Bank Slope Research Articles

Numerical analysis of failure mechanism and stability of reinforced embankment with DCM soft soil composite foundation

The deep cement mixing (DCM) method has been widely used in offshore geotechnical engineering. At present, the reinforcement form of pile has been researched widely, but there is a lack of understanding of the failure mode of DCM pile composite foundation reinforcement for bank slopes. In this paper, a series of unconfined compression tests was conducted to obtain necessary numerical analysis parameters. A series of study on the failure mechanism and stability control of DCM pile composite foundation reinforcement bank slope has been conducted through numerical analysis. The results of numerical analysis indicate that under different reinforcement conditions, there exists an optimal reinforcement depth, and the safety coefficient will gradually stabilize at 1.45; The bending moment of the piles under the bank slope the bending moment of the pile body under the road surface Under different overloads. The maximum bending moment of the pile body is located near one-third of the pile body, and the maximum bending moment of the pile body is located between the shoulder and foot of the slope.

Load-bearing response of deep content mixing soft soil composite foundation based on the geotechnical centrifugal model test

Deep cement mixing (DCM) is an effective method of treating soft underwater soil foundations. Currently, the real-time failure development of a composite foundation cannot be obtained by most model tests of DCM pile foundation reinforcement. In this study, a circuit device for identifying pile failure and that can reflect the real-time working state of piles arranged at different positions in a soft soil composite foundation was developed. By applying this device to a geotechnical centrifugal model test, the load-bearing response process of a bank slope reinforced with a soft-soil composite foundation and DCM piles was studied. The failure development law of the DCM piles, ultimate surcharge of the bank slope, failure mode of the foundation, and the pile-soil stress ratio were determined from the test results. The law obtained in this study provides a reference for the application of DCM piles in underwater soft soil foundation engineering.

Effects of freeze–thaw on bank soil mechanical properties and bank stability

Riverbank instability in the seasonally frozen zone is primarily caused by freeze–thaw erosion. Using the triaxial freeze–thaw test on the bank of Shisifenzi Bend in the Yellow River section of Inner Mongolia, we investigated the changes in the mechanical properties of the soil at different freezing temperatures and freeze–thaw times, and analyzed the bank’s stability before and after freezing based on the finite element strength reduction method. The results showed that the elastic modulus, cohesion, internal friction angle and shear strength of the soil tended to decrease with the increase in the number of freeze–thaw cycles and the decrease in freezing temperature. After 10 freezing cycles at − 5 ℃, − 10 ℃, − 15 ℃ and − 20 ℃, the modulus of elasticity of soil decreased by 40.84 ~ 68.70%, the cohesion decreased by 41.96 ~ 56.66%, the shear strength decreased by 41.92 ~ 57.32%, respectively. Moreover, the stability safety coefficient of bank slope decreased by 18.58% after freeze–thaw, indicating that the freeze–thaw effect will significantly reduce the stability of bank slope, and the bank slope is more likely to be destabilized and damaged after freeze–thaw.

The overall stability of a partially unstable reservoir bank slope to water fluctuation and rainfall based on Bayesian theory

The overall stability of a partially unstable reservoir bank slope to water fluctuation and rainfall based on Bayesian theory

Influence of bank slope on sinuosity-driven hyporheic exchange flow and residence time distribution during a dynamic flood event

Abstract. This study uses a reduced-order two-dimensional (2-D) horizontal model to investigate the influence of the riverbank slope on the sinuosity-driven hyporheic exchange process along sloping alluvial riverbanks during a transient flood event. The deformed geometry method (DGM) is applied to quantify the displacement of the sediment–water interface (SWI) along the sloping riverbank during river stage fluctuation. This new modeling approach serves as the initial step focusing on the impact of the bank slope on the hyporheic exchange flux (HEF) and the residence time distribution (RTD) of pore water in the fluvial aquifer for a sinuosity-driven river corridor. Several controlling factors, including sinuosity, alluvial valley slope, river flow advective forcing and duration of flow, are incorporated into the model to investigate the effects of bank slope on aquifers of variable hydraulic transmissivity. Compared to simulations of a vertical riverbank, sloping riverbanks were found to increase the HEF. For sloping riverbanks, the hyporheic zone (HZ) encompasses a larger area and penetrated deeper into the alluvial aquifer, especially in aquifers with smaller transmissivity (i.e., due to increased hydraulic conductivity or reduced specific yield). Furthermore, consideration of sloping banks as compared to a vertical riverbank can lead to both underestimation and overestimation of the pore water travel time. The impact of bank slope on residence time was more pronounced during a flood event for high-transmissivity aquifer conditions, while it had a long-lasting influence after the flood event in lower-transmissivity aquifers. Consequently, the impact of bank slope decreases the travel time of water discharging into the river relative to base flow conditions. These findings highlight the need for (re)consideration of the importance of complex riverbank morphology conceptualization in numerical models when accounting for the HEF and RTD. The results have potential implications for river management and restoration and the management of river and groundwater pollution.

A photographic method to identify reservoir geohazards induced by rock mass deterioration of hydro-fluctuation belt

Potential geohazards triggered by the rock mass deterioration (RMD) of the hydro-fluctuation belt (HFB) in the Three Gorges Reservoir area (TGRA) severely threaten the lives and property of people, it is necessary and urgent to timely identify this kind of potential geohazard. Aiming at this issue, several typical evolution modes of potential RMD-induced geohazards were generalized, and an unmanned aerial vehicle (UAV) photographic method integrating the orthophotography, three-dimensional multi-angle oblique photography and high-precision digital elevation model (DEM) was proposed to early recognize the newly formed potential RMD-induced geohazards. By resolving the problem of poor precision in the orthophotographic images of high steep bank slopes, the proposed method improved the recognition reliability of potential reservoir geohazards in the HFBs. Taking the bank slopes from Zigui County to Badong County as the study area, 116 new potential RMD-induced geohazard sites were identified by the presented approach, including 64 and 52 sites on the left and right bank, respectively. Through field verifications, 17 and 19 sites on the left and right bank were found to be consistent with existing hazards, indicating the effectiveness of the proposed approach in avoiding the false and missing recognitions of potential RMD-induced reservoir geohazards at current levels of knowledge and technology. The study can provide a valuable reference for the early identification of RMD-induced geohazards in reservoir areas.

Experimental investigation of the efficiency of stone revetment for different temporal variations with the static water condition

Abstract The objective of this study is to determine the optimum size of stone revetment for different water standing durations and critical drawdown rates for 80% height of flood. The model bank was constructed using soil sourced from the Parlalpur ferry ghat of the Ganga River in Kaliachak, West Bengal, with a field density of 1.5 g/cc achieved by maintaining a 10% moisture content (MC) in the model bank soil. The model river bank was prepared considering Froude (F) similitude having a distorted depth scale of 1/20 and a linear scale of 1/200. In this study, effective stone sizes (D10) – 2.3, 3.22, 4.58, 6.31, and 8.84 mm – were used. These stone sizes were investigated in conjunction with three water standing durations: 15, 30, and 45 min. The bank slope was prepared at 1V:1.5H, and a drawdown ratio of 80% was maintained. The effectiveness of stone revetment size was analysed in terms of the percentage loss of stone revetment and the percentage loss of the model bank's cross-sectional area. The outcomes of this study indicate that the 6.31 mm stone size exhibits optimal performance.

Seismic collaborative reliability analysis for a slope considering spatial variability base on optimized subset simulation

Seismic reliability analysis of actual slopes considering the spatial variability of soil materials is crucial. However, for the discretization of large-scale random fields, high-precision finite element analysis and analysis of small failure probability events, the random analysis of slopes under seismic loads is inefficient. To address this situation, this study proposes a collaborative reliability analysis framework based on the modified linear estimation method (MLEM) and optimized subset simulation (OSS). First, the random field of the uncertain parameters of the Jinping-I left bank slope model is efficiently discretized by the MLEM, and a sensitivity analysis is carried out. Then, considering the adoption of different degrees of cross-correlation of the sensitive random parameters, the OSS method is used to perform random finite element analysis on the coarse mesh model. Finally, the fine mesh samples are obtained according to the response conditioning method (RCM). The MLEM is used to ensure the consistency of the two sets of random fields, and the seismic failure probability and reliability index of the slope under different cross-correlation coefficients of uncertain parameters are obtained. The results suggest that the degree of cross-correlation of parameters has a great influence on the seismic reliability of the slope. Considering that the shear strength parameters of geotechnical materials are often negatively correlated, the fine analysis based on a fine model is necessary.

Impact pressure of waves generated by landslides on bank slopes

Impact pressure of waves generated by landslides on bank slopes

Exploring landscape and geologic controls on spatial patterning of streambank groundwater discharge in a mixed land use watershed

AbstractPreferential groundwater discharge features along stream corridors are ecologically important at local and stream network scales, yet we lack quantification of the multiscale controls on the spatial patterning of groundwater discharge. Here we identify physical attributes that best explain variation in the presence and lateral extent of preferential groundwater discharges along two 5th order streams, the Housatonic and Farmington Rivers, and 32 1st to 4th order reaches across the Farmington River network. We mapped locations of preferential groundwater discharge exposed along streambanks using handheld thermal infrared cameras paired with high‐resolution topographic and land use land cover datasets, surficial soil characteristic maps, and depth‐to‐bedrock geophysical measurements. The unconfined Housatonic River, MA, USA (12 km) had fewer discharge locations and less lateral extent (41 discharge locations with 38 m of active discharge/km of river) compared to the partially confined Farmington River, CT, USA (26 km; 169 discharge locations with 129 m of active discharge/km of river). Using a moving window analysis, we found along both rivers that discharge was more likely to occur where bank slopes were steeper, floodplain extent was narrower, and degree of confinement was higher. Along the Farmington River, groundwater discharge was more likely to occur where saturated hydraulic conductivity was higher and depth‐to‐bedrock was shallower. Among the 32 stream reaches surveyed (33.2 km of total stream length) within the Farmington River watershed, preferential discharge was observed in all but two stream reaches, varied from 0 to 25% of lateral extent along stream banks (mean = 6%), and was more likely to occur where stream reach slopes were steep, saturated hydraulic conductivity was high, and watershed urbanization was low. Our results show that, though both surface (e.g., topographic, land use land cover) and subsurface (e.g., soil characteristics, bedrock depth) factors control the prevalence of streambank preferential groundwater discharge, the dominant controls vary across valley settings and stream sizes.

A meso‐damage‐based constitutive model for yellow sandstone under dry–wet cycles

AbstractThe mechanical properties of rocks weaken under dry–wet cycles. This weakening may significantly modify the safety reserve of underground caverns or reservoir bank slopes. However, meso‐damage has not been carefully studied based on micromechanical observations and analyses. Therefore, in this study, meso‐damage of a yellow sandstone is investigated and a meso‐damage‐based constitutive model for dry–wet cycles is proposed. First, computed tomography scanning and uniaxial compression tests were conducted on yellow sandstones under different dry–wet cycles. Second, the evolution of rock mesostructures and the damage mechanism subjected to dry–wet cycles were simulated using the discrete element method with Particle Flow Code in 2 Dimensions (PFC2D) software. Third, a constitutive model was proposed based on the meso‐statistical theory and damage mechanics. Finally, this constitutive model was verified with the experimental results to check its prediction capability. It is found that the radius and number of pore throats in the sandstone increase gradually with the number of dry–wet cycles, and the pore structure connectivity is also improved. The contact force of sandstone interparticle cementation decreases approximately linearly and the continuity of the particle contact network is continuously broken. The meso‐deformation and strength parameters show similar declining patterns to the modulus of elasticity and peak strength of the rock sample, respectively. This meso‐damage‐based constitutive model can describe well the rock deformation in the initial pressure density stage and the damage stage under the coupling effect of dry–wet cycles and loads.

Rock anchor hanger effect on single-tower earth-anchored suspension bridge mechanical performance: An analytical model and multi-objective golden eagle optimization

The application of a composite saddle in single-tower earth-anchored suspension bridges (STEASBs) replaces the tower on the steep slope side, which is a cost-effective solution that improves bridge safety and provides environmental protection for the steep bank slope of the valley. However, this novel bridge design needs an appropriate model to evaluate the effect of rock anchor hangers on the structure in the non-girder area and adjust their parameters to optimize the mechanical response of the whole bridge structure. This study proposes an approach to quickly evaluate the most unfavorable load cases of the STEASB and further optimizes the structural parameters of rock anchor hangers to enhance structural safety. An analytical model for the STEASBs under the live load is proposed and verified by the finite element model (FEM), with the maximum relative error not exceeding 7.37%. Combined with the golden eagle optimizer (GEO), the most unfavorable load cases of the corresponding design indices are yielded. The Pareto optimal solutions for the spacing, cross-sectional area, and initial tension of the vertical rock anchor hangers are obtained through multi-objective optimization to improve the mechanical behavior of STEASBs. In addition, it is clarified that the main function of rock anchor hangers is to reduce the peak value of the stress amplitude of the hangers and girder-end rotation, providing a theoretical basis for the STEASB design.

A Case Study for Stability Analysis of a Toppling Bank Slope with Fault Fracture Zones Developed under the Action of Bridge Loads and Reservoir Water

The mountainous areas of Southwest China have the characteristics of valley deep-cutting, a large topographic gradient, complex geological structures, etc. With the development of infrastructure construction in the area, the construction of bridges across valleys has gradually increased, and the phenomenon of slope failure occurs more and more frequently. As the weak interlayer, the fault fracture zones have a significant influence on the geological structure and stability of slopes, while the complexity of the mechanism of the deformation and failure of slopes increases with the combination of the development of the fracture zones and toppling deformation. This paper took the toppling bank slope of bridge foundations developed with fault fracture zones in Lancang River as the research object. Through an on-site field survey and geological survey technologies, it identified the distribution range of the fracture zones on the bank slope and determined the characteristics of the rock mass in the fracture zones. A stability evaluation model for the bank slope of the bridge foundations was established using the limit equilibrium method and discrete element method. Based on the two-dimensional limit equilibrium analysis, the potential failure modes of the bank slope were explored, and the stability of the bank slope under bridge loads was calculated. Through the three-dimensional geological model of the bank slope, including the fracture zones and toppling bodies, the three-dimensional discrete element numerical simulation method was adopted to simulate and calculate the deformation and failure process of the bank slope under different bridge loads and working conditions. According to the calculation results, the influence of bridge loads and reservoir water on the stability of the bank slope was analyzed from the perspectives of displacement, plastic zone, stability coefficient, and other factors. The formation process of the plastic zone and the development of the sliding surface were revealed, the incentive mechanism of bridge loads and reservoir water on the deformation and failure of the bank slope was analyzed, and the influence of fault fracture zones on the stability of the bank slope and the development of toppling deformation was determined. The results indicate that the fault fracture zones are important geological structures that affect the deformation and failure of the bank slope as a weak interlayer. Under the influence of bridge loads and reservoir water, the stability of the bank slope is affected by the quality of the rock mass and the development of the fault fracture zones, resulting in the unmet need for safety requirements and maybe leading to instability. Based on the calculation results of the stability evaluation prediction model for the bridge foundation bank slope and the engineering geological conditions, the bridge scheme has been selected.

Phreatic Surface Calculation and Stability Analysis of Three-Dimensional Bank Slopes with Reservoir Drawdown

Phreatic Surface Calculation and Stability Analysis of Three-Dimensional Bank Slopes with Reservoir Drawdown

Variáveis ambientais como preditoras da assembleia de peixes em sistemas aquáticos semiáridos

Abstract Aim To understand the distribution of fish species and their use of habitat, a range of environmental variables were evaluated as predictors of fish assemblage composition and richness in tropical semiarid aquatic systems. Methods We surveyed the species composition of fish assemblages in semiarid aquatic systems and established their degree of association with the structure of the aquatic habitat. Sites consisted of stream reaches with surface water flow, isolated temporary pools, and man-made reservoirs. Fish sampling was conducted on four occasions during the wet (April and June 2006) and dry seasons (September and December 2006). The correlation between richness and abundance with the habitat structure was evaluated using stepwise multiple regression. Patterns of variation in fish assemblage composition across sites were evaluated using Nonmetric Multidimensional Scaling, and the Indicator Species Analysis was used to determine which species were significant indicators of sites. To establish multivariate correlations and test the hypothesis of local fish composition being associated with the environmental variables we used a Canonical Correspondence Analysis. Results Morphometric variables, stream reach width, stream length and elevation explained 75.6% of the variation in fish richness. Macrophyte cover and overhanging vegetation added to the predictive power of the model equation, where the final model explained 86.9% of the variation in fish richness. Canonical Correspondence Analysis showed a significant relationship between fish composition data and site morphology (altitude, bank slope and littoral depth). Among the water quality, habitat composition and substrate variables, temperature, sand, and gravel showed higher correlation with the CCA axes. Conclusions These results indicated that fish communities assume different structures and compositions across different habitat types following the environmental heterogeneity in dryland aquatic systems.

Risk screening of large reservoir bank slopes based on deformation monitoring using InSAR technology-A case study of the Baihetan reservoir bank

Abstract The large reservoirs in the southwestern Alpine Canyon region are characterized by long reservoir banks and complex geological structures. The problem of finding the deformation zone quickly and efficiently is urgent and needs to be resolved. In this study, taking the area 110 km upstream of the Baihetan dam site as the study area, the applicability of various interferometric synthetic aperture radar (InSAR) techniques was summarized, and the small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) method was used to carry out large-scale disaster risk screening using multi-source satellite SAR data. A total of 40 hidden danger points were identified, with 22 of them being newly discovered. The differences in the deformation results from the multi-source satellite SAR data were discussed. By analyzing ComparSAR-based deformation monitoring results of a large reservoir, a new risk screening method for slopes in alpine-canyon regions can be provided.

Geosynthetic solutions for river and coastal protection works

Riverine floods and coastal erosion are some of the most frequent natural calamities in India that affect millions of people, cause loss of lives, and damage infrastructure and agriculture. Application of geosynthetic products provides a sustainable, eco-friendly, quick & economical solution among all the conventional river and coastal protection works. This paper focuses on geosynthetic solutions to the river and coastal erosion with the help of case studies. To safeguard against the frequent floods, the banks of the river Brahmaputra near Lakhimpur were strengthened while providing geosynthetic anti-erosion measures. A sandfilled geotextile mattress of 0.1m thickness was provided on the river bank slopes of the Brahmaputra River, Assam. Also, this paper reveals the successful application of specially engineered nonwoven geotextile bags with high abrasion resistance, to mitigate the effects of erosion of the banks of Churni River, West Bengal. This solution reinforces the embankment's edge and increases the factor of safety against repeated floods. The third case study discusses the coastal protection work at Kattupalli, Tamilnadu where a 620ms long shoreline was protected against progressive beach erosion. An embankment was formed using 6 numbers of 3.0m theoretical diameter and 20.0m long high-performance geotextile tubes in crosssection and a small geotextile tube was used for scour protection ahead of the structure. The embankment thus formed also provided ways for beach nourishment and land reclamation at the site.

Investigating the role of geo-fluvial parameters on model river banks: A flume study

This experimental investigation aimed to analyze the failure profile of a model river bank composed of sand and silty clay. A model river bank with a length of 446 cm, a depth of 32 cm, and a slope of 1V:1.5H was prepared in a flume that was 550 cm long, 150 cm wide, and 60cm deep. Froude-number-based reduced-scale distorted river modeling was considered in this study. For modeling different parameters of flume, the linear scale 1:250 and depth scale 1:20 have been taken. The study was divided into two distinct series: Series-A and Series-B, each designed to explore specific soil types and moisture content variations. In Series-A, physical model tests were conducted using cohesionless soil (sand) with an initial moisture content set at 6% and 13%. Conversely, Series-B involved model banks constructed with silty clay soil, with initial moisture contents of 10% and 15%. Both series utilized a consistent model bank slope of 1V:1.5H. The drawdown conditions, set at 50% and 80% of the model riverbank’s height, were integral to the experiments in both Series-A and Series-B. The impact of moisture content, drawdown, and bank material was observed in the failure of the model bank.

Numerical Simulation of the Structural Performance of Ecological Toughness of Canal Bank Slopes and Its Influence Law Study

Numerical Simulation of the Structural Performance of Ecological Toughness of Canal Bank Slopes and Its Influence Law Study

Habitat status of the Smooth-coated Otter (Lutrogale perspicillata) in Geruwa-Khaurahi River, Bardia National Park, Nepal

Smooth-coated Otter (SCO), a top predator and health indicator of the aquatic ecosystem is included as vulnerable on the IUCN red list and listed in Appendix I. Geruwa-Khaurahi River (GKR) was observed to determine the habitat status of SCO between Bardiya National Park (BNP) and Khata Corridor (KC), and to evaluate factors affecting the SCO habitat, data on habitat parameters and SCO signs were collected in each transect of 500 m. Principal component analysis was used for the most probable habitat parameter selection. An SCO group of eight was observed at Lalmati on the broad, shallow, and fast-flowing GKR with a sandy island and a flat stone bank with a vast escape distance. All signs were found on the sandy shoreline of the riverine forest with nearby tall Saccharum coverage over a narrow escape cover with a gentle bank slope. Diversions of water from the Geruwa River to the narrow and shallow Khaurahi River resulted in fast-flowing water where SCO pugmarks were found abundant. But at KC, human disturbances, over-fishing, river mining, and infrastructures have made the river unsuitable for SCO. SCO preferred dense riverine forests where the gentle riverbank has sand and/or tall Saccharum in between a narrow escape distance. Also, the narrow river with shallow depth and slow flow of good water quality was preferred by SCO. Lastly, with minimal human disturbance, further study on feeding ecology and population dynamics is requisite to conserve the suitable habitat of the SCO.