Investigation on the properties of compacted silty clay subjected to electro-osmosis using bender element

The moisture content of subgrade soil in seasonally frozen regions is often higher than its optimum value,leading to a decline in mechanical properties and a reduction in subgrade bearing capacity.Electro-osmosis has shown promise as a technology for controlling subgrade moisture,but significant heterogeneity has also been observed in treated soil.This study investigates the impact of electro-osmosis on soil stiffness through a series of bender element tests of compacted clay.The effects of dry density and supply voltage on the performance of electroosmosis treatment and the layered structure and anisotropy of the soil were analyzed.The results show that electro-osmosis treatment increased the shear wave velocity of the soil by 140% compared to untreated saturated soil and by 70% compared to soil with optimum water content.It has also been found that layered compaction of soil resulted in a layered structure,with electro-osmosis having a more prominent impact on soil near the cathode,resulting in a more pronounced layered structure.Besides,electro-osmosis was found to enhance soil anisotropy,particularly near the anode.Increasing the dry density and voltage levels can help improve soil uniformity.These findings provide insights into the potential use of electro-osmosis in improving soil stiffness,which could benefit various engineering applications.

Field monitoring of differential frost heave in widened highway subgrade

In cold regions,the widened subgrade could produce uneven frost heave that is detrimental to the pavement.This study investigates the differential frost heave characteristics in a widened subgrade.The field monitoring system mainly consists of temperature,moisture,and displacement sensors and distributed optical fiber cables for strain measurement.The monitoring results show that the cooling period in the subgrade is longer than the warming period.Water content in the subgrade changes significantly within 0−2 m below the subgrade surface but stabilizes within 2−5 m.The maximum frost heave occurs from February to March.In comparison,the existing subgrade has a longer freezing period and larger heave value,caused by the higher density and water content inside.Water in the existing subgrade migrates into the new one after widening,leading to frost heave reduction in the existing subgrade.Simultaneously,the traffic loads result in the consolidation of the new subgrade,thus reducing the heave value in the second year.In the third year,the water supply from the existing subgrade facilitates the frost heave in the new subgrade.The tensile strain distributions obtained by the distributed optical fiber cables show that the maximum differential frost heave occurs at the joint between the existing and new subgrades.The differential frost heave gradually stabilizes after three years.Finally,an improved frost heave prediction model is developed based on the segregation potential concept and monitoring results.

A nonlinear interface structural damage model between ice crystal and frozen clay soil

The shear properties of ice-frozen soil interface are important when studying the constitutive model of frozen soil and slope stability in cold regions. In this research, a series of cryogenic direct shear tests for ice-frozen clay soil interface were conducted. Based on experimental results, a nonlinear interface structural damage model is proposed to describe the shear properties of ice-frozen clay soil interface. Firstly, the cementation and friction structural properties of frozen soil materials were analyzed, and a structural parameter of the ice-frozen clay soil interface is proposed based on the cryogenic direct shear test results. Secondly, a structural coefficient ratio is proposed to describe the structural development degree of ice-frozen clay soil interface under load, which is able to normalize the shear stress of ice-frozen clay soil interface,and the normalized data can be described by the Duncan-Chang model. Finally, the tangent stiffness of ice-frozen clay soil interface is calculated, which can be applied to the mechanics analysis of frozen soil. Also, the shear stress of ice-frozen clay soil interface calculated by the proposed model is compared with test results.

Numerical simulation of electroosmosis in unsaturated compacted clay

The moisture content of a road subgrade in cold regions will increase after freeze-thaw cycles,resulting in subgrade strength and stiffness losses.Electroosmosis is widely used in treating saturated soft soils to decrease the moisture content.The induced moisture migration during electroosmosis in unsaturated soil is much more complex than that of saturated soil because of a series of nonlinear changes in soil properties.This study first uses an exponential function to characterize the relationship between electroosmotic permeability and saturation degree.Then,a one-dimensional model is developed to simulate the electroosmosis-induced moisture migration in unsaturated soil.Simulation results show that electroosmosis reduces the saturation degree of the unsaturated soil,indicating that it can be applied to subgrade dewatering.Key parameters such as soil pore size distribution coefficient,air entry value,and effective voltage significantly affect moisture migration.Electroosmotic properties of unsaturated soils are extremely important to the efficiency of electroosmosis.

Recent developments in asphalt-aggregate separation technology for reclaimed asphalt pavement

Reclaimed asphalt pavement(RAP)has significant recycling value because it contains nonrenewable resources including asphalt and aggregate.However,thus far,only a small part of RAP materials can be used in the con-struction of recycled asphalt pavement,and the usage is regarded as a low-value utilization in the underlying layers.One of the most important reasons for this shortcoming is the problem of false particle size and pseudo gradation of RAP materials.Therefore,identifying suitable asphalt-aggregate separation technology is essential for improving the utilization of RAP materials in recycled asphalt mixture and enhancing the construction quality of recycled asphalt pavement.To address this,the paper performed a systematic review of asphalt-aggregate separation technologies for processing RAP materials and their prospects.Firstly,based on the composition of the asphalt mixture and the characteristics of RAP materials after aging,the key RAP separation technologies were proposed.Then,the concept,principle,and implementation methods of physical,chemical,and biological sep-aration methods of RAP materials were comprehensively analyzed.Moreover,the advantages and disadvantages of various separation technologies were discussed by comparing them with the related technologies in the petrochemical industry.The application prospects of various asphalt-aggregate separation methods for RAP materials can provide a reference for upgrading and expanding solid waste recycling technology for asphalt pavement.

Determination of allowable subgrade frost heave with the pavement roughness index in numerical analysis

Frost heave is an upward swelling of soil during cryogenic conditions in cold regions. It is caused by the accumulation of ice crystals in subgrade soil, which grow upwards when freezing temperatures penetrate into the subgrade. This study establishes the allowable soil subgrade frost heave based on the roughness standard of asphalt pavement in China, and aims to balance the pavement design and frost heave resistance of subgrades in cold regions. We formulated a mechanical model of pavement supported by the boundary conditions of differential frost heave, based on the elastic layered system theory. The differential soil subgrade frost heave was modeled as a sinusoidal function, and the allowable frost heave and the roughness index were modeled as the displacement boundaries for the top and bottom of the pavement structure. Then the allowable frost heave was back-calculated according to the roughness standard. Numerical results show that the allowable frost heave depends on the pavement structure, material properties, the highway grade, and other factors. In order to ensure that the actual soil subgrade frost heave is lower than the allowable frost heave, pavement structures and materials need to be selected and designed carefully. The numerical method proposed here can be applied to establish the frost heave resistance of subgrade when the pavement structure and materials are determined.

Multi-Scale Damage Model for Quasi-Brittle Composite Materials

In the present paper,a hierarchical multi-scale method is developed for the nonlinear analysis of composite materials undergoing heterogeneity and damage.Starting from the homogenization theory,the energy equivalence between scales is developed.Then accompanied with the energy based damage model,the multi-scale damage evolutions are resolved by homogenizing the energy scalar over the meso-cell.The macroscopic behaviors described by the multi-scale damage evolutions represent the mesoscopic heterogeneity and damage of the composites.A rather simple structure made from particle reinforced composite materials is developed as a numerical example.The agreement between the fullscale simulating results and the multi-scale simulating results demonstrates the capacity of the proposed model to simulate nonlinear behaviors of quasi-brittle composite materials within the multi-scale framework.

Numerical simulation of dynamic response of subgrade under moving heavy truck in cold regions

This paper reports on the dynamic response of highway subgrade under moving heavy truck in cold regions. Numerical simulations are performed in two stages. In the first stage, the moving heavy truck vibration, induced by road roughness, is calculated through a three-dimensional dynamic interaction model of heavy truck-pavement-subgrade, and the time-histories of nodal loads on the top of the base are calculated through this model. In the second stage, a two-dimensional dynamic finite element model of the base-subgrade-ground system is formulated, using the calculated nodal loads from the first stage as input. The dynamic response of the subgrade is validated by field measurements, and the effects of truck type, axle loading, running speed, and road roughness on the vertical dynamic stress in the unfrozen period and the spring thawing period are analyzed and discussed.

梯度功能复合路面设计原理与实现方法

路面是道路工程的主体结构,由多个结构层和功能层组成,它应同时满足车辆荷载、水、温度作用下的耐久性、行车安全性与舒适性要求.然而,目前沥青路面的结构寿命和服役性能远未达到人们对路面长寿命和高性能的期望.其原因不仅仅是材料因素与施工质量问题,还在于现有设计理论与指标体系尚不能满足长寿命路面设计的需要,路面材料-结构-工艺一体化的设计原则也未得到有效贯彻.由于设计年限较短,现有路面材料的力学性能与疲劳寿命很容易满足设计年限内重复荷载作用的要求.随着路面长寿命设计目标的提升,构建新的路面设计理论体系也成为关键性科学问题.因此,为探究路面结构的变革和发展,本文首先从沥青路面的结构性破坏特征出发,探讨了路面开裂类型及其产生的细观机制,明确了路面材料组成特性和层状结构界面状态对开裂控制的作用原理;其次,在总结分析路面弹性层状理论体系的基础上,提出了梯度功能复合路面设计理论与方法,并推荐了梯度功能复合路面的结构组合和设计流程;进而提出采用高性能功能复合材料,并通过弱化或消除界面效应的层间处治技术来实现梯度功能复合路面;最后,结合梯度功能结构设计理念在桥面铺装工程的实践,探索了梯度功能复合路面设计与施工中的关键技术环节.

Nanoparticles-modified polymer-based solar-reflective coating as a cooling overlay for asphalt pavement

The phenomenon of rutting is one of the most serious problems on asphalt pavements.Decreasing the surface temperature of the asphalt pavement is an effective method to solve the rutting problem on asphalt pavements.In this study,a nano-sized-particlesfilled polymer composite was developed as an overlay to reflect solar energy and decrease the surface temperature of asphalt pavements.The overlay was composed of acrylic or epoxy resin filled with nano TiO_(2) or nano TiNO_(2).The solar reflection of the nanoparticle-filled polymers was tested,and the results showed that solar reflection effectiveness of the TiO_(2)/acrylic composite reached the highest value.The results of outdoor temperature tests indicate that the solar-reflective overlay could decrease the surface temperature of asphalt pavements by about 10℃ when the pavement temperature is about 60℃.