Liquid water–vapour migration tracing and characteristics of unsaturated coarse-grained soil in high-speed railway subjected to freezing and different load types

As an important factor that affects the compaction characteristics of the coarse grained fillers in the high speed railway subgrade, the grain composition is characterized by the application of the fractal theory. Several types of the coarse grained fillers were selected for testing and the results indicated that the relationship actually exists between the compaction characteristics and the fractal dimensions. The variation law of the maximum dry density fluctuating with the quality fractal dimension was analyzed and the results were supposed to estimate the compaction characteristics of the coarse grained fillers.

Download Full-text

Studies for Frost Heave Characteristics and the Prevention of the High-Speed Railway Roadbed in the Zoige Wetland, China

Frontiers in Earth Science ◽

10.3389/feart.2021.678655 ◽

2021 ◽

Vol 9 ◽

Author(s):

Fujun Niu ◽

He Hu ◽

Minghao Liu ◽

Qinguo Ma ◽

Wenji Su

Keyword(s):

Water Content ◽

High Speed ◽

Cold Climate ◽

Coarse Grained ◽

Frost Heave ◽

Tibet Plateau ◽

High Speed Railway ◽

Fines Content ◽

Zoige Wetland ◽

Flat Ground

The Xining–Chengdu high-speed railway crosses the Zoige Wetland, located on the northeast edge of the Qinghai-Tibet Plateau and the upper reaches of the Yellow River. The cold climate and frost-heave-sensitive subgrade soil cause a large frost heave deformation of the roadbed, threatening the safety of trains. This article systematically studied the ground temperature development, frost heave characteristics, soil water content, and groundwater level variations by field investigation and monitoring. The maximum frost heave deformations of the natural flat ground and hillslope reached 25.64 and 3.17 mm, respectively, and this significant discrepancy was mainly caused by the groundwater supply conditions. Future roadbed stability on the flat ground may be compromised by frost heave deformation. To solve this problem, contrasting indoor tests were conducted to analyze the frost heave characteristics of natural ground clay and replacement coarse-grained soil (CGS). It was shown that the absorbed external water mainly changed into dispersed pore ice in the freezing CGS, while it mainly changed into the layered ice lens in the freezing clay. Further tests showed that the frost susceptibility of the CGS was proportional to the fines content and initial water content. The poorly graded CGS had weaker frost susceptibility than the well-graded CGS. The results suggest that anti-frost methods should be fully considered, including strict control of fines content and water content, prioritizing the use of poorly graded filling, and disruption of local water accumulation in the filling layer.

Download Full-text

Large-Scale Model Testing of High-Speed Railway Subgrade under Freeze-Thaw and Precipitation Conditions

Advances in Civil Engineering ◽

10.1155/2019/4245916 ◽

2019 ◽

Vol 2019 ◽

pp. 1-14 ◽

Cited By ~ 1

Author(s):

Shasha Zhang ◽

Yantao Wang ◽

Fei Xiao ◽

Weizhi Chen

Keyword(s):

Moisture Content ◽

High Speed ◽

Laboratory Tests ◽

Large Scale ◽

Saline Soil ◽

Field Monitoring ◽

Coarse Grained ◽

Scale Model ◽

High Speed Railway ◽

Freeze Thaw

To determine whether coarse-grained saline soil meets the deformation requirements of the DY high-speed railway subgrade, a study was conducted by a combination of field-monitoring and laboratory tests. First, several temperature sensors were buried vertically in the ground of a typical section, and the temperature at different depths was monitored for nearly one year and analysed dynamically. It was determined that a depth of 4.8 m can be set as the constant-temperature layer. Then, based on the field-monitoring results, laboratory tests were carried out on a large-scale subgrade model under freeze-thaw and precipitation conditions. The change of temperature, moisture content, and soil deformation of the subgrade under long-term freeze-thaw and precipitation conditions were obtained. The results show that the temperature changes periodically with a V shape during the entire cycle. Twenty centimetres below the top surface is the sensitive depth of the sample, and salinity has little effect on temperature change. In the process of cycles, the average moisture content of soils with higher salinity is about 0.5% lower than that of soils with lower salinity. After nine freeze-thaw cycles, the sample finally shows dissolved settlement deformation. Precipitation mainly affects the deformation of the sample; however, the influence on salt-expansion and frost-heave deformation is less significant. Finally, by predicting the deformation of coarse saline soil, it is proven that the soil can meet the deformation requirements of high-speed railway foundations.

Download Full-text

A frost heave model of unsaturated coarse-grained soil considering vapour transfer

E3S Web of Conferences ◽

10.1051/e3sconf/202019502017 ◽

2020 ◽

Vol 195 ◽

pp. 02017

Author(s):

Jianlong Liu ◽

Jidong Teng ◽

Sheng Zhang ◽

Daichao Sheng

Keyword(s):

High Speed ◽

Coarse Grained ◽

Frost Heave ◽

Test Results ◽

Proposed Model ◽

Laboratory Test Results ◽

Frost Depth ◽

Lens Formation ◽

Coarse Grained Soil ◽

Coarse Soil

Substantial frost heave has been observed in coarse fills in high-speed railway embankments. These coarse fills have low fine contents and very low water content. The groundwater table is located below the coarse fills. The coarse fills were considered not susceptible to frost heave. Recent experimental results in the literature showed that vapour transfer has a considerable influence on the frost heaving of unsaturated coarse-grained soil. But vapour transfer has been rarely considered in the modelling of frost heave. This study presents a new frost heave model with considering vapour transfer and its contribution to ice formation. The rigid ice theory is applied to initiate an ice lens formation in the frozen fringe. An updated computer programme PCHeave is developed by considering the vapour transfer. The results of the proposed model are compared with laboratory test results, which show reasonable agreement. The prediction of the model agrees well with the measured frost heave and frost depth, which indicates that the proposed model can reasonably reflects the process of frost heave in unsaturated coarse soil.

Download Full-text