Ni dung bi II

Cng tc thi cng nn mng

Bi 7

Cng tc thi cng nn mng

Ging vin: PGS., TS. Nguyn B K

1. Nguyn tc chung trong gim st

22. Nn mng t nhin

83. Nn cn gia c

10

3.1. Bc thm, vi a k thut

10

3.2. Bm p va

13

3.3. Gia c nn bng phng php ho hc

13

3.4. Lm cht t bng m, lu ln trn mt/chiu su

15

4. Thi cng mng cc

174.1. Cc ch to sn

194.1.1. Giai on sn xut

19

4.1.2. Giai on tho khun, xp kho, vn chuyn

22

4.1.3. La chn ba ng cc

22

4.1.4. Mi ni cc v mi cc

23

4.1.5. Trnh t ng cc

23

4.1.6. Tiu chun dng ng cc

24

4.1.7. Chn ng v ting n

25

4.1.8. Mt s s c thng gp

28

4.1.9. Nghim thu cng tc ng cc

29

4.2. Cc khoan nhi

304.2.1. Yu cu chung

30

4.2.2. Khi lng kim tra v cch x l

31

4.2.3. Kim tra cht lng l cc

34

4.2.4. Kim tra lng thp v lp t ng o

40

4.2.5. Kim tra cht lng b tng v cng ngh b tng

41

4.2.6. Kim tra cht lng thn cc

42

4.2.7. Kim tra sc chu ti ca cc

48

4.2.8. Mt s h hng thng gp trong thi cng cc khoan nhi

50

4.2.9. Nghim thu cc khoan nhi v i

53

5. Thi cng h o

54

Hnh v, biu

59thi cng nn mng PGS.TS. Nguyn B K

Gim st xy dng nn mng l mt trong nhng cng vic rt a dng v kh phc tp ti hin trng, i hi ngi k s gim st cn c trnh hiu bit, kinh nghim v phm cht cao v nhng l do sau y:

Thng c s khng n khp gia iu kin t nn lc thm d thit k v lc thi cng;

Cng ngh dng trong thi cng nn mng c th khc nhau trn cng mt cng trnh (nn t nhin, nn cc, nn cn gia c, o trn kh, di mc nc ngm, ngoi lng sng, o p ngm);

Trong qu trnh thi cng thng b chi phi bi nh hng ca s thay i thi tit (nng kh, ma bo, lt li..) iu c ngha rt ln trong vic la chn cng ngh thi cng o h mng;

Mng l kt cu b che lp sau khi thi cng xong nn cn s gim st thn trng, t m v trung thc trong sut qu trnh thi cng, mt sai st no d nh khu ny c nh hng rt ln n cht lng cng trnh bn trn, vic khc phc sa cha s c l phc tp, tn km v c khi phi lm mi thay th.

1. Nguyn tc chung trong gim st

1) Vic la chn bin php thi cng nn mng phi ph hp vi iu kin a cht cng trnh v a cht thu vn ca a im xy dng v cn son tho cng ngh thi cng tng ng cho tng loi nn (t nhin, nn gia c, nn mng cc) v cho tng loi cng vic (nh nh v cm mc, gii phng v san lp mt bng, o mng, cng tc b tng, chng thm...);

2) Cc vt liu, cu kin hoc b phn kt cu dng khi xy dng nn mng phi tho mn yu cu ca thit k v theo tiu chun sn phm ca ngi t hng yu cu;

3) Phi x l t, nc thi lc o mng, ting n v chn ng (o, ng cc, rung..) theo nhng yu cu ca tiu chun c lin quan n mi trng (i vi ngun nc, khu dn c v cng trnh ln cn.. );

4) Khi xy mng trn cc loi nn t c tnh cht c bit (t ln t, t p, t cha n nh v cu trc, t vng d trt l, t c hang ng cac-t.. ) cng nh mng ca cc cng trnh c bit quan trng phi t chc vic theo di s bin ng ca t nn (chuyn v ng-ln - v ngang, p lc nc l rng vv.. ) iu chnh tc v phng php lm mng lc thi cng cng nh nh gi tin cy ca gii php thit k - thi cng lc khai thc cng trnh. Nhng chi ph cho cng tc quan trc ny phi c lng nh trong lc thit k v nm trong gi thnh cng trnh;

5) Khi xy dng nn v mng phi c s gim st k thut v cht lng ca ch u t (thng do t chc t vn gim st thc hin), lp thnh bin bn nghim thu trung gian v nghim thu cui cng theo nhng tiu chun quy nh trc; Ni dung gim st ni y l theo tiu chun TCXD 79-1980 Thi cng v nghim thu cc cng tc nn mng.

6) Ch u t (vi s tr gip ca k s t vn) cng b vn bn ch dn k thut (Technical specification) cho nh thu bit lm cn c trong vic nh gi cht lng v nghim thu cng nh tnh ton gi thnh.

Ni dung bn ch dn k thut ni trn phi ch ra c nhng iu quan trng sau y:

C s ca thit k v thi cng;

Lit k nhng cng vic thi cng mt cch chi tit v yu cu chnh trong tng giai on thi cng, la chn thit b thch hp;

Lp danh mc, khi cn phi trch dn, tt c nhng tiu chun thi cng v kim tra, nghim thu trong nh gi khi lng v cht lng cng tc thi cng;

Trch nhim v quyn hn ca ch u t, k s t vn gim st v nh thu, cch v bin php x l cc tranh chp (k thut v kinh t) nu c xy ra.

Ch thch: Vi nhng cng trnh c gi tr khong 50 triu USD, bn ch dn k thut ni trn c th dy n 500-700 trang A4;

V d cho ring khu san nn v chun b mt bng ca cng trnh xy dng trn nn t yu, phn ch dn k thut c nhng ni dung nh:

(1) Quy nh chung (c s ca ch dn k thut san lp);

(2) nh v cng trnh: xc nh mc, li khng ch, to cc im chun.., o c hin trng, xy dng mc, thit b o, chnh xc, tiu chun dng;

(3) Cng tc gii phng mt bng: c im chnh ca a hnh, trnh t thi cng gii phng mt bng (ranh gii gii phng mt bng, dn chng ngi vt, o bc t yu);

(4) Cng tc thi cng vi a k thut v bc thm (khi x l nn t yu), thnh phn cng vic, thit b s dng;

(5) Thi cng san lp mt bng: m vt liu p, yu cu thnh phn ht v cht lng vt liu, cc giai on san lp, thit b lu ln, tiu chun cch kim tra cht t theo tng lp;

(6) K thut thi cng bc thm: yu cu k thut ca vt liu bc thm (chng ch ca nh my cung cp v kt qu kim tra ca ch u t qua mt phng th nghim no ), trnh t thi cng, hng ng p bc thm, yu cu thit b thi cng, tiu chun nghim thu;

(7) Quy trnh quan trc nn t: quan trc ln theo su v b mt, quan trc chuyn v ngang, o p lc nc l rng, s im quan trc, to cc im y, biu mu ghi kt qu quan trc, cch phn tch kt qu quan trc.

Mt v d tng t nh vy nhng vi i tng l cc khoan nhi s thy r hn mc 4.2.

y cng cn ch ra phm vi nhim v ca t vn gim st thi cng cho tng cng vic thi cng c th (thnh vn bn lu hnh trong phm vi ch u t- Nh thu T vn gim st). V d ni v nhim v ca gim st vin cho cng tc san lp mt bng:

(1) Gim st vin phi gi bo co hng tun cho ch u t. Cc bo co ny phi nu ln cc vn sau:

Cc s vic xy ra.

Tnh trng my thi cng v kh nng chp nhn.

Cc bin bn sai phm (NCR) lp.

Cc bin bn sai phm c lm sng t.

Cc bin bn sai phm cn tn ti.

Cc khuynh hng bt li.

Cc nguyn nhn chnh ca s chm tr.

Cc sai st hoc khng y trong bo co ca nh thu.

Tm tt tin trnh hin ti so vi tin yu cu.

S lng vt liu t so vi khi lng yu cu.

Quy m cho php khai thc m t.

Chu k ly mu ti hin trng v mc t tiu chun.

Gi cng gim st.

Kh nng cung cp vt liu ca nh thu.

nh gi chng ch vt liu.

nh gi tnh trng my thi cng.

Khu vc san lp.

Bn bo co hng tun phi c chun b xong trc 12 gi ca ngy th hai tun tip theo. Bn bo co hng thng tng kt cc bo co hng tun v thng k li bng th. Bn bo co hng thng phi c hon tt trc ngy th nm ca thng k tip.

(2) Gim st vin phi lp bo co chung v h thng qun l cht lng:

a) Gim st vin phi phi hp cng ch nhim qun l cht lng QA ca ch u t ch nh kim tra h thng qun l cht lng do nh thu trnh v chp nhn nh thu ph thc hin cng vic san lp;

b) H thng qun l cht lng phi da trn c s ISO 9001 v ISO 9002. Cc yu cu ti thiu ca h thng ny phi bao gm:

K hoch cht lng c th ca cng trnh (vit bng li);

K hoch qun l cht lng c th ca cng trnh (dng biu );

K hoch gim st v th nghim cng tc san lp (chung);

K hoch gim st v th nghim cho cc yu cu th nghim tng xng.

Ph lc cc th mc qun l cht lng.

Thng k bin bn bo co sai phm.

Thng k cc cng vic c u thc.

Yu sch cho quy trnh gim st.

Mu yu cu gim nh.

Quy trnh thi cng (cng tc san lp).

Mu bin bn qun l cht lng cho:

Gim st thu nhn vt t.

Ly mu th nghim.

Bin bn bo co sai phm.

Mu chp nhn mt bng c no vt.

Mu chp nhn ngun/bi vt liu.

Mu chp nhn bc thm v vi a k thut.

Chp nhn mu th nghim nn.

Bin bn th nghim nn..

Bin bn th nghim nn (bin bn th nghim trong phng).

Bin bn o ln.

Chp nhn my thi cng ca nh thu.

Ph lc cc th mc cng trnh.

Ph lc cc iu l, tiu chun, quy trnh, k hoch v tin cng trnh.

Bo co tnh hnh thi cng hng tun.

Bin bn cc cuc hp.

L lch cn b ch cht ca nh thu.

S t chc nhn s trn cng trng.

Phn cng trch nhim trn cng trng.

Ph lc cc ch k c thm quyn trn cng trng.

Chng ch vt liu.

Chng ch bc thm v vi a k thut.

Mt bng tng th cc v tr th nghim.

iu phi vt liu ti cng trng.

(c) Tt c cc bo co qun l cht lng phi c ph lc v nh du cc im lin quan ph hp vi yu cu ca ISO. Tt c cc ti liu c nh chnh v c ph lc km theo. Cc trnh t ca ti liu c nh r s ti liu, vn , ni dung, ngy bt u, ngy kt thc v s bt u v s kt thc theo th t ni dung hoc th t ngy thng.

(3) Bo co cng trnh ca gim st vin

(a) Gim st vin phi thng xuyn bo co vi yu cu ti thiu v cc vn sau:

Cc chp nhn my thi cng.

Cc chp nhn m t/bi sng.

Cc chp nhn vt liu.

Thng k bin bn sai phm.

Bo co cc bin bn sai phm.

DRRs.

Cc bn sao thay i ca bo co hng tun.

Cc bo co hng tun ca nh thu.

Cc bo co hng thng ca nh thu.

Cc bo co hng tun v hng thng ca gim st vin.

Mt bng tng th ca cc v tr th nghim.

Cc bin bn kim k.

Cc ti liu gi i v n.

Cc bin bn kim nh vi mc ch c th.

(b) Khi cng trnh c hon thnh, h s trn s c chuyn giao cho c quan ch qun.

(c) n v ch qun s kim tra li cc bo co ca gim st vin v nu sai st s khc t chng nhn hon thnh ca t vn. Gim st vin phi m bo vic chnh l tt c cc sai st trong bo co trc khi bn giao cho cng ty.

4. Bo co hon tt cng trnh ca gim st vin

(a) Trong vng 7 ngy sau khi cng vic san lp hon tt, gim st vin phi gi bo co hon thnh cng trnh cho cng ty.

(b) Bo co s ghi ghi r s thc hin ca nh thu:

Tng s bin bn sai phm gi i.

S thc hin ca phng th nghim.

S thc hin ca nh thu ph.

Cc bi hc kinh nghim.

Cc vn k thut gp phi.

Cc gii php cho cc vn k thut pht sinh.

ng gp kin ca gim st vin cho cc cng trnh trong tng li.

Cc lnh vc v phm vi m nh thu/cng ty cn ci tin.

ng gp kin o to cho cn b ca nh thu/cng ty.

(c) Bo co cng trnh ca gim st vin phi c k s trng v gim c iu hnh ca n v gim st xc nhn.

(d) Bo co hon thnh cng trnh phi c gi cho ch u t v cho nh thu/cng ty di hnh thc nh sau:

Bn gc: 01 bn.

Bn sao: 06 bn.

Trong cc vn bn trn, lc nh gi cht lng cng tc san lp mt bng cn da vo cc quy nh sau y:

Tt c cc cng vic v th nghim phi c tin hnh ph hp vi nhng tiu chun sau hoc cc tiu chun tng ng vi chng c ch u t ph duyt: Nh thu v gim st vin khng c php thay i cc iu l p dng, tiu chun, ch tiu k thut hay quy trnh khi khng c s chp thun bng vn bn chnh thc ca ch u t, v d:

(a) AASHTO M145-87- Phn loi thnh phn vt liu p theo cp ht.

(b) AASHTO T180-90 - Tng quan gia dung trng v m ca t khi m nn.

(c) AASHTO T190-86 - Xc nh dung trng ring ca vt liu p ti hin trng bng phng php phu rt ct.

(d) AASHTO T100-90 - (ASTM D854-83) - Xc nh trng lng ring ca vt liu p.

(e) ASTM D1556 - Kim tra cht ca t p.

(f) Yu cu rng buc trong qu trnh gim st.

(g) Quy trnh phi hp ca n.

(h) H thng qun l cht lng c ph duyt ca n v thi cng.

(i) Quy trnh c ph duyt ca nh thu.

(j) K hoch cht lng c ph duyt ca nh thu.2. Nn mng t nhin

Cn gim st theo mt s ni dung chnh nh:

1) Cc bin php bo v h mng t nn khng b xu i (do ma nng, nc ngm, nc mt, phong ho.. );

2) Chng vch h o gi n nh cho cng trnh ln cn;

3) Vic bm ht nc trong h mng hoc cn h mc nc ngm trong lc o mng phi c tin liu bng thit k bm ht thch hp;

4) Phi xc nhn bng o c cn thn (biu mu) v:

Tnh trng t y mng;

su y mng;

V tr v kch thc;

Cc l, hc cha sn v cc lp chng thm ca mng;

Vv...;

Mt s sai st thng xy ra trong giai on o h mng c th dn n lm cng trnh b ln ln hoc ln khng u c trnh by trong bng 2.1 v cn gim st cn thn.

Bng 2.1. Mt s sai st thng gp trong thi cng o mng ni trng tri v ni cht hp.

NoNguyn nhn v cch phng trnh khi o ni trng triNguyn nhn v cch phng trnh khi o gn cng trnh ln cn

1t y h mng b nho do nc ma hoc nc trn vo ng lu. Bo v y h mng bng h thng thu v bm nc hoc cha nn o n ct thit k khi cha chun b vt liu lm lp lt hoc lm mngBin dng nh do o h mng hoc ho gn:

Tri t y h mng mi hay chuyn dch ngang mng c do t y h mng c b trt. phng thng phi t mng mi cao hn mng c 0,5m hoc chng cn thn thnh h mng bng cc bn thp hay cc t ximng.

2t y mng b kh v nt n do nng hanh s lm hng cu trc t nhin ca t, bn ca t s gim v cng trnh s b ln.

Cn che ph hoc cha nn o n ct thit k, dng lp t cch y mng 15-20cm tu theo loi t.Bin dng nh gn do tc ng ng lc ca my thi cng:

(a) Do my o;

(b) Do ng cc.

ngn nga c th dng bin php gim chn ng hoc cc p hay cc nhi thay cho cc ng.

3Bin dng lp t st y mng do p lc thu tnh.

Cn c h thng bm chm kim h thp mc nc ngm quanh mng.Bin dng nh do ht nc ngm h mng cng trnh mi, s xy ra hin tng ra tri t y mng c hoc lm tng p lc ca t t nhin (do khng cn p lc y ni ca nc) v dn n ln thm.

phng trnh, nn dng cc bin php gim gradient thu lc i (0,6.

4y mng b bng cc lp st hoc st do b gim p lc bn thn ca t hoc do p lc thu tnh ca nc.

Phi tnh ton gi li lp t c chiu dy gy ra p lc ln hn p lc trng n. i vi nc th phng trnh ging nh nu im 3.Bin dng ca nh c trn cc ma st khi xy dng gn n nh mi trn mng b.

Vng tip gip nh mi cc chu ma st m nn t b ln v sc chu ti ca cc b gim i. Nn lm hng tng ngn cch gia hai cng trnh c-mi.

5Ra tri t trong nn nht l nn ct mn hoc t yu.

Cch phng trnh: dng tng vy hoc cn bm h mc nc ngm, phi xc nh cn thn tc bm ht c k n hin tng ra tri m bo an ton nn ca cng trnh.Bin dng nh ca nh c do vt liu gn nh hoc san nn bng t p nhn to lm hng cu trc t nhin ca t, nht l khi gp t st yu gn y mng. trnh nh hng xu phi quy nh ni vt liu v tin cht ti (thi cng nh mi theo c kt tng dn vi thi gian).

6Bng nn do tng p lc thu ng trong t thm nc.

Gim dc (gradient) thu lc (thng i(0,6) bng cch ko su tng vy hoc gia cng y mng bng bm p ximng trc khi o nh ni im 3.Hnh thnh phu ln ca mt t do o ng hm trong lng t. Nhng cng trnh ngay pha trn hoc cnh ng hm s b bin dng ln hoc nt.

Phng trnh bng cch p y cc on ng (thp/b tng ct thp) ch to sn hoc gia cng vng pha trn nc hm bng cc r cy hoc bng tr ximng t.

3. Nn cn gia c

Cn xc nh r cc thng s kim tra sau:

1) su v phm vi gia c (m nn b mt hoc nn cht su bng cc ct, cc xi mng t... hoc bng phng php ho hc);

2) Ch s cht, bn, thm xuyn nc so vi yu cu thit k;

3) Cng ngh dng trong kim tra cht lng t nn sau khi ci to/gia c (ly mu, ng v phng x, nn tnh ti hin trng, xuyn tnh/ng vv...);

4) Cng tc nghim thu kt qu ci to t nn cn quy nh tng ng vi cc yu cu ca thit k v kch thc khi t v cc c trng ca t gia c nh cc s liu sau y:

Mt bng v lt ct khi t ci to;

L lch k thut ca vt liu dng trong gia c;

Nht k kim tra cng vic;

Cc s liu v cng , tnh thm nc, n nh nc ca t ci to.3.1. Bc thm, vi a k thut

Hin nay nc ta ang p dng rng ri phng php bc thm (bng thot nc) hoc vi a k thut ci to t yu. y l nhng tin b k thut trong xy dng ng v nh t tng. V vy cn nm vng nhng hiu bit c bn sau y:

Phm vi p dng ca phng php (bng 3.1 v bng 3.2); La chn ng phng php; Thit k b tr theo nhng tiu chun tng ng. Trn hnh 3.1 trnh by v d dng phng php thot nc thng ng cho nn ng; Nm c nhng yu cu c bn ca tng phng php khi la chn cch thot nc nh: Kh nng chuyn nc, cng , do v bn ca vt liu; - c kh nng ngn chn ht t nh chui qua lm tt ng thm ca nc; v d i vi vi a k thut thng theo cc s liu kinh nghim sau:O90/O50 ( 1,7 n 3;O90/D85 ( 2 n 3; hoc O90/D85 ( 1,3 n 1,8;

O90/D50 ( 10 n 12;

Trong : O50/O90, O95 - ng knh l b lc chim 50%, 90% v 95% ton b din tch b lc;

D50, D85 - ng knh ht t tng ng vi hm lng tch lu ca ng phn tch ht l 50%, 85%.

Bng 3.1. Kh nng p dng bin php k thut ci to nn cho cc loi t khc nhau

C ch citoCtHn hp trn hay pht vam chtThot nc

Thi gian ci toPh thuc s tn ti ca th viTng i ngnLu diLu di

t hu c

t st c ngun gc ni la

t st do cao

t st do thp

t bn

t ct

t si

Trng thi ci to Tng tc gia t v th viXi mng hoDung trng cao do h s rng gim

ca t(Khng thay i trng thi t)(Thay i trng thi t)

Bng 3.2. Lnh vc ng dng v chc nng ca vi a k thut

Chc nng

Lnh vc in hnhPhn cchTiuLcGia cBo v

ng t v sn kho

ng t v bi xe

v cc cng trnh ngn nc

Gia c tng v mi dc

Tiu ngm

Lc di r

Lc qua p t

Lc qua k sng, bin

Cc cng trnh ci to t bng thu li(((O

O

(O

(O

O

O

(O

O

(O

O

O

O

((((O

O

*

(

Khp kn cc vng t cha cht thi

Ngn chn cc vng t cha cht thi

ng hm khng thm nc

Ngn chn cc ho cht tng hp

Trm bo dng ng st

Sn vn ng v sn gii tr

H thng cc sn phm c hp cht ho hcO

O(((OO

O

O

(((((((

Chc nng chnh; O Chc nng ph; * ng dng tu thuc loi tKh nng chuyn nc ca bc thm hoc vi a k thut l thng s cn thit dng trong thit k, thng khng nh hn 100m3/nm p sut khng n hng l 276 KPa (40psi).

H s thm ca vi a k thut thng bt buc ln hn hoc bng 10 ln h s thm ca t.

Ngoi nhng yu cu v vt liu lc, phng php ny cn phi dng nhng a tng thch hp ca lp t yu trong cu trc a tng ni chung, trong quan trng l p lc gia ti trc ( to ra s thot nc) c truyn y ln lp t yu v khng ln qu gy mt n nh ni chung. Chi tit v vn ny c th tm hiu trong cun Cng ngh mi x l nn t yu vi a k thut v bc thm ca Nguyn Vit Trung, H Ni, 1997.

3.2. Bm p va

Cng ngh phun p va (grouting technology), vi p lc 20-40 MPa hin ang dng trong xy dng nn mng v cng trnh ngm nhm:

Nhi lp cc l rng;

Lm chuyn v v dn cht t;

Gim ht nc, tng cng .

Vi nhiu mc tiu sau:

1) Rn ho v n nh t truyn ti trng xung su trong thi cng ng tu in ngm, ng cao tc v nn mng;

2) Cch chn cho mng my;

3) Lm h thng neo c phun va gi n nh, chu lc ko;

4) Bt lp cc vt nt trong cng trnh b tng v th xy;

5) Lm lp ph mt knh o;

6) Phun kh b tng lm lp o cho cng trnh ngm;

7) Lm ging du bng ximng ging khoan;

8) Phun va ng sut trc trn ng sng;

9) Phun va to cc hoc bo v v x l cc b khuyt tt.

Trn hnh 3.2a trnh by cch gia c nn mng, trn hnh 3.2b gia c mi dc v thi cng cng trnh ngm, v trn hnh 3.2c - bm to mng chng thm.

Trn hnh 3.3 trnh by cng ngh bm p gia c nn v trn hnh 3.4 - khi t gia c bng bm p.

3.3. Gia c nn bng phng php ho hc (ximng, thu tinh lng hoc cc cht tng hp khc..) nc ta lm thc nghim kh lu nhng dng nhiu nht l phng php bm va ximng.

Mc ch ca phng php ny thng dng :

Nng cao cng ca nn nh s dng;

Phng nga nhng bin dng c tnh ph hng ca kt cu;

Thi cng sa cha mng.

Tu theo cng ngh gia c v cc qu trnh xy ra trong t m chia phng php gia c nn lm 3 nhm chnh: ho hc, nhit v ho l. u vit ca phng php gia c ny l khng lm gin on s dng nh v cng trnh, nhanh, tin cy cao v trong nhiu trng hp l phng php duy nht tng bn ca t c sc chu ti khng .

Cc phng php thng dng l: silicat ho, in - silicat ho, silicat kh, amonic ho, thm nhp nha... v c th tm hiu chi tit trong nhiu ti liu tham kho khc.

Phng php gia c ho hc cng dng gia cng mng v tng chn, tng sc chu ti ca cc, bo v mng chng cc tc nhn n mn, gia c mi h o v cng trnh t.

Vt liu c bn gia c bng silicat l thu tinh lng - dung dch keo ca silicat natri (Na2O. nSiO2 + mH2O). Tu theo loi, thnh phn v trng thi ca t cn gia c m dng mt hay hai dung dch silicat ho.

Loi mt dung dch c da trn dung dch to keo bm vo trong t gm 2 hoc 3 cu t. Ph bin nht l xit phosphosilicat, oxit lu hunh-nhm-silicat, xit lu hunh-fluo-silicat, hydro-fluo-silicat v..v.. Phng php mt dung dch thch hp cho t ct c h s thm 0,5-5m/ngy m.

Phng php 2 dung dch dng gia c t ct c h s thm n 0,5m/ngy m v gm 2 ln bm ln lt vo t 2 dung dch silicat Na v clorua Ca. Kt qu ca phn ng ho hc l to ra xit keo silic lm cho t tng bn (n 2-6Mpa) v khng thm nc.

Phng php in ho silicat l da trn s tc ng t hp ln t ca hai phng php: silicat ho v dng in 1 chiu nhm gia c ct ht mn qu m v ct c h s thm u 0,2 m/ngy m.

Phng php amniac ho l da trn vic bm vo trong t hong th ( loi tr tnh ln sp) kh amniac di p lc khng ln lm.

Silicat ho bng kh gas dng lm cng silicat Na. Phng php ny dng gia c t ct (k c t cacbonat) c h s thm 0,1-0,2 m/ngy m cng nh t c hm lng hu c cao (n 0,2). bn ca t gia c c th n 0,5-2MPa trong thi gian ngn.

Phng php thm nhp nha dng gia c t ct c h s thm 0,5-5m/ngy m bng cch bm vo trong t dung dch nha tng hp (cacbonic, phenol, epoxy..). Tc dng ca nha ho s tng ln khi b sung vo dung dch mt t axit clohydric (i vi t ct). Thi gian keo t rt d iu chnh bng lng cht ng cng. t c gia c bng nha ho s khng thm nc v cng chu nn 1-5Mpa. Ngoi vic gia c nn, phng php ny cn dng gia c vng s o xuyn ca cng trnh ngm. Tu theo cch t ng bm, c th gia c t cc v tr khc nhau: thng ng, nghing, nm ngang v kt hp (hnh 3.5) cn s trn mt bng c th theo dng bng di, di ton b mng, gia c cc b khng ni kt hoc theo chu vi vnh mng. Vic chn phng php v s gia c ph thuc ch yu vo tnh cht ca nn, hnh dng v kch thc ca mng cng nh ti trng tc dng ln mng.

3.4. Lm cht t bng m/lu ln trn mt hoc chiu su

C cc phng php sau:

Lu ln, m nng ri t cao xung;

Ln cht t qua l khoan (cc ct, cc dm, cc t vi ximng, n mn..);

C kt ng (dynamic consolidation).

Cc cng ngh thi cng ni trn hin pht trin rt cao nh thit b thi cng ngy cng hon thin v phng php kim tra ngy cng c tin cy cao. Nhng thng s kim tra chnh nh trnh by u mc 3 v chi tit th theo nhng tiu chun thi cng c th ca tng phng php.

V nguyn tc v i vi cng trnh quan trng cn tin hnh th nghim nn v ct cho t c m cht khc nhau, trn c s xy dng biu quan h gia:

Lc dnh v cht (thng qua (kh hay h s m cht kc);

Gc ma st v cht;

M un bin dng/cng v cht.

Khi cha c s liu th nghim c th dng cc s liu tham kho cc bng sau y trong thit k s b v khng ch cht lng.

Bng 3.3. cht yu cu ca t

Chc nng ca t ln chtH s m cht kc

Cho nn mng ca nh v cng trnh hoc nn ca thit b nng cng nh nn c ti trng phn b u ln hn 0,15MPa.

Nh trn, thit b nng va, mt nn c ti trng 0,05-0,15 MPa.

Nh trn, thit b nh, mt nn c ti trng nh hn 0,05 MPa.

Vng khng c cng trnh0,98-0,95

0,95-0,92

0,92-0,90

0,9-0,88

Bng 3.4. Tr tiu chun ca mdun bin dng E mt s loi t ln chtE, MPa

t m m cht ti u trng thi bo ho nc

kc =0,92kc =0,95kc =0,92kc =0,95

ct hong th (lt)

st v st lt

Ct th

Ct trung

Ct mn20

25

30

25

1525

30

40

30

2015

20

-

-

-20

25

-

-

-

Bng 3.5. Cng tnh ton Ro ca nn t ln cht

tRo, MPa h s kc

0,920,950,97

ct

st

St

Ct th

Ct trung

Ct mn0,2

0,25

0,3

0,3

0,25

0,20,25

0,3

0,35

0,4

0,3

0,250,28

0,32

0,4

0,5

0,4

0,3

Bng 3.6. Tr khng ch v cht lng tng t ln cht (kinh nghim Trung Quc)

Loi hnh kt cuV tr lp ln chtkc m Wop %

Kt cu xy, nng v Trong phm vi tng chu lc(0,96

Kt cu khungDi phm vi tng chu lc0,93-0,96Wop ( 2

Kt cu chng vTrong phm vi tng chu lc0,94-0,97

khng phi kt cu khungDi phm vi tng chu lc0,91-0,93

Bng 3.7. Tr tham kho v m ti u v cht (kh) ln nhtLoi t m ti u (%) cht (kh) ln nht(g/cm3)

t ct

t st

t st bi

t bi8-12

19-23

12-15

16-221,8-1,88

1,58-1,70

1,85-1,95

1,61-1,80

Bng 3.8. Tr tham kho v m ti u Wop %

Ch s do ca t Ip cht kh ln nht (dmax (g/cm3) m ti u Wop (%)

(0

0-14

14-17

17-20

20-221,85

1,75-1,85

1,70-1,75

1,65-1,70

1,60-1,75(13

13-15

15-17

17-19

19-21

Khi dng phng php ng ln cht th khng ch sai khc gia m v m ti u thay i trong 6% -+2%.

4. Thi cng mng cc

Mng cc (cc ch to sn ri h vo t bng ng, rung p, p, khoam th hoc cc ch to trong l to sn bng cch nhi b tng, thng gi chung l cc nhi) l gii php a dng trong xy dng cng trnh c ti trng ln trn nn t yu.

Vic la chn cc ch to sn (cc g, b tng ct thp hoc thp) hay cc nhi l cn c vo cc iu kin c th ch yu sau y quyt nh:

c im cng trnh;

ln ca cc loi ti trng;

iu kin a cht cng trnh v a cht thu vn;

Yu cu ca mi trng (rung ng v ting n);

nh hng n cng trnh ln cn v cng trnh ngm;

Kh nng thi cng ca nh thu;

Tin thi cng v thi gian hon thnh ca ch u t;

Kh nng kinh t ca ch u t;

V..v..

C th tham kho theo kinh nghim trnh by bng 4.1.

Bng 4.1. La chn loi cc

Loi ccCc pCc ngCc nhi

Tnh hnhB tngThp

Kch thc cc v ti trng cho phpng knh (cm)

su (m)

Ti trng cho php (tn)20-30

15-20

20-4030-55

20-40

50-12050-80

25-150

100-17080-120

40-60

150-700

Phng thc chu lc ca ccChng mi

Mi + ma st

Ma st0

0

00

0

(0

0

(0

0

x

su lp t chu lcn 10 m

10-20 m

20-30 m

30-60 m0

0

(x0

0

0

(((0

0(0

0

0

Lp t xen kp dy hn 5 mSt N = 4-10

N = 10-20

Ct pha N = 15-30

N = 30-50

N ( 50

Ct ri

Cui si:

d ( 10 cm

10-30 cm

d ( 30 cm(x

0

(x

0

x

x

x0

x

0

(x

0

(x

x0

0

0

0

(0

0

(x0

0

0

0

0

0

0

((

Nc ngmKhng h c mc nc

Tc ( 0,3m/s0

00

00

00

x

nh hng n mi trngn v rung ng

Xy dng trn nc

Gn cng trnh ln cn

Din tch cht hp0

0

0

0x

0

(xx

0

(((0

((

Ch thch:

0 Thch hp trong s dng;

( - Cn nghin cu trc khi s dng;

x Ni chung l khng thch hp.

4.1. Cc ch to sn

Cc cng on cn gim st k i vi cc ch to sn ( y ch yu ni v cc BTCT) gm c:

Giai on sn xut cc (vt liu v kch thc hnh hc);

Giai on tho khun, xp kho, vn chuyn;

Chn ba ng cc/h cc;

Trnh t ng/h cc;

Tiu chun dng ng/h;

Chn ng v ting n;

Nghim thu cng tc ng/h cc.

Di y s trnh by ngn gn mt s yu cu chnh trong cc giai on ni trn.

4.1.1. Giai on sn xut - trong sn xut cc BTCT, cn ch :

Khng ch ng knh dmax ca ct liu (dmax = 1:3 n 1: 2,5 athp);

Ct liu (ct+si) khng c tnh xm thc v phn ng kim silic;

Lng dng ximng ( 300kg/m3, nhng khng vt qu 500kg/m3;

st ca b tng 8-18 cm (c gng dng b tng kh);

Dng ph gia vi liu lng thch hp.

Cc kim tra ct liu v ximng theo nh tiu chun kt cu b tng ct thp.

Sai s v trng lng cc thnh phn ca hn hp b tng khng vt qu cc gi tr sau y:

Ximng

: (2%;

Ct liu th

: (3%;

Nc+dung dch ph gia: (2%;

H s nghim thu cho cc BTCT gm:

Bn v kt cu cc;

Phiu kim tra vt liu cc;

Phiu nghim thu ct thp;

Cng p mu b tng;

Phng php dng h;

Phiu kim tra kch thc cc (bng 4.2).

Cht lng mt ngoi cc phi ph hp yu cu:

Mt cc bng phng, chc c, su b st gc khng qu 10 mm;

su vt nt ca b tng do co ngt khng qu 20mm, rng khng qu 0,5mm;

Tng din tch mt mt do lm/st gc v r t ong khng c qu 5% tng din tch b mt cc v khng qu tp trung;

u v mi cc khng c r, gh gh, nt/st.

Trn hnh 4.1 trnh by mt s bc kim tra cht lng cc trc khi ng gm c vic xc nh ng nht v cng b tng (siu m + sng bt ny theo mt s tiu chun hin hnh nh 20TCN: 87, TCXD171: 1987, v TCXD 225: 1998), v tr ct thp trong cc (cm ng in t); kch thc cc u v mi.

T l % s cc cn kim tra do t vn gim st v thit k quyt nh trn c s cng ngh ch to v trnh thnh tho ngh ca nh thu.

Bng 4.2. Sai lch cho php v kch thc ca cc b tng c sn

Loi ccHng mc kim traSai s cho php (mm)

Cc b tng ct thp c sn di cnh mt ct ngang ca cc

ng cho mt u cc

dy tng bo v

vng ca cc

Tm mi cc

xin mt u cc so vi ng tim cc

V tr l cha cho tai mc cu cc( 5

10

( 5

(1% chiu di cc, (20

10

( 3

5

Cc b tng ct thp c sn, rngng knh

dy thnh l

V tr l trn rut cc so vi ng tim cc

ng tim mi cc

xin ca mt bch u trn hoc di ca on cc so vi ng tim cc

Tng xin ca 2 mt bch ca on cc gia( 5

-5

5

10

2

3

Khung ct thp ca ccKhong cch gia cc ct ch

Tim mi cc

Khong cch gia cc ct ai dng vng hoc dng xon l xo

Li thp u cc

nh ca tai mc khi mt cc( 5

10

( 20

( 10

-0 ( 10

4.1.2. - Giai on tho khun, xp kho, vn chuyn

Nhng h hng c th xy ra giai on ny thng gp l:

Vn chuyn, xp kho khi cng b tng cha t 70% cng thit k;

Cu mc khng nh nhng, v tr v s lng cc mc thp cu lm khng ng theo thit k quy nh.

trnh hng gy cc, thng thng dng 2 mc cho cc di di 20 m v 3 mc cho cc di 20 - 30m.

Trn hnh 4.2 trnh by ni lc (m men un) xut hin trong cc khi xp kho, vn chuyn v cu lp hin trng; Tu thuc vo cch t mc cu m ni lc s c tnh ton tng ng theo nguyen tc sau: Khi s mc trn cc t hn hoc bng 3 th v tr ca mc xc nh theo s cn bng ca m men m (hnh 4.3) cn nu s mc ln hn 3 th v tr ca mc xc nh theo s cn bng phn lc (hnh 4.4).

Nhng kim ton ni trn phi c thng hiu gia ngi thit k v thi cng trnh nt hoc gy cc trc khi ng. iu ny cng c bit quan trng khi chng ta dng cc b tng ct thp di trn 30 m hay cc BTCT ng sut trc.

4.1.3. Vic chn ba ng cc

Mt s nguyn tc chung trong chn ba:

- Bo m cc xuyn qua tng t dy (k c tng cng xen kp) c mi vo c lp chu lc (cc chng), t n su thit k;

ng sut do va p gy ra trong cc (ng sut xung kch) phi nh hn cng ca vt liu cc, ng sut ko do va p nh hn cng chng ko ca b tng thng thng, cn trong cc BTCT ng sut trc nh hn tng cng chng ko ca b tng v tr ng sut trc;

Khng ch tho ng tng s nht ba + thi gian ng (chng mi v gim hiu qu ng);

xuyn vo t ca mt nht ba khng nn qu nh: ba diezen -1(2 mm/nht v ba hi 2(3 mm/nht ( phng hng ba + my ng).

Cn c chn ba ng:

Theo trng lng cc (trng lng ba ( trng lng cc);

Theo lc xung kch ca ba (lc xung kch ( lc chng xuyn);

Theo phng trnh truyn sng ng sut;

Theo cch khng ch cng (theo phng trnh viphn bc 3 v truyn sng ng sut);

Theo phng php gii kinh nghim chn ba thu lc cho thi cng cc ng thp;

Theo phng php kinh nghim so snh tng hp.

Chi tit xem trong S tay cng trnh mng cc, Bc Kinh, 1995.

4.1.4. Mi ni cc v mi cc

Mi ni gia cc on cc ch to sn (BTCT, g, thp..) c ngha rt quyt nh khi dng cc di. V phng din chu lc, mi ni c th chu lc nn v cng c kh nng xut hin lc nh, m men v lc ct. Khi ng th mi ni va chu lc nn va chu lc nh.

i vi cc b tng ct thp thng thng cc lin kt gia on cc c thc hin bng:

Hn qua mt bch + thp gc;

Hn qua thp bn ph kn mt bch;

Lin kt bng cht nm ng;

Lin kt bng cht x kiu m dng + va.

i vi cc BTCT trn, rng c th lin kt bng mi ni hn hoc ni bng bulng.

Ti cc nc c nn cng nghip pht trin cao ngi ta dng kiu mi ni ch to c kh kh chnh xc, rt ngn vic ngng ch lc h cc v c c cy cc di vi mi ni chc chn lm cho cc chu ti vi tin cy cao.

Mt s kiu mi ni va nu c th tm thy trong nhiu ti liu chuyn kho, y ch nu mt s loi tiu biu.

V mi cc, tu theo iu kin a cht cng trnh v phng thc chu lc ca cc m mi s c cu to khc nhau. Khi cc ng vo nn t mm th c th dng u cc bng phng; khi ng vo lp t cng, vo lp phong ho b ri hoc mi cc c th chng vo lp t c th nm nghing, cc ca cc cu ln, m bo sc chu ti cng nh n nh ca cc phi cu to mi cc mt cch cn thn, ng tm cc khng b lch hng khi ng/h vo trong t.

Nhng chi tit cu to v thit k mi ni v mi cc c ngha kinh t k thut trong cng trnh mng cc ni chung v cng l nhng iu kin d b xem thng ca ngi thit k ln ngi thi cng.

4.1.5. Trnh t ng cc

Trnh t ng/h cc trong cng ngh thi cng mng cc cn da vo cc yu t sau y quyt nh:

iu kin hin trng v mi trng;

V tr v din tch vng ng cc;

Cng trnh ln cn v tuyn ng ng ngm;

Tnh cht t nn;

Kch thc cc, khong cch, v tr, s lng, chiu di cc;

Thit b dng ng/h cc;

S lng i cc v yu cu s dng.

Mt s trnh t thng dng trong thi cng ng h cc trnh by hnh 4.5. Vic la chn cch ng no cn phi c s phn tch t m trong tng trng hp c th theo cc yu t nu trn.

Thng thng, nguyn tc xc nh trnh t ng cc l:

(1) Cn c vo mt ca cc v iu kin xung quanh:

Chia khu nghien cu trnh t ng;

Chia 2 hng i xng, t gia ng ra;

Chia 4 hng t gia ng ra;

ng theo 1 hng.

(2) Cn c cao thit k ca mng: Mng su hn - ng trc, nng hn - ng sau;

(3) Cn c quy cch cc: Cc ln - ng trc, cc nh - ng sau; cc di - ng trc, cc ngn - ng sau;

(4) Cn c tnh hnh phn b cc: Cc trong nhm - ng trc, cc n - ng sau;

(5) Cn c yu cu chnh xc lc ng: chnh xc thp - ng trc, chnh xc cao - ng sau.

4.1.6. Tiu chun dng ng cc

Xc nh tiu chun dng ng cc theo yu cu thit k l vn quan trng v n c ngha rt ln v kinh t v k thut. Hai du hiu khng ch dng ng l: theo su mi cc quy nh trong thit k v theo xuyn cui cng ca cc vo t (c khi cn gi l theo chi). C nhiu nhn t nh hng n hai du hiu ni trn v c khi mu thun nhau.

Tiu chun khng ch vic dng ng cc nn quy nh nh sau;

(1) Nu mi cc t vo tng t thng thng th su thit k lm tiu chun chnh cn xuyn th dng tham kho;

(2) Nu mi cc t vo lp t ct t cht va tr ln th ly xuyn su lm tiu chun chnh cn su cc - tham kho;

(3) Khi xuyn t yu cu nhng cc cha t n su thit k th nn ng tip 3 t, mi t 10 nht vi xuyn ca 10 nht ny khng c ln hn xuyn quy nh ca thit k;

(4) Khi cn thit dng cch ng th xc nh xuyn khng ch. Tham kho kinh nghim ca Trung Quc bng 4.3.

Bng 4.3. Kin ngh v tiu chun khng ch dng ng cc (kinh nghim Trung Quc)

Loi ccCc BTCT rngCc BTCT c

Kch thc cc (cm)Mi knMi hMi knMi h40x4045x4550x5050x50

t mi cc (tr s N)t ct (30-50)t st cng

(20-25)t ct (30-50)t st cng

(20-25)t st cng

(20-25)t ct (30-50)

Loi baizen20-25 cp30-40 cp30 cp30-35 cp35-45 p40-45 cp

Hi4-7 T7-10 T7 T7-10 T10 T10 T

Tr s khng ch tng s nht ng( 2000 -2500( 1500 -2000

S nht ng khng ch 5 m cui cng( 700 -800( 500 -600

Tr s xuyniezen2 - 3mm/nht2 - 3mm/nht

cui cngHi3 - 4mm/nht3 - 4mm/nht

4.1.7. Chn ng v ting n Vn nh hng v chn ng cng nh ting n i vi cng trnh v con ngi do thi cng ng cc gy ra cn phi c xem xt v n c th dn n nhng hu qu ng tic, nht l khi thi cng ng cc gn cng trnh xy hoc gn khu dn c (hnh 4.6).

Tiu chun khng ch dao ng v ting n do chn ng gy ra i vi ngi v cng trnh c th tham kho:

Tiu chun Lin X (c): Nr. 1304 75;

Tiu chun CHLB c: DIN 4150 1986;

Tiu chun Thu S : SN 640312 1978;

Tiu chun Anh : BS 5228, Part 4 - 1992a (bng 4.4a).

Tiu chun Vit nam TCVN 5949-1998 (bng 4.4b).

V n thng khng ch 70 75 dB i vi khu v 70 85 dB i vi khu thng mi; Khi n qu gii hn trn phi tm cch gim n. Cch phng chng nh hng chn ng v n:

Xc nh khong cch an ton khi ng (hnh 4.7);

Chn cch ng (trng lng + cao ri ba), loi ba hp l;

Khoan dn, ng v, p;

Lm ho cch chn;

t vt liu tng tiu m, gim thanh, m lt u m cc;

V..v..

Bng 4. 4a. nh hng ca dao ng i vi cc i tng khc nhau(theo tiu chun Anh BS 5228 Part 4 1992a)

Thng s o v phm vi nhy

V di tng quan tmChuyn v (mm)Vn tc (mm/s)Gia tc (g)

Phng tin th nghimThit b v vn hnh(0,25-1) x10-3(0,1Hz-30Hz)(0,1-5) x10-3(30Hz-200Hz)

C s vi in tThit b v vn hnh(6-400) x10-3(3Hz-100Hz)(0,5-8) x10-3(5Hz-200Hz)

My mc chnh xcThit b v vn hnh(0,1-1) x10-3

My tnhThit b v vn hnh(3-250) x10-30,1-0,25 sai s trung phng (SSTP)

(ti a 300Hz)

Vi x lThit b v vn hnh0,1-1

Bnh vin v ni c trCon ngi0,15-15 (hng ng)

(8Hz-80Hz)

0,4-40 (hng ngang)

(2Hz-80Hz)0,5-50 (SSTP hng ng)

(4Hz-8Hz)

Vn phngCon ngi0,5-20 (hng ng)

(8Hz-80Hz)

1-50 (hng ngang)

(2Hz-80Hz)

Xng myCon ngi1-20 (hng ng)

(8Hz-80Hz)

3,2-52 (hng ngang)

(2Hz-80Hz)(4-650)x10-3 (SSTP hng ng)

(4Hz-8Hz)

Khu dn c hoc thng miCng trnh1-50

ng dn kh hoc ncDch v ngm di t(10-400) x10-31-50

Bng 4.4b. Gii hn ti a cho php ting n khu vc cng cng v dn c

(tnh theo mc m tng ng dBA, TCVN 5949-1998)

Khu vcThi gian

t 6h-18ht 18h-22ht 22h-6h

1. Khu vc cn c bit yn tnh: bnh vin, th vin, nh iu dng, nh tr, trng hc, nh th, cha chin.

2. Khu dn c, khch sn, nh ngh, c quan hnh chnh.

3. Khu dn c xen k trong khu vc thng mi, dch v, sn xut50

60

7545

55

7040

50

50

4.1.8. Mt s s c thng gp

Kh xuyn v khng t c su thit k quy nh;

Cc b xoay v nghing qu ln;

Cc ng n su thit k nhng sc chu ti khng ;

S khc bit d thng v ti liu a cht lc ng so vi ban u;

Thn hoc mi ni cc b hng/gy nh hng n vic tip tc p/ng;

Cc ng trc b tri ln khi ng cc cc sau;

Khng ng tip c na do thi gian ng ko di hoc tm ngng;

Bin dng nn ln dn n trt c khi t;

Cc b lch hoc sai v tr;

V..v..

Nhng nguyn nhn trn phi c phn tch, tm cch khc phc, x l.. mi c th ng tip, c khi phi ng th tm ra cng ngh v trnh t ng cc hp l.

V d nguyn nhn gy trt nn c th l:

(1) Ti liu iu tra CCT khng ging thc t hoc sai, lm ngi thit k khng thc hin hoc thc hin sai trong kim ton n nh;

(2) Phng php v cng ngh thi cng khng ng lm tng p lc nc l rng, di tc dng ca p cht + chn ng dn n mi t b trt;

(3) Khng c bin php khng ch tc ng cc;

(4) Xp cc trn mi dc hoc b o chn dc...,

(5) Trong thi gian ng cc, mc nc ca sng gn b t ngt h thp.

Cch phng nga v x l:

(1) iu tra k t nn, gim khong cch gia cc l khoan thm d;

(2) Cn kim ton n nh trong thit k thi cng cc vng b dc;

(3) Gim nh hng chn ng (khoan dn p h cc);

(4) Dng trnh t ng t gn n xa;

(5) Tin thi cng chm;

(6) Gim thiu ti trng thi cng, nh ch gia tng ti mi dc;

(7) Theo di k mi trng xy dng: iu kin thu vn sng bin, ch s thay i mc nc, phng nga vic h thp t ngt mc nc;

(8) Nghin cu vic o h mng su trong khi ng cc, kim ton n nh ca t sau khi ng cc trc khi o mng su;

(9) Theo di o c p lc nc l rng v chuyn v khng ch tin ng cc.

4.1.9. Nghim thu cng tc ng cc

Cht lng h cc cn phi c th hin cc im chnh sau:

(1) Cht lng mi ni gia cc on cc (nu c);

(2) Sai lch v tr cc so vi quy nh ca thit k;

(3) Sai lch v cao u cc: thng khng qu 50 100mm;

(4) nghing ca cc khng vt qu 1% i vi cc thng ng v khng vt qu 1,5% gc nghing gia trc cc v ng nghing ca ba;

(5) B mt cc: nt, mo m, khng bng phng.

Tng hp nhng iu trn trong bng 4.5 (hoc bng 10 ca TCXD 79: 1980)

Bng 4.5. Sai lch cho php v v tr cc ch to sn trn mt bng

(kinh nghim ca Trung Quc)

Loi ccHng mc kim traSai lch cho php (mm)

Cc BTCT c sn, cc ng thp, cc g Cc pha trn c dm mng:

1. Hng vung gc vi trc dm;

2. Hng song song vi trc dm

Cc trong nhm 1-2 chic hoc cc trong hng cc

Cc trong mng c 3-20 cc

Cc trong mng c trn 20 cc:

1. Cc mp ngoi

2. Cc trung gian100

150

100

(1/2 ng knh cc (hoc cnh cc)

1/2 ng knh cc (hoc cnh cc)

1 ng knh (hoc cnh cc)

Cc bn (barette) bng BTCT V tr

thng ng

Khe h gia cc cc

chng thm

chn t100

1%

(20

(25

4.2. Cc khoan nhi

Cc khoan nhi trong nhng nm gn y c p dng nhiu trong xy dng nh cao tng, cu ln v nh cng nghip c ti trng ln. So vi cc ch to sn, vic thi cng cc nhi c nhiu phc tp hn, do phng php v cch gim st, kim tra cht lng phi lm ht sc chu o, t m vi nhng thit b kim tra hin i..

Di y trnh by tm tt nhng ni dung chnh m ngi k s gim st phi nm vng nng cao hn na trch nhim cng nh cht lng gim st.

4.2.1. Yu cu chung

Vic gim st phi da vo cng ngh thi cng v chng trnh m bo cht lng duyt. Trong chng trnh m bo cht lng thi cng ca nh thu cn th hin chi tit 3 khu quan trng sau:

Cng ngh to l (o, ng, khoan, p), cch gi thnh l cc (ng chng sut chiu di cc hoc dung dch) v cht lng l (ng v tr, khng nghing qu tr s cho php, cn lng y l c thi ra sch ng yu cu);

Ch to, lp lng ct thp v gi lng thp n nh trong qu trnh b tng;

Khi lng b tng, cht lng v cng ngh b tng.

V mt qun l v kim tra cht lng cc th chia lm 2 giai on: trc khi thnh hnh cc v sau khi thi cng xong cc.

Ch tiu cn phi kim tra v nh gi gm c:

Cht lng l cc trc khi b tng;

Cht lng v khi lng b tng vo cc;

Lng ct thp trong l cc (s lin tc, nghing lch, tri...);

Cht lng sn phm (tnh trng, kch thc thn cc v sc chu ti ca cc).

Nu dng dung dch st (hoc ho phm khc) n nh thnh l cc th cn phi qun l cht lng dung dch ny v cc mt:

Ch to dung dch t tiu chun ra;

iu chnh dung dch (mt v nht.. .) theo iu kin a cht cng trnh - a cht thu vn v cng ngh khoan c th;

Thu hi, lm giu v s dng li dung dch;

H thng thit b kim tra cht lng dung dch ti hin trng.

4.2.2. Khi lng kim tra v cch x l

V nguyn tc, cng trnh cng quan trng (v ngha kinh t, lch s, x hi.. .), chu ti trng ln, thi cng trong iu kin a cht phc tp, cng ngh thi cng c tin cy thp, ngi thi cng (v thit k) c trnh v kinh nghim t th cn tin hnh qun l v kim tra cht lng c mt (t l %) cao hn, tc l nu ri ro cng nhiu th mc yu cu v qun l v nh gi cht lng cn phi nghim ngt vi mt dy hn.

Mt khc, nh s c trnh by chi tit hn mc ny, cch kim tra bng phng php khng ph hng (NDT) nh nhng thit b kh hin i c nc ta, cho php thc hin vic kim tra cht lng cc ht sc nhanh chng vi gi c chp nhn c. V vy trong tiu chun TCXD 206: 1998 Cc khoan nhi - yu cu v cht lng thi cng a ra khi lng kim tra ti thiu (bng 4.6).

Bng 4.6. Khi lng kim tra cht lng b tng thn cc

(theo TCXD 206: 1998)

Thng s kim traPhng php kim traT l kim tra ti thiu, %

S nguyn vn ca thn cc-So snh th tch b tng vo l cc vi th tch hnh hc ca cc

- Khoan ly li

- Siu m, tn x gama c t ng trc

- Phng php bin dng nh (PIT, MIM), quan st khuyt tt qua ng ly li bng camera v tuyn

- Phng php bin dng ln PDA100

1-2% + phng php khc

10-25% + phng php khc

( 50

4% v khng di 5 cc

m rng hoc ngm ca mi cc vo Khoan ng knh nh (36mm) vng m rng y hoc xuyn qua mi cc2-3 cc lc lm th hoc theo bng 4.7

Cng b tng thn cc-Th nghim mu lc b tng

- Th nghim trn li b tng lc khoan

- Theo tc khoan (khoan thi khng ly li)

- Sng bt ny hoc siu m i vi b tng u ccTheo yu cu ca gim st

35

Ch thch:

1) Thng thng cn kt hp t 2 phng php khc nhau tr ln tin hnh so snh cho mt thng s kim tra nu bng ny. Khi cc c L/D(30 th phng php kim tra qua ng t sn s l ch yu (L-chiu di, D-ng knh);

2) Lp b tng bo v ng knh cc v hnh dng b ngoi ca ct thp c th kim tra ch u cc, khi loi b lp b tng cn pha trn ct u cc.

i vi nhng cng trnh c s lng cc trong mi mng l t v ti trng truyn ln mng ln, kt cu c nhy cao khi ln khng u xy ra, ngi ta yu cu t l t ng kim tra kh nhiu nh trnh by bng 4.7 di y.

Bng 4.7. Quy nh t l % cc cn t sn ng v kim tra i vi cng trnh giao thng

(DTU 13.2, P1 - 212, 9-1992, Php)

(N - tng s cc thi cng, n - s cc trong mt mng tr)

n ( 4n (4

Cch thc tip nhn lc

ca ccNS lng ng

t snS lng cc kim traS lng ng

t snS lng cc kim tra

Cc ng 50/60ng

102/114Thm d thn cc NDTKhoan ly li ti mi ccCc ng 60/60ng

102/114Thm d thn cc NDTKhoan ly li ti mi cc

Ch c ma st( 5010001000100050-1000

Cc b(501000100150-100050-1000

Ma st cc b( 50100( 5010030100( 3050-100( 20

v mi cc(50100( 3050-1002050-100( 2050-100( 10

Ch c mi( 5010010010050-10010050-10050-100( 30

cc(5010050-10050-100( 3050-100( 3050-100( 20

Khng nht thit phi kim tra tt c cc cc c t sn ng. Thng thng ngi ta ch tin hnh kim tra theo mt t l no so vi cc cc t ng, nu thy cht lng tt v t kt qu n nh th c th dng. Nu c nghi vn th phi tip tc kim tra cho ht s cc t ng.

Ngoi ra cng c th da vo s trnh by trn hnh 4.8 thc hin trnh t kim tra t n gin n phc tp theo mc khai thc ng sut cho php v ri ro c th xy ra trong qu trnh thi cng cc.

4.2.3 Kim tra cht lng l cc

Yu cu v cht lng

Cht lng l cc l mt trong cc yu t c ngha quyt nh cht lng cc. Cng vic khoan v dn l cc, sau l cch gi thnh vch l cc l nhng cng on quan trng, nh hng n cht lng l cc tt hay xu. Cc ch tiu v cht lng l cc gm v tr, kch thc hnh hc, nghing lch, tnh trng thnh vch v lp cn lng y l. Trong bng 4.8 trnh by cc thng s nh gi cht lng v phng php kim tra chng.

Bng 4.8. Cc thng s cn kim tra v l cc

Thng s kim traPhng php kim tra

Tnh trng l cc- Kim tra bng mt c thm n ri

- Dng phng php siu m hoc camera ghi chp thnh l cc

V tr, thng ng v su- o c so vi mc v tuyn chun

- So snh khi lng t ly ln vi th tch hnh hc ca cc

- Theo lng dng dung dch gi thnh

- Theo chiu di ti khoan

- Qu di

- My o nghing, phng php siu m

Kch thc l- Mu, calip, thc xp m v t ghi ln nh ng knh

- Theo ng knh, thc xp m v t ghi ln nh ng knh

- Theo ng knh ng gi thnh

- Theo m ca cch mi khoan khi m rng y

Tnh trng y l v su ca mi cc trong t+, dy lp cn lng- Ly mu v so snh vi t v lc khoan, o su trc v sau thi gian gi thnh khng t hn 4 gi (trc lc b tng)

- sch ca nc thi ra

- Phng php qu t ri hoc xuyn ng

- Phng php in (in tr, in dung..)

- Phng php m.

Bng 4.9. Sai s cho php v l ccTiu chun thng ngV tr nh cc

ADSC2% trn sut chiu di cc7,5 cm

FHWA (1998)2% trn sut chiu di cc1/24 ca ng knh cc hoc 7,5 cm

FHWA (1990)1/487,5 cm

ACI+ i vi cc khng c ct thp 1,5% trn sut chiu di cc.

+ i vi cc c ct thp 2% trn sut chiu di cc4% ca ng knh cc hoc 7,5cm

ICE1/757,5 cm

CGS2% trn sut chiu di cc+ 7,5 cm

+ 15 cm i vi cc cng trnh bin

Ch thch:

ADSC: Hip hi cc Nh thu cc khoan nhi M;

FHWA: Cc ng b Lin bang M;

ACI : Vin b tng M;

ICE : Vin Xy dng dn dng Anh;

CGS : Hip hi a k thut Canada.

V tr ca l cc trn mt bng, nghing cng nh kch thc hnh hc ca n thng khng ng vi thit k quy nh, nhng khng c sai lch qu gii hn no . Cc phm vi sai s ny do thit k quy nh theo tiu chun thit k v thi cng cc nhi. Nhng ngay tiu chun ca cc nc khc nhau cng c nhng quy nh cho php sai s khc nhau (xem bng 4.9).

Theo tiu chun ca Trung Quc th yu cu sai s v nghing cao hn nhiu so vi bng 4.9 nh sau: Phi nh hn 1/500 i vi nhng cng trnh i hi cao v thp nht l khng qu 1/100.

Trn c s tham kho cc tiu chun nhiu nc v tnh hnh thi cng thc t Vit Nam, TCXD 206 : 1998 quy nh sai s cho php v l cc nhi nh trong bng 1 ca tiu chun ny.

Khi s dng bng trn nn ch rng: i vi nhng cng trnh i hi cao, s lng cc t hoc c nhng yu cu c bit khc th cn phi gim cc tr s cho php nu trn, c bit l thng ng. V d nh cng trnh cu khu ln, nhp b tng ct thp ng sut trc lin tc, s lng cc l 10 cho mi tr th c th phi quy nh nghing cho l cc khng c qu 1/200.

Ngoi kch thc v v tr hnh hc nh ni trn cn phi m bo lng cn lng y li khng c dy qu cc gi tr sau:

Cc chng ( 50mm;

Cc ma st + chng ( 100mm;

Cc ma st ( 200mm.

Phng php kim tra

1. Kim tra kch thc v tnh trng thnh vch l cc

o ng knh l cc

Thit b o ng knh l cc gm 3 b phn cu thnh: u o, b phn phng i v b phn ghi (hnh 4.9) c th o l cc ng knh ln n 1,2m. Nguyn tc hot ng ca thit b l do c cu co dn n hi ca 4 ng ten u o m lm thay in tr, t lm thay i in p, kt qu ca s thay i c hin th bng s hoc my ghi lu gi. Tr in p biu th v ng knh cc c quan h:

( = (0 +

Trong : ( - ng knh l cc o c, m;(0 - ng knh l cc lc u;

(V - Bin i in p, vn;k - H s m /(;I - Cng dng in, Ampe.

nghing v tnh trng thnh vch l cc Khi thi cng cc trong iu kin c nc ngm v c dng dung dch st gi thnh th tnh trng thnh vch, thng ng v dy lp cn lng ch c my mc mi kim tra c.

Phng php sng m: Nguyn l l da vo hiu ng in p ca tinh th m pht sinh ra sng siu m, thng qua b chuyn i nng lng sng m t u d (pht v thu), ta o c cc i lng:

t = L/C

Trong :

t - thi gian sng m qua mi trng, giy;

L - on ng ca sng truyn qua (m trnh), m;

C - Vn tc ca sng m, m/giy.

Trn hnh 4.10 l thit b o thnh l khoan DM - 686II ca Nht theo nguyn tc sng m ni trn vi su o n 100m v ng knh l n 4m v trn hnh 4.11 l cch lp t v kt qu o.

2. o b dy lp cn lng y l cc

Phng php chu ri: Dng chu hnh cn bng ng nng khong 1kg, c tai buc dy v th chm chm vo l khoan. Phn on mt lp cn lng bng cm gic tay cm dy, dy lp cn l hiu s gia su o c lc khoan xong vi su o c bng chu ny.

Phng php in tr: Da vo tnh cht dn in khc nhau ca mi trng khng ng nht (gm nc +dung dch gi thnh v cc ht cn lng) m phn on chiu dy lp cn lng ny bng tr s bin i ca in tr.

Theo nh lut Ohm:

Trong : V1 - in p n nh ca dng xoay chiu (V);

V2 - in p o c (V);

R - in tr iu chnh (();

Rx - Tr in tr ca t y l (().

Rx ph thuc vo mi trng, Rx khc nhau s ng vi tr in p V2 khc nhau, s c c V2 my phng i. Cch o nh sau: Th chm u d vo l khoan, theo di s thay i V2, khi kim ch V2 bin i t ngt, ghi li su h1, tip tc th u d, kim ch V2, ghi li su h2.., cho n khi u d khng chm c na, ghi li su h3. su ca cc khoan bit l H nn c th tnh chiu dy lp cn lng l:

(H - h1) hoc (H - h2) hoc (H-h3)...

Trn hnh 4.12 a trnh by nguyn l xc nh chiu dy lp cn lng bng phng php in tr.

Phng php in dung: Da vo nguyn l khong cch gia hai cc bn kim loi v kch thc gia chng khng thay i th in dung v sut in gii ca mi trng t l thun vi nhau, sut in gii ca mi trng nc + dung dch gi thnh + cn lng.. c s khc bit, do t s thay i ca sut in gii ta suy c chiu dy lp cn lng. Trn hnh 4.12b trnh by s b o cn lng bng phng php in dung.

Phng php m (sonic): Da vo nguyn l phn x ca sng m khi gp cc giao din khc nhau trn ng truyn sng. u o lm hai chc nng pht v thu. Khi sng gp mt lp cn lng phn x li, ghi c thi gian ny l t1, khi gp y lp cn (t nguyn dng) phn x li, ghi c t2, chiu dy lp cn lng s l:

Trong : h - dy lp cn lng;

t1 v t2 - Thi gian pht v thu khi sng gp mt v y lp lp cn lng, giy;

C - Tc sng m trong cn lng, m/giy.

Tht ra cn lng hnh thnh trong thi gian t lc to l n lc b tng, trng thi ca lp ny t trn xung th lng ( c (ht. Do vy, th no l cn lng cng khng c nh ngha r rng v cng khng c mt b mt cn lng xc nh c th m ch yu da v kinh nghim.

3. iu ch v qun l dung dch gi thnh

Tr trng hp lp t hin trng thi cng cc khoan nhi c th t to thnh dung dch st ra hoc to l v gi thnh bng phng php c ng chng u phi dng dung dch ch to sn gi thnh l cc. Ch to dung dch phi c thit k cp phi tu theo thit b, cng ngh thi cng, phng php khoan l v iu kin a cht cng trnh v a cht thu vn ca a im xy dng quyt nh.

Trong bng 4.10 trnh by cc yu cu v cht lng ca dung dch st lc ch to ban u cn khi s dng c th tham kho bng 4.11 iu ch, qun l v kim tra.

Bng 4.10. Ch tiu tnh nng ban u ca dung dch st (nu dng)

Hng mcCh tiu tnh nngPhng php kim tra

1. Khi lng ring1,05 1,15T trng k dung dch st hoc Bom k

2. nht18 45 sPhng php phu 500/700cc

3. Hm lng ct( 6%

4. T l cht keo( 95%Phng php ong cc

5. Lng mt nc( 30ml/30 phtDng c o lng mt nc

6. dy ca o st1- 3/mm/30 phtDng c o lng mt nc

7. Lc ct tnh1 pht: 20-30 mg/cm210 pht: 50 - 100 mg/cm2Lc k ct tnh

8. Tnh n nh( 0,03 g/cm2

9. Tr s pH7 - 9Giy th pH

Bng 4.11. Ch tiu k thut ca dung dch st bentonite trong s dng (kinh nghim ca Nht)PhngaCh tiu k thut ca dung dch st

php khoantngKhi lng ring nht

(Pa.S)Hm lng ct, %T l cht keo, %Mt nc

(ml/30 min.) pH

Tun hont st1,05-1,2016-22( 8-4( 90-95( 258 - 10

thun, khoan dpt ct

t sn

Cui dm1,2-1,4519-28( 8-4( 90-95( 158 - 10

Khoan y,t st1,1-1,218-24( 4( 95( 308-11

khoan ngomt ct si sn1,2-1,422-30( 4( 95( 208-11

Khoant st1,02-1,0616-20( 4( 95( 208-10

tun hont ct1,0-1,1019-28( 4( 95( 208-10

nghcht sn1,1-1,1520-25( 4( 95( 208-10

4.2.4. Kim tra lng thp v lp t ng o

Lng ct thp ngoi vic phi ph hp vi yu cu ca thit k nh quy cch, chng loi, phm cp que hn, quy cch mi hn, di ng hn, ngoi quan v cht lng ng hn.. cn phi ph hp yu cu sau y:

Sai s cho php trong ch to lng ct thp:

C ly gia cc ct ch ( 10mm;

C ly ct ai hoc ct l xo ( 20mm;

ng knh lng ct thp ( 10mm;

di lng ct thp ( 50mm;

thng ca lng thp ( 1/100;

Sai s cho php ca lp bo v ct thp ch ca lng thp:

Cc b tng di nc ( 20mm;

Cc khng b tng di nc ( 10mm.

Cc ng o c lm bng thp hoc nha PVC (c kh nng gi ng v tr khi vn chuyn v b tng) c ni vi nhau bng mng xng (khng hn) m bo khng lt nc vo trong ng v trong ng y nc sch. Cc ng ny phi t song song v a xung ti y lng thp (hnh 4.13b), c c nh cng vo lng thp v c bt kn hai u. Nt di va m bo cho u di kn nc tuy vn cho php sau ny khoan thng c khi cn thit. Dng mt ng dng kim tra s thng sut ca ng o nhm bo m vic di chuyn cc u d trong ng s d dng. u ng pha trn c chun b sao cho cao hn mt b tng ca u cc t nht bng 0,2 m. ng knh trong ti thiu ca ng o l 40mm, khong cch gia cc ng o i vi mi cu kin mng nm trong khong 0,30m - 1,50m (hnh 4.13a).

i vi cc c tit din ngang hnh trn, ng knh D (hnh 4.13b) s lng ng d tnh nh sau:

Hai ng nu D ( 0,60m;

Ba ng nu 0,60m ( D ( 1,20m;

t nht 4 ng nu D ( 1,20m.

4.2.5. Kim tra cht lng b tng v cng ngh b tng Thi cng b tng cho cc khoan nhi trong t c nc ngm phi tun theo quy nh v b tng di nc v phi c s qun l cht lng b tng khi bng cc thng s sau y:

st (cho tng xe );

Ct liu th trong b tng khng ln hn c ht theo yu cu ca cng ngh;

Cht lng ximng;

Mc hn hp b tng trong h khoan;

su ngp ng dn b tng trong hn hp b tng;

Khi lng b tng trong l cc;

Cng b tng sau 7 v 28 ngy.

Cn thit lp cho tng cc mt ng cong b tng quan h gia lng thc t ca b tng vo cc v th tch hnh hc (l thuyt) ca cc qua tng su khc nhau. ng cong ni trn phi c t nht 5 im phn b trn ton b chiu di cc. Trng hp b tng sai lch khng bnh thng so vi tnh ton (t qu hoc nhiu qu 30%) th phi dng cc bin php c bit thm nh tm nguyn nhn v phng php thch hp.

Ngoi iu kin v cng , b tng cho cc khoan nhi phi c st ln m bo s lin tc ca cc (bng 4.12) v phi kim tra cht ch trc khi , v lng ximng thng khng nh hn 350kg/m3 b tng.

Bng 4.12. st ca b tng cc nhi (theo TCXD 205-1998)iu kin s dng st

t do trong nc, ct thp c khong cch ln cho php b tng dch chuyn d dng7,5 12,5

Khong cch ct thp khng ln, cho php b tng dch chuyn d dng, khi ct u cc nm trong vng vch tm. Khi ng knh cc nh hn 600 mm10 17,5

Khi b tng c di nc hoc trong mi trng dung dch st ben-to-nt qua ng (tremie) ( 15

Vic thi cng b tng cho cc thng tin hnh cng lc vi vic khoan to l cho cc cc khc. Nhng chn ng rung s c nh hng khng tt n qu trnh ng cng ca b tng ti.

Do vy cn phi hn ch tc hi chn ng trong mi trng t bng thng s vn tc chuyn ng cc i ca cht im nh trnh by trong bng 4.13.

Bng 4.13. Mc vn tc chn ng cho php i vi b tng

Tui ca b tngVn tc cc i ca cht im (mm/s)

0-4 gi

4 - 24 gi

1 - 7 ngyKhng hn ch

5, tt nht l khng c chn ng

50

4.2.6. Kim tra cht lng thn cc

Cht lng ca cc sau khi xong b tng thng th hin bng cc ch tiu sau:

- nguyn vn (s ton khi ca cc);

-S tip xc gia mi cc v t nn;

-Sc chu ti ca cc.

Mt s phng php kim tra thng dng gm c:

4.2.6.1. Phng php siu m truyn qua

Vic thm d bng siu m mt cu kin mng bng b tng c t trc t nht hai ng o, song song, bao gm cc bc (hnh 4.14) nh sau:

Cho mt u d (u pht) vo trong mt ng o y nc sch v pht sng siu m truyn qua b tng ca cu kin mng;

Cho mt u d th hai (u thu) vo mt ng khc cng y nc v thu sng siu m ny cng mc su ca u pht sng; khi cn (v d lc d ln l hng) c th hai u thu pht khng cng mt mc su nhng khong cch cho ny phi c xc nh.

Trn sut dc chiu cao cc ng, o thi gian truyn sng siu m gia hai u d;

Ghi li s thay i bin ca tn hiu nhn c.

Mt s cch nh gi kt qu kim tra

Phn tch v nh gi kt qu kim tra do chuyn gia t vn c trnh chuyn mn cao thc hin v chu trch nhim trc ngi t yu cu.

nh gi cht lng b tng ca cu kin mng thng phi da vo cc c trng m o c (nh vn tc, bin , nng lng, thi gian truyn.. ) hoc vo hnh dng ca sng m c ghi li trn mn hnh.

Trong bng 4.14 trnh by cch nh gi cht lng b tng theo mt s c trng sng siu m v trn hnh 4.15 trnh by v d hnh dng sng m i vi cc c khuyt tt.

Bng 4.14. nh gi cht lng b tng thn cc khoan nhi theo c trng sng mCht lngThi gian truynBin Hnh dng sng

Ttu n khng t binKhng b suy gim lnBnh thng

Phn tngTng lnC suy gimBin i l

Nt gyTng t binSuy gim r rtBin i l

Phng php kim tra cht lng b tng bng siu m khng cho thng tin v cng (hoc cc c trng c hc khc nh mdun n hi, h s Poisson). Mun c c cc thng tin ny, cc cng trng ln (vi khi lng b tng nhiu) phi tin hnh xy dng cc tng quan gia c trng c hc no (cn dng n trong kim sot cht lng) vi c trng m.

Trong trng hp mun c nhng s liu s b v cht lng hoc cng b tng thng qua cc c trng sng m c th tham kho bng 4.15 v 4.16.

Bng 4.15. nh gi cht lng b tng thn cc bng vn tc xungTc xungnh gi

ft/sm/scht lng

Trn 15.000

12.000 - 15.000

10.000 - 12.000

7.000 - 10.000

Di 7.000Trn 4570

3660 - 4570

3050 -3660

2135 - 3050

Di 2135Rt tt

Tt

Nghi ng

Km

Rt km

Bng 4.16. Cp cht lng b tng thn cc theo vn tc siu m

(kinh nghim Trung Quc)

Vn tc m (m/s)( 20002000-30003000-35003500-4000(4000

Cht lng b tngRt kmKmTrung bnhTtRt tt

Cp cht lng ca ccVIVIIIIII

4.2.6.2. Phng php ng v phng x (tia gamma)

kim tra cht lng v pht hin khuyt tt trong b tng mng, ngi ta s dng ngun ng v Cs-137 (hoc Cr-60) kho st c trng c bn ca vt liu.

Khi truyn qua b tng, cng bc x b gim yu do s hp th ca b tng. V l thuyt chng minh c: mt b tng thay i ph thuc tuyn tnh vi logarit ca cng bc x I thu nhn theo phng trnh:

( = A + B ln I

Trong : A, B c xc nh trn mu chun trong phng th nghim ph thuc vo cng bc x ban u Io, chiu dy ca mng d, h s suy gim ( v mt s tham s khc.

Khi chiu dy d khng i th vic xc nh ( ch hon ton ph thuc vo vic pht v thu phng x.

T mt ( v s phn b ca n s xc nh c cc khuyt tt v ng nht ca b tng mng.

4.2.6.3. Phng php bin dng nh (PIT)

Phng php th bng bin dng nh da trn nguyn l phn x khi tr khng thay i, ca sng ng sut truyn dc theo thn cc, gy ra bi tc ng ca lc xung ti u cc.

Nguyn l cng tc ca thit b dng trong phng php ny c trnh by v nguyn tc hnh 4.16 vi trnh t thc hin ch yu nh sau:

Dng ba tay c lp b cm bin lc, ng ln u cc;

Ghi li hnh sng lc xung lm iu kin bin;

Lc cn mt bn ca cc m phng theo lut tt dn tuyn tnh, lc cn mi cc m phng theo l xo v b phn tt dn;

Dng cc tham s gi nh ca t tnh bng phng php lp v iu chnh tr khng sao cho hnh sng tnh ton tng i khp vi hnh sng o c t thc t, t phn on v tr v ln khuyt tt.

Ngoi phng php bin dng nh PIT theo trng phi ca M, Vin c hc Vit Nam c h thng thit b MIMP-15 kim tra cht lng cc theo nguyn l tr khng c hc (MIM) ca ngi Php theo tiu chun Php NF 160-94.

4.2.6.4. Phng php bin dng ln (PDA)

Phng php th bng bin dng ln (theo m hnh E.A. Smith hoc theo Case) l phng php o sng ca lc u cc v sng vn tc (tch phn gia tc) ri tin hnh phn tch thi gian thc i vi hnh sng (bng cc tnh lp) da trn l thuyt truyn sng ng sut trong thanh cng v lin tc do lc va chm dc trc ti u cc gy ra.

Nguyn l ca phng php nh trnh by trn hnh 4.17.

Cc u o gia tc v ng sut c gn cht vo cc, cc tn hiu t u o c truyn t cc nh nng lng ln nht ca ba, ng sut ko nn ln nht ca cc, sc chu ti Case-Goble, h s nguyn vn.. c quan st trong qu trnh th nghim trn h thng my phn tch v hin th.

Cc s liu hin trng c phn tch bng chng trnh CAPWAP (hoc Case) nhm xc nh sc chu ti tng cng ca cc, sc chng ma st ca t mt bn v mi cc cng mt s thng tin khc v cng ngh ng v cht lng cc.

Kt qu kim tra cht lng cc bng phng php bin dng ln c x l bng phn mm chuyn dng v c dng nh trnh by trn hnh 4.18.

C th phn on mc khuyt tt (c tnh cht nh tnh) ca cc theo h s hon chnh ( (theo bng 4.17).

Bng 4.17. Phn on mc khuyt tt ca thn cc

H s (1,00,8-1,00,6-0,8( 0,6

Mc khuyt ttHon chnhTn tht tPh hngNt gy

Nh lu trn y, cc phng php kim tra khng ph hng va nu c nhng hn ch ca n. Do c tin cy cao hn trong vic xc nh cc khuyt tt ca cc thng phi dng khng t hn hai phng php khc nhau cng kim tra v xc nhn, khng vi tin vo mt phng php no khi c nhiu nghi ng v kt qu. C th khng nh, phi dng cc phng php trc gic tuy tn km v cng knh nh khoan ly mu hoc o khi iu kin cho php.

Trong bng 4.18 v 4.19 tm tt nu mt s u v nhc im cng nh phm vi p dng ca cc phng php kim tra ni trn.

Bng 4.18. Cc phng php truyn qua trc tip (tia gamma hoc siu m)Phng php kim tra bng siu m truyn quaPhng php kim tra bng gamma truyn qua

Nguyn tc v iu kin p dng-o sng siu m truyn qua cc ng t sn hoc cc l khoan ly mu.

-Cc dao ng c truyn t mt ng khc cng cao o thi gian n v bin dao ng-o s phng x gia cc ng t sn hoc cc l khoan ly mu.

-Ngun phng x v u thu trong cc ng gn nhau hoc i din nhau c y nc. Vng mt thp s lm tng photon trn u o.

u im-Tng i nhanh

-Xc nh c khuyt tt gia cc ng kh chun

-Khng b hn ch su

-Xem kt qu ngay trn mn hnh-Tng i nhanh

-Xc nh c khuyt tt gia cc ng kh chun

-Khng b hn ch su

-Xem kt qu ngay trn mn hnh

Nhc im-Phi t trc cc ng hoc phi khoan l

-Kh xc nh c khuyt tt gn mt bn ca cc-Phi t trc cc ng hoc phi khoan l

-C th gy nhim phng x

-Khong cch ln nht gia cc ng l 80cm.

ng dng-Kim tra ng cht ca b tng hoc xc nh bt k khuyt tt no trong cc-Kim tra ng cht ca b tng hoc xc nh bt k khuyt tt no trong thn cc

Bng 4.19. Cc phng php th ng b mt (PIT, MIM, PDA)Phng php th ng bin dng nh (g - PIT, MIM)Phng php th ng bin dng ln (PDA)

Nguyn tc v iu kin p dng-o thi gian truyn sng dc trong b tng.

-Dng ba g vo u cc truyn sng nn i xung gp mi cc hoc bt k khuyt tt no s phn x li b mt.

-Vic phn tch s tin hnh sau-o vn tc v bin dng u cc.

-Dng ba ri t do trn u cc gy ra chuyn dch cc vo trong t

-Dng l thuyt phng trnh truyn sng phn tch

u im-Khng cn chn ng trc

-Thit b gn nh xch tay

-Nhanh-Khng cn chn ng trc

-Thit b gn nh xch tay

-Nhanh

Nhc im-Khng xc nh c ng knh cc

-Khng xc nh c cc khuyt tt trong phm vi 30cm u cc hoc chiu di ln hn 30 ln ng knh-Phi c qu ba ri nng v gy va p trn u cc khoan nhi

-Vic chun b th rt phc tp v i hi s cn thn cao.

ng dng-Kim tra s b tnh ng nht ca b tng v xc nh s b khuyt tt trong thn cc-Xc nh kh chnh xc v tr v mc khuyt tt trn thn cc.

-Xc nh sc chu ti ca cc (phn b ma st thnh bn+sc chng mi)

-Xy dng c biu quan h ti trng chuyn v.

4.2.7. Kim tra sc chu ti ca cc

Sc chu ti ca cc l thng s quan trng v c ngha nht phn nh cht lng ca cc thi cng. Vic th cc xc nh sc chu ti ca n thng l cng vic tn km v khng phi bao gi cng c th thc hin c cho nhiu loi cc ti cng trng.

Th nghim bng phng php ng khi dng cc cng thc ng quen bit ca Gerxevanov v Hiley l iu m nh thu thng p dng lu nay, ch c iu l i vi cc nhi ng knh ln, phng php th ng va ni t ra khng tin cy.

Th nghim bng bin dng ln PDA tuy l mt cng c kh hin i v c dng rng ri cc nc pht trin nhng cng ch thch hp cho cc ng hoc cc nhi ng knh nh.

1. Phng php th cc bng nn tnh c xem l phng php kinh in v ng tin cy tuy rng khi so snh cc phng php nn tnh khc nhau chng t rng chng thng cho cc kt qu khng ging nhau. iu ph thuc vo phng php gia ti, quy c v ln ng vi ti trng gii hn khc nhau v cch xc nh sc chu ti gii hn khc nhau. Vy, trnh xy ra nghi ng v tranh chp cn phi xc nh quy trnh th tnh cc trong chng trnh kim tra cht lng ca mnh trn c s la chn mt trong cc tiu chun nh TCXD 88-82 (Vit Nam, sp sot xt li), ASTM D1142-81 (M) hoc CP 2004 (Anh).

Dng i trng (qu nng, vt liu xy dng, bao ct) vi h thng kch thu lc hoc dng phng php neo vi h thng kch thu lc l cch thng dng hin nay trong th tnh. Trn hnh 4.19 trnh by h thng thit b neo ca hng BAUER (CHLB) c th tnh cc nhi ng knh 1200mm, di 18,50m vi ti trng 1700 tn ln 12,1m ti A rp xut.

2. Phng php th tnh cc c gn thit b o lc v chuyn v

Quanh thn cc theo chiu su, thng tin thu c gm: Lc Qi, chuyn v (i cc su khc nhau Li ca cc. y l phng php do Hip hi th nghim vt liu ca M (ASTM) ngh. S cc c gn thit b o nh trnh by trn hnh 24 v quan h Qi v (i c th biu din:din:

Trong :

A, E - ln lt l din tch tin din v mdun n hi ca cc;

(i - chuyn v o c ca cc su Li;

Q - cp ti trng tc dng ln u cc.

Cp ti trng Q c th tin hnh nh th tnh truyn thng v kt qu thu c khng ch l chuyn v v lc tc dng u cc m ch yu l phn b ma st quanh thn cc theo chiu su v phn lc mi cc, iu ny c ngha quan trng trong thc t tnh ton v kim tra sc chu ti ca cc.

i vi cc ng, thit b o c gn trn mt ngoi ca cc, cn i vi cc nhi, gn thit b trc khi b tng.

Nh kt qu o ca phng php ny cho php xc nh hp l chiu di ca cc cng nh vic tnh ln (t p lc mi cc) s chnh xc hn so vi cc phng php th truyn thng.

3. Phng php th hin i

Khi cc nhi c ng knh v chiu di ln vi sc chu ti hng ngn tn th phng php th tnh ni trn khng th thc hin c. Hn na khi nhng cc ny gia sng hoc ngoi bin th vic cht ti hoc neo l phng php khng c tnh kh thi. Do vy ngi ta tm phng php khc th sc chu ti ca cc.

Phng php hp ti trng OSTERBERG

Nguyn l: Dng mt (hay nhiu) hp ti trng OSTERBERG (hp s lm vic nh kch thu lc) t mi khoan cc nhi hoc 2 v tr mi v thn cc trc khi b tng thn cc. Sau khi b tng cng tin hnh th ti bng bm du to p lc trong hp kch.

Theo nguyn l phn lc, lc truyn xung t mi cc bng lc truyn ln thn cc, ngc li vi lc ny l trng lng cc v ma st t chung quanh. Vic th s t n ph hoi khi mt trong hai ph hoi xy ra mi v quanh thn cc. Da theo cc thit b o chuyn v v o lc gn sn trong hp OSTERBERG s v c cc biu quan h gia lc tc dng v chuyn v mi cc v chuyn v thn cc. Tu theo trng hp ph hoi c th thu c mt trong hai dng biu quan h ti trng chuyn v c dng gn ging nh biu P-S trong th tnh truyn thng. Phng php ny ph hp vi cc cc c sc chng cho php thnh bn v mi tng ng nhau, nu khng, phi c tnh t hp p lc ti nhiu tng trong thn cc.

Phng php th tnh ng STATNAMIC

Nguyn l: t mt thit b dng ng c phn lc v i trng ln u cc. Thng qua vic t nhin liu rn trong bung p lc ca ng c s to nn mt p sut y khi i trng ln pha trn ng thi s gy ra mt lc tc dng ln u cc theo chiu ngc li. o chuyn v ca cc di tc dng ca lc n v cc thng s bin dng + gia tc u cc s xc nh c sc chu ti ca cc (hnh 4.22).

Cc s liu v quan h ti trng-chuyn v ca cc c xc nh bng hp ti trng v u o laser gn sn trong thit b STATNAMIC. Trn hnh 4.23 trnh by cu to ca thit b ny.

Trong phng php STATNAMIC ngi ta xc nh c gia tc a ca khi phn lc (F12 = ma) dch chuyn ln pha trn ln gp 20 ln gia tc ca cc dch chuyn xung pha di (F21 = -F12). Nh vy trng lng ca khi phn lc ch cn bng 1/20 i trng d kin trong th tnh to nn c mt lc ln gp 20 ln lc truyn ln u cc. Nh vic th ti bng STATNAMIC s gim rt nhiu v quy m v chi ph so vi th tnh nhng kt qu t c rt gn vi phng php tnh.

STATNAMIC c pht trin t nm 1988 vi ti trng t n 0,1MN. n 1994 c thit b th nghim n 30MN. Cc nc M, Canada, H Lan, Nht Bn, c, Israel v Hn Quc dng phng php ny. Nm1995 t vn Anh ACER ngh dng phng php ny th cc ng thp ti cng cngten Tn Thun (thnh ph H Ch Minh) vi ti trng 3MN nhng cha c pha Vit Nam chp thun.

4.2.8. Mt s h hng thng gp trong thi cng cc khoan nhi

Cc h hng thng gp trong thi cng cc khoan nhi rt a dng do nhiu nguyn nhn khc nhau. Trong bng 4.20 trnh by nhng dng h hng chnh.

y cn lu n mt s nguyn nhn chung gy ra cc km cht lng thng xy ra khu khoan ri dn l v khu b tng.

Cc nguyn nhn bao qut thng l:

-Do km am hiu mt phn hay ton b bn cht ca t nn v iu kin a cht thu vn ca a im xy dng;

-Do kim tra khng y trn cng trng ca ch u t hay nh thu v khng c hoc thiu t vn gim st c trnh chuyn mn, kinh nghim v t cht cn thit;

-Do hp ng quy nh qu eo hp hoc k hoch thi cng vi tin khng thch hp cho nhng cng vic cn phi cn thn;

-Do thiu kh nng hoc tnh cu th ca nh thu khi thi cng nhng cng vic qu phc tp;

-Sau cng l do vic hon thnh mt cc bao gm mt s thao tc n gin hp thnh nhng nhng ngi thc hin thiu tinh t v khng c nhng k xo cn thit (v t kinh nghim) mc d h c la chn kh k nhng vn khng lm ch tt.

Bng 4.20. Cc h hng c th gp cc khoan nhi. Phng php xc nh

McLoi h hngNguyn nhn c thH hng mt chH hng nhiu ch

1Sai v tr lch tmnh v sai v thn cc khng thngQuan st v o cQuan st v o c

2t gy chnThit b thi cng va phi nh ccTh bng siu m hoc g bng phng php PIT, MIN..Kim tra bng siu m hoc gamma trong cc ng chn sn hoc cc l khoan nm ngoi lng thp

3Thn phnh ra hoc tht lii qua vng t xpPhi hp kim tra cht lng bng quan st vi mt hoc t hp cc phng php NDT thng dngNh mc 2

4C hang hcDo khoan qua ct trong nc khng c ng vch hoc dng dung dchNh mc 3Nh mc 2

5Mi cc xp Do vch l hoc khng lm sch hon ton yPhi hp kim tra cht lng bng quan st vi kim tra siu m hoc gamma trong cc ng qua y cc

6Thu knh ct nm ngangDo ng b tng b ri khi b tngNh mc 3Nh mc 2

7H hng ngoi lng thpDo st ca b tng thp hoc ct thp qu dyNh mc 3Kim tra cht lng bng quan st kt hp bng siu m hoc gamma trong cc ng hoc cc l khoan nm ngoi lng thp

8R t ong hoc mt va hoc to thnh hang trong b tngDo lng nc khng cn bng hoc b tng trc tip vo ncNh mc 3Nh mc 2

9Ln cc mnh vnDo khng lm sch mn khoano cn thn khi lng b tng cng vi nh mc 3o cn thn khi lng b tng cng vi nh mc 2

cng on to l, nhng h hng c th l do hu qu ca:

-K thut thit b khoan hoc loi cc la chn khng thch hp vi t nn;

-Mt dung dch khoan t ngt (khi gp hang cc-t hoc thch cao) hoc s tri ln nhanh chng ca t b st l vo thnh l khoan, 2 s c ny d to thnh ngoi d kin thit k;

-S qun l km khi khoan to l do s dng loi dung dch c thnh phn khng tng ng vi iu kin t nn v cng ngh khoan hoc kim tra khng tt s bin i thnh phn dung dch (nht l mt v nht);

-S nghing lch, bp bnh ca h thng my khoan l khi gp m ci hoc lp nghing. Nhng sai lch v tr kiu ny ph thuc vo hiu qu v vo s kim sot ca thit b dn hng, iu t dn n tnh trng khng tn trng thng ng ca cc v vt qu nghing d kin (cho php) ca thit k;

-Lm sch mn khoan trong l cc khng tt, y l khoan c lp cn dy, sinh ra s tip xc xu vi lp t chu lc ti mi cc, lm nhim bn v gim cht lng b tng;

cng on b tng vo cc thng gp nhng sai st do mt s nguyn nhn sau:

-Thit b b tng khng thch hp hoc tnh trng lm vic xu;

-Ch o cng ngh b tng km: sai st trong vic cung cp b tng khng lin tc, gin on trong khi , rt ng qu nhanh;

-Cp liu khng u s dn n lng b tng chim ch ban u khng do qu nhanh;

-S dng b tng c thnh phn khng thch hp, st hoc tnh do khng v d b phn tng.

Mt s nguyn nhn khc lm hng cc hoc lm gim sc chu ti ca cc c th l:

-S lu thng mch nc ngm lm tri cc b b tng ti;

-S sp xp li t nn do chn ng s dn n s suy gim ma st ca mt bn hoc sc chng mi cc;

-Thi gian dn cch ko di qu quy nh gia khu khoan to l v b tng vo cc gy ra s st l vch l khoan v lng ng cn qu dy y;

-S dng khoan a cht i vi cc c ng knh qu b, lc b tng khng c thi gian chim ch trong l cc s gy ra cho cc b gin on thn hoc xp mi.

Nh vy, 3 nhm nguyn nhn ni trn (qun l v trnh , trong lc to l v giai on b tng) thng chim t trng ng k gy ra s c cht lng cho cc khoan nhi. Thng ngi thi cng d kin trc cc tnh hung, chun b sn bin php x l hoc khc phc, nhng iu khng phi lc no cng tin liu ht, nn kinh nghim trong v ngoi nc u ch ra rng phi ly vic gim st cht ch v ghi chp y l cch bo m cht lng cc tin cy nht.

4.2.9. Nghim thu cc khoan nhi v i theo TCXD 206: 1998 trong cn ch cc ni dung chnh sau y:

Phn to l:

-Mc nc ngm hoc mc nc sng bin;

-Tc v qu trnh thi cng to l;

-Kch thc v v tr thc ca l cc (mc lch tm v thng ng);

-ng knh v su lm l, ng knh v di ca ng chng hoc ng nh v tng mt; di thc t ca cc, thng ng ca cc;

-Bin bn kim tra theo bng 4.5, 4.6, 4.9,4.10, s c v cch x l (nu c).

Phn gi thnh v c thp:

-Loi dung dch gi thnh v bin php qun l dung dch;

-Thi gian thi cng cho mi cng on;

-B tr ct thp, phng php ni u v cao on u phn b tng;

-Bin bn kim tra theo bng 4.9 v 4.10;

-Nhng trc trc v s c (nu c) v cch x l;

-Loi th v s ngi tham gia thi cng.

Phn kim tra cht lng cc:

-Bo co kim tra cht lng cc v sc chu ti ca cc n;

-Bn v hon cng mng cc khi o h mng n ct thit k v bn v ct cao u cc;

Nghim thu i cc gm cc ti liu sau y:

-Bin bn thi cng v kim tra ct thp b tng i cc;

-Bin bn v ct neo gia u cc vi i cc, c ly mp bin ca cc mp i, lp bo v c thp i cc;

-Bn ghi v dy, b di v b rng ca i cc v tnh hnh ngoi quan ca i cc.

5. Thi cng h o

Khi thit k v thi cng h o(su hn 2 mt) trong khu xy dng ( gn hoc pha di cng trnh c) cn ch cc tnh hnh sau y:

Ln v bin dng ca nh gn h o;

S st l thnh h do khng chng hoc thit k bin php thi cng khng ng;

Cc gii php thng p dng trong trng hp ni trn l:

ng tng bng bn thp ngn nga bin dng nh bn cnh hoc bo v thnh h o hoc tng trong t.

Gia c nn t bng silicat hoc ximng, hay cc ximng t, cc b tng;

Dng neo gi thnh, bo v h mng.

Vic la chn bin php no trong s ni trn l ph thuc vo iu kin a cht cng trnh, a cht thu vn, su h mng v cc iu kin a phng khc.

Ngoi cc bin php thi cng ni trn, khi no trong t yu c mc nc ngm cao ngi thit k v thi cng cn phi ch n cng tc quan trc a k thut quanh h o v c cng trnh ln cn, m y ch yu l:

t ng o theo di ng thi mc nc ngm (c hoc khng c bin php h mc nc ngm). iu ny ni k trong mc 4 ca TCXD 79:1980;

t ng o s thay i p lc nc l rng phng nga thnh h mng b trt;

t ng o chuyn v ngang (inclinomet) kim sot s bin dng ca t quanh h mng v ca bn thn thnh c (cc vn thp, cc c, tng b tng...); c khi phi o ni lc trong cc thanh chng;

t mc o ln v nt ca phn cng trnh bn cnh tip gip vi h mng.

Vic quan trc a k thut ni trn (geotechnical instrumentation) thng do n v chuyn mn thc hin. Trn c s quan trc s ch o, iu khin qu trnh o h mng cho an ton v khng gy s c. Nhng s c thng gp trong thi cng o mng c trnh by trn hnh (5.1).

Tu theo tnh cht t, su ca h mng v v tr mc nc ngm m vch h mng l nghing hay thng ng. Trong t t m cho php h o c vch thng ng, khng cn chng nu thi gian o h ny khng ko di v khi khng c cng trnh gn hoc khng gn h mng tng lai, theo qui nh sau:

t hn ln, si sn, ct do... khng su qu 1m;

ct cng, ct v st do mm... khng su qu 1,25m;

st v st do cng...

khng su qu 1,5m;

st v st na cng..

khng su qu 2m;

st v st cng..

khng su qu 3m.

Trong nhng h mng c su b hn 5m c th theo cc gii php chng trnh by hnh 5.2 nu a im khng cho php o c mi nghing, cn khi cho php o c mi nghing th c th theo bng 5.1 di y:

Bng 5.1. dc ln nht ca vch h mngt dc ln nht vch h mng (cao/ngang) su, m n

1,535

t p

t ct, si, t m (khng bo ho)

t st:

ct

st

St1: 0,67

1: 0,5

1: 0,25

1: 0

1: 01:1

1:1

1: 0,67

1: 0,25

1: 0,51: 1,25

1:1

1: 0,85

1: 0,5

1: 0,5

Ngoi phng php chng gi thnh h mng bng cc bn thp (hin nay c loi bng nha ct thu tinh) nh nhiu ngi bit, ngi ta cn dng cc ximng t hoc cc b tng ct cng chng gi thnh h mng (hnh 5.3) v gi n nh cho hng cc c (1 hoc nhiu hng)) phi chng bng cc thanh chng bn trong hoc neo gi ra xung quanh theo trnh t o su dn vo t. Neo cc/tng c hay cc cng trnh chu nh/lt khc l mt cng ngh ring, rt a dng (thit b, cu to) c nhiu cng ty ni ting trn th gii thc hin (5.4).

Mt bin tng khc ca cc ximng/b tng khi dng bo v h mng su v lm lun chc nng mng ca cng trnh bn trn, hin nay thng dng phng php tng trong t b tng ti ch hoc lp vo ho o bng cc mng tng c sn (hnh 5.5).

Yu cu ca cng ngh o v phng php gi thnh bng dung dch bentonite cng tng t nh trnh by phn cc khoan nhi, khi cn phi tm hiu su hn v cng ngh tng trong t ny (mt s cng ty nc ngoi thi cng tng hm nh cao tng thnh ph H Ch Minh).

Cc phng php chng gi thnh h mng ni trn c phm vi p dng ca n (bng 5.2).

Bng 5.2. Phm vi p dng c hiu qu cc phng php o mng su

(kinh nghim ca Ucraine)

iu kin nn tDin tch cng

trnh (m2) su (m) vi phng php xy dng ngh

H o h n suGing chm su hnTng trong t su hn

Ct, m t nhin75

450

12505

6,5

11,55,5

8,5

165

6,5

11,5

st m t nhin75

450

12505

6

136

10

8,55

6

13

Ct bo ho nc75

450

12505

5

75

5

105

5

7

st bo ho nc75

450

12505,5

9

176

11,5

205,5

9

17

Cng nn thy rng hin nay, vi thit b hin i, trong t st mm hoc nn ng nht, ngi ta thi cng tng trong t su n 30-40m hoc hn. Tuy vy cng cn thy rng, phng php ny khng thch dng trong cc trng hp sau y:

t hn ln, c nhiu hang hc gia cc tng khng c lp nht bng t ht nh, do dung dch st s chy mt vo trong t v h o khng th thnh cng c;

Nn cac-t c nhiu hang hc ln v dung dch st b chy mt v do trn y trn h khng cng su cn thit v iu dn n ph hoi nhanh chng thnh h mng;

Bn nho, c bit l khi loi bn ny nm ngay trn mt t;

t p trn vng mi san nn hay vng t c gm nhiu vt cng bng thp nh ng ray, dm hoc l ch giao nhau ca cc loi cng trnh ngm v li k thut m vic di chuyn chng khng th thc hin c;

tng cng nu chng ln hn 150-200mm.

Cng nn ca b tng dng cho tng trong t ti ch (theo GOST 4798-68) l 250-300 cn cho tng c sn: mc 300. y bng b tng ct thp mc 200-250.

Khi tng trong t c chc nng chng thm th tu thuc vo gradient thu lc (5-10, 10-12 v hn 12) m dng b tng c mc chng thm tng ng B6, B8 v B12.

Khi khng c s liu th nghim, trong thit k s b c th dng mc b tng ch to t ximng pooclng nh bng 5.3.

Bng 5.3. Mc b tng dng cho xy dng tng trong tMc b tng

Theo cng nn

M200

M350

M300Theo chng thm

B6

B8

B12

Vic kim tra cht lng b tng ca tng thc hin theo nhng phng php dng trong thi cng cc khoan nhi, y thm ch tiu l tnh chng thm nc, c bit l cc mi ni/mch ngng thi cng.

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

PAGE 58Lp chuyn T vn gim st xy dng

_1014206475.unknown

_1014207252.unknown

_1014205588.unknown

_1012650681.unknown