True Tri-axial Test On Stress-strain Characteristics Of Frozen Calcareous Clay

In the construction of well in deep topsoil and subway access in soft soil area,the stress of frozen soil element is in three-dimensional state.The true tri-axial apparatus is an important instrument for studying the properties of thawed soil in the laboratory at present.In this paper,combined with the temperature characteristics,it will be applied to the study of frozen soil.In this paper,we use the ZSZ-2000 microcomputer controlled true tri-axial frozen soil testing machine jointly developed by Anhui University of Science and Technology and Changchun Zhantuo Testing Instrument Co.LTD to study the frozen calcareous clay.Taking temperature(-5?,-10?,-15?),confining pressure(?3=1MPa,2MPa,3MPa)and medium principal stress coefficient(b=0,0.25,0.5,0.75,1)as test variables,a series of constant ?3 and constant b frozen soil true tri-axial tests were carried out.Through comparative analysis of the principal strain relationship,the volume strain relationship and the stress-strain relationship.The effects of temperature,confining pressure and medium principal stress coefficient on the strength and deformation characteristics of frozen calcareous clay are studied.The test data were analyzed on the strength rule on the p-q plane,and the test points were compared with the generalized Mohr-Coulomb and the William-Warnke strength criterion on the ?plane.The conclusion is as follows:Principal strain relation,?3 direction always shows expansion,with the increase of b value,the expansion rate becomes faster;the ?1 direction always shows compression;the b value is between 0-0.25,the ?2 direction shows expansion,between 0.5-1,and the?2 direction shows compression.Volume strain relationship,the curve of ?2??1 increases first and then decreases,the maximum value of soil shear shrinkage increases with the increase of b value.When it reaches the maximum value,it develops towards the direction of shear expansion;the maximum shear shrinkage decreases with the increase of confining pressure;at 1MPa and 2MPa,the maximum value of shear shrinkage at 5? is higher than-15? and higher than-10?,and at 3MPa,the maximum value decreases with the decrease of temperature.Stress-strain relationship,the curves of(?1-?3)??1 all show strain hardening type.The deviator stress increases first and then decreases with the increase of b value,and then rises when b=1;the deviator stress increases with the decrease of temperature and the increase of confining pressure,and the larger the deviator stress is,the higher the strength of frozen calcareous clay is.Based on the test results,the strength parameters of frozen calcareous clay are calculated and analyzed:the cohesion c increases with the decrease of temperature,increases first and then decreases with the increase of b value,and rises when b=1.The internal friction angle ? increases with the decrease of temperature,and increases first and then decreases with the increase of b value.The failure stress ratio M decreases with the increase of b value,rises when b=1,and decreases with the increase of confining pressure.According to the test data,the equation of b value about the strength parameter is fitted.According to the strength law of p-q plane,it is found that the structural strength increases with the decrease of temperature,with the increase of confining pressure,first increases and then decreases with the increase of b value,and then rises when b=1.On the ? plane,the failure surface extends outward with the decrease of temperature and outward with the increase of confining pressure.It is consistent with the general Mohr-Coulomb strength criterion in b=land b=0.75;it is different from William-Warnke strength criterion in b=0.75,which is very consistent in other conditions.Figure[53]table[3]reference[69]...