Phuong phap uoc luong do dai thoi gian thuc hien cac cong viec khi lap tien do thi cong xay dung
• K S . L g DlNH U N H & • G S . TS. N G U Y £ N HUY THANH TRUCfNG DAI HOC XAV DUNG
(Bli nhan ngay 02/06/2015, hoan chinh sQa chua ngay 09/06/2015)
TCM TAT: Viec Udc lUcmg dp dai thdi gian thUc hien cac cong viec xiy duUg co dnh hudng nhat djnh den chat lUtfng va ti'nh khS tht cua bdn Ice hoach ti^n do thi cong. Ket qua tii mot CUOC dieu tra v^ each Udc lUcmg thdi gian thUc hien cong viec khi lap tien d6 thi cdng duoc sCr dung tai cac don vj thi cong tren ca nUdc cho thciy cd su khac biet dang ke giUa cac dem vj va cac gdi thau. Bai bao da chi ra nhUng ton tai trong viec Udc lUOng
thdi gian thUc hien cac cdng viec trong lap tien dp thi cdng ma cac nha thau ap dung hidn nay tai Viet Nam vh dua ra mdt sd giii phap nhSm khdc phuc tinh trang nay.
TCr khoa: l/dc lUg^g dp dai thdi gian thUc hien cdng viec, phuong phap chuyen gia, Udc luong ba ^em, Udc lUdng theo tham sd, Udcluong tuong tu
ABSTRACT: The job of estimating activity durations for construction projects decides the quality and feasibility of project schedule for construction work.
Results from a survey on the methods of activity duration estimation applied by contractors in Vietnam show a variety of approaches to this job. This paper articulates significant issues in
this practice and proposes several solutions solving issues.
for those
K e y w o r d s , Estimating activity duration, expert judgment, three- point estimation, p a r a m e t r i c e s t i m a t i o n , a n a l o g o u s estimation
T
rong thQc te hien nay lai Viet Nam da sd eic du an dau tQ xay dung, die bi^l II eac du In sQ dung vdn nha nudc, diu cham tien dd Clc du an thue hiln dQng hoac vuot tiln dp chl dat chua tdi 1% [6]. Cd rat nhilu !y do dan tdi tinh trang tren, nhung mdt trong nhQng nguyen nhan eo bin la do vilc udc luong thdi gian thuc hien cAc cdng viec trong qua trinh lap tiln do thi cdng khdng dim bio tinh khoa hoc va khi thi din tdi bin kl hoach tiln dd thi cdng dUOc lip ra, nhli la cac klhoach tien do ehi tilt, khong ed nhieu gil tri trong vile dieu hanh va chi dao thi cdng tren cdng tn/dng. Bai viet nay se neu cu t h i v l van de niy va dua ra mdl sd giai phap khac phuc tinh trang neu tren.
L CAC PHUDNG PHAP UdiC LUQNG DO DAl THdl GIAN Od dai ihdi gian thuc hien cdng vile (gpi t i t la thdi gian thuc hiln cdng viec) thudng la yeu td kho ude luong bdi vi
nd chiu sQ chi phoi eua nhilu nhan td, chang han nhu. khi nang huy ddng ngudn luc, nang suat lao ddng, nlng suat may mdc thilt b|, cac tie ddng tQ mdl trudng ben ngoai . .[3]. Hiln nay, trang cae tai lieu v l lap tien dp thi cdng ed trinh bay nhieu phuong phip xic dinh thcrt gian thuc hien cdng viec Mdi mpt phuong phip diu co nhQng Uu, nhupe diem nhat dinh vl dupc sQ dung thich hop trong nhQng dilu kiln cu the, Mdt sd phuong phap pho biln dupc trinh bay dUdi diy.
•NGHl£HCmiLtUlAH (THEORETICAL STUDY)
/ /. Phuang phdp chuyen gia (Expert Judgment)
Tbeo phuong phip niy, thdi gian thuc hien clc cdng vile se dUOc Udc lupng bdi cle chuyin gia ciia du In tren eo sd eae thdng tin cd san, thudng la tQ clc du In da thuc hien trudc dd, Clc thdng tin nay cd the khai thic 6 nhieu ngudn, chlng han nhQ' cle don vj tQ van, clc hiep hdi nghi nghiep . Kit qua Qde lupng phu thudc nhieu vao mQc dd sin cd va tinh chinh xic cQa thdng tin Ijch sQ eung nhQ kinh nghilm, trinh d$ chuyin mdn cQa chuyen gia. Trong trudng hop khdng dii clc thdng tin ehi tilt ciia du an thi ket qua hoin toan mang ti'nh ehu quan va tiem an nhilu rui ro [3].
12. Phuang phdp Udc luong ba diim PhQong phip Qde iQpng ba dilm (Three-Point Estimates), hay cdn goi la phuang phip xae suit Theo phuong phip niy, ngudi ta dUa vao y kiln danh gil cCia ehuyin gia de Udc luong ba dilm thdi gian lae quan, bl quan va cd khi nang xiy ra nhat de tQ dd Qde iQong thdi gian ky vong thQc hien cdng vi$e,
•Thdi gian lae quan t^ (OptimisticTime):
11 thdi gian de hoan thanh edng tac trong dilu kiln tdt nhat (cd nghTa day II thdi gian ngin nhat de hoan thanh cdng tie)
-Thdi gian bi quan tp (PessimisticTime):
11 thdi gian de hoan thanh edng t^e trong dilu kien xau nhat (cd nghia diy II thdi gian dai nhat de hoan thinh cdng tie).
- Jhtii gian thudng xay ra nhat t^ (Most Likely Time): 11 ihdi gian d l hoin thanh cdng tic trong dieu kien binh thudng NhQvSy,tg5t^stp
Ba loai thdi gian nay deu dupc gil thilt II tuin theo phin phdi Beta hoac phin phdi tam gilc, Neu tuan theo phin phdi Beta, thdi gian ky vong (Expected Time - tE) eQa clc cdng viec dupc xac dinh theo cdng thQc [1], [3], [7]:
6 (1)
TrQdng hap ba loai thdi gian ke trln nlu dupe gia thiet 11 tuin theo phan phdi tam giac thi thdi gian ky vpng cua cae cdng viec dupc xac dinh theo cdng thQc [3]:
1.3. Phuang phdp udc luong theo tham so
Phuang phap udc luong theo tham sd (Parametric Estimahng) xac dinh thdi gian thue hiln cdng viec dUa vao cac tham sd nhQ khdi iQpng cdng vi&e, dmh mQc, iQc iQpng tham gia thi cdng vl sd ca \km vi|e trong ngay. Thdi gian thi cdng cung phu thude vao each thQc thuc hiln clc cdng vi^e Theo do, thdi gian thuc hien clc cong vi^c dupe Ude iQOngnhUsau:
+ Ddi vdi cac edng vilc dUOc thue hiln bSng thil edng la chinh, thdi gian thuc hi&n phu thudc vao nang suat ngudi lao ddng va dupe xae dinh theo cdng thQc:
Qj X DMj HPLDj (ngay)
(3) + Ddi vdi clc cdng vilc dUOc thUe hien bing CO gidi hda la chinh, thdi gian thQc hien phu thude vao nang suat thuc t l cQa miy thi edng (hoac dinh mQe hao phi miy):
Qi '• NSj X M , X N j ,
HPCMj - M , X N , , ( " « ^ * ^
Trong dd:
Q; 11 khdi lupng cdng vile hien;
can (4)
thi;e
DM; 11 dmh mQc hao phi thdi gian khi
thuc hien mdt don vi khdi luong cdng viec 1,
NS; la nang suit thuc te ciia may tham gia thuc hien cdng viec I, HPID: la tdng sd ngay edng can thilt de thuc hien cdng viec i;
N la tdng sd cdng nhan tham gia thue hien cdng viec i,
M:la tdng sd may tham gia thuc hien cdng viee i,
N la sd ca lam viec trong ngay Viec bd rri td dgi cdng nhan hoac sd may tham gia thuc hien cac edng viec phli dua tren dieu kien nang luc ciia don VI thi cdng, co eau ciia cdng viee (thanh phan cdng viec) va sQe ehQa eua mat bang thi edng nham dim bao tinh khoa hoc, kha thi cua ban ke hoach tien , dd thi cdng [2], [4], [5]
Theo phuang phap nay thdi gian thuc hien cong viec c6 the duoe xac dinh I tuong doi chinh xac va thdi gian hoan , thanh chl chenh lech rat it so vdi gil tn da du tinh neu don vi thi cdng xac dmh chinh xac khdi luong edng vie:
can thuc hien va cd du dmh mQc thi cdng Thdi gian duoc Udc luong theo phuong phap nay la thdi qian thuc te duoe yeu eau de hoan thanh cong viec ma khdng bao gdm khoan du trQ cho bat ky trudng hop ngau nhien nao, Tuy nhien, trong nhieu trudng hap khi xay ra cac su cd do cac nguyen nhan ngau nhien dan tdi thdi gian thuc hien tUng ' edng viec va thai gian thue hien tien dd
thuc te se thay doi so vdi du kien Chinh vivay khi sQdung phuang phap nay de udc luong thdi gian thuc hien cac cdng viec la can thiet phai tinh den thdi gian du tru cho cac cdng viec hoac cho el kl hoach tien do
J 4 Phuong phap udc luang tuong tu Phuong phap Udc luong tuong tU (Analogous EsUmating) sU dung thdi gian thuc t l cua clc cdng viec tuong IU da thuc hien de Udc luong thdi gian thuc hien eiia cac cdng vile se dien ra trong tUOng lai [3]
I
NGHltN Ciru Lt LUAN >
Phuong phap nay thich hop ap dung cho cae eong viec co tinh chat don gian hoac trong trudng hop cae thdng tin chl tiet ve cdng viec khdng day dii.
Phuang phap ude luong tuonq tuduoe xem nhu la mdt dang ciia phuong phap chuyen gia, tUc la ngudi cd kmh nghiem se dua tren eac sd lieu tU edng viec tuong t u da thuc hien, ddi chieu vdi cac dieu kien eu ihe eua cdng viec dang xet de quyet dinh thdi gian thUc hien cdng viee do, Nhu vay, do tin cay eOa phuang phap nay phu thudc nhieu vao chat lUong ciia sd lilu lieh sQ eung nhu trinh dd chuyen mon cua cle chuyen gia
1 5 Phuong phdp mo phong Phuong phap md phdng udc luong thoi gian dua tren eo sd gia dinh rang cac sd lieu rdi rac tuan theo quy luat phan phdi xae suit, sau do sQ dung cac cdng cu mo phdng, thdng dung nhat la md phdng Monte Carlo de Udc luang thdi gian thuc hien cac cdng viee [3]
Phuong phap nay thich hop diing de xac dmh cac khoan thai gian du phdng eho cdng viec do cac yeu td ngau nhien nhu thdi tiet, may mdc thiet bi hdng ddt xuat, edng nhin dm dau , gayra Ngoai nhUng phuong phap neu trln edn ed rat nhieu phuong phap cd the van dung de Udc luong thdi gian thuc hien eac cdng viee, ch^ng han nhu phuong phap Delphi .
2. CAC PHUONG PHAP XAC DINH THOI GIAN THUC HIEN C 6 N G VmC DUOC AP DUNG TRONG THUC T^ TAI VIET NAM Ivldt nhom nghien cuu da tien hanh mdt cudc dieu tra ve cach thuc thdng thudng lap tien dd thi edng eua 82 gdi thau d Vilt Nam, trong do co 60 goi thau thi cdng cong trinh din dung, 16 gdi thau thi cdng edng trinh ha ting ky thuat, 05 gdi thau thi edng cdng trinh giao thdng va 01 goi thau thi cdng cdng trinh thuy loi Cle gdi thau nay duoe lua chon ngau nhiln tren pham vi toan qudc nhung tap trung chii yeu tai HI Noi,Thanh phd Hd Chi (vlinh. Can Tho, Phu Yen va eae tinh khac d khu vUc mien Tay Nam Bd va Nam Trung 66 Nhom nghien eUu da gui phieu khao sat thdng qua dudng thu dien tQ eho cac ca nhan tham gia true tiep vao qua trinh lap, quan ly thue hien tien dd thi cdng hoac can bd quan ly du an ciia chii dau tu truc tiep tham gia vao cac gdi thau neu tren
Ket qua cudc dieu tra eho thay - Cd 32 tren tdng sd 82 goi thau (39%) sU dung phuong phap uoe luong theo tham sd dua tren khdi luong cdng viec, dieu kien cu the eua gdi thau, nang lue cua don VI thi cdng va dmh mUe hao phi thdi gian. Trong sd dd, co 04 goi thau noi rd sQ dung dmh mQe do Nha nudc cdng bd so cdn lai khdng neu ro la can cQ dmh muc Nha nudc hay ndi bd nha thiu Do hien nay, bd dinh mUc ma Nha nude cdng bd la dinh mUc du toan nen viee sQ dung nO nham muc dieh td ehUc thi cdng II khdng phan
anh dung thuc t l khach quan nen din toi ban ke hoach tien dd thi cdng khong dam bao tinh khoa hoe va kha thi - Cd 07 (8,5%) goi thau Udc lupng thdi gian thue hien cac edng viec bang each phan bd nguoc tQ thdi gian thue hien gdi thiu duoe rang budc trong hop ddng cho cac cdng viec dUa tren ca sd ddi chieu vdi kha nang cung cap ngudn lUc cho gdi thau va dieu kien cu the eua gdi thau De lam duoe dieu nay can thiet sQ dung den kmh nghiem eua ngudi lap NhU vay day ed the xem II mdt dang ciia phuong phip chuyin gia Tinh chinh xac cua kit qua luflc luong phu thudc vao trinh do chuyen mdn va kmh nghiem cua ngUdi true tiep thuc hien
-43 gdi thau cdn lai (52,5%) sUdung kit hop cac phuong phap phan bd nguoe tU thai gian yeu clu, phuong phap chuyen gia, phuong phap udc luong tuong tu va phuong phap udc luong theo tham sd de xac dinh thai gian thue hien eac cong vile Trong do, cd t h i m 04 gdi thiu sQ dung dinh mQc nha nude khi Udc luong theo tham sd, dan tdi ket qui khdng dam bao tmh ehinh xac Khdng ed gdi thiu nao trong tdng sd 82 goi thiu su dung phuong phap udc luong ba diem (uoc luong xac suat) khi xae dmh thai gian thuc hien cac edng viec Oieu nay cd the duoc ly giai tU thuc te hien tai d Viet Nam ehua co don VI nao thdng k l cae so lilu lich sQ cd lien quan den ba diem thdi gian m l phuang phap sQ dung khi ude luong thdi gian thUc hiln edng viec hoac do ddi ngu true tiep lip tien dd khdng biet
•IIGBl£HCMLtUl|M [THEORETICAL STUDY)
den phuong phip nay | - Oa sd eae gdi thiu cf Viet Nam hiln
nay khi xic dinh thdi gian thuc hiln clc edng viec diu khdng tinh den khoan du phdng do ylu td thdi tilt hoac do | cac nguyin nhin riii ro khac. Cu thi, cd I tdi 65 trln tdng sd 82 gdi thau (79,3%) ! da khdng tinh din thdi gian du phdng cho ylu td thdi tiet, cac gdi thau edn j lai ed tinh dua trln kmh nghiem cua ngudi lip tiln dp nhung khong cd mdt \ phuong phip tinh cu thi, dii co sd khoa hpc. Chi ed 12 tren tdng sd 82 gdi thau (khoing 14,6%) cd tinh den du phdng thdi gian cho clc ylu td khic. Cac riii ro I duoe xet din chii yeu theo clc nguyin | nhin nhU' khdng huy ddng dUOe nhan cflng thue hiln clc edng viee bdi vi nlu roi vio thdi dilm diln ra 11 hdi tai clc dia phuong, mua mang,,,, thi cdng nhin se ve que d l tham dU; cung d p ' hd so thilt kl khdng dung tiln dd I hoae phli dilu chinh thilt kl, khio I sit thilt kl khflng ky,., Clc khoin thdi gian niy cung dupe xae dinh dua vao , kinh nghiem, khdng sQ dung phuang phip md phdng vl chl xet din nhQng : cdng viec hay ehju tic ddng ciia riii ro Thdi gian dy phdng thudng duoe cdng thim vao thdi gian thue hien edng vi§e Cd thi ndi, kit qui nghiln cQu cho thiy vilc Udc lupng thdi gian thuc hien c^c cflng vi^e trong lap tiln dd thi edng hi^n nay 6 Vilt Nam edn tdn tai nhilu vin de, la phin Idn clc nguyen nhin din tdi tlnh trying chim tiln do d da sd cle du kn hi|n nay tai Viet Nam Cung VI ly do lap tiln dd khdng khoa hpc, khdng khi thi, khdng phu hop voi dieu kifn thue t l mci din tdi viec chl dao, dilu dd sin xuit trln cdng trudng gap rit nhilu khd khan, thim ehi khdng thi sir dung k l hoach tdng tien dd da lip ml phli dUa vSo kinh nghilm ciia chi huy trudng edng trudng. D l khic phuc nhQng han chl dd, cd the Ip dung mdt sd gill phip sau:
- cac dan vi thi cdng eln phli xiy dung dinh mQc ndi bfl dim bio tinh chinh xie, tinh thyc tiln d l Ilm can cQ udc iQpng thdi gian thyc hiln clc cdng viec nhim dim bio tinh khoa hpc, khi thi vl chfnh xac eua kit qui, - Odi vdi clc d y i n ldn, cd tinh phQe tap
tiln do thi cdng nen lip theo phuong phap so dd mang (PERT) vdi vilc sQ dung phuong phip Udc luong ba diem (phQPng phip xie suit) 6e Udc lupng thdi gian thyc hien eac cdng viec. Do vay, eln thiet tdng hop clc sd lieu lich sQ, tong hpp y kiln ciia cac chuyin gia ve ba dilm thdi gian ml phuong phap nay xlt den nham tao tiln de cho viec sQ dung phQOng phip nay vio thuc . tien tai Viet Nam;
- Bi dim bio tinh khach quan khi van dung y kiln chuyen gia, cd the i^g dung phuang phip Delphi nhim tranh hien tUPng clc chuyen gia chiu sp chi phdi bdi y kiln eiia nhau;
- Can thiet phli tinh toin thdi gian du phdng cho ylu td thdi tilt vl eie yeu | td rui ro khic, bdi clc ylu tfi nay cung la mdt trong nhQng nguyen nhan gay ra ehim tiln dd nlu phit sinh trong qua trinh thi cdng. Nhim dim bio tinh khoa hoe va tinh chinh xac cua kit qui , Ude lupng, nin dUa tren cac sd lieu lich ' sQvl sif dung phuong phip mfl phdng de Qde iQOng cac khoin thdi gian nay;
- Vl Ilu dai eae doanh nghiep xay dQng eln xiy dung xiy dyng Co sd dQ lieu phyc vu cho vilc lap kl hogch tiln dd de tao tien de va dim bio dd tin ciy cho viee Ip dung cac phuong phap Qde luong d l nlu;
- O l dim bio tinh khoa hgc, khi thi ciia bin kl hoach tien dd thi edng can chuyin nghidp hda vi§c l|p tiln dd bing cich dao tao chuyin siu cho dpi ngu nhan lUc phyc vu cdng viec nay ve clc khia canh c6 liln quan din vi|c udc luong thdi gian thuc hien cdng viec vl cae ndi dung khac khi lap tien dd thi edng xay dung;
- Nha nudc nen ed nhuing quy dinh, hudng din eu t h i v l vin d l bd tri clc khoin thdi gian du phdng cho tiln dp ' thi cdng
Nghiln cQu tdng quan clc vin de v l vile Qde luong thdi gian thyc hiln clc edng vile trong hoat ddng lip tiln dd thi edng trong nginh x5y dung 6 Viet Nam cho thiy eac don vj thi cdng cdn gap nhilu vin de trang qui trinh thyc
hien Udc iQOng thdi gian thuc hi^n cle cdng viee khong dim bao tinh khoa hpc, kha thi dan tiS bin ke hoaeh tien dp thi edng duoc lap ra khd cd the sQ dyng de dieu hanh vl chi dao thi cdng ngoai hien trudng, v l dd la mdt trong sd clc nguyen nhin dan tdi tinh trang cham tien dp. Bli bio da he thdng hda clc phQOng phap Qde iQwig thdi gian thyc hiln eac cflng viec, chi ra dQoc thuc trang va cac tdn tai trong vi|c Qde lupng thdi gian thuc hien cac cdng vi$c khi lap tien do thi cdng hien nay tai Vilt Nam v l dua ra mdt sd gili phip khic phuc clc tdn tai nay. Cac kit qui cQa bli bio ed the coi la tiln d l de thuc hiln clc nghiln cQu siu hon v l vin d l quin ly thdi gian thQc hien dy an diu tu xiy dimg, vdn II vit d l rit ndng, nfii cdm hien nay trong thuc t l nginh xiy dung Viet Nam •
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