The Problem S T

FINITE ELEMENT ANALYSIS OF REASONABLE FOUNDATION FOR SUPPORTING SILO’S TOWER Analisis Elemen Hingga Beberapa Tipe Fondasi Untuk Mendukung Perencanaan Tower Silo Sukiman Nurdin Jurusan Teknik Sipil Universitas Tadulako-Jalan Soekarno Hatta Km. 8 Palu 94118, Email : sukimanyahoo.com ABSTRACT The limitation of soil data due to poor soil investigation process is a common problem in civil engineering project. The finite element method was used to analyse the compatibility of foundation to support silos in Liverpool Docks. Both shallow foundation and pile foundation were considered. The results of the analyses are presented by comparing analytical and numerical solution. Parametric study was considered for each case. There are different results for two types of shallow foundation that had been considered. Strip foundation seemed more reliable than pad foundation, while Pile foundation considered to be first choice due to the satisfactory condition for all factors. Key Words: finite element, silo, shallow and pile foundation . ABSTRAK Keterbatasan data tanah karena tidak dilakukannya investigasi tanah secara menyeluruh sebelum proses desain dan konstruksi adalah problem yang umum yang terjadi pada proyek-proyek teknik sipil. Metode elemen hingga adalah dipakai untuk menganalisa jenis pondasi yang dapat mendukung dari silos di Pelabuhan liverpol. Pondasi dangkal maupun pondasi tiang keduanya dipertimbangkan untuk digunakan. Analisa tersebut membandingkan metode numerik maupun analitik. Hasil dari analysa tersebut memperlihatkan hasil yang berbeda dari dua tipe pondasi dangkal. Pondasi strip memberikan nilai yang lebih optimal daripada fondasi pad. Sementara pondasi tiang menjadi pilihan pertama karena kelayakan dari semua faktor yang ditinjau. Kata Kunci : elemen hingga, silo, pondasi tiang dan dangkal INTRODUCTION a. Background Ten tower silos are used to store combined weight of approximately 3000 tonnes of load. Tower silos were erected at quayside of Alexandra docks in Liverpool. Over the years silo builders have improved the design and construction of the above-ground portion of silos, in contrast, very little has been done to improve the foundation. Towers have generally been erected on foundations constructed by Fugro Limited. Who have the necessary technology for adequate design and constructed. The practice was reasonably successful when silos were developed. As bigger silos were erected, however, and the applied foundation pressures approached the bearing capacity of the soils, many structures settled considerably, some tilted, and some overturned completely. This digest outlines the problem and indicates the need for a soil investigation to determine the allowable bearing capacity and compressibility of the soil and thus enable proper foundation design.

b. The Problem

Many tower silos constructed on clay soils have ring-shaped concrete foundations. To reduce costs, concrete floors are seldom provided. When the silos are developed for any purposes, part of the load is transmitted through the cylindrical walls to the footings and the remainder is carried directly by the soil inside the ring foundation. The underlying clays compress vertically under the weight of the loaded structure in such a way that the applied loads are distributed uniformly to the soil over the whole area enclosed by the circular foundation. This uniform pressure is distributed to the foundation soil in the form of a pressure bulb; its size and shape, determined by elastic theory, are related directly to the diameter of the loaded area as shown in Figure 1. Here, two footings of different size carry the same uniform load, but the pressure bulb under the larger foundation is much larger and deeper. In each case the maximum vertical pressure occurs immediately below the footing and diminishes to 10 per cent of this value at a depth equal to twice the diameter of the foundation. If the applied stresses within the 2 bulb do not structure wi Figure 1 Non- loading has from the we centre the p in Figure 2 produce the the foundati problem is the silo ove Figure 2. Press Figure 2b close to eac the resulting will extend zone will b foundations causing the Most when a silo filling proc skeleton an voids of th t exceed the ill be stable.

1. Pressure bu

round f uniform pl s caused man eight of the pressure bulb a. Strong w e same effec ion soil may remedied it rturns. Non-uniform b sure bulbs w , if two or m ch other. Bec g pressure b to greater de be subjected s over this silos to tilt t t foundation o is quickly ceeds, the lo d to the pore he clay. Pres shear streng ulbs under la foundations. lacement o ny problems silos and the b will be dis winds acting ct. The local y cause tilting may increas m and overla bulbs. will overlap more silos are cause pressu bulb will be epths. The so d to higher region wi towards each failures in loaded for th oads are app e water cont ssures gener gth of the soi arge and sma f silos du s. When the e live load i storted, as sh on a tall silo overstressin g, and unless e with time apping pressu p, as shown e constructed ures are addi much larger oil in the ove stresses and ill settle m h other. clay soils o he first time plied to the tained within ated in the il the all uring load s off hown o can ng of s the until ure n in d too itive, r and erlap d the more, occur e. As soil n the pore wate part the stren the pore con be s seep incr the beco the thes

c. S

wid proj larg aspe geot need appr man all,2 dire soil to p the stren Alex site prop bore

d. T

foun Buil poin stru 1. R stre the base stren stee stre insu of t er tend to ticles and he soil. If, at th ngth is grea structure w e water pres solidate and stable for sub In silos w p into the u reased even shear streng ome underm soil under h se actions can ite Investiga Reliable dely apprecia ject, the gro gest risk el ect. Almos technical inv ded to char ropriately by nager are w 2005 Bearing c ectly related at a site, so provide infor groundwate ngth and com The site xandra dock investigatio per foundat eholes were d Technical As Every ow ndation for lding Digest nts should ucture: Reinforced Fo A ring sses from ve circumferent e of the sil ngth, the fo el to resist s sses. If the ufficient rein the ring fou reduce the ence decreas he end of loa ater than the ill be stable ssures will gain strengt bsequent load without floor underlying s more, causin th of the soi mined when hydraulic pre n trigger a be ations and effectiv ated in civil e ound conditi ement of f st exclusiv vestigation i racteristic th y how much willing to capacity and to the engin o that a soil rmation on er table, in mpressibility investigation ks by Fugro on lacked dat tion to sup drilled aroun spects of Silo wner should his silo as t CBD 80, C be consider ootings foundation ertical wall l tial loads tha lo. As conc undation sho such bendin foundation s nforcement, t undation wil e friction b se the shear ading, the ava e applied sh e. With time dissipate, th th, and the s dings. s, silage juic soil. Pore p ng a further l. The footin the liquid fl essure. Eithe earing capac ve site inve engineering a on is usuall financial an vely, the is governed he subsurfac h the client spend M.B d vertical se neering prop investigation soil profile, ndex prope y. n was carrie Limited. H ta to ensure pport the s nd the site. o Foundatio d insist on a proposed b CBD 81. Th red to ensu is subject oads, soil pr at exist in the crete has a ould be rein ng moments should crack the monolith ll be destro etween soil r strength of ailable shear hear stresses, e the excess he soils will tructure will ces normally ressures are decrease in ngs may also flow through er or both of ity failure. estigation is and building ly given the nd technical scope of by what is ce condition and project B. Jaksa et ettlement are erties of the n is required location of erties, shear ed out along However, the a design of silos. Some on an adequate by Canadian he following ure a stable to bending ressures, and e walls at the low tensile nforced with and tensile k because of ic behaviour oyed and its l f r , s l l y e n o h f s g e l f s n t t e e d f r g e f e e n g e g d e e h e f r s ability to su be reduced. 2. Concrete It is concrete in sides are ne disturbed so boulders, fo must be pl followed in no quality workmansh 3. Centring Load footings w uniform loa full use of it Large soils to m allowable b foundations often used overturning reasons of foundation diameter of loads applie ring founda sections unl the footing local overs occur. With extending t contact pre uniformly a deform wou the silage on because mo silo walls th 4. Silo Grou To a constructed allowable b the minimu should be foundations should be c foundation applied ben 5. Silo Load Large contents of moisture c upport the su Foundation most impo a well prepa eatly trimmed oil. In granu ormwork may laced with t n constructin y control hip is unaccep Silo on Foot d-bearing wa whenever po ads to the fou ts allowable e foundation maintain app bearing cap s projecting to provide g. The interio economy. T is normally f the silo w ed to the inn ation it could less it is prop g pressures stressing of h adequate r the footing essures wou and any ten uld be reduc n the extend ost of the sila hrough frictio ups avoid any on compre bearing capa um horizont not less tha s. If a smalle constructed o adequately nding momen d e quantities the silos are content is uperstructure ortant to us ared excavat d and the flo ular soils or y be necessa the same ca ng the silo w on either ptable tings alls should ossible in undation soil bearing capa ns are requir plied pressu pacity. Larg beyond the maximum or floor is usu The inner d slightly les all. Because ner edge ten