tinh toan tuong chan dat theo trang thai toi han

1TNH TON TNG CHN T THEO TRNG THI GII HNVI S H TR CA PHN MM A K! THU#T CHUYN DNG

GS. Nguy+n Cng M.n, KS. Tr1n Th3 Vi5ti hc Thy li

Tm t9tBi bo so snh cch tnh ton mt bi tp v tng chn t cho hc sinh thuc mn C#

hc t theo truyn th'ng t( 50 n+m nay v-i cch tnh c s/ h0 tr1 c2a ph3n mm chuyn dng SIGMA/W v SLOPE /W @ nh gi s/ lm viBc c2a tng chn theo trCng thi gi-i hCn theo Quy phCm hiBn hnh. T( kGt quI so snh chK ra tnh u viBt c2a viBc dng ph3n mm v cc mLt m hnh ha bi ton st ng th/c tG h#n, pht hiBn mt s' i@m m-i l bi@u thP 1c nm n hQingay st y mng tng v tc dRng c2a n 'i v-i s/ tp trung Sng sut t+ng thm ngay st y mng. Cc output cho thy ton cInh phn b' p sut - biGn dCng c2a hB tng - t, gip cho viBc nh gi ng n s/ lm viBc c2a tng theo trCng thi gi-i hCn 1c thun l1i. MLt khc, nh phn tch kGt quI, hc sinh c th@ tiGp nhn 3y 2 h#n s/ lm viBc tXng th@ c2a hB tng - t v c th@ nhanh chng chn 1c ph#ng n t'i u khi thiGt kG mttng chn t. Yiu ny cZng rt c3n thiGt cho cng tc thiGt kG tng chn trong th/c tG.

M: ;1uTrong thiGt kG tng chn t, c3n chn mLt ct h1p l c2a tng. MLt ct h1p l c3n

bIo Im iu kiBn h1p l v k\ thut v kinh tG.Theo H.D.T.L C 4 76 [1], iu kiBn h1p l v k\ thut 1c ki@m sot theo trCng

thi gi-i hCn. HiBn nay, e n-c ngoi c hai hB Tiu chufn Xy d/ng chnh thSc nh gi iukiBn lm viBc c2a tng chn theo TTGH l hB c2a Lin bang Nga [2] v c2a Euro Code 7- Geotechnical design Cng Qng Chu u [3].

Ni dung thiGt kG tng chn 1c th/c hiBn tCi cc n-c khc, trn th/c tG cZng 1cth/c hiBn theo ph#ng php lun trCng thi gi-i hCn [4], [5], [6] T( nhmng n+m 60 - 70 c2a thG kn tr-c v hiBn nay, bi tp thiGt kG tng chn c2a sinh vin YCi hc th2y l1i ngnh cng trnh cZng 1c nh gi theo TTGH [7] [8]. Tuy nhin, @ th/c hiBn viBc ny theo truyn thng mt rt nhiu thi gian. Bi bo ny trao Xi viBc dng SIGMA/W v SLOPE/W @ th/c hiBn bi tp thiGt kGtng chn t theo TTGH nhpm gip sinh vin khqi mt nhiu thi gian vo s v tnh ton @ ginh nhiu thi gian khai thc ni dung c# bIn c2a bi tp @ c thm kiGn thSc m-i. .

1. Th>c hi5n tnh ton theo truyDn thEng

www.vncold.vn www.vncold.vn www.vncold.vn

2 bi: C3n xy mt tng chn trng l/c c mLt ct ngang nhHnh 1. Tng Lt e su h = 1m ngang m/c n-c ng3m, trong nnc cc l-p t nh sau:

L-p trn l mn hmu c# dy 1m, ud = 18kN/m2 ; k = 5.10-5 m/s L-p d-i y tng l t st e trCng thi dxo, dy v hCn

5,19=bh kN/m3; 76,00 = ; 015= ; c = 15 kN/m2 ; 4,00 = ; k =1,5.10-7 m/sec

Th nghiBm nn ne hng t nn st c kGt quI sau:

Hnh 1

Yt p sau tng dng loCi t st 18= kN/m3; 024= ; c = 10 kN/m2Vt liBu xy tng l b tng M200; 24= kN/m3, thi gian thi cng tng l 6 thng.

Yu c3u1. Tnh p sut y mng 2. Ki@m tra Xn Pnh v tr1t c2a nn mng tng chn3. Tnh ln c2a mng tng chn.

Gii: Lp m hnh lm viBc c2a tng v ki@m tra theo tnh ton, gQm cc ni dung sau:.

- Trong trng h1p ny, xem kh'i p 4 nh l mt ph3n c2a tng, v trng l1ng tng bpng tXng trng l1ng cc kh'i: 1, 2, 3, 4 (Hnh 1). - Tnh mun biGn dCng trung bnh c2a nn t theo TCVN 4253 00.. mEE ii = (1)

Trong : ( )iii

iiiE 1

21

12 1

+

= (2)

V-i

====

667,0/100635,0/150

12

1

22

2

ii

ii

mkNmkN

Thay vo cng thSc (2)

(kN/m2) 0 50 100 150 200 0,76 0,708 0,667 0,635 0,620

1

2

3

4

1m


3( )667,01635,0667,0100150

+

=iE = 2604,7 kN/m2

Yt nn l st = 0,40 nn 0 = 0,47 Do khng c iu kiBn th nghim hiBn trng, nn e y ly m0 = 1, do vy

20 /122447,07,2604 mkNEE ii ===

- Xc Pnh p sut y mng (Sng v ngang) theo cng thSc nn lBch tm, p l/c ttheo ph#ng php Rankine; - Dng ph#ng php nu trong TCVN 4253- 86 @ d/ on - ki@m tra dCng tr1t timn+ng theo cng v sSc chPu tIi nh cc chK s' m hnh, chK s' khng ct v hB s' c' kt thm. Bi tp c th@ cho tr1t phng hoLc tr1t h0n h1p. - Ki@m tra ln tCi ba i@m d-i y mng (tnh S theo su) theo ph#ng php cng ln sau hiBu chnh mng cSng @ xc Pnh nghing c2a tng theo ph#ng th1ng hC lu.

Bnh lun v ph#ng php truyn th'ng - Khi lp s# Q tnh ton khng xt t-i trng l1ng bIn thn t p sau tng; - p sut ngang y mng khng phn b' u m tn lB v-i p sut Sng. MLt khc kh'il1ng tnh qu nhiu, v trong qu trnh tnh, sinh vin khng c iu kiBn phn tch nh gi tr/c quan s/ lm viBc c2a tng @ lm tin chon mLt ct h1p l.

2. Th>c hi5n tnh ton c s> hL trM cNa ph1n mDm SIGMA/W v SLOPE/W K3t quW tnh ton

S# Q tnh ton nu trong Hnh 2

Hnh 2: S# Q mLt ct ngang tng chn t


4Cc kGt quI phn tch nu trong cc hnh v sau + 36,8

+31,0

-1 1 3 5 7 9 11 13 15 17 19 21 23 2519

21

23

25

27

29

31

33

35

37

Hnh 3 L-i tXng chuy@n vP c2a tng + 36,8

+31,0

-1 1 3 5 7 9 11 13 15 17 19 21 23 2519

21

23

25

27

29

31

33

35

37

Hnh 4 Vc t# tXng chuy@n vP, vng dxo (yield zone) trong kh'i t


5+ 36,8

+31,0

-0.1

-0.09

-0.07

-0.05

-0.05

-0.04

-0.04

-0.03

-0.03

-0.03

-0.02

-0.02

-0.01

0.01

0.02

0.03

0.03

0.04

0.05

0.06

25

27

29

31

33

35

37

+ 36,8

+31,0

-0.32

-0.31-0.29-0.28 -0.25 -0.22 -0.19 -0.16

-0.13

-1 1 3 5 7 9 11 13 15 17 19 21 23 2519

21

23

25

27

29

31

33

35

37

Hnh 5: Cc ng ng chuy@n vP theo ph#ng Sng + 36,8

+31,0

-0.1

-0.09

-0.06 -0.05

-0.04

-0.03

-0.02

-0.02

-0.02 0

0.02

0.04

0.06

-1 1 3 5 7 9 11 13 15 17 19 21 23 2519

21

23

25

27

29

31

33

35

37

Hnh 6: Cc ng ng chuy@n vP theo ph#ng ngang

A


6Y-To

talSt

ress(

kPa)

X(m)

60

80

100

120

140

10 11 12 13 14 15

X-To

talSt

ress(

kPa)

X(m)

-50

-100

-150

-200

-250

-300

0

10 11 12 13 14 15

027,00047,08,603,0

8,6)052,0(02,0tan

===

==

YX

038,0007,03295,0315,0tan ===

Hnh7: Vng dxo (yield zone), nm n hQi,ng ng chuy@n vP ngang trong hB tng t

Hnh 8: Chuy@n vP ngang dc theo Hnh 9 Chuy@n vP Sng theo lng tng mLt y mng tng

Y-Di

splac

emen

t(m)

X(m)

-0.25

-0.30

-0.35

-0.20

10 11 12 13 14 15

0

Y(m

)

X-Displacement (m)

30

32

34

36

38

-0.02-0.03-0.04-0.05-0.06 -0.01

Y nghing lng tng rt nhq Y nghing y mng tng rt nhq


7a) p sut Sng b) p sut ngang Hnh10: Phn b' p sut tXng dc y mng tng

(a) (b)

(c) (d) Hnh 11 Phn b' tXng p sut Sng dc ng thng Sng

qua gt tri (a), gt phIi (b), qua tm (c) v p sut bIn thn d-i y mng tng (d) Phn tch cc k3t quW tnh ton v nh\n xt

4.1.KGt quI phn tch theo SIGMA/W cho thy tXng th@ cc trng Sng sut v chuy@nvP c2a tng cZng nh cc trP s' c2a chng tCi t(ng i@m, th@ hiBn t#ng 'i ng th/c tGlm viBc c2a tng. Yiu ny gip cho hc sinh cIm nhn tr/c quan 1c iu kiBn lm

Y(m

)

Y-Total Stress (kPa)

20

22

24

26

28

30

30 50 70 90 110 130

Y(m

)


20

22

24

26

28

30

40 50 60 70 80

Y(m

)


20

22

24

26

28

30

40 45 50 55 60 65 70

63

Y(m

)


20

22

24

26

28

30

0 50 100 150 200 250 300

63 kN/m2


8viBc c2a tng chn. MLt khc nh Pnh l1ng 1c cc chuy@n vP c2a tng nn c th@nh gi iu kiBn lm viBc c2a tng theo trCng thi gi-i hCn v biGn dCng v cng .

4.2 Yt p sau tng chn khng chK gy p l/c ngang tc dRng ln tng m cn gy p l/c thng Sng lm cho tng chuy@n vP v pha t, Lc biBt 'i v-i tng trng l/c[G.A Dubrova, 1963] (Hnh 3, 9). Yiu ny khng 1c m phqng trong cch tnh truynth'ng. 4.3 Ngay st y mng hnh thnh vng thng 1c gi l nm n h"i, tCi cc hCtt 1c nn chLt m khng c chuy@n vP (Hnh 4, 7) nh thng thy trong cc th nghiBmm hnh nn ct trong phng th nghiBm. Do c nm ny nn xIy hiBn t1ng tp trung Sng sut tCi ph3n trn c2a ng phn b' Sng sut t+ng thm Sng dc theo ng thng Sng qua tm mng (Hnh 11c). MLt khc, SIGMA/W cZng cho ng phn b' p sut bIn thn c2a t k@ t( y tng (Hnh 11d). 4.4 Trong trng h1p bi ton ny, iu kiBn quy Pnh v biGn dCng cho php theo trCng thi gi-i hCn v iu kiBn lm viBc bnh thng c2a tng l thqa mn (Hnh 8 v 9). 4.5 NGu kGt quI phn tch theo SIGMA/W cho thy vng biGn dCng dxo pht tri@n rng v cc chuy@n vP l-n qu mSc quy Pnh, th c th@ dng SLOPE/W nh gi iu kiBn lm tXng th@ c2a tng chn. Phn tch bi ton ny theo ph#ng php Bishop cho kGt quI K = 1,372 (Hnh 12); VP tr mLt tr1t trong hnh cZng ph h1p v-i iu kiBn t nn, mLt khc tng khng th@ bP lt.

Theo TCXD VN 285:2002, tnh tng theo trCng thi gi-i hCn thS nht 1c th/c hiBn nh sau:

RkmNn

nc .

Hay: mkn

NRK nc.=

Trong trng h1p ny: m = 1, nc= 1 v kn = 1,15, do vy theo kGt quI tnh ton Xn Pnh tXng th@c2a tng K = 1,372, do vy K > 1,15. Do quy Pnh nh vy, khi thfm Pnh cng trnh S#n La, chuyn gia Nht cho rpng, hB s' an ton ly theo quy phCm c2a ViBt Nam l nhq.

C3n ch rpng, cc Lc trng trong tnh ton e y c3n ly theo gi tr& tnh ton.


91.372 + 36,8

+31,0

0 5 10 15 20 2520

22

24

26

28

30

32

34

36

38

Hnh 12. Phn tch Xn Pnh c2a tng theo PP Bishop 3. K3t lu\n

KGt quI dng ph3n mm SIGMA/W trong thiGt kG tng chn t cho mt s' nhn xt sau: 1. u viBt c2a viBc dng ph3n mm nh gi iu kiBn lm viBc c2a tng chn l gip ngis dRng c th@ thy bSc tranh tXng th@ c2a t#ng tc gima tng chn v kh'i p. MLt khc c th@ki@m sot Pnh l1ng trCng thi Sng sut - biGn dCng c2a hB tng - t tCi bt k i@m no trong phCmvi lm viBc c2a hB th'ng. Nh , gip SV tch lZy v c thm nhiu kiGn thSc m-i bX ch cho ngik\ s sau ny. 2. M hnh tnh ton theo ph#ng php truyn th'ng cha h1p l v cha xt t#ng tc gimatrng l1ng bIn thn tng v-i kh'i p trong hB cng trnh v kh'i p, do vy nh gi iu kiBnlm viBc c2a tng cha h1p l. 3. M hnh ha c2a SIGMA/W cn cho thy nm n h"i xut hiBn st y mng, iu pht hiBn trong cc th nghiBm m hnh tm nn cSng trn nn ct tr-c y. Cng v-i bi ton thm d-itng c( khi dng SEEP/W [12] cng b' tr-c y, mt l3n nma lCi thy s/ k diBu c2a m hnh s', th@hiBn 1c bpng hnh Inh t#ng t/ cc nghin t#ng Sng trong m hnh vt l v c# hc t. 4. Khai thc cc ph3n mm Pa k\ thut SIGMA/W, SEEP/W, SLOPE/W hay PLAXIS @ th/chiBn thiGt kG cng trnh theo trCng thi gi-i hCn rt u viBt v mLt tin cy cZng nh tiGt kiBm thigian, do vy chng ta nn quan tm v tX chSc hiBu quI h#n nma cc l-p tin hc Sng dRng v Pa k\thut trong cng tc o tCo Ci hc cZng nh cao hc.


10

Ti li5u tham khWo1. HDTK C.4-76, 1977. H-ng dn thiGt kG tng chn cng trnh th2y l1i. N.C.Mn - N.X.BIo2. 2.06.07- 87 "Tng chn t, u thuyn, cc cng trnh dn c v bIo vB c 1 01 1988 3. Eurocode 7, 2009. Geotechnical design - Part 1: General rules 4. Braja M.Das. Principles of foundation engineering 6th Ed. - Thomson Learning 5. Joseph E. Bowles, Foundation Analysis and Design. 5th Ed. - McGraw-Hill 6. Geotechnical Engineering Handbook, 2002. Volume 1 Fundamentals - Ulrich Smoltczyk 7, 8. Bi tp TK tng chn t: Nguy)n Chi+n - Kha 11C, 1973; Nguy)n N Duy Kha 47B, 2008 9. TCVN 4253 86. TCTK Nn cc cng trnh th2y cng Nh XB Xy d/ng (N.C.Mn bin soCn) 10. TCXD VN 285 : 2002. Cng trnh th2y l1i Cc quy Pnh ch2 yGu thiGt kG - H Ni 2002 11. GeoStudio 2004 M un SIGMA/W v SLOPE/W 12.Nguyn Cng Mn 2003. Phn tch thm trong mi trng t theo SEEP/W (bi giIng cao hc) 13. G.A Dubrova, 1963. T#ng tc t v cng trnh. NXB Vn tIi ng sng. Moskva-1963

Synopsis

A traditional practical exercise on retaining wall of Soil Mechanics in the past 50 years for the students of the university has been calculated in two manners: one belonging to traditional method and the other with the aid of geotechnical softwares - SIGMA/W and SLOPE/W - in order to evaluate its working condition according to limit state method. From the comparison of results given by the two above manners of analysis, one realizes the preeminences in using the softwares: modeling the problem more realistically, detecting some new things as the development of elastic wedge under foundation bottom and its effect on the stress concentration in this zone. On the other hand, the output of the software gives again all view of the strain and stress field in the system of soil - wall, that allows to rationally evaluate the working condition of the wall according to limit state method. Besides, from the analysis of the results, the student can accept more completely the general working of the wall - soil system and can quickly select the optimum plan when designing a retaining wall that is also very necessary in practice.


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