Study Of Deformation And Wave Velocity Characteristics Of Deep Clay With Different Stress Paths Under Freeze-thaw Conditions

In deep alluvial freezing method well drilling,deep soil undergoes a freeze-thaw cycle under high stress,which will induce structural changes within the soil.This leads to changes in strength and deformation characteristics.The propagation characteristics of acoustic waves are closely related to the interior of the geotechnical medium,and it is important to understand the mechanical properties and wave velocity of deep soil under different stress states during freezing and thawing.It is of some significance to reveal the freeze-thaw mechanism of deep soil.In this paper,we studied the deep remodeling clay and developed a new method of freeze-thaw unloading under different stress paths such as isostatic consolidation,freeze-thaw loading and unloading.Strength and creep tests were conducted to systematically investigate the deformation and wave velocity characteristics of deep soil before and after freeze-thaw.A three-axis bending element freeze-thaw test device was developed to meet the needs of indoor testing.The three-axis bending element freeze-thaw test device is equipped with a side-mounted bending element system,and can achieve radial strain measurement,the maximum axis pressure 200KN,the maximum circumferential pressure of 10MPa,can be uniform temperature control,temperature range in the-40??40?.First,the deep clay was subjected to isoconfusion and loaded freeze-thaw tests.The high stress environment of the deep soil is simulated by means of isocompressive consolidation,followed by a freeze-thaw cycle under load,during which the deformation and wave velocity characteristics of the soil are monitored in real time.It was found that freeze-thaw has a significant effect on the internal and macroscopic mechanical properties of dense deep soils.Under the test conditions,the deep clay was subjected to 4?8MPa stress.The freezing temperature T_fwas about-6?.When the temperature is higher than the freezing temperature T_f,the radial strain and shear wave velocity of the earth body basically does not change;when the temperature is in the near-phase zone,the radial deformation expands sharply and the shear wave velocity increases sharply;when the temperature is lower than the phase change interval,the deformation and wave velocity and other indicators tend to change slowly.For the melt process no obvious characteristic demarcation points were found,and the deformation and wave velocity indicators varied sharply from-5°C to 0°C,the results show that there is a significant difference between the freezing process and the melting process.At the same time,the shear modulus of soil decreased after a freeze-thaw cycle.In general,the freeze-thaw cycle reduced the shear modulus by 11.6%.Secondly,the shear resistance of deep clay after freeze-thawing was investigated under the path of constant axial pressure unloading circumferential pressure,and the stress-strain curve was obtained under the unloading path,and it was found that the stress-strain curve showed strain hardening phenomenon.The lower the freezing temperature under the test conditions,the lower the damage strength and E_sec of the thawed soil.The lateral deformation coefficient variation law was obtained for the unloading path of the thaw soil.At the same time,the E_d is about 10 times higher than the E_sec under this test condition.Lastly,the creep test was carried out in deep thawed clay with constant axial pressure-unloading circumferential creep and the obtained creep curves consisted of three stages:instantaneous creep,decay creep and steady creep,and the axial creep rate was greater than the radial creep rate.The lower the freezing temperature,the lower the long-term intensity.In addition,it was found that the shear wave speed showed a decreasing trend during the triaxial shear creep.There are 108 figures,28 tables and 81 references in this paper.