Mechanical Responses Of Buried HDPE Pipes Subjected To The Ground Subsidence

Underground pipeline work plays a significant role in people's daily life and is the base of urban production and development.The serviceability loss of buried pipelines caused by the ground subsidence has occurred in many cities for the past few years,especially for the buried flexible pipes due to its low flexure stiffness.Therefore,it is necessary to investigate the mechanical responses of buried flexible pipes subjected to the ground subsidence.With the financial support of Natural Science Foundation of Jiangsu Province?Grant No.BK20131294?,the Scientific Research Foundation of Graduate School of Southeast University?Grant No.YBJJ1632?and the Fundamental Research Funds for the Central Universities,Colleges and Universities in Jiangsu Province Plans to Graduate Research and Innovation?Grant No.KYLX₀144?,the mechanical responses of buried flexible pipes subjected to the ground subsidence were investigated by conducting the field trial,numerical modeling,laboratory model test and theoretical calculation.Conclusions drawn are as follows:?1?The field trial and numerical modeling were conducted to investigate the structural responses of High Density Polyethylene?HDPE?double-wall corrugated pipes during the construction phase.It is found that the pipe diameter increased in the vertical direction and decreased in the horizontal direction due to the compaction of the sidefill in the initial backfilling process,which is refered to as peaking behavior.The numerical parametric study was conducted on the effect of pipe diameter,pipe stiffness,soil modulus,trench width,compactor type and soil cover thickness on the performance of the HDPE pipe during installation.It is found that the effects of the trench width and soil cover thickness on the earth pressure at the pipe top and springline were more significant compared to the pipe diameter and compactor type.The pipe stiffness,soil modulus,compactor type and soil cover thickness had more significant effects on the pipe deflection compared to the trench width.Based on the numerical results,empirical equations were proposed for prediting the earth pressure at the top and springline of the pipe,and the pipe deflection in both vertical and horizontal directions.The validity of the proposed equations was evaluated using the field data obtained from published studies.It is found that the proposed equations for calculation of earth pressure at the top of the pipe improved the accuracy of AASHTO's method by 20% to 40%,and the accuracy of equations proposed for the vertical deflection of the pipe was 50% to 70% higher than that of the equation proposed by Masada and Sargand and AASHTO's method.?2?A series of physical model tests were conducted to investigate the structural responses of HDPE double-wall corrugated pipes and settlement propagation through the soil during the localized ground subsidence.It is found that the earth pressure at the top of the pipe subjected to localized ground subsidence was affected by the soil arching triggered in both transverse and longitudinal directions of the pipe,which is referred to as ?three-dimensional?3D?soil arching?.The current method,which is without consideration of soil arching triggered in the pipe transverse direction,underestimated the measured earth pressure at the top of the pipe in the model tests.An approach,named ?3D soil arching method?,which was able to consider the ?3D soil arching? triggered in the soil cover of the pipe was proposed in this study.A comparison was made between the calculated earth pressure using the ?3D soil arching method? and the measured data from the model tests.It is found that the ?3D soil arching method? could provide a conservative design for the earth pressure at the top of the pipe subjected to the localized ground subsidence.?3?A series of physical model tests and numerical modeling were undertaken to investigate reinforcement benefits of geosynthetics on buried HDPE double-wall corrugated pipes subjected to localized ground subsidence.Test results showed that a woven geotextile layer and a biaxial geogrid layer reinforced underneath the pipe were both effective to reduce vertical displacements of the pipe caused by localized ground subsidence;however,it is found that a woven geotextile layer placed above the pipe would significantly increase vertical displacements of the pipe.A woven geotextile layer placed underneath the pipe can effectively reduce the increase of earth pressure at top of the pipe suffering from localized ground subsidence compared to the pipe reinforced by a geogrid layer.It is suggested that a geotextile layer with tensile stiffness ranging from ? to 200 kN/m should be reinforced underneath the pipe to resist the ground subsidence when the minimum soil cover thickness of the pipe?i.e.,0.7 m?outlined by China design standard?GB 50015-2003?was used,where the vaule of ? depends on the magnitude of ground subsidence and the longitudinal bending stiffness of the pipe.It is also found that the benefits from increasing the number of reinforced layer of geotextile with tensile stiffness of 200 kPa for protecting the pipe from the ground subsidence were insignificant.The vertical displacement of the pipe decreases with increasing width of the geotextile until the ratio of width of the geotextile to the pipe diameter is greater than 3.?4?A split-box model test was conducted to investigate the structural responses of the HDPE double-wall corrugated pipe subjected to normal fault.It is found that the bending strains at valley of the pipe wall were much larger than those at the liner.The range of longitudinal bending strain of the pipe distributed along the pipe segment at the footwall side is greater than that along the pipe segment at the hanging wall side.It is also found that the pipe cross-section nearby the fault suffered the most distortion.?5?The mechanical responses of HDPE double-wall corrugated pipe segments connected by a spigot-and-bell joint were investigated by conducting two split-box model tests.It is found that the bending strains of the pipe segments contributing the spigot and the bell were much smaller than those of the continuum pipe.The pipe segment at the footwall side and the joint crossing the fault both suffered the most cross-section distortion.The gasketed pipe-joint assembly was vacuumed to capture the leakage of the pipe joint.The calculation of shear force across the pipe joint was also conducted.It is found that the shear deformation of the pipe joint was within the range of elasticity when it leaked.