Study On The Physico-mechanical And Thermal Properties Of Fiber-Reinforced Clay Under Freeze-thaw Cycles

In accordance with the special zone of seasonal frozen soils,in this work,clay is considered as an object of study,the physic-mechanical properties of clay modified with fiber and clay modified with fiber and cement are studied.Clay has been tested after various freeze-thaw cycles using dynamic and static triaxial tests,thermal conductivity tests and electron microscopy.The main content of the research and innovative achievements of this article:1.The basic physical properties of the soil were determined in accordance with the technical conditions.In order to assess the impact of the freeze-thaw process and the content of reinforcing materials on the height of the samples and on water content of the samples,changes in these parameters were measured.The results showed that when the number of freeze-thaw cycles did not exceed 5 times,the water content in all samples increased most with an increase in the number of freeze-thaw cycles,but when the number of cycles exceeded 5 times,the increase slowed down;when the number of freeze-thaw cycles exceeded 10,the height of samples modified with fibers remained almost constant,and the change in water content in the soil modified with polypropylene fiber was the smallest.2.In order to consider a number of static properties of modified clay after the freeze-thaw cycle,we considered a series of static triaxial tests with improved single-fiber clay(polypropylene,basalt)or cement in combination with fiber with some variables,such as fiber content,number of freeze-thaw cycles,limiting pressure,etc.The results show that in comparison with clay,the inclusion of fiber significantly increases the strength of the modified clay before and after exposure the freeze-thaw cycles;with increasing limiting pressure,the strength of the modified clay increases more than that of the clay;In accordance with the deviator stress and stress-strain,the cohesion,friction angle and the modulus of elasticity were discussed depending on the ratio of the modified material and content.3.To determine the dynamic properties of the fiber-modified clay after many influencing factors,such as type of fiber,content of fiber and the number of freeze-thaw cycles,was carried out a dynamic triaxial test,which corresponding to the experimental static triaxial test plan,at which the dynamic load frequency was 1 Hz.The results show,that the dynamic modulus of elasticity is less and less after exposure to freeze-thaw cycles;The dynamic modulus of elasticity changes most when the limiting pressure is 0.5 MPa;The damping coefficient is weakly dependent on the change in the limiting pressure;The influence of the freeze-thaw cycle on the damping coefficient is not large,but the fiber content has a great influence.The corresponding skeleton curve,dynamic shear modulus and damping coefficient were obtained in accordance with the dynamic ratio of shear to dynamic shear strain of the reinforced soil under the influence of freeze-thaw cycles,then the calculated skeleton curve and test according to the constitutive model Hardin-Drnevich and the constitutive model Davidenkov were obtained.Comparing the obtained skeleton curves,it was found that the Davidenkov model has the best degree of compliance with the experimental results of the dynamic shear stress and the dynamic shear stress of the modified clay.The Hardin-Drnevich model cannot be applied for the entire range of dynamic shear strain of the cemented soil,therefore the dynamic shear strain is chosen in the range of 0-0.1%.Due to this condition,the experimental results are in good agreement with the model.4.In order to clarify the patterns of changes in the thermal conductivity of clay and modified soil at different soil temperatures,taking into account was carried out the action of freeze-thaw cycles an experimental study of the thermal conductivity of the improved soil.The results show that the reinforcing material reduces the thermal conductivity of the clay,and the thermal conductivity of the modified soil decreases with an increase in the number of freeze-thaw cycles.Comparison of the calculated values of the three thermal conductivity models with the measured values of the thermal conductivity coefficients in this work shows that the Johansen model has the worst prediction accuracy,the improved Johansen model and the Usowicz model have relatively high prediction accuracy and little difference between them.5.An electronic scanning test was conducted,the microstructure of polypropylene and basalt fibers was studied,the microstructure of cement-modified soil and clay was classified and described.Microstructure parameters selected.The structural relationships between soil particles and reinforcing fibers after various freeze-thaw cycles are determined.The microstructural characteristics of the soil reinforced with clay-cement were classified and qualitatively described.According to the results of electron microscopy experiments,was studied the ion composition of soil and fiber samples.A full-scale porosity research method was carried out,the software of data processing software as well as data processing software and other computer image processing methods were used to visually analyze the geometric results of the three-dimensional anisotropy of the interaction between soil particles and cement particles in cement-reinforced clay.