Study On Uplifting Mechanism And Mitigation Measurement Of The Pipelines Buried At Shallow Depth During The Earthquake

The uplift of pipelines buried at shallow depth in liquefiable soil due to earthquake induced liquefaction may lead to severe damage. The study of uplifting mechanism and mitigation measurement of pipelines is important subject for geotechnical engineering and lifeline engineering. The present research is supported by the National Science Foundation Project-Study on Uplifting Mechanism and Mitigation Measurement of the Pipelines Buried at Shallow Depth during the Earthquake (No. 50278009) and the National Science Foundation Project-Study on Liquefaction and Relationship Between Parameters of Deformation and Strength of Saturated Sand-gravel Composites (No. 50578029). The main contents of the current research are as follows:(1) A series of shaking table tests are conducted by analogy method. The acceleration and excess pore water pressure response behaviors of soil foundations are studied. The uplift mechanism of pipeline and the effectiveness of different types of drainage or reinforcement measures are discussed.(2) Based on the Windows Operation System and Visual C++ MFC development tools, a saturated soil nonlinear FEM program-GEODYNA and its post-process program-POST2D are implemented by the Object-oriented method. Some advanced techniques are adopted in GEODYNA, such as Multi-Core parallel computing, command line input. A lot of soil models and FEM elements are implemented in GEODYNA. GEODYNA is verified by using analytical solution for one-dimensional saturated porous elastic consolidation and dynamic problem, and it is shown that the accuracy of the numerical solution is comfortably high.(3) An effective stress Finite Element Method is implemented for simulating the shake table test on pipelines buried in the saturated sand foundation. This method is based on generalized Biot's equations. The hyperbolic stress and strain relationship is used in the numerical model. Pore pressure generation due to earthquake loading is calculated via the pore pressure model developed by Seed et al. The excess pore water pressure response behaviors of soil foundations, the effectiveness of different types of drainage measures arecompared with the results of tests.(4) The floation of pipelines is analyzed by the equivalent linear method and liquefaction flow method. The effects of diameter and depth of pipelines, groundwater level, and relative density of soil on the uplift behavior are studied.(5) On the base of generalized Biot theory of consolidation and Pastor-Zienkiewicz Mark-Ill generalized plasticity constitutive model, the effective stress Finite Element Procedure is implemented in the frame of GEODYNA, which is used to study the effectiveness of gravel drainage as mitigation method against the uplift of pipelines buried in liquefiable soil. Some parametric studies are conducted to investigate the influence factors of pipeline floatation, including the width of vertical drainage, the distance between vertical drainage and pipeline, the thickness of horizontal drainage, and the permeability of drainage.