共查询到20条相似文献，搜索用时 810 毫秒
1.
两种典型高等级公路路基断面风沙过程的风洞模拟 总被引：1，自引：0，他引：1
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。 相似文献
2.
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. 相似文献
3.
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... 相似文献
4.
The temperature distributions of different parts of a subgrade were analyzed based on the results of three years of monitoring data from the Harbin-Qiqihaer Passenger Dedicated Line, a high-speed railway, including the slope toes, shoulders, and natural ground. The temperature variation with time and the maximum frozen depths showed that an obvious sunny-shady effect exists in the railway subgrade, which spans a seasonal frozen region. Development of frost heave is affected by the asymmetric temperature distribution. The temperature field and the maximum frozen depths 50 years after the subgrade was built were simulated with a mathematical model of the unsteady phase transition of the geothermal field. 相似文献
5.
Recent years have seen a large number of high-speed railways built and will be built in seasonal frozen soil regions of China. Although high-speed railways are characterized by being fast, comfortable and safe, higher standards for deformation of the railways' frozen subgrade are required. Meanwhile, changes in subgrade soil temperatures are the main factors affecting the deformation of frozen subgrade. Therefore, this paper selected typical test subgrade sections of the Harbin–Qiqihar Line, a special line for passenger transport built in the deep seasonal frozen soil regions of China, to monitor field temperatures. Also, the temperature changing laws of railways' subgrade in this region was analyzed by using testing data, the aim of which is to provide a technical support for future design and construction of buildings and structures in a deep seasonal frozen soil region. 相似文献
6.
中国沙漠地区风积沙路基强度参数试验研究——以塔克拉玛干、毛乌素沙漠公路为例 总被引：1，自引：1，他引：0
在中国沙漠地区选取典型路段,对风积沙路基进行强度测定。通过现场承载板试验,并分析已有的各种资料,发现野外实测的风积沙路基回弹模量普遍较高,明显高于现行有关规范推荐的砂性土或土质砂的路基回弹模量建议值,高出部分多在30%以上,已经明显地对路基路面的结构设计产生了不利影响。在此基础上,为能充分利用风积沙的强度特性,降低沙漠公路造价,通过进一步分析,提出了中国各主要沙漠地区及不同等级公路的风积沙路基回弹模量设计值。 相似文献
7.
In order to improve the engineering stability of saline soil of high chloride content in the Chaerhan salt lake region, six typical characteristics saline soil samples were selected, and tests on their... 相似文献
8.
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. 相似文献
9.
In order to assess and improve the engineering stability of saline soil with high chloride content along a 40-km section of the Chaerhan-Golmud Highway in northwestern China, more than 200 monitoring p... 相似文献
10.
不同坡角公路路基流场的风洞实验 总被引：2，自引：2，他引：0
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。 相似文献
11.
Alexander Isakov 《寒旱区科学》2013,5(4):0353-0362
The main reasons for a breach of trouble-free operation of the subgrade are the different kinds of deformation, such as train load impact on
subgrade surface, loss of stability to subgrade slope, weight of embankment on the base, and partial or complete failure of the railway track
due to frost heaving. This paper gives a summary of deformation analysis methods being developed in Russia to estimate the operating conditions
of the railway subgrade. 相似文献
12.
Accounting for the solar radiation in thermal regime prediction for railway subgrade in cold regions
This paper presents a comparative analysis of simulation processes of seasonal freezing-thawing of railway subgrade and permafrost degradation, with and without accounting for solar radiation. Also, the effect of sun screens to reduce the degradation of subgrade permafrost under different climatic conditions is numerically substantiated. And finally, the temperature criterion of the origination of permafrost is illustrated. 相似文献
13.
According to the technical characteristics of short fixed wheelbase of a high-speed carriage, a subgrade-track integrated space mechanical response analysis model is proposed for trains under the action of biaxial load after the comparison of the stress distribution characteristics of the ballast track subgrade bed structures for high-speed railway under the action of uniaxial load and biaxial load. The loading threshold value (high-cycle long-term dynamic strength) under the circumstance where the cumulative deformation of subgrade structure gradually develops and finally reaches the convergent state, and its relationship with the foundation coefficient K30 were deduced, based on the characteristics of cumulative deformation evolution obtained from the unit structure filling model test under the action of cyclic loading. In view of structure stability and frost resistance requirements of the railway subgrade in cold regions, technical conditions to maintain good service performance of subgrade structure of high-speed railway ballasted track are discussed and analyzed. Study results show that the additive effect manifests itself obviously for railway train bogies under the action of biaxial load than uniaxial load, which has a significant dynamic effect on the subgrade bed bottom and a slight effect on the surface layer. Thus, the adoption of a biaxial load model in the design of a high-speed railway subgrade accurately reflects the vehicle load. Pursuant to the structure design principle, the design method of the subgrade structure of high-speed railway ballasted track is proposed to meet the technical requirements such as structural strength, bearing stiffness and high-cyclic and long-term stability. Technical indicators are obtained for the variation of thickness of the surface layer of reinforced subgrade bed in the double-layer subgrade mode along with the change of K30 at the subgrade bed bottom. The double-layer structure mode of "closure on the upper layer and drainage on the lower layer" was proposed in order to meet the waterproofing and drainage requirements of the upper layer of the subgrade bed in cold regions. A dense-framework graded gravel filler with weak water permeability at a coefficient of 10-4 cm/s is used on the upper layer and the void-framework graded gravel filler at the water permeability coefficient of 10-2 cm/s is adopted on the lower layer. 相似文献
14.
Temperature and moisture variations were experimentally investigated for the subgrade of the Astana-Burabai Highway, located in the northern region of Kazakhstan.Temperature and moisture were measured by means of specially manufactured sensors,including an element for temperature measurement based on the effect of thermal resistance and an element for moisture measurement through diamagnetic permeability.It was determined that the long-term average depth of frost penetration was 237 cm.In the upper part of the subgrade with 1 m of thickness,the average duration of a frozen condition decreases toward the bottom from 131 days to 117 days,with an average rate of 0.133 day/cm.The unfrozen water content decreases with the negative temperature reduction.In the case of high values of initial moisture (12%~22%),the unfrozen water content does not depend on the initial moisture;and it decreases under the power law,with reduction of negative temperature.In the case of the lowest values of moisture (9%~12%),the unfrozen water content depends also on negative temperature;but its values are considerably lower. 相似文献
15.
16.
In-situ tests and numerical manipulations were conducted for comparison of superior/inferior quality of casing-tube-vacuumized
insulation and polyurethane insulation of freezing apparatuses in relation to non-uniform cold distribution in the multi-coil freezing
layout and the contradiction between large-coil diameter layout of the freezing holes and stability of the headframe base. Tests
show that: (1) under current technology, vacuumized insulation is of short duration due to lack of appropriate applied vacuum; (2)
after the freezing pipe is insulated with polyurethane, the temperature gradient is less than no insulation, and the temperature difference
between insulated and non-insulated apparatuses is stable as the freezing period increases. Finally, it is pointed out that
polyurethane insulation is quite efficient in present technical freezing construction. 相似文献
17.
In order to study the shear behavior of coarse-grained fillings taken from the subgrade bottom layer of a cold region high-speed railway, large scale direct shear tests were conducted with different normal pressures, water contents and temperatures. The results indicate that the relationship between shear displacement and shear stress changed from strain-softening at lower normal pressures to strain-hardening at higher normal pressures, in both unfrozen and frozen states. This phenomenon was mainly due to the shear dilatation deformation effect. The shear displacement-shear stress curves show similar stages. Besides, the shear stress rapidly increased and there was not an increment in the shear displacement during the initial stage of the shear process in the frozen state. In both the unfrozen or frozen states at the same water contents, the shear strength increased with increasing normal pressure. 相似文献
18.
In the numerical simulation of long-term subgrade temperature fields, the daily variation of soil temperature at a certain depth h is negligible. Such phenomenon is called the "boundary layer theory."Depth h is defined as the boundary layerthickness and the soil temperature at h is approximately equal to a temperature increment plus the average atmosphere temperature. In the past, the boundary layer thickness and temperature increment were usually extracted from monitored data in the field. In this paper, a method is proposed to determinate the boundary layer thickness and temperature increment. Based on the typical designs of highway or railway, the theoretical solution of boundary layer thickness is inferred and listed. Further, the empirical equation and design chart for determining the temperature increment are given in which the following factors are addressed, including solar radiation, equivalent thermal diffusivity and convective heat-transfer coefficient. Using these equations or design charts, the boundary layer thickness and temperature increment can be easily determined and used in the simulation of long-term subgrade temperature fields. Finally, an example is conducted and used to verify the method. The result shows that the proposed method for determining the upper thermal boundary of subgrade is accurate and practical. 相似文献
19.
《Urban geography》2013,34(4):375-396
This research investigates the evolution of the system of Canadian decision-making centers using the location of corporate board members as a surrogate for the location of economic control. The major premise examined by this study states that, through much of the study period, board linkages should tend to concentrate on Toronto, Canada's dominant corporate administration center. While Toronto gains importance, Montreal loses connections, devolving from close competition with Toronto for national influence to become a major regional center for Quebec. At the same time, cities in other parts of the country gain importance as they evolve into major centers for their region. The result of these changes is the emergence of a dominant national center, along with a second tier of cities of regional importance. The results of the board member analysis reveal that the economy as a whole increasingly concentrates control in Toronto through the 1970s and 1980s. Montreal loses director connections with the rest of the country through the same period. While the economy as a whole centralizes in Toronto, certain sectors of the economy decentralize their directors to regional centers. Calgary, in particular, emerges as a major regional center for western Canada. The paper relates these observations to the dual conceptual frameworks of quaternary location theory and the resource dependence perspective. 相似文献
20.
Three stages of complex technological monitoring for the increase of high-temperature-permafrost soil bearing capacity are described. The feasibility of process monitoring to improve the targeted strength properties of subgrade bases on frozen soils is demonstrated. The rationale for the necessity of predictive modeling of freeze-thaw actions during the subgrade construction period is provided. 相似文献