KHOA HOC VA CONG NGHE MO
XAC DINH CHIEU SAU LO MIN HOP LY KHI THI CONG GIENG DUING CO SUTDUNG CAC VONG CHONG TAM THOfI
GS.TS. VO TRQNG HUNG Trifc/ng Dai hoc Md-Dia chat
1. NhCPng nghien ciiu tdng quan
Trong so dd ndi tilp hoac song song thi cdng gilng diing, d l ehong giu tam thdi cho gilng diing ngudi ta thudng sii dung cae vdng chdng tii thep ehu "C" hoae mdt to hgp k i t elu chdng giu thilu hoac dly du tii vi neo, ludi thep va be tdng phun.
Viec Sli dung eae loai vdng chdng d l chong giu tam thdi gilng diing eho thiy, budc chong (khoang each giua cae vdng chdng) tam thdi se gay nen hien tugng khdng hgp ly sau day. Khoang each giua eae vdng chdng "Ivc" dugc xae djnh tren CO sd kha nang chju lyc cua chung loai vdng ehong duge ehgn (do bin, kich thude elu tao mat elt ngang....) va cae dieu kien dja ca hgc eua mdi trudng dit da bao quanh gilng diing.
Theo nguyen tie, gia trj khoang each nay la mdt dai iugng khdng thay ddi trong nhung dilu kien sau: ehung loai k i t c l u chong giu da ehgn; cac dac tinh c l u tao khdng ddi eua gilng diing; cac dilu kien mdi trudng dja co hgc khdng ddi.
/-/. 1 So 66 xac djnh mdi quan he giCra gia tri bmyc tien guvng "Ick- d" va khoang each giiia cac vong chong \c"-
Trong khi dd^ hien nay cac phuang phap tinh toan chieu sau Id min "Ick" nhim thoa man cae didu
kien ky thuat-cdng nghe-tl chiic thi cdng gilng diing khdng ehu y tdi ydu to gia trj khdng ddi da dugc tinh toan eua khoang each giua cac vdng chdng. Didu nay se dan d i n hien tugng: trong met chu ky thi edng, gia trj budc tiln guong "lck-ii" (n - He so su dung lo min) thdng thudng khdng t h i bang mdt gia tri bdi sd nguyen (sd lln nguyen) eua dai lygng khoang each giua cac vdng chdng "Ivc" (H.1).
Tai H.1: 1 - Guang thi edng eho chu ky thii "i"; 2 - Guong thi edng thyc td tiln dugc sau khi hoan thanh ehu ky thi cdng thii "i"; 3 - Guong ly thuyit ky vgng tiln duge sau khi hoan thanh chu ky thi edng thii "i"; 4 - Guong thi cdng thyc t l tiln dugc sau khi hoan thanh ehu ky thi cdng thii "i+l"; 5 - Guang ly thuyit ky vgng tiln dugc sau khi hoan thanh chu ky thi cdng thii "i+T'; 6 - Vdng chdng.
Hien tugng nghjch ly cdng nghe thi cdng tren day se d i n den nhu'ng hau qua sau day:
••• s l lugng vdng ehong tinh cho mdt ehu ky thi cdng se la mdt sd le (sd khdng nguyen);
•:• Khdi lugng cdng tac lip dyng phin le cho mpt vdng chdng se gay nen nhung khd khan v l td ehiic- ky thuat-cdng nghd cho chu ky thi edng nhu sau:
-f D I hoan thanh toan bd khdi lugng cdng tac thi edng trong thdi gian cua mdt chu ky ehgn trudc (Tck) va khdng pha vd chu ky thi edng da tinh theo
"Ick", thi ddi thg ehi cd the thyc hien mdt phin (phin Id) khdi lugng edng vide l i p dyng eua vdng chdng cudi eung sat guong thi cdng. Nhu vay, edng tae chdng giu cho gilng diing tai mdi chu ky thi cdng se phai k i t thue bing mdt vdng chong khdng trgn ven. Cdng vide thi cdng nhiing phin kit c l u edn lai trong vdng chdng sat guong se dugc hoan thanh tai chu ky tilp theo. Day la mdt vin d l khdng Idn vd khdi lugng thi cdng nhung se mang lai sy phiie tap vd cdng tac td chiic.
•¥• Trong khi cac cdng tac thi cdng khae dugc lap di lap lai trong tiing ehu ky thi cdng, thi khdi lygng cdng vide, tinh chit edng viec cua rieng khau chdng giu lai hoan toan khdng giong nhau (khdng gidng nhau d phin noi tilp, hoan thanh not cdng viee l i p dyng vdng chdng dang dd cua chu ky trudc cdn lai va vide cd thd phai d l lai mdt phin CONG NGHIEP MO SO 2 - 2 0 1 1
KHOA HOC VA CONG NGHE MO dang dd cua khdi lygng cdng tac thi cdng vdng
chdng cudi cung g i n gyang tai chinh chu ky thi cdng dang thyc hien).
• N l u trong chu ky thi cdng chi tidn hanh l i p dyng mdt sd lygng nguydn ven Idn n h l t cd thd cac vdng chong hoan chfnh va khdng l i p dyng p h i n Id cua vdng chdng cudi cung thi se xay ra hidn tugng sau;
-f Chu ky cdng tac dang thyc hidn se bi pha vd vi mdt phin cdng vide thudc chu ky se khdng dugc thyc hien;
-•- Phin Id khoi lugng cdng vide l i p dyng cua vdng chdng g i n guang tai mdi chu ky se tich luy d i n d i n thdi dilm du mgt vdng chdng hoan chfnh.
Didu nay se lam gia tang khoang each luu khdng tli vdng chdng eudi cung d i n guong thi cdng. K i t qua se lam eho cdng tac thi cdng trong guong sd trd ndn kem an toan.
-f Tai ehu ky tieh luy du cd thd l i p dyng mdt vdng chdng hoan chinh tii cac "phin Id" cua mdt vdng chdng tii cac chu ky thi cdng trudc, khdi lu'png edng tae chdng giO' se gia tang dot ngdt. Tai day phai chdng thdm mdt vdng chdng so vdi sd lugng vdng chdng cua cac chu ky trudc. Dilu nay eung se pha vd ehu ky thi edng gidng diing.
-f Phai tiln hanh bd sung cac bien phap chdng dd, lien kit... dd dam bao cho nhu'ng. phin k i t c l u vdng chdng g i n gyang (cd c l u tao chua trgn ven) cd thd lam vide trong trang thai dn djnh, an toan d i n thdi dilm tilp tuc l i p dyng vdng chdng mdi d chu ky tilp theo.
Nhung nhuge dilm, nghjch ly cdng nghd tren day cd thd hoan toan dugc loai bd trong trudng hgp ehidu sau Id min da tinh toan "Ick" sao cho gia tri tiln guong thyc td "Ick TI" bang dung mdt bdi sd nguyen (sd l l n nguyen) cua dai lugng khoang each giQ'a eae vdng chdng "Ivc". Dudi day gidi thieu k i t qua nghien ciiu bude d i u eua ehung tdi ve phuang phap xac djnh chidu sau Id min hgp ly "Ick"
sao cho gia tri tiln guang thyc t l "Ick-Ti" bing dung bdi sd nguyen (sd l l n nguyen) eua dai lugng khoang each giua eae vdng chdng "Ivc".
2. Nghien CLFU xay d y n g phu'O'ng phap xac djnh chieu sau Id min dung bang boi sd nguyen cua khoang each giiia cac vdng chdng
Elk xae djnh chidu sau lo min hgp ly "Ick" sao cho gia tri tiln guong thyc t l "Ick-Ti" dung bing mdt bdi s l nguyen (sd l l n nguyen) cua dai lugng khoang each giu'a cac vdng chdng "Ivc" theo chung tdi nen tiln hanh theo trinh ty nhu sau:
•:• Bu'dc 1 - Lya ehgn vat lieu, k i t c l u vdng chdng cho gilng diing; tinh toan khoang each giua cac vdng chdng "Ivc".
• BiPO'c 2 - Tinh toan chidu sau Id min "U" theo phuong phap nhim thoa man cac didu kidn ky thuat-cdng nghe-td chiic thi cdng gidng diing eu thd. Theo Pokrovski N. M., trong so dd cdng nghe ndi tilp va sa dd cdng nghd song song thi cdng gilng diing chidu sau Id khoan "Ick" du-gc xae djnh nhu sau [1], [2]:
Ick - •
'ck (Tl n n + t t g + T , at + "'"ph)
N Ste.|i.Tl.kp Hcg.Tl.cPk m. (1)
k.v xb ll-^cg
Trong dd: Tck - Thdi gian eua mdt chu ky thi edng da ehgn trydc, gid; Tnn - Thdi gian nap thude nd vao cac Id khoan; gid; Ttg - Thdi gian thdng gid sau edng tae khoan nd min, gid; Tat - Thdi gian dua guong vao trang thai an toan, gid; Tph - Thdi gian thyc hien cac cdng tac phu trg, gid; N - Sd lygng Id khoan trong guang thi edng; k - Sd lygng may khoan lam viec ddng thdi tren guong thi cdng; v - Tdc do khoan Id khoan tren thyc td, m/gid; Stc - Dien tich mat elt ngang dao cua gidng diing, m^; |^
- He sd thiia tilt dien; r| - He sd sii dung Id khoan;
kp - He sd nd rdi cua d i t da sau khi nd min; P^b - Nang suit xuc bde d i t da; m^/gid; Hcg - Djnh miic thdi gian l i p dat mdt vdng chdng tam thdi eho gidng diing, ngudi.gid/vdng chdng; cpk - He sd phdi hgp thyc hidn cac cdng tac chong giu' tam thdi va xuc boc d i t da; ii - Khoang each giu-a hai vdng chong tam thdi, m; ncg - Sd lu'png edng nhan ddng thdi tham gia l i p dat cac vdng chdng tam thdi.
•:• Bu'dc 3 - So sanh hai dai lugng "Ick-ri" va
"Ivc": Vide so sanh duge tiln hanh nhu sau tien tinh gia trj cua ty sd "n
"Ick-Ti" va "Ivc":
giua hai dai D i u lugng Ick-n
V 'vc y
(2) Tai day cd thd xay ra hai trudng hgp:
-f Trudng hgp thii nhlt: gia trj "n" hoan toan la mdt sd nguyen duong (trudng hgp g i n nhu khdng bao gjd xay ra tren thyc td). Khi dd, gia trj chieu sau lo min "Ick" xac djnh theo cdng thiic (1) hoan toan thoa man cac ydu c l u ky thuat-cdng nghe-td chiic thi cdng gilng diing;
-f Trudng hgp thii hai: gia trj "n" khdng chin (trudng hgp thudng xay ra). Khi dd, gia trj chidu sau lo min "Ick" xac djnh theo cdng thiic (1) khdng thoa man cac ydu c l u ky thuat-cdng nghe-td chiic thi edng gilng diing. Trong trydng hgp nay, gia tri eua "n" cd thd phan bidt cho hai tnydng hgp nhu sau:
^ Khi gia trj phin sd thap phan "ai" cua "n" sau d i u phly nhd han 0,5:
n = (a + a.,). (3)
CONG NGHIEP MO SO 3 - 2 0 1 1
m mM KHOA HOC VA CONG NGHE MO Trong dd: a - P h i n sd nguyen cua gia trj "n", a=(n-
ai); ai - P h i n so thap phan ( p h i n sd sau d i u p h l y ) eua "n"; trong t r u d n g hgp nay ai<0,5.
Trong trudng hgp nay, dd dam bao d i l u kien gia tri c h i l u sau Id min "Ick" xac djnh theo cdng thiic (1) b i n g mdt sd nguyen d u o n g , n g u d i thiet kd phai loai bd thanh p h i n ai trong tdng gia trj cua n tinh toan theo (3) d l nd trd nen b i n g mgt s l nguyen d u o n g "a".
•^ Khi gia tri phan so thap phan "ai" eua "n" sau d i u p h l y Idn hon 0,5:
n = (a + ai). (4) Trong dd: a - P h i n sd nguyen eua gia trj "n"; ai -
Phan sd thap phan (phan sd sau d i u p h l y ) eua "n";
trong trudng hgp nay ai>0,5.
Trong trudng hgp nay, d l dam bao dieu kien gia tri c h i l u sau Id min "Ick" xae djnh theo edng thiic (1) b i n g mdt sd nguyen d u o n g , n g u d i t h i l t kd nen bu them vao gia tri "n" mdt gia tri a2<0,5 d l gia trj cua chung trd nen la mdt sd nguyen d u o n g "nbu":
n , „ = ( a + a i + a 2 ) = (a + 1). (5) Gia tri cua dai l u g n g bu a2<0,5 phai d u g e ehgn
sao cho thoa man d i l u kien:
(a, +a2) = 1 hay a^ ={^-a.^).
Nhu vay, t i i (4) va (5) ta cd:
n = (nbu-a2).
(6) (7) '> Bu'dc 4 - Xac djnh chidu sau lo min hgp ly khi gia trj p h i n sd thap phan "ai" cua "n" sau d i u p h l y nhd hon 0,5. Khi dd, sau khi k i t hgp (2) va (3) ta ed:
ck-n V 'vc J
= (a + ai). (8)
T l i day:
Ick-n = (lvc-a + lvc-ai)- (9) N h u vay, dd gia trj chidu sau Id min tfnh toan
theo edng thiie (1) trd thanh mdt sd l l n nguyen d u a n g bude chdng (Ivc.a), thi tdng gia trj cua chung phai giam bdt mgt gia tri b i n g (Ivc.ai). Viec lam suy giam gia trj c h i l u sau lo min tinh toan theo cdng thiic (1) ed thd thyc hien bang td hgp cae giai phap nhu sau:
-¥• Giai phap t h i i 1 - G i u nguyen gia trj m i u s l eua cdng thiic (1);
-•- Giai phap t h i i 2 - G i u nguyen cac thdng sd vd thdi gian Jck, Tnn, Ttg, Tat;
-f Giai phap t h i i 3 - Tang thdi gian cua cac edng tae phu trg t i i "Tph" len thanh "Tph2":
Tph2=(Tph+Tp,i) (10) Tai day: Tphi - P h i n gia trj tang them thdi gian cho
cac cdng tac phu trg "Tph" sao eho chidu sau Id min khi tinh toan se giam di mdt dai l u g n g b i n g "Ivc.ai"
CONG NGHIEP MO SO 3 - 2 0 1 1
va t r d thanh mdt sd l l n nguyen d u o n g b u d c chdng bingjivc.a).
D d tim gia trj thay ddi cua thdi gian Tph2 c i n phai xac djnh thdi gian Tphi. Vide xae djnh thdi gian Tphi cd thd tidn hanh n h y sau.
Sau khi k i t h g p (1) v d i (9), ta ed:
(lvc-a+lvc-a,)=n Tck-(Tr nn + tfg + Tat -Tph) k.v
fStc-^i-nkp]
V ^xb , +
iu \
[ ll-a:g J
.(11)
Sau khi bidn ddi bieu t h i i c (11) va dat A i
ta cd:
Ivc-a- _N_
k.v Pxb
H eg •^•9k
'ck"
11--
Tnn+Ttg+Tgt+Tph
h-ncg
^i}yo^^j^
(12)
A l
(13) T u day, gia trj chieu sau Id min hgp ly trong mdt ehu ky thi edng "Ick.hi" pd thd dam bao ydu e l u gia trj t i l n g u o n g t h y c td b i n g sd l l n nguyen duong cua b u d c chong sd du'oc xae dinh theo cdng thiic:
"Ick"
lck.hFlvca=Tl-
"'nn+Ttg+"I^t+"I^h+"
Tl
'-A
A,
(14) _ N h y vay, gia trj thdi gian bd sung Tphi c i n thilt dd lam gia tang thdi gian cua cac cdng tac phu trg se d y g c tinh theo cdng thiic:
(lvc-ai) 'phi _ Vvc- ' . A ,
Tl
(15)
•:• Bu'd'c 5 - Xac djnh chidu sau lo min hgp ly k h i g i a trj p h i n sd thap phan " a i " cua "n" sau d i u p h l y idn han 0,5. Khi dd, theo (5), (6), (7) trong nhu'ng didu kidn cd thd n g u d i t h i l t k l nen bu them vao gia trj "n" mdt dai l u g n g a2<0,5 dd gia tri eua chung trd ndn la mdt sd nguyen d u o n g "nbu=(a+1)".
Tai day, sau khi ket hgp (2) va (7) ta cd:
n = 'ck-TI V 'vc y
(n T l i day:
lckTl = (lv vc-"bu • ' v c ' ^ 2 .n
bu ' . ) •
>.}
(16)
(17) N h u vay, de gia trj chidu sau Id min tinh toan theo cdng t h i i c (1) t r d thanh mgt sd nguyen duong (Ivc-Hbu), thi gia trj cua chung phai tang them mdt dai l y g n g b i n g (Ivc.a2).
Vide lam gia tang gia trj chidu sau Id min tinh toan theo edng t h i i c (1) cd thd t h y c hidn b i n g to hgp cac giai phap n h u sau:
-•• Giai phap t h i i 1 - Giu' nguydn gia trj m i u s6 eua edng t h i i c (1);
KHOA HOC VA CONG NGHE MO mu
-f Giai phap thii 2 - Giu nguyen cac thdng sd vd thdi gian Tck, Tnn, T,g, Tat;
4- Giai phap thii 3 - Giam thdi gian cua cac edng tac phu trg tii "Tph" xudng thanh "Tph2". Trong dd:
\U2={\U-\J (18) Tai day: Tphi - Gia trj thdi gian loai bd d l lam
suy giam thdi gian eua eae edng tae phu trg "Tph"
sao cho chilu sau Id min khi tinh toan se tang them mgt gia trj bing (lvca2) va trd thanh mdt sd lln nguyen duong bude chong bing (Ikc-Hbu).
Dd tim gia tri thay doi cua thdi gian Tph2 c i n phai xae djnh thdi gian Tphi. Vide xac djnh gia tri thdi gian Tphi cd thd tiln hanh nhu sau.
Sau khi k i t hgp (1) va (17) ta cd:
Jvc-'^bu •Ivc-a2) = T1--
Tck - y n n + ttg + Tat + Tph)
il
k.v
Stc.n.Ti.kp xb
r H,
eg •Tl-Cpk \ '
l i . n . 'eg
. - , (19) Sau khi bien ddi bilu thtic (19) va luu y ky hieu
(12), tacd:
'• , . a . T c k "
lvcnbu=Tl-'
Tnn+Ttg+Tat" 'ph" .'kc-^2J
•Al A i
(20) Tai day: Ai - Bieu thiie duac lay theo cdng thiie (12).
Tli day, gia tri ehidu sau lo min hgp ly trong ringt ehu ky thi cdng "Ick hi" cd thd dam bao ydu elu gia tri tiln guong thyc t l bing sd lln nguyen duong eua bude chdng se duge xac djnh theo cdng thiic:
(lkc-a2)
T
ck' ck.hj-•X •nbu = T l -Tnn+T, tg "Tat + T p h - - •Ai
(21)_
Nhu vay, gia tri thdi gian "Tphi" c i n loai bd d l lam giam thdi gian eua eae cdng tac phu trg "Tph"
sao eho chieu sau lo min khi tinh toan cd t h i tang them mdt gia trj bing "Ivca2" va trd nen bing sd l l n nguyen duong cua budc chdng (IvcHbu) se dugc tinh theo edng thiic:
'phi
(Ikc-a^)
A, (22)
Trong trudng hgp gia trj thdi gian Tphi (tinh theo cdng thiic (22) ) qua Idn, lam cho Tph2 cd gia tri trd nen qua nhd, bing khdng hoac gia tri am (xem edng thiie (18) ), ngudi thilt kd phai xem xet cae giai phap bu them thdi gian c i n thilt d l hoan thanh cac cdng tac phu trg bing cac bien phap sau: giam thdi gian nap-nl min Tnn; giam thdi gian dua guong vao trang thai an toan Tat. N l u cac bien phap nay khdng mang lai hidu qua c i n thilt thi
ngudi thilt kd phai t i l n hanh giam gia trj cua m i u sd trong edng thiic (1) nhd cac bien phap td chiic- ky thuat thfch hgp tugng iing.
3. Kit luan
Cac gia trj thay ddi (tang hoae giam) thdi gian eho cdng tac phu trg Tphi tinh theo cae cdng thuc (15) va (22) dd gia tri chidu sau tiln guong thyc t l sau mdi chu ky thi cdng gilng diing trd nen bing mdt sd nguyen l l n gia tri khoang each giua cac vdng chdng "Ivc" ("a.Ivc" hoae "nbu.Ivc") khdng chf lien quan tdi gia trj thdi gian cho cdng tac phu trg don thuin Tph.
Tai day, ngudi thilt ke cdn cd the xem xet cac giai phap ky thuat thay doi thdi gian khdng ehi Tph ma edn ca cac dai lugng thdi gian Tat, Tnj.
Trong nhung trudng hgp khdng the gia tang duge thdi gian Tph (trong trudng hgp ai>0,5), ngudi thiet kd ed thd sii dung phuang phap giam miu sd eua bilu thiic sd (1) nhd giai phap dua vao he sd song song tidn hanh hai cdng tae xuc bde va chdng giu k (k<1) hoae nghien cuu su dung cae loai thilt bj thi edng tidn tiln hon ed nang suit cdng tae Idn hon.
Ngoai ra, cac loai k i t elu chdng giu l i p rap tii eae khdi chdng due s i n , khdi tu-bin... hoan toan cd dac dilm ve cdng nghd thi edng tuong duong nhu vdng chdng. Mdi vdng khoi chdng due s i n (vdng tu-bin) ed thd xem nhu la mdt vdng chdng.
Vi vay, phuang phap tinh toan chilu dai lo min hgp ly khi sCr dung cho loai hinh k i t c l u chdng giu' tren day eung se dugc tidn hanh hoan toan tuong ty nhu ndi dung phuang phap da dd xult tren day.CD
TAI LIEU THAM KHAO
1. noKpoBCKMPi H. M. Coopy>KeHMe n yrnydKa CTBonoB liiaxT. MocKsa. HsflaTen-bCTBO
"Heflpa". 1975.
2. KapT03Mfl B. A., Oeflyney B. H., LUynxiHK M.
H. M flpyrne. LLlaxTHoe n noflaoMHoe eiponTenbCTBo.
MsflaTejTbCTBO AKafleMnn TopHbix HayK. MocKBa.
2003. TOM 1.
Ngudi bien tap: Ho ST Giao
SUMMARY I The paper shows results of stud\
3 estimating the proper length fori the support metal circles.
CONG NGHIEP MO SO 3 - 2011 M l