Experimental Study On Freezing Characteristics Of Saline Calcareous Clay

Calcareous clay layers are widely distributed in the Huanghuai area,and many frozen tube fracture accidents have been caused due to insufficient understanding of them.This paper takes a calcareous clay in a Huainan mine as an object,and conducts a series of experimental studies on freezing characteristics of frozen calcareous clay caused by freezing pipe breakage and freezing fluid leakage,and draws the following conclusions:(1)The NMR T2 spectrum reflects that the calcareous clay's water in the unsaturated state exists in the form of strong and weak bound water,with small pores and poor connectivity;in the early stage of freezing,the bound water content at different salt rates Basically,the combined water content continued to decrease rapidly,but with the increase of salt content,the downward trend gradually slowed down.At-18?,the combined water content in frozen soil remained basically unchanged.And the higher the bound water content of the higher salt content.The freezing point temperature of the unwashed soil is lower than that of the washed soil.At the same salt content,the combined water content of the unwashed soil group is less than that of the washed soil group.(2)In the uniaxial experimental process of frozen soil,in the elastic phase,acoustic emission events begin to appear and increase with increasing stress.In the plastic phase,the number of acoustic emission events continues to increase.When the stress reaches the peak value,the number of acoustic emission events maximum.During the destruction phase,there are still a number of acoustic emission events.(3)The uniaxial compressive strength of frozen soil increases linearly with decreasing temperature and decreases exponentially with increasing salt content;its elastic modulus increases with a quadratic function with decreasing temperature,As the salt content increases,it decreases exponentially;its Poisson's ratio decreases linearly with decreasing temperature,and linearly increases with increasing salt content.(4)The entire frost heave process is divided into three stages:rapid frost heave stage,linear frost heave stage,and stable frost heave stage.In the first stage,frost heave was mainly caused by freezing of water in situ in the soil.In the second stage,frost heave is mainly caused by the condensation effect of the ice lens body near the freezing front.In the third stage,frost heave is mainly caused by the thickening of the ice lens body.The amount of frost heave decreases with the increase of salt content in the range of 0%?2%of salt content.Figure[42]Table[18]Reference[88]...