In-place Pile Foundation for a Tower-building Project

In-place locoweed animal foot for a Tower- grammatical construction ProjectCHAPTER 11 IntroductionPile foundations ar utilise to sustain a de coarse and exile the preventive of a given(p) over structure to the ground mission, which is found on a lower floor the ground at a considerable sense. The foundation consists of some(prenominal) hemorrhoid and voltaic cat sleep-caps. Pile foundations atomic number 18 gener altogethery long and lean, that conveyancings the structure core to the underlying blur (at a greater depth) or either fluctuate having a great elongate- complaint ability.The important typecasts of real(a)s used for lashings be Wood, steel and concrete. Piles do from these materials atomic number 18 driven, drilled or jacked into the ground and connected to quid caps. Depending upon type of district, mickle material and extend transmitting lineament tons argon discipline accordingly. (Pile Foundation externalise A Student Guide by Asca lew Abebe Dr Ian GN Smith).The objective of this project is to identify the figure of speechure of speech use of a cast-in-place mint shagdy foundation, for the tower-building project.The tower building project is called the Gemini Towers. The purpose of this construction (building) is to facilitate transcend executive spaces. This also resides on a excitey rural firmament. The building has been designed as per state-of-the-art conniving concepts which be basically to attract foreign investors to invest in Oman. The Gemini Building has 1 basement, 1 ground and 19 floors.Cast-in-place concrete sets are scapes of concrete cast in thin shell pipes, expire driven in the dirt, and usually closed end. Such pot doorbellys tolerate provide up to a 200-kip substance. The chief advantage oer precast heap is the ease of changing lengths by cutting or splicing the shell. The material cost of cast-in-place packages is relatively low. They are non feasible when whimsical by hard res publicas or rock.1.1 AimThe aim of this project is to design and propose cast in-place band foundation for a tower-building project and speculate the efficiency for the resembling. To come through this aim the following objective has to be achieved.1.2 ObjectivesThe objectives of this project are as followingTo canvass the eye socket soil condition, suitability of fold and investigate the soil.To study the advantages and efficiency of using cast-in-place visual modality for the building.To study the guidelines for the design of cast in-place structure according to BS 8004, 8110, 8002, etc.To design the hummock foundation as per the guidelines and the soil conditions (analyse the load, calculate the moment and determine the length and diameter and reinforcement).To use computer structural purpose program for performing design (CAD and STAD).1.3 MethodsThe modes followed in preparing this project is by collecting the project plan and the soil investigation repo rt. Then after that, research has been make on in-situ sens foundation type, to identify its characteristics.The neigh dull step is to study the the great unwashed designing criteria by referring to BS 8004, 8110 8002 codes to understand the guidelines, which shall be followed to turn over the corporation design. For this, the structural loads energize to be analysed and set using ultimate state design method. Then the design is processed depending on the data gathered on soil conditions, design loads and BS code guidelines.Thus, a proposal for the suitable volume provide be prepared by identifying the reasons over the proposal.The commonest function of arrange is to enrapture a load that back endnot be adequately shoped at shallow depths to a depth where adequate maintenance becomes available, also against excite forces which cause cracks and other(a) damages on superstructure.Chapter 2 Literature Review2 Pile FoundationPile foundations are used extensively in bridges, high-rise buildings, towers and special structures. In practice, rafts are generally used in conferences to transmit a column load to a deeper and stronger soil stratum. Pile whitethorn respond to loading each or as a base. In the latter case, the group and the surrounding soil will formulate a block to resist the column load. This whitethorn lead to a group faculty that is several(predicate) from the total capacity of individual heap making up the group. (Adel M. Hanna et al, 2004).Pile foundations are the part of a structure used to carry and carry the load of the structure to the commission ground rigid at some depth below ground surface. The main components of the foundation are the pile cap and the scores. Piles are long and slender members which air the load to deeper soil or rock of high bearing capacity avoiding shallow soil of low bearing capacity. The main types of materials used for wads are Wood, steel and concrete. Piles made from these materials a re driven, drilled or jacked into the ground and connected to pile caps. Depending upon type of soil, pile material and load transmitting characteristic set up are classified accordingly. (Ascalew Abebe et al, 2005)2.1 Functions of PilesThe purposes of pile foundations areto transmit a foundation load to a solid ground.to resist upended, squint-eyed and uplift load.A structure can be founded on piles if the soil now beneath its base does not have adequate bearing capacity. If the results of identify investigation show that the shallow soil is unstable and untoughened or if the order of the estimated small town is not acceptable a pile foundation whitethorn become considered. Further, a cost estimate may request that a pile foundation may be cheaper than any other compared ground proceeds costs. Piles can also be used in normal ground conditions to resist crosswise loads. Piles are a convenient method of foundation for works over water, such as jet draws or bridge piers. (Pile Foundation anatomy A Student Guide, by Ascalew Abebe Dr Ian GN Smith, 2003).2.2 classification of Piles2.2.1 Classification of pile with respect to load transmissionEnd-bearing. encounter-piles.Mixture of tackiness piles attrition piles.2.2.1.1 End bearing pilesThis type of piles is designed to transfer the structural load to a stable soil layer which is found at a greater depth below the ground. The load bearing capacity of this stratum is found by the soil penetration bulwark from the pile-toe (as in figure 1.2.1.1).The pile normally has attributes of a normal column, and should be designed as per the guidelines. The pile will not collapse in a reeking soil, and this should be studied merely if a part of the given pile is unsupported. (Eg If it is erected on water / air). Load transmission occurs through cohesion / friction, into the soil. At times, the soil around the pile may stick to the pile surface and starts negative genuflect friction. This phenomenon may h ave an inverse movement on the pile capacity. This is mainly caused due to the soil consolidation and ground water drainage. The pile depth is determined after reviewing the results from the soil tests and site investigation reports.2.2.1.2 Friction piles (cohesion)The bearing capacity is metrical from the soil friction in contact with the pile blastoff. (as in Figure 1.2.1.2).2.2.1.3 Mixture of cohesion piles friction piles.This is an extended end-bearing pile, when the soil underneath it is not hard, which bears the load. The pile is driven deep into the soil to gain efficient frictional apology. A modified version of the end-bearing pile is to have overdone bearing base on the piles. This can be achieved by immediately pushing a turgid portion of concrete into the piano soil layer right above the firm soil layer, to have an enlarged base. kindred result is made with bored-piles by creating a bell / chamfer at the bottom by the implys of reaming tools. Bored piles are used as tension piles as they are provided with a bell which has a high tensile- qualification. (as in figure 1.2.1.3)2.3 Cast-in- military position Pile FoundationCast-in-place piles are installed by driving to the desired penetration a heavy-section steel vacuum tube-shaped structure with its end temporarily closed. A reinforcing cage is next position in a tube which is filled with concrete. The tube is withdrawn while placing the concrete or after it has been placed. In other types of pile, thin steel shells or precast concrete shells are driven by means of an internal mandrel, and concrete, with or without reinforcement, is placed in the permanent shells after withdrawing the mandrel.2.3.1 AdvantagesLength of the pile can be freely alter to cater varying ground conditions. undercoat removed during the boring process can be verified and further tests can be made on it.Large diameter installations are possible.End enlargements up to twain or tether diameters are possible in clays.Pile materials are independent during driving / handling. nominate be installed to greater depths in the soil.Vibration-free and noise-free while installation.Can be installed in conditions of very low headroom.Ground shocks are completely nil.2.3.2 DisadvantagesSusceptible to make out or wasting in pressing ground.Concrete is not pumped under suitable conditions and cannot be inspected.The cement on the pile shaft will be washed up, if there is a sudden blow up of waster from any pressure caused underground.Special techniques need to be used to ensure enlarged pile ends.Cannot be easily prolonged above ground-level oddly in river and marine structures.Sandy soils may loosen due to boring methods and base grouting may be required for gravely soils to improve base resistance. sink piles may result in ground-loss, leading to settlement of nearby structures.CHAPTER 33 Load DistributionTo a great extent the design and calculation (load analysis) of pile foundations is carried out using computer finespunware. The following calculations are also performed, expect the following conditions are metThe pile is rigid.The pile is pinned at the top and at the bottom.Each pile receives the load only plumbly (i.e. axially apply).The force P playing on the pile is proportional to the sack U due to concretion.Therefore, P = k USince P = E AE A = k Uk = (E A ) / UWhereP = vertical load componentk = material constantU = displacementE = rubber band module of pile materialA = cross-section(a) area of pile (Figure 3 load on angiotensin converting enzyme pile)The length L should not necessarily be equal to the certain length of the pile. In a group of piles. If all piles are of the same material, have same cross-sectional area and equal length L, because the value of k is the same for all piles in the group3.1 Pile foundations vertical piles only3.1.1 Neutral axis loadThe pile cap is make the vertical contraction U, whose magnitude is equal for all members of the group. If Q (the vertical force acting on the pile group) is utilise at the neutral axis of the pile group, then the force on a single pile will be as followsPv = Q / nWherePv = vertical component of the load on any pile from the resultant load Qn = number of vertical piles in the group (see figure 3.1.2)Q = total vertical load on pile group3.1.2 Eccentric LoadIf the same group of piles are subjected to an eccentric load Q which is causing rotation around axis z (see fig 3.1b) then for the pile i at distance rxi from axis zUi = rxi . tan Ui = rxi = Pi = k . r xi . is a small careen tan (see figure 3.1.2).Pi = force (load on a single pile i).Ui = displacement caused by the eccentric force (load) Q.rxi = distance surrounded by pile and neutral axis of pile group.rxi positive measured the same direction as e and negative when in the opposite direction.e = distance between insinuate of intersection of resultant of vertical and horizontal loading with underside of pile.(Fig ure 3.1.2 Example of a pile foundation vertical piles)The sum of all the forces acting on the piles should be zero Mxi = Pi . rxi = k . rxi . rxi = k . r2xi == Mxi =From preliminary equation,Mz = MzApplying the same principle, in the x direction we get equivalent equation. If we embrace that the moment MX and MZ generated by the force Q are acting on a group of pile, then the sum of forces acting on a single pile will be as followsIf we dividing each term by the cross-sectional area of the pile, A, we can establish the working stream CHAPTER 44 Load on Pile4.1 IntroductionPiles can be arranged in a number of ways so that they can support load imposed on them. Vertical piles can be designed to carry vertical loads as well as lateral loads. If required, vertical piles can be combined with raking piles to support horizontal and vertical forces. (Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith)Often, if a pile group is subjected to vertical force, then the calculation of load distribution on single pile that is member of the group is assumed to be the total load divided by the number of piles in the group. (Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith)However, if a given pile group is subjected to eccentric vertical load or combination of lateral vertical load that can start moment force. Proper charge should be given during load distribution calculation.4.2 Pile ArrangementNormally, pile foundations consist of pile cap and a group of piles. The pile cap distributes the applied load to the individual piles which, in turn, transfer the load to the bearing ground. The individual piles are spaced and connected to the pile cap. Or tie beams and trimmed in order to connect the pile to the structure at cut-off level, and depending on the type of structure and eccentricity of the load, they can be arranged in different patterns. (Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith)(Figure 2.2 Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith))In this section, considering pile/soil interaction, calculations on the bearing capacity of single piles subjected to compressive axial load has been described. During pile design, the following divisors should be taken into considerationPile material compression and tension capacity.Deformation area of pile, bending moment capacity.Condition of the pile at the top and the end of the pile.Eccentricity of the load applied on the pile.Soil characteristics.Ground water level.4.3 The behaviour of piles under loadPiles are designed in line with the calculations base on load bearing capacity. It is based on the application of final axial-load, as per the given soil conditions at the site, in spite of appearance hours after the installation.This ultimate load capacity can be determined by eitherThe use of empirical formula to predict capacity from soil properties determined by testing. orLoad test on piles at the site.When increasing compressive load is applied on the pile, the pile soil musical arrangement reacts in a linear elasticized way to tailor A on the above figure (load settlement). The pile head rebounds to the original level if the load realises above this portend.When the load is development beyond point A there is yielding at, or close to, the pile-soil interface and faux paspage occurs until point B is reached, when the maximum pelt friction on the pile shaft will have been mobilised. If the load is realised at this fix up the pile head will rebound to point C, the amount of permanent settlement being the distance OC. When the stage of full mobilisation of the base resistance is reached (point D), the pile plunges downwards without any farther increase of load, or small increases in load producing large settlements. (Pile Foundation Design A Student Guide).4.4 Geotechnical design methodsIn order to separate their behavioural responses to applied pile load, soils ar e classified as either starchlike / noncohesive or clays/cohesive. The generic formulae used to predict soil resistance to pile load accommodate empirical modifying ciphers which can be adjusted according to previous engineering experience of the influence on the accuracy of predictions of changes in soil type and other factors such as the time delay before load testing.From figure 4.1b, the load settlement response is composed of two separate components, the linear elastic shaft friction Rs and non-linear base resistance Rb. The concept of the separate evaluation of shaft friction and base resistance forms the bases of static or soil chemical mechanism calculation of pile carrying capacity. The basic equations to be used for this are written asQ = Qb + Qs WpRc = Rb + Rs WpRt = Rs + WpWhereQ = Rc = the ultimate compression resistance of the pile.Qb = Rb = base resistance.Qs = Rs = shaft resistance.Wp = weight of the pile.Rt = tensile resistance of pile.In terms of soil mechani cs theory, the ultimate skin friction on the pile shaft is related to the horizontal effective stress acting on the shaft and the effective remoulded angle of friction between the pile and the clay and the ultimate shaft resistance Rs can be pass judgmentd by integration of the pile-soil gazump strength a over the surface area of the shaft.a = Ca + n tan aWhere n = Ks v a = Ca + KS v tanawherep = pile perimeterL = pile length = angle of friction between pile and soilKs = coefficient of lateral pressureThe ultimate bearing capacity, Rb, of the base is evaluated from the bearing capacity theoryAb = area of pile base.C = undrained strength of soil at base of pile.NC = bearing capacity factor.CHAPTER 55 Calculating the resistance of piles to compressive loads5.1 Cast in Place Piles Shaft resistanceThese piles are installed by boring through soft overburden onto a strong rock the piles can be regarded as end-bearing elements and their working load is determined by the safe working stress on the pile shaft at the point of minimal cross-section, or by code of practice requirements. Bored piles drilled down for some depth into weak or weathered rocks and terminated in spite of appearance these rocks act partly as friction and partly as end-bearing piles.The author Duncan C. Wyllie, gives a detailed account of the factors governing the development of shaft friction over the depth of the rock socket. The factors which govern the bearing capacity and settlement of the pile are summarized as the followingThe length to diameter ratio of the socket.The strength and elastic modulus of the rock around and beneath the socket.The condition of the side walls, that is, harshness and the presence of drill cuttings or bentonite slurry.Condition of the base of the drilled hole with respect to remotion of drill cuttings and other loose debris.Layering of the rock with seams of differing strength and moduli. colony of the pile in relation to the elastic limit of the side-wall strength.Creep of the material at the rock/concrete interface resulting in increasing settlement with time.The effect of the length/diameter ratio of the socket is shown in Figure 5.1a, for the condition of the rock having a higher(prenominal) elastic modulus than the concrete.It will be seen that if it is desired to utilize base resistance as well as socket friction the socket length should be less than quadruple pile diameters. The high interface stress over the f number part of the socket will be noted.The condition of the side walls is an important factor. In a weak rock such as chalk, impenetrable shale, or clayey weathered marl, the action of the drilling tools is to cause softening and slurrying of the walls of the borehole and, in the most adverse case, the shaft friction corresponds to that typical of a smooth-bore hole in soft clay. In stronger and fragmented rocks the slurrying does not take place to the same extent, and there is a angle of dip towards the enlargement of the drill hole, resulting in better keying of the concrete to the rock. If the pile borehole is drilled through soft clay this soil may be carried down by the drilling tools to fill the cavities and smear the sides of the rock socket. This behaviour can be avoided to some extent by inserting a instance and sealing it into the rock-head before go along the drilling to form the rock socket, but the interior of the casing is likely to be heavily smeared with clay which will be carried down by the drilling tools into the rock socket.As mentioned in Duncan C. Wyllie, suggests that if bentonite is used as a drilling fluid the rock socket shaft friction should be reduced to 25% of that of a clean socket unless tests can be made to verify the actual friction which is developed.It is evident that the keying of the shaft concrete to the rock and hence the strength of the concrete to rock bond is dependent on the strength of the rock. Correlations between the unimprisoned compression str ength of the rock and rock socket bond stress have been established by Horvarth(4.50), Rosenberg and Journeaux(4.51), and Williams and Pells(4.52). The ultimate bond stress, fs, is related to the honest unconfined compression strength, quc, by the equationWhere = reduction factor relating to, quc as shown in Figure 5.1b = correction factor associated with cut-off spacing in the mass of rock as shown in Figure 5.1c.The shorten of Williams and Pells in Figure 5.1b is higher than the other two, but the factor is angiotensin-converting enzyme in all cases for the Horvarth and the Rosenberg and Journeaux curves. It should also be noted that the factors for all three curves do not allow for smearing of the rock socket caused by dragdown of clay overburden or degradation of the rock.The factor is related to the mass factor, j, which is the ratio of the elastic modulus of the rock mass to that of the intact rock as shown in Figure 5.1d. If the mass factor is not known from loading tes ts or seismic swiftness measurements, it can be obtained approximately from the relationships with the rock quality designation (RQD) or the discontinuity spacing quoted by Hobbs (4.53) as follows5.2 End Bearing CapacitySometimes piles are driven to an underlying layer of rock. In such cases, the engineer must evaluate the bearing capacity of the rock. The ultimate social unit point resistance in rock (Goodman, 1980) is approximately.N = tan2 (45 + / 2)qu = unconfined compression strength of rock= drained angle of friction circuit card 5.2aTable 5.2bThe unconfined compression strength of rock can be determined by laboratory tests on rock specimens collected during field investigation. However, extreme caution should be used in obtaining the proper value of qu, because laboratory specimens usually are small in diameter. As the diameter of the specimen increases, the unconfined compression strength decreases a phenomenon referred to as the scale effect. For specimens larger than about 1 m (3f) in diameter, the value of qu remains approximately constant.There appears to be fourfold to fivefold reduction of the magnitude of qu in the process. The scale effect in rock is caused primarily by randomly distributed large and small fractures and also by progressive ruptures along the slip lines. Hence, we always recommend thatThe above table (Table 5.2a) lists some representative value of (laboratory) unconfined compression strengths of rock. Representative values of the rock friction angle are given in the above table (Table 5.2b).A factor of safety of at least(prenominal) 3 should be used to determine the allowable point bearing capacity of piles. ThusCHAPTER 66 Pile Load Test (Vesics Method)A number of settlement analysis methods for single piles are available. These methods may be broadly classified into three categoriesElastic continuum methodsLoadtransfer methodsNumerical methodsExamples of such methods are the elastic methods proposed by Vesic (1977) and Po ulos and Davis (1980), the alter elastic methods proposed by Randolph and Wroth (1978) and Fleming et al. (1992), the nonlinear loadtransfer methods proposed by Coyle and Reese (1966) and McVay et al. (1989), and the numerical methods based on advanced constitutive models of soil behaviour proposed by Jardine et al. (1986). In this paper, three representative methods are adopted for the calibration exercise the elastic method proposed by Vesic (1977), the simplified analysis method proposed by Fleming et al. (1992), and a nonlinear loadtransfer method (McVay et al. 1989) implemented in program FB-Pier (BSI 2003).In Vesics method, the settlement of a pile under vertical loading, S, includes three componentsS = S1 + S2 + S3WhereS1 is the elastic pile compression.S2 is the pile settlement caused by the load at the pile toe.S3 is the pile settlement caused by the load transmitted along the pile shaft.If the pile material is assumed to be elastic, the elastic pile compression can be cal culated byS1 = (Qb + Qs)L / (ApEp)Where Qb and Qs are the loads carried by the pile toe and pile shaft, respectively Ap is the pile cross-section area L is the pile length Ep is the modulus of elasticity of the pile material and is a coefficient depending on the nature of unit friction resistance distribution along the pile shaft. In this work, the distribution is assumed to be uniform and hence = 0.5. Settlement S2 may be expressed in a form similar to that for a shallow foundation.S2 = (qbD / Esb) (1-v2)IbWhereD is the pile width or diameterqb is the load per unit area at the pile toe qb = Qb /AbAb is the pile base areaEsb is the modulus of elasticity of the soil at the pile toe is Poissons ratioIb is an influence factor, generally Ib = 0.85S3 = (Qs / pL) (D / Ess) (1 2) IsWherep is the pile perimeter.Ess is the modulus of elasticity of the soil along the pile shaft.Is is an influence factor.The influence factor Is can be calculated by an empirical relation (Vesic 1977).Is = 2 + 0.35 (L/D)With Vesics method, twain Qb and Qs are required. In this report, Qb and Qs are obtained using two methods. In the first method (Vesics method I), these two loads are determined from a nonlinear loadtransfer method, which will be introduced later.In the second method (Vesics method II), these two loads are determined using empirical ratios of Qb to the total load applied on pile Q based on field test data. Shek (2005) reported loadtransfer in 14 test piles, including 11 piles founded in soil and 3 piles founded on rock. The mean ratios of Qb /Q for the piles founded in soil and the piles founded on rock are summarized in Table 3 and applied in this calibration exercise. The mean values of Qb /Q at twice the design load and the failure load are very similar. Hence, the average of the mean values is adopted for calibration at both twice the design load and the failure load.In the Fleming et al. method, the settlement of a pile is given by the following approximate closed- form solution (Fleming et al. 1992)Wheren = rb / r0, r0 and rb are the radii of the pile shaft and pile toe, respectively (for H-piles, ro2 = rb2 = Dh, h is the depth of the pile cross-section)G = GL/Gb, GL is the shear modulus of the soil at depth L, and Gb is the shear modulus of the soil beneath the pile toe. = Gave/GL, Gave is the average shear modulus of the soil along the pile shaftp is the pile stiffness ratiop = Ep / GL = ln0.25 +(2.5(1 v) 0.25) G L/r0L = (2/)1/2(L/r0). If the slenderness ratio L/r0 is less than 0.5p1/2 (L/r0) the pile may be enured as effectively rigid and eq. 7 then reduces toIf the slenderness ratio L/r0 is larger than 3p1/2, the pile may be treated as infinitely long, and eq. 7 then reduces toIn this case, GL is the soil shear modulus at the bottom of the active pile length Lac, where Lac = 3r0p1/2.In the nonlinear loadtransfer method implemented in FB-Pier, the axial Z curve for modelling the pilesoil interaction along the pile is given as (McVay et a l. 1989)In-place Pile Foundation for a Tower-building ProjectIn-place Pile Foundation for a Tower-building ProjectCHAPTER 11 IntroductionPile foundations are used to carry a load and transfer the load of a given structure to the ground bearing, which is found below the ground at a considerable depth. The foundation consists of several piles and pile-caps. Pile foundations are generally long and lean, that transfers the structure load to the underlying soil (at a greater depth) or any rock having a great load-bearing ability.The main types of materials used for piles are Wood, steel and concrete. Piles made from these materials are driven, drilled or jacked into the ground and connected to pile caps. Depending upon type of soil, pile material and load transmitting characteristic piles are classified accordingly. (Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith).The objective of this project is to identify the design use of a cast-in-place pile foundation, fo r the tower-building project.The tower building project is called the Gemini Towers. The purpose of this construction (building) is to facilitate office spaces. This also resides on a rocky area. The building has been designed as per state-of-the-art designing concepts which are basically to attract foreign investors to invest in Oman. The Gemini Building has 1 basement, 1 ground and 19 floors.Cast-in-place concrete piles are shafts of concrete cast in thin shell pipes, top driven in the soil, and usually closed end. Such piles can provide up to a 200-kip capacity. The chief advantage over precast piles is the ease of changing lengths by cutting or splicing the shell. The material cost of cast-in-place piles is relatively low. They are not feasible when driving through hard soils or rock.1.1 AimThe aim of this project is to design and propose cast in-place pile foundation for a tower-building project and study the efficiency for the same. To achieve this aim the following objective has to be achieved.1.2 ObjectivesThe objectives of this project are as followingTo study the field soil condition, suitability of pile and investigate the soil.To study the advantages and efficiency of using cast-in-place pile for the building.To study the guidelines for the design of cast in-place structure according to BS 8004, 8110, 8002, etc.To design the pile foundation as per the guidelines and the soil conditions (analyse the load, calculate the moment and determine the length and diameter and reinforcement).To use computer structural designing program for performing design (CAD and STAD).1.3 MethodsThe methods followed in preparing this project is by collecting the project plan and the soil investigation report. Then after that, research has been done on in-situ pile foundation type, to identify its characteristics.The next step is to study the pile designing criteria by referring to BS 8004, 8110 8002 codes to understand the guidelines, which shall be followed to accomplis h the pile design. For this, the structural loads have to be analysed and identified using ultimate state design method. Then the design is processed depending on the data gathered on soil conditions, design loads and BS code guidelines.Thus, a proposal for the suitable pile will be prepared by identifying the reasons over the proposal.The commonest function of piles is to transfer a load that cannot be adequately supported at shallow depths to a depth where adequate support becomes available, also against uplift forces which cause cracks and other damages on superstructure.Chapter 2 Literature Review2 Pile FoundationPile foundations are used extensively in bridges, high-rise buildings, towers and special structures. In practice, piles are generally used in groups to transmit a column load to a deeper and stronger soil stratum. Pile may respond to loading individually or as a group. In the latter case, the group and the surrounding soil will formulate a block to resist the column l oad. This may lead to a group capacity that is different from the total capacity of individual piles making up the group. (Adel M. Hanna et al, 2004).Pile foundations are the part of a structure used to carry and transfer the load of the structure to the bearing ground located at some depth below ground surface. The main components of the foundation are the pile cap and the piles. Piles are long and slender members which transfer the load to deeper soil or rock of high bearing capacity avoiding shallow soil of low bearing capacity. The main types of materials used for piles are Wood, steel and concrete. Piles made from these materials are driven, drilled or jacked into the ground and connected to pile caps. Depending upon type of soil, pile material and load transmitting characteristic piles are classified accordingly. (Ascalew Abebe et al, 2005)2.1 Functions of PilesThe purposes of pile foundations areto transmit a foundation load to a solid ground.to resist vertical, lateral and u plift load.A structure can be founded on piles if the soil immediately beneath its base does not have adequate bearing capacity. If the results of site investigation show that the shallow soil is unstable and weak or if the magnitude of the estimated settlement is not acceptable a pile foundation may become considered. Further, a cost estimate may indicate that a pile foundation may be cheaper than any other compared ground improvement costs. Piles can also be used in normal ground conditions to resist horizontal loads. Piles are a convenient method of foundation for works over water, such as jetties or bridge piers. (Pile Foundation Design A Student Guide, by Ascalew Abebe Dr Ian GN Smith, 2003).2.2 Classification of Piles2.2.1 Classification of pile with respect to load transmissionEnd-bearing.Friction-piles.Mixture of cohesion piles friction piles.2.2.1.1 End bearing pilesThis type of piles is designed to transfer the structural load to a stable soil layer which is found at a g reater depth below the ground. The load bearing capacity of this stratum is found by the soil penetration resistance from the pile-toe (as in figure 1.2.1.1).The pile normally has attributes of a normal column, and should be designed as per the guidelines. The pile will not collapse in a weak soil, and this should be studied only if a part of the given pile is unsupported. (Eg If it is erected on water / air). Load transmission occurs through cohesion / friction, into the soil. At times, the soil around the pile may stick to the pile surface and starts negative skin friction. This phenomenon may have an inverse effect on the pile capacity. This is mainly caused due to the soil consolidation and ground water drainage. The pile depth is determined after reviewing the results from the soil tests and site investigation reports.2.2.1.2 Friction piles (cohesion)The bearing capacity is calculated from the soil friction in contact with the pile shaft. (as in Figure 1.2.1.2).2.2.1.3 Mixture of cohesion piles friction piles.This is an extended end-bearing pile, when the soil underneath it is not hard, which bears the load. The pile is driven deep into the soil to create efficient frictional resistance. A modified version of the end-bearing pile is to have enlarged bearing base on the piles. This can be achieved by immediately pushing a large portion of concrete into the soft soil layer right above the firm soil layer, to have an enlarged base. Similar result is made with bored-piles by creating a bell / cone at the bottom by the means of reaming tools. Bored piles are used as tension piles as they are provided with a bell which has a high tensile-strength. (as in figure 1.2.1.3)2.3 Cast-in-Place Pile FoundationCast-in-place piles are installed by driving to the desired penetration a heavy-section steel tube with its end temporarily closed. A reinforcing cage is next placed in a tube which is filled with concrete. The tube is withdrawn while placing the concrete or afte r it has been placed. In other types of pile, thin steel shells or precast concrete shells are driven by means of an internal mandrel, and concrete, with or without reinforcement, is placed in the permanent shells after withdrawing the mandrel.2.3.1 AdvantagesLength of the pile can be freely altered to cater varying ground conditions. Soil removed during the boring process can be verified and further tests can be made on it.Large diameter installations are possible.End enlargements up to two or three diameters are possible in clays.Pile materials are independent during driving / handling.Can be installed to greater depths in the soil.Vibration-free and noise-free while installation.Can be installed in conditions of very low headroom.Ground shocks are completely nil.2.3.2 DisadvantagesSusceptible to necking or wasting in pressing ground.Concrete is not pumped under suitable conditions and cannot be inspected.The cement on the pile shaft will be washed up, if there is a sudden surge o f waster from any pressure caused underground.Special techniques need to be used to ensure enlarged pile ends.Cannot be easily prolonged above ground-level especially in river and marine structures.Sandy soils may loosen due to boring methods and base grouting may be required for gravely soils to improve base resistance.Sinking piles may result in ground-loss, leading to settlement of nearby structures.CHAPTER 33 Load DistributionTo a great extent the design and calculation (load analysis) of pile foundations is carried out using computer software. The following calculations are also performed, assuming the following conditions are metThe pile is rigid.The pile is pinned at the top and at the bottom.Each pile receives the load only vertically (i.e. axially applied).The force P acting on the pile is proportional to the displacement U due to compression.Therefore, P = k USince P = E AE A = k Uk = (E A ) / UWhereP = vertical load componentk = material constantU = displacementE = elasti c module of pile materialA = cross-sectional area of pile (Figure 3 load on single pile)The length L should not necessarily be equal to the actual length of the pile. In a group of piles. If all piles are of the same material, have same cross-sectional area and equal length L, then the value of k is the same for all piles in the group3.1 Pile foundations vertical piles only3.1.1 Neutral axis loadThe pile cap is causing the vertical compression U, whose magnitude is equal for all members of the group. If Q (the vertical force acting on the pile group) is applied at the neutral axis of the pile group, then the force on a single pile will be as followsPv = Q / nWherePv = vertical component of the load on any pile from the resultant load Qn = number of vertical piles in the group (see figure 3.1.2)Q = total vertical load on pile group3.1.2 Eccentric LoadIf the same group of piles are subjected to an eccentric load Q which is causing rotation around axis z (see fig 3.1b) then for the pi le i at distance rxi from axis zUi = rxi . tan Ui = rxi = Pi = k . r xi . is a small angle tan (see figure 3.1.2).Pi = force (load on a single pile i).Ui = displacement caused by the eccentric force (load) Q.rxi = distance between pile and neutral axis of pile group.rxi positive measured the same direction as e and negative when in the opposite direction.e = distance between point of intersection of resultant of vertical and horizontal loading with underside of pile.(Figure 3.1.2 Example of a pile foundation vertical piles)The sum of all the forces acting on the piles should be zero Mxi = Pi . rxi = k . rxi . rxi = k . r2xi == Mxi =From previous equation,Mz = MzApplying the same principle, in the x direction we get equivalent equation. If we assume that the moment MX and MZ generated by the force Q are acting on a group of pile, then the sum of forces acting on a single pile will be as followsIf we dividing each term by the cross-sectional area of the pile, A, we can establ ish the working stream CHAPTER 44 Load on Pile4.1 IntroductionPiles can be arranged in a number of ways so that they can support load imposed on them. Vertical piles can be designed to carry vertical loads as well as lateral loads. If required, vertical piles can be combined with raking piles to support horizontal and vertical forces. (Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith)Often, if a pile group is subjected to vertical force, then the calculation of load distribution on single pile that is member of the group is assumed to be the total load divided by the number of piles in the group. (Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith)However, if a given pile group is subjected to eccentric vertical load or combination of lateral vertical load that can start moment force. Proper attention should be given during load distribution calculation.4.2 Pile ArrangementNormally, pile foundations consist of pile cap and a group of pi les. The pile cap distributes the applied load to the individual piles which, in turn, transfer the load to the bearing ground. The individual piles are spaced and connected to the pile cap. Or tie beams and trimmed in order to connect the pile to the structure at cut-off level, and depending on the type of structure and eccentricity of the load, they can be arranged in different patterns. (Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith)(Figure 2.2 Pile Foundation Design A Student Guide by Ascalew Abebe Dr Ian GN Smith))In this section, considering pile/soil interaction, calculations on the bearing capacity of single piles subjected to compressive axial load has been described. During pile design, the following factors should be taken into considerationPile material compression and tension capacity.Deformation area of pile, bending moment capacity.Condition of the pile at the top and the end of the pile.Eccentricity of the load applied on the pile.Soil ch aracteristics.Ground water level.4.3 The behaviour of piles under loadPiles are designed in line with the calculations based on load bearing capacity. It is based on the application of final axial-load, as per the given soil conditions at the site, within hours after the installation.This ultimate load capacity can be determined by eitherThe use of empirical formula to predict capacity from soil properties determined by testing. orLoad test on piles at the site.When increasing compressive load is applied on the pile, the pile soil system reacts in a linear elastic way to point A on the above figure (load settlement). The pile head rebounds to the original level if the load realises above this point.When the load is increase beyond point A there is yielding at, or close to, the pile-soil interface and slippage occurs until point B is reached, when the maximum skin friction on the pile shaft will have been mobilised. If the load is realised at this stage the pile head will rebound to point C, the amount of permanent settlement being the distance OC. When the stage of full mobilisation of the base resistance is reached (point D), the pile plunges downwards without any farther increase of load, or small increases in load producing large settlements. (Pile Foundation Design A Student Guide).4.4 Geotechnical design methodsIn order to separate their behavioural responses to applied pile load, soils are classified as either granular / noncohesive or clays/cohesive. The generic formulae used to predict soil resistance to pile load include empirical modifying factors which can be adjusted according to previous engineering experience of the influence on the accuracy of predictions of changes in soil type and other factors such as the time delay before load testing.From figure 4.1b, the load settlement response is composed of two separate components, the linear elastic shaft friction Rs and non-linear base resistance Rb. The concept of the separate evaluation of shaft fri ction and base resistance forms the bases of static or soil mechanics calculation of pile carrying capacity. The basic equations to be used for this are written asQ = Qb + Qs WpRc = Rb + Rs WpRt = Rs + WpWhereQ = Rc = the ultimate compression resistance of the pile.Qb = Rb = base resistance.Qs = Rs = shaft resistance.Wp = weight of the pile.Rt = tensile resistance of pile.In terms of soil mechanics theory, the ultimate skin friction on the pile shaft is related to the horizontal effective stress acting on the shaft and the effective remoulded angle of friction between the pile and the clay and the ultimate shaft resistance Rs can be evaluated by integration of the pile-soil shear strength a over the surface area of the shaft.a = Ca + n tan aWhere n = Ks v a = Ca + KS v tanawherep = pile perimeterL = pile length = angle of friction between pile and soilKs = coefficient of lateral pressureThe ultimate bearing capacity, Rb, of the base is evaluated from the bearing capacity theoryAb = area of pile base.C = undrained strength of soil at base of pile.NC = bearing capacity factor.CHAPTER 55 Calculating the resistance of piles to compressive loads5.1 Cast in Place Piles Shaft resistanceThese piles are installed by drilling through soft overburden onto a strong rock the piles can be regarded as end-bearing elements and their working load is determined by the safe working stress on the pile shaft at the point of minimum cross-section, or by code of practice requirements. Bored piles drilled down for some depth into weak or weathered rocks and terminated within these rocks act partly as friction and partly as end-bearing piles.The author Duncan C. Wyllie, gives a detailed account of the factors governing the development of shaft friction over the depth of the rock socket. The factors which govern the bearing capacity and settlement of the pile are summarized as the followingThe length to diameter ratio of the socket.The strength and elastic modulus of the rock aroun d and beneath the socket.The condition of the side walls, that is, roughness and the presence of drill cuttings or bentonite slurry.Condition of the base of the drilled hole with respect to removal of drill cuttings and other loose debris.Layering of the rock with seams of differing strength and moduli.Settlement of the pile in relation to the elastic limit of the side-wall strength.Creep of the material at the rock/concrete interface resulting in increasing settlement with time.The effect of the length/diameter ratio of the socket is shown in Figure 5.1a, for the condition of the rock having a higher elastic modulus than the concrete.It will be seen that if it is desired to utilize base resistance as well as socket friction the socket length should be less than four pile diameters. The high interface stress over the upper part of the socket will be noted.The condition of the side walls is an important factor. In a weak rock such as chalk, clayey shale, or clayey weathered marl, the action of the drilling tools is to cause softening and slurrying of the walls of the borehole and, in the most adverse case, the shaft friction corresponds to that typical of a smooth-bore hole in soft clay. In stronger and fragmented rocks the slurrying does not take place to the same extent, and there is a tendency towards the enlargement of the drill hole, resulting in better keying of the concrete to the rock. If the pile borehole is drilled through soft clay this soil may be carried down by the drilling tools to fill the cavities and smear the sides of the rock socket. This behaviour can be avoided to some extent by inserting a casing and sealing it into the rock-head before continuing the drilling to form the rock socket, but the interior of the casing is likely to be heavily smeared with clay which will be carried down by the drilling tools into the rock socket.As mentioned in Duncan C. Wyllie, suggests that if bentonite is used as a drilling fluid the rock socket shaft fric tion should be reduced to 25% of that of a clean socket unless tests can be made to verify the actual friction which is developed.It is evident that the keying of the shaft concrete to the rock and hence the strength of the concrete to rock bond is dependent on the strength of the rock. Correlations between the unconfined compression strength of the rock and rock socket bond stress have been established by Horvarth(4.50), Rosenberg and Journeaux(4.51), and Williams and Pells(4.52). The ultimate bond stress, fs, is related to the average unconfined compression strength, quc, by the equationWhere = reduction factor relating to, quc as shown in Figure 5.1b = correction factor associated with cut-off spacing in the mass of rock as shown in Figure 5.1c.The curve of Williams and Pells in Figure 5.1b is higher than the other two, but the factor is unity in all cases for the Horvarth and the Rosenberg and Journeaux curves. It should also be noted that the factors for all three curves do n ot allow for smearing of the rock socket caused by dragdown of clay overburden or degradation of the rock.The factor is related to the mass factor, j, which is the ratio of the elastic modulus of the rock mass to that of the intact rock as shown in Figure 5.1d. If the mass factor is not known from loading tests or seismic velocity measurements, it can be obtained approximately from the relationships with the rock quality designation (RQD) or the discontinuity spacing quoted by Hobbs (4.53) as follows5.2 End Bearing CapacitySometimes piles are driven to an underlying layer of rock. In such cases, the engineer must evaluate the bearing capacity of the rock. The ultimate unit point resistance in rock (Goodman, 1980) is approximately.N = tan2 (45 + / 2)qu = unconfined compression strength of rock= drained angle of frictionTable 5.2aTable 5.2bThe unconfined compression strength of rock can be determined by laboratory tests on rock specimens collected during field investigation. However, extreme caution should be used in obtaining the proper value of qu, because laboratory specimens usually are small in diameter. As the diameter of the specimen increases, the unconfined compression strength decreases a phenomenon referred to as the scale effect. For specimens larger than about 1 m (3f) in diameter, the value of qu remains approximately constant.There appears to be fourfold to fivefold reduction of the magnitude of qu in the process. The scale effect in rock is caused primarily by randomly distributed large and small fractures and also by progressive ruptures along the slip lines. Hence, we always recommend thatThe above table (Table 5.2a) lists some representative values of (laboratory) unconfined compression strengths of rock. Representative values of the rock friction angle are given in the above table (Table 5.2b).A factor of safety of at least 3 should be used to determine the allowable point bearing capacity of piles. ThusCHAPTER 66 Pile Load Test (Vesics Met hod)A number of settlement analysis methods for single piles are available. These methods may be broadly classified into three categoriesElastic continuum methodsLoadtransfer methodsNumerical methodsExamples of such methods are the elastic methods proposed by Vesic (1977) and Poulos and Davis (1980), the simplified elastic methods proposed by Randolph and Wroth (1978) and Fleming et al. (1992), the nonlinear loadtransfer methods proposed by Coyle and Reese (1966) and McVay et al. (1989), and the numerical methods based on advanced constitutive models of soil behaviour proposed by Jardine et al. (1986). In this paper, three representative methods are adopted for the calibration exercise the elastic method proposed by Vesic (1977), the simplified analysis method proposed by Fleming et al. (1992), and a nonlinear loadtransfer method (McVay et al. 1989) implemented in program FB-Pier (BSI 2003).In Vesics method, the settlement of a pile under vertical loading, S, includes three componen tsS = S1 + S2 + S3WhereS1 is the elastic pile compression.S2 is the pile settlement caused by the load at the pile toe.S3 is the pile settlement caused by the load transmitted along the pile shaft.If the pile material is assumed to be elastic, the elastic pile compression can be calculated byS1 = (Qb + Qs)L / (ApEp)Where Qb and Qs are the loads carried by the pile toe and pile shaft, respectively Ap is the pile cross-section area L is the pile length Ep is the modulus of elasticity of the pile material and is a coefficient depending on the nature of unit friction resistance distribution along the pile shaft. In this work, the distribution is assumed to be uniform and hence = 0.5. Settlement S2 may be expressed in a form similar to that for a shallow foundation.S2 = (qbD / Esb) (1-v2)IbWhereD is the pile width or diameterqb is the load per unit area at the pile toe qb = Qb /AbAb is the pile base areaEsb is the modulus of elasticity of the soil at the pile toe is Poissons ratioIb is an influence factor, generally Ib = 0.85S3 = (Qs / pL) (D / Ess) (1 2) IsWherep is the pile perimeter.Ess is the modulus of elasticity of the soil along the pile shaft.Is is an influence factor.The influence factor Is can be calculated by an empirical relation (Vesic 1977).Is = 2 + 0.35 (L/D)With Vesics method, both Qb and Qs are required. In this report, Qb and Qs are obtained using two methods. In the first method (Vesics method I), these two loads are determined from a nonlinear loadtransfer method, which will be introduced later.In the second method (Vesics method II), these two loads are determined using empirical ratios of Qb to the total load applied on pile Q based on field test data. Shek (2005) reported loadtransfer in 14 test piles, including 11 piles founded in soil and 3 piles founded on rock. The mean ratios of Qb /Q for the piles founded in soil and the piles founded on rock are summarized in Table 3 and applied in this calibration exercise. The mean values of Qb /Q at twice the design load and the failure load are very similar. Hence, the average of the mean values is adopted for calibration at both twice the design load and the failure load.In the Fleming et al. method, the settlement of a pile is given by the following approximate closed-form solution (Fleming et al. 1992)Wheren = rb / r0, r0 and rb are the radii of the pile shaft and pile toe, respectively (for H-piles, ro2 = rb2 = Dh, h is the depth of the pile cross-section)G = GL/Gb, GL is the shear modulus of the soil at depth L, and Gb is the shear modulus of the soil beneath the pile toe. = Gave/GL, Gave is the average shear modulus of the soil along the pile shaftp is the pile stiffness ratiop = Ep / GL = ln0.25 +(2.5(1 v) 0.25) G L/r0L = (2/)1/2(L/r0). If the slenderness ratio L/r0 is less than 0.5p1/2 (L/r0) the pile may be treated as effectively rigid and eq. 7 then reduces toIf the slenderness ratio L/r0 is larger than 3p1/2, the pile may be treated as infinitely long, and eq. 7 then reduces toIn this case, GL is the soil shear modulus at the bottom of the active pile length Lac, where Lac = 3r0p1/2.In the nonlinear loadtransfer method implemented in FB-Pier, the axial Z curve for modelling the pilesoil interaction along the pile is given as (McVay et al. 1989)