Behavior of Flexible Buried Pipes Under Geocell Reinforced Subbase Subjected to Repeated Loading

Behavior of Flexible Buried Pipes Under Geocell Reinforced Subbase Subjected to Repeated Loading

Mohammed Yousif Fattah (Building and Construction Engineering Department, University of Technology, Baghdad, Iraq), Waqed Hammed Hassan (University of Kerbala, Karbala, Iraq) and Sajjad Emad Rasheed (University of Kerbala, Karbala, Iraq)
Copyright: © 2018 |Pages: 20
DOI: 10.4018/IJGEE.2018010102


The present article constitutes an experimental investigation of the behavior of buried PVC pipes. A number of laboratory experiments were conducted using PVC pipes which were buried in a medium sand layer, below a subbase layer, reinforced with geocells. They were subject to repeated dynamic load amplitudes of 0.5 and 1 ton and loading frequencies of 0.5, 1 and 2 Hz, to study the effects of the geocell reinforcement layer, in terms of the amount of stress reaching the pipe crown and the vibration of the pipe. A 3D numerical model was also developed to investigate the performance of the geocell above the buried pipe. The predicted characteristics of the buried pipes were validated using the experimental data. The results showed that geocell reinforcement decreases both crown vibration by 35%, and the vertical pressure reaching the pipe by 41%. The numerical models have a good fit with the experimental work results, both confirming that geocell reinforcement has a significant role to play regarding increasing the safety of pipes.
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In general, soil has low resistance to tensile stress action. Therefore, in order to protect buried pipes from damage, it is necessary to improve soil bearing capacity to enhance soil stability thus reducing soil settlement and lateral deformation. Soil reinforcement using polymeric materials, is considered one of the most efficient techniques available to enhance soil strength, offering financial savings in comparison to traditional designs. Specifically, geocell reinforcement has recently become recognized as an efficient soil engineering application. Used to protect underground pipes from external dynamic traffic loading, geocells are three-dimensional, honeycomb-shaped, soil-reinforcing geosynthetics composed of polymeric materials, primarily used to confine granular materials. The cellular structures of geocells provides lateral and vertical confinement and a tensioned membrane effect, thereby increasing soil bearing capacity and providing a wider area for the distribution of stress (Rea & James, 1978). Recently, researchers have successfully increased the bearing capacity of soil by using three-dimensional reinforcement (Zhang et al., 2010; Huang et al., 2011; Lambert et al., 2011; Boushehrian et al., 2011; Mehrjardi et al., 2012). Emersleben and Meyer (2010) conducted radial load tests to estimate the influence of a range of parameters such as interconnected cell numbers, stiffness of the geocell, height of the geocell and the height of soil cover on the mechanism of interaction between earth resistance and hoop stress. The test results have revealed that the most important parameters in the behavior of the system are the number of adjacent cells and geocell material stiffness.

Leshchinsky and Ling (2013) investigated the geocell effect on ballasted embankments above a subgrade reinforced with geocells. They developed an acceptable material model which was validated using finite element analysis. The subsequent analysis suggested that the geosynthetic reinforcement was adequate for a wide range of subgrade stiffness. Geocell reinforcement distributed the stress over a wider area and provided less settlement. Corey et al. (2014) evaluated the protection level provided by geogrid reinforcement for steel-reinforced, high density Polyethylene (HDPE) pipes. They performed five rod penetration tests, seven static plate load tests and three cyclic plate load tests. The results indicated that the type of backfill material played an important role in the performance of buried pipes and geogrid reinforcement. An inverted U-shape geogrid reinforcement was more effective than single and double reinforcement layouts. Sanjei and De Silva (2016) focused on developing a three-dimensional model to simulate the behavior of geocell reinforcement using PLAXIS 3D. The geocell shape was imported from AutoCAD to PLAXIS 3D, the three-dimensional model then verified by experimental results. The experimental and numerical results revealed that the highest load carrying capacity was found at a ratio of depth to width u/b < 0.5 for a square pad footing. Hegde and Sitharam (2016) examined the results of laboratory tests on reinforced and unreinforced clay beds subjected to cyclic plate load tests. Their results showed that the presence of geocell and geogrid reinforcement increased the foundation-soil system’s natural frequency by 4 times and that vibration was reduced by 92%.

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