Explore the vast range of titles available.

Many experiments were done over a relatively wide range of effective parameters to determine the stable size of riprap stones around wing-wall abutments. The experiments involved five sizes of riprap stones, three abutment lengths, and various flow depths and velocities. The results of this study indicate that in the range of tested parameters, the most important factors influencing riprap instability are the upstream Froude number, the ratio of abutment length to flow depth, and the ratio of abutment width (thickness) to flow depth. Based on the experimental results, a relation for designing the stable size of riprap around wing-wall abutments is presented and compared with previous equations developed for different shapes of bridge abutments.

The installation of steel casings in riprap-covered macro-tidal estuarine mudflats is governed by a complex interplay of soil, tidal and pore-water pressures, frequently causing the casing to refuse to penetrate or to deviate from its design alignment. Perforating steel casings can effectively mitigate the adverse pressure build-up described above, yet it simultaneously compromises casing strength and stability. Taking the steel casings of a typical Chinese seawall project as the reference, this study employs finite-element modelling to simulate the entire installation process and quantify how varying perforation patterns alter the internal forces and stress-concentration factors at the openings when the casing is driven through riprap-armoured macro-tidal estuarine mudflats. The results indicate that perforations lower the casing’s global shear and bending capacity, which in turn loosens the soil plug at the tip and markedly reduces penetration resistance. This reduction in resistance, however, amplifies both the horizontal and vertical displacements generated when the casing strikes riprap blocks. Under dynamic impact and riprap-reaction forces, the stress-concentration curves for openings situated closer to the load becomes flatter and the corresponding factor diminishes, signifying a more uniform stress distribution over the cross-section. Moving the perforation away from the casing head progressively raises the stress-concentration factor and intensifies the local peak. Star-shaped perforations yield markedly smoother stress-concentration curves than either single- or twin-directional patterns. These findings furnish a quantitative basis for selecting perforation geometry and placement when driving steel casings through riprap armour in macro-tidal estuarine mudflats.

The widespread distribution of riprap in estuarine mudflats has brought significant challenges to the penetration construction of steel casings. To reveal the effects of casing length, diameter and wall thickness on the stress and deformation, as well as the deformation characteristics and mechanical behaviors of the steel casing during the sinking process, the paper utilizes finite element method to construct a three-dimensional numerical model of the collision between steel casings and riprap in mudflat. The research results indicate that longer steel casing has better crushing effect on the riprap, smoother deflection curve of the casing body and smaller deformation at the casing end under the same casing diameter and wall thickness conditions. Under the same casing length and wall thickness conditions, the steel casing with a larger diameter has a better crushing effect on the riprap and smaller deformation at the casing end. As the casing diameter increases, the stress values of S11 and S33 in the soil at the casing end gradually decrease, and the range of stress concentration gradually increases. This study can provide a theoretical basis for the design and construction of steel casings in the riprap environment of the mudflat near the estuaries.

Riprap stones are frequently applied to protect rivers and channels against erosion processes. Many empirical equations have been proposed in the past to estimate the unit discharge at the failure circumstance of riprap layers. However, these equations lack general impact due to the limited range of experimental variables. To overcome these shortcomings, support vector machine (SVM), multivariate adaptive regression splines (MARS), and random forest (RF) techniques have been applied in this study to estimate the approach densimetric Froude number at the incipient motion of riprap stones. Riprap stone size, streambank slope, uniformity coefficient of riprap layer stone, specific density of stones, and thickness of riprap layer have been considered as controlling variables. Quantitative performances of the artificial intelligence (AI) models have been assessed by many statistical measures including: coefficient of correlation (R), root mean square error (RMSE), mean absolute error (MAE), and scatter index (SI). Statistical performance of AI models indicated that SVM model with radial basis function (RBF) kernel had better performance (SI = 0.37) than MARS (SI = 0.75) and RF (SI = 0.63) techniques. The proposed AI models performed better than existing empirical equations. From a parametric study the results demonstrated that the erosion-critical stone-referred Froude number (Fs,c) is mainly controlled by the streambank slope.

One of the common methods for scour protection around bridge piers is riprap layer. In previous studies, sizing riprap layer was used to ensure 100% protection against scouring. However, in many cases, limited scour depth around a pier may be accepted if only smaller riprap sizes are available. In the present work, the effects of the smaller size of riprap stones compared to their stable size on the scour depth around a bridge pier were studied. Circular and oval shapes for riprap extent and both round and angular stone shapes were also tested. All tests were conducted at the threshold of bed sediment motion, and the maximum scour depth was measured. The results of these experiments showed that with stone sizes closer to stable riprap material, the efficiency of both round and angular stone shapes was identical. As the size of riprap reduced, deeper scour holes were observed with both round and angular shape materials. The results also indicated that increasing the extent of the riprap layer from circular to oval with 5 times more riprap volume had insignificant effects on scour hole for angular shape riprap and, also, reduced the scour hole depth with round shape material. Based on experimental data, a method was developed to calculate a smaller riprap size based on an accepted limited scour hole.

Protecting coastal communities has become increasingly important as their populations grow, resulting in increased demand for engineered shore protection and hardening of over 50% of many urban shorelines. Shoreline hardening is recognized to reduce ecosystem services that coastal populations rely on, but the amount of hardened coastline continues to grow in many ecologically important coastal regions. Therefore, to inform future management decisions, we conducted a meta-analysis of studies comparing the ecosystem services of biodiversity (richness or diversity) and habitat provisioning (organism abundance) along shorelines with versus without engineered-shore structures. Seawalls supported 23% lower biodiversity and 45% fewer organisms than natural shorelines. In contrast, biodiversity and abundance supported by riprap or breakwater shorelines were not different from natural shorelines; however, effect sizes were highly heterogeneous across organism groups and studies. As coastal development increases, the type and location of shoreline hardening could greatly affect the habitat value and functioning of nearshore ecosystems.

A 1:15 scale physical hydraulic model was designed and constructed to investigate the incipient failure conditions of large angular riprap. A total of 32 tests were performed on angular riprap dumped on steep bed slopes of 0.333 to 0.5, and against a steep side-bank slope of 0.4 in a wide trapezoidal channel. The critical movability number value defining the critical incipient failure conditions of angular riprap on steep bed slopes and steep side-bank slopes was determined to be 0.12 and 0.227, respectively. Based on the HECRAS 1-dimensional (1-D) steady-state flow analysis, it was identified that HEC-RAS overestimates the critical incipient failure movability number of the steep bed and steep side-bank riprap by a critical factor of 1.91 and 1.35, respectively. The applicability of the study's findings is limited to prototype riprap D50 sizes of 0.57 m to 1.125 m, and a trapezoidal canal bottom-width to D50 ratio of 16:31 (Wbase: D50).

Lee, B.W.; Yoon, J.-S.; Ko, D., and Song, H.-G., 2023. Optimization of structural scales for ripraps and gabions at seadike closure. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, pp. 6-10. Charlotte (North Carolina), ISSN 0749-0208. This paper presents the results of a long-term hydraulic experiment examining the fabricated ripraps and gabions used in the construction of the final closure on the Saemangeum seadike. While focusing on a sill-crest, a bottom protection, and a dam face, the critical velocities were measured at different cross-sections in this experiment. Due to limitations in terms of the size and volume of ripraps that could be collected on-site for this experiment, an alternative study was conducted to compare the critical velocities of fabricated gabions with those of ripraps. Moreover, critical velocities were measured in cases where ripraps and gabions were used together. Based on the above investigations, this study provides suitable mixing ratios for gabions in cases where the sizes and critical velocities of ripraps are insufficient. Critical velocities were obtained from data for previously predicted daily and hourly velocities during the construction of the final closure. Further, riprap sizes were provided for different water depths with consideration of the changes in water depth caused by the construction. As a result, losses of materials (i.e., ripraps and gabions) were minimized during the construction, and this study could contribute to the final closure on the Saemangeum seadike.

In order to solve the construction problem of deep ripped-rock cofferdam occluding pile under complex geological conditions, this paper studies the occluding pile engineering of Shenzhen-Zhongshan Link Construction pipe prefabrication yard as carrier. The research contents of this paper include the formation of occlusal pile, the reasonable combination of construction equipment, the optimization of concrete mix ratio, the treatment of isolated rock and the demolition of occlusal pile, etc., forming the key technology of the construction of cofferdam concrete occlusal pile under complex geological conditions at sea. Through the construction practice, the application of this technology has obtained a good effect of water sealing, and can provide reference for subsequent similar projects.

Karangnongko Weir is planned to be located in the Bengawan Solo River (Lower Solo River Basin) about 15 km downstream of the confluence of Bengawan Solo River with the Madiun River in Ngelo Village, Margomulyo Sub-District, Bojonegoro Regency, and Ngrawoh Village in Kradenan Sub-District, Blora Regency. This study aims to determine the Depth and pattern of scouring in downstream energy dissipation through physical model tests based on initial planning. Downstream protection of energy dissipation in the original design model combines 50 m of riprap rocks and 50 m of riprap concrete for a total length of 100 m of protection. The maximum scouring pattern occurred at elevation + 17.64 m, where the scouring was 4.36 m deep, from the planned essential height of Height 00 m. Thus, the downstream protection of energy dissipation was extended to 112 m in riprap concrete blocks for the final design model. Scouring at the end of riprap was 3.04 m, the original elevation of the river bottom of + 22.00 m, down to + 18.96 m. It is concluded that the protection is effective in reducing scouring by up to 30.27%.