tai lieu dcct

Khoa Cng Trnh B Mn K thut c s

Ti liu a cht cng trnh GV: Phm Th Thy An

CHNG I :

M U

I.1. a cht cng trnh v nhim v ca n I.1.1 nh ngha : a cht cng trnh l mn hc nghin cu iu kin a cht xy dng cc cng trnh khc nhau v a vo s dng c hiu qu v n nh. Cc iu kin CCT 1. iu kin a mo. 2. iu kin cu trc a cht 3. iu kin cc tc ng a cht 4. iu kin a cht thy vn 5. iu kin vt liu xy dng.

I.1.2-

Nhim v ca a cht cng trnh :

Xc nh cc iu kin a cht ca khu vc xy dng, so snh, la chn v tr thch hp cho cng trnh. Nu ln cc iu kin thi cng, d on cc hin tng a cht c th xy ra khi thi cng hay s dng cng trnh. ra cc bin php phng nga v ci to cc iu kin a cht khng c li cho cng trnh. Cho bit kh nng cung cp vt liu xy dng ti a phng phc v cho xy dng cng trnh.

I.2. Ni dung ca a cht cng trnha cht cng trnh nghin cu nhng vn c bn sau : Nghin cu t lm nn thin nhin, mi trng v vt liu xy dng cho cc cng trnh Nghin cu cc hot ng a cht hin i (hin tng trt t, t chy, xi mn, cact, phong ha) ,tm hiu nguyn nhn pht sinh v iu kin pht trin ra bin php x l trong khi xy dng, s dng v khai thc cng trnh. Nghin cu nc di t khc phc cc kh khn do nc gy ra trong khi thit k v thi cng cc cng trnh Nghin cu cc phng php kho st CCT. Nghin cu a cht cng trnh xy dng lp quy hoch cc khu vc xy dng cc cng trnh khc nhau nh dn dng cng nghip, cu dng, cc cng trnh thy li

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I.3. Phng php nghin cu a cht cng trnhMi mn hc c phn bit khng nhng bi i tng nghin cu m cn bi cc phng php m mn hc s dng thc hin nhim v ca n t ra. Khi nghin cu CCT ngi ta thng s dng tng hp 3 loi phng php ch yu sau y : 1. Phng php a cht hc

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y l phng php quan trng nht v cho kt qu st thc nht trong vic nghin cu CCT

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Tm hiu s pht trin cc hin tng a cht trong qu kh c lin quan n s thnh to cc dng a hnh, tnh cht ca t v quy lut phn b sp xp ca n trong khu vc. T c th nh gi ng n nhng iu kin a cht ca khu vc xy dng cng trnh v d bo s thay i nhng iu kin di tc dng ca cng trnh, a cht cng trnh Khi thc hin pp ny ngoi vic phi thc hin cc cng tc khoan o vo cc tng thu thp cc ti liu v cc iu kin a cht m cn phi tin hnh th nghim trong phng v ngoi tri xc nh cc c trng c l ca t .

2. Phng php tnh ton l thuyt Lp cc phng trnh ton hc th hin bn cht vt l ca cc hin tng a cht, cc c trng vt l, c hc ca t . V khng phi lc no cng c th quan trc hay dng cc phng php thc nghim xc nh bn cht vt l c hc ca t nhng khu vc c a hnh phc tp. Pp ny c th cho kt qu nhanh chng v kh chnh xc. Ngi ta thng dng pp ny tnh ton mc n nh, ln ca cng trnh, lng nc chy vo h mng, mc n nh ca mi dc, tc ti to b 3. Phng php th nghim m hnh v tng t a cht c p dng trong trng hp lin quan n qui m ca cng trnh thit k hoc tnh cht phc tp ca iu kin a cht. Pp th nghim m hnh l lp m hnh trong phng th nghim hoc ngoi tri da trn s tng ng gia mi trng a cht t nhin ca khu vc xy dng v mi trng vt l c iu kin tng t. Pp ny gip ta nghin cu c chun xc hn cc hin tng a cht s xy ra trong qu trnh thi cng v khai thc Pp tng t a cht l s dng cc ti liu a cht ca khu vc c nghin cu y cho khu vc c iu kin a cht tng t. Pp ny c tnh cht kinh nghim da trn nguyn l t c hnh thnh trong cng iu kin, tri qua cc qu trnh a cht nh nhau th c cc c trng vt l, c hc tng t nhau.

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CHNG II : T II.1. V qu t v cc hin tng a cht din ra trong II.1.1 Cu trc bn trong ca Tri tQu t c hnh cu, xch o phnh ra, 2 cc hi dt i, do tc quay ca qu t quanh trc bc-nam kh ln. B mt qu t li lm bt thng, ni nh ln to thnh cc dy ni, v ni lm su to thnh cc i dng. Ni li nht l nh Chomolungma ca dy Hymalaya cao 8890m, ni lm nht l l h i dng Marian su khong 11.034m. o Kh quyn Tri t : l lp cc cht kh bao quanh hnh tinh Tri t v c gi li bi lc hp dn ca Tri t. o Thy quyn : bao gm cc bin, i dng, h, sng sui, chim b mt qu t. Ngoi ra cn nc trong cc l rng v khe nt ca t nc di t. V Tri t c chia thnh cc quyn ng tm. o Quyn ngoi cng ca qu t l quyn t , hay cn gi l v qu t, c b dy trung bnh khong 35km. quyn ny ch yu l macma ri n bin cht, trm tch. V T chim khong 1% th tch v 0.5% khi lng ca T. B dy v qu t thay i nh sau : y i dng : v qu t c b dy t 8-10km cc vng ng bng : v qu t c b dy thay i t 30-40km cc vng ni cao : v qu t c b dy thay i t 55-75km o Di l quyn manti phn b t lp v n su 2900km. Quyn ny chim 83% th tch v 67% khi lng T.Quyn manti th rn, vt cht l cc dng hp cht oxit silic, oxit mangan v oxit st. Manti c phn ra 2 loi nh sau : Manti trn : phn b t lp v qu t n su 800km, y chnh l ngun nhit ln bn trong ca v qu t do lng nguyn t phng x phn hy ln. Manti di : phn b su t 800-2900km, do lp vt cht ny phn b su v trng thi nn cht nn c nhit cao (2800-3800 0C) v p lc ln (100.000-1.300.000at) o Nhn qu t nm trung tm c su trn 2900km. Nhn qu t c cu to ch yu t cc hp cht ca st v niken. p sut trung tm qu t rt cao (t 3,5triu at) v nhit rt ln (40000C). Hin nay, ngi ta vn cha c nghin cu chnh xc v nhn qu t.

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vo da 8-10km : y a dng : y a i 30-40km : ng ba g o n 55-75km : ng nu vu i

manti : t e vo n o u 2900km sa

nha : 2900-6370km n

II.1.2

Cc trngvt l ang hot ng ca tri t

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Do s vn ng, s phn b v thuc tnh ca cc vt cht trong v ngoi qu t m hnh thnh nn cc trng vt l c bn nh trng trng, t trng, trng nhit o Trng nhit : T nhn c 2 ngun nhit ch yu, mt t mt tri (ngoi nhit) v mt ngun t lng T to ra (ni nhit). Ngoi nhit ch yu sinh ra do nh sng mt tri hun nng phn bn trn v tri t. N thay i theo thi gian v khng gian. nh hng ca nhit mt tri khng su lm, khong vi chc mt v chiu su. Vo su trong lng tri t l chu nh hng ca ni nhit. Ngun nhit ny sinh ra do cc phn ng ha hc, ht nhn. (cc nguyn t phng x khi hot ng s nhit rt cao) o Trng t : Qu t l mt nam chm khng l c 2 cc Bc Nam gn trng vi 2 a cc. Hin ti a cc t gn trng vi cc a l. nhng vng phn b hay qung t tnh cao s hnh thnh t tnh bt thng. Nguyn nhn ca t trng Tri t : s i lu ca lp nhn ngoi v s t quay ca T to ra t trng T. V phn nhn nng duy tr t trng v n nh t trng sinh ra bi lp li ngoi lng. o Trng trng Mt vt trn mt t chu s tc ng ca 2 lc : lc ht ca T, lc ly tm sinh ra do s t quay ca T. Trng lc chnh l tp hp ca 2 lc , do bn knh ca T cc ngn hn xch o nn trng lc tng dn t cc n xch o. M .m F =G . g = F + Vi R2 Trong F : lc hp dn gia hai vt th M, m : khi lng R : khong cch gia 2 vt G : hng s hp dn v tr

II.1.3 -

Cc hin tng a cht ang xy ra trong T

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Hin tng mcma : l hin tng cc khi dung nham nng chy su trong lng t theo cc khe nt dng ln xm nhp vo phn trn ca v tri t hay phun tro ln trn mt t. Hin tng kin to : l hin tng xy ra do ni ng lc pht sinh trong v tri t lm thay i cu trc cc lp t cu to nn v tri t, tch v tri t thnh nhiu mng v cc mng ny tng tc vi nhau to nn cc dng a hnh trn tri t. Hin tng xm thc : cc hot ng a cht - a l ngoi sinh lm mt i mt phn hay ton b t trn b mt, dn ti s h thp a hnh. Qu trnh xm thc din ra do cc tc nhn ch yu sau: 1) Tc nhn c hc - lc ca dng chy ph hu, xi l, mi mn v cun tri vn theo dng nc; 2) Tc nhn ho hc - nc ho tan v cc sn phm phong ho ri cun tri i, do gc cng b mn nhanh chng. Hin tng trm tch : l s ph hu c hc v ho hc cc do tc dng ca cc nhn t khc nhau trn mt hoc phn trn cng ca v T to ra cc sn phm ph hu. Sn phm ny c gi, nc, bng h mang i v tch ng li bin, h v 1 phn lng ng trn ng vn chuyn gi l hin tng trm tch.

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II.2. Khong vt v khong vt to II.2.1 Khi nimKhong vt l nhng hp cht ha hc hoc cc nguyn t t sinh c hnh thnh trong qu trnh l-ha xy ra bn trong hay pha trn ca v tri t. Khong vt trong thin nhin c th kh (kh H2S, CO2), th lng (nc, thu ngn), th rn (thch anh, fenpat, mica). Khong vt rn hu ht trng thi kt tinh (tinh th). Trong s 3000 khong vt, ch c hn 50 khong vt tham gia to . Cc khong vt ny gi l khong vt to . Ty thuc vo vai tr ca cc nguyn t cu to nn khong vt ta c th chia ra khong vt chnh v khong vt ph. o Khong vt chnh ng vai tr ch yu trong vic cu to nn t . Cng v tnh cht ca t ch yu do cng v tnh cht ca loi khong vt ny quyt nh o Khong vt ph chim hm lng nh hn (c mt s khong vt l khang vt chnh ca ny nhng c khi l khang vt ph ca khc) Theo ngun gc hnh thnh, khong vt c chia ra khong vt nguyn sinh v khong vt th sinh. o Khong vt nguyn sinh : c thnh to do s ngui lnh ca macma hoc do kt ta t dung dch. o Khong vt th sinh : c thnh to t nhng khong vt khc (do phn ng ha hc ca nc vi khong vt nguyn sinh, do tc dng ca p sut, do nhit cao ) Theo mc ch xy dng, khong vt c phn loi da trn cc dng lin kt ha hc ca n. Bi v c trng cu to tinh th v bn cht mi lin kt ha hc gia cc nguyn t quyt nh nhiu tnh cht vt l v c hc rt quan trng.

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II.2.2-

Mt s c tnh ca khong vt

a. Hnh dng tinh th ca khong vt Dng tinh th ca khong vt : tinh th l nhng vt rn trong cc phn t nh sp xp theo 1 quy lut u n to thnh dng khng gian Tnh oi xng cua tinh the bao gom: o Tam oi xng: (C) la mot iem tng tng nam trong tinh the, ma tai iem o moi ng thang i qua no, nam trong gii han tinh the c chia lam hai phan bang nhau o Truc oi xng: (L) la mot truc tng tng i qua tinh the e khi quay tinh the theo mot goc co nh xung quanh truc th lap lai tat ca cac yeu to cua tinh the nh v tr ban au. o Mat phang oi xng: (P) la mat phang tng tng i qua tinh the, chia oi tinh the ra hai phan bang nhau, moi yeu to cua tinh the hai phan eu oi xng nhau qua mat phang oi xng ta nh anh cua mot vat qua gng.

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Bng phn loi h thng tinh th

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Mu ca khong vt Mu ca khong vt ch yu do thnh phn ha hc v cc tp cht trong n quyt nh.

b.

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Khi quan st mu khong vt cn ch n iu kin nh sng, trng thi ca khong vt Tuy nhin, du hiu ng tin cy hn nhn bit mu ca khong vt l mu ca bt khong vt. Ch cn vch mt khong vt trn mt tm s nhm, chng s li mt vt di c mu c trng cho bt khong vt y. c. trong sut v nh ca khong vt trong sut l kh nng ca vt th khi cho nh sng i xuyn qua. Khi nh sng chiu vo mi trng khc nhau s b khc x, thay i tc v tiu hao nng lng. Mt phn nh sng chiu ln khong vt s b phn x tr li trn mt khong vt to thnh nh ca khong vt. Cc loi nh c trng ca khong vt : o nh kim : khi s phn x ca nh sng trn b mt cao, l cc khong vt m c, c kh nng hp th nh sng mnh. V d : nhng kim loi trong t nhin nh vng, bc, c cc biu hin lin quan n kim loi v chng c nh kim. o nh phi kim : trn cc khong vt cn li c nhiu dng nh phi kim khc nhau. nh phn x lp lnh ca kim cng gi l nh kim cng; thy tinh thng thng, thch anh c nh thy tinh; mt s khong vt khc c m t nh l nh m, nh t, nh t d. Tnh ct khai v vt v Tnh ct khai (d tch) ca khong vt l kh nng b tch ra ca cc ht tinh th hay ht kt tinh theo cc mt song song. C cc mc d tch nh sau : o Ct khai rt hon ton : tinh th c kh nng tch ra rt d dng bng tay o Ct khai hon ton : dng cc loi vt dng (nh ba ) tc dng vo tinh th v n s v ra theo cc mt tch tng i bng phng o Ct khai trung bnh : trn nhng mt v ca tinh th, va thy cc mt tch tng i hon chnh, va thy vt v khng bng phng theo cc phng khc nhau o Ct khai khng hon ton : tinh th kh tch ra, thng thy cc vt v khng c quy tc Vt v : l cc mt v khng theo quy tc ca khong vt khi b p v. Phn ln cc vt v tng i g gh v bt quy tc. Da theo hnh dng vt v c th chia ra : o Vt v phng : v theo cc mt d tch. o Vt v dng v s : vt v ca thch anh o Vt v dng t : vt v ta nh t bt, v d nh vt v ca Kaolinit. o Vt v sn si : b mt vt v sn si nh vt v ca thch anh dng tr. e. cng ca khong vt cng l kh nng chng li tc dng c hc bn ngoi ln b mt ca khong vt. Tnh cht ny c lin quan n kin trc v s lin kt gia cc cht im ca khong vt. S lin kt ny cng chc th cng cng cao. nh gi cng tng i ca khong vt, ngi ta dng thang cng Mohs gm 10 cp , sp xp theo chiu tng cng, mi cp c i din bng mt khong vt ph bin. 1. Tan Mg3[Si4O10][OH]2 2. Thch cao CaSO4.2H2O 3. Canxit CaCO3 4. Flourit CaF2 5. Apatit Ca3[PO4]3(F,Cl,OH) 6. Octocla K[AlSi3O8] 7. Thch anh SiO2 8. Topaz Al2[SiO4][F,OH]2

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Al2O3 10. Kim cng C cng tuyt i c xc nh bng my rt kh khn ( cng tuyt i ca Tan 2,4kG/mm2; Canxit - 109 kG/mm2; Thch anh - 1120 kG/mm2; Kim cng - 10060 kG/mm2). Nhng iu cn ch : o Khng dng thang Mohs so snh cng A hn cng B my ln. xc nh c phi dng cng tuyt i. o Hu nh cc khong vt c cng t 2-7. Cc khong vt to thng c cng nh hn 7. cha khong vt c cng cao th thng c cng ln. f. T trng ca khong vt T trng ca khong vt c biu din bng t s gia trong lng khong vt chia cho trng lng ca th tch nc tng ng. T trng ca khong vt thay i trong phm vi tng i ln v c chia thnh 3 nhm : nh ( 200mmm : kin trc hc, dm 200-20mmm : dm, cui 20-2mm : si, sn 2-0.05mm : ct 0.05-0.005mm : bi 2mm : cui kt, si kt vn trung bnh d=2-0.5mm : ct kt vn nh d chnh lc ko cng P ny lm nc dng ln trong ng Trng lc ca ct nc trong ng lm ko nc h xung G = r2 .Hmd . . g r : bn knh ng mao dn Hmd : chiu cao mao dn khi cn bng g : gia tc trng trng : khi lng ring ca nc chiu cao mao dn t gi tr cc i khi P = G => 2 r. cos = r2 .Hmd . . g => chiu cao mao dn H md =2.. cos r..g

T cng thc trn ta nhn thy chiu cao mao dn ph thuc vo bn knh ng, khi lng ring ca cht lng v vt liu lm ng (v gc t chu nh hng ca vt liu lm ng v loi cht lng) cao mao dn ca mt s t t Hmd ct trung ct mn ct pha st st pha ct st 15-35 35-160 100-150 150-400 400-500

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Ti liu a cht cng trnh Chng I : M u

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nh hng ca mao dn : gy m t cho cng trnh, tnh cht c l ca t gim xung Nguyn nhn: lc tng tc ca nc v kh vi cc ht t, th hin s tm t cc ht t, to nn trong cc l rng nhng mt khum v mt s hin tng khc. Chiu cao dng mao dn t l nghch, cn tc dng th t l thun vi ng knh cc mao qun. Trong t st dng ti hng mt, trong nhng loi t khc, hng centimt n vi mt.

IV.1.3

Tnh cha nc ca t

+ t l mt tp hp cc ht khang vt th rn, cc l rng cha nc v khng kh - Th rn gm cc ht khang vt thng gi l ht t. Tnh cht ca t phn ln ph thuc vo ln, hnh dng ht v cc thnh phn khong vt khc ca chng - Trong t iu kin t nhin lc no cng cha 1 lng nc nht nh. Lng nc ny l pha lng trong t. Nc c tc dng mnh vi cc ht khong vt trong t. - Nu cc l rng trong t khng cha y nc th khng kh s lp y cc ch . V khng kh ny chnh l pha kh ca t . + Do vy, thun tin, ngi ta a ra m hnh t gm 3pha c tch ri ra vi cc lng ring bit nhng vn gi c t l chun xc gia chng M hnh t chi tit biu th cc lng th tch v khi lng khc nhau.

k h o l n g i

th e tc h

n Qk = 0 k h o g k hVk Q Qn Qh n c Vr Vn Vh V

ra n

* Tnh cht nc ca t c nh gi bi 2 ch tiu a/ m t nhin (W) : m t nhin ca t c biu th bng t s gia khi lng nc cha trong t iu kin t nhin vi khi lng ca ht t Q W = n .100% Qh Qn : khi lng nc c trong t Qh : khi lng phn ht rn b/ bo ho (G) : l t s gia m t nhin v m bo ho (bo ho khi nc chim ton b l rng) W V G = tn = n Wbh V r Da vo bo ho nc phn chia t loi ct lm 3 loi : 0 < G 0.5 t hi m 0.5 < G 0.8 t m 0.8 < G 1 t bo ha

IV.1.4-

Tnh khng n nh vi nc ca t (trng n v co ngt)

a/ Tnh trng n : Tnh trng n l hin tng tng th tch ca t khi tc dng tng h vi nc hay dung dchTrang 25 / 67



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Cc c trng ca t trng n + Bin dng trng n : bin dng ca t trc v sau khi t trng n (c th so snh v chiu cao mu t hoc th tch mu t trc v sau khi trng n) V Vs h hs Rtn = tn x100% = tn x100% Vs hs Vtn , htn : th tch v chiu cao ca t khi trng n Vs , hs : th tch v chiu cao ca ca mu t + p lc trng n : l p lc pht sinh trong qu trnh trng n. p lc ny c o bng lc tc dng ln mu t khi lm t v nn khng n hng, v c bin dng trng n bng khng. + m trng n : l m ng vi trng thi m qu trnh hp th nc hay dung dch lng khc ca t ngng li (khi s trng n kt thc) m ms Wtn = tn .100% ms mtn : trng lng mu t sau khi trng n ms : trng lng t kh tuyt i t trng n c bit l t trng n khng u khng nhng ch lm gim cng ca t thng qua s ph v ni lin kt gia cc ht m nhiu khi cn ph hoi c khi t thng qua h thng cc khe nt pht sinh trong qu trnh trng n. b/ Tnh co ngt Ngc vi trng n l co ngt, do t b thot nc Tnh co ngt ca t l s gim th tch ca t khi b hong kh Trong xy dng cng trnh, c bit l khi thi cng h mng, t nn c th n, c th co lm cho tnh cht vt l, c hc ca t nn b thay i, khng cn ph hp vi thit k v l nguyn nhn gy ra h hng cng trnh

IV.2. Tnh cht vt l ca t IV.2.1 Tnh l rng v khe ntTnh l rng ca t : c trng bi cc ch tiu sau : rng : l t s gia th tch phn rng ca t vi th tch ton b t . V n = r .100% V Vr : th tch phn rng (th tch ca phn khng kh v nc trong t ) [m3] V : th tch tan b t bao gm phn rn, khng kh v nc trong t ). [m3] - rng thay i trong cng 1 loi t cc trng thi kt cu khc nhau (xem qua bng sau) rng (%) Kt cu t Cht Cht va Cht t Ct ln si, ct ht to v ht va < 35 35 40 > 40 Ct ht nh v ht mn, ct pha st < 38 38 44 > 44 nh St, st pha ct, ct pha st nng < 30 30 45 > 45

a.

H s rng : l t s gia th tch phn rng v th tch ca phn ht t e= Vr VhTrang 26 / 67



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Vr : th tch phn rng (th tch ca phn khng kh v nc trong t ) [m3] Vh : th tch phn ht rn trong t [m3] H s rng l 1 ch tiu c th cho bit s b c tnh cng ca t do dng nh gi cht ca t (xem bng phn loi theo cht) H s rng cht Cht Cht va Cht t t Ct ln si, ct ht to v ht va < 0.55 0.55 0.7 > 0.7 Ct ht nh v ht mn, ct pha st < 0.6 0.6 0.75 > 0.75 nh Ct bt (ct bi) < 0.6 0.6 0.8 > 0.8 St, st pha ct, ct pha st nng < 0.4 0.4 0.8 > 0.8

*** Trong thc t i vi t loi ct v t loi st , vic dng rng v h s rng cha th hin trng thi l rng ca t m cn phi dng cc ch tiu tng i i vi t loi ct th phi xc nh cht tng i D : e e D = max emax emin emax : h s rng ca ct khi kt cu xp nht (trng thi rng nht) emin : h s rng ca ct khi kt cu cht nht e : h s rng ca ct trng thi t nhin Da vo cht tng i D, ngi ta chia ra 3 trng thi nh sau : 0 < D 0.33 : trng thi ri xp 0.33 < D 0.67 : trng thi cht va 0.67 < D 1 : trng thi cht nhtrxo i p 0 0.33 chav t a 0.67 chanha t t 1 D

i vi t loi st th dng ch tiu c ca t dnh. Ta so snh c ca t st c kt cu t nhin vi c ng vi kt cu trng thi chy v do W Wch : t trng thi chy Wd > W Wch : t trng thi do W Wd : t trng thi cngcg n Wd de o Wch cha y W

Ch tiu c tng i B nh sau : W Wd B= Wch Wd Wch : m gii hn khi t chuyn t trng thi do sang trng thi chy Wd : m gii hn khi t chuyn t trng thi cng sang trng thi do W : m gii hn ca t trng thi t nhin Da vo c tng i B c th bit c trng thi vt l ca t st : : trng thi chy B 1 1 > B 0 : trng thi do B 1 St pha ct : B 0 : trng thi cng 0 < B 0.25 : trng thi na cng 0.25 < B 0.5 : trng thi do cng 0.5 < B 0.75 : trng thi do mm 0.75 < B 1 : trng thi do chy : trng thi chy B >1 nt n ca t -b Nt n l hin tng b ph hoi v mt cu to cng nh thnh phn lm cho chng khng cn c tnh lin tc na -b Tnh nt n ca c nh gi qua 2 ch tiu sau : nt n: l s lng khe nt ca trn 1 n v chiu di (mt) khe h: khe h l t s gia din tch khe h to bi cc khe nt v din tch k c khe nt trn 1 mt ct no - khe h thng c xc nh trn sn dc, vch h o, nc ng hm vi din tch khe t 4-8m2. - Phn loi nt n ca : Kk 2% : nt n yu 2% < Kk 5% : nt n va 5% < Kk 10% : nt n mnh 10% < Kk 20% : nt n rt mnh

b.

IV.2.2 -

Dung trng ca t

Dung trng ca t l khi lng ca 1 n v th tch t. Ty theo lng cha tng i ca cc pha trong t, c th phn dung trng ra thnh cc loi nh sau : a. Dung trng t nhin (dung trng t) : l khi lng ca mt n v th tch t trng thi t nhin - Dung trng t nhin l t s gia khi lng t trng thi t nhin v th tch ca n Q Q + Qn W = = h V Vh + Vr Qh : khi lng phn ht ca t (g) Qn : khi lng phn nc trong t (g)Trang 28 / 67



Vh : th tch phn ht trong t (cm3) Vr : th tch phn nc v khng kh trong t (cm3) Dung trng t nhin ca t thay i trong phm vi 1,5-2,0 g/cm 3, i vi cng chc th dung trng t nhin xp x bng dung trng ht. Dung trng t nhin c trng cht kt cu ca t v vy cho php nhn xt gin tip v bn, tnh bin dng v n nh. Ngoi ra, dung trng t nhin cn c s dng trc tip trong tnh tan cng trnh. Dung trng bo ha nc l dung trng t nhin ln nht, l khi lng 1 n v th tch t trng thi no nc (tc l ton b l hng ca t u cha y nc) Q Q + Qr bh = bh = h V V Qh : khi lng phn ht ca t (g) Qr : khi lng phn nc trong t k c phn khng kh b nc chim ch (g) V : th tch t t nhin (cm3) b. Dung trng kh : l khi lng kh (ct t ) ca mt n v th tch t t nhin. -b Dung trng kh l t s gia khi lng t trng thi kh chia cho th tch ton b t . Q Qh k = h = V Vh + Vr Qh : trng lng phn ht ca t (g) Vh : th tch phn ht trong t (cm3) Vr : th tch phn nc v khng kh (phn rng) trong t (cm3) -c Dung trng kh tng i n nh v n khng ph thuc vo m. l rng cng nh(mc nn cht cng cao), t cha nhiu khong vt nng th dung trng kh cng cao. -d Dung trng kh c dng lm ch tiu kim tra ch yu v mc nn cht ca t trong thn cng trnh bng t (p, , nn ng). Mt s cng trnh p t nc ta thit k vi dung trng kh gk=1,45-1,70 g/cm3 c. Dung trng ht : l khi lng ca 1 n v th tch ht rn ca t . -b Dung trng ht l t s gia khi lng ht rn v th tch ca phn ht Q h = h Vh Qh : trng lng phn ht ca t (g) Vh : th tch phn ht trong t (cm3) -c Dung trng ht ch ph thuc vo thnh phn khang vt, khng ph thuc vo kin trc, cu to, m. Dung trng ht ca t thng thng thay i trong phm vi 2,0-3,0 g/m3. Cc baz c dung trng ht ln hn t 3,0-3,3 g/cm3. -d Dung trng ht cn ph thuc vo s c mt cc tp cht trong thnh phn t . V vy mi loi t c th c mt s gii hn bin i dung trng. d. Dung trng y ni : l khi lng trong nc ca n v th tch t trng thi t nhin Dung trng y ni hay dung trng ca nc nm di mc nc ngm c tnh bng khi lng ca n v th tch t c k n lc y ni ca nc dn = bh n

Trang 29 / 67



gbh : dung trng bo ha ca t (g/cm3) gn : dung trng nc (g/cm3)

IV.2.3 -

T trng ca t

L t s gia khi lng t v khi lng nc c cng th tch. h Cng thc : = (l i lng khng c th nguyn) n h : dung trng ht ca t (g/cm3) n : dung trng nc (g/cm3)

IV.2.4

Bng lin h cc ch tiu vt l ca t xac Cong thce=e=

Ch tieu can nh He so rong e

. n (1 + 0,01W )

W

1

e=

h 1 k

o rong n (%) o bao hoa G Dung trong hat (g/cm3)

n 1n e n= .100 % 1+ e

G=

h =

. W .0,01W . n .(1 + 0,01W ) W k1 0,01n

G=

0,01W . e

h = . n

Dung trong kho k = h (1 0,01 .n) (g/cm3) Dung trong ay noi ( 1). n dn = (g/cm3) 1+ e

k =

W1 + 0,01W

dn = bh n

IV.3. Tnh cht c hc ca t IV.3.1 Tnh bin dng trong t Di tc dng ca ti trng , th t b co p li v thay i hnh dng cng nh kch thc. Th tch cc l hng trong t b gim nh do cc ht khong vt dch chuyn tng i tng i vi nhau, do bin dng ca chnh cc ht t v do nc hay kh cha trong cc l rng t thng thng c nn cht ch yu do th tch l rng gim, nn bin dng nn ca t c biu hin qua tr s bin i ca h s rng, cn i vi t bo ho nc th c biu hin thng qua tr s bin i ca m. Tnh bin dng ca t thng nh gi bng cc ch tiu nn ln. Cc ch tiu c trng ca bin dng nh : h s nn ln, modun bin dng cho php ta d tnh ln, n nh v kh nng chu ti ln nht ca nn t

-

IV.3.2-

bn ca t

bn ca t c th hin bng sc chng ct thng qua lc dnh kt v gc ma st trong . Cc ch tiu ny gip ta c th thit k nghing ca mi dc t pTrang 30 / 67



-

sao cho hp l, nh gi kh nng n nh ca mi dc, tnh p lc t sau lng tng chn, sc chu ti ca nn t . bn ca t thng c nh gi qua cc ch tiu : cng chng nn v ko, cng chng trt i vi : trong cng lc chng trt ph thuc vo bn lin kt gia cc ht. Trong t , lc chng trt rt ln v cc ht khong lin kt cht vi nhau. Lc chng trt trong cng m bo n nh cho cng trnh xy dng ln n. i vi t ri : lc chng trt trong t ri rc ch yu ph thuc vo lc ma st xut hin khi cc ht dch chuyn ln nhau. i vi t loi st (t dnh) sc chng ct khng ch ph thuc vo lc ma st trong m cn ph thuc vo lc dnh ca cc ht. V cc ht t c lin kt vi nhau bng cc loi keo kt dnh nn chu tc dng ca lc dnh. Cc ht sp xp theo cc gc cnh v c kh nng trt ln nhau khi chu ti trng ngoi, do vy n cng chu nh hng ca lc ma st gia cc ht vi nhau to nn gc ma st trong..

IV.4. Phn loi t IV.4.1 Phn loi t theo quan im CCT a.Nhm cng Cc loi macma, bin cht, trm tch ha hc v trm tch gn kt chc cha b phong ha Nhm ny c t trng ln (2.65 3.1 g/cm3), rng nh (khong vi phn trm), hu nh khng thm nc, cng chu nn cao (500 4000kG/cm 2),sc chng ct ln (200 4000 kG/cm2) y l loi hon ho nht v mt xy dng cng trnh. Chng c phn bit bi bn v n nh cao, bin dng b v ngm nc yu. Cc khonh phn b cc loi nh vy l thun li xy dng bt c cng trnh no m khng gp nhng hn ch ng k, v thng khng phi p dng cc bin php m bo n nh ca cng trnh. Nhm na cng Bao gm cc loi cng b phong ha, nt n mnh, cc trm tch gn kt yu Tnh cht xy dng ca nhm ny ph thuc vo mc phong ha, thnh phn khong vt v mc gn kt ca T trng t 2.2 2.65, rng khong 10-15%, c kh nng cha nc v thm nc nhiu. d b nc ph hoi. Khc vi cng bi bn v n nh thp, bin dng ln, ngm nc ng k hoc cao. Chng thng b nt n nhiu, cn cc b ha tan th thng c hang hc, tuy vn c bn cao mu th nghim. Trong nhiu trng hp, nhng khonh phn b na cng u l thun li cho vic xy dng cc cng trnh khc nhau, k c nhng cng trnh quan trng, nhng u phi tun th nhng iu hn ch nht nh v phi p dng nhng bin php cng trnh phc tp m bo n nh v khai thc bnh thng ca cng trnh Nhm t ri rc So vi cng v na cng c c trng bi bn, n nh thp v bin dng ln. Mt s loi t thuc cc nhm ny u ngm nc mnh. Nhng nhm t ri xp v t mm dnh bao gm cc kiu ngun gc khc nhau ca t trm tch. Chng c c im l trng thi vt l v tnh cht bin i nhiu. iu kin xy dng cng trnh trn nhng loi t thng km theo nhiu hn ch ln.Trang 31 / 67

-

b.-

c.-



-

d.-

e.-

Nhm ny bao gm : dm, cui, si, ct. c tnh chung l khng c lin kt kin trc gia cc ht, t trng nh 1.4-1.9, rng ln 25-40%, c kh nng cha nc v thm nc cao. Tnh n nh ca t ph thuc vo cht ca chng. Nhm t mm dnh Bao gm : st, st pha, ct pha. Nhm t c tnh cht c bit Bao gm : bn, than bn, t mui ha, ct chy, th nhng. Cc loi t ny thng yu v mt xy dng

IV.4.2

Phn loi t theo TCVN

Da vo ch s do ngi ta phn ra loi t dnh (Id 1) v t ri (Id 17 b. t ri Da vo hm lng ht chim u th c ng knh >2mm - Hm lng ht chim trn 50% : t hn ln ( dm, cui, sn, si) - Hm lng ht chim nh hn 50% : t ct - Da vo hm lng v ng knh ht m phn loi t ri nh sau : 0.1 75% Ct nh < 75% Ct bt 0.25 > 50% Ct va 0.5 >50% Ct th 2 >50% Si >25% Ct si 10 >50% Dm cui d(mm)

c.

t bn t bn khi tha cc iu kin sau y : W > Wch v e > egh Loi bn Bn ct Bn st Bn st H s rng e e 0,9 e1 e 1,5

d.

t cha tn tch thc vt Tn t cha tn tch thc vt q ( than bn) t c cha tn tch thc vt t ct c cha tn tch thc vt 0,03 < q 0,1 t dnh c cha tn tch thc vt 0,05 < q 0,1 t dng than bn t c t than bn 0,1 < q 0,25 t c than bn va 025 < q 0,4 t c nhiu than bn 0,4 < q 0,6 t than bn 0,6 < q

Trang 32 / 67



q : t s khi lng ca tn tch thc vt trong mu t sy 100o 105oC v khi lng ca phn ht rn ca mu t.

IV.4.3 a.-

Phn loi t theo USCS

Nguyn tc phn loi : Da trn thnh phn kch thc ht chim u th c ng knh 0,074mm trong t phn chia thnh 2 nhm : ht th v ht mn i vi nhm ht th : da trn cc ht c ng knh 4,76mm phn chia thnh cc ph nhm i vi nhm ht mn : da trn cc gi tr gii hn chy, gii hn do, ch s do phn chia thnh cc ph nhm Tn ca cc loi t c kt hp 2 nhm k t sau : Tn t Cui, si Ct Bi St Hu c K hiu G (gravel) S (sand) M (silt) C (clay) O (organic) Cp phi Tt Km Do cao Do thp Than bn K hiu W (well graded) P (poor graded) H (high plasticity) L (low plasticity) Pt (peat)

b.

Tm tt phn loi Da vo hm lng ht c kch thc 0,074mm (ry No200) phn thnh 2 nhm ln nh sau : * t ht th: Hm lng cc ht c kch thc t 0,074mm tr ln chim trn 50%. Gm 2 nhm l cui si (G) v t ct (S) - t cui si (G) : hm lng ht c kch thc ln hn 4,76mm chim trn 50% - t ct (S) : hm lng ht c kch thc ln hn 4,76mm chim nh hn 50% Mi loi c chia thnh 4 nhm : - t cha t hoc khng cha ht mn, khng c loi ht no chim u th v hm lng, cp phi tt, c kt hp bng ch W Kt hp vi hai ch ci ca tn t c GW v SW khi hm lng ht mn chim t hn 5% tng trng lng t v tha iu kin v cp phi: Cu > 4 (i vi si sn), Cu > 6 (i vi ct) & Cc =1-3 d 60 H s khng u : Cu = - nh gi ng u ca cc ht t d102 d 30 d10 .d 60 da : ng knh m ht c kch thc bng hoc nh hn chim a% tng khi lng t kh. t cha t hoc khng cha ht mn, c mt loi ht chim u th v hm lng, cp phi km, c k hiu bng ch P Kt hp vi hai ch ci ca tn t c GP v SP khi hm lng ht mn chim t hn 5% tng trng lng t v khng tha iu kin v cp phi t. t ht th cha mt lng ng k ht mn (ch yu l ht bi) khng c tnh do, c k hiu bng ch M Kt hp vi ch ci ca tn t c GM v SM khi hm lng ht mn chim hn 12% tng trng lng t t ht th c cha mt lng ng k ht st k hiu bng ch C

H s phn loi : Cc =

-

-

-

Trang 33 / 67



-

Kt hp vi ch ci ca tn t c GC v SC khi hm lng ht mn chim hn 12% tng trng lng t v ch s do phn ht mn >7 i vi t ht th c lng ht mn chim t 5% n 12% tng trng lng t hoc khng thuc hn nhm no th dng k hiu kp nh GP-GC, GW-SW, Hm lng ht mn < 5% (cha t hoc 5% - 12% trong tng trng khng cha ht mn) lng t Cp phi Cp phi s tt km GW,SW GP,SP GP-GC >12% (cha nhiu hat mn) Ht bi Ht st (c (khng c tnh do) tnh do) GM,SM GC,SC

* t ht mn

Trang 34 / 67



Chng V

NC DI AT

Khai niem c ban ve nc di at

-

1.

Nc di t bao gm cc loi nc c trong l rng, khe nt v cc hang hc ca cc lp t . Nc cn tham gia vo thnh phn cu to mng tinh th ca khong vt to ra cc . Lng nc ngm di t nhiu hay t tu thuc vo iu kin c th ca tng ni (a hnh, thnh phn t , lng ma ) Nc di t c nh hng rt mnh n tnh cht vt l v c hc ca t : o Chng lm thay i trng thi, bn v tnh bin dng, tnh n nh ca khi t o Gy ra cc tc dng ho tan, n mn hoc cun tri cc ht t theo dng thm o L mt trong nhng nguyn nhn quan trng gy ra hin tng ln, trt t mi dc, hin tng ct chy hoc xi ngm o Gy kh khn cho vic thi cng h mng, lm mt n nh nn mng cng trnh. Nc di t l ngun ti nguyn rt qu gi, phc v i sng cho con ngi, cho s tn ti v pht trin nn cng nghip v nng lm nghip Ngun gc hnh thnh nc di t

o Nc c ngun gc kh quyn ( nc thm) c thnh to do nc kh quyn ngm vo trong t , do nc sng h, chy theo cc khe nt, l hng ca t hoc hi nc xm nhp t khng kh ri ngng t li - Qu trnh c bn quyt nh thnh phn ho hc ca nc c ngun gc thm l s ho tan v ra la t , s ho ln vi nc c ngun gc bin, s trm ng mui; s c c do bc hi, qu trnh ho l ho keo v hot ng ca vi sinh vt o Nc c ngun gc bin (nc trm tch) - c hnh thnh trong qu trnh thnh to t trm tch bin. V vy, thnh phn ho hc rt phc tp. - S bin i thnh phn ha hc ca nc i dng bt u trong cc loi bn y. Do s vn ng kin to, s thnh to cc tng trm tch bn trn, qu trnh bin i ca nc c ngun gc bin xm nhp t i dng, bin, vng vnh vo cc c thnh to hoc nc b p y ra t cc b nn cht (st kt, ct kt) thc y qu trnh thay th nc c ngun gc thm c t trc, s pha trn v trao i cation o Nc c ngun gc macma (nc nguyn sinh) - L nc nguyn sinh c tch ra trong qu trnh to v tri t v qu trnh hot ng ca th macma xm nhp v phun tro - Nc nguyn sinh thuc qu trnh sau macma ch chim khong 5-10% nc di t o Nc c ngun gc bin cht (nc th sinh) - L nc ti sinh hoc tch c ra t v hydrat ca ht t, trong qu trnh bin i nhit hoc bin cht ng lc (do p sut ln). - Nc th sinh cng c th c hnh thnh do cc phn ng ho hc khi iu kin ho l ca mi trng trong t thay i cc phn ng ho hc c s tch nc. Thc t rt kh xc nh ngun gc nc di t v cc loi nc c thnh phn ho hc ging nhau, nhng li c ngun gc khc nhau. Tuy nhin, c th da vo c im ca thnh phn nguyn t vi lng, cc cht ho tan hoc cc cht ng v n nh ca tng loi nc di t phn bit.

-

Trang 35 / 67



2. -

Cc dng nc tn ti trong t Trong t nhin, t thng cha mt lng nc nht nh v tn ti cc dng : th hi, nc kt tinh (thng xut hin vng n i v hn i tuyt), nc lin kt ha hc, nc lin kt vt l, nc mao dn v nc trng lc (nc t do). 1. Nc lin kt ha hc : nm trong thnh phn cu to mng tinh th ca khong vt. o Lng nc lin kt ha hc thay i ph v tnh ng nht ca vt cht, cn cc tnh cht vt l th thay i t t ( trong sut, chit sut, t trng ) o Trong thc t xem nh nc thuc phn ht rn ca t v loi nc ny khng nh hng trc tip n tnh cht ca t . 2. Nc lin kt vt l : nc lin kt mt ngoi ca ht t do lc tng tc gia cc phn t nc vi b mt ht t, ch yu l lc ht tnh in. Lng nc lin kt vt l thay i ty thuc vo tnh a nc ca khong vt, phn tn mn ca ht t, thnh phn v hm lng ca cc cht ha tan trong nc l rng ca t 3. Nc mao dn (l 1 dng nc t do): tn ti trong cc l rng v khe nt nh (khe nt c b rng vt m Fr = nF = F Fr 1+Trang 44 / 67



-

Vy vn tc nc thm thc t ln hn l thuyt. V mt an ton, ngi ta thng s dng vt. b) i vi t dnh

Hin tng t thm xy ra trong t dnh khc vi t ri. : i bin i t 0 i0 : vt = 0 : Hin tng thm cha xy ra 1 : i0 < i < i2 : vt 0 : Hin tng thm xy ra nhng mi quan h gia v t v i l phi 2 tuyn. 2 : i > i2 : tuyn tnh : Quan h gia vt v i ging nh trong t ri. 3 - Trong xy dng, thc t ch yu xy ra trong on t 2-3, do s dng trong t dnh, nh lut Darcy c dng: vt = kr (i i0) vi i0: gradien thy lc ban u tnh ton.0 1

-

VI.2.

Xc nh lu lng cho dng thm phng n nh VI.2.1. Lu lng thm n nh cho tng cha nc khng p a) y cch nc nm ngang

Xt mt n v tit din thm c b rng l 1m. q = K.F.I = K.h.I (F = 1m x h)

Trang 45 / 67



Xc lp h trc ta : I = Thay vo q = K .h.

dh (gi tr ca h gim cn gi tr ca x tng) dx

dh hay qdx =K .h.dh dx

Ly tch phn t tit din (1) n tit din (2)

q dx = K h.dhx1 h1

x2

h2

q( x2 x1 ) = K

2 h2 h12 2

q=Kq=K2 h12 h2 2L

2 h12 h2 2( x2 x1 )

Nu x2 x1 = L ( khong cch gia 2 h khoan)

Chn im M bt k, cch tit din (1) mt khong l x 2 2 h 2 h2 h 2 hx Ti tit din (1) : q1 = K 1 ; Ti tit din qua M : qM = K 1 2L 2x 2 2 h h2 h 2 hx2 Dng chy n nh nn q1 = qM: K 1 =K 1 2L 2xhx = h12 x 2 (h12 h2 ) L

b) y cch nc nm nghing

Xt mt n v tit din thm c b rng l 1m. h +h q = K.F.I = K.htb.I htb = 1 2 2 vi I = x2

dH dx

q = K .htb .H2

dH hay qdx = K .htb .dH dx


q dx = Khtbx1

H1

dH

q ( x2 x1 ) = K .htb .( H 2 H1 )

q = K .htb .

H1 H 2 L

q = K.

h1 + h2 H1 H 2 . 2 L

Trang 46 / 67



Chn im M bt k, cch tit din (1) mt khong l x h + h2 H1 H 2 . Ti tit din (1) : q = K . 1 2 L h + hx H1 H x . Ti tit din qua M : qM = K . 1 2 L h1 + h2 H1 H 2 h + hx H1 H x . = K. 1 . Dng chy n nh nn q1 = qM : K . 2 L 2 L Vi hx = Hx z VI.2.2. Lu lng thm n nh cho tng cha nc c p

a) y cch nc nm ngang

Xt mt n v tit din thm c b rng l 1m. q = K.F.I = K.M.I (F = 1m x M) M : chiu su ca tng cha nc c p vi I = x2

dH dx

q = K .M .H2

dH hay qdx = K .M .dH dx


q dx = KMx1

H1

dH

q ( x2 x1 ) = K .M ( H 2 H1 )

Vy q = K .M

H1 H 2 ( x2 x1 )

q = K .M

H1 H 2 L

Chn im M bt k, cch tit din (1) mt khong l x Ti tit din (1) : q1 = K .MH1 H 2 H Hx ; Ti tit din qua M : qx = K .M 1 L x

Dng chy n nh nn q1 = qx:

H1 H 2 H1 H x = L x

H x = H1

x ( H1 H 2 ) L

Trang 47 / 67



b) y cch nc nm nghing

-

Cch gii quyt Xt mt n v tit din thm c b rng l 1m. M M1 dH .x v I = q = K.F.I vi F = 1m x M = M 1 + 2 dx L q.dx M 2 M 1 dH = KdH .x . q = K . M 1 + M 2 M1 (1) M1 + .x L dx L L M M1 M M1 .du .x du = 2 .dx hay dx = t u = M 1 + 2 M 2 M1 L L Ly tch phn t tit din (1) n tit din (2)

qL (1) M 2 M1q = K.

u2

x1 = 0 u1 = M1 ; x2 = L u2 = M2

2 du = K dH u u1 H1

H

M 2 M 1 H1 H 2 . M L ln 2 M1

Ti

Chn im M bt k, cch tit din (1) mt khong l x M M 1 H1 H 2 q = K. 2 . M2 tit din (1) : ; Ti L ln M1

tit

din

qua

M

:

q = K.

M x M 1 H1 H x . Mx x ln M1

Trang 48 / 67



Dng chy n nh nn q1 = qx :

M 2 M 1 H1 H 2 M x M 1 H 1 H x . = . M2 Mx L x ln ln M1 M1

Mx M 1 H1 H 2 M 2 M 1 H x = H1 . . .x M2 L M x M1 ln M1 ln

VI.2.3.

Trng hp tng cha nc gm nhiu lp

a) Dng chy song song vi mt phn lp (i) Tng cha nc gm 2 lp vi h s thm lp trn km hn lp di

Tng di c h s thm nh hn tng trn, chu p lc tng nc bn trn tng di c coi l tng c p.dH dh q = q1 + q2 = K 2..M . + K1..h. dx dx

q1 : lu lng n v ca tng trn, c mt thong t do. q2 : lu lng n v ca tng di, nc c p

qdx = ( K 2..M .dH + K1..h.dh ) = q dx = K 2 Mx1

x2

H2

H1

dH K hdh1 h1

h2

q ( x2 x1 ) = K 2. .M ( H1 H 2 ) + K1..

2 h12 h2 2

Vi x2 x1 = Lq=2 K 2. .M h 2 h2 ( H 1 H 2 ) + K 1. . 1 L 2L

(ii) Tng cha nc gm nhiu lp

Trang 49 / 67



Trong trng hp ny ta c: q = q1 + q2 + q3 + + qn ; h = h1 = h2 = h3 = = hn do : i = i1 = i2 = i3 = = in Lu lng qua mi tng: q1 = F1 . k1 .i vi F1 = B.d1 q2 = F1 . k2 . i vi F2 = B.d2 q3 = F1 . k3 . i vi F3 = B.d3 qn = F1 . kn . i vi Fn = B.dn Tng lu lng: q = q1 + q2 + ... + qn = (k1.d1 + k2.d2 + k3.d3 + .+ kn.dn)B.I Lu lng dng thm l q = K.F.I (vi B =1m) q = K.H.I H = d1 + d2 + d3 + + dn Nh vy ta c:K TB = k1.d1 +k 2 .d 2 +... +k n .d n d1 +d 2 +... +d n

b) Dng chy vung gc vi mt phn lp (i) Tng cha nc gm 2 lp c h s thm thay i t ngt theo phng ca dng thm

Lu lng thm qua thm bc 2 : q = K1 Lu lng thm qua thm bc 1 : q = K 2

2 2q h12 h2 h12 h22 = L1 K1 2L1 2 2q hs2 h2 L2 hs2 h22 = K2 2L2

Trang 50 / 67



L L 2 2 T suy ra : h1 h2 = 2q 1 + 2 K 1 K2

q=

h12 h22 L L 2 1 + 2 K K 2 1

Tnh chiu cao hs : K1

2 h12 hs2 h 2 h2 = K2 s 2 L1 2 L2

hs =

2 K1L2 h12 + K 2 L1h2 K1L2 + K 2 L1

(ii) Tng cha nc gm nhiu lp

Trong trng hp ny ta c: q = q1 = q2 = q3 == qn ; h = h1 + h2 + h3 + + hn do : i = i1 + i2 + i3 + + in Lu lng qua mi tng : q1 = F1 . K1 . i1 vi F1 = d1 . B q2 = F2 . K2 . i2 vi F2 = d2 . B q3 = F3 . K3 . i3 vi F3 = d3 . B . qn = Fn . Kn . in vi Fn = dn . B

q q q q = + +... + KTB .d .B K1.d1.B K 2 .d 2 .B K n .d n .BKTB = d1 + d 2 + ... + d n K1 K 2 K + + ... + n d1 d 2 dn

Nh vy ta c :

VI.3. -

Xc nh lu lng cho dng thm gn ging khoan ng VI.3.1. Cc c trng dng thm gn ging khoan thng ng n gin trong tnh ton, ch tnh ton ging vi iu kin: ging khoan thng ng vung gc vi tng cha nc, tng cha nc ng nht, dng chy n nh. Khi bm ht nc t ging khoan th mc nc trong ging b h thp xung v to ra xung quanh ging phiu h thp mc nc hay mc p lc. Ty theo ng nht ca tng cha nc m phiu h thp c th i xng hoc khng i xng. Bn knh phiu h thp mc nc l bn knh nh hng R. Khi ging khng khai thc th mc nc trong ging khoan l mc nc tnh. Khi khai thc vi lu lng Q khng i mc nc s h thp n nh c gi l mc nc ng. Dng thm c lin quan mt thit vi cu to ng lc ca ging. Ty theo kt cu ca ng lc, ging khai thc nc c chia lm hai loi:Trang 51 / 67

-



-

Ging hon chnh: L ging c chiu su xuyn qua ton b chiu dy tng cha nc. Nc vn ng vo ging ch qua phn ng lc xung quanh ging. Ging khng hon chnh: L ging c chiu su khng xuyn qua ton b chiu dy tng cha nc, v nc vn ng vo ging qua phn ng lc xung quanh ging, ng thi c th vn ng t y ging vo. Trong tnh ton lu lng khai thc nc ca ging cn thit phi bit bn knh nh hng R. mc chnh xc cho php, ngi ta c th dng cc cng thc kinh nghim sau y tnh ton gi tr ca bn knh nh hng R: CT I.Sulxe : khng xt n lu lng bm ht nc, ch quan tm n thi gian bm ht nc (khng ph thuc vo S h thp mc nc khi bm ht)R = 6 HKt

( m)

a : 47 74; t: thi gian bm ht (gi) m: h s thot nc (ty theo loi t) Cui si sch: 0,35 0,3; t ct: 0,15 0,10; st pha: 0,1 0,01 H : chiu dy tng cha nc (m) t : thi gian bm ht (h) K : h s thm CT Coden : R =12 t QK

( m) - c xt n lu lng bm ht

CT Kusakin : vi qui m khai thc nh v trong tng cha nc khng p R = 2 S H .K K(m/ng) R =575 S H .K K(m/s) CT Zikhard : vi tng cha nc c p K(m/ng) R =10 S K R =3000 S H .K K(m/s) VI.3.2. Xc nh lu lng thm vo ging khoan hon chnh

a) Trng hp tng cha nc khng p

- Lu lng thm ca ging khoan Q = K.F.I Tit din l hnh tr trn F = 2rh Gradien thy lc I =dh dr

Q = K .2r.h.

dh dr

Qdr = K .2.h.dh rTrang 52 / 67



Tch phn 2 v r = ro h = ho = H S r=R h=H R H 2 dr R H 2 ho Q = 2.K h.dh Q ln = 2 .K r ro 2 r ho o

Q = .K

2 2 H 2 ho H 2 ho (2 H S ) S = 1,366 .K = 1,366 .K R R R ln lg lg ro ro ro

Nu c 1 ging quan trc

Q = 1,366 .K

2 h12 ho r lg 1 ro 2 h2 h12 r lg 2 r1

-


Q = 1,366 .K

Xc nh chiu cao mc nc ti 1 im bt k Nu ch c 1 ging khai thc (vi H=Hx v R=x)x r Hx = h + 1,366 K2

Q lg

Nu c 1 ging quan trc (vi h=h1 v r=r1)H x = h2 + (h12 h 2 ) lg lg r1 r x r

b) Trng hp tng cha nc c p

- Lu lng thm ca ging khoan Q = K.F.I Tit din l hnh tr trn F = 2rM Gradien thy lc I =dh dr dh Qdr Q = K .2r.M . = K .2.M .dh dr r

Trang 53 / 67


Ti liu a cht cng trnh Chng I : M uH

dr Q = 2.M h.dh r ro ho

R

Q ln

2 R H 2 ho = 2 .K ro 2

Q=

2..KM ( H ho ) 2,73 KM ( H ho ) 2,73 K .M .S = = R R R ln lg lg ro ro ro


Q=

2,73 K .M .( h1 ho ) r lg 1 ro 2,73 K .M .( h2 h1 ) r lg 2 r1

-


Q=

Xc nh chiu cao mc nc ti 1 im bt k Nu ch c 1 ging khai thc (vi H=Hx v R=x)Q x Hx = + h lg 2,7 K .M 3 r

Nu c 1 ging quan trc (vi h=h1 v r=r1)Hx = h + h1 h x lg r r lg 1 r

VI.3.3. -

Xc nh lu lng thm vo ging khoan khng hon chnh

a) Phng php Focgeimer Do dng chy vo ging khng hon chnh b un cong nhiu hn so vi ging han chnh chho nn dng thm b sc cn ln hn khi nc chy vo ging, do lu lng thm b gim i 1 lng nht nh Tng cha nc khng p : Qkhc = Qh.c . akk =l 4 2h l h h

-

Tng cha nc c p : Qkhc = Qh.c . acc =l M4

2M l M

-

l : chiu di ng lc h : b dy tng cha nc khng p M : b dy tng cha nc c p b) Phng php Zamarin Khi tng cha nc c b dy ln hn so vi chiu di phn cng tc ca ng lc, phi xc nh chiu su ca i nh hng (Ha) tnh t mc nc tnh tr xung v gi tr ca L = S + l Xc nh gim mc nc trong ging S v chiu di phn cng tc ca ng lc l Bng xc nh Ha = S + ha L = f(S) Ha = f(L) L = 5S Ha = L= 1,3L 3,3S Ha = L= 1,5L 2,0S Ha =Trang 54 / 67



L= 1,25S L=S

1,7L Ha 1,8L Ha = 2L c) Phng php Gerinski-Vavuski (i) Trng hp tng cha nc v hn (coi nh l dng im)

-

-

Xung quanh dng im ca mt nc l mt cu ng tm. Cc tia ng dng hi t vo tm. Vn tc ti 1 im A bt k trn mt cu: Q v= vi : bn knh mt cu , Q : lu lng thm 2 4 o Theo nh lut Dacxiv = K . dS do

dS : gim p lc trn phn t di dng thm Q.do Q.do dS = dS = 2 2 4Ko 4Ko Ly tch phn 2 v -

dS = 0

S

Q 4K

0

d2

S=

Q 4K

(ii) Khi xem ng lc c chiu di l (dng chy c xem l 1 ng) Xt 1 phn t nh dz, phn t coi nh 1 im Lu lng qua phn t dQ =dQ 4K

Q .dz 2m2

dS =

dS =

Qdz 8Km r + z2

dS =0

S

Q 8Km

+m m

dz r + z22

ly tch phn ta c S =

Q 2m ln 4Km r

Q=

4KmS KlS = 2,73 2m l ln ln r r

VI.3.4. -

Tnh ton h thng ging khoan c nh hng ln nhau

Khi khai thc nc dng cho sinh hot hoc cng nghip, cn b tr khong cch gia cc ging t gy nh hng nhau l hp l nht l 2R.

Trang 55 / 67



-

tho kh h mng hoc h thp mc nc ngm i khi cc ging c nh hng ln nhau _ phu h thp mc nc ca cc ging gy ra hin tng giao thoa mc nc, lu lng nh hn tng lu lng cc ging bm hot ng ring bit.

-

a) Tnh ton h thng ging khoan hon chnh trong tng cha nc khng p Gi s c n ging khoan sp xp xung quanh im A v cch n nhng khong x 1, x2, , xn

-

Q1 R lg 1,366 .K x1 Q2 R 2 2 lg Trng hp c ging HK2 hot ng H h2 = 1,366 .K x22 2 Trng hp c ging HK1 hot ng H h1 =2 2 Trng hp c ging HKn hot ng H hn =

R Qn lg 1,366 .K xn

Khi tt c cc ging cng hot ng, ta c nh sau: Q1 R Q2 R Qn R H 2 h2 = lg 1 + lg 2 + ... + lg n 1,366 .K x1 1,366 .K x2 1,366 .K xn h : chiu cao mc nc ti A khi cc ging cng hot ng Q = Q1+Q2++Qn R=R1=R2 = = Rn

H 2 h2 =-

Q1 (n lg R lg x1.x2 ... xn ) 1,366 .K .n

Trng hp b tr cc ging cch u im A (xem nh b tr trn ng trn bn knh xo) vi x1= x2 = = xoTrang 56 / 67



-

Trng hp ging b tr trn chu vi hnh vung hoc hnh ch nht th coi cc ging ny c b tr trn ng trn c bn knhS A = H h =

xo =

F

b) Tnh ton h thng ging khoan hon chnh trong tng cha nc c p Tnh ton tng tQ 1 (lg R lg x1.x2 ... xn ) 2,73 .K .M n

Tng lu lng ca h thng ging khoan hon chnh

Q = 2,73 .K .M

H h R lg xo

Tng t nh i vi tng khng p trong trng hp b tr theo hnh trn, hnh vung hay hnh ch nht VI.3.5. Trnh t thit k h thp mc nc ca 1 h thng ging khoan

VI.4.

Xc nh bn knh nh hng ca h thng ging h thp mc nc cn thit. Xc nh bn knh ging ln. Xc nh tng lu lng ca h thng ging. Xc nh kh nng thu nc ca 1m ng lc. Tnh tng chiu di ng lc cn thit cho c h thng. Tm s lng ging n. Chn cch b tr v khong cch gia cc ging. Kim tra lu lng ca mt ging m nhn v nng lc thc t ca mt ging ring bit. Tin hnh kim tra chiu cao mc nc ti cc im bt k, nu khng tha yu cu tho kh h mng th phi thit k tnh ton li. Cc phng php xc nh h s thm K VI.4.1. Phng php bm nc th nghim trong ging khoan a) c im ca phng php

-

So vi th nghim trong phng th thit b v thao tc phc tp hn, tn nhiu thi gian v chi ph cao hn nhng chnh xc hn. S dng ging khoan thm d v ging quan trc o lu lng v gim mc nc trong qu trnh th nghim. Qu trnh th nghim gm t nht 3 giai on cho n n nh v c trnh by bng th quan h Q = f(S). b) Th nghim bm ht trong tng cha nc c p (i) Phng php x l s liu theo R.Whitlow

-

B tr mt ging th nghim v 2 ging quan trc v o gim mc nc 10 30/ln. Nu 3 ln o lin tip c Sn-2 = Sn-1 = Sn = const coi nh n nh. r Q ln 2 2. .KM (h2 h1 ) r1 Q= K = r 2. .M (h2 h1 ) ln 2 r1 Khi ging th nghim l ging quan trc: r 1,2r do ht nc xung quanh ging b xo ng. h h1 = H 0,8S1 do ma st dn n c bc nhy mc nc.

Trang 57 / 67

Khoa Cng Trnh B Mn K thut c sQ (ln r2 ln 1.2r ) 2..M ( h2 H +0.8S1 )


K =

(ii) Phng php x l s liu theo phng trnh ThesisPhng trnh c bn ca ThesisS= 0.183Q 2.25at lg T r2

Trong : T: h s dn nc (m2/ngm); a: h s truyn p (i vi nc c p) hay h s truyn mc nc (i vi nc khng p) c trng cho tc pht trin phu h thp. ( : h s nh nc) hay a = 0.183Q 2.25a 0.183 lg + lg t Bin i phng trnh trn ta c S = T T r2 0.183Q 2.25 a 0.183Q lg t A = v C = S = A + Clgt 2 T T r o c gim mc nc S1, S2, S3 ... ti cc thi im t1, t2, t3 v v th S = f(lgt)a= KM Kh

Gi tr A : khong cch t gc Q n giao im ca th v trc tung Gi tr C : C = tg T=0.183Q C

lga = 2 lg r 0.35 +

A T K= C M

c) Th nghim bm ht trong tng cha nc khng p (i) Phng php x l theo R.Whitlow b tr 1 ging th nghim v 2 ging quan trcv o gim mc nc

h2 h12 Q = .K r Quan h gia gim mc nc v lu lng nh sau : ln 2 r1

2

Trang 58 / 67



T phng trnh trn ta c :

K =.

Q h2 2 h12

ln

r2 r1

Trng hp coi ging th nghim l ging quan trc :K . 2.5Q ( H S n )( 2 H + S h )

(ii) Phng php x l theo phng trnh Thesis Phng trnh Thesis cho tng nc khng p c dng(2H - S)S = 0.366 Q 2.25at lg K r2

t A = 0.366

Q 2.25at 0.366 Q lg v C = 2 K K r

(2H S)S = A + Clgt gim mc nc S1, S2, S3 ti cc thi im t1, t2, t3 v v th.

lg a = 2 lg r 0.35 + K =0.366 Q C

A C

VI.4.2.

Phng php xc nh trong phng th nghim

a) Th nghim bng dng c gradient p lc khng i Th nghim ct nc c nh c dng xc nh h s thm ca t ht th nh ct v cui c K > 10 m/s. Thit b thm c s nh sau:-4

Trang 59 / 67



Tng lu lng nc thu c : Q = A.v.t = A(k.i)t Q : lu lng nc thu c trong thi gian t(s) A : Din tch mt ct ngang ca mu t Thay gradient thy lc vo cng thc trn Q = A kQL h t hoc K = Aht L

b) Th nghim bng dng c gradient p lc thay i Th nghim vi ct nc gim dn dng xc nh h s thm ca t ht mn nh ct mn, bi v t st c tnh thm km K = 10 10 m/s. Khi cho nc thm qua mu t. Ti thi im t = t tng ng vi chnh lch ct nc h1. Ti thi im t = t tng ng vi chnh lch ct nc h , mt lng nc thm qua mu t.-4 -7 1 2 2

Trang 60 / 67



Lu lng nc chy qua mu t ti thi im t : q = k Trong : q : lu lng dng chy a : din tch mt ct ngang ca ng o p A : din tch mt ct ngang ca mu t Phng trnh trn c vit li : dt =aL dh Ak h

h dh A = a L dt

Sp xp li ri tch phn theo phng trnh trn, ta c :k= h aL ln 2 A(t 2 t1 ) h1 h 2.3aL hay k = lg 1 A(t 2 t1 ) h2

Ak aL

t2

t1

dt =

h2

h1

dh h

Trang 61 / 67



CHNG VII : VII.1. -

CC HIN TNG A CHT LIN QUAN N XY DNG

Hin tng phong ha t VII.1.1. Khi nim phong ha

-

Tc dng phong ha l tc dng ph hy do cc nhn t trong kh quyn, thy quyn v sinh quyn. Cc c to thnh di su trong iu kin ging nh iu kin lc hnh thnh ngha l tn ti cng su trong iu kin nhit v p lc cao th chng s trng thi cn bng. Nhng nu v mt l do no , cc y b phi ra b mt t chu nhng iu kin mi: iu kin v nhit v p lc thp v cc iu kin vt l ca mi trng xung quanh khc hn mi trng khi chng cn nm su th cc dn dn b bin i. Qu trnh bin i gi l qu trnh phong ha. Khi phong ha, cc b bin i v thnh phn, kin trc v c v tnh cht vt l v c hc ca . Cc phong ha c h s thm thay i, dung trng phong ha thng gim, rng n tng ln, bn gim xung. Ni chung cc tnh cht vt l v c hc c chiu hng xu i so vi gc. VII.1.2. Cc kiu phong ha t

a) Phong ha vt l L qu trnh lm cc b bin i m khng km theo s bin i v thnh phn khong vt m ch bin i v kin trc, cu to ca v bin t nguyn khi thnh cc, vn, ht. C th phn bit 4 kiu phong ha vt l. (i) Phong ha nhit ng lc thc y cc qu trnh phong ha nhit l s nung nng bi bc x mt tri: cc lp t nhng su khc nhau c nhit khc nhau, do b gin n khc nhau, khin cho lin kt gia cc lp b ph hy dn ri v thnh nhiu mnh vn. Cc loi c cu to tinh th, v d granit hoc c dng cu to ht nh ct kt, cui kt, v.v, c cc ht vi thnh phn khong vt khc nhau, do c hp ph nng lng mt tri v gin n khc nhau, dn n s ph hy cc khi cng chc thnh nhng ht vn, nh trong trng hp thnh to ct kt acko cc vng kh nng. Nhn chung, cc loi c mu sm v c thnh phn a khong b phong ha mnh lit hn c. Mt khc, trong nhng iu kin t ging nhau th khi dao ng nhit cng t ngt v c bin cng ln, hiu ng phong ha nhit cng mnh. Nh vy, i vi loi phong ha ny, dao ng nhit gia ngy v m ng ch hn c. Phong ha nhit hot ng rt mnh cc kh hu kh nng cc vng sa mc v bn sa mc, cc vng m t, do lp ph thc vt v th nhng pht trin mnh, b mt gc c che ph, bin dao ng nhit gia ngy v m nh, nn qu trnh xy ra yu hn. (ii) Phong ha bng gi V thc cht, y cng l mt hin tng phong ha nhit, nhng ch xy ra nhng vng lnh c dao ng nhit qua im 0, nham thch b ph hy ch yu do th tch nc thay i khi chuyn ha t trng thi lng sang trng thi ng bng.Trang 62 / 67



Trong bao gi cng c t nhiu l hng v khe nt, ni c th lu gi nc v hi nc. Khi nhit h thp ti 00, nc trong khe nt ng bng, ng thi th tch ca n tng thm, do tc ng ln thnh khe nt nhng p lc rt ln. V vy, sau mi ln nc trong khe nt ha bng, bn thn khe nt li b gin ra thm mt cht. Nu hin tng ha bng tan bng xy ra nhiu ln, khi b phong ha bng gi c th b v thnh nhiu nhng tng v mnh vn. (iii) Phong ha c hc do mui khong kt tinh Trong cc min kh hu kh khan, do hin tng bc hi rt mnh m lun xy ra vn chuyn nc mao dn ln mt t. Trn ng di chuyn, nc mao dn c th ha tan cc loi mui khong v khi nc bc hi, mui khong s ng li. Trong qu trnh mui khong kt tinh, thnh mch mao dn cng phi chu p lc ln khin cho b mt t b rn nt v v vn. Do hin tng ny m nhiu mnh trong sa mc tuy b ngoi c v cng chc nhng li c th b bp vn d dng. Trong cc min kh hu kh khan, do hin tng bc hi rt mnh m lun xy ra vn chuyn nc mao dn ln mt t. Trn ng di chuyn, nc mao dn c th ha tan cc loi mui khong v khi nc bc hi, mui khong s ng li. Trong qu trnh mui khong kt tinh, thnh mch mao dn cng phi chu p lc ln khin cho b mt t b rn nt v v vn. Do hin tng ny m nhiu mnh trong sa mc tuy b ngoi c v cng chc nhng li c th b bp vn d dng.

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(iv) Phong ha c hc do sinh vt Trong qu trnh sng ca mnh, cc sinh vt, v nht l h thng r cy, cng gy tc dng ph hy t . R cy cm su vo khe nt, ln dn ln v cng lm cho cc khe nt ny ngy cng m rng. Hin tng ny cn c th quan st rt r trn vch vi. b) Phong ha ha hc Phong ha ha hc l qu trnh ph hy c km theo s bin i thnh phn ha hc v khong vt. Nhng tc nhn ch yu ca phong ha ha hc l hot ng ha hc ca nc v cc hp cht ha tan trong nc, ca mt s hp cht ha tan trong nc, ca mt s hp phn khng kh, nh CO2, O2 v tc dng ha sinh ca sinh vt. Nc t nhin c kh nng hot ng ha hc ca nc l v n c b phn phn li thnh cc ion H+ v OH-. c bit khi trong nc c CO2 ha tan th kh nng hot ng ha hc ca n cng r rt. V nhng l , tc dng phong ha ca nc th hin mnh hn ti cc vng nng m, cn 101 cc vng kh hu lnh, kh nng y km dn v khi nhit h xung di 00C th hu nh khng cn na. Nhng hin tng phong ha ha hc thng gp l cc qu trnh ha tan, thy phn, oxy ha, hydrat ha, v.v.. (i) Qu trnh thy phn Trong qu trnh thy phn xy ra hin tng thay th cc ion kim loi kim v kim th ca cc alumosilicat bng cc ion H+ ca nc v sinh ra cc hydrosilicat nhm v gii phng cc oxyt kim v kim th ngm nc. V d: octocla to thnh hydrosilicat nhm K2Al2Si6O16 + 2H2O = H2Al2Si6O16Trang 63 / 67



(ii) Qu trnh hydrat ha Qu trnh hydrat ha l qu trnh trong cc phn t nc kt hp vi cc khong vt khng cha nc bin chng thnh cc hydrat. V d: Fe2O3 + 2H2O Fe2O3 . H2O (Hematide Limonite) CaSO4 + 2H2O CaSO4 . H2O (Anhydrite Thch cao) (iii) Qu trnh oxy ha Cc khong vt to thng c thnh to trong mi trng thiu oxy di su, nn hoc l khng c cha oxy, hoc ch kt hp vi n thnh nhng hp cht ha tr thp. Khi b a ln b mt, nn chng tc dng d dng vi cc cht oxy ha trong kh quyn v trong lp v phong ha tr thnh hp cht cha oxy dng ha tr cao hn, bn vng hn trong mi trng mt t giu oxy. V d : Pyrite Limonite (FeS2) Fe2O3 . 2H2O (iv) Hin tng ha tan i vi mt s khong vt v nh mui m (NaCl), thch cao, nc c kh nng ha tan rt mnh, i vi mt vi t khc nh vi, olomit nc cng gy tc dng ha tan nhng vi tc nh. Cng v mc phong ha ha hc ph thuc vo thnh phn t , ngoi ra vai tr kh hu c ngha rt ln, chng hn trong iu kin kh hu nhit i m, qu trnh ny cn c th tin ti giai on tn cng, l giai on latert, cn trong iu kin n i m th n ch dng li giai on st, trong iu kin kh nng ca cc sa mc v bn sa mc, phong ha ha hc pht trin rt km, v phong ha cha ch yu thnh phn mnh vn. Cc vi sinh vt cng ng vai tr quan trng trong qu trnh phong ha ha hc. Khi cn sng cng nh khi cht i, c th sinh vt, nm to xanh, to diatomit, a y tit ra nhiu axit cacbonit v cc axit hu c khc c tc dng ph hy t . VII.1.3. c im tng tn tch

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Qu trnh m lm cho b bin i trn b mt hnh thnh lp khc lp gc gi l v phong ha. Phong ha cng xung su cng gim i, do mc bin i ca cng gim i theo chiu su. Da vo mc lp y cc cht nht trong khe nt ca , da vo mc d kh khi bp vn , da vo s bin i thnh phn khong vt ca , da vo s thay i cc tnh cht vt l v c hc ca , thng v phong ha c chia thnh 4 i: i vn bt (i ht mn) : i ny cc m hon ton bin thnh t, hon ton khng cn thy nhng vn nh ca m na, cn trong t th bao gm cc khong vt c hnh thnh do qu trnh phong ha, h s thm rt nh, hu nh bng 0, nn ln ln, sc chng ct nh, t c tnh dnh v c kh nng trng n khi gp nc. i vn nh (i ht vn) : B ngoi khc xa vi m. t bao gm cc vn nh hoc cc ht ring bit, cc mu nh ca i phong ha thng bao gm cc khong vt ca m v mt s ln khong vt c hnh thnh do qu trnh phong ha. i ny kh nng thm nc tng hn vn bt, sc chng ct ca i ny cao hn i vn bt v nn ln nh hn.Trang 64 / 67



i dng tng : i ny c xut hin khe nt phong ha, thnh phn khong vtc bn cha thay i my so vi m v mt s khong vt c hnh thnh do qu trnh phong ha ch phn b vch cc khe nt m thi. Cc tnh cht ca t y c tng ln so vi i vn nh. i nguyn khi : B mt ging m cha phong ha nhng sc lin kt gia cc ht cng gim nhiu. Trong xut hin cc khe nt kn m mt thng kh nhn thy c, cc tnh cht c l ca hu nh khng khc my so vi m. VII.1.4. VII.2. iu tra nghin cu v x l tng phong ha trong xy dng

Chn v tr xy dng cng trnh (v v phong ha khng u nhau theo chiu ngang hay thng ng). Xc nh chiu dy phong ha cn phi bc b. Chn c bin php ngn nga phong ha (nhng phi bit tc phong ha v tc nhn gy phong ha). Hin tng t chy VII.2.1. Khi nim

Nhng du hiu c trng ca ct chy: trng thi t nhin, ct chy thc c mu xm sng, xm lc, xm xanh, vi cc sc thi m hoc nht, ty theo lng cha cc tp cht hu c v cc thnh phn khc. Ra ngoi khng kh, mu ca chng thay i nhanh v khng ng u. Chng tr thnh sng hn, pht vng, i ch pht hng do s oxy ha. Khi b bc l bi cng trnh khoan o hoc cc h mng, ct chy bt u chy nh mt cht lng nht. Nu nh trng thi ng sut ch do trng lng bn thn, th ct chy chy chm, cn nu nh do tc dng ca p lc thy ng hoc p lc thy tnh c gi tr ln v rt ln, th chng s vn ng nhanh hoc rt nhanh v n y ln. c im tiu biu l khuynh hng bin i xc bin, tc l ha lng khi b rung v chn ng do tc ng c hc, ri sau khi tc ng chm dt, chng t khi phc li mt phn hoc ton phn trng thi ban u vi tc no . Khi b hong kh, ct chy tr thnh loi t dnh kh cng sng mu hn so vi trng thi ban u v kh c th bp vn bng tay. iu ny chng t ct chy khng ch cha ht bi m cn cha mt lng ht st nht nh. VII.2.2. iu kin pht sinh ct chy

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iu kin v kt cu ca t: d 60 10 d pht sinh ct chy. d10 iu kin v dng thm: Igh = (D 1)(1 n) Trong : D l t trng ca ct, n l rng ca ct. Nu Ithc t > Igii hn xy ra ct chy VII.2.3. Bin php ngn nga

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Khi xy dng trong khu vc c ct chy cn phi xc nh: S phn b v iu kin th nm ca chng. iu kin a mo khu vc phn b ct chy. Thnh phn tnh cht c l ca ct chy, c bit l cht kt cu. c im a cht thy vn ca khu vc c ct chy, chiu su mc nc. Mt s bin php ngn nga nh h thp mc nc ngm, gim p lc thy ng. C th dng mt h thng ging, h khoan, rnh; bo v mi dc, mi h t khng b nc chy lm tri t. VII.3. Hin tng xi ngm t VII.3.1. Khi nim

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Hin tng xi mn ngm ch yu xy ra trong ct ri rc di tc dng ca dng thm lm cho nhng ht nh trong khi t b cun tri i khi l rng gia cc ht ln, cn cc ht ln th vn gi nguyn v tr. Hin tng ny lm cho b mt t tt xung thnh cc h ging nh ci phu. Hin tng xi ngm ny gy nguy him cho cc cng trnh thy cng. N thng pht sinh h lu cc cng, pht sinh trong bn thn , p t, khi cc cng trnh lm vic vi u nc cao, lm cho cng trnh b r r dn n hin tng tri t mnh lit, lm sp cng trnh. cc mi dc thin nhin cng c th pht sinh xi ngm v l mt trong nhng nguyn nhn pht sinh dc trt. VII.3.2. iu kin pht sinh xi ngm

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iu kin v kt cu ca t: Thnh phn cp phi ht. Trong t phi c 2 loi ng knh d 60 D 20 pht sinh xi ngm. 20 hay Cu = ht chim u th v d10 d iu kin v dng thm: dc gii hn cc ht ct bt u b y i c xc nh theo cng thc: Igh = (D 1)(1 n) + 0,5n Trong : D l t trng ca ct, n l rng. Nu Ithc t > Igii hn xy ra xi ngm. VII.3.3. Bin php ngn nga

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iu tit dng chy, lm cho cc cng trnh tiu thot nc, ngn nga khng cho nc chy trong cc tng t . Thit b tng lc phng cc ht b cun tri. Thay i kt cu cng trnh lm gim tc dng ngm di nn hay trong bn thn cng trnh. Dng cc bin php nhn to nhng phng php keo kt bng cht silic, nha ng ci to tnh cht ca t . VII.4. Hin tng cc t VII.4.1. Khi nim

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Cct l hin tng a cht t nhin sinh ra do tc dng ha tan ca nc di t v nc trn mt trong cc d ha tan to ra trn b mt v bn trong khi nhng hnh thi c bit nh: hang ng ngm, sng ngm, nhng h trng dng phu hoc nhng ging dng phng bn trong khi .Trang 66 / 67



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Do , lm kt cu ca thay i : kh nng thm nc tng v kh nng chu lc ca gim. l 2 vn m a cht cng trnh cn phi gii quyt khi xy dng cng trnh trn vng Cact. VII.4.2. iu kin hnh thnh v pht trin cct

- Gm 4 iu kin : o Cc phi c tnh ha tan: bao gm cc mui khong NaCl, KCl, CaSO4, CaSO4.2H2O, CaCO3, CaMg(CO3)2, v.v o Hin tng cact ph bin nht trong cc carbonate ( vi) v loi ny ph bin nht trong v Tri t. o Cc nt n: nh c cc khe nt nn nc mi vn ng c v to c hnh thi cact. o Nc phi c kh nng n mn.Nc phi vn ng: s vn ng ca nc quyt nh hnh thi v mc pht trin cact. - Nc vn ng trong cact lm cho hnh thi Cact khc nhau theo chiu su v thng c chia lm 4 i: o i I: i bo ha kh Nc vn ng ch yu theo phng thng ng. Do hnh thi cact l nhng ging hnh phu hoc thng ng. o i II: i vn ng theo ma V ma kh, nc vn ng theo phng thng ng. V ma ma, nc vn ng theo phng nm ngang. Do hnh thi cact l nhng ging thng ng hoc nhng con sng ngm. o i III: i bo ha nc Nc vn ng theo phng nm ngang. Hnh thi cact l nhng con sng ngm. khu vc y sng nc vn ng i ln. o i IV: i vn ng su Nc vn ng theo phng nm ngang, hnh thi cct l nhng con sng ngm. Cng v pha sng mc pht trin Karst cng tng v c s hn hp gia 2 loi nc: nc ngm v nc sng to ra mt loi nc c kh nng n mn. VII.4.3. iu tra nghin cu v x l tng cc t trong xy dng

Dng bin php iu tit dng chy v thit b tiu nc ngn chn khng cho nc trn mt v nc di t chy vo tng b Karst ha nhm hn ch ngn nga Karst pht trin. Ph v nh cc hang hc Karst. p v t st vo nhng hang hc Karst ngn nc chy ra. Xy cc tng chn nc ngn nc t cc rnh Karst. Dng xi mng keo kt nn cng trnh, pht xi mng qua cc h khoan bt kn cc k nt v hang hc Karst to thnh mt mng khng thm tng thm cng ca .

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