ANALYSIS OF THE WIDTH OF PROTECTION ZONE NEAR A WATER SUPPLY NETWORK

K e y w o r d s : Failure; Water network; Protection zone; Tolerance intervals. 1/2019 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 123 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 1/2019 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 9 0 1 1 M . I w a n e k , P. S u c h o r a b , Ł . S i d o r o w i c z 124 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 1/2019 water pipes failures or evaluating leakage potential [18–22]. These activities are very important in the aspect of water distribution quality and reliability, but they are not the only way to limit problems connected with pipes failures. Even the best high-tech systems do not protect against randomly-occurring failures. Thus, we propose to support the existing methods and activities by establishing a protection zone on the soil surface over a buried water network, where the outflow of water is possible after a potential failure of the pipe. Infrastructure and settlement in this zone should be carefully planned in order to exclude the possibility of diminishing stability of objects as well as to limit the social, economic and environmental costs in the case of leakage from a water pipe. The presented investigations include the laboratory tests of a buried water pipe breakage for different cases of leak areas and values of hydraulic pressure head in the pipe and analysis of a distance between the place of water outflow on the soil surface and the location of the water failure, in the aspect of protection zone determination. 2. MATERIALS AND METHODS The first part of investigations involved physical simulations of a water pipe breakage, conducted in a laboratory on the setup reflecting the actual conditions scaled 1:10. The main part of the setup was an intentionally damaged water pipe buried in sand, supplied with water from a container located on the assumed height. The tests were conducted for four different values of leak areas (4.71, 9.42, 15.07 and 18.84 cm2) and hydraulic pressure head in a pipe varied in the range from 3.0 to 6.0 m H2O, each 0.5 m. Detailed descriptions of the laboratory setup and realisation of the tests are given in the papers [2, 23 ,24]. The statistical analysis, including the normality evaluation of measurements results obtained during physical simulations of a water pipe breakage in a laboratory, is presented in the article [25]. The subject of investigations in the range of the presented paper is a horizontal distance (y) between a leaking pipe and a location of water outflow on the soil surface (called “suffosion hole” in this paper) in the aspect of a protection zone determination. The analysis was based on tolerance intervals calculations with two assumptions. At first, it was assumed that the occurrence of water on the soil surface right above a leak is always possible and this assumption imposed the value of the lower tolerance limit as equal to 0 for all calculation cases. The second assumption – that all suffosion holes occur on one side of the leaking pipe, enabled to treat the upper tolerance limit as a half of protection zone width (Fig. 1). Upper limit (UTL) calculations were conducted for a tolerance level of 70%, 80% and 90%, and a confidence level of 95%, in Statistica 13 software (StatSoft, Inc.). Depending on the kind of data distribution (normal or non-normal – Tab. 1), a mean or a median was taken as a nominal specification, as well as the way of tolerance intervals determination was selected. The results of calculations for different cases corresponding to the test variants were analysed considering the influence of operating pressure in a pipe on a protection zone width and selection of an optimal value of tolerance level in calculations. The results of the analysis enabled to propose the width of a protection zone for the conditions of the investigations. Figure 1. Scheme of protection zone along a water pipe Table 1. Kind of data y distribution depending on a leak area and hydraulic pressure head H in a pipe [25] H [m H2O] Data y distribution for leak area [cm2] 4.41 9.42 15.07 18.84 3.0 N N N N 3.5 NN N N N