Estimation of the bulk and shear moduli of soil surrounding a plastic water pipe using measurements of the predominantly fluid wave in the pipe

Abstract

Leak noise correlators are commonly used to detect and locate leaks in buried water pipes. They use the cross-correlation function between leak noise signals measured using hydrophones or accelerometers placed on the pipe either side of the leak. The efficacy of a correlator is dependent upon knowledge of the speed at which the leak noise propagates along the pipe as well as how much it attenuates with distance. The leak noise is carried in a predominantly fluid-borne wave in the pipe, which is heavily influenced by the pipe and soil properties. Although the pipe properties can be determined relatively easily, estimation of the soil properties surrounding the pipe is more problematic. It is desirable to have an accurate estimate of the soil properties, so that current models can be developed and used to improve understanding of leak noise propagation and hence leak detection capabilities. In this paper a novel approach to determining the bulk and shear moduli of the soil from measurements of the predominantly fluid-borne wave in a buried plastic pipe, is described. The measured data are compared with corresponding data predicted from a model, and the soil properties are determined using an optimization algorithm. The method is applied to two different sites, one in the UK, where the soil properties surrounding the pipe are representative of sandy soil, and one in Brazil, where the surrounding soil has properties that are representative of clay soil. It is found that the bulk and shear modulus can be estimated in the pipe buried in sandy soil, but in the clay soil it is only possible to estimate the shear modulus.

Estimating the spectrum of leak noise in buried plastic water distribution pipes using acoustic or vibration measurements remote from the leak

“…Note, that the effects of the soil and the pipe properties on the bandwidth over which leak noise is measured is not discussed here, as this has been treated in refs. [8,16,19].…”

“…6. In this test-rig, the pipe system and the pipe diameter are much smaller than the other two test-rigs and the surrounding soil is very stiff clay [19]. The measurements were made over 5.5 m, which is a much shorter distance than in the other cases, so the bandwidth in which leak noise is found to be much higher, 273 746 − Hz.…”

“…Pipe properties of each experimental test rig. The pipe properties for the Ottawa test rig are given in [6], the pipe properties for Blithfield test rig are given in [16] and the pipe properties for the São Paulo test rig are given in [19]. Poisson's ratio 0.5 0.39 0.49 Table 2.…”

“…The São Paulo test rig is a close circuit system where a centrifugal pump is used to pressurize the system. The PVC pipe is buried at a depth of approximately 0.5 m with an outer radius and wall thickness of 35.8 mm and 3.4 mm, respectively [8,19]. The measurement positions were at access points P1 and P2 with the leak located 1.25 m away from P1 as shown in Fig.…”

A Comprehensive Review of Acoustic Methods for Locating Underground Pipelines

“…Furthermore, accurate evaluation in-situ acoustic properties of soils, especially wave speed, plays a significant role in the seismic wave method [101,102] and pipe leakage detection [143], as wave speed is directly related to the interpretation of measurement results. Therefore, many studies have been conducted on measurement of soil properties, which can be found in [144][145][146][147][148].…”