Vấn đề dự báo thời gian ổn định không chống của công trình ngầm sau khi đào

Thuc t l eung chirng minh dilu nay qua su phIt triln djch chuyin, bien dang v l eac hipn tupng phi hOy, xay ra trong khIi da sau khi dio, chlng gift khoang khdng gian ngam, theo thdi gia

w

i VAN DEDlTBAOIHdl GIAN ON DMH KHONG GHONG

CUfl CONG TRJNH NGflN SfiU KHI {>flO

The term "stand-up tmte'is used Hist time in Lauffefs lock mass

dassifKatkm (1958) In relatkm to the so called 'effedis/B unsupported

span" and then modified by Bieniawski (1973) Until now the

stand-up time Is a useful parameter in rock mechanics and tunnel

design It affects the selection of excavation method, excavation

cyde, the nxk reinforcement method and time to Install rock support

In other words, the sland-up time Is a tunctkm not only of rock mass

properties but also of excavation technique Because c/assificaSon

methods are based on rock mass quality empirical evaluation

through specific parameters, however, the determination of the rock

mass properties to evaluate rock mass quality and also the

sjand-up time Is very difficult in In-s'itu Therefore, the development

of mathematk:al models Is necessary and has great meaningful to

estimate the stand-up time in the tunneling This articte presents a

theoretical solution for determination of the stand-up time or 'rock

mass failure-time of geo-hazards'

GS TS NGUYEN QUANG PHlCH

Hdl Cdng tilnh ngim VI0t Nam

Bien t$p: TS Pham Minh Di>c

1.D|tvin de

Trong thuc t l xiy dung cac cdng trinh ngim

dan dung v l khai thie mo ham 16 hipn tuang

phi huy khoi d l (trie va trdc Id sap Id, trupl

Id ) thudng cd t h i xay ra v i o thdi dilm nhat

djnh sau khi die n l u khdng tien hinh gia cd khIi

d l hole lap dung ket cau chlng hap 1;^ v l kip

thdi Thdi dilm niy phu thupc v i o kich thudc

khoang khdng gian trdng ehua dupe gia c l ,

chlng dd, v i o c i c die dilm dia chit v l c i c tinh

chit ca hpc cua khIi d l Khoang thdi gian k l tir

khi die khoang trlng nhung ehua gia co, chlng

dd eho d i n khi xay ra p h i huy thudng dupe gpi

la thdi gian I n ffinh khing chlng (the stand-up

time), hay thdi gian luu khong Khai nipm n i y

xuat hien d i u tien trong eich phan loai khIi d l

cua Lauffer (1958) [1] v l sau nay trong each

phln lopi ciia Bieniawski (1973) [1] Trong eac

cleh phln loai d6, m l i lien quan giOa thdi gian

I n dinh khdng chlng v l khiu dp khdng chlng

hCru hipu (chieu rpng hc|c khoing eleh tir

guang dap den k i t eau chlng) duac si? dung

d l xiy dyng hay tinh toin t l chirc chu ky dio,

sao cho k i t c i u chlng tam phai duac hoan

chinh trudc thdi diem ed the xay ra p h i huy

M|c dCi cic phuang phip n i y dang dupe sir

dyng p h i biln d Ao v l tren t h i gidi, nhung eung

phai thiy rang mdi lien hp neu tren ciia cac t i c

gia d i u mang tinh kinh nghiem, theo danh gia ehu quan, khdng duac x i y dung trdn ea sd Up luan v|t ly chat che Cung vi v|y, xic dinh thdi gian I n i^nh khdng chlng I I v i n d l ludn dupe quan t i m trong ITnh vuc ea hpe d l v l xiy dyng cdng trinh ngim X l e dinh thdi gian I n dinh khdng chdng eung d i n g nghTa vdi x i c dinh thdi gian xay ra tai bien dia chit (rock mass failure-time of geo-hazards)

B i i viet n i y gidi thipu mpt Idi gill 1;^ thuyit xac ^ n h thdi gian dn d[nh khdng chlng hay thdi gian on the xay tai biln dja chit trong xiy dyng cdng trinh ngam

2 IWo hinh bai toan va cac d i l u kipn v l khdi da

Trong khdi d l ludn t i n tai cac m|t phln each khac nhau Su cd mat cua chiing d i n d i n tinh chit luu biln v l ea hpc, tire I I su phy thupc cua

c i e tinh chat ca hpc v i o thdi gian Thuc t l eung chirng minh dilu nay qua su phIt triln djch chuyin, bien dang v l eac hipn tupng phi hOy, xay ra trong khIi da sau khi dio, chlng gift khoang khdng gian ngam, theo thdi gian Tinh chit luu biln eiia khIi da duac md phong bdi cac md hinh luu biln, dupe nhilu n h i khoa hpc

de xuit [2]

Trong bai niy, tlnh chit ca hpc ciia khdi d l phy thupc v i e thdi gian dupe md phpng bing

md hinh luu biln nhu trong hinh 1, bao gIm md

hinh dan hdi HOOKE ghep n l i tiep vdi md hinh

dec ly tudng SAINT VENNANT, sau dd ghep

song spng vdi md hinh nhdt NEWTON nhu tren

hinh 1 Md hinh luu bien nay edn dupe gpi 11 md

hinh LOON EN [3] B | c diem v l bilu hipn ea hpc

cua md hinh nay d trang thai nen dan tme I I :

- Khi t i e dung ca hpc chua dat den gidi han

chay (hay gidi han dec), hay gidi han b i n md

hinh CO bleu hipn biln dpng d i n hoi - nhdt;

- Sau khi t i c dyng ea hpc dpt dupe gidi hpn

chay bilu hipn cua md hinh la d i n h l i nhdt

-deo

I — = ™ —

Hinh I.Md hinh lau biin

De phan tich q u i trinh biln d l i ca hpc, d o

thanh phin irng suit tong t h i lydn bao gdm hai

thanh phin I I ;

- Cac thinh phin irng suit tTnh (static), t i e

dyng len phan md hinh HOOKE n l i tiep vdi

SAINT VENNANT

C i c thinh phin u'ng suit ddng (kinematic

-dynamic), t i c dyng len p h i n md hinh nhdt

NEWTON

Ky hieu cac thinh p h i n irng suit tTnh v l

ddng, lin luat vdi cac chi s l trdn la s v l d, khi

dd cd mli quan hp;

cr„=CTj+crJ (1)

Gidi han deo, hay gidi han pha huy ciia khdi

da dupe xac djnh tir c i e k i t qua thi nghipm d l

v l c i c phuang phip tinh chuyen ddi khic nhau

Trong b i i niy, gidi hpn deo dupe chpn thee tieu

ehuin dec eua PF!AGER-DRUCKER [4] cd dpng

( y / ) 5 - a i / , ' - a , = 0 (2)

Trong dd;

Id bat bi^n thi> hai cua ten xa l^ch Crng suSt

tTnh;

j^ ^(j-'^+tx', +at la bat bien thu" nhat cua

ten xo irng su^t ttnh;

ai, 02 l^n lu-ol la cac hang so vat li$u Bai toan du-p-c nghien ciru la du-org ham, du-ang 16 nam ngang, tiet dien tron v6i ban kinh

blng R, chi^u dai L, nam o do sau H, diroc dao

trong khoi da la dong nhSt, dang hu'dng, co bi^u ht^n dan hoi - nhot - deo, khdng chju nen t h i tich (he so Poinson v = 0,5 Vo'i cac gia thiet nay, trang ttiai Cpng su^t nguydn sinh trong khoi da la thuy tTnh, voi ap lire ban dau la

p = p.gJi = cr^ = o"^ (3)

Trong do:

p - la khoi lu'p'ng the tich cua khoi da;

g - la gia toe trong tn/cyng;

H - la dp sau bo tri du-ong h^m, k l tir mat d i t

(gia thiit td bang phang) den tam duang him;

av Oh - la cac thanh phan iing suat chinh theo phu'ong thang du-ng (chF so v) va theo phu-cng

n l m ngang (chTsi h)

Vffi gia thiet du-cvng ham nam o dp sau du Ion

( H » R ) vd dai ( L » R ) , co the du-a van de nghien CLTU cac quy lu|t biin doi ca hpc trong khoi da

vk bai toan biin dgng phing, d i i xiJ-ng tdm, trong

he tpa dp dpc cyc, nhu" tren hinh 2

1 3 P=7H

0-Hinh 1 Sodd vi cic (Tiiu kidn bidn tdng quit

cOa bii toin

3 Cac phu'O'ng trinh cv ban

Vai cac dieu kien vd mo hinh bdi toan da grd-i thieu, trong khoi da xung quanh du'dng ham se khong co cac thanh phan u'ng suit tiep, khi do

ba thanh phln Crng suit phap chinh la Crng suit phdp tiip tuyin, irng suit phdp hu-ang tam va LFng suit phap hu'ong tn^c, l l n lu-pl du'gc bieu diin qua cac chf s6 du'a! Id 6, r, z a dang Id t i n g cua cdc thdnh phln Crng suit tTnh(s) va dpng(d) nhu sau:

(7,=a',+af (4)

Do khdi da dupe gia thilt I I khdng chju nen

the tich, nen cae thinh phin bien dang the tich,

biln dpng thing t i l p tuyen bien dang thing

• liudng t i m v l bien dang thing dpc tnjc ham, lan

lupt vdi cac ehi s l dudi v, 9, r, z cd dpng;

' (5)

lis dd cd:

e.=-£, (6)

Xuit phit tir eic m l i quan hp quen bilt chp

md hinh KELVIN, cd t h i bilu diSn m l i lien hp

giua cac thinh phan irng suit phip chinh v l cac

thinh phin bien dpng d l i chinh nhu sau [5];

ag-a=20s,+2rii,

a, -a= IGE^ -I-2I7£, n\

N l u tich rieng ra cae thinh phin u'ng suit

tTnh v l dpng nh|n dupe;

a.-a =2G£

<r;-a'=20£

a',=a' =a,=-{a'.+t7')=-{t7.+<T,)

(8)

(9)

v l

«•? = ' 7 ^ ,

erf = 2ri£,

trf =0

^ Trpng cac phuang trinh (7).(8),(9) eac tham

s l G v l n l i n lupt I I md dun trupt v l dp nhdt

(dpng) cua khdi d l

KhIi da xung quanh dudng h i m se chuyin

tir trpng thai d i n h l i - nhdt sang trpng thai d i n

h l i - nhdt - deo, khi cae thinh phan Crng suit

tTnh tren bien dat tieu ehuan (2) Tip eic k i t qua

phan tich, tieu ehuin (2) duac dua v l dang

, i+3a, _ ^ 2a,

Chu y I I , thing thudng, dieu kien b i n

MOHR-COULOH/I v i n dupe sir dung, qua phuang trinh;

<rs-k.af-a'r

K=~ v a a , =^"=2 (12)

(13)

= 0 (11)

1-sin^ _

Trpng dd;

<p - I I gde ma s i t trong;

e - I I lue dinh ket dan v j ;

r'l =ol la dp b i n nen dan tn,ic cua khdi d l ,

trong trudng hap nay cOng cd the hieu I I gidi han chay hay gidi hpn deo cua khdi d l Chi s i p

ed nghia I I deo, C eo nghTa I I nen (dan tnjc), cac d i u (*) bieu thj trang thai gidi hpn deo hay gidi hpn bin

So sinh (10) vdi (12), n l u chip nh|n cletidu chuan I I nhu nhau trong b i i toin dupe xet, thi

cd t h i xac djnh cac tham s6 ca hpc theo tilu chuin DRUCKER-PRAGER tir tieu chuin bin MOHR-COULOIVIB qua cac bieu thirc

a = * > " ' _ s i i i ^

• 3(fc, H-l) 3

a, - "': _ ' ^ c ( ' - " ' ( ° )

*:, + ! 2 Trong trang thai d i n hii-nhdt-deo d c thinh phin irng suit ludn thda man dilu kien (10) cQng nhu (12) TCr phuang trinh (8) ed chu y din eic gia thilt neu trong mye 2 cd duac cic mil quan hp giu'a cae thinh phin ung suit v l biln dang nhu sau;

GiOa cae thinh phin img suit dpng va biln dpng v l n tuan then quy luat (9) nghTa I I ;

cr' = rts,

<^f'=2T}i, (15) erf = 0

Tuy nhien d d l y khdng phln tich q u i trinh bien dang sau khi xuat hien trang thii hoa deo

vi d l xac 3vn\\ thdi gian I n djnh khong chlng hay

thdi gian ed t h i xay ra tai bien dia chit chi cin chu y den thdi diem khdi da ehuyin tir trang thii dan h l i nhdt (dn djnh), sang trang thai deo

4 v i tieu chuin I n djnh cho cac cong trinh nginn khong chdng

Thuc te, trong x i y dyng edng trinh ngim cho thiy ed ba dpng m i t I n djnh I I :

1) Sau khi dao, d i n mpt thdi dilm nao do xung quanh khoang trong n g i m xuit hipn cac

(14)

hi$n tu-p-ng troc la, sgp la cdc tang da vao

khoang tring, n i u khong ching giCr kjp thai;

2) Djch chuyen cua khoi dd tang theo thai

gian, khong xay ra hipn tu'p'ng phd huy, nhu-ng

dich chuyin gay thay doi lan kich thu-ac cua

khoang tring ngim;

3) K i t hp'p ca hai dgng gay m i t i n dinh tren

D i n nay, d i ddnh gia mCrc dp on dinh cua

khoi da xung quanh cac khoang trong ngim, co

nhiiu tieu chuin va gia thiet khac nhau

Thuin tCiy ve mgt co hpc, khoi da se chuyen

sang trgng thai pha huy, neu tieu chuin pha huy

bi vi pham, vi du theo cdc thuyit ben khdc nhau,

nhu- MOHR-COULOMB, HOEK-BROWN

Trong xay dyng cong trinh ngim, dich chuyin

cua khoi da la dai lu'p'ng d i quan trac, theo doi

trong qua trinh thi cong Thyc te cho thiy, khi

djch chuyin tren bien dgt du-p-c gia trj nao do,

hogc quy ludt phdt trien cua djch chuyen c6 biin

dpng thi se dan den trgng thai phd huy khoi da

Theo phan logi khoi da cua Nga, SNIP 11-94-80

[6] khoi da du'p'c phdn loai theo gid trj djch

chuyin lan nhat trong thai gian t i n tai Ngodi ra

,trong [7] cQng sy dung djch chuyin cyc dai tr^n

bidn khoang trong d i x i p loai khii da theo d p

i n djnh (stability ranking) N i u chap nhgn quan

diim ndy, c6 t h i gia thiet rang, khoi da se

chuyin sang trgng thai mat on djnh, neu:

UrTm-U* = 0 (16)

Trong do:

Umax - la djch chuyen lan nhit tren bien, co t h i

Unh du-p-c bang ly thuyet hoac do du'p'c trong qua

trinh thi c6ng;

U* - la gid trj djch chuyin'gidi hgn

Vai mo hinh ca hoc sir dyng trong bai viet

ndy cho khii da, gia thiit rang, khii da con la on

djnh, chCrng nao c6n co biiu hien ddn hii - nhat

Khii dd b i t d i u m i t on djnh, n i u no bat dau

chuyin sang trgng thai ddn h i i - nhdt -dec 0

ddy, su' dyng tieu chuan b i n

DRUCKER-PRAGER, vdi gia thiit ring khoi dd chuyen sang

trgng thai phd huy (deo) khi cac thanh phln Crng

s u i t tTnh thoa mdn tieu chuin

DRUCKER-PRAGER, vdi cac tham so du'p'c xac djnh dya

vdo tinh tu'ong du'ang so vai tieu chuin

MOHR-COULOMB, Nhu- v|y tieu chuin nay mang y

nghTa ca hpc

5 Qud trinh biin d i i ca hpc trong khdi da

va thm gian on dinh khdng ching

K i t qua phan tich qua trinh biin doi ca hpc trpng khii da vai sa d i phdn tich vd cac biiu hi^n ca hpc da trinh bay cho thay, qud trinh biin doi ca hoc diin ra theo thai gian Ban dau khii

da a trgng thdi dan h i i nhat, sau do, khi cdc thdnh phln u'ng s u i t tTnh thoa man dieu ki#n

b i n , khii da chuyin sang trgng thai dan hit-nhot-deo Khi do, vung dan hii-nhol-deo se lan tmyin d i n tCr bien khpang tring ngim vdo sau trong khii da, cho d i n khi dgt du'p'c trgng thai

c i n blng cuii cung

Tuy nhien, voi myc tieu la xac dmh thai diim khoi da bit d i u chuyin tCr trgng thdi dan h i ! -nhat sang trgng thai dan hoi - -nhat -deo, du'gc gpi la thai gian on c^nh khong ching (stand up time), nen a day khong de cap d i n cac quy lugt bien doi ca hpc sau thai diem nay Trong thyc

t i , k i t c l u chong co the du-ac lap dyng, sao cho qud trinh bien dgng deo khong hinh thdnh Bdi toan du'gc giai bang tich phan tryc tiep he cdc phu'ang trinh vi phan du'gc du'a ve dgng dan gian, hogc theo nguyen ly tu'ong ty ddn hii vai ddn hoi nhat, cung con gpi Id nguyen ly Voltera [8]

Trong trang thdi dan h i i - nhat, cung vai qua trinh biin dgng, cac thanh phln Crng suit tTnh tang din, thanh phln Crng suit dpng giam d i n , tuan theo quy lugt:

j=4.(.-.^>-] (17)

a-;=p

c i e thinh phln u'ng suit dpng biln dpi thep quy luat

''' ^ % R'

^ r '' V (18)

o-,'=0 Cie thinh phin irng suit tpin phan I I khdng

d l i thep thdi gian

•+*?] (19)

Chuyin vj hudng t i m cua c i e dilm tren bien (hay chu tuyen) cua khoang trdng ngim dupe xac dmh theo bilu thCre;

- ^ ( - " )

(20) Trong eic bieu thu'c (17), (18), (20), dai lupng

to= r\IG dupe gpi I I thdi gian tir bien

Kit qua nhan dupe che thay, c i c thanh phan

Crng suit tpIn phin I I khdng doi hay c l dinh,

nhung c i c thinh phan Crng suit tTnh va dong

biln doi theo thdi gian, vdi xu t h i thanh phan

U'ng suit tTnh tang d i n , cdn thinh phin Crng suit

dpng giam din

6 Xac dinh thdi gian I n djnh khdng chdng

Nhu da gia thilt d c i c myc trudc, khdi d l bat

d i u chuyin sang trang thii dee (dan

hli-nhdt-deo), khi c i c thinh phin irng suit tTnh thda man

tieu chuan ben (10) Gpi I I thdi gian on dinh

khdng chlng, khi dd tai thdi dilm niy, cae thanh

phin irng suit tTnh tren bien khoang trlng nhan

eic gia tri:

.-x\

(21)

H-Cdc thdnh phan Crng suit ndy thoa man dieu

ki^n bin, nghTa Id t vdo (21), co:

.'A

l-SfMfe-hay

f(,-;^).]-4-[i-/x)-Giai (23) theo t* nhpn duac;

k, + l

0 (22)

(23)

(24)

'2-a-/p

Cung tai thdi dilm niy, chuyin vj trdn bien

khoang trlng ngim dat gia tri:

I 2-o-;/pJ 2G 2-a[

p£.\

(25)

Bpl lupng chuyin vj gidi hpn U* tren biln

khoing trlng, nh|n dupe d bilu thirc (25) se

dupe sir dung lim tieu chuin canh b i o trong

q u i trinh do dpc, quan trie dich chuyen khi thi

cdng

7 K i t luan Tip k i t qua nh|n dupe, eung nhu eic k i t qua nghien euu da cing b l tif c i e cong trinh nghiln eCru khic, nhu trong [1], [7] cho thiy ring e6 t h i

d u b i o dupe thdi gian I n djnh khing chlng eung nhu "thdi gian tai biln dia chit" [9], tren ca

sd nghien cCru b i i toan v l quy lu|t biln doi ea hpe trpng khll d l thdng qua eic md hinh luu biln va tieu chuin thich tipp v l I n djnh cdng trinh ngim

D l ed the phat triln hudng nghien eCru niy,

e i n thilt phai cd duac cac thilt bi thi nghipm co kha nang x i c dinh dupe su phu thupc v i e thdi gian ciJa c i e tinh chit ea hpc cua khii d l

7a/ //pu tham khao:

[1] Nguyen Quang Phich Ca/)pc d l Nha xuit ban X i y dung H I Npi

[2] Fritz, R An analytical splution for axisymet-rics tunnel problems in elasto-viscoplastie media International Journal for Numerical and Analytical IVIethods in Geomeehanics, Vol 8,325-342 (1984) [3]L00NEN,H.E.: Theoretische Berechnung der

um einen zylinderischen Hohlraum in einem visko-elastisch-plastisehem IVIedium auftretenden Span-nungen und Verschiebungen Central Proefstation

in Limburg 1962

[4] DRUCKER, D and PRAGER.W: Soil Me-chanics and Plastic Analysis or Limit Design Quar-teriy of Applied Mathematics (1952)

[5] SALUSTOVVICZ,A.; Der Gebirgsdmck auf den Streckenausbau als Funktion der Zeit Bericht

ijbet das 6 Landertretfen des intemationalen

BDros fur Gebirgsmechanik Akademie-Verlag Beriin1965 S.85-92

[6] CrpoMTenbHbie Hopiubi H npaBHnaCHHfl II-94-80 «npq3eMHbie ropHbie Bbipa6oTKM» [7] Lianjin, T, Panfeng, L, Zhouyaun Z Stability ranking system of rockmass surrounding a large-scale underground excavations IAEG2006 Paper number 390 pp 1-6

[8] Van-Manh Nguyen, Quang-Phich Nguyen

(2015) Analytical solution for estimating the

stand-up time of the nxk mass surrounding tunnel Tun-nelling and Underground Space Technology 47

[9] IVIufundirwa A & Fujii Y Prediction of rock mass failure-time of geo-hazards Graduate School

of Engineering, Hokkaido University, Sapporo, Japan