DESIGN OF DEEP FOUNDATIONS ON BORED PILES
DESIGN OF DEEP FOUNDATIONS ON BORED PILESLinas Gabrielaitis1, Vytautas Papinigis21,2Vilnius Gediminas technical university, Saulėtekio ave. 11, LT-10223 Vilnius, Lithuania.E-mail: 1linas.gabrielaitis@vgtu.lt; 2Vytas@proex.ltAbstract. The paper describes the design of pile foundation on the site of the Elektrenai power plant, Lithuania. Thefoundation is aimed to support equipment of the power plant consisting of the gas turbine, the steam turbine and thegenerator. Besides high loads, the equipment had a strong dynamic impact on the foundation due to its working conditions and vibration. The pilling solution was adopted due to different reasons: i) the capacity of the soil to supportgreat stresses over it; ii) the special requirements of the main equipment about settlements, movements and stresses.Pilling foundation was evaluated through immediate settlement analysis, which was carried out employing four mostwidely used methods. It included analysis of the soil data from cone and dynamic penetration tests, boreholes andlaboratory tests. Soil properties were estimated from site investigation and soil exploration program according toLithuanian standards. Pile settlement analysis showed that settlement value was 14 mm (pile toe settlement), and settlement value of elastic deformation of pile from vertical compressive loads was 3 mm. For such structure, foundationsettlement should not be more than 16 mm (i.e., no more than 2 % of pile diameter). It was estimated that for pile ofdiameter 800 mm, pile length of 24 m was sufficient to endure overall loads.Keywords: deep foundations, bored piles, foundation for gas and steam turbine, pile settlement analysis, cone penetration test.1. IntroductionFoundation has to be proportioned both to interfacewith the soil at a safe stress level and to limit settlementsto an acceptable amount. Settlement analysis plays animportant role in building foundation, even though onlyfew modern buildings collapse from excessive settlements, it is not uncommon for a partial collapse or a localized failure in a structural member to occur (Kempfertand Gebreselassie 2006). Excessive settlement and differential movement can cause distortion and cracking instructures (Salgado et al. 2007). In other words, currentstate-of-the-art design methods may greatly reduce therisk factor of settlement problems. A major factor thatgreatly complicates foundation design is that the soilparameters have to be obtained on construction site priorthe project calculation. Great care should be exercised indetermining the soil properties at the site for the depth ofpossible interest so that one can as accurately as possibledetermine whether a pile foundation is needed and, if so,that neither an excessive number nor lengths are specified. In this work, pile foundation was used to controlsettlement at marginal soil site and care was taken toutilize the existing ground so that a necessary pile lengthand minimum settlements are ensured.The scope of this work was to design the pile foundation that will be needed for gas and steam turbineequipment on the site of the Elektrenai power plant,Lithuania. In the design of a pile foundation, the requiredpile length was estimated based on the load from thesuperstructure, allowable stress in the pile material, andthe in situ soil properties. Soil properties were estimatedfrom site investigation and soil exploration program according to Lithuanian regulations. Investigation data werebased on cone penetration and dynamic penetration tests,boreholes, excavations and soil as well as laboratory investigations. From these data, four geological layers weregeneralized that were applied in design of pile foundation.Pilling foundation was evaluated through immediatesettlement analysis, which was carried out employingfour most widely used methods. The results showed negligible difference in estimation of immediate settlements;however they presented significant difference in estimation of required pile length and pile capacity. The resultsthat were the same in majority of methods were acceptedin this work. Pile settlement analysis estimated that totalsettlement value was 17 mm, including 3 mm settlementsof elastic deformation of pile from vertical compressiveloads. For such structure, foundation settlement shouldnot be more than 2 %D (where D is a diameter of the1104
pile). Such settlement criteria was taken according toequipment settlement guidelines (General Electric DesignBasis Document, Volume 1, 2008) and it means pileshould be working within the limit of mobilization of itsshaft resistance. It was estimated that for pile of diameter800 mm, necessary length of 27 m was sufficient to handle overall loads.The most reliable means of determining the actualpile capacity is pile-load tests. It helps to evaluate pileperformance and determine whether the piles are adequately designed and placed. Therefore, the performanceof load test for determining the actual pile capacity is atopic of future research.4.The next step is the design of pile-groups,which settlements are larger than that obtainedfor a single pile. However this research evaluates a single pile, which can be considered as afirst step in design of pile foundation. Settlement of a single pile is a prerequisite for estimation of pile-group settlements (either fromempirical and theoretical approach). Estimationof pile-group settlement is a topic of further investigations long with designing the group geometry that satisfy a given problem.These steps (except the last one) are described in thefollowing sections.2. Pilling foundation consideration3. Physical and mechanical properties of the soilSoil propertied were determined from site investigaPilling foundation was chosen due to two differenttion and soil exploration program on site of Elektrenaireasons:power plant, Lithuania. Geological investigation involved The capacity of the soil to support great stressesboreholes (BH), cone and dynamic penetration tests (PT)over it. In other words, bearing capacity of soilsand trial pits (TP). Totally 8 boreholes of the depth of 30represents the ability of soil to safely carry them were drilled. Soil samples were taken from trial pits inpressure placed on the soil from pile withoutorder to determine granulometric composition, plasticityundergoing a shear failure with accompanyingand Proctor density. 21 tests of cone penetration (CPT) oflarge settlements.the depth of up to 15 m were carried out. At 4 points The special requirements of the main equipbelow 15 m precise measurement of pore pressure havements about settlements, movements andbeen carried out (CPTu). There were 16 dynamic penetrastresses. The equipment consisted of the gastion (DPSH) tests performed in the depth of up to 15 m.turbine, the steam turbine and the generator.XIII engineering geological layers (EGL) were deterThe generator is coupled to the gas turbinemined in investigation area based on investigation data ofthrough a rigid coupling and is connected to theCPT and DPSH of boreholes, excavations and soil as wellsteam turbine by a flexible coupling. Theas laboratory investigations.equipment induced high loads, which, in turn,Surface of investigation site was levelled and theinduced great stresses on the foundation. Themajor part of area was replaced with manmade soilcombined unit of gas turbine, generator and(tplIV) consisting of silty sand (SU, SUo), low plasticitysteam are founded with a unique foundation. Itclay (TL), intermediate plasticity clay (TM), silty clayhas to provide the adequate resistance and(TU) and gravel sand (GU). The thickness of manmadecomportment for all the static and dynamicsoil layer ranges from 0.5 m to 2.20 m with the altitudesequipment conditions.ranging from 96.0 m to 97.9 m. The depth of the limAs the main purpose of the foundation is to receivenoglacial sediments ranges from 13.20 m to 15.80 m. Thethe loads from the equipments and to transmit these loadsaltitudes of the layer sole ranges from 82.14 m to 84.93 mto the piles, it should satisfied settlement and dynamicof altitude. Below that, the silty sand (SU, SUo) was precriteria. According to analyses of the stresses induced bysent to 67.7 m of altitude.the loads, the gas and steam turbine equipment requiredFrom the investigation of engineering geologicaldeep pile foundation.layers,four geological layers were generalized:For a design deep pile foundation, the required pile1. Medium to firm clay sediment, TU, TL, TMlength (for a given pile diameter) was estimated from the(the depth of this layer is up to 15 m from surload from the superstructure, allowable stress in the pileface).material, and the in situ soil properties. It was based on2. Medium to coarse silty sand, dense (the depththe following steps:of this layer is up to 19 m from surface).1. Soil propertied were determined from site in3. Medium to coarse silty sand, medium densevestigation and soil exploration program ac(the depth of this layer is up to 25 m from surcording to Lithuanian regulations.face).2. Superstructure loads were obtained from the4. Medium to coarse silty sand, very dense (themanufacturer of gas and steam tribune (Generaldepth of this layer is up to 30 m from surface).Electric). It included design verification load ofThese four layers were used in the design and calcu2500 kN and service working load of 2239 kN.lations of piling foundation. Description of these layers is3. The bored cast-in-place piles were adopted ofpresented in Fig 1.diameter 800 mm that rested on the sandy bed.Based on the data from previous two steps, estimation of pile length was performed along thepile capacity and settlements.1105
OGwhere i is a soil layer index, and the summation is overthe number n of layers crossed by the pile.The design compressive resistance, Rc,d, is estimatedfrom the equation 4:0.802.500.30FGz 12.0015.00Rc,dGWT27.004.006.005.00Fig 1. Geotechnical profile of the site where gas turbine is planned4 Evaluation of bearing capacity of bored pileBearing capacity was evaluated through the basiccondition for ultimate limit stage. The basic condition forultimate limit state being:Fc,d R c,d(1)where Fc,d is ultimate limit state design load normal to thefoundation and R c,d is the design bearing resistance of thefoundation against loads normal to it. F c,d includes theweight of the foundation and of any backfill materialplaced on top of it. Earth pressures on structural elementsabove the foundation level are geotechnical actions andare also included in F c,d where relevant.The basic inequality F c,d R c,d has to be checked forthe recommended partial safety factors for persistent andtransient situations (Eurocode 7). In our case the value ofFc,d was calculated and accepted equal to 2500 kN.The value of R c,d may be calculated using analyticalor semi-empirical models. The concept of the separateevaluation of shaft friction and base resistance forms thebasis of all ‘static’ calculations of pile carrying capacity.The basic equation is:Rc,d Rb,d Rs ,d(2)where Rc,d represents the total load carried at the pilehead, which is the summation of base and shaft resistances. The base and shaft resistances, in turn, are themultiplication of base and shaft areas, Ab and As, by therespective unit of characteristic value of the resistancesqb,k and qsi,k. (Tomlinson 2001):Rc,d Ab qb,k An i 1si qsi ,k N q σ v' Abξ γ b n i 1''K s σ vo tan δ Asiξ γ s(4)The first term on the right-hand side of the equation(4) represents base resistance divided by partial safetyfactors (ξ ,γ). Base resistance is described by a bearingcapacity factor, Nq, and overburden earth pressure, σ'v. Abearing capacity factor, Nq, is related to the peak angle ofshearing resistance φ’ of the soil and the slenderness ration (L/D) of the pile. The values of the effective angle ofshearing resistance, φ’, is required to obtain the factor Nq(Peck et al. 1974). In our case φ’ is derived from SPTresults which were obtained from DPSH test and described in Table 1. Herein, to apply DPSH data in theeq.4, the N20 DPSH data were converted to N30 SPT values (Spagnoli 2007), where N is the blow count recordedin an standard penetration test. Although the SPT is notconsidered as a refined and completely reliable method ofinvestigation, the N values give useful information withregard to consistency of cohesive soils and relative density of cohesionless soils. The accepted values of shearingresistance φ’ for the active zone is presented in Table.1.The overburden earth pressure, σ'v, is shown in Table 2.The second term on the right-hand side of the equation (4) represents shaft ultimate resistance divided bypartial safety factors (ξ ,γ). Shaft ultimate resistance, Rs,d,is described by a coefficient of horizontal earth pressure,Ks, the average of effective overburden earth pressureover the depth of the soil layer, σ'vo, and the value of δ’which is the characteristic or average value of the angleof friction between pile and soil. The angle of friction, δ’,between the pile surface and the soil is related to the average effective angle of shearing resistance, φ’, over thelength of the pile shaft (Tomlinson 2001). Coefficient ofhorizontal earth pressure, Ks, is not constant over thedepth of the pile shaft and depends on the relative densityof the soil and state of consolidation of the soil, the volume displacement (L/D) of the soil by the pile. It wasestimated from geological investigation and presented inTable 3. Their values are depicted in Table 3. Estimationof shaft ultimate resistance is presented in Table 4 layerby layer.Equation (4) includes partial resistance factors (ξ ,γ),estimated from the Eurocode 7 and presented in Table 5(Frank 2006). Simplified subsoil structure (worst situation site-wide) is presented in Table 1.Average of effective overburden earth pressure atpile toe is described in Table 2.Coefficient of horizontal earth pressure is depictedin Table 3.(3)1106
6.912.24285.710.0515.0810.05ΣRs,kKsφ’Rs (kN)4145.3203.3261.3As (m2)12.20.400.430.37Average σvo' ateach level(kPa)120.9Layer12γ’ (kN/m )5.23-191381328900Table 5. Safety factors applied in eq.4BaseShaftShaft ultimate resistance Rs,k is presented in Table 4.It should be noted that applied safety factors areslightly higher than required by Eurocode 7 (Frank 2006)for the worst combination at bored piles, and using onepile test (n 1). The safety factors are summarized inTable 5.1.41.41.61.32.241.82Applied410ºξ .γ79-7358.510 32 30 34 γ (for R 4)3398-8383-7979-7373-69ξ(for n 1)83-7919.51234Resistance2σ' at levelbottom (kPa)95-83Clayey deposit,medium to firmconsistency GWLClayey deposit,medium to firmconsistency GWLMedium tocoarse slightlysilty sands,denseMedium tocoarse slightlysilty sands,medium denseMedium tocoarse slightlysilty sans, denseto very dense.Clayey deposit,medium to firmconsistency.Medium to coarseslightly siltysands, dense.Medium to coarseslightly siltysands, mediumdense.Medium to coarseslightly silty sans,dense to verydense.Table 4. Shaft ultimate resistance Rs,kThickness (m)1bLithologyLevels (m)Layer98-9598-8325301822Table 2. Overburden earth pressure at pile toe1a1φ’φ’10º(*)Ks 0.85 K0-Lithology-Levels (m)Clayey19.5deposit,medium tofirm consistency283-79 Medium to26.0coarse siltysands, dense379-73 Medium to26.0coarse siltysands, medium dense473-68 Medium to26.0coarse siltysans, denseto verydense.(*)obtained from direct shear testingLevels (m)98-83N30SPTN20DPSHγd (kN/m3)LithologyTable 3. Coefficient of horizontal soil stress (Ks) (K0 – coefficient of earth pressure at rest, K0 1-sin φ’):Layer1Levels (m)LayerTable 1. Simplified subsoil structure32For the worst site-wide situation, the sum of shaftand base resistances Rc,d was equal to 3801 kN. Thisvalue satisfied equation 1, where the sum of shaft andbase resistances Rc,d should be larger than (or equal to) adesign axial compression load on single pile at the ultimate limit state Fc,d.5. Pile settlement analysisTotal settlement can be assessed (Bowles 1997) asthe sum of the axial and the point settlement. For a conservative end-bearing behavior, considering low or negligible contribution of shaft resistance:1107
Hp P LA E p q D 1 μ2 mI s I F F1Estimes larger than value of pile capacity obtained byBowles method (Bowles 1997).(5)The first term (before the sum sign) on right-handside of the equation (5) described the average pile axialsettlement for pile length, L, average cross-section area,A, and an elastic modulus of the pile, Ep. Length, L, isestimated to be 67 % and 100 % of the total pile length,taking 100 % at clayey part and 75% at embedment sand.It is equal to 23.5 m. Elastic pile modulus, Ep, is determined according to the cylinder compressive strength fck(for fc 30 MPa, Ep 32.000 MPa). Maximum appliedload at pile head, P, is equal to service working load ofP 2239 kN.The second term in the equation (5) describes thepoint settlement, which depends on pile load, q, representing pile bearing pressure at a point. It is equal to inputload divided by Ap, i.e., 4450 kPa. Stress-strain modulusof soil below the pile point, Es, is obtained from: for thedense and very dense sands with N20 30N30 50 itequals Es 100 MPa. Poisson ratio for sand soil, μ, equalsto 0.3, while shape factor, mIs, equals to 1.0. Embedmentfactor, IF, has value of 0.50, because pile length, L, anddiameter, D, ratio is larger than 5. Reduction factor, F1,was set to 0.75, since point bearing and considering someskin resistance.According to equation (5) the total value of settlement, Hp, was estimated to be equal to 17 mm. This valuecould be considered as maximum, obtained from the conservative side, based on end-bearing behavior of the pile.Pile settlement analysis showed that total settlementvalue was 17 mm. It includes 3 mm settlements of piledeformation from vertical compressive loads. For suchstructure, foundation settlement should not be more than2 % of pile diameter. For the pile of 800 mm diameter,the foundation settlement should not be more than16 mm. The calculation shows, that for pile of diameter800 mm, the necessary length was 27 m. Such length issufficient enough to endure overall loads. 6 Comparison between different methodsTo evaluate obtained results, pile settlement analysiswas performed employing three other, most widely used,standards and approaches. Approaches of Schmertmann(Schmertmann 1986), vertical bearing capacity– Springmethod and CPT (ENV 1997-3) standard were appliedfor estimation immediate settlement, required pile lengthand pile capacity. The results are presented in Table 6.As can be seen, the settlement values are nearly thesame irrespective of applied method. However, the situation regarding values of estimated pile length and pilecapacity is different. Bowles method (Bowles 1997) presents the longest necessary pile length, i.e., 27 m, whileother methods indicate the necessary pile length to beabout 24 m. Even larger differences are revealed, whencomparing values of pile capacity obtained by differentmethods. Schmertmann method (Schmertmann 1986)indicates the largest value of pile capacity, which is 2.8Table 6. Comparison between results obtained by differentmethods for loading P 2500 kN.MethodsBowles(Bowles, 1997)Schmertmann,(Schmertmann,1986)CPT (ENV1997-3)Vertical bearingcapacity–Spring methodPilelength,mImmediatesettlement, mmOverall pilecapacity, e Schmertmann and CPT (ENV 1997-3) methodsdiffer from other methods in determination of the toe andshaft bearing capacities. The determination of total pilebearing capacity, and calculation of settlement is thenperformed in the same way as presented in previous sections.In Schmertmann method, the maximum bearing capacity of a single pile based on the values of tip resistanceqc of the ith static penetration test is given by:Fmax,i Fmax,toe,i
4. The next step is the design of pile-groups, which settlements are larger than that obtained for a single pile. However this research evalu-ates a single pile, which can be considered as a first step in design of pile foundation. Settle-ment of a single pile is a prerequisite for esti-mation of pile-group settlements (either from
f) of the foundation (i.e., D f 5B f). As indicated previously, axial resistancetypically governs the design of deep foundations not settlement. The resistance of deep foundations is based on either the end (R t) or resistance side resistance(R s) along the shaft of the foundation acting independently of the other
In contrast, pile-supported foundations transmit design loads into the adjacent soil mass through pile friction, end bearing, or both. This chapter addresses footing foundations. Pile foundations are covered in Chapter 5, Pile Foundations-General. Each individual footing foundation must be sized so that the maximum soil-bearing pressure does not exceed the allowable soil bearing capacity of .
Little is known about how deep-sea litter is distributed and how it accumulates, and moreover how it affects the deep-sea floor and deep-sea animals. The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) operates many deep-sea observation tools, e.g., manned submersibles, ROVs, AUVs and deep-sea observatory systems.
2.3 Deep Reinforcement Learning: Deep Q-Network 7 that the output computed is consistent with the training labels in the training set for a given image. [1] 2.3 Deep Reinforcement Learning: Deep Q-Network Deep Reinforcement Learning are implementations of Reinforcement Learning methods that use Deep Neural Networks to calculate the optimal policy.
It is an honour for Assifero to present this guide to community foundations in Italy. The community philanthropy movement is growing rapidly all over the world. In Italy, the establishment of community foundations began in 1999 with foundations in Lecco and Como. There are now 37 registered Italian community foundations (based on the atlas of
Foundations may be classified based on where the load is carried by the ground, according to Terzaghi: Shallow foundations: termed bases, footings, spread footings, or mats. The depth is generally D B 1 but may be somewhat more (fig. 4.1.3a) Deep foundations: piles, drilled piers, or drilled caissons. Lp B 4 With a pile
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Why Deep? Deep learning is a family of techniques for building and training largeneural networks Why deep and not wide? –Deep sounds better than wide J –While wide is always possible, deep may require fewer nodes to achieve the same result –May be easier to structure with human
