Examining the conditioning factors that influence material shear strength of particle deposits in a full-scale drinking water distribution laboratory

Understanding the factors that influence the shear strength properties of material accumulated on the internal surface of water pipes is an important step in the development of mitigation strategies to protect drinking water quality. The aim of this paper is to examine what factors influence the rate of material accumulation on the internal surface of drinking water pipes at different material shear strengths (MSS). A full-scale, controlled laboratory water distribution system was used to examine three factors: i) the method of particle addition (direct injection of particles or the introduction of particles into a continuously-stirred tank upstream of the pipe); ii) the suspended solid concentration of particles introduced into the pipe, and; iii) the conditioning velocity in the pipe during the addition of particles. Experimental results show that particles at all MSS levels accumulate simultaneously. The concentration of particles was the major factor that affected the particle accumulation load, while particle MSS was mostly governed by the relationship between particle size and pipe wall roughness elements. The new particle wall attachment theory proposes that particles entrapped in the pipe wall roughness "valleys" become sheltered from the flow shear forces at the wall and can achieve elevated MSSs which limits the impact of the fluid velocity on the mobilization of fine accumulated particles.