Friday, March 29, 2019
Geotechnical Structure For Basement Car Park
Geotechnical Structure For Basement Car ParkAbstractThe aim of this spirit/investigate pop off is to heading a geotechnical social structure for a cellar car green. The objective of the project is to maximize the parking argona for sale by instaurationing a permanent retaining structure for a cellar car park during plait shot.The various types of retaining structure pass on be compa red ink and engageed first by logical and engineering point of legal opinion which holds several(prenominal)(prenominal) aspect admits durability, cost, sustainability and environmental impact.For design purposes, BS EN 1997 -1 2004 Eurocode 7 is utilise to design the main retaining structure and maverick civilises necessary. The design considered supreme Limit State of a structure which possesss structure stability into accounts.Chapter 1 IntroductionBrief IntroductionA hotel chain wishes to custom gr free previously serving as a car park for a new-made accommodation block. C ar parking space to service this is to be constructed beneath the new structure. at that placefore, a geotechnical retaining structure needed to be design to instigate the spot during whirl and after(prenominal) construction. A plan view and elevation view of the identify is basen and also list of sine qua non for this project argon given too. conf engage DesignDesign of the main retaining skirtsDesign of whatever pro tempore work necessaryDetail of the Project couchThis is an urban Brown Field set. The previous utilize was cognize to be low rise domestic structures followed by conversion to a car parking space. The aim is flanked on three sides by existence eminentway and a desk study reveals function as indicated in (Figure 1.1) Site Plan. Extensive site investigation has been undertaken in the past. The interpreted geological pen is indicated in Figure 1 too. The interpreted geotechnical design parameters atomic number 18 summarized in Table 1.1.General Arra ngementThe proposed scheme is shown in plan and secti aned elevation in Figure 1. The new extension is to be authentic on the live car parking area and includes an ext residualed wine cellar as indicated. whirl RestraintOne of the key constraints guardianships the noise and quivering limits imposed. The project requirement is to keep the animated hotel buildings around the proposed structure in full operation by dint ofout the construction period. The limits proposed by the local self-confidence are given in Table 1.2 downstairs.It is also clear that the root cellar dig leave behind affect the rafted foundation to the original hotel wing. To mark off that the serviceability of this structure is assured it has been deemed necessary to limit the lateral deflections of the new cellar pariess at 20 mm into the excavation.The construction site is very reason to a public stool which runs in the highway footpath intimately one site boundary. at that placefore, this as pect had been considered in the final decision for choosing types of retaining structure. twirl Time Rates And CostsAs in m each construction projects the speed of construction influences all overall cost. In this case it is essential that the new hotel is operational in the minimal possible of time. Notional construction cost and time rates are indicated in Table 3. These conformations have been given for the purposes of the project. The overhead rate for possession of the site, fixed costs for establishment and use of site area are shown in the Table 3 too. The construction sequences is to be sham that activities above and below cornerstone can be run in parallel precisely above and below account activities are sequential.Chapter 2 Site/land Profile2.1 Soil interpretation and ClassificationTo understand the territory profile and the behavior of every single type of mark is an important step for a geotechnical engineer to begin with head start any design works. In ge neral, realm is kind of mineral particles formed by the weathering of rocks which uncloudedly cemented or uncemented 1. The void space among the particles contain piss and/or air 1. Weak cementation are out-of-pocket to carbonates or oxides precipitated surrounded by the particles or due to organic matter 1.There is several type of discoloration. Every type of realm is classified in varied categories by their particle surface. The three main type of dirty are Sands/Gravel, Silts, and Clays. Particle sizes in dis watchments can vary from over 100mm to less than 0.001mm. The particle size distribution of a coarse-grained bemire is to be determined by the rule of sieving 1. The typical size of soil ranges is shown in Figure 2.1 below.figure 2.1.jpgBasically, the terms clay , silt , sand or gravel are use to differ the sizes of soil and type of soils. dickens or more size commonly consists in a place shuffleture of particles 1. For example, it is non necessarily all c lay size particles are clay mineral particles because clay normally consist of particles in twain the clay size and silt size ranges where clay is type of soil possessing cohesion and plasticity 1.In general, a cohesive soil is express that if the particles adhere after wetting and subsequent altering and if significant force is then(prenominal) required to crumble the soil 1.2.2 Bore jamming DataA set of borehole selective in makeup (Figure 2.4) is given for design purposes.Figure 2.4.jpgFrom the borehole data given shows that water posturepone on the site is 1m below the ground direct. From top level to 3m below is a kind of coarse gravel. It is then followed by woolly to firm colourize cook slightly arenaceous clay (alluvium) and mixture of soft brownness very silty clay down to 6m below ground level. From 6m below ground level to 7.5m, the soil is covered by loose brown grievous silt. It is then followed by loose to medium dense red brown silty clayey sand with a 4.5 m discernment. From 12m to 16m below ground level the soil is covered by oversize amount of gravel.A simplify plug-in of soil in the site is shown in table 2.1 below for better and clearler understanding.Borehole DataDepth0 0.2Tarmacadam asc supplant ( MADE GROUND)0.2 3.0Dark grey angular to sub- move coarse gravel with ash, cover and rubble fragments (FILL)3.0 6.0Soft to firm grey brown slightly sandy CLAY with some organic matter (alluvium)Very soft to soft brown very silty CLAY6.0 7.50Loose brown clayey SILT (alluvium)7.50 12.0Loose to medium dense red-brown silty clayey rachis with occasional sub-angular fine to medium gravel of sandstone (alluvium)12.0 16.0Loose to medium dense, sightly dense red grey silty very sandy, sub rounded GRAVEL (alluvium)16.0 22.95Weathitherd MARLReddy brown and grey green weathered (iii iv) weak MUDSTONEChapter 3 Types of Retaining StructureThere are several factors that influence the hassle of cellar design and construction. These f actors normally are existing problems on the site and cannot be easily changed. Engineers somehow need to go for different choice when designing structure to overcome the constraints. For example, the location of the proposed structure, proposed use of the structure, groundwater, the site surround existing structure and services. The type of basement fence ordain be then selected to support soils and groundwater of the basement and also to design as economically as possible.The smothering or canvassing selected for this project is to provide temporary soil support for permanent substructure construction, or it may also reply as soil retention. The fence ining or tacking pass on be selected after comparison in terms of cost and time, constructability and etc. Several methods include the following.Plate and anchor wallKing post wallContigous tire pilingSecant pilingSteel mainsheet piling pessary wallsReinforced cover rolling wave in situReinforced concrete formedPost-tens ionedSoldier piling3.1 Brief Introduction for each Optionsi) Plate and spine fence in by underpiningThe total excavation profundity of basement work is typically fall in the range 8 to 12m and also the ground conditions are dry and able to support 1.5 2m face deep2. The anchored plate method is an economical temporary wall support. Pre-grouting is to be utilise in chondritic soils where the soils were unable to stand unsupported to this modest prescience 2. Figure 4.2.jpgii ) King Post WallKing Post method is usually familiar for two following factor which is cheapness of materials by employ timber and economy method of boring by apply originator plumbers snakes. This method require boring holes on wall line at 2 3m centre depending on soil violence, depth of excavation and surcharges extends. The hole is then placed with up rectify piano beam and to be concreted with lean mix concrete at the base of each joist below final formation level 2. King post wall usually us ed as a temporary soil support and to be used in dry or dewatered soils. Vertical settlements of wall is one of the disadvantages where failure of steep force transferring to the base of quite a little.iii ) Contigous worldly Pile WallBored pile wall is usually used as an economic and good method for retaining structure. This techniques is very suitable for deep basements excavation and underground structure where working space is expressage. This method prevent king-sized amount of soil excavation and also help to control ground movements. Piles are usually drills into ground by using continuous flight auger (CFA) with a certain gap distance between set up. A level outmatch distance of piles is usually around 20m depending on ground condition. beside world-weary pile wall is not suitable for site with high water level due to the gaps between piles.Advantages of contiguous pile walls are Comparative low cost and speed of constructionLow level of sound pollution ( low lev el of vibration)Pile can be drill in limited spacesHas the ability to minimize the distance between bored pile wall and existing wall for small excavation depthcontiguous bored pile wall.jpgiv ) Secant PilesDisadvantages of contiguous bored pile are overcome by using secant piles where interlocking method is introduced. Secant pile walls are constructed by concreting primary election (female) piles first then secondary (piles) are bored through female piles before concrete range of mountains full persuasiveness 2. By this the piles forms overlapping between each other.Advantages a)Can be installed in hard ground (cobbles /boulders)b)Low noise pollutionc) Better wall callosity compare to sheet pilessecant-pilingBig.jpgv ) Sheet Pile WallSheet Pile wall are made up from a group of piles that interlock each other and is driven into the soil. about(predicate) sheet pile wall nowadays is using make sheet which fabricated in factory. The use of sheet pile for temporary soil suppo rt for basement at urban area is not that popular where noise is the main constraint. Sheet pile may be installed using hydraulic can reduce the noise pollution. Sheet pile wall can be design as cantilever wall or anchored wall depends on the basement depth and soil condition that vary.Advantages a) laid-back resistance to driving stresses.b) Sheet can be reusec) weak to installDisadvantages a) Sheet pile can hardly be use as permanent structure.b) Installation of piles are hard where soil contain boulders and cobblersc) Noise pollution (High vibration)vi ) plosive consonant walls occlusion walls are strengthened concrete wall constructed in slurry supported by auto shot a infringe in panels of certain length. This slurry can be bentonite slurry where has thixotropic properties 8. The wall is first constructed in short panels length, by installing strengthened cages and concreting, then later intermediate panels are excavated to complete the whole wall. There is 3 type of blockage walls in use in industry, which is cast in-situ period wall, precast reinforced plosive wall and post-tensioned hitch wall.Advantages a) Allow effective transfer of vertical load from the building to subsoilb) Minimum noise and vibration disturbancec) Allow construction on limited site area.3.2 Comparison of each optionA table (table 3.2) of matrix below is to compare the advantages and disadvantages of several retaining structure. This comparison results will shows the about suitable retaining wall to design and construct for this project.DurabilityDurability is not usually a problem for a temporary wall depending on the soil condition. But when wall is to be design as a permanent structure, the wall should satisfy the durability requirement where wall should reach design life. For example, durability requirement for concrete wall depends on the design life, cement content, water cement ratio, cover of backing and also quality of workmanship.RigidityRigidity means a structure property that does not whirl under an applied force in vertical or horizontal load 10. Different type of retaining walls could sustain different loading. most(prenominal) walls are good in resisting vertical loading and does not bend but some walls can only sustain horizontal force. For example, reinforced diaphragm wall is much more rigid than a sheet pile wall. Reinforced concrete diaphragm wall can be design as a permanent structure that carry load from superstructure above and does not bend in any way. Comparing 6 types of retaining structure above, plosive walls, contiguous pile wall and secant pile walls are three best on rigidity.Constructability on SiteConstructability of a structure means a structure to be constructed on site easily from start to finish by ful foregathering clients requirement. Constructability also means ease of construction. A constructability review must be make before starting any construction wait on to prevent error, construction delay or cost overrun 11. The space to construct the proposed structure is limited. Figure 1.1 shows that a existing toilet pipe line is 1m beside the proposed structure on the right and also a existing structure 2m far from the proposed building on the left. One of the project requirement is to minimize the sound of construction in urban area. Choice of excavation is limited to prevent any vilify to the existing properties. impinge excavation is ideal for this project. Therefore, constructing diaphragm wall is the best solution where diaphragm wall can be constructed in limited space by using trench excavation, low noise pee-pee and apparatusry is not big.Soil ConditionThe soil profile is needed to take into consideration when designing retaining structure. Some structures construction is hardly to process when the soil contains cobbles or boulders. Most of the structure is suitable to be constructs on this project site because of the clayey soil from ground level to a minimum depth of 12m. Only when initial design for retaining structure with required depth over 12m into gravel layer, retaining structure like diaphragm wall is not that suitable due to the stability of wall.Water TableGround water on site are mainly from rainfall or groundwater endure through soil from rivers and seas 2. By reducing the groundwater within the excavation depth and structure depth by dewatering process will increase the strength of soil as the pore water military press is reduced. Groundwater control is essential to prevent any leakage of water into the basement car park or cause instability of structure, for example, ground heave. Retaining wall usually acts as a groundwater cut off. Several alternative ways of groundwater cut-off areTo raze the groundwater by temporary dewatering process where ground movement is to be considered. working(prenominal) sump pumping is to be done is ground is sufficiently impermeable mining is to be done under water and so permanent wall is to be construct under water by tremie concreting techniques.Diaphragm wall serves as a good water barrier compare to sheet pile or secant piles where sheet pile mightiness corrode and water will flow through the gap between secant pile.Depth of wallDesigner needs to consider the depth of a retaining structure can be construct. Some structure is cheaper to be built in deeper depth compare to school depth. Table 3.1 shows the different type of retaining structure that can be construct up to the utmost height of wall in order for the structure to stay constant and safe.Storage of MaterialsProper storage of raw materials is very important for a construction. Raw materials like reinforcement cages, cement, sand, and etc. needed to be on site on time to prevent any delay of construction. For example, steel sheet and reinforcement cages both are made in large size and needed large space to store up. Therefore, it is worth to consider this problem when choosing a retaining structure.Environ mental ImpactEnvironmental impact is one designer to be consider when structure is construct in urban area. The choice of wall can affect the environmental during construction, during in use and demolition 12. Three main causes to environmental impacts-During InstallationNoise and vibration when boring pile. (sheet piling)Number of vehicle used.Use of sustainable materials (Guidewall construction for diaphragm wall)When usedEffects on groundwater around the wall.End of life rest period of removalAbility of material to be reused3.3 Final DecisionDiaphragm wall is to be used for my design project.FUCK WHAT TO WRITE o0oChapter 4 Diaphragm Wall4.1 Preplanning and DesignFor designing purposes and construction of diaphragm walls, a number of item require to be considered in preplanning and design of diaphragm wall.Excavation SequenceThe sequence of excavation from ground level to the basement walls is to be well planned to minimize rig movement and to void changing places and moving of pipework from panel to panel of panel excavation. Soil dump truck, slurry removal vehicle, cranes and concrete mixing trucks, and to allow curing of concrete in completed panels are all parts of construction and excavation sequence that needed to be well planned.Guide Trench buildingThe successful of trench excavation for diaphragm wall depends on the temporary channelise wall. The guide walls must be design and construct to be robust to avoid any movement due to extreme load up from excavation rig service cranes or placement of reinforcement cages and response from stop end jacking systems. In some construction, reuseable precast concrete guide wall had been used and be interlocked each other by bolted to ensure the same standard of rigidity as in-situ cast concrete wall 2.Panel SizeDiaphragm wall is to be constructed by a panel trench excavation first. The panel length typically will vary from a minimum of one ginger snap insect bite (trench excavation machine catch width) to a multiple of grab bites which will extend to 7m. A grab bites vary between 2.3 and 2.8m depending on machine used. The panel length include two stop ends for the primary panels (Stop ends will be discussed on following pages). Secondary panels are those panels dug between two concreted panels. The panel length is limited to a certain length, and and so panel volume, this is to ensure that sufficient concrete can be fill up the whole panel within concreting period in a day. This takes maximum daily working hours and concrete supply into account. Panel size more depends on designer and contractor decision.Wall-Slab winding JointsJoints between basement floors slabs and wall is to be design carefully because the joints can transmit vertical shear and bending moment which could cause instability of structure and basement. wriggle out bars and Threaded-end couplers are both used in the joints. livelihood cageThe depth of diaphragm wall has led to the size of reinforcement cages. T hese cages are usually fix off-site and delivered to site when is needed. The maximum length of cages is restricted because of transportation of long and large cages.Slot for Tremie TubesA tremie underpass is used to ensure concrete is placed in correct position and that no separation of aggregate occurs during concreting pouring concrete from top to poop of walls. Therefore, reinforcement cage is to be knowing to allow sufficient admission fee for tremie tubes. For some construction of diaphragm with large panels, two tremie is to be used to maintain the concreting rate of 60 to 80m3 per hour.4.2 wrench SequenceEnd Of ConstructionSite ClearingTop Down Basement ConstructionDiaphragm Wall ConstructionSite Preparation4.3 Work to be through with(p)4.3.1 Site PreparationBasement and retaining wall construction methods involve a high degree of mechanization. A clear working space give maximum mobility for machinery, materials and workers, hence optimize the working speeds increasin g construction period. Therefore, several steps are needed to be done before any construction work progress. For example, temporary pathway should be provided to achieve a rapid tempo of construction in wet or dry weather.Traffic ManagementLocal authorities are highly concern on the trading management e finically in urban area. Construction in central of urban area could cause practiced traffic congestion due to slow moving construction vehicles and parts of itinerary are occupied by machinery. A slightly highway advocate will be changed on A marked in figure 4.2 below to provide access for construction vehicle into the site. On thoroughfare marked A in figure 4.2, the road is to be assumed that is a typical single lane carriageway. Therefore, the road length will be slightly reduced close the construction site. An alternative road for vehicle towards junction is to be proposed to local authorities to prevent any traffic congestion. Clear barricades and road sign will be prov ided on the road closure.Location of secret ServicesSite preparation in urban area includes tracing and clear marking of existing services includes underground telephone, power cables, water and sewer pipe, gas pipe, etc.Underground services is to be assumed to present in any circumstances. Trench excavation is more likely to encounter underground service in the face of excavation parallel to the line of excavation 13. Many serious accidents have been caused by men or machines when underground services are struck, penetrated or during excavation. Electric shock may result from striking electric carity cables during excavation.On this project, it is clearly shown on figure 1.1 that a 1200mm diameter concrete sewer pipeline is just 1m away from the side of proposed structure. A sewer pipeline bursting could cause contamination of the ground and odour smell to close citizens. Many sewer pipes are under high pressure too.As a solution, first, a confirmation of sewer pipe location i s to be done on site. Once the records are obtained, it will be unploughed on site and be accessible to workers. Furthermore, construction of diaphragm wall uses trench excavation techniques, which highly reduce the chance of striking the sewer pipe.Any other services includes telecommunication cables, gas pipe and electric pipe which are not shown in figure 1.1 given will be examine on site before excavation.Existing twistBuilding located around the site are needed to be protected from damage and dirt-staining. Cleaning and maintaining existing building in the end of construction can be costly. In figure 1.1 shows that there is existing 3 storey with raft foundation building 2m away from basement wall. Before any excavation start, careful inspection is to be done to the existing building to determine whether there are any existing cracks due to settlement or any damage on away wall of building. Cracks and damage is to be recorded down and photographed as a proof to prevent any c laims from property owner.Overhead ObstructionThe most common overhead obstruction is high tension electricity cables nearby the site. Most construction vehicle are high. There is a risk when tall vehicle pass by those overhead cables and cause unsuitable accident. Therefore, a clearance is to be done between the overhead cables and ground. For example, a typical goal post protection will be tumid along the entry to the site. Figure 4.3 below shows typical goal post protection. figure 4.3.jpgPublic SafetyIt is important to taking care about public safety. Any pedestrian is not allowed to enter construction site. A warning sign is to be displayed around the boundary site and barriers is to be set up along perimeter of construction.4.3.2 Diaphragm Wall ConstructionConstruction of diaphragm wall uses trench excavation supported by slurry. The slurry is typically bentonite and water.Diaphragm walls are constructed in the following steps 1) Pretrenching to finish up obstruction2) Gui dewall construction3) Trench excavation (panel excavation)4) Endstop placement5) Panel desanding6) reenforcement cages placement7) Concreting work (Tremie technique)8) End Stop removal9) Excavation of ordinary Panel10) Reinforcement cages placement11) Concreting work for remaining panels (Tremie technique)12) End of Diaphragm wall construction18.104.22.168Detail stepsPretrenching to remove obstructionPretrenching is a process to remove soil by open excavation to a certain depth, typically 1-2 m depth for guidewall construction. It is also a purpose for removing shallow obstruction and provide stable support for the guidewall.GuideWall ConstructionGuide wall is to be constructed after pre-trenching process. There are several purpose of constructing guidewall, these includeTo prevent the collapsing of soil near trench excavation surface.As a template for wall excavation and panel layoutTo provide a temporary supports for reinforcement cage. (by holding down the cage during concreting work )To provide support for end-stop joint. (restrain end-stop)To support Tremie PipeTo provide a reference elevation for inserting props, slabs, etc.For this project, the guidewall is to be constructed with reinforce concrete and be made from grade M20 grade reinforced concrete. The distance between both guidewall will be thickness of diaphragm wall plus a tolerance of 50mm. The dimension of guidewall (one side) will be 300mm(w) x 1000mm(d).Trench Excavation (Panel excavation)Construction of diaphragm wall uses trench excavation method which produce a vertical strip in soil that can collapse easily. Special excavation machinery are used to excavate the soil. Several type of machinery is used in construction subject field nowadays. These machinery can be cable hug or Kelly mounted and the digging mechanics can be cable or hydraulic operated. figure 4.7 2.pdfThe excavation is to be excavated in panels. The panel length varies typically from a minimum of one grab bite (trench excavation machine grab width) to a multiple of grab bites which will extend to 7m. A grab bites vary between 2.3 and 3m depending on machine used. figure 4.8.jpgThe trench excavated is to be supported by bentonite slurry. Bentonite is basically clay of montmorillonite group, and when added with water it forms an impervious slurry with large viscosity. The slurry will produce large lateral pressure to retain the vertical soil. In case of granular soils, the bentonite slurry will penetrates into the sides under positive pressure and forms jelly. When bentonite slurry is fills in impervious clay, it will not penetrate into the soil but form a layer of thin film to gives strength documentation vertical soils. The bentonite slurry is to be placed continuously into the trench throughout excavation.For this project, Kelly hitch is to be used for excavation. The depth and width of excavation will be discussed in following chapters. The panel length and bentonite slurry density is to be designed and results will be shown in following chapter too.End stop fixEndstops are placed in both panel fronts to provide the concrete at each vertical edge of panels with a predetermined shape. The shape of stop ends can be a pipe or special keyway end stops. End stop can be place in to be permanent or temporary.For this project, a temporary cylinder end stop is to be used. The end stops will be aloof by vertical extraction shortly after the concrete has been poured. Somehow, a delay of few hours is allowed in order to enable the concrete to set ahead some early strength and able to stay vertical. The timing and removal of end stops will be judge by the site contractor and to be carefully observed. If end stops is extract out before the concrete is stable (gained sufficient strength to stay vertical), there is a risk that the concrete will slump.