A methodology for prioritizing water mains rehabilitation in Egypt

Peer review under responsibility of Housing and Building National Research Center.

Figures & data

Fig. 1 Overall research methodology.

Fig. 2 Steps of water mains rehabilitation priority index model development.

Table 6 Factors weights and grading scale (score).

ID	Factor	Factor weight (Wj) by Simos	Factor’s grade scales (Scores) (Cij) identified by experts
			1	2	3	4	5
F1	Pipe age	0.05	<20	20–30	30–40	40–50	>50
F2	Pipe material type	0.05	PVC	Steel	Ductile iron	Cast iron	Asbestos
F3	Pipe diameter (mm)	0.09	>300	300	200	150	⩽100
F4	Pipe lining and coating condition	0.18	Excellent	Very good	Good lined	Fair lined	Unlined
F5	Pipe wall thickness(mm)	0.13	>30 mm	30 mm	20 mm	15 mm	⩽10 mm
F6	Type of joints	0.08	Excellent	Very good	Good	Fair	Poor
F7	Thrust restraint	0.02	Excellent	Very good	Good	Fair	Poor
F8	Pipe installation practice	0.065	Excellent	Very good	Good	Fair	Poor
F9	Pipe manufacturing	0.1	Excellent	Very good	Good	Fair	Poor
F10	Soil type	0.09	Sand	Silty sand	Silt	Silty clay	Clay
F11	Trench backfill corrosivity (PH)	0.11	7.5–8	6–7	5–6	4–5	<4
F12	Ground water aggressiveness (PH)	0.06	7.5–8	6–7	5–6	4–5	<4
F13	Stray electrical current	0.04	Not found	Very low	Low	High	Very high
F14	Pipe location from the surface (meter)	0.04	1–1.2	1.2–1.5	1.5–1.8	1.8–2	>2
F15	Pipe bedding condition	0.02	Excellent	Very good	Good	Fair	Poor
F16	Water quality aggressiveness (PH)	0.05	7.5–8	6–7	5–6	4–5	<4
F17	Leakage	0.05	Very low	Low	High	Very high	Excessive
F18	Internal pressure	0.05	>15 m	12–15	9–12	6–9	<6
F19	Operational and maintenance practice	0.02	Excellent	Very good	Good	Fair	Poor
F20	Flow velocity	0.0221	No lining damage	Small lining damage	Large lining damage	Very large lining damage	Most lining damage

Table 7 Calculation of the pipe priority index for a water main sample.

Factors contributing to the water main rehabilitation priority index (PI)	Data collected from municipality’s records	Factor weight calculated by Simos (Wj)	Factor’s grade scale assigned by experts (Cij)	Factor’s adjusted value = Wj * Cij
Pipe age	22	0.05	2	0.1
Pipe material type	CI	0.05	4	0.2
Pipe diameter (mm)	200	0.09	3	0.27
Pipe lining and coating condition.	No lining	0.18	5	0.9
Pipe wall thickness (mm)	20	0.13	3	0.39
Type of joints	Silty clay	0.09	4	0.36
Thrust restraint	7	0.11	2	0.22
Pipe installation practice	7.5	0.06	2	0.12
Pipe manufacturing	Not found	0.04	1	0.04
Soil type	1.2	0.04	1	0.04
Trench backfill corrosivity (PH)	Good	0.02	3	0.06
Ground water aggressiveness (PH)	7.5	0.05	1	0.05
Stray electrical current	30	0.05	5	0.25
Pipe location from the surface (meter)	15	0.05	2	0.1
Pipe bedding condition	Good	0.02	3	0.06
Water quality aggressiveness (PH)	7.5	0.034	1	0.034
Leakage	High	0.0561	3	0.1683
Internal pressure	12	0.0459	2	0.0918
Operational and maintenance practice	Good	0.0119	3	0.0357
Flow velocity	Small	0.0221	2	0.0442
Priority index (PI) = ∑ Wj * Cij				3.534

Fig. 3 Final list of the priority index factors.

Table 1 Preliminary list of the condition factors for water mains [1].

Cluster	Factors	Description
Physical factors	1) Pipe material	Pipes have different materials and fail in different ways
	2) Pipe wall thickness	Corrosion penetrates the thinner pipe quickly
	3) Pipe age	Pipes deteriorate over time
	4) Pipe vintage	Pipe made at a particular time and place may be more vulnerable to failure
	5) Pipe diameter	Small diameter pipes are more susceptible to beam failure
	6) Type of joints	Some types of joints have experienced premature failure (e.g., leadite joints)
	7) Thrust restraint	Inadequate restraint can increase longitudinal stresses
	8) Pipe lining and coating	Lined pipes are less susceptible to corrosion
	9) Dissimilar metals	Dissimilar metals are susceptible to galvanic corrosion
	10) Pipe installation	Poor installation practice can damage pipes
	11) Pipe manufacture	Defects in the pipe wall produce errors and failures
Environmental factors	12) Pipe bedding	Poor pipe bedding causes soil movement and pipe failure
	13) Trench backfill	Determination of soil corrosivity around pipes
	14) Soil type	Determination of soil drainage characteristics
	15) Ground water	Determination of the aggressiveness of ground water
	16) Climate	Climate influences soil moisture
	17) Pipe location	Determination of the migration of road salt
	18) Disturbance	Leading to damage
	19) Stray electrical current	Causes electrolytic corrosion
	20) Seismic activities	Earthquake activities.
Operational factors	21) Internal water pressure	High internal pressure causes deteriorated pipe to fail
	22) Break rate	The indicator factor of the structural condition of pipes
	23) Water quality	Aggressive water causes pipe corrosion
	24) Flow velocity	Influences unlined pipes
	25) Back flow potential	Cross connection causes backflow
	26) Operational and maintenance (O&M) practice	Poor Operational and maintenance practices (O&M) decreases pipe structural integrity and water quality

Table 2 Factor’s frequency of importance (The questionnaire’s feedback).

Cluster	Factor	Frequency
		1	2	3	4	5
Physical factors	1) Pipe material	0	0	7	9	8
	2) Pipe wall thickness	1	3	5	11	4
	3) Pipe age	0	0	8	8	8
	4) Pipe vintage	8	4	2	6	4
	5) Pipe diameter	2	5	7	5	5
	6) Type of joints	0	5	2	10	7
	7) Thrust restraint	4	3	4	3	10
	8) Pipe lining and coating	2	2	3	7	10
	9) Dissimilar metals	7	5	2	6	4
	10) Pipe installation	2	4	5	6	7
	11) Pipe manufacture	2	3	0	4	15
Environmental factors	12) Pipe bedding	0	2	4	8	10
	13) Trench backfill	0	0	7	8	9
	14) Soil type	0	0	3	7	14
	15) Ground water	3	2	7	8	4
	16) Climate	11	3	3	3	2
	17) Pipe location	1	4	9	6	4
	18) Disturbance	3	6	7	1	7
	19) Stray electrical current	0	5	6	4	9
	20) Seismic activities	14	4	3	1	2
Operational factors	21) Internal water pressure	0	0	2	12	10
	22) Leakage	2	4	4	6	8
	23) Water quality	5	5	3	8	3
	24) Flow velocity	6	2	7	6	3
	25) Back flow potential	4	6	7	3	4
	26) O&M practice	1	4	4	8	7

Fig. 5 Structural rehabilitation/replacement selection procedure.

Table 3 Second questionnaire feedback.

Factor	Relative weights
	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9	Q10	Q11	Q12	Q13	Q14	Q15	Q16	Q17	Q18	Q19	Q20	Q21	Q22	Q23	Q24
1) Pipe material	8	3	1	9	1	9	1	9	3	8	6	5	5	7	1	3	1	8	5	1	5	1	9	4
2) Pipe wall thickness loss	2	1	3	1	3	5	5	6	2	3	5	4	4	8	2	2	2	1	4	6	4	2	4	3
3) Pipe age	9	7	2	7	5	6	6	5	4	4	7	3	3	9	3	1	3	9	3	2	3	3	5	2
4) Pipe diameter	7	5	7	8	5	8	3	1	5	5	4	2	2	6	4	5	4	7	7	7	6	4	8	1
5) Type of joints	6	6	8	9	6	7	7	2	6	6	3	1	1	5	5	4	5	6	2	8	7	5	7	5
6) Thrust restraint defects	1	2	6	6	1	1	2	3	1	7	2	6	6	4	6	6	6	2	1	3	9	6	3	6
7) Pipe lining and coating	4	8	9	5	8	4	4	4	8	2	8	7	7	3	7	7	8	5	8	9	8	7	6	7
8) Pipe installation defects	3	4	4	4	10	2	8	7	7	1	1	8	8	1	8	8	7	3	6	4	2	8	1	8
9) Pipe manufacture defects	5	9	5	3	7	3	9	8	9	9	9	9	9	2	9	9	9	4	9	5	1	9	2	9
1) Pipe bedding defects	3	3	4	3	6	1	2	1	3	2	3	3	3	4	6	4	3	3	4	4	3	6	3	3
2) Trench backfill corrosivity	6	4	6	4	5	4	3	2	4	4	4	4	4	5	5	5	4	4	3	6	4	5	4	2
3) Soil type of expansive	5	6	3	5	4	3	6	4	5	3	5	5	5	6	4	6	5	5	5	3	5	4	2	1
4) Ground water aggressivity	1	5	2	1	3	2	5	3	2	1	2	2	2	3	3	1	2	6	6	2	6	3	1	4
5) Pipe location due to salt immigration	4	1	5	2	2	5	1	6	1	5	1	1	1	2	2	3	1	2	2	5	2	2	5	5
6) Stray electrical current	2	2	1	6	1	6	4	5	6	6	6	6	6	1	1	2	6	1	1	1	1	1	6	6
1) Internal water pressure	1	5	4	4	5	1	3	2	4	5	5	5	4	5	1	5	4	1	5	4	4	5	1	1
2) Leakage	5	3	3	5	5	4	2	1	5	4	4	4	5	2	2	4	5	4	2	3	5	4	4	2
3) Water quality aggressivity	2	4	2	3	4	5	4	5	3	3	2	1	1	1	3	3	3	5	4	2	3	3	5	3
4) Flow velocity	3	1	5	2	3	3	5	3	2	2	3	2	2	3	4	1	2	2	3	5	2	1	2	4
5) O&M practice defects	4	2	1	1	2	2	1	4	1	1	1	3	3	4	5	2	1	3	1	1	1	2	3	5
1) Physical	3	3	3	3	1	2	3	1	3	3	3	2	2	3	2	1	3	3	3	3	3	1	2	1
2) Environmental	2	2	2	2	2	3	2	2	2	2	2	2	2	1	3	3	2	2	2	2	2	2	3	2
3) Operational	1	2	1	3	2	1	1	3	1	1	1	3	3	2	1	2	1	1	2	1	3	2	1	3
	Average of factor’s frequency	Simos’ Rank
1) Pipe material	4.708	4
2) Pipe wall thickness loss	3.416	1
3) Pipe age	4.625	3
4) Pipe diameter	5.041	5
5) Type of joints	5.291	7
6) Thrust restraint defects	4	2
7) Pipe lining and coating	6.375	8
8) Pipe installation defects	5.125	6
9) Pipe manufacture defects	6.75	9
1) Pipe bedding defects	3.333	3
2) Trench backfill corrosivity	4.208	5
3) Soil type of expansive	4.375	6
4) Ground water aggressivity	2.83	2
5) Pipe location due to salt immigration	2.75	1
6) Stray electrical current	3.5	4
1) Internal water pressure	3.5	4
2) Leakage	3.625	5
3) Water quality aggressivity	3.083	3
4) Flow velocity	2.708	2
5) O&M practice defects	2.25	1
1) Physical	2.375	3
2) Environmental	2.125	2
3) Operational	1.75	1

Table 4 Factor’s relative weight calculations.

Factor	Number of factors	Positions Simos’ Rank	Non normalized weight	Normalized weight	Normalized weight * 100	Normalized weight
1) Pipe material	1	4	4	0.089	8.9	9
2) Pipe wall thickness loss	1	1	1	0.022	2.2	2
3) Pipe age	1	3	3	0.067	6.7	7
4) Pipe diameter	1	5	5	0.111	11.1	11
5) Type of joints	1	7	7	0.156	15.6	16
6) Thrust restraint defects	1	2	2	0.044	4.4	4
7) Pipe lining and coating	1	8	8	0.177	17.7	18
8) Pipe installation defects	1	6	6	0.133	13.3	13
9) Pipe manufacture defects	1	9	9	0.2	20	20
Sum	9		45		100	100
1) Pipe bedding defects	1	3	3	0.142	14.2	14
2) Trench backfill corrosivity	1	5	5	0.238	23.8	24
3) Soil type of expansive	1	6	6	0.285	28.5	29
4) Ground water aggressivity	1	2	2	0.095	9.5	10
5) Pipe location due to salt immigration	1	1	1	0.047	4.7	5
6) Stray electrical current	1	4	4	0.190	19.0	19
Sum	6		21		100	101
1) Internal water pressure	1	4	4	0.266	26.6	27
2) Leakage	1	5	5	0.333	33.3	33
3) Water quality aggressivity.	1	3	3	0.2	20	20
4) Flow velocity	1	2	2	0.133	13.3	13
5) O&M practice defects	1	1	1	0.066	6.6	7
Sum	5		15		100	100
1) Physical	1	3	3	0.5	50	50
2) Environmental	1	2	2	0.333	33.3	33
3) Operational	1	1	1	0.166	16.6	17
Sum	3		6		100	100

Table 5 Factor’s global weight calculations.

Factor	Normalized weights	Cluster weights	Global weights = normalized weight * cluster weight
1) Pipe material	9	50	0.045
2) Pipe wall thickness loss	2	50	0.01
3) Pipe age	7	50	0.035
4) Pipe diameter	11	50	0.055
5) Type of joints	16	50	0.08
6) Thrust restraint defects	4	50	0.02
7) Pipe lining and coating	18	50	0.09
8) Pipe installation defects	13	50	0.065
9) Pipe manufacture defects	20	50	0.1
10) Pipe bedding defects	14	33	0.0462
11) Trench backfill corrosivity	24	33	0.0792
12) Soil type of expansive	29	33	0.0957
13) Ground water aggressivity	10	33	0.033
14) Pipe location due to salt immigration	5	33	0.0165
15) Stray electrical current	19	33	0.0627
16) Internal water pressure	27	17	0.0459
17) Leakage	33	17	0.0561
18) Water quality aggressivity	20	17	0.034
19) Flow velocity	13	17	0.0221
20) O&M practice defects	7	17	0.0119

Fig. 4 The PI-GIS integration.

Fig. 6 Rehabilitation technology selection system interface.

Table 8 Technology selection factors.

Cluster	Factor
Technical factors	1) Structural capacity 2) Hydraulic capacity
Contractual factors	1) Duration of technology 2) Local availability of technology (locality) 3) Number of years in business
Cost factors	1) Technology total capital cost 2) Operational and maintenance cost (O&M)

Table 9 Questionnaire feedback.

Factor	Relative weighting																				Average	Simos’ Rank
	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9	Q10	Q11	Q12	Q13	Q14	Q15	Q16	Q17	Q18	Q19	Q20
Structural capacity	1	2	2	3	1	1	2	2	1	1	1	1	1	1	1	1	2	1	1	1	1.35	1
Hydraulic capacity	2	4	3	3	4	2	2	1	2	2	2	2	2	2	2	2	2	2	2	2	2.25	2
Duration of technology	2	3	2	3	3	2	3	2	2	3	3	3	1	2	3	1	3	3	2	3	2.45	3
Local availability of technology (locality)	1	2	3	1	2	1	3	3	3	3	2	2	2	1	2	2	1	1	1	2	1.9	1
Number of years in business	3	2	1	2	2	3	3	2	2	3	3	2	3	3	1	3	2	2	3	1	2.3	2
Technology total capital cost	1	2	2	2	2	1	2	2	2	2	2	2	2	1	1	2	2	2	1	2	1.75	2
Maintenance and operational cost (O&M)	2	1	1	1	2	2	1	1	1	1	1	2	1	2	2	1	1	2	2	1	1.4	1
Technical factors	2	3	1	2	1	1	3	1	1	3	2	1	2	2	3	1	2	1	1	1	1.7	1
Contractual factors	3	2	3	2	2	3	2	2	2	2	3	2	1	3	2	3	2	2	3	2	2.3	3
Cost factors	1	1	2	3	2	2	1	3	3	2	1	3	1	1	2	2	3	2	2	3	2	2

Table 10 Relative weight calculations.

Factor	Number of factors	Positions (Simos’ Rank)	Non normalized weight	Normalized weight
1) Structural capacity	1	1	1	(1/3) = 0.33
2) Hydraulic capacity	1	2	2	(2/3) = 0.67
Sum	2	3		1
1) Duration of technology	1	3	3	(3/6) = 0.5
2) Local availability of technology(locality)	1	1	1	(1/6) = 0.17
3) Number of years in business	1	2	2	(2/6) = 0.33
Sum	3	6		1
1) Technology total capital cost	1	2	2	(2/3) = 0.67
2) Maintenance and operational cost (O&M)	1	1	1	(1/3) = 0.33
Sum	2	3		1
1) Technical factors	1	1	1	(1/6) = 0.17
2) Contractual factors.	1	3	3	(3/6) = 0.5
3) Cost factors	1	2	2	(2/6) = 0.33
Sum	3	6		1

Table 11 Global weight calculation.

Factor	Normalized weight	Cluster	Global weight
F1) Structural capacity	0.33	0.17	0.0561
F2) Hydraulic capacity	0.67	0.17	0.1139
F3) Duration of technology	0.5	0.5	0.25
F4) Local availability of technology(locality)	0.17	0.5	0.085
F5) Number of years in business	0.33	0.5	0.165
F6) Technology total capital cost	0.67	0.33	0.2211
F7) Maintenance and operational cost (O&M)	0.33	0.33	0.1089
Sum			1

Table 12 Factors’ grade scales (score).

No.	Factors	Factor weight (Wj)	Factor’s grade	Current practice factor’s grade scale (score-Sij)
F1	Structural capacity	0.0561	Full-structural Semi-structural Non-structural	10 6 1
F2	Hydraulic capacity	0.139	Adequate capacity In adequate capacity	10 1
F3	Technology’s duration	0.25	High Medium Low	1 6 10
F4	Local availability	0.085	Available Not available	10 1
F5	Number of years in business	0.165	Low Medium High	1 8 10
F6	Operational and maintenance (O&M) cost	0.1089	High Medium Low	1 5 10
F7	Technology’s total cost	0.2211	High Medium Low	1 6 10

Table 13 Rehabilitation technology alternatives evaluation.

Alternative	Type	F1	F2	F3	F4	F5	F6	F7	TS = ∑ Wj * Sij
Open cut technology	Wj	0.0561	0.139	0.25	0.085	0.165	0.1089	0.2211	6.5721
	Sij	10	10	1	10	10	5	6
Sliplinning technology	Wj	0.0561	0.139	0.25	0.085	0.165	0.1089	0.2211	8.8215
	Sij	10	10	10	10	10	5	6
Pipe bursting pipe	Wj	0.0561	0.139	0.25	0.085	0.165	0.1089	0.2211	4.8162
	Sij	1	1	1	10	10	5	6
Cured in place pipe	Wj	0.0561	0.139	0.25	0.085	0.165	0.1089	0.2211	8.5265
	Sij	10	10	10	0	8	5	10