The service life of rigid sewer pipes is often controlled by joint integrity. Leaking joints can cause ingress of water and develop voids where surrounding soil has eroded. The influence of soil voids on the stability of buried rigid pipes is investigated, considering the effects of void size, void location and void shape. A series of simplified void geometries are defined, and their influence on bending moments in the rigid sewer is studied through finite element analysis. Elastic analysis indicates that the bending moments from expanding voids at the springline will increase slowly, accelerating once the void spans a 45 degree arc, approximately doubling at 90 degrees, and tripling if the loosened backfill is modeled for shear failure. This preliminary study suggests that the growth of erosion voids should be stopped before they reach 45 degrees, but validation through physical testing is necessary. Elastic-plastic finite element analysis is used to calculate the deformation of rigid fractured pipe with different thicknesses, considering both bonded and full-slip interface conditions. The analysis confirms that bonded idealized flexible pipe theory is very effective for calculation of increases in horizontal diameter of the fractured pipe. Furthermore, decreases in vertical diameter can be simply related to increase in horizontal diameter using (1-2t/OD) obtained from fractured pipe kinematics. Both elastic and elastic-plastic finite element analyses used to study the deformations of fractured rigid pipe reveal that contact angle appears to be the dominant factor affecting fractured pipe deformations. Deformation of the damaged rigid pipe increases dramatically with void growth and accelerates when erosion void contacts with the outer surface of the pipe over an arc greater than 45 degrees. Computational analyses examine the behavior of centrifuge model tests which examine soil load transfer to flexible sewer liners after fracture and erosion voids form nearby. The magnitude of deformation changes for finite element models is found to be comparable to observations when voids are formed at springline. However the development patterns are dramatically different as voids located under the invert, and it appears that the laboratory test featured physical characteristics that are not modeled in the analysis. / Thesis (Master, Civil Engineering) -- Queen's University, 2007-09-24 20:33:29.689

Recent developments in constructions have heightened the need for protecting existing buried infrastructure. New roads and buildings may be constructed over already existing buried infrastructures e.g. buried utility pipes, leading to excessive loads threatening their stability and longevity. Additionally applied loads over water mains led to catastrophic damage, which result in severe damage to the infrastructure surrounding these mains. Therefore, providing protection to these existing buried infrastructure against increased loads due to new constructions is important and necessary. In this research, a solution was proposed and assessed, where the protection concept would be achieved through the inclusion process of geogrid-reinforcing layers in the soil cover above the buried infrastructure. The controlling parameters for the inclusion of geogrid-reinforcing layers was assessed experimentally and numerically. Twenty-three laboratory tests were conducted on buried flexible and rigid pipes under unreinforced and geogrid-reinforced sand beds. All the investigated systems were subjected to incrementally increasing cyclic loading, where the contribution of varying the burial depth of the pipe and the number of the geogrid-reinforcing layers on the overall behaviour of the systems was investigated. To further investigate the contribution of the controlling parameters in the pipe-soil systems performance, thirty-five numerical models were performed using Abaqus software. The contribution of increasing the amplitude of the applied cyclic loading, the number of the geogrid-reinforcing layers, the burial depth of the pipe and the unit-weight of the backfill soil was investigated numerically. The inclusion of the geogrid-reinforcing layers in the investigated pipe-soil systems had a significant influence on decreasing the transferred pressure to the crown of the pipe, generated strains along its crown, invert and spring-line, and its deformation, where reinforcing-layers sustained tensile strains. Concerning rigid pipes, the inclusion of the reinforcing-layers controlled the rebound that occurred in their invert deformation. With respect to the numerical investigation, increasing the number of the reinforcing-layers, the burial depth of the pipe and the unit-weight of the backfill soil had positive effect in decreasing the generated deformations, stresses and strains in the system, until reaching an optimum value for each parameter. Increasing the amplitude of the applied loading profile resulted in remarkable increase in the deformations, stresses and strains generated in the system. Moreover, the location of the maximum tensile strain generated in the soil was varied, as well as the reinforcing-layer, which suffered the maximum tensile strain. / Government of Egypt

Protection of buried pipes is a serious issue that concerns countries around the world. Therefore, there is a need for new soil improvement techniques such as geosynthetic materials installation to protect these pipes from damage. This study used large-scale laboratory tests to study the behaviour of buried pipes. A total of 22 large-scale tests were performed to study the behaviour of buried flexible HDPE pipes with and without void presence under the protection of the geogrid reinforcing layers subjected to incrementally increasing cyclic loading. The presence of voids located at the spring-line of the flexible buried pipes, led to a considerable increase in the soil surface settlement, pressure recorded at the pipe crown, spring-line and invert, pipe deformation and strain recorded in the pipe wall. Increasing the pipe burial depth contributed to significant reductions in the soil surface settlement, pressure recorded at the pipe crown and invert, pipe deformation and strain recorded in the pipe wall. However, the void presence limited the contribution of increasing the pipe burial depth. The inclusion of a geogrid reinforcing layer contributed to a considerable reduction in the soil surface settlement, pressure recorded at the pipe crown, spring-line and invert, pipe deformation and strain recorded in the pipe wall. The use of a combination of geogrid reinforcing layers and increasing the pipe burial depth contributed in diminishing the ground void presence effect, where better pressure distribution inside the system was achieved. Consequently, more protection was provided to the buried pipe.