5/14/2018 Gi o tr nh X y d ng c ng tr nh tr n n n t y u

Tmirng O~I HQC BAcH KHOA oA NANGB{j mon ClI sil kj thuv.t Xay dvng NhOm chuyen mon CHO-N@n MongBai giang N~n vaM6ngCHUONGIV: 1 .1.1.

xlY DVNG CONG TRINH TREN NEN BAT YEUKHAINI~MKhal ni~m v@n@ndit y~u

N~n d~t y~u la n~n d~t khong du sire chiu tai, khong du dO b~n va bi~n dangnhieu, do v~y khong th~ lam n~n thien nhien cho cong trinh xay dung,

Khi xay dung cac cong trinh dan dung, cAuduong, thuong g~p cac loai n~n d~ty~u, my thuoc vao tinh ch~t cua lap d~t y~u, d~c di~m c~u tao cua cong trinh rna nguoita dung phirong phap xu ly n~n mong cho phu hop d~ tang sire chiu tai cua n~n d~t,giam dO lim, dam bao di~u kien khai thac binh thirong cho cong trinh.

Trong thuc t~ xay dung, co r~t nhieu cong trinh bi lim, s~p hir hong khi xaydung tren n~n d~t y~u do khong co nhirng bien phap xu ly phu hop, khong danh giachinh xac duoc cac tinh ch~t co ly cua n~n d~t. Do v~y vi~c danh gia chinh xac va ch~tche cac tinh ch~t co ly cua n~n d~t y~u (chu y~u b~ng cac thi nghiem trong phong vahien tnrong) d~ lam co s a va d~ ra cac giai phap xu ly n~n mong phu hop la mOtv~n d~h~t sire kho khan, no doi hoi sir k~t hop ch~t che giira kien thirc khoa hQCva kinhnghiem thuc t~ d~ giai quyet, giam ducc t6i da cac sir c6, hir hong cong trinh khi xaydung tren n~n d~t y~u.1.2. Mi}t s a die di~m cua n@ndit y~u

Thuoc loai n~n d~t y~u thuong la d~t set co l~n nhieu hiru co;Sire chiu tai be (0,5 - IkG/cm2);D~t co tinh nen lim Ian (a> 0,1 cm2/kG);H~ so r6ng e Ian (e > 1,0);DOs~t Ian (B > 1);Mo dun bien dang be (E< 50kG/cm2);Kha nang chong c~t be ( rp, c be), kha nang tham mnrc be;Ham hrong mroc trong d~t cao, dObao hoa mroc G> 0,8, dung trong be;

1.3. Cac logl n@ndit y~u thuimg gip+ D~t set mem: gam cac loai d~t set hoac a set wang d6i chat, a trang thai baohoa mroc, co cuong dOth~p;+ Bun: Cac loai d~t tao thanh trong moi tnrong mnrc, thanh phAn hat r~t m in200J..lm) a trang thai luon no mroc, h~ s6 r6ng r~t Ion, r~t y~u v~ m~t chiu hrc;+ Than bun: La loai d~t y~u co nguon g6c hiru co, ducc hinh thanh do k~t quaphan huy cac ch~t hiru co co a cac dAmlAy(ham IUQ"nghiru co ill20 - 80%);+ Cat chay: Gam cac loai cat min , k~t c~u hat rei rae, co th~ bi nen ch~t hoac phaloang dang k~. Loai d~t nay khi chiu tai trong dOng thi chuyen sang trang thai chay goila cat chay,

+ D~t bazan: Day cling la d~t y~u voi d~c diem dO r6ng Ion, dung trong kho be,kha nang tham mroc cao, d~ bi hm s~p.1.4. Xii'lf n@ndit y~u

Voi cac d~c di~m cua d~t y~u nhir tren, muon d~t mong xay dung cong trinhtren n~n d~t nay thi phai co cac bien phap ky thuat d~ cai tao tinh nang xay dung cuano. N~n d~t sau khi xu ly goi la n~n nhan tao,

Vi~c xu ly khi xay dung cong trinh tren n~n d~t y~u phu thuoc vao nhieu di~u kiennlnr: D~c diem cong trinh, d~c diem cua n~n d~t.v.v. Voi rung di~u kien C\! th~ rnaDeln~ng 9/2006 CHUONG VI TRANG 136

5/14/2018 Gi o tr nh X y d ng c ng tr nh tr n n n t y u

Tmirng O~I HQC BAcH KHOA oA NANGB{j mon ClI sil kj thuv.t Xay dvng NhOm chuyen mon CHO-N@n MongBai giang N~n vaM6ngnguoi thiet k~ dua ra bien phap xu ly h9]J Iy , Trong pham vi chuang nay se d~ c~p d~ncac bien phap xu ly cu th~ khi g~p n~n dAty~u nhir:+ Cac bien phap xu ly v~ k~t cAucong trinh;+ Cac bien phap xu ly v~ mong;+ Cac bien phap xu ly n~n.2. cAc BI~N PHAp XULYVEKET cAu CONGTRINH

K~t cAucong trinh co th~ bi pha hong C\lC bi) hoac toan bi) do cac di~u kien bi~ndang khong thoa man: LUn hoac lun lech qua Ian lam cho cong trinh bi nghieng,lech, d6 . .. hoac do ap lire tac dung len m~t n~n qua Ian trong khi n~n dAty~u, sirechiu U ti be.

Cac bien phap v~ K~t cAu cong trinh nham lam giam ap lire tac dung len m~tn~n h~c lam tang kha nang chiu lire cua k~t cAucong trinh. Nguoi ta tlnrong dungcac bien phap sau:+DUng v~t lieu nhe va k~t cAunhe;+ Lam tang di) mem cua k~t cAucong trinh;+ Lam tang cuong di) cho k~t cAucong trinh.

2.1. Dung v~t Ii~n nhe va k~t cAn nheM\lC dich: Lam giam trong hrong ban

than cong trinh, giam duoc tinh tai tac dunglen mong.

Bien phap: Co th~ sir dung cac loaiv~t lieu nhe, k~t cAu thanh manh, nhungphai dam bao cuong di) cong trinh.2.2. Lam tang di} m~m cua k~t cAn congtrinh

M\lC dich: Lam tang di) mem cua k~tcAucong trinh k~ ca mong d~ khir ducc irngsuAt phu them phat sinh trong k~t cAu khixay ra lun lech hoac hm khong d~u. Hinh 4.1: Ba tri khe [un

Bien phap: DUng k~t cAu tinh dinhhoac phan c~t cac bi) phan cua cong trinhb~g cac khe hm.2.3. Tang them cufmg di} cho k~t cAn congtrinh

M\lC dich: Lam tang cuong di) cho k~tcAucong trinh d~ du sire chiu cac irng hrc sinhra do hm lech va hm khong d~u.

Bien phap: Nguoi ta dung cac dai betong c6t thep d~ tang kha nang chiu irng suAtkeo khi chiu u6n, d6ng thai co th~ gia c6 tai Hinh 4.2: Ba tri ilaiBTCTcac vi tri du doan xuAt hien irng suAt C\lC bi)Ian.D a n~ng 9/2006 CHUONGVI TRANG 137

". .

......I II I

5/14/2018 Gi o tr nh X y d ng c ng tr nh tr n n n t y u

Tmirng O~I HQC BAcH KHOA oA NANGB{j mon ClI sil kj thuv.t Xay dvng NhOm chuyen mon CHO-N@n MongBai giang N~n vaM6ng3. cAc BI:E:NPHAp XU LY VE MONG

Khi xay dung cong trinh tren n~n dAty~u, ta co th~ sir dung mot s6 phirong phap xirly v~ mong thuong dung nhir sau:+ Thay d6i chieu sau chon mong;

+ Thay d6i kich thuoc mong;+ Thay d6i loai mong va dQ cimg cua mongo3.1. Thay d6i chi~u sau chon mong

Dung bien phap thay d6i chieu sau chon mong co th~ giai quyet v~ m~t hin vakha nang chiu tai cua n~n.

Khi tang chieu sau chon mong se lam tang tri s6 sire chiu tai cua n~n. Tri s6 tangcua ap lire tieu chuan i\R khi tang chieu sau chon mong co th~ tinh thea cong thirc:

M = [1+ 7f 7f ].Y.!J.h = B.y.!J.h (4.1)cotgtp- tp+-

2Trong do:y - Dung trong cua dAtn~n;i\h - DQtang them chieu sau chon mong;B =f ( q tra bang;Ngoai ra khi tang dQ sau chon mong thi se giam duoc irng suAt gay hin cho

mong nen giam duoc dQhin cua mong;()gl =()t~ -y(h+!J.h) (4.2)D6ng thai tang dQ sau chon mong co th~ d~t mong xuong cac tAng dAtphia

diroi ch~t han, 6n dinh han. Tuy nhien viec tang chieu sau chon mong phai can nhacgitra hai y~u t6 kinh t~ va ky thuat,MQt s6 tnrong hQ'Pd~ giam bot dQ chenh l~ch hm giira cao trinh d~t mong thi~tk~ voi cao trinh day mong sau khi hm 6n dinh, thirong phili nang cao trinh d~t monglen mQt tri s6 du phong,

1Sdp = -( S + StJ2 (4.3)DDDDDDDDDD

~~bD~D D D .;;;D~~~rong do:S - DQhm 6n dinh tinh toan;S tc - DQ hin xay ra khi thi cong

(voi cong trinh dan dung S d p =O ,7 S ).Truong hQ'Pn~n dAty~u co chieuday thay d6i nhieu, d~ giam chenh lechhm co th~ d~t mong a nhieu cao trinh

khac nhau (Hinh 4.3).3.2. Bi~n phap thay d6i kich thutrc mong

Thay d6i kich thuoc va hinh dang mong se co tac dung thay d6i true ti~p ap liretac dung len m~t n~n, va do do cling cai thien ducc di~u kien chiu tai cling nhir di~ukien bien dang cua n~n.

ffinh 4.3

D a n~ng 9/2006 CHUONGVI TRANG 138

5/14/2018 Gi o tr nh X y d ng c ng tr nh tr n n n t y u

Tmirng O~I HQC BAcH KHOA oA NANGB{j mon ClI sil kj thuv.t Xay dvng NhOm chuyen mon CHO-N@n MongBai giang N~n vaM6ng

Khi tang dien tich day mong thuong him giam duoc ap hrc tac dung len m~t n~nva lam giam dQ lim cua cong trinh. Tuy nhien voi dAt co tinh nen lim tang dAn theachieu sau thi bien phap nay khong t6t.

Neu tAng dAt y~u chiu nen cochieu day khac nhau, co th~ dung bienphap thay d6i chieu rong mong d~ canb~ng irng suAt cho toan bQ cong trinh(Hinh 4.5).3.3 . Thay dAi lo~i mong v a dO cti'ng cua : :-:~ - ....... ---- '1- -mong

Khi thiet k~ my S \I phan b6 taitrong tac dung len mong va dieu kien diachAtrna chon k~t cAumong cho phu hQ'P.

Vai n~n dAt y~u, khi dung mongdon, dQ lim chenh l~ch se Ion, do vay d~giam anh huang cua lim lech ta co th~thay th~ b~ng mong bang, mong banggiao thoa, mong be hoac mong hop,

Truong hQ'P su dung mong bangrna bien dang v~n Ian thi cAn tang themcuong dQ cho mongo DQ cimg cua mong ban, mong bang cang Ian thi bi~n dang be vadQlim l~ch se be. Ta co th~ su dung cac bien phap nhu: Tang chieu day mong, tang c6tthep doc chiu hrc, tang dQ ctmg k~t cAuben tren, b6 tri cac siren tang cuong khi mongban co kich thuoc Ian.

DDDDDDDDDDDDDDD

Thay d6i b~ rl)ng m~t- - f - -------- ong:0 --Innh4.5

4 .1 . M1 }.c d ic hcAc BI~N PHAp XU LY NEN BAT YEU4.

Xu ly n~n dAty~u nham muc dich lam tang sire chiu tai cua n~n dAt, cai thienmQt s6 tinh chAt co ly cua n~n dAty~u nhir: Giam h~ s6 r6ng, giam tinh nen lim, tangdQchat, tang tri s6 moduynh bien dang, tang cuong dQchong c~t cua dAt .v.v.

D6i voi cong trinh thuy loi, viec xu ly n~n dAty~u con lam giam tinh tham cuadAt,dam bao 6n dinh cho kh6i dAtd~p.

Cac bien phap xu ly n~n thong thirong:+ Cac bien phap co hoc: Bao g6m cac phuong phap lam ch~t b~ng dAm, dAmchAn dQng, phirong phap lam chjit b~ng cac loai CQC(cQCcat, CQCdAt, CQCbalat, CQCvoi ... ), phuong phap thay dAt,phirong phap nen truce ...+ Cac bien phap v~t ly: G6m cac phirong phap ha rmrc mroc ngam, phirongphap dung gi~ng cat, bActham, di~n tham ...+ Cac bien phap hoa hoc: G6m cac phirong phap keo k~t dAtb~ng xi mang, vfraxi mang, phirong phap silicat hoa, phirong phap dien hoa ...

D a n~ng 9/2006 CHudNGVI TRANG 139

5/14/2018 Gi o tr nh X y d ng c ng tr nh tr n n n t y u

Tmirng O~I HQC BAcH KHOA oA NANGB{j mon ClI sil kj thuv.t Xay dvng NhOm chuyen mon CHO-N@n MongBai giang N~n vaM6ng4.2. Phirong phap xu If n~n bing d~m cat

Lap dem cat sir dung hieuqua cho cac lap dAty~u (y trang thaibao hoa mroc (set nhao, set phanhao, cat pha, bun, than bun ... ) vachieu day cac lap dAt y~u nho hon3m.

Bien phap ti~n hanh: Dao bo(tnrong hQ'Plap dAty~u co chieu daybe) va thay vao do b~ng cat hattrung, hat tho dAmchat,

Vi~c thay th~ lap dAt y~ub~ng tAng dem cat co nhimg tacdung chu y~u sau: . .... .... ....+ Lap d~m cat thay th~ lapdAt y~u n~m true tiep duoi daymong, d~m cat dong vai tro nhir motlap chiu Uti, ti~p thu Uti trong congtrinh va truyen tai trong do cac lap dAty~u ben duoi,+ Giam ducc dQ lim va chenh lech hm cua cong trinh vi co Sl,I phan b6 lai irngsuAtdo tai trong ngoai gay ra trong n~n dAtdmri tAng d~m cat.+ Giam ducc chieu sau chon mong nen giam ducc kh6i hrong v~t li~u lammongo + Giam ducc ap lire cong trinh truyen xuong d~n tri s6 rna n~n dAty~u co th~ti~p nhan duoc,+ Lam tang kha nang 6n dinh cua cong trinh, k~ ca khi co tai trong ngang tacdung, vi cat duoc nen chjit lam tang hrc rna sat va sire chong tnrot.

Tang nhanh qua trinh c6 k~t cua dAtn~n, do v~y lam tang nhanh kha nang chiutai cua n~n va tang nhanh thai gian 6n dinh v~ hin cho cong trinh.+ V~ m~t thi cong dan gian, khong doi hoi thiet bi plnrc tap nen ducc sir dungwang d6i rQng rai,

Pham vi ap dung t6t nhAtkhi lap dAty~u co chieu day be han 3m. Khong nen sirdung phirong phap nay khi n~n dAtco mire mnrc ngam cao va mroc co ap vi se t6n kernv~ viec ha rmrc mnrc ngam va dem cat se kern 6n dinh,4.2. Xac dinh kich thurrc d~m cat

NQ~~M

~,~,~\. . ~\

LO p dem cat

,!!!

L...- +-' .............! O" pI. . . . . . . .

O"bt

ffinh 4.6: SO'd8 b a tri dfm cat

Vi~c xac dinh kich thuoc lap d~m cat mot each chinh xac la mdt bai toan phirctap vi tinh chAtcua dem cat va lap dAty~u hoan toan khac nhau. D~ tinh toan, ta xemd~m cat nhir mdt bQphan cua dAtn~n, nrc la d6ng nhAtva bien dang tuyen tinh.4.2.1. Ki~m tra An dinh va ap I\l'C t~i mit ti@pxuc gifra d~m cat va lOp dit y@u

D~ dam bao cho dem cat 6n dinh va bi~n dang trong gioi han cho phep thi phaidam bao di~u kien sau:

0"1 + 0"2 ~ R d yTrang do:D a n~ng 9/2006

(4.4)CHudNGVI TRANG 140