Shuwang Yan

Model Test Studies on Soil Restraint to Pipeline Buried in Bohai Soft Clay

Abstract Under high thermal stress, buckling of submarine pipelines may occur to release the stresses accumulated in the walls of the pipelines. The likelihood that buckling occurs is largely determined by the capability of the soil to resist pipeline movements. Therefore, it is very important to determine the soil resistance in upheaval buckling when designing submarine pipelines. A series of large-scale model tests were carried out with soft clay chosen as the supporting medium in view of Bohai Sea geotechnical conditions. Pipe segments with diameters of 30, 50, and 80xa0mm were used. The pipes were buried in different depth-to-diameter ratios between 1 and 9. The uplift, lateral, and axial resistances were recorded during the tests. The test results have shown that the soil resistance depends on the pipe’s diameter and cover depth. According to the uplift test results, the load-displacement relationships with smaller depth of cover differ greatly from those with larger depth of cover. The results of the ...

Numerical Solutions for Consolidation of Under-Consolidated Dredger Fill under Vacuum Preloading

ABSTRACT Sun, L.; Jia, T.; Zhuo, R.; Yan, S., and Guo, B., 2015. Numerical solutions for consolidation of under-consolidated dredger fill under vacuum preloading. This paper presents the numerical solutions for consolidation of the under-consolidated dredger fills. By a field test the delivery rules of negative vacuum pressure in the PVDs are studied, the relationship between permeability and effective stress of the high water content soil is also studied by an experiment, then a plain strain FEM program was coded for the dredger fills consolidation analysis in which the nonlinearity constitutive relation Duncan-Changs model is applied into the Biots consolidation theory, and the nonlinear permeability law is also employed in the Biots consolidation theory. As an under-consolidated soil, the self-weight that is not consolidated before the enforcement and negative vacuum pressure is included as the consolidation load in this paper. At last, two project cases were calculated using this program, the result showed that the program was suitable to analyze the under-consolidated soil consolidation under vacuum preloading or surcharge preloading method.

Finite-Element Study of Methods for Triggering Pipeline Global Buckling Based on the Concept of the Perfect VAS Length

AbstractWith the increase in pipeline operating depth, research on pipeline global buckling during the process of oil and gas transport is drawing considerable attention. Numerical simulation is an important method that is used to analyze pipeline buckling, which is immediately caused by the combined action of high temperature and high pressure. Two important problems must be solved before simulating submarine pipeline global buckling. Because the finite-element (FE) model length greatly affects analysis of the buckling results, finding a reasonable model length is the first problem in finite-element analysis (FEA). The second is how to trigger global buckling in the pipeline because the ideal pipeline would not buckle in FEA. Previous studies only state that geometric initial imperfection and interference force could trigger pipeline global buckling. Therefore, simulating pipeline global buckling in FEA becomes a problem. In this paper, an effective method for calculating the reasonable model length (als...

High-order lateral buckling analysis of submarine pipeline under thermal stress

The lateral buckling is the main failure mode for unburied submarine pipelines. Buckling mode analysis shows that the second lateral buckling mode has greater probability of occurrence. Analytical solution to the second buckling mode is obtained based on small deformation theory and Hook’s law. The relationships between the buckling temperature and the amplitude or the wavelength of the buckle segment are established as well. Analytical tools are applied to predict the occurrence and the consequence of in-service buckling of a heated pipeline in an oil field. The effects of temperature difference and properties of subsoil on the buckling mode are investigated. The analyzing results show that buckling will occur once the temperature difference exceeds the safe temperature and the larger the friction coefficients, the safer the submarine pipeline.

Study on liquefaction behavior of saturated silt in Anhui area by dynamic triaxial test

The liquefaction failure is the most and direct reason that can make the saturated silty foundation invalidate and the structure collapse. Herein, it is quite necessary to analyze the liquefaction behavior of the saturated silty soil in Anhui area under high earthquake shock by performing a series of dynamic tri-axial tests. In the testing, the test sample is remolded according to the given density of the saturated silt collected from Anhui area. And the test is carried out with the remolded samples under different confining pressure varying from 1 m to 15 m depth. During the dynamic triaxial test, the increasing law of liquefaction resistance, the active influence of the radial pressure and dry density of the remolded saturated silt are all obtained. Meanwhile, the maximum liquefaction depth of the saturated silt in Anhui area are also obtained, which can provide valuable data for the further research of the engineering measures such as gravel piles that can prevent from liquefaction.

Finite element analysis of reducing the high-speed railway vibration effect on environment with open trench

The high-speed railway vibration effect on environment is more and more concerned in recent years. Technical measurements are needed to minimize the damage to the environment, which is caused by the new transportation vehicle. It has been improved that the open trench can be used for this purpose because of its easy construction and the relatively good isolation effects. The finite-element software ABAQUS is adopted to analyze the open trench isolation effects. In order to simulate the semi-infinite space of soil condition, the infinite element and visco-elastic boundary is used in this model. The parameter ARF is introduced in the calculation procedure. The reduction effect of different factors which influence resulting vibration reduction, such as the depth, the width, the location of the trench and the frequency of the vibration load are also discussed. The obtained approaches can be referred by the designer in this area.

Research on the ability to pump sediment through pipe

Soda residue is the industrial waste materials occurring during producing the pure alkali by ammonia soda process, it also can be used in the reclamation project after the research on its engineering characteristics. In the construction, the soda residue is pumped through a pipe and then is disposed by vacuum preloading method and so on. During pumping the soda residue, the pumping pressure, the pipe resistance and the diameter of the pipe are all relevant to the transportation distance. Based on the theories in hydromechanics, the law of transporting soda residue in the pipe is deduced, the formula for calculating the rule is applied and the algorithm for solving this formula is proposed. Viscosity and initial shear strength are determined by rotating viscometer; average flow velocity is measured by designed experimental appliance, and is proved to be in concordance to the field test result.