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

w Thdng tin khoa hpc c6ng ngh^ m o 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' 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 v i o thdi dilm nhat djnh sau die nlu 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 die khoang trlng nhung ehua gia co, chlng dd eho din xay 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 niy xuat hien diu tien eich phan loai khIi d l cua Lauffer (1958) [1] v l sau 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 kit eau chlng) duac si? dung d l xiy dyng hay tinh toin t l chirc chu ky dio, cho kit c i u chlng tam phai duac hoan chinh trudc thdi diem ed the xay p h i huy M|c dCi cic phuang phip niy dang dupe sir dyng phi 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 KHCNM SC 7/2015' CNKT HAM LO GS TS NGUYEN QUANG PHlCH Hdl Cdng tilnh ngim VI0t Nam Bien t$p: TS Pham Minh Di>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 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 ding nghTa vdi x i c dinh thdi gian xay tai bien dia chit (rock mass failuretime of geo-hazards) B i i viet niy 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 xiy dyng cdng trinh ngam 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 Su cd mat cua chiing din din tinh chit luu biln v l ea hpc, tire I I su phy thupc cua cie tinh chat ca hpc v i o thdi gian Thuc t l eung chirng minh dilu qua su phIt triln djch chuyin, bien dang v l eac hipn tupng phi hOy, xay khIi da sau 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 nhi 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 Th6ng tin khoa hoc cong nghe mo md hinh luu biln nhu 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 Md hinh luu bien edn dupe gpi 11 md hinh LOON EN [3] B|c diem v l bilu hipn ea hpc cua md hinh 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 bin md hinh CO bleu hipn biln dpng d i n hoi - nhdt; - Sau 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 phin irng suit tong t h i lydn bao gdm hai 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 phin md hinh nhdt NEWTON Ky hieu cac thinh phin irng suit tTnh v l ddng, lin luat vdi cac chi s l trdn la s v l d, dd cd mli quan hp; cr„=CTj+crJ (1) Gidi han deo, hay gidi han pha huy ciia khdi da dupe xac djnh tir cie k i t qua thi nghipm d l v l c i c phuang phip tinh chuyen ddi khic Trong b i i niy, gidi hpn deo dupe chpn thee tieu ehuin dec eua PF!AGER-DRUCKER [4] cd dpng (y/)5-ai/,'-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 sau H, diroc dao 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 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 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 phan iing suat chinh theo phu'ong thang du-ng (chF so v) va theo phu-cng nlm 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 khoi da vk bai toan biin dgng phing, d i i xiJ-ng tdm, he tpa dp dpc cyc, nhu" tren hinh P=7H 0Hinh Sodd vi cic (Tiiu kidn bidn tdng quit cOa bii toin Cac phu'O'ng trinh cv ban Vai cac dieu kien vd mo hinh bdi toan da grd-i thieu, khoi da xung quanh du'dng ham se khong co cac phan u'ng suit tiep, ba 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 ting cua cdc thdnh phln Crng suit tTnh(s) va dpng(d) nhu sau: KHCNM S 7/2015* CNKT HAM LO Thong tin khoa hpc cong nghe m o (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 tilp 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\ K=~1-sin^ vaa, =^"=2 _ (12) Trpng dd;