of three dimensional finite elements mentioned above,several major factors of influencing the distance between two anchorages hasbeen found out. They are cohesive force of grout and cemented interfacebetween concrete and bedrock, types of rocks, and the diameters of cableholes etc.Cable hole with high accuracy refers to the slope deviation of the end anchorhole and two-ended cable hole is respectively less than 2% and 1% according tothe design requirements. The main influencing factors of slope deviation arelithology of earth layer, mechanical equipment, and operations etc. To keep thehole straight by using fulcrum deviation correction principle through mechanicalanalysis of straight guide technology for horizontal hole and gentle inclined hole.Moreover, Specific measures have been represented in this paper. Then researchon flexural property and rules of horizontal holes in down-hole hammer drillingis performed. The conclusion is that the main influencing factors on hole bendingin down-hole hammer horizontal drilling are geological factors and technologicalfactors. Construction technology is found out by the productive tests ofpreventing slope of holes. Horizontal cable holes with high straightness can bedrilled by down-hole hammer so as to meet the construction requirements of theprestressed anchor cable with huge tonnages.Roof bolter is very important equipment in anchor rod construction. DKM-1borer is developed in order to meet the technical requirements of high accuracyanchor cable hole. This borer has the following characteristics:( ⅰ ) Small volume and weight, excellent property, suitable for steep slope,cavity, and narrow and small fields.(ⅱ) High stability(ⅲ) Flexible to move the borer, having locating system, conveniently andaccurately locating(ⅳ) Drilling rod is dual wall rod in borerPatent drilling rod with high strength is developed in order to drill the holeswith high accuracy with DKM-1 borer. Patent drilling rod with high strength issuitable for horizontal anchor hole with high strength and it can keep the holestraight and prevent the hole slope by contrast to well drilling rod with highstrength. It meets the technological requirements of horizontal anchor hole withhigh accuracy by using preventing inclination structure in drilling tool.The performance parameters of borer are:Performance parameters of DKM-1borerdepth of drilling 100m stroke 1700mmfeed force 0～20KN diameter of hole 59～180mmangle of drilling 0～±15° diameter of spindle 93mmdrawing force 0～40 rotating speed 30r/minmass 960kg profile size 2750×1250×1200mmThe engineering characteristics of horizontal anchor cables with high accuracyin Three Gorges Water Conservancy Engineering are:( ⅰ) Advanced structural design(ⅱ) complicated geological conditions(ⅲ) High requirements of rock mass quality and deformation control(ⅳ) Anchoring engineering is the basic conditions and main measures toassure safety of construction and structureThe technical characteristics are:( ⅰ ) Horizontal hole(ⅱ) Deep hole and long anchor cable(ⅲ) High accuracy of the hole(ⅳ) Projects in a large amount and with many types(ⅴ) Design in pace with machine(ⅵ) Hard working conditions(ⅶ) Many contradictions and big disturbanceIt assured the successful completion of Three Gorges WaterConservancy Engineering by using new techniques and a series ofconstruction measures, such as utilizing DKM-1 roof bolter developedby ourselves for horizontal anchor cable engineering with highaccuracy. The main measures include:( ⅰ) Improvement of drilling technology(ⅱ) Deviation measuring technology(ⅲ) Technology improvement of braiding bundle(ⅳ) Methods of anchor cable passing through(ⅴ) Grouting technology(ⅵ) Tension technologyIn view of a series of problems in construction, test is done and technicalconstruction technology of prestressed anchor cable is improved. Construction ofmore than 4,000 cables is finished on time. Engineering operation and dataanalysis show that excellent anchoring quality and good results are obtained.Through theoretical analysis and engineering practice of Three Gorges WaterConservancy, Basic theory is established for technique of horizontalanchor cable hole drilling with high accuracy, and a set of typicaltechniques are groped. They will offer reference to similarengineering. |
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