This paper presents the dynamic compressive stress response of pavement‐subgrade induced by moving heavy‐duty trucks. In order to study the distribution characteristic of dynamic pressure of pavement‐subgrade in more detail, truck loadings, truck speeds, and dynamic pressure distributions at different depths were monitored under twenty‐five working conditions on the section of Qiqihar‐Nenjiang Highway in Heilongjiang Province, China. The effects of truck loading, truck speed, and depth on dynamic compressive stress response can be concluded as follows: (1) increasing truck loading will increase the dynamic pressure amplitude of subgrade‐pavement and dominant frequencies are close to the characteristic frequencies caused by heavy‐duty trucks at the speed of 70 km/h; (2) as truck speed increases, the dynamic pressure amplitudes of measuring points have an increasing tendency; the dynamic pressure spectrums are also significantly influenced by truck speed: the higher the truck speed, the wider the spectrum and the higher the dominant frequencies; (3) as depth increases, the dynamic pressure amplitudes of measuring points decrease rapidly. The influence of the front axle decreases gradually until disappearing and the compressive stress superposition phenomenon caused by rear double axles can be found with increasing depth.

Although frozen soil is in nature the discrete material, it is generally treated as the continuum material. The mechanical properties of frozen soil are so complex to describe adequately by conventional continuum mechanics method. In this study, the nonlinear microcontact model incorporating rolling resistance is proposed to investigate the particle-scale mechanical properties of frozen soil. The failure mechanism of frozen soil is explicated based on the evolution of contact force chains and propagation of microcracks. In addition, the effects of contact stiffness ratio and friction coefficient on stress-strain curve and energy evolution are evaluated. The results show that the nonlinear microcontact model incorporating rolling resistance can better describe the experimental data. At a higher axial strain, the contact force chains near shear band which can give rise to the soil arch effect rotate away from the shear band inclination but not so much as to become perpendicular to it. The propagation of microcracks can be divided into two phases. The stress-strain curve is strongly influenced by contact stiffness ratio. In addition, friction coefficient does not significantly affect the initial tangential modulus. Compared with frictional coefficient, the effect of contact stiffness ratio on stress-strain curve and energy evolution is greater.

As is widely accepted, cumulative strain and improvement mechanisms of stabilized soil are critical factors for the long-term reliable operation of expressways and high-speed railways. Based on relevant research findings, xanthan gum biopolymer is regarded as a green and environmentally friendly curing agent in comparison to traditional stabilizers, such as cement, lime, and fly ash. However, little attention has been devoted to the cumulative strain and improvement mechanisms of soil reinforced by xanthan gum biopolymer under traffic loading. In the current study, a series of laboratory tests, including cyclic triaxial tests and scanning electron microscopy (SEM) tests, were performed to investigate this issue in more detail. The influences of xanthan gum biopolymer content, curing time, moisture content, confining pressure, and cyclic stress amplitude on cumulative strain were analyzed. In addition, the cumulative strain model was proposed to provide a good description of experimental data. Finally, the microscopic structure of soil reinforced by xanthan gum biopolymer was analyzed to discuss the improvement mechanisms. The results show that the cumulative strain is strongly influenced by xanthan gum biopolymer content. For a given number of loading cycles, the greater the confining pressure, the smaller the cumulative strain. The calculated results of the cumulative strain model show a good agreement with test data. The “flocculent” hydrogel can form a denser structure and greater bonding strength in comparison to the “branch-like” and “net-like” hydrogels.

The accumulative strain of sand-containing soft soil is crucial to the stability of the construction of embankment engineering such as expressways and high-speed railways. However, little attention has been devoted to the accumulative strain of sand-containing soft soil. In the current study, a series of cyclic triaxial tests were performed to investigate the accumulative strain of sand-containing soft soil reinforced by cement and sodium silicate under traffic loading. In addition, the accumulative strain model was proposed to describe the characteristic of accumulative strain. The results show that for the specimens with a high sand content (25%, 30%, and 35%), the accumulative strain increases obviously with the increase of the sand content. For the specimen with a cement content of 3%, the accumulative strain increases distinctly with the increasing loading time. The accumulative strain is strongly influenced by confining pressure. When the repeated cyclic stress amplitude is greater than 0.17 kN, the increase rate of accumulative strain is greater. The shorter the curing time is, the greater the accumulative strain is. The calculated results of the accumulative strain model show a good agreement with test data. Hence, the accumulative strain model can better describe the characteristic of accumulative strain.

Land resources are being depleted due to global climate change, and as a result, infrastructures such as expressways and high-speed railways have no option but to be built in soft soil regions. Hence, the cyclic and post-cyclic behaviors of soft soil are vitally important. However, little attention has been devoted to this issue. In the current study, a series of cyclic triaxial tests and standard monotonic loading tests were carried out in order to investigate the cyclic and post-cyclic behavior of stabilized sand-containing soft soil. In addition, the stiffness evolution index model was proposed to describe the characteristics of stiffness evolution. The results show that for a given number of loading cycles, stiffness almost linearly decreases with the increase in sand content. The higher the confining pressure is, the greater the stiffness is. The cement content has the greatest impact on the stiffness evolution index. The stiffness evolution index model can provide a good description of experimental data. The initial value of post-cyclic axial strain is non-zero due to the accumulative strain caused by previous cyclic loading. Post-cyclic stress increases rapidly within a small range of strain and can reach peak stress with great speed. The post-cyclic initial tangent modulus increases from 1602 kPa to 4803 kPa as the cement content increases from 6% to 12%.

For the major projects built on the soft soil area in cold regions, the effective treatment of deep soft soil layer and the stable bearing capacity of foundation are of great importance. In this paper, the finite element model of embankment-CFG piles composite soft soil foundation for D3K629-D3K629+950 of Harbin-Dalian railway is established based on ABAQUS. The depth and regional distribution of freezing and thawing and distribution law of temperature field of CFG piles are studied. The results show that the horizontal position of 0-degree line is higher and the protective effect of embankment on the foundation is obvious when the embankment is higher. The embankment almost has no effect on the CFG piles near embankment foot. For the middle pile at the center of the embankment, the protection effect of the embankment is remarkable.