A QUANTITATIVE APPROACH TO CONSTRUCTION POLLUTION CONTROL BASED ON RESOURCE LEVELING

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1 A QUANTITATIVE AOACH TO CONSTUCTION OLLUTION CONTOL BASED ON ESOUCE LEVELING Heng L 1, Zhen Chen 2, Conrad T C Wong 3 and eter E D Love 4 ABSTACT: A quanttatve approach for constructon polluton control that s based on constructon resource levelng s presented. The parameters of constructon polluton ndex (CI), hazard magntude ( h ) are treated as a pseudo resource and ntegrated wth a proect s constructon schedule. When the level of polluton for ste operatons exceeds the permssble lmt dentfed by a regulatory body, a Genetc Algorthm (GA) enhanced levelng technque s used to re-schedule proect actvtes so that the level of polluton can be re-dstrbuted and thus reduced. The GA enhanced resource levelng technque s demonstrated usng 20 on-ste constructon actvtes n a proect. Expermental results ndcate that proposed GA enhanced resource levelng method performs better than the tradtonal resource levelng method used n MS roect. The proposed method s an effectve tool that can be used by proect managers to reduce the level of polluton at a partcular perod of tme; when other control methods fal. INTODUCTION olluton and hazards generated from constructon stes nclude nose, sold and lqud wastes, dust, and harmful gases. In many cases, especally f the constructon stes are n the densely polluted areas, the level of polluton emsson can not exceed a lmt specfed. For example, the Nose olluton rotecton Act n Chna (NA 1993) specfes that the level of nose cannot exceed 75 db (A), above whch ste operatons wll be stopped by legal actons. In a constructon ste, the level of polluton emsson from ndvdual operatons may not exceed the legal lmts specfed under the regulatons however the aggregated level of polluton from multple sources may exceed the lmt. To prevent ths and ensure that the level of polluton emsson wll not exceed the legal lmts durng the duraton of a constructon proect, ths paper descrbes a two-step quanttatve method that can be used to control constructon polluton. Frst, the method can predct the dstrbuton of polluton emsson levels throughout a proect s duraton. Second, f t detects that the level of 1 Assocate rofessor, Department of Buldng and eal Estate, The Hong Kong olytechnc Unversty, Hong Kong. 2 Doctoral Canddate, Department of Buldng and eal Estate, The Hong Kong olytechnc Unversty, Hong Kong. 3 Managng Drector, Yau Lee Constructon Co Ltd, 10/F Tower 1, Enterprse Square, 9 Sheung Yuet oad, Kowloon Bay, Kowloon, Hong Kong 4 Assocate rofessor, School of Archtecture and Buldng, Deakn Unversty, Waterfront Campus, Geelong, Australa 1

2 polluton exceeds the lmt at a certan pont of tme, then on ste actvtes are re-scheduled so that the level of polluton can be re-dstrbuted. Ths paper presents a quanttatve approach for constructon polluton control based on resource levelng. Our expermental results ndcate that the use of constructon polluton ndex (CI) and ts nterrelated hazard magntude ( h ), as knd of pseudo resources, and ts ntegraton wth a proect s constructon schedulng can practcally combne constructon polluton control wth schedulng. The quanttatve approach can ensure that the level of constructon polluton s wthn the a legal range throughout the entre proect duraton. The lmtaton of the quanttatve approach presented here s that t has not been endowed wth a capablty towards adustng polluton level of a constructon procedure when the polluton level s hard to be relayed down. CONSTUCTION OLLUTION MEASUEMENT olluton Control n Constructon roects The polluton control n constructon proects s defned here as the control of all human actvtes that have an ether sgnfcant or small negatve mpact on the envronment durng the whole constructon process (Grffth, et al. 2000). Constructon polluton has receved much attenton n the ndustry over the past 30 years. At the same tme, there have been many studes related to polluton control n constructon. For example, a study on nose polluton, ar polluton and sold waste polluton from constructon stes was conducted n early 1970s (U.S. EA, 1971, Jones, 1973, Skoyles and Hussey 1974; Spvey, 1974). The concepton of envronmental management durng constructon s put forward n late 1970s, and a role of envronmental nspector s ntroduced n the desgn and constructon phases of proects. The envronmental nspector s a specalst whose academc background or experence results n consderable understandng of envronmental mpacts and applcable control measures. The envronmental nspector, a specalst wth professonal knowledge n envronmental mpacts and applcable control measures, s an advsor to constructon engneers on all matters of envronmental management on (Hennngson, 1978). There have also been some studes engaged to the quanttatve measurement and effectve control of constructon polluton, usng methods such as lfe-cycle costng; effcent energy consumpton; reducton, reuse, and recycle of constructon and demolton materal/debrs; degradaton and abatement of constructon nose and dust; and envronmental mpact assessment, etc. However, there was lttle enthusasm for establshng an envronmental management system n a commercal constructon company untl two man mportant standards, BS 7750 (1992) and ISO seres 2

3 (1996), are promulgated. As the envronmental management system s a formal structure of a constructon organzaton that mplements envronmental management (Grffth, et al. 2000), quanttatve approaches to constructon polluton control are therefore more useful and effectve n constructon proects managed by such a constructon organzaton. Constructon olluton Index A method for quantfyng constructon polluton, known as the Constructon olluton Index (CI) has been proposed by Chen et al. (2000) and has been adopted n ths paper. The CI s shown n Formula 1: CI n = CI = n = 1 = 1 h D (1) Where CI s the Constructon olluton Index of an urban constructon proect, CI s the CI of a specfc constructon operaton, h s the Hazard magntude per unt of tme generated by a specfc constructon operaton, D s the Duraton of the constructon operaton that generates polluton and/or hazard h, n s the number of constructon operatons that generate polluton and hazards. In Formula 1, parameter h s a relatve value ndcatng the magntude of hazard generated by a partcular constructon operaton n a unt of tme. Its value s lmted n the range of [0,1]. If h = 1, t means that the hazard may cause fatal damage or generate a catastrophe to people and/or propertes nearby. For example, f a constructon operaton can generate some nose and the sound level at the recevng end exceeds the threshold of pan, whch s 140 db (McMullan, 1998), then the value of h for ths partcular constructon operaton s 1. If h = 0, then t ndcates that no hazard s detectable from a constructon operaton. It s possble to dentfy values of h for all types of polluton and hazards generated by commonly used constructon operatons and methods. Informaton and data such as the emsson of nose levels, harmful gases and wastes quanttes are normally avalable n the specfcatons of relevant constructon machnery and plant, or can be convenently measured. These data can then be converted to h values by normalzng them nto the range of [0,1]. In case that there s not enough 3

4 data avalable for such converson at present, then h values have to be determned usng experence and expert opnons. Examples of h values from some constructon operatons are lsted n Table 1. Table 1. h Values of some constructon operatons Task Name h Value (per day) Demolton 0.7 Ste preparaton 0.7 Cast-n-place C le 0.5 Excavaton & support system 0.7 Foundaton baseplate 0.3 C framework 0.5 Steel framework 0.2 oof works 0.5 Water supply & sewerage works 0.1 ower supply system 0.1 Lghtng system 0.1 Ar condtonng 0.1 Computer & communcaton network 0.1 Floor fnsh & polshng 0.7 Internal wall fnsh 0.4 External wall fnsh 0.2 Internal partton wall 0.1 Celng work 0.2 Ste mprovements 0.2 Landscapng work 0.1 Fgure 1 llustrates an example of proect schedule that ncludes 20 actvtes. h values of each actvtes are ndcated at the rght sde of the bars. For example, the h value for C framework s calculated to be

5 Fgure 1: Intal schedule of a proect Fgure 2: Hstogram of h n the ntal schedule. In Fgure 2, the y-axs represents the accumulated h value and the x-axs the proect duraton. Thus, the shaded area s the total CI value. It s suggested that the maxmum permssble level of h s 0.8 at any pont of tme. It s necessary to note that the defnton of maxmum level of h value s based on the authors estmate of the average allowable polluton level. The value of maxmum h value can be adusted to reflect the level of polluton control: the lower the maxmum h value, the tghter control on polluton, and vce versa. It s necessary to note the hstogram s produced by lnearly accumulatng h values. Ths may cause naccuraces as some polluton measurements cannot be lnearly added up. For example, the nose levels. We are currently examnng the effect of nonlnearty and amng to develop a revsed method to accumulate h values so that accurate hstograms can be produced. From Fgure 2, t can be seen that durng the perod Dec to Mar of the proect duraton, the level of h values wll exceed ts maxmum value, ndcatng that durng ths perod, the 5

6 accumulated level of polluton wll exceed the lmt. Therefore, t s necessary to re-arrange the proect schedule so that the excessve level of polluton can be reduced to a level below the lmt. A SEUDO ESOUCE AOACH FO LEVELING CONSTUCTION OLLUTION esource levelng s an effectve tool for proect schedulng when there s a conflct or shortage of resources. Ths secton presents a method to combne the polluton control wth resource levelng at proect schedulng stage. h values are treated as a pseudo resource, and the maxmum h value as the lmt of the resource. Ths resource together wth other types of resources can be leveled by usng the tradtonal proect resource levelng methods (lcher, 1992). In order to test the pseudo resource approach for reducng constructon polluton level n a proect schedule, we used the Mcrosoft roect 98 as a tool for schedulng and resource levelng. The proect schedule leveled by the MS roect as well as the hstogram of h values are llustrated n Fgure 3 and 4. Fgure 3. Mcrosoft roect 98 leveled proect schedule 100% Aug 25, '96 Oct 6, '96 Nov 17, '96 Dec 29, '96 Feb 9, '97 Mar 23, '97 May 4, '97 Jun T S W S T M F T S W S T M F T S W S 80% 6

7 Fgure 4. Hstogram of h value assocated wth the schedule leveled by Mcrosoft roect 98 Expermental results from Fgure 3 and 4 ndcate that constructon polluton level spreads out under the lne of the maxmum permssble level of h (Maxmum h =0.8) when other fve resources (Table 2) are also leveled down to ther ndvdual resource lmt. So the pseudo resource approach for reducng constructon polluton level s feasble at proect schedulng stage. However, the total constructon perod s stretched 22 days, about 8 percent longer than the orgnal schedule n Fgure 1, after resource smoothng. Smlar results also occurred from our other expermental schedules whch are not presented here. It s necessary to fnd an alternatve approach to get a shorter schedule wth every resource leveled, ncludng the pseudo resource. COMBINING CONSTUCTION OLLUTION CONTOL WITH ESOUCE LEVELING USING GA esource levelng and allocaton can be performed manly by heurstc methods and analytc methods (Fard and Manoharan, 1996). In recent years, there have been several studes on applyng heurstc methods as well as analytcal methods n solvng resource-levelng problems. For example, artfcal neural networks (ANN) s used to mnmze proect duraton and cost by usng a mathematcal model based on precedence relatonshps, multple crew-strateges, and tme-cost tradeoff (Adel and Karm, 2001; Senouc and Adel, 2001), and genetc algorthms (GA) s used to search for near-optmum soluton to the problem of resource allocaton and levelng ntegrated wth tme-cost tradeoff model, resource-lmted/constraned model, and resource levelng model (Chan, 7

8 et al., 1996; Chua, et al., 1996; L and Love, 1997; Hegazy, 1999; Leu, et al., 1999; and Leu and Yang, 1999). To ntegrate varous heurstc methods nto the resource levelng, the methods used by Harrs (1978) and Hegazy (1999), whch mnmze both daly fluctuatons n resource use and the resource utlzaton perod, have been adapted. Accordng to Hegazy (1999), the moment of fluctuatons n daly resource use can be calculated as follows: n M x = = (2) and the moment for measurng the resource utlzaton perod s calculated as: n M = ( k) y = k...(3) The above two moment calculatons can be used n ether reducng resource fluctuatons, or mnmzng the duraton of resource use, or mnmzng both resource fluctuatons and duraton s. However, concurrent optmzaton of resource levelng and polluton control s a nonlnear searchng problem that s sutable for usng the Genetc Algorthm (GA) to solve. Gene Formaton In a number of commercal resource levelng software packages, the user s allowed to set prorty levels to tasks. rorty s an ndcaton of a task s mportance and avalablty for levelng (that s, resolvng resource conflcts or over allocatons by delayng or splttng certan tasks). The task prorty settng controls levelng, whch allows users to control the order n whch software systems, such as MS roect, delay tasks wth over allocated resources. Tasks wth the lowest prorty are delayed or splt frst, and tasks wth a hgher prorty are not leveled before other tasks sharng the over allocated resources. Thus, to apply the GA system to solve the multple resources levelng problem, t s essental to have a gene structure that facltates the operatons of GA. Bearng ths n mnd, the followng gene format used by Syswerda and almucc (1991), Grobler, et al. (1996), Boggess and Abdul (1997), and Hegazy (1999) has been adopted: Note: 1. s the prorty of actve, [ 0,8]. 8

9 =0, actvty prorty s hghest; =2, actvty prorty s very hgh; =4, actvty prorty s medum; =6, actvty prorty s very low; =1, actvty prorty s hgher; =3, actvty prorty s hgh; =5, actvty prorty s low; =7, actvty prorty s lower; =8, actvty prorty s lowest 2. The prorty values are n accordance wth the prorty grades of actves n Mcrosoft roect 98. Fgure 5: Gene formaton (adopted from Hegazy (1999)) In Fgure 5, a strng has genes, and each box represents a gene. The number nsde the box s the prorty settng for a partcular task labeled by the number above the box. A strng s a partcular combnaton of prorty settngs that determnes a specfc schedule. The ftness of the strng s evaluated by the followng set (Hegazy 1999), ω ( D d n / D0 ) + [ ω ( M = 1 x + M y ) /( M x0 + M y0 )]...(4) Where M s the moment of fluctuatons of daly resource use as defned n (2); M s the moment x x of fluctuatons of resource use n a specfc schedule determned by strng n day ; ntal value of M x n day ; M x 0 s the M y s the moment of resource utlzaton perod, as defned n (3); M y s the moment of resource utlzaton perod of a schedule determned by a strng n day ; M y 0 s the ntal value of M y n day ; D s the new proect duraton of schedule determned by strng, D 0 s the ntal proect duraton determned by any resource allocaton heurstc rule, ω d s the weght n mnmzng proect duraton, ω s the weght n levelng every resource n day, s the generaton number of genes, s the representatve day durng a proect's total workng-day, and n s the workng-day number of a proect's duraton. By selectng dfferent weghts, the ftness functon (4) enables the user to conduct dfferent heurstcs based resource levelng ncludng reducng resource fluctuatons, or mnmzng the duraton of resource use, or mnmzng both resource fluctuatons and duratons. EXEIMENTAL ESULTS 9

10 Ths secton presents expermental results from usng GA to combne polluton control and resource allocaton nto the task of resource levelng. The schedule used n the experment s collected from a constructon proect n Shangha n whch there are 20 actvtes for general control, and ntal schedule of the actvtes and ther assocated level of polluton emsson ( h value) are shown n Fgure 1. From the hstogram of h value, whch s llustrated n Fgure 2, t can be detected that the accumulated level of polluton emsson exceeds the permssble lmt. In ths proect, there are sx knds of constructon resources, whch represent workers, materals, machnes, nstruments, and power denoted as 1, 2, 3, 4, and 5. olluton s treated as a pseudo resource and s denoted as 6. These resources are lsted n Table 2. For the purposes of convenence n calculaton, the values of the resources are adusted so that there wll be no very large or small fgures. Table 2. esources treatment of ntal constructon schedule esource Name Mark Max unts avalable Adustment Workers Workers No. 10 Materals Materals Cost 0.01 Machnes Machnes Cost 0.01 Instruments Instruments Cost 0.01 ower ower Cost 0.01 h 6 80 CI 100 In the experment, the ntal populaton sze s set at 100. Also, to mnmze both resource fluctuatons and perod, the weghtngs n (4) are gven an equal weghtng of 1. The resultant schedule and assocated hstogram of value are llustrated n Fgure 6 and 7. 10

11 Fgure 6. GA optmzed constructon schedule Aug 25, '96 Oct 6, '96 Nov 17, '96 Dec 29, '96 Feb 9, '97 Mar 23, '97 May 4, '97 Jun T S W S T M F T S W S T M F T S W S 100% 80% 60% 40% 20% eak Unts: 70% 70% 70% 70% 50% 50% 50% 60% 80% 80% 80% 80% 80% 50% 30% 20% CI Overallocated: Allocated: Fgure 7. Hstogram of h value assocated wth the schedule leveled by GA Comparng the GA leveled schedule wth the MS roect leveled schedule, t can be seen that the prortes of resource use n the GA leveled schedule are set at dfferent values (Fgure 6); whereas 11

12 prortes n the MS roect leveled schedule (Fgure 3) do not have any changes from the orgnal schedule (Fgure 1). In addton, the duraton of the GA leveled schedule s 298 days, whch s shorter than the duraton of the schedule leveled by the MS roect (302 days). Our addtonal two experments wth dfferent number of populatons also lead to smlar results. From the experments, we can conclude that the GA system can adust the task prortes that lead to the re-dstrbuton of resources that meets the resources constrants and produces a shorter schedule. The GA system enhances the levelng functon of MS roect, as t enable the user to dentfy the optmal settngs of task prortes automatcally n resource levelng. CONCLUSIONS AND DISCUSSIONS A quanttatve approach to constructon polluton management by ntroducng parameters of constructon polluton ndex (CI) and hazard magntude h has been proposed. Usng these parameters, a method to predct the dstrbuton of accumulated polluton level generated from constructon operatons s presented. It s suggested that f the polluton level exceeds the allowable lmt, then constructon actvtes need to be re-scheduled to spread the polluton emssons. In dong so, polluton emsson s treated as a pseudo resource, and then appled to a GA based levelng technque to re-schedule the proect actvtes. The GA system allows the user to concurrently mnmze fluctuatons and perod of resource use by assgnng dfferent prortes to proect actvtes. Expermental results ndcate that GA enhanced resource levelng performs better than the tradtonal resource levelng method used n the MS roect. The authors suggest that the proposed method for controllng constructon polluton s an effectve tool that can be used by proect managers to reduce the level of polluton generated from a proect at a certan perod of tme. Ths method s useful when there s no other ways to reduce the level of polluton. However, t s necessary to pont out that the method proposed here can only redstrbute the amount of polluton over a proect duraton so that at any specfc perod of tme, the level of polluton wll not exceed the legal lmt. In order to reduce the overall amount of polluton, other methods, such as alternatve constructon technologes, new materals, have to be appled. ACKNOWLEDGEMENT The research s supported by a postgraduate studentshp provded by The Hong Kong olytechnc Unversty. 12

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