The solution of the double-sphere model and experimental research of the longterm shear strength of frozen sand based on spherical template indenter test北大核心CSCD

The distribution of frozen soil in our country is very broad, and the area of permafrost alone accounts for 22. 4% of the total land area. As a special kind of soil, frozen soil has many properties that thawing soil does not have due to the influence of ice cement in the soil. Among the many properties of frozen soil, the deformation and strength of frozen soil are the basic problems affecting engineering construction in frozen soil areas. The spherical template indenter test is widely used in the test of the mechanical properties of frozen soil because of its simple test process and relatively accurate test results. Compared with the conventional triaxial test or direct shear test, the test process of the spherical template indenter test is simple and easy to implement, the test period is short, and the sample preparation requirements are low. The advantage of effective cohesion is more significant. Therefore, based on the spherical template indenter test of the frozen soil, this paper estimates the strength and mechanical index of the soil through the indentation depth of the spherical template indenter test, and establishes the relationship between the force of the sample and the indentation depth of the indenter test. The specific test method is as follows:take the water-saturated frozen sandy soil made of different particle size groups(the moisture content of the sample is affected by the particle size in the saturated state)as the research object, study the variation law of the depth of the frozen soil sample pressed into the soil by the spherical indenter with time under the conditions of different fixed loads. By comparing and referring to the frozen sands of each particle size group, the long-term equivalent cohesion of the frozen sands of different particle size groups is summarized. The change law of force(long-term shear strength)with time, and the research method of elastic mechanics to solve space problems, summed up the mutual conversion between the depth St of spherical template indenters pressed into frozen sand samples under different fixed load test conditions relation. The research results show that the long-term shear strength of frozen sand based on the spherical mold test is positively correlated with its particle size. At the same time, since the ice content of frozen soil samples is proportional to its particle size, the long-term shear strength of frozen sand is also proportional to the test. The ice content of the sample increases year-on-year;the long-term shear strength of the frozen sand is related to the maximum contact pressure on the contact surface between the frozen soil and the indenter during the test, which can be expressed as Ct = γq0. The size of the relationship coefficient γ is inversely proportional to the diameter of the spherical indenter. In this paper, the spherical indenter is selected as 22 mm, and γ=3. 82×10-3. By establishing the relationship between the maximum contact pressure q0 and the long-term shear strength Ct When the maximum contact pressure q0 is the same under different fixed loads, the long-term shear strength Ct is also the same. According to this, the depth curve and the freezing depth of the frozen sand pressed into the soil by the spherical indenter over time under different fixed loads can be converted. Long-term shear strength curve of frozen sandy soil with time. It has been verified by experiments that the conversion curve of the depth of the indenter pressed into the soil with time under a fixed load of 7. 0 kg is highly consistent with the measured curve of the depth of the indenter pressed into the soil with time under a fixed load of 5. 1 kg and 7. 0 kg. © 2022 Nanjing Forestry University. All rights reserved.

The solution of the double-sphere model and experimental research of the long-term shear strength of frozen sand based on spherical template indenter test

The distribution of frozen soil in our country is very broad， and the area of permafrost alone accounts for 22.4% of the total land area. As a special kind of soil， frozen soil has many properties that thawing soil does not have due to the influence of ice cement in the soil. Among the many properties of frozen soil， the deformation and strength of frozen soil are the basic problems affecting engineering construction in frozen soil areas. The spherical template indenter test is widely used in the test of the mechanical properties of frozen soil because of its simple test process and relatively accurate test results. Compared with the conventional triaxial test or direct shear test， the test process of the spherical template indenter test is simple and easy to implement， the test period is short， and the sample preparation requirements are low. The advantage of effective cohesion is more significant. Therefore， based on the spherical template indenter test of the frozen soil， this paper estimates the strength and mechanical index of the soil through the indentation depth of the spherical template indenter test， and establishes the relationship between the force of the sample and the indentation depth of the indenter test. The specific test method is as follows： take the water-saturated frozen sandy soil made of different particle size groups （the moisture content of the sample is affected by the particle size in the saturated state） as the research object， study the variation law of the depth of the frozen soil sample pressed into the soil by the spherical indenter with time under the conditions of different fixed loads. By comparing and referring to the frozen sands of each particle size group， the long-term equivalent cohesion of the frozen sands of different particle size groups is summarized. The change law of force （long-term shear strength） with time， and the research method of elastic mechanics to solve space problems， summed up the mutual conversion between the depth S_t of spherical template indenters pressed into frozen sand samples under different fixed load test conditions relation. The research results show that the long-term shear strength of frozen sand based on the spherical mold test is positively correlated with its particle size. At the same time， since the ice content of frozen soil samples is proportional to its particle size， the long-term shear strength of frozen sand is also proportional to the test. The ice content of the sample increases year-on-year； the long-term shear strength of the frozen sand is related to the maximum contact pressure on the contact surface between the frozen soil and the indenter during the test， which can be expressed as C_t=\mathrm{\gamma }{q}_{\mathrm{0}}. The size of the relationship coefficient \gamma is inversely proportional to the diameter of the spherical indenter. In this paper， the spherical indenter is selected as 22 mm， and \gamma=3.82×10^-3. By establishing the relationship between the maximum contact pressure q_{\mathrm{0}} and the long-term shear strength C_t When the maximum contact pressure q_{\mathrm{0}} is the same under different fixed loads， the long-term shear strength C_t is also the same. According to this， the depth curve and the freezing depth of the frozen sand pressed into the soil by the spherical indenter over time under different fixed loads can be converted. Long-term shear strength curve of frozen sandy soil with time. It has been verified by experiments that the conversion curve of the depth of the indenter pressed into the soil with time under a fixed load of 7.0 kg is highly consistent with the measured curve of the depth of the indenter pressed into the soil with time under a fixed load of 5.1 kg and 7.0 kg.