DESIGN OF CANTILEVER RETAINING WALLS

Transcription

1 DESIGN OF CANILEVER REAINING WALLS Ammara Nusra, UE, Lahore, Pakisan M. Akram ahir*, UE, Lahore, Pakisan nd Conference on OUR WORLD IN CONCREE & SRUCURES: 8-9 Augus 7, Singapore Aricle Online Id: he online version of his aricle can be found a: hp://cipremier.com/ his aricle is brough o you wih he suppor of Singapore Concree Insiue All Righs reserved for CI Premier PE LD You are no Allowed o re disribue or re sale he aricle in any forma wihou wrien approval of CI Premier PE LD Visi Our Websie for more informaion

2 nd Conference on OUR WORLD IN CONCREE & SRUCURES: 8 9 Augus 7, Singapore DESIGN OF CANILEVER REAINING WALLS Ammara Nusra, UE, Lahore, Pakisan M. Akram ahir*, UE, Lahore, Pakisan Absrac Design of canilever reaining walls involves sabiliy checks for overurning, sliding and bearing. Firs of all a rial secion is assumed and calculaions are made for he sabiliy checks. he imporan parameers involved are uni weigh of backfill soil, soil-concree fricion facor and bearing capaciy of soil. he base lengh and i componens namely oe land heel lenghs, and base hickness are highly dependan upon hese facors and vary sharply wih sem heigh and surcharge. o reach a suiable rial secion is someimes a edious job. A window based compuer program has been developed for designing such walls. he program performs checks for sabiliy on rial secions and hen designs he suiable secion for srengh. his paper presens proporioning chars prepared wih he help of his compuer program. he rial secion geomery for a given wall heigh, soil daa and srengh of concree can be read from hese chars and final secion profile may be decided wihin a minimum ime. he chars have been prepared for a wide range of values of soil uni weigh, soil bearing capaciy, concree srengh and soil-concree fricion facor. he compuer program can be downloaded from Keywords: Bearing capaciy, overurning, reaining wall, sliding, reaining wall.. Inroducion Reaining wall, as he name implies, is used o hold he loose earh or backfill in posiion. I should be capable of reaining earh mass wihou overurning and sliding under he acion of acive earh pressure generaed due o reained soil and surcharge if any [,]. In hese wo sabiliy cases he weigh of soil and self weigh of wall ac as sabilizing forces. he hird imporan sabiliy consideraion in he design of wall is o spread he resuling forces over sufficien area so ha acual pressure does no exceed he allowable bearing capaciy of soil. he design for srengh or deerminaion of seel o resis he bending and shear in hree slabs i.e., sem, oe and heel is he las sep and i is possible only once adequae facors of safey have been ensured agains overurning, sliding and bearing. I may be noed ha for performing he hree sabiliy checks a rial secion of wall is required. In case of overurning he desabilizing forces are he acive earh pressure due o backfill soil and pressure due o surcharge when surcharge is acing over he backfill away from heel and noable sabilizing agencies are he weigh of soil on heel and self weigh of he wall. he momens of hese forces are aken abou oe and raio of resising momen o

3 overurning momen is designaed as facor of safey agains overurning. he loose soil presen on fron of he wall is ignored quie ofen [,]. In case of sliding once again he sliding forces are same as in case of overurning and resising forces are fricion beween soil and base of wall and passive earh pressure of soil presen in fron of wall alhough he laer is ignored a imes. In case he resising forces are insufficien, wo soluions are possible, he conac beween soil and concree is increased or preferably a key is provided under he base slab eiher under he sem or away from ha on he heel side. he presence of key generally increases he resising force as he fricion facor in fron of key is increased o a value equal o inernal fricion of soil, which is greaer han soil-concree fricion facor. In he hird sep acual bearing pressures disribuions under base slab is deermined for boh he condiions; he surcharge presen and absen on he heel. he maximum pressure should no exceed he safe bearing pressure. he design for srengh is made only afer saisfying all he hree sabiliy checks.. Design of Wall I may be concluded from he foregoing inroducion ha design of reaining wall is a edious job, which requires several rials before reaching a suiable secion ha can be designed for srengh. he ieraive naure of he problem makes i well suied for a compuer soluion. his paper describes he oulines of such a compuer program, which was wrien in Visual Basic for execuion in Windows environmen over personal compuers. Fig. - Inerface of Compuer Program

4 - Compuer Program he visual inerface of he compuer program is shown in Fig.. he program can work in any of he hree sysems of unis, Engineering, SI or Meric. A choice can be made by he user by selecing an opion amongs from he hree unis. welve inpus are necessarily required o complee he geomery of wall secion, which are explained in Fig.. Fron corner offse is zero unless sem is apered on boh sides. his is horizonal disance beween he op fron corner and he sem-oe juncion. he program provides four opions for aper provision in sem as can be seen in Fig.. A check box is provided o place a key a desired locaion from oe or he user may op for no Key a all. he 8-day cylinder srengh of concree and yield srengh of seel are also inpu by user. In he las, five mos imporan inpus are made including he soil uni weigh, angle of repose, soil concree fricion, bearing capaciy of underlying soil and surcharge acing on backfill. Once he desired inpu daa have been provided, he Design Wall Buon on he ool bar is clicked. he calculaions for sabiliy checks are made and facors of safey agains overurning, sliding & bearing are oupu along wih he amoun of six seel reinforcemens. he inerface is user-friendly and a number of menus and ool bars are made available. he user can preserve various rials of a wall secion. e can move hrough he resuls of hese rials using Nex, Previous and Specific Secion Buons. A repor can also be generaed using Preview Buon. he repor can be prined or copied o any desired Microsof Office Applicaion. O s h h k b w k B F LEGEND h= Sem eigh =op hickness of sem b =Boom hickness of sem Os=Fron Corner Offse = hickness of Base =oe Lengh =eel Lengh h k =eigh of Key w k =Widh of Key l=locaion of key from oe F=Fron Soil eigh B=Back Soil eigh Fig.. Schemaic Geomery of Wall Secion (Neiher proporionae nor o scale) -Proporioning Chars I may be noed from Fig. ha inpus are required for geomery and 5 more for soil properies, he inpus of nex rial may be refined by user from he resuls of previous rial. he whole process can be made swif enough by providing daa inpu for a firs rial from Proporioning Chars. Several such chars are presened in his paper, where four major parameers i.e., sem hickness, oe lengh, heel lengh and base hickness can be read from hese chars vs sem heigh. he oher facors which affec hese dimensions are soil uni weigh, bearing capaciy of soil, surcharge pressure, fricion facor, angle of repose and provision or absence of key.

5 and h, mm 8 5 and, m Sem eigh, m Fig.. Proporioning Char for =5.7 kn/m, Bearing= kn/m, Surcharge =9. kn/m wih Key of heigh 5mm under sem and soil fricion facor=.5 5 and h, mm 9 6 and, m Sem eigh, m Fig.. Wall Proporioning Char for =5.7 kn/m, Bearing= kn/m, Surcharge=9. kn/m wih Key eigh=5 mm under sem and soil fricion facor=.. 5 and h, mm 9 6 and, m Sem eigh, m Fig. 5. Wall Proporioning Char for =5.7 kn/m, Bearing= kn/m, Surcharge 9. kn/m wih Key of 5 mm a m from oe and soil fricion facor=..

6 5. Discussion he oulines of a compuer program have been presened, which can design RC reaining walls for a variey of siuaions. he essenial checks for sabiliy are performed and repor is generaed ha includes on all he deailed calculaion for safey agains overurning, sliding and bearing in addiion o main and secondary reinforcemens in sem and base slabs. he process of proporioning can be made more swif and convenien if proporioning chars are consruced for desired range of parameers. he proporioning chars can be prepared wih he help of compuer program by providing erminal values of sem heigh wih oher necessary parameers relaed o soil and fixing reasonable values of facors of safey agains hree sabiliy checks. Four proporioning chars have been presened in his paper. he soil uni weigh equal o 5.7 kn/m and soil bearing capaciy equal o kn/m have been aken in hese char wih hree soil concree fricion facors of.,. and.5. wo values of surcharge 9. kn/m and.6 kn/m have been considered in he preparaion of hese chars. he range of he sem heigh was aken from o 7m, and is ploed on he x-axis of hese chars. he op hickness of he sem was aken no less han mm and he minimum oe lengh was aken equal o.7m. he main objecive of preparing hese chars was o choose direcly hose geomeric dimensions which ensured wall sabiliy agains sliding, overurning and bearing. hese vales can be provided as firs rial o avoid he edious rial and error procedure and beer geomeric values can be decided for second rial. More proporioning chars can easily be prepared wih he help of compuer program for ready reference. 5 and h, mm 9 6 and, m Sem eigh, m Fig. 6. Wall Proporioning Char for =5.7 kn/m, Bearing= kn/m, Surcharge=.6 kn/m wih Key a. m from oe and soil fricion facor=.. I may be noed from Figs. o 6 ha eel lengh, varies more sharply as compared o oe lengh,. I is quie ineresing o noe ha varies sharply for greaer values of soil fricion facor. For example, varies beween.7m o.m for soil fricion facor of.5 as compared o a variaion of.9m o.m for soil fricion facor equal o.. Similarly he eel lengh, varies from.9m o m for soil fricion facor equal o.5 and from. o. m for soil fricion facor equal o.. 6. Conclusions he compuer program in combinaion wih he proporioning chars presens an easy and efficien soluion o he problem of proporioning and designing he RC reaining walls. he program is effecive even in he absence of such chars. A number of soluions can be saved in he memory or on disk for comparison purpose. he user-friendly compuer program can be used o sudy he comparaive cos of various opions for any given problem. he program may effecively be used boh for design and research.

7 7. General References [] Nilson A., "Design of Concree Srucures welfh Ediion, Mcgraw ill Company, Inc.,. [] Nawy, E.G., Reinforced Concree: A fundamenal Approach, Fifh Ediion, Pearson Educaion Inc. Upper Saddle River, New Jersy. [] MacGregor J.G.,.Reinfored Concree Mechanics and Design, hird Ediion, Pearson Educaion Inc. Upper Saddle River, New Jersy. [] ACI 8-5, Building Code Requiremens for Reinforced Concree American Concree Insiue, Deroi, USA.