الأداء المختبري للانابیب البلاستیكیة المدفونة بعمق قلیل تحت طبقة سبیس مسلحة بالجیوسیل تحت تأثیر احمال داینامیكیة متكررة

Laboratory Performance of Shallow Buried Plastic Pipes below Geocell Reinforced Subbase Layer Under Repeated Load

     Developing a physical model is a common method to obtain the information involving soil-pipe interaction, which can provide different testing conditions. The present study deals with the experimental investigations of the behavior of buried PVC pipes. A number of laboratory experiments were conducted using PVC pipes which were buried in medium sand layer and below a subbase layer reinforced with geocells and subjected to two dynamic repeated loading amplitudes (0.5 ton and 1 ton) and three different loading frequencies (0.5 Hz, 1 Hz, 2 Hz) to study the effects of the geocell reinforcement layer inclusion on the stress reaching the pipe crown, vibration of the pipe and the soil surface settlement. The results of the experimental work showed that the reduction of surface settlement due to the geocell reinforcement ranges from 29 to 43 % when the amplitude of load is (0.5) ton, whereas, the reduction varies from 32 to 41% when the load amplitude is up to (1) ton. When using geocell reinforcement, the amplitude of crown displacement is reduced by about 25 to 35% and 13 to 18% when the load amplitude is 0.5 and 1 ton, respectively. When using geocell reinforcement, the value of vertical pressure is decreased by about 13 to 41 % when the load amplitude is 0.5 ton and by about 25 to32 % when the load amplitude is 1 ton.

     The results of experimental work were verified using the finite element software PLAXIS 3D. The geocell reinforcement was modeled using the geogrid element, which is defined as a slender structure element that has the ability to withstand axial stresses but no bending stiffness. Geogrids cannot sustain compression; however, they provide a high tensile resistance. The results of the numerical simulation of the experimental work showed that the maximum percentage of error between the experimental and the numerical results in terms of surface settlement is about 10%. The maximum percentage of error between the experimental and the numerical results in terms of crown displacement is about 6%. The maximum percentage of error between the experimental and the numerical results in terms of vertical stress reaching the crown is about 11%. This modeling was found successful through good convergence with experimental results. Study results showed that the numerical modeling compares well with the experimental work results, and showed that geocell reinforcement has a significant positive change of reduction of the surface settlement, vertical stress above the pipe crown and the vertical displacement of the pipe crown. A parametric study was also developed based on the literature review, the experimental results, and the calibrated numerical models to study the effect of multiple parameters on a full-scale model.