Experimental investigation on static and dynamic resilient moduli of compacted fine soil

To investigate the static and dynamic resilient modulus of fine soil, and adapting to the new design code and maintenance system of highway subgrade in China, a series of static and dynamic tests were carried out according to the standard laboratory test methods (JTG E40-2007 and JTG D30-2015, respectively). The effects of initial water content, compactness and freeze-thaw cycles on the static and dynamic resilient moduli of fine soil were investigated and analyzed. Experimental test results show that with increasing water content, dry density and freeze-thaw cycles, the static moduli reduces about 10.2%~40.0%, 14.4%~45.5%, and 24.0%~50.3%, and dynamic moduli reduces about 10.9%~90.8%, 2.5%~38.4%, and 0.0%~46.0%, respectively. Then, the empirical mathematical relationship between static and dynamic resilient moduli was established under different water content, dry density and freeze-thaw cycles. The investigation results can be used to determine the dynamic modulus of fine soil by widely used static modulus, which could meet the requirement of adopting dynamic modulus index in new specification.     

Influence of repeated freeze-thaw on dynamic modulus and damping ratio properties of silty sand

Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which...     

Finite element analysis on deformation of highembankment in heavy-haul railway subjected to freeze-thaw cycles

Finiteelement simulations are increasingly providing a versatile environment for this topic. In this study, a two-dimensional finite element analysis is conducted to predict the deformation of highembankment in Bazhun heavy-haul railway, China. A recently developed nonlinear softening-type constitutive model is utilized to model the behavior of subgrade filling materials subjected to freeze-thaw cycles. For the convenience of practical application, the dynamic loading induced by a vehicle is treated as a quasi-static axle load. The deformation of this embankmentwith different moisture content under freeze-thaw cycles is compared. The results show that when subjected to the first freeze-thaw cycle, the embankmentexperienced significant deformation variations. Maximum deformation was usually achieved after the embankment with optimum moisture content experienced six freeze-thaw cycles, however, the embankment with moisture content of 8.0% and 9.5% deforms continuously even after experiencing almost ten freeze-thaw cycles. Overall, this study provides a simple nonlinear finite element approach for calculating the deformation of the embankmentinchanging climate conditions.     

不同坡角公路路基流场的风洞实验

根据内蒙古S315一级公路黑风口路段风沙危害现状,基于风洞模拟实验,采用毕托管测定不同坡角路基模型断面的风速,通过对流场分布、风速廓线及风速减弱率的分析探讨沙漠公路风沙危害的形成机理。结果表明：坡角对路基两侧的积沙范围和风蚀强度有重要影响。风速一定时,坡角越大,路基两侧积沙范围越大,与之对应的防护范围也应加大。路基坡角一定时,路基背风侧积沙范围随风速增大整体可能呈扩大趋势,坡角越大,扩大趋势越不明显,导致大量沙粒堆积在背风坡脚附近,这就需在坡角较大的公路背风侧多设置几道阻沙栅栏和固沙方格来降低风速、防治沙害。风沙流对迎风坡脚和迎风坡肩的风蚀作用最强,在实际应用中,应重点对这两个部位进行工程砌护,以防路基塌陷造成交通事故威胁公路安全运营。     

Influence of fines content on the anti-frost properties of coarse-grained soil

This paper aims to determine the optimal fines content of coarse-grained soil required to simultaneously achieve weaker frost susceptibility and better bearing capacity. We studied the frost susceptibility and strength properties of coarse-grained soil by means of frost heaving tests and static triaxial tests, and the results are as follows:(1) the freezing temperature of coarse-grained soil decreased gradually and then leveled off with incremental increases in the percent content of fines; (2) the fines content proved to be an important factor influencing the frost heave susceptibility and strength properties of coarse-grained soil. With incremental increases in the percent content of fines, the frost heave ratio increased gradually and the cohesion function of fines effectively enhanced the shear strength of coarse-grained soil before freeze-thaw, but the frost susceptibility of fines weakened the shear strength of coarse-grained soil after freeze-thaw; (3) with increasing numbers of freeze-thaw cycles,the shear strength of coarse-grained soil decreased and then stabilized after the ninth freeze-thaw cycle, and therefore the mechanical indexes of the ninth freeze-thaw cycle are recommended for the engineering design values; and (4) considering frost susceptibility and strength properties as a whole, the optimal fines content of 5% is recommended for railway subgrade coarse-grained soil fillings in frozen regions.     

Application of dynamic compaction and rolling compaction in the subgrade improvement of Qarhan-Golmud Highway

Melt shrinkage, salt bulge, and corrosiveness are common problems with saline soils, which damage highway foundations and cause huge financial losses. In order to improve the saline soil subgrade, dyna...     

The effect of subgrade inhomogeneity induced by freeze-thaw on the dynamic response of track-subgrade system

The developed vertical coupling model of Vehicle-Track-Subgrade which considered subgrade layer vibration is present-ed. The equations of motion for the ballast, top and bottom subgrade layers are pres...     

大柴旦盐湖采卤区地层剖面盐渍土基本类型及其抗剪强度试验研究

选取柴达木盆地大柴旦盐湖采卤区作为试验区,对区内地层剖面盐渍土的基本类型进行划分,即通过测定Na+、Mg2+、Cl-等易溶盐离子的方法,得出区内采卤区地层剖面盐渍土的主要类型是以亚氯盐渍土为主。在此基础上,对盐渍土进行扰动试样的室内直剪试验研究,以获取抗剪强度指标粘聚力c值与内摩擦角φ值。试验结果表明,该区盐渍土的含盐量由地表开始向下呈逐渐降低趋势,即由地表的6.89%降到地下4.5 m处的1.11%。粘聚力c值主要受试样含水量大小的影响,表现出随着含水量的增加,粘聚力c值呈降低现象,即当含水量由19.8%上升至23.3%时,粘聚力c值由35.4 k Pa下降至24.9 k Pa,下降率约为29.7%;而当含水量由23.3%下降至17.4%时,粘聚力c值则由24.9 k Pa上升至34.1 k Pa,上升率约为36.9%。内摩擦角φ值则受试样粒径影响相对较为明显,随着试样中粘粒含量的增多,粗粒含量相对减少,内摩擦角呈逐渐增大的趋势,即由24.1°上升至33.3°,增加率约为37.3%。随着试样中含盐量的增加,粘聚力c值和内摩擦角φ值均呈线性增加趋势。该研究成果将有助于进一步探讨含水量、颗粒大小以及含盐量对盐渍土试样抗剪强度变化的影响,且对区内盐田及其相应的基础设施建设有一定的理论指导意义。     

Laboratory and field performance of recycled aggregate base in a seasonally cold region

The objective of this project was to characterize the freeze-thaw properties of recycled concrete (RCA) and asphalt (RAP) as unbound base and to assess how they behaved in the field for nearly 8 years. This paper includes an examination of existing information, laboratory studies of freeze-thaw behavior, and evaluation of data from MnROAD field-test sections in a seasonally cold region, i.e., in Minnesota, USA. Test sections were constructed using recycled materials in the granular base layers at the MnROAD test facility. One test section included 100% RAP, another 100% RCA, a third one a 50/50 blend of RCA/natural aggregate, and a fourth one only natural aggregate (Class 5) as a control. The stiffness (i.e., elastic modulus) was monitored during construction and throughout the pavement life by the Minnesota Department of Transportation, along with the variation of temperatures and moisture regimes in the pavement to determine their effects on pavement performance. The resilient modulus of each material was determined by bench-scale testing in accordance with NCHRP 1-28a, as well as by field-scale tests incorporating a falling-weight deflectometer. Specimens were subjected to as many as 20 cycles of freeze-thaw in the laboratory, and the change in their resilient modulus was measured. In the field-test sections constructed with the same materials as the base course, temperature, moisture, and field modulus (from falling-weight deflectometer tests) were monitored seasonally for nearly 8 years. From the temperatures in the base course layer, the number of freeze-thaw cycles experienced in the field was determined for each test section. Inferences were made relative to modulus change versus freeze-thaw cycles. Conclusions were drawn for long-term field performances of the recycled base (RAB) in comparison to natural aggregate.     

两种典型高等级公路路基断面风沙过程的风洞模拟

高等级公路路基中央构筑物不同,对路基断面风沙输移-堆积过程产生的影响不同。选取两种典型高等级公路路基,对其风沙输移-堆积过程进行了风洞模拟试验。结果表明：当路基模型高度为4 cm（路基模型与实际路基比例为1∶100）时,随着风速增大,防眩板路基背风侧积沙范围增大较为明显;在相同风速条件下,防眩网路基两侧积沙范围较大,对应的工程防护范围也应较大。当路基模型高度为8 cm时,防眩网路基路面积沙较多,背风侧积沙范围较大。路基越高,相应的工程防护范围应设置的较大一些,并加强对路基迎风坡的维护。建议在两种高等级路基背风侧5H（H为路基高度）以外范围增设风沙防护设施,尤其是防眩网路基,防止沙粒堆积被反向气流携带上路,影响交通安全。防眩板路基背风坡沙物质积累较多,为了防止背风坡积沙变成二次沙源危害道路行车安全,防眩板路基背风侧也需重点防护。在主风向单一的沙漠地区,高等级公路路基中央隔离带的防眩设施宜选择防眩板。     

Test on dynamic characteristics of subgrade of heavy-haul railway in cold regions

Dynamic characteristics of heavy-haul railway subgrade under vibratory loading in cold regions are investigated via low-temperature dynamic triaxial tests with multi-stage cyclic loading process. The relationship between dynamic shear stress and dynamic shear strain of frozen soil of subgrade under train loading and the influence of freezing temperatures on dynamic constitutive relation, dynamic shear modulus and damping ratio are observed in this study. Test results show that the dynamic constitutive relations of the frozen soils with different freezing temperatures comply with the hyperbolic model, in which model parameters a and b decrease with increasing freezing temperature. The dynamic shear modulus of the frozen soils decreases with increasing dynamic shear strains initially, followed by a relatively smooth attenuation tendency, whereas increases with decreasing freezing temperatures. The damping ratios decrease with decreasing freezing temperatures. Two linear functions are defined to express the linear relationships between dynamic shear modulus (damping ratio) and freezing temperature, respectively, in which corresponding linear coefficients are obtained through multiple regression analysis of test data.     

Sandstone-concrete interface transition zone (ITZ) damage and debonding micromechanisms under freeze-thaw

The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete surface is easily affected by freeze-thaw cycles, resulting in interface damage, debonding and even supporting failure. Understanding the micromechanisms of the damage and debonding of the rock-concrete interface is essential for improving the interface protection.Therefore, the micromorphology, micromechanical properties, and microdebonding evolution of the sandstone-concrete interface transition zone(ITZ) under varying freeze-thaw cycles(0, 5, 10, 15, 20) were studied using scanning electron microscope, stereoscopic microscope, and nano-indentation. Furthermore, the distribution range and evolution process of ITZ affected by freeze-thaw cycles were defined. Major findings of this study are as follows:(1) The microdamage evolution law of the ITZ under increasing freeze-thaw cycles is clarified, and the relationship between the number of cracks in the ITZ and freeze-thaw cycles is established;(2) As the number of freeze-thaw cycles increases, the ITZ's micromechanical strength decreases, and its development width tends to increase;(3) The damage and debonding evolution mechanisms of sandstone-concrete ITZ under freeze-thaw cycles is revealed, and its micromechanical evolution model induced by freeze-thaw cycles is proposed.     

Investigation of insulation layer dynamic characteristics for high-speed railway

Dynamic performance of insulation is one of the key parameters during the insulation application for high-speed railway subgrade. This paper conducted laboratory and field tests for the materials and dynamic load,especially for thermal performance, elastic deformation, and accumulated deformation of insulation materials.Experiment results show that mechanical properties of insulation layer structure are stable, which satisfies the requirements of the high speed railway.     

The influence of freeze-thaw cycles on the granulometric composition of Moscow morainic clay

The freeze-thaw cycling process considerably changes the composition,structure,and properties of soils.Since the grain size is the most important factor in determining soil characteristics,our current research primarily aims to investigate dynamic changes of the soil fraction when exposed to freeze-thaw conditions.We observed two series of Moscow morainic clayey specimens(g QmII):(I) the original series,and(II) the remolded series.We subjected each series of soil specimens to different frequencies of freeze-thaw cycles(3,6,20,and 40 cycles),and we used granulometric tests to analyze both series before and after exposure to freeze-thaw conditions.As a result of our experiments,the granulometric compositions tended to be distributed evenly after 40 freeze-thaw processes(i.e.,content of fraction for 0.1–0.05 mm was increased after 40 freeze-thaw cycles) because the division of coarse grains and the aggregation of fine grains were synchronized during the freeze-thaw process.The soil grains in both series changed bi-directionally.In the original series,changes of the sand grains were conjugated with the clay grains,and in the remolded series,changes of the sand grains were conjugated with the silt grains,because potential energy difference caused the division and aggregation processes to relate to the counteraction process.The even distribution of soil grain size indicated the state of equilibrium or balance.The granulometric compositions were altered the most during the sixth freeze-thaw cycle,because the coefficient of the intensity variation of the grain fineness(Kvar) had its maximum value at that time.     

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.     

Investigation of Soil Shear-Strength Parameters and Prediction of the Collapse of Gully Walls in the Black Soil Region of Northeastern China

The collapse of gully walls is an important mode of gully erosion, and it depends strongly on two soil shear-strength parameters: cohesion and the internal friction angle. However, little research has examined these parameters in China's black soil region. In the present study, we sampled six groups of surface soils from four different land uses, and two groups of soils at depths of 30 cm and 60 cm. The cohesion (c) and internal friction angle (φ) of each group were determined at 10 levels of water content. The results show that c increased with increasing water content until a certain level (12% for the surface soils, and 14% for the deeper soils), after which c decreased. Internal friction angle generally decreased with increasing water content. We developed a model predicting collapse of gully walls based on four parameters: dry bulk density, water content, crack depth, and the width of the soil collapse. The model predicts that soil collapse would occur at two levels of water content: dry and wet conditions. Field data showed that collapse only occurred under the wet condition; the critical mass water content given by the model is between 31.0% and 33.8% moisture.     

Determination of long-term strength of frozen loess after numerous freeze-thaw cycles

In order to determine the changing rule of long-term frozen soil strength and elucidate the connection between long-term strength and soil physical properties,frozen loess was subjected to 4,6,8,10,and 50 freeze-thaw cycles,under closed-state conditions in a constant-temperature box.The frozen samples were tested on a spherical template indenter,and the results show that under the effect of repeated freeze-thaw cycles,the long-term strength of frozen loess decreased; changes in the mechanical property indices were highly unstable during the first 10 cycles; the soil strength and density were the greatest at the eighth cycle while the void ratio was the smallest; and after eight cycles all of the indices had less fluctuation and certain rising or falling tendencies.By converting the number of freeze-thaw cycles into elapsed time in the tests,three different forecasting methods of long-term soil strength could be assessed and the soil equivalent cohesive force after 10 years,20 years,or 30 years could be estimated.     

大型振动台试验相似材料研究

在分析总结近几年岩土工程物理模拟试验中常用的岩质相似材料研究现状的基础上,采用重晶石粉、石英砂、石膏、甘油配制振动台模型试验相似材料,通过不同配比的材料力学试验,考虑相似材料的含水率,分析研究了各种材料含量以及含水率变化对相似材料物理力学性质的影响规律,发现含水率对材料的抗压强度、粘聚力、弹性模量、摩擦角有较大影响,根据试验结果最终确定了振动台试验相似材料配比.试验结果证明,该相似材料力学指标稳定,能很好地满足相似材料的选材要求,便于一次性浇注较大尺寸规模的模型试件,适用于大型振动台等物理模拟试验.     

沙土内摩擦角与粒径、含水率及天然坡角的关系

沙的摩擦性质是影响沙丘形态的重要因素之一,研究沙土内摩擦角对于探讨床面沙波形态、沙丘流动性、沙丘稳定性、沙丘防护等都具有实际意义。本文实验研究了内摩擦角与粒径、含水率及天然坡角的定量关系。结果表明:当粒径从<0.125 mm增大到0.315～0.4 mm时,内摩擦角从32.25°减小到28.06°; 而粒径从0.315～0.4 mm增大到0.63～0.8 mm时,内摩擦角却从28.06°增大到31.47°。主要原因是,粒径小时颗粒的比表面积大,颗粒间接触面积大使得内摩擦角大。粒径大时,颗粒表面棱角突出,颗粒间嵌入咬合作用明显使得内摩擦角大。当含水率从0%增加到15%时,内摩擦角从29.07°增大到31.84°; 而含水率从15%增加到20%时,内摩擦角却从31.84°减小到30.75°。主要原因是一定含水率下沙土表现出黏聚性,而高含水率下水的润滑作用使得颗粒间摩擦力减小。内摩擦角与天然坡角都反映沙土摩擦特性,两者相等。     

Review of the influence of freeze-thaw cycles on the physical and mechanical properties of soil

Seasonally frozen soil is a four-phase material and its physical-mechanical properties are more complex compared to the unfrozen soil. Its physical properties changes during the freeze-thaw process; repeated freeze-thaw cycles change the characteristics of soil, which can render the soil from an unstable state to a new dynamic equilibrium state. The freezing process changes the structure coupled between the soil particle arrangements, which will change the mechanical properties of the soil. The method of significance and interaction between different factors should be considered to measure the influence on the properties of soil under freeze-thaw cycles.