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The safety of buried pipes under repeated load has been a challenging task in geotechnical engineering. In this paper artificial neural network and regression model for predicting the vertical deformation of high-density polyethylene (HDPE), small diameter flexible pipes buried in reinforced trenches, which were subjected to repeated loadings to simulate the heavy vehicle loads, are proposed. The experimental data from tests show that the vertical diametric strain (VDS) of pipe embedded in reinforced sand depends on relative density of sand, number of reinforced layers and height of embedment depth of pipe significantly. Therefore in this investigation, the value of VDS is related to above pointed parameters. A database of 72 experiments from laboratory tests were utilized to train, validate and test the developed neural network and regression model. The results show that the predicted of the vertical diametric strain (VDS) using the trained neural network and regression model are in good agreement with the experimental results but the predictions obtained from the neural network are better than regression model as the maximum percentage of error for training data is less than 1.56% and 27.4%, for neural network and regression model, respectively. Also the additional set of 24 data was used for validation of the model as 90% of predicted results have less than 7% and 21.5% error for neural network and regression model, respectively. A parametric study has been conducted using the trained neural network to study the important parameters on the vertical diametric strain.

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The results of laboratory model tests and numerical analysis on circular footings supported on sand bed under incremental

cyclic loads are presented. The incremental values of intensity of cyclic loads (loading, unloading and reloading) were applied

on the footing to evaluate the response of footing and also to obtain the value of elastic rebound of the footing corresponding

to each cycle of load. The effect of sand relative density of 42%, 62%, and 72% and different circular footing area of 25, 50,

and 100cm2 were investigated on the value of coefficient of elastic uniform compression of sand (CEUC). The results show that

the value of coefficient of elastic uniform compression of sand was increased by increasing the sand relative density while with

increase the footing area the value of coefficient of elastic uniform compression of sand was decreases. The responses of footing

and the quantitative variations of CEUC with footing area and soil relative density obtained from experimental results show a

good consistency with the obtained numerical result using “FLAC-3D”.

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A numerical simulation of laboratory model tests was carried out to develop an understanding of the behaviour of pipes in a trench prepared with 3-Dimensional reinforced (namely "geocell-reinforced" in the present study) sand and rubber-soil mixtures, under repeated loadings. The study reports overall performance of buried pipes in different conditions of pipe-trench installations and the influence of pipe stiffness on backfill settlements, stress distribution in the trench depth and stress distribution along the pipe's longitudinal axis. Good agreements between the numerical results and experimental results were observed. The results demonstrate that combined use of the geocell layer and rubber-soil mixture can reduce soil surface settlement and pipe deflection and eventually provide a secure condition for buried pipe even under strong repeated loads.