DIEN DAN KHOA HOC CONG NGHE
Cf^U.i^ Hf
ANH HUdNG CUA DAO LEM DEN DO LUN CUA MAT DAT KHI DAO NOAM
( t i l p theo)
2. D u t f n h d o lem khi d a o n g l m
Nhu da b i l t t d bai "Du tfnh dp lun mat d i t khi dao n g l m " tren Tap chf Ngudi Xay dung s i 5&6 nam 2014, qua bieu thdc (1.2) va hlnh 4 t h I y r i n g dp lun eiJa mat d i t phu thudc vao kfch thudc h i m D va dp lem V L cua d i t quanh h i m ; nhu vay, khi the tfch d i t bj dao lem cang Idn thi lun mat d i t cang n h i l u . D i l u vda neu tuy thudc vao edng nghe thi edng dao h i m va tfnh c h i t eiJa d i t quanh h i m . Tren hlnh 1 trinh bay eae thanh p h i n gay ra lem d i t khi dao b l n g TBM va thudng gdm CO lem d guong dao, d d i u khien va d dudi khien ca sau khi da bom ep vda (Nagen Loganathan, 2011) nhu trinh bay tren hlnh 2.1...
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Hinh 2.1. Cic thinh phan giy tdi xop dit/ lem khi dao him bing TBM Kinh nghiem chl ra r i n g khi dao b l n g TBM, VL ed trj sd nhu neu trong bang 2.1 va bang 2 . 2 , trong dd dp lem V L tfnh theo bieu thdc (1.3) eua bai bao neu tren.
Khi dao bang phuong phap NATM, lun mat d i t la do chuyen vj eua vd h i m va d i t bj chuyen vj trong qua
Bang 2 . 1 . Dp lem cua d i t khi dao h i m trong d i t dfnh (Theo O'Reilly and New, 1982)
Loai dit S^ cQtig nin n6 Trim tfch bang hi
Trim tich bang hi
S^t trim tich tr§
(C„ =10-40 kN/m')
set trim tfch tr6
(c.=io, 0-40,0 mm')
PhUUng phdp ch6ng
glfir him KhiSn hoac khflng c6 Khi§n khfing cd khf n^n Khi§n c6 khf n^n
Khi§n khdng cd khf n^n Khign cd khf n^n
ga lem VL
(%) 0 , 5 - 3 , 0 2 , 0 - 2 , 5 1 . 0 - 1 , 5
30,0-45,0
5,0-20,0
Ghi chii Thi/flng dungl- 2%
Khfn^ndDngde kh6ng chl chuyen vj cija dit Gi/dng dio bj phi hoai hay gin phi hoai
Mdt phin giTdng dio bj hdng
PGS. TS. NGUYEN BA KE
Hoi Cd hoc Ddt va Dja Ky thuat Viet Nam
Bang 2 . 2 . Do lem cua dit khi dio him trong cat (Theo b' Reilly and New, 1982)
Loai dat Cit chat Cit chit Vila Cit tdi x6p
flfi lem V, (%) 0 , 5 - 1 , 0 1,0-2,5 3, 0 - 5, 0
Ghi chu
Tri/flng hdp (Jit tn/dng nd:1%
Tunen diJng iiy 1 - 2%
eit rdi dim nen iiy 5%
trinh dao; ngoai cac nguyen nhan tren eon do ha muc nude n g l m va giam dng s u i t eiJa d i t quanh h i m .
The tfch lem VL tfnh theo edng thdc (Jan Niklas Franzius, 2003):
VL
V.
n-
D'
(2.1)Trong dd Vs la the tfch cua p h l u lun tren 1m dai cua h i m va tfnh theo edng thdc:
r^ = 00 ^Sydx = -Jlni^S^
V.msx. (2.2)Sv, ix va Sv,max trong bieu thde ( 1 . 6) ed cung y nghTa nhu S, i va Sn,ax trong eae bieu thdc (1.1) va (1.2) ndi trong bai "Du tfnh dp lun mat d i t khi dao
nglm".
Ndi mdt each tong quat, d day b i l n dang cCia d i t phu thudc vao n h i l u thdng sd, nhu la:
- Phuong phap thi cdng va ky thuat khoan;
- Op sau va dudng kfnh h i m ; - D i l u kien nude n g l m ;
- S u ed mat eua eae tunen lan can;
- Trang thai dng s u i t ban d i u ciJa d i t ;
- Trang thai dng suit biln dang eiJa d i t quanh h i m ;
- Kinh nghiem va tay n g h i ciJa nha t h i u .
Khi e I n ed Idi giai ehfnh xac thi phai ke d i n mdt sd hay t i t ea eae thdng sd ndi tren va bai toan nhu t h i dupe giai b l n g nghiem giai tfch hoac phuong phap sd.
Nhdng ldi giai ly t h u y i t khac nhau nhu vay d i u dupe kiem chdng b l n g k i t qua quan t r i e chuyen vj cua cdng trinh thuc t l . D.R.Wu va C.J.Lee (2003) da tong k i t va so sanh k i t qua tfnh toan vdi k i t qua quan t r i e t d 12 cdng trinh h i m d Nhat Ban va Dai B l e va da chi ra dp tin cay eua eae ldi giai da dung. Vf du tren hlnh
N G U d l X A Y D U N G SO T H A N G 7 & 8 • 2 0 1 4
ANH HUCfNG CUA PAO LEM BEN PO LUN
2.2a la kit qua nghidn cdu eiJa Hanya (1977): ham dao blng khien can bang bdi ap luc d i t EPB, cac Idp d i t set, cat, set (CL/SM/CL - phan loai theo dudng Casagrande), dudng kfnh h i m D = 7, 06m, dp sau him z = 27, 5m, sdc chIng elt khdng thoat nude Idp' set thd 2, Su = 70kPa, dd lun S„,ax = 30,4mm, dp lem VL = 4,18%. Td dd thIy kit qua tfnh rIt g i n vdi kit qua quan trie.
Tren hlnh 2.2b la trudng hpp lun mat d i t do lam dudng tau dien nglm ddi d Dai Bac vdi ty sd khoang each d/D > 3 (d-khoang each dudng kfnh - dudng kfnh gida 2 him), dp lun tfnh toan vdi i (dudng liln) va vdi 0, 85i (dudng ddt net) so vdi dp lun do dupc (cac chIm den) khi him dao blng khien can blng bdi ap luc d i t EPB, dit td tren xudng gdm eae Idp set /eat/set (CiySM/CL), dudng kfnh him D=6, 05m, dp sau h i m z=16m, sufC chdng elt khdng thoat nude Sy =37kPa, Smax= 30. 6mm, dp lem V L = 2 , 38%.
O l tfnh dp lun mat d i t cho h i m ddi da diJng phuong phap edng tac dung (Superimposition method, xem Cyrus D.Garner, 2010 ) va dp lun tfnh toan vdi 0,851 cho kit qua g i n vdi dp lun quan trie.
Dp lun mat dat tfnh theo cdc bieu thdc tren Id chua ke d i n dp lun ed kit. Cd t h i tlm hieu Idi giai ly thuyit eua Jerry Jwo-Ran Chen (1995) (hlnh 2.3a) va trong nghien cdu cua Chung C. Kao (2008) khi quan trie liin tai mat e l t 0128B tren mdt doan h i m g i n san bay Chongshan d Dai Ble, cho thIy dd lun cd kit trong trudng hpp nay la dang ke (hlnh 2.3b).
V i n d l lun mat d i t do thi edng h i m ed ke din ylu td thdi gian (ed kit) la bai toan kha phde tap. Hon nOa, n l u phfa tren h i m khdng ed tai trpng (dit trdng/green- field ground) va cac Idp d i t phfa tren edng trinh nglm gdm eat chat hay da edng thi dp lun eua mat dit chii y l u gay ra bdi phin d i t bj dao lem thudng Idn hon tilt dien h i m thilt k l (hlnh 1.12). Tuy nhien khi eIn kl d i n y l u t l thdi gian khi tfnh phlu lun tai mat dit thi cung ed the dijng mdt sd Idi giai da ed, vf du xem Taiyue Ql, Bo GAO (2011), hay don gian hon khi dung phuong phap logarit, phuong phdp hypeebdiic hay phuong phap k i t hpp (hybrid model) de tfnh dp lun c6 k i t td k i t qua do lun trong thdi gian ngIn (xem Richard N. Hwang, Za-Chieh Moh, 2008).a
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Hinh 2.2. So sinh dd lun tinh toin va dd lun quan trie mit dat l(hixiy dung dUdng tiu dien nghm ddn cQa Nhit (a) va dUdng tku di$n ngkn ddi dat cich nhau d/D = 3 tai Dai Bic(b) (Theo D.R.Wu, C.J. Lee, 2003)
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Hinh 2.3: Dd lun theo thdi gian vdi ldi giai cua Jerry Jwo-Ran Cheng(1995) (a) vi theo kk qui do cua Chung C.Kao (b) tai mit cit 0128B, Chongshan, Dii bic
NGUdl XAY DUNG SO THANG 7 & 8 • 2014
