Search Results (69)

Accurate inspection of retaining walls is crucial for ensuring structural integrity and public safety. Current assessment methods rely predominantly on qualitative visual evaluations that inform numerical structural ratings. These ratings lack the comprehensive quantitative measurements that 3D imaging can provide. This study evaluates the feasibility and accuracy of drone-based lidar platforms for retaining wall inspection as an alternative to traditional terrestrial laser scanning (TLS) that improves accessibility on hard-to-reach sites and may increase efficiency on site due to preplanned flights. Data was collected from three representative walls exhibiting diverse conditions using TLS and drone-lidar. To provide additional information on the site to use for alignment and checks, both Global Navigation Satellite System (GNSS) control and total stations were employed. The study provides a comparative analysis of the accuracy and practicality of each lidar method, aiming to determine the most effective techniques for routine inspection applications given varying site conditions. When compared against a finely registered TLS ground truth, drone-lidar was found to have root mean square errors of 2.3 cm in areas with low vegetation and 24.2 cm in densely vegetated areas. The findings highlight potential improvements in the precision of retaining wall assessments, proposing a shift from current qualitative practices to reliable, data-driven evaluations. Key limitations in GNSS accuracy and sites with dense vegetation are discussed. Full article

This study investigates the displacement behavior of excavations under asymmetric loading conditions and proposes optimized support design strategies from the perspective of displacement control. Physical model tests reveal that, in excavation projects under eccentric loading conditions, the retaining structure as a whole tends to deform toward the non-surcharge side rather than following the conventional symmetric deformation pattern. Displacement increases nonlinearly with surcharge intensity, but the growth rate diminishes as the load further increases due to localized surcharge effects and structural restraints. Numerical analyses further demonstrate that increasing embedment depth and wall thickness effectively mitigates lateral displacement, although a marginal effect is observed beyond critical thresholds. For instance, at an embedment depth of 12 m (twice the excavation depth), maximum lateral displacement decreases by nearly 50%, and when combined with a wall thickness of 13 cm and a depth of 14 m, the reduction reaches approximately 90%. These findings establish a quantitative basis for deformation control in excavations subjected to asymmetric loading and guide the efficient optimization of retaining systems. They enhance design reliability and construction efficiency, offering practical value for improving safety, performance, and overall project economy. Full article

This paper focuses on a deep foundation pit project of a metro shaft constructed by the cover-and-excavation reverse method in a section of Guangzhou Metro Line 13. This study integrates field monitoring data, three-dimensional finite element simulations, and parametric analyses to propose a systematic optimization design framework, providing a more comprehensive and reliable quantitative basis for the design of support structures for deep metro foundation pits constructed using the cut-and-cover top-down method. The study examines the effects of pile diameter, pile spacing, embedment depth, and types of retaining structures on pit deformation. The results indicate that increasing the pile diameter from 800 mm to 1000 mm reduces the maximum lateral displacement of the retaining structure by 30.7%, while decreasing the pile spacing from 2000 mm to 1600 mm results in a 17.5% reduction in deformation. However, beyond these thresholds, the marginal improvement becomes less significant. An embedment depth of 4 m for shallow sections and 2.5 m for deep sections is recommended to balance deformation control and construction economy. Diaphragm walls outperform bored piles and secant piles in deformation control. The optimized design achieves an estimated cost reduction of approximately 15% while maintaining safety requirements. The optimized parameters and comparative conclusions derived from this study can be directly applied to the design of deep foundation pits for metro stations under similar geological conditions. These findings provide crucial data support and theoretical reference for formulating more economical and safer design codes and standards. Full article

Reinforced soil retaining walls (RSWs) for railways are key subgrade structures that bear cyclic loads from trains, and their long-term durability directly affects railway operation safety. The mechanical behavior of RSWs under cyclic loading has been extensively investigated in previous studies, primarily focusing on seismic conditions or conventional structural configurations. While these works have established fundamental understanding of load transfer mechanisms and deformation patterns, research on their responses to long-term train-induced vibrations, particularly for concrete-block-panel-wrapped RSWs, an improved structure based on traditional concrete-block-panel RSWs, remains limited. To investigate the dynamic responses of the concrete-block-panel-wrapped RSW, a model test was conducted under cyclic loading conditions where the amplitude was 30 kPa and the frequency was 10 Hz. The model size was 3.0 m in length, 1.0 m in width, and 1.8 m in height, incorporating six layers of geogrid. Each layer of geogrid was 2.0 m in length with a vertical spacing of 0.3 m or 0.15 m. The results indicate that as the number of load cycles increases, deformation, acceleration, static and dynamic stresses, and geogrid strain also increase and gradually stabilize, exhibiting only marginal increments thereafter. The maximum horizontal displacement reaches 0.08% of the wall height (H), with horizontal displacement increasing uniformly along the height of the wall. The vertical acceleration in the non-reinforced soil zone is lower than that in the reinforced soil zone. The horizontal dynamic stress acting on the back of the panel remains minimal and is uniformly distributed along the height of the wall. The maximum geogrid strain was found to be 0.88%, corresponding to a tensile stress amounting to 20.33% of its ultimate tensile strength. The predicted failure surface approximates a bilinear configuration, consisting of one line parallel to the wall face at a distance of 0.3H from the back of the soil bags and another line inclined at an angle equal to the soil’s internal friction angle (φ) relative to the horizontal plane. This study has important reference significance for the application of concrete-block-panel-wrapped RSWs in railways. Full article

This study focuses on the mathematical method developed by integrating the surrogate model as constraints for wall stability into the heuristic optimization algorithm to gain the optimum cost and ${\mathrm{CO}}_2$ emission value of the gabion retaining wall (GRW). This study also includes the comparison of optimum GRW results with optimum cantilever retaining wall (CRW) designs for different design cases. The Harmony Search Algorithm (HSA), which efficiently explores the design space and robustly reaches the optimum result in solving optimization problems, was used as the heuristic optimization algorithm. The primary construction scenario was considered as an optimization problem, which involved excavating the slope, constructing the wall, and compacting the backfill soil to minimize the cost and CO${}_2$ emissions for separate objective functions of GRW and CRW designs. Comparative results show that GRWs outperform CRWs in terms of sustainability and cost-efficiency, achieving 55% lower cost and 78% lower CO${}_2$ emissions on average, while the HSA–surrogate model provides a fast and accurate solution for geotechnical design problems. The surrogate models for sliding, overturning, and slope stability safety factors of GRW exhibited exceptional accuracy, characterized by minimal error values (MSE, RMSE, MAE, MAPE) and robust determination coefficients ($R^2\approx 0.99$), hence affirming their dependability in safety factor assessment. By integrating the surrogate model based on the statistical method into the optimization algorithm, a quick examination of the wall’s stability was performed, reducing the required computational power. Full article

By critically reviewing pseudo-static methods, it is demonstrated that approximating the earth pressure on a short heel’s vertical face (V-plane) using the Rankine solution for long-heel walls induces a negligible error. A finite element analysis is deployed to validate the pseudo-static results, with dynamic simulations incorporating 1–5 Hz sinusoidal seismic excitations to probe the resonance effects. The key results show that disregarding the impact of layered backfill placement on the initial stress states leads to non-conservative estimates of active earth pressure. Furthermore, the point of application of earth pressure rises significantly during strong shaking, and although the transient safety factors against sliding and overturning may fall below 1.0 during seismic events, the residual deformation analysis suggests that this does not necessarily lead to collapse. A significant amplification of bending moments and greater reductions in post-earthquake safety factors occur when the input frequency approaches the natural frequency of a wall. Finally, the paper proposes resonance prevention strategies for the seismic design of cantilever retaining walls, a methodology incorporating construction effects into the initial stress field modeling, and recommendations for selecting effective safety factors. Full article

Mechanically stabilized earth (MSE) retaining walls have become a favored substitute for traditional poured concrete walls due to their affordability, minimal site preparation needs, and practical construction advantages. However, using backfill material with too many small particles and poor drainage qualities may cause the wall to rotate and shift a lot or collapse completely, especially when water pressure is present. This study examines an MSE wall considering different variables, such as water pressure, the type of soil materials in the backfill materials, external load, and the type of analysis. To this aim, both PLAXIS V20 and SLOPE/W (GeoStudio 2019 Suite) software were employed, and after the verification, further investigations were carried out. These numerical analyses aligned with the real-world failure reported by previous researchers, departments, and companies. The findings suggest that the elevated presence of fine particles likely contributed to the wall’s excessive shift. Also, hydrostatic pressure behind a wall, especially in the rainy season, plays a crucial role in the factor of safety reduction by 45% and wall failure, which leads us to consider it an appropriate factor of safety for the MSE wall. Full article

This article provides a concise overview of the existing tunnels located within the historic cultural heritage site of Gediminas Hill in Vilnius, with particular emphasis on the implications of a recently discovered tunnel. This newly identified tunnel is of particular interest due to its location beneath a retaining wall in close proximity to an adjacent structure. Long-term structural monitoring data indicate that the building has experienced displacement away from the retaining wall. Although the precise cause of this movement remains undetermined, the discovery of the tunnel adjacent to the structure has raised concerns regarding its potential role in the observed displacements. To investigate this hypothesis, a previously developed numerical model was employed to simulate the tunnel’s impact. The simulation results suggest that the tunnel’s construction was executed with careful consideration. During the excavation phase, the retaining wall exhibited displacements in a direction opposite to the expected ground pressure, indicating effective utilization of the wall’s gravitational mass. However, historical records indicate that no retaining structures were present in the area during the tunnel’s initial period of existence. Consequently, an additional simulation phase was introduced to model the behavior of the surrounding loose soil in the absence of retaining support. The results from this phase revealed that the deformations of the retaining wall and the adjacent building were elastically interdependent. The simulated deformation patterns closely matched the temporal trends observed in the monitoring data. These findings support the hypothesis that the tunnel’s construction may have contributed to the displacement of the nearby building. Full article

Cylindrical retaining structures are widely adopted in intercity railway tunnel engineering due to their exceptional load-bearing performance, no need for internal support, and efficient utilization of concrete compressive strength. Measured deformation data not only comprehensively reflect the influence of construction and hydrogeological conditions but also directly and clearly indicate the safety and stability status of structure. Therefore, based on two geometrically similar cylindrical shield tunnel shafts in Shenzhen, the surface deformation, structure deformation, and changes in groundwater outside the shafts during excavation were analyzed, and the deformation characteristics under the soil–rock composite stratum were summarized. Results indicate that the uneven distribution of surface surcharge and groundwater level are key factors causing differential deformations. The maximum horizontal deformation of the shafts wall is less than 0.05% of the current excavation depth (H), occurring primarily in two zones: from H − 20 m to H + 20 m and in the shallow 0–10 m range. Vertical deformations at the wall top are mostly within ±0.2% H. Localized groundwater leakage in joints may lead to groundwater redistribution and seepage-induced fine particle migration, exacerbating uneven deformations. Timely grouting when leakage occurs and selecting joints with superior waterproof sealing performance are essential measures to ensure effective sealing. Compared with general polygonal foundation pits, cylindrical retaining structures can achieve low environmental disturbances while possessing high structural stability. Full article

Penetration points on walls must include firestop measures to prevent the spread of fire. Countries worldwide have established standardized testing protocols for firestop methods, and firestop products must pass relevant tests before they can be used in buildings. In the present study, a simple method was developed to enhance the smoke leakage performance and fire resistance of existing polyvinyl chloride (PVC) pipes passing through walls. Two sets of smoke leakage tests were performed, followed by two sets of fire tests. The smoke leakage tests were nondestructive and thus did not damage the specimens; consequently, the same specimens could be used in the smoke leakage and fire tests. The results of the smoke leakage tests indicate that the method using PVC pipes wrapped with galvanized steel sleeves outperforms the method without such wrapping. Moreover, the results of the fire tests suggest that galvanized steel sleeves considerably improve thermal insulation and safety. This finding is explained as follows: PVC pipes may burn and break apart at high temperatures, compromising fire compartmentation. A galvanized steel sleeve can retain a burning, broken pipe piece, thereby preventing injuries and stopping the detached pipe from continuing to burn on the ground. Full article

Shallow landslides are often unpredictable and seriously threaten surrounding infrastructure and the ecological environment. Traditional landslide prediction methods are time-consuming, labor-intensive, and inaccurate. Thus, there is an urgent need to enhance predictive techniques. To accurately predict the runout distance of shallow landslides, this study focuses on a shallow soil landslide in Tongnan District, Chongqing Municipality. We employ a genetic algorithm (GA) to identify the most hazardous sliding surface through multi-iteration optimization. We discretize the landslide body into slice units using the dynamic slicing method (DSM) to estimate the runout distance. The model’s effectiveness is evaluated based on the relative errors between predicted and actual values, exploring the effects of soil moisture content and slice number on the kinematic model. The results show that under saturated soil conditions, the GA-identified hazardous sliding surface closely matches the actual surface, with a stability coefficient of 0.9888. As the number of slices increases, velocity fluctuations within the slices become more evident. With 100 slices, the predicted movement time of the Tongnan landslide is 12 s, and the runout distance is 5.91 m, with a relative error of about 7.45%, indicating the model’s reliability. The GA-DSM method proposed in this study improves the accuracy of landslide runout prediction. It supports the setting of appropriate safety distances and the implementation of preventive engineering measures, such as the construction of retaining walls or drainage systems, to minimize the damage caused by landslides. Moreover, the method provides a comprehensive technical framework for monitoring and early warning of similar geological hazards. It can be extended and optimized for all types of landslides under different terrain and geological conditions. It also promotes landslide prediction theory, which is of high application value and significance for practical use. Full article

The sheet pile wall, a widely used retaining structure in railway construction, faces limitations such as restricted height, construction difficulties, and high costs. While geosynthetic-reinforced soil technology enhances soil tensile strength, it often lacks sufficient stiffness and strength. To address these issues, this study proposes a “prestressed” geosynthetic-reinforced sheet pile retaining wall structure. The geosynthetic-reinforced soil was subjected to preloading to induce “prestress”, with enhanced soil reinforcement interaction improving load-bearing capacity, reducing horizontal displacement, and ensuring railway safety. Indoor model tests were conducted on sandy soil foundations to investigate the structure’s load settlement behavior, pile horizontal displacement, earth pressure distribution, pile bending moments, and reinforcement strain development. The results show that applying “prestress” significantly enhances soil reinforcement interaction, enabling the pile–slab wall to better retain soil and improve overall performance. The load-bearing capacity increased by 21.7% and 16.6% in two respective tests, while horizontal displacement was effectively reduced. The maximum earth pressure was observed on the right side of the pile, 20 cm above the base, and the maximum bending moment occurred in the anchored section. Prestressing also enhanced the utilization of the tensile reinforcement. The proposed structure offers a promising approach for optimizing railway retaining structures. Full article

The rapid development of coastal cities has intensified land resource constraints and is leading to an increasing number of foundation pit projects near existing operational tunnels. This necessitates careful consideration of coastal excavation impacts on adjacent tunnels. Taking a foundation pit project in Qingdao as a case study, this paper investigates tunnel deformation through statistical analysis, numerical simulation, and field monitoring. By adjusting numerical model parameters, the research examines the influence of horizontal clearance distances, existing structure burial depths, and different retaining structure configurations on tunnel deformation, providing guidance for deformation control. Key findings include the following: (1) Statistical analysis reveals that tunnels in silty clay strata experience more significant excavation-induced deformation compared to those in silt strata, with relative positional relationships between pits and tunnels playing a critical role. (2) Numerical and monitoring results demonstrate that pit excavation induces tunnel displacement towards the excavation zone. Maximum lateral displacement reached 3.57 mm (simulated) and 4.79 mm (measured), while maximum vertical displacement was 3.11 mm (simulated) and 3.85 mm (measured), all within safety thresholds. (3) Sensitivity analysis shows that shallower tunnels exhibit more pronounced deformations. Increasing horizontal separation distance from 10 m to 25 m reduces deformation by one-third. However, adjusting diaphragm wall thickness and retaining structure embedment depth proves limited in deformation control, necessitating reinforcement measures on the tunnel side. These findings provide valuable references for protecting coastal silty clay stratum tunnels. Full article

In order to exploit the deep underground space, the construction of ultra-deep excavation in Shanghai is growing rapidly. In multi-aquifer strata, deep excavations typically require dewatering of confined aquifers to ensure engineering safety. However, existing studies have seldom conducted in-depth analysis on the influence of the soil parameters and construction measures on the deformation of retaining structures. In this study, a three-dimensional hydro-mechanical numerical model was developed to evaluate the performances of excavation and dewatering of the foundation pit. The model was validated by comparing the calculated and measured wall deflections and groundwater drawdowns of a 45 m ultra-deep double-wall excavation in Shanghai. According to the characteristics of soil stratification and construction activities, three parameters were selected for subsequent analysis, including the hydraulic conductivity of aquitard below the bottom of the pit, the pumping rate in the second confined aquifer and the construction of TRD wall. The stress distributions on both sides of the diaphragm wall were examined to elucidate the deformation mechanism. The results indicate that the aquitard hydraulic conductivity directly affects the effective stress of the overlying aquifer, which plays a crucial role in resisting wall deflection. An increase in the hydraulic conductivity leads to smaller effective stress, greater wall deflection and larger ground settlement. While an appropriately increased pumping rate enhances effective stress, over-pumping may induce excessive wall deflection at depth and disproportionate ground settlement. The TRD wall is quite useful in terms of waterproofing but the effect on deformation control is limited. The findings of this study provide valuable insights for engineering practices and the optimization of deep excavation construction measures in multi-aquifer strata. Full article

Used for soil and weathered rocks, soil nails are rigid reinforcements positioned at certain angles on the ground to provide slope stability. A rigid reinforcement element placed in a well filled with cement grout mix after completing drilling will generate adherence stress between the grout-mixed nail bar and soil. Due to this stress, load is transferred to the soil along the soil–grout interaction surface. In the case discussed herein, the slope at the parcel border needed to be made steeper in order to accommodate the construction of a facility in the Taşkısığı region of Sakarya province. Soil-nailed walls, which are inexpensive and suitable for weathered rocks, were needed as a support system because the slope was too steep to support itself. Support system performance was measured using two inclinometers and two soil nail pull-out tests conducted on different sections observed during and after construction. Contrary to the design-phase prediction, it was determined that the stresses started to dampen in the region closer to the slope-facing zone. Field measurement data and numerical analysis revealed that higher parameters than necessary were selected. In this context, sensitivity and parameter analyses were carried out using the Hoek–Brown constitutive model. The GSI value was re-evaluated and found to be compatible with the observation results obtained from the field performance. Since the retaining wall performance observed was higher than expected, geometric parametric analysis of the structural elements was performed; high safety coefficients were found across variations. The effects of the inclination of the slope, nail length, nail spacing, and nail slope design parameters on the safety coefficient and horizontal displacement were examined. The optimal design suggested nail lengths of 4.00 m, a spacing of 1.60 m, and slopes of 20°. It was discovered that the effect of the inclination degree of the slope on the safety coefficient was lower than expected. The results revealed that a more economical design with a similar safety factor can be obtained by shortening the lengths of the nails. Full article