Low-grade Highway Research Articles

Numerical evaluation of thermal stability of a W-shaped crushed-rock embankment with shady and sunny slopes in warm permafrost regions

The crushed-rock interlayer structure, crushed-rock revetment, and insulation board have been successfully applied in low-grade highways in low-temperature permafrost regions. However, it is doubtful whether the composite structure of the W-shaped crushed-rock embankment (W-CRE) composed of the three measures can be applied to high-grade highways in warm permafrost regions. For this reason, a model coupled with water, heat, and deformation in unsaturated soil was established for the high-grade highway with the W-CRE in warm permafrost regions. The cooling effect of the composite structure on the embankment with shady and sunny slopes in 20 service years was evaluated by numerical calculation, and the unfrozen water distributions and deformation characteristics were analyzed. The results show that (1) the W-CRE can cool the embankment of the high-grade highway in warm permafrost regions and improve the asymmetric ground temperature distributions caused by the shady and sunny slopes. (2) the W-CRE can improve the asymmetry of unfrozen water distributions, reduce the uneven settlement, and thus improve the mechanical stability of the embankment. (3) Although the cooling mechanisms of the three measures are different, the complementary thermal regulation mechanism formed by them in the composite structure effectively improves the thermo-mechanical stability of the embankment.

Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions

Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions

Performance and Hydration Mechanism of Modified Tabia with Composite-Activated Coal Gangue

The feasibility of modified tabia (MT) with composite-activated coal gangue (CACG) as the subgrade material of low-grade highways was experimentally investigated. A composite activation method was employed to improve the pozzolanic activity of coal gangue. The effect of CACG content on the mechanical properties of MT was investigated through a series of experiments. It was found that the pozzolanic reactivity of coal gangue was remarkably enhanced by the composite activation method. Compared with traditional tabia (TT), the unconfined compressive strength, splitting strength, and flexural tensile strength of the MT with 50% of CACG content increased by 5.03 times, 9.71 times, and 1.50 times, respectively. The impermeability of specimens with CACG significantly improved. Furthermore, the mass loss rate of MT was less than 2.83%, while it reached up to 34.20% in TT after being conditioned to 40 freeze–thaw cycles. Finally, the microstructure change and hydration mechanism of MT are discussed and revealed.

Numerical evaluation for cooling performance of a composite measure on expressway embankment with shady and sunny slopes in permafrost regions

As an efficient engineering measure for protecting permafrost from thawing, the composite measure composed of L-shaped two-phase closed thermosyphons (TPCTs), insulation board and crushed-rock revetments (CRs) is applied to the low-grade highway in the Qinghai-Tibet Plateau. However, it is uncertain whether this composite measure can be available for an expressway embankment with wide bituminous pavement and strict deformation requirement, and the deformation performance of the embankment with composite measure is the key factor controlling safe operation. In this study, a hydro-thermo-mechanical coupled model for the expressway embankment combined with the composite measure is developed, the working process and mechanism of L-shaped TPCTs, insulation board and CRs are analyzed, respectively, and the cooling and reinforcing effects of the composite measure for the embankment with shady and sunny slopes are evaluated. The numerical results show that: (1) The working process and mechanism of L-shaped TPCTs, insulation board and CRs are different. (2) The composite measure can not only prevent the permafrost degradation, but also relieve the asymmetric geotemperature and moisture distributions caused by shady-sunny slope effect. (3) The composite measure can significantly reduce the embankment deformation, reliably alleviate the deformation difference and reinforce the stability of the expressway embankment in permafrost regions.

Effectiveness of Warning Piles on Driving Behavior on the Curve of Low-Grade Highway

To develop a scientific and practicable guideline for implementing warning piles on Chinese low-grade highways, it is necessary to study the effect of warning piles on driving performance in different road alignments and environments. Based on a driving simulator, this paper evaluates the effect of unilateral and bilateral warning piles on vehicle speed and lateral position on a two-lane rural highway curve with different road geometries. The results show a significant effect of bilateral warning piles on speed control, which becomes more obvious as the radius of the curve decreases and the superelevation increases. In sharp curves, vehicle speed increases rapidly in the second half of the curve, and bilateral warning piles could significantly control speed increase to prevent danger. Meanwhile, the effect of bilateral warning piles on keeping vehicles in a safer lane position is also statistically significant in the second half of the curve. With a decreasing radius and an increasing superelevation, the value of the maximum lateral position will increase. Bilateral warning piles could reduce the lateral position to keep the vehicle on a stable track. Moreover, bilateral warning piles could also perform better at night. This paper studies both unilateral and bilateral warning piles’ effects on driving behavior in different road geometries, thus providing a theoretical basis for the engineering application of warning piles.

Evolution characteristics of crack and energy of low-grade highway under impact load

ABSTRACT To analyse the feasibility of the low-grade highway as a launch site in military applications and improve the pavement crushing technology in civilian applications, this study investigates the evolution characteristics of a low-grade highway under impact load, including deflection, crack, and energy, via the continuum–discontinuum element method (CDEM). To this end, this paper proposes an energy statistics algorithm, and the correctness is verified. Then, a quarter three-dimensional numerical model of an asphalt concrete highway is established, and the effectiveness of CDEM in simulating the deflection of the highway under impact load is validated. Finally, an existing asphalt concrete highway structure is selected to study the evolution characteristics via numerical simulation. The results demonstrate the consistency between the variations of deflection at the load centre and the impact load. The deflection is primarily caused by the compressive deformation of subgrade. Crack planes mainly occur when the impact load increases rapidly. The variation of various constituent energies is different but closely related to the change in impact load.

低等级公路施工期的环境管理问题及对策

低等级公路施工期的环境管理问题及对策

Engineering prevention and treatment of salt soil diseases caused by pulping on low-grade highways in xinjiang

The frost boiling disease caused by saline soil is a common disease of grade three and four highways at present. In this paper, the mechanism of frost boiling highway disease in saline soil is analyzed. And through simplified calculation combined with engineering experience, the concrete measures for preventing and curing the disease are put forward. Finally, through engineering practice verification, the expected results have been achieved.

A full-scale field experiment to evaluate the cooling performance of a novel composite embankment in permafrost regions

High-grade highways designed for large traffic volumes need wider embankments than railways and low-grade highways. In permafrost regions, a wide and dark-colored asphalt pavement surface of high-grade highways may destabilize underlying permafrost if the embankment is insufficiently cooled, especially under a warming climate. However, the embankments with single commonly cooling technique, e.g. two-phase closed thermosyphon (TPCT) embankment and crushed-rock embankment cannot satisfy the cooling requirement of high-grade highways because of their limited cooling capacities. Here, we use a full-scale field experiment of a separated high-grade highway with double lanes each direction at Beiluhe in the Qinghai-Tibet Plateau to investigate the thermal characteristics of a novel composite embankment combined with L-shaped TPCTs, crushed-rock revetments and insulation, as well as an unprotected embankment (as a control). Experimental results indicate that the composite embankment can effectively cool the underlying permafrost and raise the permafrost table under the separated high-grade highway with a wide and dark-colored pavement, whereas the unprotected embankment cannot. This composite embankment should be considered for application to separated high-grade highways with double lanes each direction in permafrost regions, such as the planned Qinghai-Tibet Expressway.

Performance of cement-stabilised crushed brick aggregates in asphalt pavement base and subbase applications

Demolished brick is one of the main components of construction waste, and its recycling for use in asphalt pavement base and subbase is a relatively new technique. This work studies the performance of cement-stabilised crushed brick aggregates (CSCBA) and proves the applicability of crushed brick aggregates (CBA) in asphalt pavement base. A scanning electron microscope (SEM), X-ray diffractometer (XRD) and Fourier infrared spectrum (FIS) were used to investigate the micro performance of CBA. Six types of CSCBA were designed with the following CBA contents: 0%, 20%, 40%, 60%, 80% and 100%. The properties of CSCBA were investigated, including compaction properties, compressive strength, split strength, compressive resilient modulus, shrinkage performance and fatigue performance. SEM was also used to analyse the strengthening mechanism of CSCBA. This study's results are useful for engineering practice, particularly for identifying (a) the properties of CSCBA and (b) the upper limits of CBA applicability for asphalt pavement base and subbase for low-grade highway.

Integrated Application of Micro Steel Pipe Piles and Soil Nailing Frame Beam for Loose Deposit Slopes

Loose deposit is widely distributed along the south route of Sichuan-Tibet highway (in Tibet). Slope disasters often occur because of the broken loose deposit and the low grade highway without complete safeguards for the slope. The paper proposed the integrated treatment technology with micro steel pipe piles and soil nailing frame beam and its work theory and structure design. The slope stability was simulated numerically with Midas-GTS on typical sections to verify the effectiveness of the technology. During simulation, the stable coefficient of slope with or without the integrated treatment technology was calculated. Results showed that the technology with micro steel pipe piles and soil nailing frame beam can improve the stability of loose deposit cutting slopes greatly.

Effect of Visual Range on Driving Speed on Low-grade Highway

Visual range from road alignments plays an important role in traffic safety since it is a key factor for drivers to adopt an appropriate speed. It is especially true to low-grade highways where speeds tend to reach a high value when sections have a relatively good linearity. High speeds on low-grade highway are considered a main contributor to traffic accidents. This paper studied the relationship of maximum visual range and driving speed on low-grade highways to put forward a suggested visual range for safe driving. Four typically mountainous highway models with the same driving environment but different visual ranges were constructed to analyze the effect of visual range on driving speed. A driving simulator with eight degrees of freedom was used to carry out the experiments. Data of driving speed, acceleration and deceleration were collected to study the speed and acceleration trends. The conclusion drawn is that the appropriate value of maximum visual range on low-grade highways is recommended to be 80m to ensure safety driving.

Research on Application of Iron Tailings on Road Base

In order to make good use of waste iron tailings considering energy conservation and environment protection, a new research on the use of tailings in road base has been carried out in this study. A type of iron tailings stabilized with cement made of appropriate amount of cement was firstly selected as the semi-rigid base material. After the mix proportion design based on material characteristics, compaction tests, unconfined compression tests and economic analysis were conducted on the mixture. It shows that iron tailings stabilized with cement with a more than 15% cement content meets the test requirements well and can be applied on the base and subbase course of low-grade highway. Helping to save road materials and reduce project costs, the study has a promising application prospect.

Research on Evaluation Model and Application of Highway Alignment in Mountainous Area Based on Operating Speed

Based on the road conditions of the low-grade highway (lower Grade 2) in China southwest mountainous area and speed investigations under different conditions, the estimation model of running speed in this region was established, meanwhile, the criteria for the safety appraisal of line based on running speed in southwest is put forward. Finally, according to the above achievement we developed software for the safety appraisal of line that oriented the low class highway in southern mountainous area in China, and achieve a real-time evaluation of visualization in its design and service life. This method is available for multiple engineering projects.

Research on Evaluation Model and Application of Highway Alignment in Mountainous Area Based on Operating Speed

Based on the road conditions of the low-grade highway (lower Grade 2) in China southwest mountainous area and speed investigations under different conditions, the estimation model of running speed in this region was established, meanwhile, the criteria for the safety appraisal of line based on running speed in southwest is put forward. Finally, according to the above achievement we developed software for the safety appraisal of line that oriented the low class highway in southern mountainous area in China, and achieve a real-time evaluation of visualization in its design and service life. This method is available for multiple engineering projects.

Optimal Design of Low-Grade Highway Barrier

Aiming at the weak protection capability of current barrier in low-grade highway, an optimized barrier is designed and computed in this paper. The dynamic characteristics of vehicle in traffic accidents are simulated by LS-DYNA, and the performances of intermittent low-grade highway concrete barrier are improved by different shape, size and spacing. The final optimized barrier can orient vehicles and ensure vehicles do not roll or cross the barrier.