I """''"" W I li'lii'l l!LM
NGHIEN ciru HIEU QUA SUY GIAM tTNG SUAT TAI DAY IMONG KHOl N^M TREN MO HINH VAT LY
Nguyin Quoc Dung, Phung Vinh An, Do The Quynh Vien Thuy edng Tom tat: Mdng khdi nem Id mil dgng mong ndng dp dung cho khdi ddp Iren dit yiu Kit cdu mong cou tgogomnhteu khdi nem xip cgnh nhau phia Iren phu mgt lip vdi dia ky thudt chiu keo Tdi h-ong khoi dap qua mong khdi nem Uuy-en xuing nin bi suy gidm do ca chi Iruyin luc qua mdl vdt xien. Bat bao nghien cmi su suy gidm img sudt lg, ddy mong khii nem uen mo hinh vdt ly Tir khda: Mong khoi nem, mgt vdl xien, khdi nem.
Summary: Wedge block foundal,on below Ihe embankmem on soft sod is a lype af shallow faundadon This foundation compr,ses many adjoimng wedge blocks covered on Ihem by tensile geolexttle fabric The load ofembgnkmeni ,s reduced al Ihe bottom of wedge block foundation due to the lateral oblique surfaces ofthe w-edge blocks. Tins paper research into Ihe reduction of loadal the bottom of wedge block foundation basing onphysical model.
Keywords: Wedge block foundation, oblique surface, wedge black.
1. DAT VAN DE
De XUI ly nSn dat ySu cho khoi dip tren nSn ddt yeu hi|n nay thucmg su dyng cac giai phap sau:
- Dap nhiSu dgt theo thai gian;
- Thong dgng nhjt la thay thS dit: Tiiy theo chieu cao de, nguai ta dao bo mgt lap dit yeu va thay the vao do bing cat.
- Cach lam dan gian la dimg be cay, be da, ...
de lam mong.
- Hign d^ han eo cac phuang phap: C6 kSt bang bac thim, hut chan khong, cgc tiSt dien nho (piled embankment),...
Vcii de bao, ba bao vimg ddng bang song Ciiru Long, tuy chiSu cao khSi dip khong Ion (chi tir 2j3m) nhtmg nSu khong xir Iy nSn thi khdi dip khgng dn dinh. Mgt s6 tuySn de biSn 6 tinh Ca Mau dugc dip nhiSu dgt tir n5m 1978-^1980 hien nay bj lun chim sau trong
nen. Hign nay chu yeu dang sii dyng giai phap thay thS nen (bing cat). Tuy nhien, ngu6n cat de phuc vu dip de phai van chuySn tir xa, mat khac viec khai thac ve lau dai sS hi han chS vi anh huong den mgi trucmg.
DS tim kiSm giai phap lam mgng cho khdi dip tren nen dat yeu co chiSu cao nho, cac tac gia da dS xiiit ket ciu mdng khdi nSm, ciu tag gdm nhiSu khdi nem xSp cjnh nhau, phi'a tren phli mgt lop vai dia ky thujt chju keo (xem Hinh 3, 4, 5). Tai trgng khdi dip qua khoi mdng truySn xudng nSn bi suy giam do eg chS truySn lire theo mat vat xien. Hi$u qua suy giam img suit qua mdng dat dugc cao han kieu mdng ndng thdng thudng.
CCI ehe truySn Igc theo mat vat xien thudng thay d cac phuong ti$n banh xich (xem Hinh 1).
Ngay nhjn bai: 25/8/2016 Ngay thong qua phan bien: 30/9/2016 Ngay duyet dSng: 26/10/2016
Hinhl: Mat vdl xien ciia bdnh xich Trong xay dung dan dung, ngugi ta cilng dS c sang ChS sir dung eg chS tucmg tg, thudng gi
TAP CHl KHOA HOC VA CONG NGHE THCiV L0I S<5 35 - 2016
KHOAHQC ~ 1 ^ E S 3 I S I I M
la mong Top-base (xem Hinh 2). Tuy nhifin, ket cau mong Top-base co nhieu khac biet so vai mong khoi nem 6 nhiing diem sau:
- Khoi vat bang be tong, dang hinh non tru;
- Khoi vat gom 2 phan: Phan khoi non tru phia tren va phan dinh (ciing hinh tru) noi dai;
- Tren mat khoi vat co mgt san be tong co thep c6 nhifim v\i lien kfit cac khoi vat thanh mpt khoi;
- Giiia cac khoi vat chen bang da dam.
Be long CO thep
Hinh 2: Mdng Top - base
Doi voi khoi dap de bao, bo bao a d6ng bfing song Cuu Long, do chieu cao khong Ion nen viec ap dung sang che Top - base se khong co hifiu qua kinh te. De bao, bo bao khong c6 yeu cau khong che lun, chenh lech liin nghiem ngat nhu cong trinh nha ciia. Tuyen de Ihucmg dai hang chuc ki 16 met, day de rgng hang chuc met. De di qua viing dkt yeu ngap nuoc h ^ chfi tigp can bang co gidi neo viec Sli dung v$t lieu tai ch6 dfi dap de la huong nghien cuu can thiet.
Cau tao mong khoi nem, co che truyfin lyre tfii trgng khoi dap qua mong, uu nhugc difim va pham vi iing dung cua mong kh6i nem dS dugc trinh bay trong tai lieu [3]. Trong bai bao nay chi trinh bay kfit qua nghien ciiu hi$u qui suy giam iing suat tai day mong kh6i nem tren mo hinh vat ly.
Phialroiigde TMnde
Cade
i^L=j2L-^^ Nudc biin
— ^Nenmtyeu- ^ .-. ^Zll
Hinh 3: Vi tri mong khdi nem xu ly nin ddt yiu cho de biin
1 ;l '- j J j- J 1 J- J 1 ,1, .!- 1
Hinh 4 Mdl bdng cdc khd, nem khi dgl trong mdng
Hinh 5: Mdl dimg cdc khdi nem (mgt cdt A - A) 2. iViyC TIEU NGHIEN ClTU
NghiSn ciru hieu qua suy giam irng suit tai day mdng khdi nem trSn md hinh vat ly dudi tac dung ciia tai trgng ben tren.
M TAP CHI KHOA HOC VA C O N G N G H E TOUV LOI Sfl 35 . 2016
3. PHU'ONG PHAP NGHIEN CUtJ 3.1. Mo ta thiet ke mo hinh
I KHOA HOC ^Bg!?icncni^B
- Md ta mdng khdi nem trong md hinh:
+ Hinh dang va kich thuoc khdi nem: Xem Hlnh 6.
0.15m 0.2m a) M^t bing khoi nem
Hinh 6. Hinh dgng - + Lap dat khdi nem vao mdng tren md hinh Xem Hmh 7, 8, 9.
b) MJt cat B - B 3 kich Ihuic khii nim [31 J.
Tai IronE ben tren q
KAJirlJca; /l O.Sm I O.Sm | 0.5m 1 ' ' Hm ' Hinh 7: Mat bdng khoi nem tren md hinh
r l a i trong ben tren q
Hinh 8: Sa do thi nghiam Iren md hinh Igi mdl cdt 1-1
Hinh 9- Sodd thi nghi?m tren mo hinh Igi mdl cdt 2-2 + Vat lifu khdi nem: Cac khdi nem dugc che tao tit dat set ySu (xem Bang 1) trdn vdi xi mang PCB40 la 200kg/m' dit va phu gia 2kg Roadcem (ty 1? 1%), dugc thi cdng bSng diic dam. Khdi nem dugc bao duong 28 ngay dat cudng dg 7 kg/cm^ md dun bien dang bine 350 kg/cml
+ Dac diem dit nSn va cat chen khe: Dit nSn trong md hinh thugc lgai dit set yeu (tugng tu g ddng bing Nam Bg), d trang thai deo chay, CO chi tieu ea ly neu d Bang 1. Cat chen khe rong giiia cac khoi nSm thugc CiSt hat trung, mau xam nau, cd cac chi tieu ea ly neu d Bang 2.
TAP CHl KHOA HOC VA C O N G NGHf T H O Y LOI Sc5 35-2016
KHOA HOC ^ E I M E I ^ B
Bang 1. Chi tieu cff l> dat yeu trong mo hinh TT
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Chi Hen Thanh phan hat Hat set (<0,005mm) Hat bui (0,O05-O,O5m) Hat cat (0,05-2mm) Dd am tu nhiSn (\V) Khoi lugng the tich tu nhiSn (Y„) Khdi iugng the tich khd (y^) Khdi lugng riSng (A) Do bao hda (G) Dp Id rdng (n) He sd rdng (eo) Gicri han chay (WL) Gicri ban deo (Wp) Chi sd deo (lp) Do set (11) Gdc ma sat trong (cp) Luc dinh (C) He sd nen liin ai.2 He sd tham (K)
Sire khang tir TN cat canh (Cu)
DoTi vi
% %
% %
g/cm^
g/cm^
% -
% -
%
%
Dg Kg/cm^
cm^/kg Kg/cm^
Giatri 54,3 19,5 26,2 63,1 1,54 0,94 2,61 93,4 63,72 1,76 66,70 36,95 29,75 0,88 2<'56' 0,09 0,131 6,87*10"'
0,13 Bang 2. Chi tieu co- Iy cat trong mo hinh
Chi ticu Thanh phan hat Cat hat min (0,05-0,10mm) Calhatnhd(0.l0-0,25mm) Cat hat trung (0,2S-0,50mml Cat hat thd (0.50-2.00mm) Hat soi. san (2-60mm) Do am ttr nhien (W) Khoi lugng thS tich tu nhiSn (y,) Khdi lucmg thS tich khd (y^) Khdi lugng neng (Al Do chat (K)
Gdc ma sat trong khi khd l,f,) Gdc ma sat trong khi udt icp..'!
Bffn vj
g/cm
Dg Bg - Gidi ban bien md hinh. Gidi han bien ciia md
hinh ty le thirc dugc thiSt kl va xa^ dung sao cho phan inh diing idi thuc IS. gidi han nay phu Ihuoc Nio tai trgng tac dung la gidi han
mat trugt pha hoai ciia md hinh. Qua tinh toan, xac djnh duge gidi han cua md hinh USn mit dung (cat ngang mdng) nhu tren Hinh 10. Gidi han theo phuang dgc mdng lay rdng lm tucmg
TAP CHl KHOA HOC VA CONG N G H E THUY LOI SO 35 - 2016
I KHOAHQC ^psin^rSiiM
Sing^Manh '.°*",'''«" . ' ' ^ 8 Pl'S^S '""> <i«- '=hang dS giu 6n dinh cho md hinh (xem Aung quanh giai han bien cua md hinh duac Hinh 10 11)
xay gach Ml 00 day 35cm kSt hgp thanh
Hinh 10: Giii hgn bien md hinh.
- Lap dat thiSt bi thi nghiSm cho md hinh:
+ Lip djt cam biSn ung suit: DS dg sir thay ddi ling siiat dudi tac dung ciia cac cip tai trgng bSn IrSn, lap dat 3 cam bien ling suit Sl, S2, S3 tai cac vj ui nhu trSn Hinh 11, Htah 12 va Hail 13.'
H,nh 11: Vi tri cam biin img sudt Iren mgl bdng md hinh.
Hmh 12: Mat cdl 1
Hinh 13: Mdl cdl 2-2 + Lip dat tim nen, khung truySn lgc va kich gia tai: Chi tiSt xem tren Hinh 10.
+ ThiSt bi khac: ThiSt bj ghi dir lifu tir cam bien ung suat dS chuySn vag may tmh phuc vg xit ly kSt qua thi nghiem (Data Taker), ddng hd dg tai trgng dS theo dai va duy tri tai trgng khdng ddi eho moi cip tai trgng, ...
Cac thiSt bi dua vag thi nghiem da dugc higu ehinh trudc khi lip dat.
3.2. Quy trinh thi nghifm
- Thdi gian duy tri cip tai trgng: Tham khag quy chuan ctia Nhat Ban JSF-T2S-80T thdi gian duy tri cho mSi cjp tai trong duac lua chgn la 30 phiit, trong thdi gian nay tai'trong dugc giir khdng ddi.
TAP CHl KHOA HOC VA CONG NGHE THUY LOI SC3 35 - 2016
KHOAHQC ^ E ! ! 3 I B ! ^ B
- Quy dinh d p lai trgng: Mo hlnh thi nghiem voi 8 cip tai trong tac dung len tim nen. Tri so mfii cap gia tai tap trung bing 0,6T tircmg iing voi lire phan b6 0,4T/m^ (phii hop \-ai chieu day lap dkt ddp de la 25cm). Cip tai trong thu 8 CO gia tn bang 4,8 Tan, tucmg iing lire phan bfi 3,2 Tin/m^, quy dfii ra chi6u cao de H=2m.
- Do ung suat tang them: Sau klii tac dung moi cap tai trong len mong, do gia tri ung suat tang
them len nen tai day mong khoi nem a mSi cam bien ung suat phuc vu cho vi?c xu- Iy k^t qua thi nghiem. Do ung suat tang them lan lugt cho 8 cap tai trong, ke qua do dugc l ^ thanh bang de ti?n nghien cuu, binh luan.
4. KET QUA THI NGHIEM
Ket qua thi nghiam la cac tri so ung suat tSng them len nen tai day mong khoi nem 6 c^c cam bien iing suat. Cac tri so nay ghi 6 Bang 3.
Bang 3. Ket qua do ung suat tang them tai day m6ng khoi nem Cap
gia tai 1 2 3 4 5 6 7 8
Life kich kichQ
(T) 0,60 1,20 1,80 2,40 3,00 3,60 4,20 4,80
Tii trgng q
(Tim')
0,40 0,80 1,20 1,60 2,00 2,40 2,80 3,20
LTng suat tang them tai day mong (Tim'}
Sl 0,15 0,50 0,73 0,92 1,38 1,84 2,23 2,69
S2 0,20 0,52 0,56 0,71 0,95 1,31 1,35 1,71
S3 0,24 0,74 1,00 1,28 1,60 2,03 2,31 2,51
Ung suat t i n g them trung binh tai day mong q' (Tim')
0,17 0,54 0,74 0,93 1,34 1,77 2,09 2,50
H | so giam l u c K (q'/q) 0,43 0,67 0,61 0,58 0,67 0,74 0,75 0,78
Hi^u qua giam irng suit tnmg binh(%)
57 33 39 42 33 26 25 22 5. BilVH LUAN K^T QUA
Ket qua do dac img suit tSng thSm ISn nen g day mdng khdi nSm tai cac vi tri cam bien ting suit Sl, S2 va S3 ling voi cac cip tai trpng tac dung nSu d Bang 3 cho thiy ling suit tang them giam di rd ret, mirc dg giam tai eac vi tri cam biSn la khac nhau: LTng suit tang UiSm nhd nhit tai S2 (vj tti khe rong khdng cd khdi nSm), ung suit tang thSm ldn nhit tai S3 (vi tri tai day khdi nSm).
Cd sg khac nhau vS gia tri img suit tang them tai eac vj tri cam biSn ling suit la do md dun bien dang (dg eimg) ctia mdng khdi nSm khdng ddng deu: Md dun biSn dang eiia cat chen khe rong nhd hon md dun bien dang ciia khdi nem lam tii dit set ySu trdn vdi xi mang
va phu gia, do dd kha nang tap trung tai trgng vao vi tri khdi nem Itin hem cac vj tri khde, dd ia Iy do ling suit tang thSm tai cam biSn ling suit S3 ldn han iing suit tSng them tai cic vj tri cam biSn img suat cdn lai.
Nhin chung, img suat tang them trung binh day mdng khdi nem da giam so vdi tai trgng tac dung iSn mdng, mirc giam img suit trung binh tir 22»/. den 42%, ca biet dSn 57% tuy thugc vao cap tai trgng ngoai tac dyng. Mitc giam nay cd su sai khac so vdi gia thiet ban dSu la tir 20% dSn 30%.
6. KET LUAN VA KIEN NGHJ Bai bao da trinh bay kSt qua nghien eiiu iing suat tang thSm len nen tai day mdng khoi nem
TAP CHI KHOA HOC VA C O N G NGHE T H O Y LOI s d 35 - 2016
I KHOA HOC ^BSggl!H^I^B
tren mg hinh vat ly ty le thuc dudi tac dung LTng dung mdng khdi nem vao xay dung de cua tai trgng ngoai. Ket qua thi nghiem la tm biSn la rit kha quan, cin tiSp hic sir dung kSt cay phan anh dugc thuc te khach quan, bdi sti qua thi nghiSm trong bai bao nay dS nghien dgng phuang phap nghiSn ctiu tren md Unh eiru tdi uu hda hmh dang khdi nem ciing nhu vat ly ty le 1:1 va cac thiet bi do dugc kiSm phuc ^•u viec thiSt lap cdng thiic giai tich tmh nghiem trudc khi dua vao lap dat. ,„4„ dng suit tang them tai day mdng.
TAI LIEU THAM KHAO
[1]- f^C-NJlOll). TCVN 1)354:2012-Ddt xdy dung-Phuang phdp xde dinh mo dun biin dgng tg, h,en truing bdng tdm nen phdng Ha Ngi.
'^'' HiNdi ^''° ^ ™ ™ ' ^ ° ^ ' ^ ^ ' " * * ^ " ^'""' <^'"'^'' "^^ '""' ''*• ^^™ ^y '*V"B' [3]. Nguyin Qude Diing, Phimg Vmh An, Dd ThS Quynh va mik (2015), Bdo cdo ting kit li
la, cgp Bg:Ngh,en dm gidi phdp cong nghi xir ly nin ddt yiu bdng thiit bi trdn ddt lai chd ffi NM * " ' ' ™ "" ^'""^ ™ ""^ ''™^ """^ "•'"* " " * '"'• ^ ' ^ ° ™ ' " - '^'«' '^™- Hiep hdi dia ky thuat Nhat Ban, Quy chuin JSF:T25-80T - Phuongphap thi nghiim ban
nen h,en Irucmg cho ddt nin. ' Nguyin Nggc Phue (2014), "Hieu qua gia cudng mdng ndng va quy tnnh ttnh toan sir
dung giai phap top-base", Tgp chi kil cdu vg cdng nghi xdy dung, (14/1-2014), tr. 5-11.
R.withlow (1996), ca hoc ddi, ldp II (bdn dich), NXB Giao due. Ha Ndi.
Banseok Top Base Co., ltd, In-plgce Top bgse melhod - New foundotion method on soft
ground, Korea. ^ Jeong et al (2011), Melhad of analysing load-selllemenl charaeleristics of Top-base
foundation. Patent Applieatign Publicatign, Pub. No: US 2011/0208445 Al Pub nar,- Aug. 25, 2011, United States. ' ""•"'"'=•
[4].
[5].
[6).
[7].
[8].
TAP CHIKHOAHOCVA CONG NGHETHUV LOI 5(535-2016