Precast Segmental Construction for Concrete Foundations for Transmission Line Towers and other Structures

Abstract

The present invention provides a precast concrete segment construction (121) for foundations of power transmission line towers, comprising of :atleast a base plate (122); a plurality of anchor bolts (124a, 124b); atleast a chimney (125); a plurality of pre cast blocks (126a,126b); atleast a horizontal shear key (130); atleast a central block (127); a plurality of vertical anchor bars (128a, 128b); and a plurality of untensioned reinforcement bars (129a, 129b). The precast concrete segmental construction of present invention is assembled using post-tensioned prestressing technology, with the advantage of minimizing construction activities at the site and with larger load baring capacity resisting uplift. The present invention provides a small-dimension precast concrete foundation blocks which are assembled in the location using medium tensile steel bars post-tensioned to assemble the individual segments into an integral foundation pad would be quite convenient and ensure superior quality as all the elements can be prefabricated in factory-like conditions. (Figure to be published along with abstract: Figure 1).

Description

Field of InventionThe present invention relates generally to the field of towers and other infrastructuretechnologies. More specifically, the present disclosure relates to a precast concreteprefabricated segmented foundation for a power transmission line and other tower likestructures and construction method thereof.Background of the InventionDue to the increased demand for covering each area with information facilities and the wholenetwork with the development of science and technology, construction demand iscontinuously increasing. There is a need for large amount of transmission lines for electricitythat need to be built up under severe conditions such as high altitude and severe cold. Thesepower transmission lines need to be installed from sources of power generation to usercentres all over the world. More and more power transmission lines pass through difficultterrains,high mountains and remote areas and have the complex service environments.Constructing foundations in these areas is a demanding task, due to mainly the geotechnicaland geological problems such as saline soil and frozen soil and severe difficulties fortransport of building materials. The importance of selecting the most suitable foundationincreases as the transmission network continues to expand across varied terrain conditions.These lines are usually supported on tall steel towers, which need to rest on good foundations.Oftentimes these lines pass through difficult terrains where it is difficult to do much site workto construct these foundations. In general, construction of power transmission line, windturbine and other tower like structures mainly consists of cast-in-place concrete foundationsto safely transmit the loads from the superstructure to the foundation soil strata below. Inother words, the current construction scenario of foundations for the tall transmission linetowers are with cast in-situ integral concrete foundations reinforced with conventional steelreinforcement, reinforcing bars and framework is installed on site and concrete is alsoinstalled on site. Also, one has to wait for a few days till the concrete hardens enough tosupport the backfill soil and the tower coming up on top, thus losing precious time as well astying up resources in such remote areas,Because the construction period of these tower structures project are generally short, areinforced concrete independent foundation or a cast-in-place pile foundation are usuallyadopted for the soft soil foundation. However, the construction period of the soft soilindependent foundation and the drill hole cast-in-place pile foundation is long, theconstruction difficulty is high, the project amount is large, and the construction cost is alsovery high. Also, these foundations which are usually in reinforced concrete take time toconstruct, get cured and attain strength over time before the towers can be erected on them.This type of conventional construction method undergoes a series of processes such asground excavation, foundation concrete placement, reinforcing steel reinforcement, bodyconcrete place structure, and backfill construction. In addition, when the height of the toweris high, there is a chance that concrete cannot be poured at a time. In this way, the existingtower construction directly in the field has the following problems.First, curing time of more than 7 days is required for concrete to maintain strength for selfreliance,and framework should be dismantled after completion of curing. In addition thelines which carry higher voltages require bigger and heavier tower foundations. Therefore,on site construction of tower structure foundation has a problem in economical andconstructability because it takes several steps of construction process and long constructionperiod. Also, for large foundations large quantities of basic materials such as cement,aggregates, sand, water, reinforcing bars, shuttering materials, etc must be carried to thelocations. Due to these diverse requirements, it is important to focus on building appropriate,quick, and robust tower foundations. Incorporating new construction methodologies whichhelps to overcome these constraints in foundation construction and reduction of time andthereby cost of project.Therefore, employing precast concrete foundation instead of cast in-place foundation hasmany advantages in terms of time and cost savings. Prestressed concrete foundation isconvenient for construction, saves construction period and cost, and can ensure its reliableconnection with transmission line iron tower and it addresses the problem to be solved.Precast block foundations are much more convenient and economical. Extending this further,wherever the foundations must be constructed faster, or where it is inconvenient to transportlarge quantities of individual materials the concept of precast segmental block constructionis very appropriate. Further, in cold climates where it is difficult to mix concrete, the use ofprecast concrete blocks is ideal.The prefabricated assembly type foundation is applied to engineering practice gradually inthe advantages of rapid construction, easy quality control, good durability and concentratedtransportation of building materials, and the excavated foundation is high in bearing capacityand less in earthwork operation due to the characteristic of original soil, so that large-areadamage to terrain and environment caused by excavation of foundation types such as platetype foundations and pile group foundations is avoided, and the prefabricated assemblytype foundation is widely applied to power transmission lines in mountainous areas andtower positions with high requirements of environmental protection. Theassembled foundation and the digging type foundation are combined together to form theassembled digging type foundation which has the advantages of wide application range, shortconstruction period, good durability, high bearing capacity, easy quality control, less terraindamage and environmental protection.On the other hand, with the enlargement of the scale of the power grid, the safe operation ofthe power grid is increasingly threatened by extreme severe weather and sudden disasters,which easily causes the damage of the power grid. In the foundation process, the assemblytype digging foundation can save the concrete pouring and maintaining time with largervolume, and accelerate the repair speed of the transmission line tower foundation, especiallythe repair speed under the complex mountain terrain.For solving the above-mentioned problem, to improve the bearing performance and to makethe construction convenient, fast and suitable under multiclass environment, the presentinvention provides prefabricated precast concrete segments which are assembled using posttensionedprestressing technology, with the advantage of minimizing construction activitiesat the site.Chinese utility patent CN203782733U relates to a precast concrete bearing platform withreserved foundation ring hole and pile socket holes. The reserved foundation ring holecoaxial with a concrete body is formed in the center of the top surface of the concrete bodyof the precast concrete bearing platform; a plurality of reserved pile socket holes areuniformly distributed in the outer side of a vertical surface on which the circumferential wallof the reserved foundation ring hole and the bottom surface of the concrete body are arranged;a mortar grouting hole channel penetrating through the top surface of the concrete body isformed in the top of each reserved pile socket hole. Compared with the multiple-pilefoundation (a high-rise bearing platform foundation) construction scheme used in an existingoffshore wind turbine generator, the precast concrete bearing platform eliminates an offshoremold mounting and dismounting procedure, can complete binding of plenty of offshore onsitesteel bars in a precast factory at the same time, greatly improves the constructionefficiency, saves the offshore bearing platform construction time, and meanwhile reduces theconstruction cost.Chinese utility patent CN212294721U discloses a prestressing force tubular pile basis andwith 35KV transmission line iron tower's connection structure thereof, prestressing forcetubular pile basis includes: precast tubular pile, rag bolt stirrup, the steel reinforcement cage,the layer board, fill out core concrete and top steel sheet, precast tubular pile contains a cavityin, rag bolt and rag bolt stirrup ligature to it is fixed rather than outside steel reinforcementcage, the layer board is connected in the bottom of steel reinforcement cage, rag bolt afterthe fixed connection, rag bolt stirrup, steel reinforcement cage, the layer board cooperationsets up in precast tubular pile's cavity and pours and fill out core concrete, top steel sheetfixed connection is in precast tubular pile's top, rag bolt stretches out the top steel sheet. Theprestressed pipe pile foundation and the connection structure of the prestressed pipe pilefoundation and the 35KV transmission line iron tower meet the national specifications andstandards, are convenient to construct, can reduce the excavated volume of earth, reduce theuse amount of concrete and steel bars, reduce the working area, have small damage to thesurrounding environment and have high structural reliability.Chinese utility patent CN204139195U provides a prefabricatedassembled transmission line of electricity column foot, comprise base plate and cylinder,cylinder is connected by slab column connection part with base plate, and base plate is splicedby bottom board unit, and cylinder is formed by cylinder unit spliced. The bottom board unitat base plate bottom layer center and slab column connection part are carried out assembled,afterwards by order from inside to outside assembled go out whole base plate bottom layer,and adjust its level; Begin from base plate bottom layer center, assembled base plate upperstrata or cylinder bottom, complete until cylinder is assembled from bottom to top, will adjustthe verticality of cylinder in assembled process at any time. The concerned process steps suchas the utility model decreases cast-in-situ concrete, mixes and stirs, builds, maintenance,can foundation ditch whole good after namely to carry out tower-base structure assembled,significantly reduce labour intensity, and the reduction of erection time.Chinese patent Application CN112252355A relates to a prefabricated expanded packing keytype digging foundation for a power transmission line and a construction method thereof,wherein the foundation comprises a concrete assembly, prestressed reinforcements andprefabricated root keys; the concrete assembly is a disc expanding component, and the middlepart of the concrete assembly is of a hollow structure; the concrete assembly is provided witha plurality of penetrating reserved prestressed holes along the height direction, and a pluralityof root key reserved holes along the bottom surface direction; the plurality of concreteassemblies are sequentially stacked in the foundation pit, and the prestressed reinforcementpenetrates through corresponding reserved prestressed holes in the plurality of concreteassemblies to assemble the concrete assemblies to form a foundation main body; and theprefabricated root key penetrates through the root key preformed hole and is inserted into theside wall of the foundation pit. The prefabricated expanded packing key typedigging foundation provided by the invention can obviously save the construction period,fully play the synergistic effect of the foundation and the soil body, improve the horizontalload resistance and the overturning resistance of the foundation, and reduce the constructionsafety risk and the construction cost.All of the cited documents relates basically for supporting single poles, mainly flag poles orsmall communication towers. Even though all of the cited documents relates to the basicconcept of assembling precast components using prestressing, none of them provides asolution for larger loads including uplift and for buried foundations, mainly for Transmissionline towers. All of the cited documents are apparently for foundations resting on the ground.The present invention is proposed to overcome the above said challenges by providing afoundation using precast concrete segments assembled using post-tensioned prestressingtechnology, to safely transmit the loads from the superstructure to the foundation soil stratabelow, with the advantage of minimizing construction activities at the site. The presentinvention provides a small-dimension precast concrete foundation blocks which areassembled in the location using medium tensile steel bars post-tensioned to assemble theindividual segments into an integral foundation pad would be quite convenient and ensuresuperior quality as all the elements can be prefabricated in factory-like conditions. Byemploying precast concrete segmented foundation according to the present invention,reduces the time consumed at each foundation site as there is no time lost waiting for theconcrete to attain required strength over time. Further the present invention involves lesslabour involvement, carriage of lesser quantum of materials and equipment from foundationto foundation, better quality, and faster construction at individual foundation sites.Objects of the Invention:The main object of the present invention is to provide a precast concrete segment constructionfor foundations of power transmission line towers to safely transmit the loads from thesuperstructure to the foundation soil strata below.The primary object of the present invention is to provide a foundation using precast concretesegments assembled using post-tensioned prestressing technology, with the advantage ofminimizing construction activities at the site.It is another object of the present invention to provide a precast concrete segmentedfoundation with larger load baring capacity resisting uplift and for buried foundations fortransmission line towers.Still another object of the present invention is to provide a precast concrete segmentedfoundation with reduced time consumption at each foundation site and faster construction atindividual foundation sites.It is another object of the present invention is to provide a precast concrete segmentedfoundation with less labour involvement and carriage of lesser quantum of materials andequipment from foundation to foundation.Although the present invention is mainly the foundation designed specifically proposed forTransmission line towers. However, it can be very well applicable for all foundations ofresidential and commercial buildings.SUMMARY OF THE INVENTIONThe present invention provides a precast concrete segment construction for foundations ofpower transmission line towers to safely transmit the loads from the superstructure to thefoundation soil strata below, with larger load baring capacity resisting uplift and for buriedfoundations. The precast concrete segmental construction for foundations of presentinvention is assembled using post-tensioned prestressing technology, with the advantage ofminimizing construction activities at the site. The present invention provides a smalldimensionprecast concrete foundation blocks which are assembled in the location usingmedium tensile steel bars post-tensioned to assemble the individual segments into an integralfoundation pad would be quite convenient and ensure superior quality as all the elements canbe prefabricated in factory-like conditions.The precast segmental construction of foundation system for transmission line of the presentinvention, comprising of : atleast a base plate, connected to the tower leg stub; a plurality ofanchor bolts, embedded in the central block to connect and be tightened with nuts therebyanchoring the tower to the foundation; atleast a chimney, which is lower portion of tower legusually encased in concrete; a plurality of precast blocks, assembled and connected usingaxial pre-stressing in the two perpendicular horizontal directions; a plurality of horizontalshear keys, provided on the side faces of the said precast blocks in both the directions forenabling shear transfer; atleast a central block, provided with embedded anchor bolts on topsurface for fixing the base plate of the tower; a plurality of vertical anchor bars driven intothe soil through vertical holes in the said precast blocks to resist uplift and side shear; and aplurality of untensioned reinforcement bars, provided in the said precast blocks of thefoundation base.In the preferred embodiment of the present invention, Wherein said orthogonally pre-stressedsystem with shear keys provides prestressing adequate to ensure no tension exists in any ofthe block interfaces and further enables an orthogonal plate type behavior for the foundation,which is analyzed as a single slab.In an embodiment of the present invention, provides a method of construction of precastsegmental foundation system for transmission line, comprising steps of : making a pit byexcavation of soil layer and sub soil for a required depth; casting mud mat at the bottom ofthe excavation as per specified dimensions to provide a levelled, unyielding surface;assembling of pre cast concrete blocks of specified dimensions on top of the mud mat;threading of medium tensile steel bars through the plurality of horizontal holes provided nearthe centroid of the pre cast blocks in both the directions; stressing the pre cast block inspecified sequence using appropriate jacks; grouting the holes using cement grout for bondas well as corrosion protection; driving the vertical anchor rods through the vertical holesprovided in the pre cast concrete blocks for specified anchor length inside the soil and groutedwhich resists the uplift; painting the whole assembly with anti-corrosive bituminous paintafter packing the anchorages using epoxy mortar for better corrosion protection; andbackfilling the excavation.In the preferred embodiment of the present invention, wherein PVC or plastic sheet are alsoused to provide a level, unyielding surface.In the preferred embodiment of the present invention, wherein the type of foundation isselected based on soil conditions and the type of tower to be installed.In the preferred embodiment of the present invention, wherein the Input design parametersincluding values such as slope of tower leg, unit weight of soil with and without the effect ofwater table, bearing capacity of soil, angle of repose of soil, unit weight of concrete,characteristic strength of concrete, yield strength of reinforcement, cover of concrete, averagecohesion and adhesion factor values are all selected based on the type of foundation.The Precast foundation of the present invention will have an edge over the existing In-situfoundations in Transmission Lines including lesser time, lesser overheads, reduced projecttime, better quality and monitoring, leak resistant, lesser skilled labour, repeatability, costeffectiveness,and carriage of lesser quantum of materials and equipment from foundation tofoundation.Other features and advantages of embodiments will be apparent from the accompanyingdrawings and from the detailed description that follows.Brief Description of the DrawingsFig. 1 represents the precast segmental construction of foundation system (121) fortransmission line according to the present invention.Fig. 2 represents the precast segmental construction of foundation system (121) fortransmission line with precast connections showing the assembly of precast blocks (126a,126b), base plate (122), tower leg stub (123), horizontal reinforcing bars (129a, 129b) andvertical anchoring bars (128a, 128b) according to the present invention.Fig. 3 represents the Central block (127) arrangement with plurality of anchor bolts (124a,124b), base plate (122) and anchor nuts according to the present invention.Fig. 4 represents the end block reinforcement, the peripheral blocks provided with specialembedded spiral reinforcement bars (131) at the anchorage location.Fig. 5 represents the horizontal shear key (130) arrangement provided on the side faces ofthe said precast blocks (126a, 126b) in both the directions for enabling shear transfer.Fig. 6 represents the untensioned reinforcement bars (129a, 129b) along with anchor plate(136) and washer (135) provided in the said precast blocks (126a, 136b) of the foundationbase.Fig. 7 represents the base plate assembly (122) showing the tower leg stub (123) and pluralityof anchor bolts (124a, 124b)While the invention is amenable to various modifications and alternative forms, specificsthereof have been shown by way of example in the drawings and will be described in detail.It should be understood, however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of the invention.Hereinafter, preferred embodiments of the present invention will be described in detail withreference to the accompanying drawings. Prior to this, terms and words used in the presentspecification and claims should not be construed as limited to ordinary or dictionary terms,and the inventor should appropriately interpret the concept of the term appropriately todescribe its own invention in the best way. The present invention should be construed asmeaning and concept consistent with the technical idea of the present invention based on theprinciple that it can be defined. Therefore, the embodiments described in this specificationand the configurations shown in the drawings are only the most preferred embodiments ofthe present invention and do not represent all the technical ideas of the present invention.Therefore, it should be understood that equivalents and modifications are possible.Detailed Description of the Invention with Respect to the DrawingsThe present invention as embodied by "Precast segmental construction for concretefoundations for transmission line towers and other structures" succinctly fulfils the abovementionedneed(s) in the art. The present invention has objective(s) arising as a result of theabove-mentioned need(s), said objective(s) being enumerated below. In as much as theobjective(s) of the present invention are enumerated, it will be obvious to a person skilled inthe art that, the enumerated objective(s) are not exhaustive of the present invention in itsentirety, and are enclosed solely for the purpose of illustration. Further, the present inventionencloses within its scope and purview, any structural alternative(s) and / or any functionalequivalent(s) even though, such structural alternative(s) and / or any functional equivalent(s)are not mentioned explicitly herein or elsewhere, in the present disclosure. The presentinvention therefore encompasses also, any improvisation(s) / modification(s) applied to thestructural alternative(s) / functional alternative(s) within its scope and purview. The presentinvention may be embodied in other specific form(s) without departing from the spirit oressential attributes thereof.Throughout this specification, the use of the word "comprise" and variations such as"comprises" and "comprising" may imply the inclusion of an element or elements notspecifically recited.The present invention provides a precast segmental construction (121) of foundation systemfor transmission line, comprising of : atleast a base plate (122), connected to the tower legstub (123); a plurality of anchor bolts (124a, 124b), wherein said base plate is provided witha plurality of holes to allow protruding the said anchor bolts embedded in the central blockto connect and be tightened with nuts thereby anchoring the tower to the foundation, anglesection of the bottom-most member of the tower is coupled to the said base plate; atleast achimney (125), which is lower portion of tower leg usually encased in concrete; a pluralityof precast blocks (126a, 126b), assembled and connected using axial pre-stressing in the twoperpendicular horizontal directions, wherein said precast blocks are provided with horizontalholes in X & Z directions for reinforcement bars and vertical holes for anchor bars; atleast ahorizontal shear key (130), provided on the side faces of the said precast blocks in both thedirections for enabling shear transfer; atleast a central block (127), provided with embeddedanchor bolts on top surface for fixing the base plate of the tower; a plurality of vertical anchorbars (128a, 128b) driven into the soil through vertical holes in the said precast blocks to resistuplift and side shear, wherein said plurality of vertical anchor bars enables anchoring theprecast segmental assembly into the foundation soil against lateral movements; and aplurality of untensioned reinforcement bars (129a,129b), provided in the said precast blocksof the foundation base, wherein said untensioned reinforcement bars does not contribute toredistribution of moments, Wherein said orthogonally pre-stressed system with shear keysprovides prestressing adequate to ensure no tension exists in any of the block interfaces andfurther enables an orthogonal plate type behaviour for the foundation, which is analysed as asingle slab.In the preferred embodiment of the present invention, wherein area of the said base plate(122) is calculated based on the applied and permissible stresses from the values of grade ofconcrete and the load intensity.In the preferred embodiment of the present invention, wherein the gross area of the said baseplate (122) should be greater than or equal to the computed area.In the preferred embodiment of the present invention, wherein thickness of the said base plate(122) is calculated based on the appropriate clearance values provided for the column in bothX & Z direction.In the preferred embodiment of the present invention, wherein said thickness of base plate(122) provided should be greater than thickness of flange of stub.In the preferred embodiment of the present invention, wherein grade of the said anchor bolts(124a, 124b) are selected based on the calculated tension capacity of the said anchor bolts.In the preferred embodiment of the present invention, wherein number of the said anchorbolts (124a, 124b) required to hold against the upward load are calculated based on the valueof tension capacity of the anchor bolts.In the preferred embodiment of the present invention, wherein minimum edge and gaugedistances are evaluated based on the diameter of hole for the said anchor bolt. The saidplurality of anchor bolts (124a, 124b) on the base plate (122) should have sufficient edge andgauge distances to be provided between them.In the preferred embodiment of the present invention, Wherein said holes on the pre castblocks are sized to keep the diameter of the reinforcing bar used including sufficientclearance. In addition a cardboard washer (135) is inserted on the inner face of precast blocks,so that when bars are stressed the washers get compressed and do not allow grout to leakthrough the joints.In the preferred embodiment of the present invention, wherein the untensioned reinforcementfunction is performed by the MTS bars (129a, 129b) used for post-tensioning provided withnominal reinforcement. Wherein the secondary reinforcement provided releases theshrinkage and temperature stresses present in the foundation.In the preferred embodiment of the present invention, wherein the end blocks must beprovided with sufficient end-block reinforcement bars (131) to take care of bursting andspalling stresses while post-tensioning.In an embodiment of the present invention, wherein said anchor bolts (129a, 129b) selectedare High Strength Friction Grip (HSFG) bolts which provides additional safety.In the preferred embodiment of the present invention, wherein the total downward loads,upward loads and resultant side thrust from longitudinal and transverse directions acting onthe foundation due to different types of towers are taken into consideration while designingthe precast segmental foundation system.In the preferred embodiment of the present invention, wherein the base of foundation isaligned along the diagonal of the tower. Then instead of considering two side thrust values,in the present invention only one resultant horizontal force is considered. The downward loadand upward load are two different load cases and they both do not act at the same time.In the preferred embodiment of the present invention, wherein during the calculations foruplift, the effect of vertical dowel anchor bars which provides resistance against upward forceis considered. The upward load acting on the foundation shall be less than the yield strengthof steel used in anchor bars. The shear strength should be more than maximum sidetransverse / longitudinal loads. The factor of safety against uplift should be greater than orequal to 1.5. The width of the foundation or the depth of excavation can be increased toincrease the factor of safety against uplift, to mobilise more weight of soil resting over thefoundation.In the preferred embodiment of the present invention, wherein for designing the foundationsthe bearing pressure due to vertical and horizontal component of downthrust and bearingpressure due to resultant side thrust should be calculated. The maximum bearing pressuredue to loads shall be less than 1.25 times the bearing capacity of soil. The factor of safetyagainst bearing should be greater than or equal to 1.0In the preferred embodiment of the present invention, wherein for designing the foundationstotal lateral forces acting at the base of foundation is evaluated. The total lateral resistantforce available at the base shall be more than the maximum resultant horizontal thrust,including base friction below the foundation slab. The factor of safety against sliding shouldbe greater than or equal to 1.0 Additional sliding resistance can also be built up from thevertical anchor bars.In the preferred embodiment of the present invention, wherein to calculate the total resistingmoment acting on the foundation, the effect of moment due to soil frustum above, momentdue to self-weight of concrete, moment due to anchor bars are considered. To calculate thetotal overturning moment, the moments due to upward load and horizontal load areconsidered.In the preferred embodiment of the present invention, wherein following loads acting on thefoundation are considered for designing the foundation, first downward loads and resultanthorizontal loads, second accounts for net upward load and resultant horizontal loads. Theupward load is resisted by the effect of the weight of concrete, weight of soil frustum abovethe foundation. The anchor bars will come into play only if there is a net upward load, i.e. ifthe bars tend to experience a movement upwards. The pull-out capacity of the bars will alsocome into play only when there is an incipient movement upwards. However, if the weightof concrete and weight of soil above footing are more than the uplift then the bars will onlyplay a passive role.In the preferred embodiment of the present invention, wherein while calculating the stressesin Z-direction the bending moments and bending stresses due to different load cases arecalculated. If there is net uplift acting on the foundation, then the effect of anchor bars arealso considered in calculating the resistant bending moment. The axial and bending stressesdue to pre-stressing are calculated based on the appropriate diameter, yield strength, numberof reinforcement bars used and the eccentricity of the bars. Total stresses for both load casesat top and bottom fibres are calculated based on the axial and bending stresses developed.In the preferred embodiment of the present invention, wherein while calculating the stressesin X-direction, the eccentricity of the bar in X-direction is used to calculate the bendingstresses due to pre-stressing.The method of construction of precast segmental foundation system for transmission lineaccording to present invention, comprises steps of :a) Making a pit by excavation of soil layer and sub soil for a required depth;b) casting mud mat (132) at the bottom of the excavation as per specified dimensions toprovide a levelled, unyielding surface;c) Assembling of pre cast concrete blocks (126a, 126b) of specified dimensions on topof the mud mat;d) threading of medium tensile steel bars (129a,129b) through the plurality of horizontalholes provided near the centroid of the pre cast blocks in both the directions;e) stressing the pre cast block in specified sequence using appropriate jacks;f) grouting the holes using cement grout for bond as well as corrosion protection;g) driving the vertical anchor rods (128a,128b) through the vertical holes provided inthe pre cast concrete blocks for specified anchor length inside the soil and groutedwhich resists the uplift;h) painting the whole assembly with anti-corrosive bituminous paint after packing theanchorages using epoxy mortar for better corrosion protection; andi) backfilling the excavation.In the preferred embodiment of the present invention, wherein PVC or plastic sheet (132) arealso used to provide a level, unyielding surface.In the preferred embodiment of the present invention, wherein the type of foundation isselected based on soil conditions and the type of tower to be installed.In the preferred embodiment of the present invention, wherein the Input design parametersincluding values such as slope of tower leg, unit weight of soil with and without the effect ofwater table, bearing capacity of soil, angle of repose of soil, unit weight of concrete,characteristic strength of concrete, yield strength of reinforcement, cover of concrete, averagecohesion and adhesion factor values are all selected based on the type of foundation.In the preferred embodiment of the present invention, wherein said pit making and excavationis carried out as per the approved tower schedule and the respective foundation drawing forthat location. Wherein excavation is done by giving sufficient margin on two adjacent facesof foundation to allow jacking. This depends on and varies according to the diameter of thereinforcing bars used for prestressing. During excavation shoring and shuttering is done toprevent collapse. Keep the pits dry to avoid water ingress, slush formation and weak base.Dimensions of e xcavated pits should be as per the foundation drawing.In the preferred embodiment of the present invention, wherein the said precast blocks (126a,126b) which are specifically match-cast for the foundation being constructed are brought tothe location, arranged and dry-matched to check proper fitting against each other. The precastblocks are numbered while casting and the same numbering system is adopted whileassembling enabling proper matching of the blocks. A suitable template is used for fixing thenuts in the concrete blocks ensuring that the anchor bolts are at proper centres to match withthe tower leg base plate. During dry matching, the tower leg base plate having bolt holesshould match with the embedded anchor bolts. The anchor bolts passing through the holes ofbase plate must be tightened using nuts after final arrangement. The peripheral blocks arealso provided with special embedded spiral reinforcement bars (131) at the anchoragelocation.In the preferred embodiment of the present invention, wherein the precast concrete arelowered into the pit and arranged over the mud mat on top of a layer of building paper or tarpaper to facilitate free sliding during stressing. The hooks provided on top of the precastblocks are used with a crane lifting sling for shifting. The precast blocks are oriented correctlywith respect to each other and according to the tower orientation.In the preferred embodiment of the present invention, wherein said jacking is performed atone end only. A suitable post-tensioning jack is used with a maximum pre-stressing force of450kN. Therefore, clearance required to be provided during excavation is only on twoadjacent sides rather than all four sides of the foundation.In the preferred embodiment of the present invention, wherein said reinforcement bars (129a,129b) of specified diameter are inserted into the holes provided on the precast blocks in onedirection. Anchorage bearing plate (136) is installed at both ends of the reinforcement bars.All the connections of components are sealed with tape. Jack with wedge seating device isinstalled over the reinforcement bar so that the wedge seating device is in complete contactwith the surface of anchor plate. Then the jack is aligned with the axis of the reinforcementbar to be stressed. The stressing head is positioned onto the end of the reinforcement barconnecting with the back of the piston of jacking unit. Finally, the stressing nut is screwedon the stressing head until it is in full contact with the piston's surface and the pressure hosesrelate to the jack and the pump. After ensuring that the pressure hoses are intact and the jackis properly aligned with the bar axis and the wedge seating device in contact with the surfaceof the bearing plate and all stressing wedges are properly installed and the stressing nut fullyengaged on the stressing head, the actual stressing operation is started.In the preferred embodiment of the present invention, wherein said reinforcement bar (129a,129b) is stressed initially to a pressure of 25% of total prestress force. The pressure isincreased in steps of 100 bar up to the required design jacking load. The reinforcement barload is determined using a calibration chart and the piston stroke is measured. Thereinforcement bar load is uniformly transferred from the jack to anchor head with even draw20in of all the anchor wedges. If one piston stroke is not sufficient to stress the bar to its fulldesign jacking load, re-gripping is required, wherein the piston stroke is fully retracted byactivating the return pressure of the pump. The stressing head and nut are pushed back to beagain in contact with the retracted piston. The lever of the valve at the pump is moved toforward and increase the pressure until it reaches the same value as before re-gripping. Atthis point, the piston stroke is measured and recorded. Subsequently standard stressingprocedure is followed again. Upon successful completion of stressing of the bar, the jackingunit can be removed and installed on the next bar.In the preferred embodiment of the present invention, wherein the precast blocks (126a,126b) should be stressed in both X and Z directions after placing the reinforcing bars (129a,129b) at an eccentricity with respect to the centre of gravity of the foundation slab to carryout the post-tensioning operation. Essentially the reinforcement bars will be located belowthe centre of gravity to create a hogging moment on the foundation which will counteractagainst the sagging moment due to downward loads. When there is any net resultant upwardload, the consequent hogging moment, when coupled with that due to the prestressing, theresulting stresses should still be within limits. The difference between eccentricity values inboth directions should be greater than or equal to 2 times the diameter of the bar, to ensureproper spacing of the bars in the two directions for concrete to flow in between, etc.In the preferred embodiment of the present invention, First the central block line is stressedfor X direction bars, and then the two outer blocks lines. Then the central block line in Zdirection is stressed, followed by the two outer block lines. The bar is now ready for grouting.In the preferred embodiment of the present invention, grouting is performed immediatelyafter the stressing operation is complete for both X and Z direction bars. Grout vents (137)are provided at anchorages for each reinforcement bar. The anchorage pockets is capped withconcrete or suitable capping material prior to grouting operation. After capping the anchoragepockets the reinforcement bar is water flushed through the grout holes present at theendplates, after which the grout operation is started. Grout mix should have the mixproportion of water / cement ratio as specified by weight. The additive admixture is mixedcement in proportion as recommended by additive manufacture. After completion of groutingthe projected portion of grout vent is cut flat to the slab level by means of abrasive disc.Finally two ends of each reinforcement bar is capped using epoxy concrete to completelycover the bearing plates and nuts to safeguard them from corrosion.In the preferred embodiment of the present invention, wherein grout samples is collected andtests are carried for compressive strength at 7 days and 28 days and the results should satisfy17 N / mm2 and 27 N / mm2 respectively.In the preferred embodiment of the present invention, wherein maximum of two days shallelapse between stressing and grouting of a reinforcement bar.In the preferred embodiment of the present invention, the said reinforcement bars (129a,129b) are threaded at the top end and pointed at the lower end and of specified length toprovide enough anchorage length inside the soil. These reinforcement bars shall haveadequate corrosion protection, ex. bituminous coating but with sand sprayed on to the wetbitumen before setting, to provide a rough surface to promote anchorage inside the soil.In the preferred embodiment of the present invention, installation of vertical anchor bars(128a, 128b) involves driving the bar through the vertical holes in the precast blocks and theembedded PVC pipes in the mudmat concrete into the soil to the required depth, wherein saidvertical bars (128a, 128b) are installed one by one, symmetrically with respect to the towercentre. Then the capping nut is screwed tightly on to the threaded portion. Finally the exposedportions of the reinforcement bars are covered with epoxy concrete to prevent corrosion.In the preferred embodiment of the present invention, wherein if the foundation is sitting onrock instead of soil then the anchor bars is installed inside pre-drilled holes in the rock afterplacing a measured quantity of thick cement grout in the drilled holes to develop anchorageby bond.In the preferred embodiment of the present invention, Finally the base plate (122) of thetower leg (123) is installed over the pre cast blocks (126a, 126b) by screwing down theanchorage bolts (124a, 124b) and nuts embedded in the central block (127). After which theexcavation is backfilled and compacted as required.Advantages of the present inventionThe Precast foundation of the present invention will have an edge over the existing In-situfoundations in Transmission Lines as following:1. All the benefits of Precast modular construction i.e lesser time, lesser overheads areachieved and project cycle is expedited.2. Transmission line Projects are subjected to several ROW issues; hence the projectsneed to be scheduled to be completed in shorter time span. The Precast technologycan be very much effective in reducing the duration of the project time.3. Seasonal changes and monsoons can lead to abrupt stoppage of work at sites. Precastmodular construction of foundation can avoid this problem.4. Better quality and monitoring are ensured with Precast technology compared to insitumethod of construction.5. Precast modules in foundation are leak resistant and have little or no cracking.6. Less labour is required, and also less skilled labour are only required in case of Precastfoundation construction compared to conventional in-situ foundations.7. Repeatability is a major advantage of this method. It is easy to make many duplicatesof the same precast product in terms of shape and size. There are repeatable sets oftower foundation designs across the entire length of project. Hence, adapting Precastmethodology can be very effective in this case for faster execution of project.8. Precast foundations will be more cost- effective if material optimization is doneproperly and there will be good reduction in the cost for overheads.9. The dimensions selected for tower foundations can be modified according to thedifferent projects. Choosing one common dimension is however easy to manufactureelements in bulk, thus making it more feasible. This makes the execution easier thanin-situ foundations.10. In most of the remote sites where the access to the locations is a major constraint, thetransport of materials to the site and construction is a major challenge. In suchconditions, a suitable crane which can be used to lift the precast foundations can beused which results in more efficient and easier execution.EXAMPLE 1The present invention provides a precast segmental construction of foundation system (121)for transmission line and construction method thereof, comprises steps of : selecting the typeof foundation based on soil conditions and the type of tower to be installed. Making a pit byexcavation of soil layer and sub soil for a required depth as per the approved tower scheduleand the respective foundation drawing. The excavation is done by giving sufficient marginon two adjacent faces of foundation to allow jacking. Shoring and shuttering is done toprevent collapse. The pits are kept dry to avoid water ingress, slush formation and weak base.Then casting mud mat (132) at the bottom of the excavation as per specified dimensions toprovide a levelled, unyielding surface. Instead PVC or plastic sheet can also be used toprovide a level, unyielding surface. A plurality of precast blocks (126a, 126b) which arespecifically match-cast for the foundation are brought to the location, arranged and dry10matched to check proper fitting against each other. The precast blocks (126a, 126b) areconnected using axial pre-stressing in the two perpendicular horizontal directions, whereinsaid precast blocks are provided with horizontal holes in X & Z directions for reinforcementbars (129a, 129b) and vertical holes for anchor bars (128a, 128b). Threading of mediumtensile steel bars (129a, 129b) through the plurality of horizontal holes provided near thecentroid of the pre cast blocks in both the directions. Cardboard washer is inserted on theinner face of precast blocks so that when bars are stressed the washers get compressed anddo not allow grout to leak through the joints. After assembling the pre cast block is prestressedin specified sequence using appropriate jacks. The jacking is done at one end only,a suitable post-tensioning jack is to be used for this purpose. The maximum pre-stressingforce exerted by the jack is 450kN. First the central block (127) line is stressed for X directionbars, and then the two outer blocks lines. Thereafter the central block (127) line in Z directionis stressed, followed by the two outer block lines. Grouting should be performed as soon asthe stressing operation is complete for both X and Z direction bars.Grout vents are provided at anchorages for each bar. The anchorage pockets should be cappedwith concrete or suitable capping material prior to grouting operation. Grouting the holesusing cement grout for bond as well as corrosion protection. Installation of vertical anchorbars (128a, 128b) involves driving the bar through the vertical holes in the precast blocks andthe embedded PVC pipes in the mudmat (132) concrete into the soil to the required depth,wherein said vertical anchor bars are installed one by one, symmetrically with respect to thetower centre. Then the capping nut is screwed tightly on to the threaded portion. Finally theexposed portions of the anchor bars (128a, 128b) are covered with epoxy concrete to preventcorrosion. Finally the base plate (122) of the tower leg (123) is installed over the pre castblocks by screwing down the anchorage bolts (124a, 124b) and nuts embedded in the centralblock (127). The base plate is provided with a plurality of holes to allow protruding the saidanchor bolts embedded in the central block to connect and be tightened with nuts therebyanchoring the tower to the foundation, angle section of the bottom-most member of the toweris coupled to the said base plate. The whole assembly is painted with anti-corrosivebituminous paint after packing the anchorages using epoxy mortar for better corrosionprotection After which the excavation is backfilled and compacted as required.Although the proposed concept has been described as a way of example with reference tovarious models, it is not limited to the disclosed embodiment and that alternative designscould be constructed without deviating from the scope of invention as defined above.It will be apparent to a person skilled in the art that the above description is for illustrativepurposes only and should not be considered as limiting. Various modifications, additions,alterations, and improvements without deviating from the scope of the invention may bemade by a person skilled in the art.

Claims

1. A precast segmental construction of foundation system (121) for transmission line, comprising of : atleast a base plate (122), connected to the tower leg stub (123), wherein angle section of the bottom-most member of the tower is coupled to the said base plate (122); a plurality of anchor bolts (124a, 124b), wherein said base plate (122) is provided with a plurality of holes to allow protruding the said anchor bolts (124a, 124b) embedded in the central block (127) to connect and be tightened with nuts thereby anchoring the tower to the foundation; atleast a chimney (125), which is lower portion of tower leg (123) usually encased in concrete; a plurality of precast blocks (126a, 126b), assembled and connected using axial pre-stressing in the two perpendicular horizontal directions, wherein said precast blocks are provided with horizontal holes in X & Z directions for reinforcement bars (129a, 129b) and vertical holes for anchor bars (128a, 128b); atleast a horizontal shear key (130), provided on the side faces of the said precast blocks in both the directions for enabling shear transfer; atleast a central block (127), provided with embedded anchor bolts (124a, 124b) on top surface for fixing the base plate (122) of the tower; a plurality of vertical anchor bars (128a, 128b) driven into the soil through vertical holes in the said precast blocks to resist uplift and side shear, wherein said plurality of vertical anchor bars (128a, 128b) enables anchoring the precast segmental assembly into the foundation soil against lateral movements; and a plurality of untensioned reinforcement bars (129a, 129b), provided in the said precast blocks of the foundation base, wherein said untensioned reinforcement bars does not contribute to redistribution of moments, Wherein said orthogonally prestressed system with shear keys provides prestressing adequate to ensure no tension exists in any of the block interfaces and further enables an orthogonal plate type behaviour for the foundation, which is analysed as a single slab.

2. The precast segmental construction of foundation system for transmission line, as claimed in claim 1, wherein the total downward loads, upward loads and resultant side thrust from longitudinal and transverse directions acting on the foundation due to different types of towers are taken into consideration while designing the precast segmental foundation system.

3. The precast segmental construction of foundation system for transmission line, as claimed in claim 1, wherein the base of foundation is aligned along the diagonal of the tower considering the one resultant horizontal force.

4. The precast segmental construction of foundation system for transmission line, as claimed in claim 1, wherein area of the said base plate (122) is calculated based on the applied and permissible stresses from the values of grade of concrete and the load intensity, wherein the gross area of the said base plate is greater than or equal to the computed area.

5. The precast segmental construction of foundation system for transmission line, as claimed in claim 1, wherein thickness of the said base plate (122) is calculated based on the appropriate clearance values provided for the column in both X & Z direction, wherein said thickness of base plate provided is greater than thickness of flange of stub.

6. The precast segmental construction of foundation system for transmission line, as claimed in claim 1, wherein said each of the plurality of anchor bolts (124a, 124b) on the base plate is provided with sufficient edge and gauge distances between them.

7. The precast segmental construction of foundation system for transmission line, as claimed in claim 1, wherein the untensioned reinforcement bars (129a, 129b) selected are MTS bars with nominal reinforcement.

8. The precast segmental construction of foundation system for transmission line, as claimed in claim 1, additionally atleast a cardboard washer (135) is inserted on the inner face of the said precast blocks, so that when bars are stressed the washers get compressed and do not allow grout to leak through the joints.

9. A method of construction of precast segmental foundation system for transmission line according to present invention, comprising steps of : a) making a pit by excavation of soil layer and sub soil for a required depth; b) casting mud mat (132) at the bottom of the excavation as per specified dimensions to provide a levelled, unyielding surface; c) assembling of pre cast concrete blocks (126a, 126b) of specified dimensions on top of the mud mat; d) threading of medium tensile steel bars (129a, 129b) through the plurality of horizontal holes provided near the centroid (127) of the pre cast blocks in both the directions; e) stressing the pre cast blocks (126a, 126b) in specified sequence using appropriate jacks; f) grouting the holes using cement grout for bond as well as corrosion protection; g) driving the vertical anchor rods (129a, 129b) through the vertical holes provided in the pre cast concrete blocks for specified anchor length inside the soil and grouted which resists the uplift; h) painting the whole assembly with anti-corrosive bituminous paint after packing the anchorages using epoxy mortar for better corrosion protection; and i) backfilling the excavation.

10. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein the type of foundation is selected based on soil conditions and the type of tower to be installed.

11. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein PVC or plastic sheet is used to provide a level, unyielding surface.

12. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein the input design parameters includes, values such as slope of tower leg, unit weight of soil with and without the effect of water table, bearing capacity of soil, angle of repose of soil, unit weight of concrete, characteristic strength of concrete, yield strength of reinforcement, cover of concrete, average cohesion and adhesion factor values are all selected based on the type of foundation.

13. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, Wherein excavation is done by giving sufficient margin on two adjacent faces of foundation to allow jacking, wherein said margins depends on the diameter of the reinforcing bars used for prestressing.

14. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, during excavation shoring and shuttering is performed to prevent collapse.

15. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein the tower leg base plate provided with bolt holes is matched with the embedded anchor bolts.

16. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein the pre cast blocks (126a, 126b) are oriented correctly with respect to each other and according to the tower orientation17. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein the peripheral blocks are provided with special embedded spiral reinforcement bars (131) at the anchorage location.

18. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein said jacking is performed at only one end.

19. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein the precast blocks should be stressed in both X and Z directions after placing the reinforcing bars at an eccentricity with respect to the centre of gravity of the foundation slab to carry out the post-tensioning operation.

20. The method of construction of precast segmental foundation system for transmission line, as claimed in claim 9, wherein first the central block line is stressed for X direction bars, and then the two outer blocks lines, then the central block line in Z direction is stressed, followed by the two outer block lines.