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XAC DINH CAC THONG SO CiroTNG DO CUA NEN D\t(tl TAM BE TONG XI MANG MAT DITCTNG BANG THIET Bf GIA TAI DONG
FWD PRIMAX 1500
Tdm tit: Bii bio gi&i thiiu thiet bi FWD Primax 1500, cic sd liiu dau ra cua thiit bi va vigc si>
dyng chOng di danh gii cw&ng dd nin dat cua mat dw&ng BTXM. Cic kit qui giOp chung ta cd nhung dinh gii vi chit Iwgng thyc ti cOa cic idp vit iiiu va nin dit cung nhw dw bio kha nang lam viic con Igi cOa mat dw&ng. Diy li cdng viec rat cd ^ nghTa khi khio sit dinh gia cac tuyin dLf&ng cu hoic phyc vy cdng tic nghiim thu nin mit dwdng.
Tip khoa: Mgt dwdng bi tdng xi ming, nen dat, tai trong ddng, thiit bj do ddng FWD.
Abstract: This paper introduce a FWD Primax 1500 device, and its outputs that are used to evaluate strength of subgrade of pavement structure. The result of this prediction can evaluate quality of cunent subgrade and rest capacity of the pavement. This evaluation is essential for assessing existing roads and acceptance inspection of pavement structure.
Keywords: Cement concrete, subgrade, dymamic load, dynamic instrumentation FWD.
TS. NGO VIET DtPC
Khoa Xdy dung C i u dudng, Trudng Dai hgc Xay dyng TS. H d A N H C U ' a N G
Khoa Cdng trinh, Trudng Dgi hgc Giao thdng van tai NCS. N G U Y i N THj N G A N Khoa Xay dyng - Kien true, Trudng Dgi hgc Dgi Nam
1.2. K i t qua d o t h u duo-c t i i t h i i t bl FWD Primax 1500
Dg vdng cda mat d u d n g tgi tung diem d u g c xde djnh t d cae d i u do chuyen vj bo tri dgc thdn may. Tren t h i i t bj FWD Primax 1500 cd 10 d i u do vdi khoang cdch den tam tam gia tal l i n luot la: 0, 20, 30, 45, 60, 90, 120, 150, 180 vd 210em. Tri s i do vdng lgi cae dau do md td mgt nua hinh ddng eua ehgu vdng;
p h i n mem tfnh loan di kem tinh ra md dun ddn hoi dgng tuang iing tgi tiing vj Irf do.
Vdi moi cap tai trgng khai bdo, gia trj dg vong vd md dun ddn h i i dgng se d u g c tinh lai l u n g vj tri dgt dau do. Bang 1. Trdn Hinh 1 la hinh dnh mgt niia chdu vdng linh l u tam ban ep va s a do phdn b i md dun dan hoi lgi tdng vj tri dgt dau do.
1. c a s d L y T H U Y t T SCP O y N G T H I ^ T B i FWD Ot KHAO S A T cub'NG DO cAc L O P K^T C A U NiN MAT DU'O'NG
1.1. Nguyen tac hoat d d n g c h u n g cua t h i i t b i FWD Phan ehfnh cda t h i i t bj la bg phdn gia tai, cdc d i u do do vdng vd p h i n mem tfnh toan. Mdt k h i i tai trgng Q rai t u do eao H, lao nen mgt lye P (kN) xuong l i m dp ed bdn kinh a (cm), thdng qua bg phgn giam c h i n gdy ra mdt ap lyc p (kPa) len mat d u d n g . Do vdng cua mat dudng d tam t i m dp vd d cdc vj tri each t i m ep mdt khodng quy djnh se d u g c cac d i u cam bien do vdng (sensor) ghi lgi. Cdc t h i n g so d u g c ghi lai nhu: tai trgng P (kN), ap iuc p (kPa) tae dung len mat dudng,
K t u ^ (jdi tir tim bte «p (on]
Hinh 1. Dd vdng va gia tri md dun din hdi ddng cua nin mit ducmg tgi timg vi tri dit diu do 1.3. Xdc d j n h m g t s o t h d n g s o v e c u d ' n g d d c u a nen lu'O'ng d u c n g
Nen l u a n g d u a n g diygc hieu la bdn khdng gian tfnh dd vong mgt d u d n g I (^m) d cac vj tri quy djnh Id c a t i i day l i m BTXM mgt d u d n g , ed the gom nen dat va s d de xae djnh eudng dg k i t c i u nen mat dudng. cdc Idp mdng (vdi mat d u d n g BTXM nhieu Idp) hodc
Bang 1. Vi dy kit qua do dd vong, md dun din hdi ddng cua thiit bi FWD Tal t r o n g
( k N j / A p l i p c (kPa) 50/692
0^ vong (ijm)/li4d dun dan hoi ddng (IMpa) t^i cac dau do each tam ban 6p (cm) 0
780/233 20 648/105
30 566/80
45 449/67
60 356/63
90 227/67
120 159/72
150 118/77
180 94/81
210 79/83
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chinh Id d i l nen (khi mgt d u d n g BTXM ddt trye tiep trdn nen d i t ) . Trong p h i n nay, chung tdl tgp trung vdo m i l sd thdng s i dgc Irung v i cudng dd hay d u g c Sli dung trong cdc bdi lodn t h i i t k i , dd Id hd so nen K vd md dun dan hoi cua n i n E.
1.3.1. Hgsdnen K
Bang phuang phap thyc nghiem, AASHTO da dua ra m i i tuang quan giu'a hinh dang ehgu vdng (thdng qua gid trj dg vdng tai mgt so d i i m ) vdi trj so cua hg so n i n l u a n g duong d u d i t i m BTXM, t h i hign bdng trj so AREA.
. Theo AASHTO-1993 ehi so AREA4 (mm) d u g e tinh thdng qua gid trj do vdng tgi 4 dau do [1]:
AREA^ =152.4x\l + 2x-^+2xf + I. (1)
Trong dd: l^, / „ l^, l^ l i n lugt la gid trj do vdng do 6uiac tgi cdc dau do cd khoang each t i i tdm t i m ep 0 , 1 2 , 2 4 va 36 inch (tuang d u a n g 0, 3 0 , 6 0 , 90 cm).
Gid trj eda hg so nen K (pei) d u g c tra t u loan d i lgp san (Hinh 2), phy thuOc vdo tai trgng tdc dyng P (pound), bdn kfnh dfa gia tai a (inch), do vdng do lgi tam vd gid In AREA^ tfnh todn (inch).
Hinh 2. Toan do xac dinh hi so nin ddng K (pci) theo AASHTO-1993 [1]
- Theo AASHTO-1998 ehi so AREA7 (mm) d u g e tfnh thdng qua gid trj do vdng lai 7 d i u do [2]:
Aff£A,-25.4x4+6>:-!-+5x
/„
L „ = 2 5 . 4 x
1524 •AREA^\
-0.698
Gid trj he so n i n K_ (kPa/mm) vdi l i m BTXM ed kfch thudc vd han:
mm
-986866: PxL (4)
(3)
Trong dd: l^* la hg so khdng t h u nguyen cua do vong tgi tam cua tam dgt tai, tfnh theo phuang trinh:
,(-0 07565-i,)]
/ : = 0 . 1 2 4 5 x e H>-14707xe^" (5) Hg so n i n K (kPa/mm) vdi t i m BTXM eo kfch thudc h i i u hgn d u y c tinh n h u sau:
K f^— (6) Trong do; AF, vd AF^ Id cdc hd so d i i u ehinh v i kfch
t h u d c huu han cda l i m BTXM, phy thuOc vao kich t h u d c vd do Cling t u a n g d i i cda l i m BTXM:
A7^=l-0.89434xe ^^' (7) -0 718781 — I
A F j = l - 1 . 1 5 0 8 5 x e ^^' (8) Trong dd, D (mm) phy thudc vao chieu ddi L, (mm)
vd c h i i u rCing B, (mm) cda tam BTXM, d u g c xac dinii n h u sau: n i u L, £ 2Bt thi D = (LjXB,)0.5; neu L, > 2B, thi D = 20.5xL,.
- Tinh theo bai todn cda Westegaard
Phuang phdp ndy xay d y n g quan hg giua do vdng, tai trong tae dyng len mat dudng vd hd s6 nen dudi tam BTXM cho bdi todn c a ban tam tren nen ddn hbi [3]. Vdi ldi trgng dgt tgi giua t i m , hd s i n i n K (N/m^) d u g c tfnh theo dg vdng Idn n h i t nhu sau:
i^hY^y
(9)Trong do: /^ Id dg vdng Idn nhat tal tam tam (m); P la tai trgng (kN); a Id ban kinh dTa gia tai (m); y = 0.5772156449 Id hg so Euler; L Id ban kinh dg ciing l u a n g d u a n g cua t i m BTXM (m), duge xac d|nh theo gia trj AREA:
- ( 2 ) Trong dd: l^, /,, l^, /„, l^. /g, /^ lan luot Id gid tri dd vdng do duge lai cdc ddu do cd khodng cdch tu lam lim ep 0, 20, 30, 45, 60, 90 va 150cm.
Ban kinh dd ciing tuang doi cda tam BTXM cd kfch thude vd hgn L_ (mm) d u g c xac djnh theo phuang Irinh:
fln-*
-AREAB C
(10)
V6i cac hang so thu-c nghiem: A = 36; B = 1812,279;
C = -2,449; D = 4,387 [IJ
Theo khuyen c4o cua AASHTO, ma dun phan Ivc nen tTnh K„„j dung trong tinh to4n dyp'o l4y bang 0.5 lan gia tri K xac flnh bang c i c thi nghi#m gia tai dpng.
1.3.2. M6 dun dan hdi E
N l u coi n i n d i t va tling mong ciJa mat du'dng BTXM la mpt nen tuong di/crng thi mo dun dan h6i dpng cua nin ttiang duong E«„ (Mpa) c6 th4 d u p c xac dinh tir cong thCpc ciia Gluskov [4]:
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KHOA HOC - C O N G NGHE l l l l l
Eti 0.385 x P : •.[l-,^\
l,xL (11)
Trong dd, P Id tdi trgng ldc dyng khi thf nghidm (kN), [1 la hg so pooatson cda nen.
Theo k i i n nghj cua GS. Phgm Cao Thang vd cdc cgng s u , md dun dan hoi tTnh cua n i n (E,) ed t h i l i y bdng 0.45 den 0.6 md dun dan h i i dgng (E^), phy thuOe vdo vdt lieu lam mdng vd toai d i l nen [5], Theo 22 TCN 233-06, khi s i i dyng t h i i t bj FWD, md dun dan hoi tTnh cda nen d i t E, = 0.33xE^ [7].
2. DIADI^IM VA S D D d DO TR§N DOAN THl NGHlCM De ed so Iidu t h y c t i so sanh doi c h i i u vdi eac edng thdc thyc nghiem, ehung tdi chgn dogn t u y i n thi nghi&m tai dja phdn thdnh phd Yen Bdi, tinh Yen Bai.
Day id mdt tuyen d u d n g thugc hd thong giao thdng ndng Ihdn ven thdnh phd Ydn Bdl, v u a d u g c xdy dyng, mdi bat dau khai thdc, do dd cae thdng so ve eudng dd cda nen mat d u d n g vdn ehua b| tae dgng bdl eac yeu to thdi t i i t vd giao thdng. Mat d u d n g BTXM phdn tam cd kich t h u d c 3.5x5m, d i y 22em, dgt trye t i i p trdn n i n dat da lu len tgo phang vd giua eae t i m khdng bo trf thep lien k i t . Cdc diem do d u g c b i tri giua ede l i m , h u d n g dat may dgc theo llm dudng, nhu md td tren Hinh 3.
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Hinh 3. Hucmg miy va sa dd cic diim do trdn mit ducmg BTXM phan tim 3. D A N H GIA K i T QUA T I N H THEO C d N G THO'C VA K £ T Q U A D O TCP FWD PRIMAX 1500 3.1. Xac d j n h cac t h o n g s 6 c u a dat nen Vdi tai trgng thi nghiem Id 50kN, k i t qua tinh md dun dan hoi E, hd s i n i n K, theo cdc p h u a n g phap da gidi thigu d tren va theo k i t qua do t n j c t i i p t d thiet bj FWD Primax 1500 d u g c t i n g hgp trong cac Bdng 2 vd Bang 3.
3.1.1. Md dun dan hoi:
Md dun ddn h i i cda n i n d i t d u d i tam BTXM d u y c do tgi tam eua tiing tam BTXM mat d u d n g . So ligu Irong Bdng 2 d u g c do tgi 12 tam BTXM khdc nhau dgc Iheo t u y i n d u d n g khao sal.
Bing 2. So sanh gii tri md dun din hdi ddng tinh toan va do ti/ thiet bi FWD
Thirti^
dilm do 1 2 3
Mo dun dan hdi dong (Mpa) E„
71 71 70
E-o 7 4 75 73
Sai so ciJa Z phuwng phdp tinh
(%)
4.8 5.4 5.0
4 5 6 7 8 9 10 11 12
85 72 70 70 71 69 70 80 85
85 76 74 74 75 73 73 85 85
0.1 5.8 5.0 5,7 5.2 5.5 4.8 6.5 0.4 Trong Bdng 2, E^ d u g e tinh ICrng cdng thue (11) thdng qua trj s i AREA; gid trj E ^ d u a c l i y trye t i i p t u mang so Iidu d i u ra eua t h i i t bi FWD Primax 1500, chinh la gid tri md dun dan hdi nhd n h i t do d u g c lai cac dau do (Bang 1) hogc fa gia tri dat cue l i i u tren d u d n g cong t h i hidn md dun dan hoi trong Hinh 3.
Sai so kha nhd giO'a 2 k i t qud xdc djnh md dun ddn h i i cho thay s u h y p ly cua vide sd- dyng gid tri nhd n h i l trong so cac gid trj do lam In so u d e lugng eua md dun ddn h i i n i n d i t . Gia trj md dun dan hoi dgng Irung binh tfnh lodn Id 73.6 Mpa, n i u lay theo s i do cda thiet bi FWD la 76.8 Mpa, md dun ddn h i i tTnh t u a n g i i n g vdi hai trudng hgp ta 24.3 va 25.3 Mpa.
Cd the gidi thfch viec lay gia tri nhd n h i t trong so cdc gid trj do md dun ddn h i i Id md dun ddn h i i cda n i n d i t thdng qua sa do vung phan bo ung s u i t trong cac Idp k i t cau ao dudng d u d i lae dyng cua tai trgng, Hinh 4. Khi cd tdi trgng tac dyng, iing s u i t sinh ra d u g c truyin qua cdc Idp vdt Iidu x u i n g phia dual.
Vdt Iidu cdng cdng (md dun ddn hoi cang Idn) thl gdc phdn b i x u i n g Idp d u d i eang rgng (bdn kfnh vung phdn bo ling s u i t do tai trgng gay ra cang rdng). Do vdy, ndn khi dau do ehuyen vj cda t h i i t bl ndm ngoai phgm vi phan bo ung s u i t tai ddy Idp vat lieu thl tn so do d u g c chi phdn dnh dd vdng/kha nang chju tai cua cdc Idp n i m d u d i Idp do [3]. So lieu khao sat Ihyc t i tren cae l i m BTXM mac 250, d i y 22cm, cho t h i y gid trj toi Ihieu dgt dugc ludn lim Ihay d vi trf dau do each ldm 60 va 90cm. Tuy vay, day ehi la cac nhdn xdt ban d i u cda eac tac gia, d i xdc dinh chinh xdc vj Iri dau do n i m ngoai phgm vi phdn bd iing s u i t tai ddy lam BTXM, can bo trf Igi vj tri eac dau do vdi m | l dg day han trong khoang u d c luang nay
Cic sensor do d^ vOng
Ph^m vi vftng iVrg
^ suit tnmg k ^ d o D ^ mit dirimg
Hinh 4. Vung ung suit trong kit cau ao dw&ng dw&i tic dung cua tai trgng FWD
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3.12. Hgsdnen;
He so n i n K cua n i n d i t d u d i tam BTXM d u g c tinh theo cac edng thuc da gidi thidu trong mye 1, lgi tdng vj trf d i i m do, k i t qud tinh d u g c tong hgp trong Bang 3.
Bang 3. So sanh gia tq hi sd nin tfnh tinh theo cic phucng phap khic nhau
Bing 4. Hi sd nin tinh toin K va md dun din hoi E cua dit (Phy luc C) [6]
T h i p t v diem
do
1 2 3 4 5 6 7 8 g 10 11 12
H f so nen tmh (MN/m^)
K-W
45 44 45 45 45 44 44 45 43 45 38 44
K-98
39 39 39 41 39 38 38 39 38 39 37 41
K-93
37 37 36 37 35 35 35 36 34 35 30 37
Sai s o giu-a K - W v ^
K-98
(%)
13.6 13.1 14 2 8.6 12.6 13,2 12,7 13.3 13.2 14.3 0.3 8.1
S a i s d giii'a K-Wva
K-93
(%)
18.2 17.6 18,8 17.5 21.0 21.8 21.1 20.1 22.4 22.2 19.9 17.0 Trong Bang 3, cdc ky higu K-W, K-98 vd K-93 t u a n g ling vdi tri s i cCia he sd n i n linh theo bdi todn cua Westepaard, AASHfO-1998 vd AASHTO-1993. Cd the thay, sai khae giua k i t qua tfnh hd s i n i n Iheo Westegaard va AASHTO-1998 trong khoang 10 d i n 15%, n i u so vdi AASHTO-1993 khoang chenh Igch td => 20%, s y sal Idch ndy cd t h i do qud Irinh s i i dyng toan do Hinh 3 hoac do trong AASHTO-1993 chi so dign tich AREA d u g c tinh chi thdng qua gia tri do tai 4 d i i m , vide ndy cd t h i Idm gidm do chfnh xdc cda k i t qud. Theo cdc k i t qud tinh, ed the u d e luyng he so n i n d u d i t i m BTXM mat dudng dgt gid tri trong khoang 39 d i n 44 MN/m^
3.2. Danh gia cac t h d n g s i c u d n g do cua nen dat Dh cd t h i ddnh gia them v i do tin edy cda cac k i t qua tfnh, lac gid da so sdnh trj so md dun ddn h i i trung binh cda dogn Ihi nghiem E^ = 25 Mpa vd he so nen Irung binh K,^ = 42 IV1N/m^ vdi quan hg da d u g e gidi thieu trong TCVN 10907:2015 [6], Bdng 4.
Co the thay, s y tuang quan cua hai thdng s i nen dat (K va E) viia d u a c u d c luang Id kha hgp ly, g i n vdi loai d i t a cat va d set hgt bui trong khu vuc khi hgu I vd II.
4. K^T LUAN
Vdi k i t qud do Id sa do hinh dang eh^u vdng hinh thanh va cdc gid tri md dun dan hoi l u a n g iing vdi tling vj trf ddu do, thiet bj FWD Primax 1500 gidp ddnh gia nhanh chdng vd ehfnh xae mOl so thdng so eudng do cda mat d u d n g BTXM.
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eo 60 60 50 40
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eo 60 so 70 so
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«0 100 100 ao 70
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Md dun ddn hoi eua nen t u a n g d u a n g dudi tam BTXM mat d u d n g cd I h i d u g c ii/ac lugng nhanh tO k i t qud do cda t h i i t bj FWD Primax 1500. Vdi chiiu day lam BTXM 22em, trj so nay la gia trj do tai vj trf d i u do edeh ldm t d 60 d i n 90em. Tuy nhidn de xdc djnh chinh xac vj tri dau do higu qua, can thdm cdc nghidn eiiu eu the han v i van dd ndy.
K i t qua linh he so nen theo phuang phdp 1;^ thuyit vd thue nghi&m khd d i n g n h i t . N i u b i i t logi d i t nen, cd the d y doan khoang gia tri cda he so nen luang l i n g vdi gia Iri do cua md dun ddn h i i •
T A I LIEU THAM K H A O
1. AASHTO 1993, Guide for Design of Pavement Structures.
2. AASHTO 1998, Guide for Design of Pavement Structures.
3. D u a n g Hgc Hdi, N g u y i n Xudn Trye (2014), Thiit ki dw&ng d td tip 2, Nhd xuat ban gido dye Vidt Nam.
4. Gluskov (1977), Khio sit thiet ki kit ciu mat dtr&ng cung d td vi sin bay, Nhd xuat ban Maxcova.
5. Tran Thugn L y i , Phgm Cao Thang, Nguyin Van Hieu (2012), "Nghien ciru thuc nghiim xac dinh md dun dan hdi dgng cua nen mit dw&ng BTXM". Tgp ehi C i u d u d n g s i 3 nam 2012):19-25.
6. TCVN 10907:2015, Sin bay din dyng - Mgt duang sin bay - Yeu ciu thiit ke. Bg Khoa hgc va Cdng ngh$.
7. 22 TCN 233-06, Quy trinh thi nghiim vi danh gia cw&ng dd nen dw&ng va kit cau mit dw&ng mim cua dw&ng d td bing thiit bi do dgng FWD, B0 Giao thdng vdn tdi.
