Transportation Geotechnics最新文献

Of late, deformation of subgrade soil has led to an increasing number of road subsidence diseases. Real-time monitoring of subgrade deformation is critical to ensure the safety of subgrade operations. In this paper, a sensor-enabled piezoelectric geoelectric cable (SPGC) with impedance strain effect and piezoelectric effect is tested. The SPGC impedance and voltage signals obtained by cyclic shear test under vertical static load and cyclic shear test under vertical cyclic load are used to evaluate the monitoring effect. The results showed that normal stress had the greatest effect on the shear strength of the soil, whereas the normal stress and horizontal shear displacement amplitude significantly influenced the strain in the soil. Varying the normal and horizontal shear frequencies had little effect on the shear strength and strain of the soil. The normalized impedance and voltage of the SPGC, respectively, decreased and increased rapidly during the initial stage of the shear cycle; these changes were relatively small during the middle and late stages of the shear cycle. The SPGC voltage waveform revealed the changes in the shear stress and vertical displacement under different normal and horizontal shear frequencies, from which the stability of the subgrade soil under the aforementioned conditions could be evaluated. The variations in the SPGC impedance and effective voltage from the cyclic shear tests under both vertical static and vertical cyclic loads remained essentially consistent with the number of cycles. However, there was a difference in that the trough of the SPGC impedance under the vertical cyclic load was larger than that under the vertical static load; likewise, the effective SPGC voltage under the cyclic load was larger than that under the static load. Through an analysis of the SPGC impedance and voltage signals in the subgrade soil, the consistency of the SPGC-normalized impedance and effective voltage with shear stress was clarified; this helped us evaluate the health of the subgrade and monitor the characteristics of the precursor signals before a slide were to occur, thereby affording us an opportunity to issue timely warnings.

Many public utility lines to transport power, water, natural gas, water, sewer, and communication are placed beneath trafficable areas. However, insufficient or inadequate backfill induces sudden subsidence, damage, or pothole on the road. This study aims to develop lightweight controlled low-strength materials (CLSM) with low thermal conductivity using the ternary mixtures of red mud to replace aggregate sand, high carbon fly ash, and preformed foam. Changes in flow consistency, air void characteristics, bulk unit weight, unconfined compressive strength (UCS), and thermal conductivity (k) of the tested materials with varying red mud contents were investigated as a function of the foam volume ratio (FVR). The results demonstrate that the UCS and k of tested materials decreased with increasing FVR due the decrease in unit weight, and a greater UCS but smaller k was observed at a given FVR with increasing red mud content because the inclusion of red mud in the lightweight CLSM mix design helps improve the stability of air bubbles and achieve uniform distribution of air voids. In addition, the red mud can act as a NaOH supplier, leading to the developed material had additional strength gain from the alkali activation. Thus, the developed insulating backfill material showed 43 % decrease in k while maintaining UCS similar to non-foam CLSM without red mud.

Railway ballast bed defects, including subsidence, mud pumping, and abnormal water, pose significant safety risks by destabilizing the railway ballast beds. Timely detection and repair of railway ballast bed defects are vital for safeguarding the security of both the trains and their passengers. Ground-Penetrating Radar (GPR) is widely used for railway ballast beds inspection and evaluation owing to its high speed and non-destructive characteristics. However, GPR image data contain considerable noise, and the distinct shapes and sizes of each ballast bed defect renders it challenging to apply a unified data annotation standard, which hampers the development of railway ballast bed defect detection models. Considering the distinct wave-like characteristics of GPR data and the vaguely contours of the defects to be identified, we propose a convolutional augmentation operation tailored for GPR images. Furthermore, we also investigate Semi-Supervised Learning by employing limited annotated railway ballast bed inspection data along with a vast amount of unlabeled data to joint train the DETR detection model. To sum up, we proposed a semi-supervised DETR model supplemented with convolutional augmentation for railway ballast bed defect detection, termed as Semi-Conv-DETR model. Experimental outcomes indicate that Semi-Conv-DETR shows an improvement of 58.6 % in accuracy when compared to the classical Faster-RCNN model.

Geocell has a confinement effect, limiting the deformation of soil and enhancing the strength of reinforced soil, and has a wide range of application prospects in traffic transportation subgrade engineering. To investigate the confinement effect of geocell on the mechanical characteristics of reinforced sand subgrade, this paper analyzes the macro-mechanical properties of reinforced sand subgrade using triaxial tests, investigates the micro-reinforcement mechanism employing discrete element method (DEM)-based simulations. The potential macro–micro linkages are studied. The experimental results revealed that the volumetric strain of the geocell-reinforced samples increased with the material’s elastic modulus, exhibiting a shear shrinkage phenomenon. The deformation pattern of the reinforced samples presented “segmental deformation,” which differed from that of the unreinforced sand samples. The geocell enhanced the cohesion intercept of the sand samples while having a minimal impact on friction angle. Through the analysis of numerical simulation results, it was found that the geocell constrained the displacement of the soil particles, altering the shear band development trend of the sample and resulting in “segmental deformation”. The geocell facilitated the concentration of force chains, enhancing their stability and resulting in improving the strength in the macro. Additionally, it was observed that the confinement effect of the geocell significantly reduced the fabric and force anisotropy of the granular soil, promoting consistent vertical alignment of force chains. This, in turn, enhanced the vertical force transmission capacity of the sample, explaining the micro-mechanism by which the confinement effect of the geocell increases the peak shear strength of the samples.

In order to ensure the safe operation of high-speed trains in cold regions, frost heave is one of the basic problems in the research for prediction and control roadbed deformation in such regions. In this paper, based on the classical hydrodynamic model we developed a method of studying thermal regime of soils and predicting frost heave deformations of subgrade soils. Our coupling model takes into account the mutual influence of temperature and soil moisture during non-stationary processes of heat and moisture transfer, calculation of frost heave deformation based on calculated result of the temperature and moisture fields of the roadbed. We have also observed the change of the soil temperatures and frost heave deformation in a freezing-thawing cycle at the geodesic center of PGUPS. The field observation results show that the soil temperature variations amplitude decreases with depth. The simulation verification results and the field observation data show good reproducibility, thus the reliability of the model is confirmed. At last, the paper presents the application of the method in improving high speed railway lines (HSRL) subgrade design in order to reduce frost heave deformations. Based on the results of calculations, it is recommended to lay a thermal insulation layer at the depth of 0.2 m below the subgrade and on the slopes to reduce frost depth and frost heave deformations of subgrade soils.

The liquefaction potential of saturated sand can be significantly reduced by inducing partial saturation in the soil. Conventional soil liquefaction mitigation methods, namely soil densification, drainage, cementing, and groundwater lowering, pose environmental concerns and are challenging to apply to pre-existing structures. However, the microbially induced partial saturation (MIPS) method is emerging as a novel and eco-friendly approach to mitigate liquefaction. The MIPS method involves microbial denitrification, which produces nitrogen gas and results in a desaturating effect in the saturated soil. The current study conducted a series of stress-controlled undrained cyclic triaxial tests on saturated sandy soil and microbially-desaturated sandy soil under different relative densities and loading conditions. In addition, the study systematically analyzed the effects of temperature and pH on bacterial activity and the denitrification process. Batch experiments were conducted to establish a relationship between the initial nitrate concentration in the bacterial media and the resulting desaturation.Comprehensive analyses of cyclic resistance curves were performed to gain a thorough understanding. Additionally, the study conducts detailed analyses of the accumulation of excess pore pressure and the resulting axial strains and deformation patterns in both treated and untreated sand. This study demonstrates that the MIPS treatment considerably enhances the liquefaction resistance of treated sand.

Long-term performance of tunnels usually depends on their interaction with surrounding environment induced by various internal and external, natural and anthropogenic factors. Understanding these long-lasting impacts is paramount and crucial for the sustainable lifelong management of tunnel infrastructures. Considering prolonged rainfall, sea level rise and other extreme geohazards partly due to climate change, this paper specifically reviews previous studies examining the hydraulic influences on the long-term performance of tunnels. The variation in groundwater levels, changes in the hydraulic permeability of the surrounding ground and tunnel linings, water leakage, and tunnel deterioration are key hydraulic factors that critically affect the long-term performance of tunnels. The primary objective is to identify research gaps and limitations and provide insights for future research directions to improve our understanding of the long-term performance of tunnels under hydraulic influences. It is found that previous studies often fail to quantify these effects, exemplified by subjectively varying groundwater levels, ground and tunnel permeability and assuming random distribution of tunnel deteriorations. Therefore, future research should focus on adopting laboratory/field data-based, realistic assumptions, aiming to advance the understanding of the performance of tunnels across their lifespan and eventually enhance the principles of tunnel design, construction, and maintenance.

Characterizing subgrade in terms of resilient modulus is a crucial aspect of flexible pavement design. This paper proposes a methodology and predictive model to estimate the resilient modulus with better consideration of subgrade soils’ in situ stress state using a simple Repeated Load CBR (RLCBR) test. RLCBR tests were conducted on eight subgrade soils at three moisture contents. Numerical studies were conducted by simulating the CBR test in the commercial package LS-DYNA® to understand the stress state under plunger loading concerning field conditions. A new model was proposed for the characterization of subgrade soils based on laboratory RLCBR tests and the FEM, considering the stress state experienced by subgrade soils in the field. The proposed model was validated using data from four other soils and showed good agreement. The study model showed a better predictive capacity for the low plastic subgrade soils than previously developed models. Practicing engineers can use the developed model for estimating the subgrade resilient modulus at the recommended stress state for mechanistic pavement design while understanding the soil’s load-deformation behavior.

Efficient and accurate pavement surface crack detection is crucial for analyzing pavement survey data. To achieve this goal, an improved lightweight semantic segmentation model based on BiSeNetv2, utilizing the detail branch, the semantic branch, and the guided aggregation module, is refined for automatic pavement surface crack detection. With the detail branch and the semantic branch, the low-level details and the high-level semantic context of pavement surface crack can be represented. Taking advantage of the guided aggregation module, the low-level and high-level crack features are mutually connected and fused. The gradient-weighted class activation mapping (Grad-CAM) is adopted to visualize the details of the evolution of crack feature extraction, fusion, and representation. Based on the evaluation results, the proposed lightweight model demonstrates its effectiveness and robustness in accurately segmenting pavement surface crack. Maximumly, it is 10.14% higher than the other model on F1 score, indicating its great potential for pavement crack detection.

This study conducted large-scale cyclic loading experiments on the base layer overlying a weak subgrade soil. Geotextile and cement-treated geotextile were utilized to reinforce the base material and to separate the interface of soils between the base layer and the subgrade. The results obtained from the repeated loading tests using geotextile and cement-treated geotextile were analyzed and evaluated in terms of some benchmark indicators such as total deformation, permanent deformation, elastic deformation, percentage of elastic deformation, traffic benefit ratio (TBR), elastic modulus (M_R), improvement factor (I_f), and rut depth reduction ratio (RDR). Based on the experimental results, the use of cement-treated geotextile as a base layer reinforcement element or as an interfacial separation element demonstrated better performance compared to the use of geotextile. Utilization of a cement-treated geotextile as both reinforcement and separation element resulted in an RDR value of 49.26 % after 5000 cycles. Additionally, using a cement-treated geotextile for both reinforcement and separation increased the TBR value to 14.62 at 27 mm deformation, decreased the permanent deformation value from 53.67 mm to 27.23 mm, and approached approximately 2 improvement factor values, compared to using the geotextile solely for separation.