T lap dp gian phap dp

Phuong phap uoc luong dp dai thoi gian thuc hien cac cong viec khi lap tien dp thi cong xay dung

• K S . Le DiNH UNH & • GS. TS. NGUYiN HUY THANH TRUONG DAI HOC XAY DUNG

(Bai nhin ngay 02/06/2015, hoan chinh sQa chQa ngay 09/06/2015)

TOM TAT: Viec Udc li/crng do dai th6i gian thiic hien cac cong viec xay diing co knh hiidng nhat djnh den chat iUdng va tmh kha thi cua ban ke hoach tien dp thi cong. K^t qu^ tif mdt cuoc ^eu tra ve each udc lUcfng thcri gian thuc hien cong viec khi lap tien dp thi cong duoc suf dung tai cac don vj thi cong tren ca nUdc cho thay co sU khac bi§t dang ke giCra cac don vi va cac goi thau. Bai bao da chi ra nhCTng ton tai trong viec Udc lupng

thdi gian thUc hien cac cong viec trong lap tien dp tht cong ma cac nha thau ap dung hien nay tai Viet Nam va dUa ra mpt so giai phap nhSm khac phuc tmh trang nay.

TLI khoa: Udc lUdng dp dai thdi gian thiic hien cong viec, phuong phap chuyen gia, Udc lUdng ba diem, Udc lupng theo tham so, Udc tupng 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 for solving 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 thyc t l hiln nay tai Vilt Nam da sd d c dQ an diu tu xly dQng, die bilt II d c dQ In sQ dung vdn nhi nudc, diu cham tien dp. CIc dU In thye hiln dung hole vupt tiln dp ehi dat ehua tdi 1% [6] Cd rat nhieu ly do dan tdi tinh trang tren, nhung mdt trong nhutig nguyin nhin eo bin II do wee Udc luong thdi gian thuc hien cac edng vile trong qui Irinh lip tien dp thi cdng khdng dam blo tinh khoa hpc va khi thi dan tdi ban k l hoach tien do thi eong dupc lap ra, nhat la c^c ke

hoach tien dd chi tiet, khdng cd nhilu gil tri trong viec dieu hinh va chi dao thi edng trin cdng trQdng. Bai viet nay se nlu cu the ve van de niy va dQa ra mdt sd gill phip khae phyc tinh trang nlu trin.

L cAc PHiroNG PHAP u d c LITQNG Dd DAI THdl OAN THVC HI£N COHC Viec Dd dai thdi gian thue hien cdng vile (ggi t i t la thdi gian thQc hiln edng vile) thQdng la yiu td khd udc luong bdi vi

nd chiu sy ehi phdi ciia nhilu nhin td, ching han nhQ khi nang huy ddng nguon lUc, nlng suit lao ddng, nlng suat may mdc thiet bi, d c tie dpng tQ mdi trudng bin ngoai .,.[3]. Hiln nay trong eic tli lilu v l l|p tien dd thi cdng cd trinh bay nhieu phuong phip xic dinh thdi gian thyc hiln edng vile Ivldi mdt phuong phap deu ed nhufng Uu, nhuoc dilm nhat dinh va dQoc sQ dyng thich hop trong nhQng dieu kiln cy the, Mdt sd phUOng phip phd bien duoc trinh bay dua day

KINH T^XAT DUNG 1 2 1

mmanSMcatsLltwim (THEORETICAL STUDY)

r /. Phuang phdp chuyin gia (Expert judgment)

Theo phuong phap nay, thdi gian thyc hien cic cdng vile se dUOc Udc luong bdi d c chuyen gia cua duan trin cosd cle thdng tm cd s3n, thudng la tQ cic du In da thue hiln trudc dd Gc thdng tin nay cd the khai thic d nhieu ngudn, ching han nhU: cle don vi tQ van, d c hilp hdi nghe nghiip . Ket qui Qdc iQong phu thudc nhilu vao mQc do sin ed vl tinh chinh xac cua thdng tin lich sQ cting nhu kmh nghi|m, trinh dd ehuyen mdn ciia chuyen gia. Trong trudng hop khdng du d c thdng tin chi tiet cua dQ i n thi kit qui hoin toan mang tinh chu quan va tiem an nhieu riii ro [3].

1.2. Phuang phdp udcluangba diem Phuong phap udc luong ba diem (Three-Point Estimates), hay cdn gpi ta phuong phip xic suit. Theo phuong phip nay, ngQdi ta dQa vio y kiln dinh gii ciia chuyen gia de Qdc iQong ba dilm thdi gtan lae quan, bi quan va cd khi nlng xiy ra nhit de tQ do udc lupng thdi gian ky vpng thuc hiln cdng vile.

-Thdi gian lac quan t^ [OptimisticTime):

II thdi gian de hoan thanh cdng tac trong dilu kiln tdt nhat (ed nghia day la thdi gian ngin nhit d l hoan thinh cdng tie),

-Thdi gian bi quan tp (PessimisticTime), la thdi gian de hoan thanh cdng tic trong dteu kiln xau nhit (cd nghia day la thdi gian dai nhat de hoan thanh cdng tie).

-Thdi gian thudng xay ra nhat t^, (Most Likely Time), la thdi gian de hoan thinh cdng tac trong dilu kien binh thudng Nhuvly,tQ£tj^<t^

Ba loai thdi gian niy diu duoc gia thilt la tuan theo phin phdi Beta hoic phin phdi tam giic. Nlu tuin theo phan phdl Beta, thdi gian ky vong (Expected Time - tE) cua eic cdng viec dUOc xac dmh theo cdng thQc [1], [3], [7]-

ta+4t^+t^

(1) TrQdng hop ba loai thdi gian ke tren nlu duoc gil thiet II tuin theo phan phdl lam gilc thi thdi gian ky vong eiia d c edng viee dQOc xac dmh theo cdng thQc [3]:

13. Phuang phdp Udc luang theo tham so

PhQOng phap I'dc lupng theo tham sd (Parametric Estimating) xac dinh thdi gian thQc hiln cong viec dQa vao d c tham sd nhU khdi iQOng cdng viec, dinh mQc, iQc lUong tham gia thi cdng va sd ca ilm vile trong ngay Thdi gian thi cdng cung phu thudc vio each thQc thuc hien cac cdng viec Theo dd, thdi gian thuc hiln cle cdng vile duoe Qdc iQongnhQsau.

+ Ddi vdi d c cdng vile dUOc thUc hien bing thil cdng la chinh, thdi gian thuc hien phu thudc vao nang suit ngUdi lao ddng va duoe xac dmh theo cdng thQc

Qi X SMi HPLDj (ngay)

(3) + Ddi vdi d c edng vile dupc thuc hiln bing eogidi hda la chinh, thdi gian thue hien phu thudc vao nlng suat thuc t l ciia may thi cdng (hole dinh mQc hao phi miy)

NSi X Mj X Nc, HPCMj M i X N , Trong dd:

-(ngay)

Q,. la khdi luong cdng vile i d n thyc hiln;

DM^, la dinh mQc hao phi thdi gian khi

thuc hien mdt don vi khdi lupng edng viec i;

NS: la nang suat thuc t l cua miy tham gia thuc hien edng vile i;

HPID: la tdng sd ngay cong can thilt de thuc hien edng viec i;

N^ la tdng sd cdng nhin tham gia thuc hiln cdng viee i;

M;Ja tdng s6 may tham gia thuc hien cong viec i,

N^^ II sd ca lam viec trong ngiy Vile bd tri td ddi cdng nhan hole sd may tham gia thuc hiln d c cdng viec phli dua trin dilu kiln nlng lUe cita don vi thi edng, eo cau cua cdng viec (thanh phin cong vile) vl sQc chQa ciia mat bang thi edng nham dim blo tinh khoa hoc, khi thi ciia bin ke hoach tien ddthicdng[2],[4],[5].

Theo phuong phip nay, thdi gian thUc hien edng vile cd the duoe xac dmh i tuong ddi ehinh xae va thdi gian hoan thanh chi chlnh lich rat it so vdi gia j tn da du tinh neu don vi thi cdng xic dinh chinh xie khoi lUong cdng vile can thue hi|n v l cd dii dmh mQc thi cdng Thdi gian dQOc Udc luong theo phuong phip nay la thdi gian thuc t l duoc yeu d u de hoin thanh cdng vile ml khdng bao gdm khoin dQ trQ cho bat ky trQdng hop ngau nhiln nio Tuy nhien, trong nhilu trudng hop khi xly ra d c su cd do d c nguyin nhan ngau

• nhien dan tdi thdi gian thue hiln tQng cdng viec va thdi gian thQc hien tiln dp thQc te se thay ddi so vdi dQ kiln Chinh vi vay khi sQdung phuong phip nay d l Qdc iQpng thdi gian thQc hien d c cdng vile la can thiet phli tinh din thdi gian dy trQ cho d c cdng viec hole cho ei kl hoach tien dd

14. Phuongphdp Udc tuang tuang tu PhQong phip Qdc iQong tUOng tQ [Analogous Estimating) sQ dung thdi gian thQc t l cda d e cdng vile tQOng tQ da thyc hien d l Udc luong thdi gian thuc hiln eiia cle edng vile se dien ra trong tQOng lai [3].

[1HEORET1CALSTU0V) HGO^CSULia^X I

PhQOng phap niy thich hop ap dung cho cac cdng viec ed tinh chat don gian hoac trong trudng hap cic thong tin chi tilt ve cdng vile khong day dii Phuong phap udc lupng tuong tQ duoc xem nhu II mdt dang cQa phuong phap chuyen gia, tQc la ngudi cd kinh nghiem se dQa tren cac sd lilu tQ cdng viec tQong tQ da thyc hiln, ddi chieu vdi d c dieu kiln cu the ciia cdng viec dang xet de quyet dinh thdi gian thuc hiln cdng vile dd. Nhu vay, dp tin eay cua phuong phap nay phu thudc nhilu vao chat lupng ciia sd lilu lich sQ cung nhu trinh do ehuyin mdn ciia de chuyin gia

1.5. Phuang phdp md phdng Phuong phip md phong Udc luong thdi gian dUa trin cO sd gia dinh rang cle sd lieu rdi rac tuan theo quy luat phin phdl xic suit, sau do sQ dung cle cdng cu md phdng, thdng dung nhat la md phdng Ivlonte Carlo de Udc luong thdi gian thue hien cic cdng viec [3]

Phuang phip nay thich hop dung d l xic dinh d c khoan thdi gian du phdng cho cdng vile do cie yeu td ngau nhien nhu thdi tiet, miy mdc thilt bi hdng ddt xuit, cdng nhin dm dau . . gay ra, Ngoai nhQng phQong phap nlu trin cdn cd rit nhilu phuong phip cd the van dung de Qdc lupng thdi gian thuc hiln cic cong vile, ching han nhu phuang phip Delphi...

2. CAC PHUONG P H A P X A C DINH T H O I GIAN THirC mEN CONG v i £ c D u q c A P D U N G TRONG THUC TE T^I VI^T HAM iVldt nhdm nghien eUu da tien hanh mot cudc dilu tra v l each thUc thdng thudng lip tien dp thi cdng ciia 82 gdi thiu d Viet Nam, trong dd cd 60 gdi thau thi cdng edng trinh dan dung, 16 goi thau thi cdng cdng trinh ha tang ky thuat, 05 gdi thau thi cong cong trinh giao thdng va 01 gdi thau thi cdng cdng trinh thiiy loi Cic gdi thau nay duoc lUa chon ngau nhiln trin pham vi toan qude nhung tap trung chii yiu tai HI Ndi,Thanh phd Hd ChilVlinh, Can Tho, Phu Yen vl d c tinh khac d khu vuc mien Tay Nam Bd va Nam Trung 6d Nhdm nghien cdii d l gOi phieu khio sat thdng qua dudng tho diln tQ cho cac ci nhan tham gia trQc tiep vao qui trinh lip, quln ly thuc hiln tien do thi edng hoac d n bd quan ly dQ In ciia chu dau tQ tryc tilp tham gia vao d c gdi thau neu trin.

Ket qua cudc dieu tra cho thay - Cd 32 tren tdng sd 82 gdi thau (39%) sQ dung phQong phip Udc tuong theo tham sd dQa tren khdi iQong cong viee, dieu kiln cu t h i cua gdi thau, nang lUc ciia don VI thi cdng vl dmh mQc hao phi thdi gian. Trong sd dd, cd 04 gdi thau ndi rd sQ dung dmh mQc do Nha nudc cdng bd, sd edn lai khdng neu rd la ein cQ dinh mUe Nhi nudc hay noi bd nha thau. Do hiln nay, bd dinh mQc ml Nha nQde cdng bd la dmh mQc dQ toln nen vile sU dung nd nhim muc dich td chQc thi cdng la khong phin

Inh dung thQc t l khach quan nin dan tdi ban ke hoach tien do thi cdng khdng dam blo tinh khoa hoc va khi thi - Cd 07 (8,5%) gdi thau Qdc luong thdi gian thuc hiln cle cdng viec bang each phan bd ngQOc tQthdi gian thQc hiln gdi thiu dQoc rang bude trong hpp ddng cho cle cdng vile dua trin CO sd ddi ehilu vdi kha nlng cung d p ngudn lyc cho gdi thau va dieu kiln eu the ciia gdi thiu De Ilm duoe dieu nay can thiet sQ dyng din kmh nghiim cua ngudl lap. Nhu viy, day cd the xem II mpt dang ciia phuong phap chuyin gia. Tinh chinh xic cua kit qui !ude iQong phu thudc vio trinh dp chuyin mdn vl kmh nghiem ciia ngUdi trQc tiep thQc hiln,

-43 goi thau cdn lai (52,5%) sQdung kit hop d c phuong phap phan bd ngupc tQ thdi gian yiu eau, phQong phip chuyin gia, phQOng phip Qdc iQong tQOng tu vl phUOng phap Udc iuang theo tham sd de xae dmh thdi gian thUe hiln d c cdng vile Trong dd, cd thim 04 gdi thau sQ dung dinh mQc nhi nude khi udc iQong theo tham sd, dan tdi ket qui khdng dim blo tinh chinh xic Khdng cd gdi thau nao trong tdng sd 82 gdi thau sQ dung phQong phap udc iQong ba diem (Qdc luong xic suit) khi xic dmh thdi gian thQc hiln d c cdng vile, Dieu nay cd the dQoc ly giai tQ thQc te hien tai d Vilt Nam chua ed don vi nio thdng kl cic sd lieu Ijch sQ cd lien quan den ba dilm thdi gian ml phuong phip sQ dyng khi Udc luong thdi gian thuc hien cdng vile hole do ddi ngu true tiep lip tien dp khdng biet

c m i Lt UllM (THEORETICAL STUDY)

den phuong phip nay.

- E)a so d c gdi thau d Viet Nam hiln nay khi xie dinh thdi gian thuc hien de edng vric deu khdng tinh din khoin du phdng do yiu td thdi tiet hole do d c nguyin nhan rui ro khic Cu the, cd tdi 65 trin tdng sd 82 gdi thau (79.3%) da khdng tinh din thdi gian du phdng cho yiu td thdi tilt; d c gdi thiu edn lai cd tinh dua trin kinh nghiim ciia ngudi lip tlln dp nhQng khdng cd mdt phQong phap tinh cy the, du CO sd khoa hpc Chi cd 12 trin tdng sd 82 goi thau (khoing 14,6%) cd tinh den dQ phong thdi gian cho d c yiu td khic CIc rui ro ducK xit den chd yeu theo cac nguyin nhin nhQ khdng huy ddng dupc nhin cdng thuc hien cic cdng vile bdi vi nlu roi vio thoi diem dien ra le hdi tai de dia phuong, miia mang,... thi cdng nhan se v l qui d l tham dU; cung d p hd so thiet kl khdng dung tien dd hole phli dieu chlnh thilt kl; khio sat thilt ke khdng ky... CIc khoin thdi gian nay eung duoc xie dinh dya vio kmh nghiim, khdng sQdung phuong phap md phdng vl chi xet din nhQng cdng vi|c hay chiu tic ddng cua riii ro.

Thdi gian du phdng thudng dUOc cdng thim vIo thdi gian thue hiln edng vile Cd the ndi, kit qui nghien cQu eho thiy vile Udc iQong thdi gian thyc hiln cle cdng viec trong l|p tiln dd thi cdng hiln nay d Viet Nam cdn tdn tai nhieu van de, la phan Idn de nguyen nhin dan tdi tinh trang chim tien dp 6 da so d c du In hien nay tai Vi|t Nam. Ciing vi ly do lip tlln dd khdng khoa hpc.

khdng khi thi, khdng phu hop vdi dieu kiln thuc t l ml dan tdi vi|c chi dao, dilu dd sin xuat trin cdng trudng gip rat nhilu khd khan, thim ehi khdng the sQ dung ke hoach tdng tien dd da lap ml phii dua vio kmh nghiim ciia chi huy tn/dng edng trudng. De khic phuc nhQng ban che dd, cd i h l Ip dung mdt so gill phap sau.

- Qc don VI thi cdng d n phli xiy dQng dinh miJc ndi bd dim blo tinh chinh xac tinh thyc tien de Ilm d n cQ Qdc iQong thdi gian thoc hiln d c cdng viec nhim dim bao tinh khoa hoc khi thi va chinh xac cua kit qua, - Ddi vdi cic du In Ion, cd tinh phQc tap

tien do thi cdng nin lip theo phuong phap so do mang (PERT) vdi viec sQ dung phQOng phap Qdc lupng ba diem (phuong phap xic suit) de Udc lupng thdi gian thuc hiln eae cdng vile. Do vay can thilt tdng hop cac sd lieu lieh sis, tdng hap y kien ciia cie ehuyin gia ve ba diem thdi gian ma phuong phip nay xit den nham tao tiln de eho vi|c sir dung phuong phip nay vio thuc tien tai Viet Nam;

- De dim blo tinh khach quan khi van dung y kiln chuyin gia, cd the Qng dyng phuang phip Delphi nhim tranh hiln tuong d e chuyin gia chju sQ ehi phdi bdi y kien cua nhau;

- Can thiet phii tinh toln thdi gian du phdng cho yiu to thdi tilt v l d c yeu td nJi ro khic bdi d c yeu td nay cung II mdt trong nhQng nguyen nhan giy ra cham tiln dd neu phat smh trong qua trinh thi cdng, Nham dim blo tinh khoa hpcva tinh ehinh xac cQa kit qua Udc luong, nin dua trin cic so lilu lich sQ va sQ dyng phuong phip md phdng d l udc luong d c khoin thdi gian nay;

- Vl Ilu dli d c doanh nghiip xay dung can xiy dung xiy dyng Co sd dQ lilu phuc vu cho vi|c lip kl hoach tiln dp d l tao tiln de va dam bio do tin ciy cho viec ip dyng cac phuong phip udc luong d l nlu;

- De dim bio tinh khoa hpc khi thi ciia bin ke hoach tiln dd thi cdng can chuyin nghiep hoa vile lip tiln dd bing each dao tao chuyen sau cho dpi ngu nhin lyc phyc vu cdng vile nay v l cle khia canh cd lien quan den vile Udc lupng thdi gian thue hiln cdng vile va cle ndi dung khic khi lip tien do thi edng xly dyng,

- Nha nude nen cd nhQng quy djnh, hQdng dan cu the ve van d l bd tri d c khoin thdi gian du phdng cho tiln dd thi edng.

3 . K ^ L U A N

Nghiin eOu tdng quan d c van de ve vile Qdc iQong thdi gian thQc hien d e cdng vile trong boat dpng lap tiln do thi cdng trong nganh xly dQng d Vilt Nam cho thay d c don vi thi cdng cdn gap nhieu van d l trong qua trinh thuc

hiln. Udc luong thdi gian thyc hien d c cdng vile khdng dim blo tinh khoa hpc, kha Ihi dan tdi ban k l hoaeh tien dd thi cdng duoc lip ra khd ed the sQ dyng de dieu hanh va chi dao thi cdng ngoai hiln trQdng, vl dd la mpt trong sd d e nguyin nhan din tdi tinh trang chim tlln dp. Bli blo da he thdng hda d c phQong phap Qdc iQOng this gian thQC hiln d e cdng vile ehi ra dQoc thyc trang vl d e tdn tai trong vile Qdc luong thdi gian thue hiln eic cdng vile khi l|p tlln dp thi edng hien nay tai Viet Nam v l dua ra mot sd gili phip khic phuc cac tdn tai nay Cic kit qui ciia bli bao cd the coi II tiln de de thuc hien cac nghien cQu sau hon v l van dl quln ly thdi gian thyc hiln du in diu tu xay dung, vdn II vai de rat ndng, ndi cdm hien nay trong ihuc te nglnh xiy dyng Viet Nam.*

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Thdnh phd Hd Chi Minh.

[2] Bd Xdy dung (2003), Gido trinh T6 chdc thi cdng xdy dt/ng, Nhd xudt bdn Xdy dUng. Hd Ndi.

[3] PMBOK (2012), A Guide to the Project Management Body of Knowledge, 5th ed.. Project Management Institute.

[4J Li Hdng Thdi (2007). To chdc thi cdng xdy dung, Nhd xudt bdn Xdy ddng, HdNdL

[5] Nguyen Huy Thanh (2010). To chdc xdy dung cong trinh • Tdp 1, Nhd xudt bdn Xdy dUng, Hd Ngi.

[6] Tdng hgi xdy dUng Viit Nam (2011), Ihdng cdo bdo chi gidi thiiu Hdi thdo: Thdi gian thuc hiin dudn ddu tUxdydung d Wet Nam - Thuc trgng vd gidiphd/f.

[7} TU Quang PhUOng, chd biin (2005), Gido trinh Qudn 1^ dUdn ddu tu, Nhd xudt bdn Lao dpng - xdhdi,HdN6L