| There are few reports on the long-term service characteristics of liquefied natural gas(LNG)storage tanks at present.If the settlement of LNG storage tank foundation is too large,it may bring catastrophe to the whole structure.With the increase of natural gas production in the Qaidam Basin,the number of LNG storage tanks built in Qinghai will also increase.Collapsible loess is widely distributed in Qinghai area,and the temperature difference between day and night and seasonal precipitation vary greatly.Therefore,the loess near the foundation of a LNG storage tank in Xining area and limestabilized loess were taken as the research objects,based on the summary of relevant research status at home and abroad,and based on the GDS standard stress path test system,the influence of water content on the strength characteristics of loess and the influence of freeze-thaw cycle on the strength characteristics of loess and limestabilized loess are studied,which provides a reference for the basic design of LNG storage tank.The main research results include the following aspects:(1)Consolidation undrained tests of undisturbed loess with different water content(? =8%,14%,20%)were carried out.The results show that:(1)The type of stressstrain curve of the specimen was strain-hardening,and the maximum deviatoric stress of the specimen decreases with the increase of water content under the same confining pressure.(2)The elastic modulus increases with the increase of confining pressure,however,it decreases with the increase of the water content.(3)The Coulomb shear strength formula with the water content as the variable can be obtained by fitting the curve of the cohesion and the internal friction angle with the change of water content.(4)The normalized stress-strain relationship considering the influence of water content as well as confining pressure was established which can predict the stress-strain relationship of undisturbed loess compared with the experimental date.(2)Unconsolidated undrained tests after different number of freeze-thaw cycles of undisturbed loess(freeze-thaw cycles = 0,1,3,7,11,15),compacted loess(freeze-thaw cycles = 0,1,3,7,11,15,20)and lime-stabilized loess(freeze-thaw cycles = 0,1,3,7,11,15,20)were carried out.The results show that under the action of freeze-thaw cycles:(1)The volume fluctuation range of undisturbed loess was the largest,followed by compacted loess,lime-stabilized loess was relatively stable.The water content of three types of soil samples reduced.(2)In terms of stress-strain relationship.For the undisturbed loess,the stress-strain curves are characterized with strain hardening.The stress-strain curves for compacted loess showed characterized with strain hardening at the high confining pressures and weak strain softening at a lower confining pressure.The stress-strain curve of lime-stabilized loess can be divided into three stages.(3)In terms of elastic modulus and maximum deviatoric stress,undisturbed loess and compacted loess had large change after 1 and 3 freeze-thaw cycles,and the limestabilized loess reached a minimum after 3 cycles of freeze-thaw cycles,then it increases with the increase of the number of freeze-thaw cycles.(4)In terms of cohesion and internal friction angle,there is no obvious regularity in undisturbed loess and remolded loess.The change trend of cohesion of lime-stabilized loess with freeze-thaw cycles is the same as that of elastic modulus and maximum deviatoric stress.(5)The stress-strain curve under freezing and thawing of undisturbed loess and remolded loess can be predicted by the normalized stress-strain relationship.By comparing the mechanical properties of three types of soil samples under the freeze-thaw cycle,the strength characteristics of different foundation soil layers were obtained. |
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