Áp lực đất và tường chắn đất

PHAN T R U O N G PHIET GlAO Sir TIEN ST DIA Ki THUAT Ap luc dat VA tudng chan dat (Tai ban) NH A X U A T B A N X A Y Dl/NG HA NOI - 2008 LOI NOI DAU Tinh todn dp luc dd't vd tuang chan dd't Id m ot nhung van de ldn cua dia ki thuat Trong n h u n g ndm gdn day, li thuye't ve dp luc ddt duoc ph a t tr ii’n vd hoan chinh them theo ba hudng chinh: H oan chinh cach gidi theo li thuyet cdn bdng gidi han cho nhung so dd tuong chdn th u a n g gap thuc te nhdm ldp dugc he thd'ng bdng bieu tien dung hodc ldp dugc chuong trinh tinh todn bdng m ay tinh dien tii: Ung dung li thuyet phdn m dnh (thoi) vd van dung phep phdn tich he thd'ng d $ giam bdc sieu tinh cua bai todn dang ndng cao hieu qua phep tinh tren m dy tinh dien tii H oan chinh li thuye't dp luc dd't Coulomb cho dd't ddp thuoc loai da't dinh hodc d d t cd cd't vd gidi chinh xdc cho cac trudng hop phiic tap ve lung tuong, m dt ddt ddp vd tai trgng ngoai Ke't qua d a t dugc theo ba hudng n iu tren cdng khdng dinh tinh uu viet cua li thuyet dp luc dd't ciia Coulomb m dc du khdi diem xud't la xa xua nhdt (1776) Sai sd' tinh todn truong hop tinh dp luc dd't chu dong la khdng dang ke nhung truong hop ap luc dd't bi ddng vdi tudng lung nhdm (cd q>0 > 0,3cp) thi sai so m dc p h a i la qua ldn Cud'n sach gidi thieu loi gidi chinh xdc theo li thuyi't Coulomb ve ap luc dd't chu ddng vdi ca c sa dd tudng chdn dd't, m dt dd't ddp vd cac dang tdi trgng, thudng gdp thuc te xd y dung ddn dung, giao thdng vd thuy Igi, Ldi gidi ddp ung td't hai yeu cdu cdn thie't: m dt Id xet dugc dp luc nude Id rdng dm khd'i dd't ddp khdng bao hoa nude; xet dugc tdc dung cua cd't dd't khd'i ddt ddp H la ldp trinh tinh todn d i ddng vi vdi m dt thudt todn nhdt md cd the tinh todn cho td't cd cac trudng hop v i tudng chdn, m at dd't ddp, cdc loai tdi thudng gap theo nguyen li cdng tdc dung V i dp luc dd't tinh vd dp luc dd't bi dong, cud'n sach trinh bay nhung phuong phdp tie'll bo hien duoc gidi thieu n h iiu d nude ngoai Chung tdi hi vong cud'n sach ddp ung dugc yeu cdu thiet ke, hge tdp va nghien ciiu hien P h a n T r iw n g P h ie t Chtromg I NHUNG KHAI NlfiM MQ DAU T udng ch£n Sa cong trinh g ia cho m dat ds'p hoftc m hd' dko khoi bi sat truat T udng chkn dat duac su dung rdng rai cac ngknh xay dung, thuy lai, giao thdng Khi 1km vide, iung tudng chan tie'p xuc vdi khd'i d it sau tudng va chiu tac dung cua dp luc da't T rong cac cdng trinh thuy cdng, cd m dt sd' bd phan cua k i t cku cdng trinh khdng phai lk tu d n g chan dkt nhung cd tac dung tuang hd vdi da't va cQng chiu kp luc cua da't gid'ng n h u tu d n g c h in da't Do do, khai niem v l tudng chan da't duac m d rQng cho tk't ca nhtfng bd phan cua cdng trinh cd tac dung tuang hd giaa da't tilp xuc vdi chung vk ap luc dk't len tudng chan cdng dugc h ilu nhu ap luc tie'p xuc g iaa nhOng bQ phan a'y vdi da't T ud n g chan dat cac cdng trinh thuy cdng lam viec nhOng d ilu ki£n r i t khac so v di d ilu kien lam viec cua tudng chkn dk't giao thdng vk xay dung dkc d ilm cu a cdng trinh thuy lai q u y lt djnh Dk't dkp sau tudng chan, ydu cau chd'ng tham nude tu thugng luu xud'ng hfl luu cua cdng trinh thuy cdng, thudng dOng dat lo^ii set cd tinh chd'ng thkm td't D ilu nky dkn d in vide tinh toan thie't k l tudng chkn phuc tap han so vdi trudng hgp ddng d it lo^ii ckt dkp sau tudng chan I PH A n l o a i t u On g CHAN DAT T u d n g chkn dk't thudng dugc phan loai theo bd'n ckch sau day nhkm muc dich khac nhau: P h a n lo th eo dd c u n g B iln dan g cua bkn than tudng chkn dk't (dd ud'n) 1km thay ddi d ilu kien tie'p xuc giaa lung tudng chkn vdi khdi dk't dkp sau tudng, do lam thay ddi tri sd' ap luc dk't tac dung len lung tu d n g va c an g 1km thay doi dang b ilu d phan bd ap luc dkt theo c h iiu cao tudng Thi nghigm cua G,A D ubrdva da chung td tu d n g bj b iln dang chju ap luc dkt thi b ilu dd phan bd' ap luc dk't cd dang dudng cong (hinh I - ), n lu phan giaa thkn tudng bj bie'n dang n h ilu thi bieu phan bd' ap luc dk't ckng cong va cu d n g dd ap luc dat d phkn tren tkng len (dudng ), n lu chkn tu d n g cd c h u y ln vj ve phia trudc thi d phan tren tudng tkng len Hinh /-/ ra't nhidu, co de'n ,5 lan so voi cuang d ap lire ban dau, cu an g dQ ap luc d phan dudi tuang thi lai giam (duang 3) Theo cach phan loai nay, tuang duac phan lam hai loai: tuang cung va tuang m£m T uang co bidn dang udn chiu ap luc da't nhu neu tren day goi la tudng mem hoac tudng m dng T uang mdm thudng la nhung ta'm g , thep, be tOng cdt thep ghep lai T u an g cu cung xep vao loai tuang mdm Tuang cieng khdng co bien dang udn chiu ap luc da't ma chi co chuyen vi tinh tid'n va xoay Ne'u tuang cung xoay quanh mep dudi, nghla la dinh tudng co xu nudng tach rdi khdi khd'i dat dap va chuydn vi vd phia trudc thi nhidu thi nghiem da chung td la bidu d phan bd ap luc cua da't rdi co dang dudng thang va co tri sd cudng dQ ap luc dat ldn r.hat a chan tudng (hinh I-2a) Ddi vdi da't dinh (da't d ip sau tudng), theo ke't qua thi nghiem cua B.L Taraxdp thi bidu phan b d ap luc da't co dang hai cong va cung co tri sd cudng dQ ap luc ldn nha't d chan tudng (hinh I-2b) Ne'u tudng cung xoay quanh m ep tr n, nghla la chan tudng rdi khdi khd'i da't dap va chuydn vi ve phia trudc thi theo ke't qua thi nghiem cua nhidu tac gia (K T erzaghi, G A D ubrdva, I.V Y ardpdnxki, I.P Prdkdfiep v.v ) bidu d phan b d ap luc da't (da't rdi cQng nhu d^t dinh) co dang cong, tri sd ldn nhat phu thuQc vho muc dQ chuydn vi cu a tudng va & vho khoang phan giua lung tudng (hinh I- c) T udng cung thudng la nhdrng khd'i be tdng, be tdng da hQc, gach da xay nen goi la tudng khdi T udng chan bang be tdng cd't thep co dang ta'm hoac ban nhung tao vdi cac bd phan khac cua cdng trinh nhttng khung hoac hdp cung cung duac xe'p vao loai tudng cung N hu trSn da phan tich, cdch ti'nh toan tri sd' ap luc dat len tudng cung va tudng mdm khac A = \ ~~~A — ■ ■■■ \ \ \ = - \ ) \ \ = = -\\ \ - \ \ — ' -\ ' \ b) / / / / I I / / c) Hinh 1-2 P h a n loai th eo n g u y en ta c lam viec T udng c h in da't la loai cdng trinh thudng xuyen chiu luc dSy ngang (ap luc da't), dd tinh dn dinh chdng trugt chie'm m ot vj tri quan dd'i vdi ti'nh dn dinh ndi ch u n g cua tudng Theo quan diem tudng chan dugc phan lam ma'y loai sau day: Tu&ng luc (hinh I-3a): dn dinh dugc dam bao chii yeu lugn g ban than tudng Cac loai tudng cung deu thuQc loai tudng luc Tu&ng nua luc (hinh I-3b): dd dn djnh dugc d im bao khdng nhtfng chi lugng ban than tudng va ban m dng ma cdn lugng cua khd'i da't dap n a m tren b in m ong Loai tudng thudng lam be tdng cd't thep nhung chidu day cua tudng tving kha ldn (do dd loai tudng cdn cd ten goi l i tudng day) Tuong bdn goc (hinh l-3c): d 6’n dinh dirge dam bao chu ye'u lugng khdi dat d ip de len ban m ong T uong va m ong la nhtfng ban, tam be tdng cd't thep m ong nen lugng cua ban than tuong va m ong khong ldn T udng ban goc cd dang chtf L nfin cd cdn goi la tudng chu L Tucrng m ong (hinh I-3d): sir dn dinh cua loai tudng dugc dam bao bang cach chdn chan tudng vao ndn Do dd loai tudng cdn goi la tudng coc va tudng cu giam bdt dd sau chdn dat cua tudng va dd tang dd cung cua tudng ngudi ta thudng dung day neo Hinh 1-3 P h a n lo th e o ch ieu cao Chidu cao cua tudng thay doi m dt pham vi kha ldn theo yeu cdu thie't ke Hien nay, chidu cao tudng chdn da dat de'n 40m (tudng chdn d nha m ay Thuy dien L nin tren sdng V onga) Trj sd' dp lyc da't tac dung len lung tudng chdn ti le bac hai vdi chidu cao cua tudng T heo chidu cao, tudng thudng dugc phan lam loai: Tuong thd'p: cd chidu cao nhd hon 10m Tudng cao: cd chidu cao ldn hon 20m Loai tudng cndn co chidu cao vao khoang trung gian cua hai loai trdn (tuc cao ti* 10 de'n m) dugc xe'p vao loai tuang trung binh Theo quy pham tam thdi thie't ke' tudng chdn da't QP-23-65 cu?\ ta thi la'y gidi han phan chia ba loai tudng tha'p, cao, trung binh la va 10m: tudng chdn tha'p cd chidu cao nhd hon 5m , tudng chdn cao cd chidu cao ldn hon 10m P h a n lo th e o goc n g h ien g c u a lu n g tu d n g Theo cach phan loai nay, tudng dugc phan tudng dd'c va tudng thodi Tuang doc iai phan tudng dd'c thuan (hinh I-4a) va tuang doc nghich (hinh I-4b) T rong tru d n g h g p cua tudng dd'c khdi dat trugt cd m dt m at gidi han trung vdi lung tudng Ne'u gdc nghieng a cua lung tudng ldn qua m dt muc nao dd thi khd'i ddt trugt sau lung tirdng khdng lan de'n lung tudng (hinh I-4c); tudng loai dugc goi la tudng thodi Nguyfin tic tinh toan ap luc d i t tic dyng len lung tudng dd'c vd lung tudng th o ii k h ic Phuang p h ip tinh toan i p luc d it chu dQng len tudng th o ii dugc trinh bdy myc chuang VIII Hinh 1-4 P h i n loai th eo k e t cau V m at ke't c iu , tudng c h in dugc chia thdnh tudng lien khQi v i tudng lip ghep Tudng liin khdi lim bang be tdng, be t&ng d i hQc, gach xay, d i xdy hay bang be t ng cd't thep T udng lidn khdi dugc xay (gach d i) hoac dd (be tOng, be tOng d i hQc, be tOng cdt th p) true tie'p h d m ong H d mQng p h ii rQng han m dng tud n g c h in mQt k h o in g d£ ti^n thi c&ng vd dat v in khuOn MQng cua tudng be tfing v i be tdng cdt thep liSn khdi vdi b in than tudng, cQn mQng cua tudng c h in b&ng gach d i xay thi cd th£ l i nhtfng ke't c iu d&c lap bdngda xay hay be t&ng M$t c it ngang cua tud n g lidn khdi l i t k h ie MQt s&' dang tudng loai n iy dugc trinh b iy tren hinh 1-5 vdi nh&ng ten goi nhu sau: a) H inh ch& nhat, b) Hinh thang c nguc tudng nghieng, c) H inh thang cd lung tudng nghieng, d) H inh thang cQ nguc vd lung nghieng, e) H inh thang nghieng v phia d it d ip , g) CQ m ong nhd phia trudc, h) Cd lung gay khuc, i) Cd lung bac c ip , k) CQ be g iim tii, 1) Co m ong nh& hai phia T udng ban gQc (hay tudng cho- L) ki£u cOngxon (hinh I- a) ho$c ki£u cQ bSn sudn (hinh I- b) cQng thudng lim b in g be tdng cd't th p dd liSn khdi Do vay, ngo&i viec tinh tri sd an toan tdng th6 K theo cong thuc X V III-3-1, c&n ph&i d i m bao di£u kien sau day ddi voi dat rdi: b iiu dd phdn bd' dp luc dd't chu dong p h a i ndm Itpt b iiu dd phdn bd' dp luc bun bent&nit Trong vi du X V III-1, bun bentdnit d6 d&y de'n mi^ng hao n6n di£u kien dugc thoa man Qua vay, goi z la dd sau cua di^m dang xet cua tuong mang thi v6 phia hao c6: Pb = Yb7 = 12 x z = 12 z (kN /m 2) v6 phia dS't co: pa = yw zK a = 19 x z x 0,26 = 4,9.z (kN /m 2) Vay o moi vj tri d£u co pb = 2,4 pa va bi^u d6 pa nam lot bi£u d6 pb Trong hinh XVIII-2-1, tuong hao dao da't roi nhung bun bentdnit lai dd khdng ddy hao, cat lop tren day AD, co nguy co bi sat d£ dSm b£o 6n dinh vdi gdc mai tu nhi6n cua cat Tuy nhien co tac gi& cho rang, giai doan hinh tudng m ang, biln bentdnit da xam nhap vao da't cat d hao va tao cho cat co m d t luc dinh n hat djnh nao dd D£ an toan, tdt nh£t la d6 ddy mieng hao bang bun bentdnit Ngoai ra, cd nude ngam cat, phia hao chiu d6ng thdi ap luc da't chu d0ng va ap luc nude ngam; ne'u muc nude ngam d cao thi nguy co pha hoai cue bQ c u a tudng m ang bentdnit cflng cd th£ xSy Dd'i vdi hao dao da't dinh thi chi c£n xac djnh h$ sd an toan dn djnh tdng th£ K la du vi thuc te' khdi d£t truot ABC lam viec nhu mdt chinh th£ V i du X V III-2 : S d lieu cho nhu vi du X V III-1 nhung ng£m cach mat da't h n = 2m da'tcat cd nude Gidi: - Xac dinh ap luc bun P b Pb = ^ x 12 x = 216 kN/m - Xac dinh ap luc d£t chu dOng P a Pa = Pal + Pa2 Trong dd Paj la ap luc da't tac dung pham vi khdng ngap nude ngdm (2m) p = ~ 19 x 22 x 0,26 = 9,9 kN/m P a2 1^ ap luc d^ft tac dung pham vi ngap nude ngdm (trong lugn g rieng bao h o a ciia cat ybh = 20 kN /m 3) P a2 = ^ ( p a! + Pa2) (H - h n) Trong dd: pal = 19 x x 0,26 = 9,9 kN /m pa2 - :20 - 9,8) x A2 x 0,26 = 42,4 kN /m (Ynirtc = 9,8 kN /m 3) P a = (9,9 + 42,4) x 0,5 x = 104,6 kN/m 346 V&v co: P a = 9,9 + 104,6 = 114,5 kN/m N goai P a cdn co ap luc nude ngam Pn P„ = \ y n Hn = ^ x 9,8 x = 19,6 kN/m Jm* JL* - X ac dinh hg so an loan dn djnh hao K = 216 = 216 = 1,6 (dn dinh) 1 ,5 + ,6 134,1 N h u vay, nude ngam dat lam gi&m he sd an toan dn djnh h&o Muc nude ngam dat cat c&ng cao thi nguy c a mat dn dm h cua tudng mang bentonit c&ng ldn D o c v i tang tri sd lugng dan vi cua bun bentfinit Ti'nh toan dn djnh cua hao theo he s6' huy dong cudng d6 chong cdt F So va da giac lire khep kin de xac djnh hg sd huy dOng F dugc trinh bay d hinh XV III-3-2 H in h X V III-3 -2 : Sa dd luc de tinh F Trong dd: vai tgCPn = is? XVIII-3-3 T m = c m B C = c m m H cotg ( 45° + vai 347 R la phan luc nghieng vdi phap tuyg'n cua mat trugt BC goc Pc.) thi p h d i gidm goc ma sdt (p va luc dinh c bao nhieu ldn? Vay can xac dinh