Experimental Research On The Interfacial Stress Of Pipe-Soil In Buried

With the continuous improve of China is comprehensive national power,people have accelerated the construction of urbanization and the rapid development of economy.However,with the construction of cities and economic growth,oil and gas resources have gradually become an important basis for urban operations and economic development.Due to the buried pipeline transportation has the advantages of small disturbance,low transportation cost,low transportation loss and high safety performance,people have accelerated the laying of burial pipeline,which has become a major transport method for long-distance oil and gas transmission.However,due to the wide scope of buried oil and gas pipelines,which will inevitably pass through various unfavorable soil layers,such as permafrost zones and fracture zones.As a result,people are paying more and more attention to the safety problems of buried pipelines such as earthquake resistance,frost heave expansion,and thaw settlement.The land area of our country is covered by 75% of permafrost and seasonally frozen grounds,so that many of China's important oil pipelines will cross the permafrost.The change of ambient air temperature has a great impact on the physical and the mechanics properties of the soil.When the ambient temperature drops below zero degrees Celsius,the soil will experience frost heave.When the ambient temperature rises above zero degrees Celsius,the soil will experience a thaw phenomenon.As a result,the physical and mechanical properties of the soil surrounding the buried pipeline are change,which is extremely unfavorable to the safe operation of the pipeline.Therefore,the problem of interfacial stress between buried pipeline and permafrost and the interface stress between buried pipeline and normal temperature soil are of great guiding significance for the further development of seismic design and construction of buried pipelines.In this paper,the test method and the theoretical method are used to study the interface stress of buried pipe and soil.The main contents of the research on the interface stress of buried pipe and soil are as follows:1.Experimental study on physical and mechanical properties of soil(1)The basic physical parameters such as soil density,water content and plasticity index were measured by experimental method,and the soil samples were classified.(2)This experiment mainly studies the influence of water content on the physico mechanical properties of unfrozen soil and frozen soil.Therefore,the soil samples with different moisture content were tested and studied,and the mechanical properties of normal temperature soil after freezing were studied.The influence of water content on the physical and mechanical properties of unfrozen soil and frozen soil is studied,and the physical and mechanical characteristics of soil samples with different moisture content after freezing are analyzed.(3)Important soil mechanical properties such as shear strength,compressive strength,and compression properties of the soil were studied through experiments.Triaxial shear test and direct shear test were used to study the shear strength properties of normal temperature soil and frozen soil.The cubic compressive strength test method was used to study the compressive strength of frozen soil.The single-lever consolidation instrument was used to study and analyze the soil.(4)The effects of water content on the shear properties of soil and frozen soil are studied and analyzed,and the relationship between the shear strength and the shear strength parameters of the soil and the frozen soil and the moisture content are obtained.(5)The compressive strength of frozen silty clay increases with the increase of water content,and increases to a certain extent with the increase of water content,but the compressive strength of frozen sand increases with the increase of water content.2.Experimental study on interfacial stress between buried pipe and soil(1)In this paper,the stress test of soil and soil types of soil and silty clay was carried out in this paper,and the stress problems of the buried pipeline under the unfrozen and frozen conditions of the two types of soil were analyzed.(2)The stress calculation model of buried pipeline interface is established.(3)Using the test data to fit the equations for the interface soil stress of buried pipelines under different soils.3.Analysis of stress interaction between buried pipe pipe and soil interface(1)The stress values obtained from the theoretical model of pipe soil interface agree well with the experimental data.(2)By comparing the stress displacement curves of the room temperature tube and soil interface with the stress displacement curves of the permafrost tubes,it is found that the stress value of the interface between the soil and the soil is far greater than the stress value between the pipe and soil interface at normal temperature.Permafrost has a great influence on the interaction of pipe and soil.