Roughness Coefficient Research Articles

Unloading effect of the shear resistance of rock joints

To investigate the stress path dependent of rock joints, a series of tangential loading tests and normal unloading tests were conducted using 32 cement mortar replicas of artificially split rock joints with 4 different joint roughness coefficients (JRC). The critical normal stresses of the unloading tests were recorded, and a comparative study was conducted by referencing the results under different loading paths and joints conditions. The test results indicate that the shear resistance has a distinct unloading effect, which is mainly influenced by the morphologic characteristics, normal stress levels and stress paths. By analyzing the results, it can be concluded that the variation trend of shear/normal stress ratio against the normal stress and JRC of the two test conditions were identical. However, under low normal stress condition, the stress ratio of the joints under normal unloading stress path is the higher one; while under higher normal stress, the relationship becomes converse. Compared to that of the tangential loading condition, shear/normal stress ratio of the unloading stress path reduces rapidly as the increasing of normal stress, and the influence of the morphology is masked under lower normal stress.

Correction of Empirical Equations Known as “Strickler-Type” for the Calculation of the Manning’s Roughness Coefficient for Costa Rica’s Northern Pacific Conditions

When using numerical models for hydraulic simulations of rivers, calibration is key to be able to reflect accurately the interaction of water flow in the channel and to make it resemble what is observed. In this study, a calibrated two-dimensional hydraulic model was created for two control paths located in the Ahogados and Tempisquito rivers. Paths were analyzed morphologically from a grain-size analysis and the different roughness coefficients were calculated through a numerical model using the empirical equations known as “Strickler-type” as a first approximation and later adjustment by a factor obtained from comparing the observed and simulated data. It was identified that both paths are mountain rivers with beds of coarse material, mostly boulders (cobble gravel) and pebble gravel. Calibrated roughness coefficients were determined with an error percentage between the area of the pattern formed by the simulated and observed of less than 10%, and new empirical equations adjusted to the characteristics of the riverbeds were formulated.

Mechanism and Internal Stability of Supportive Stone Constructions.

Natural stone constructions for the protection of slopes, banks and riverbeds are widely used in infrastructure engineering. These structures are made of stacked natural stones, which can be placed loosely on top of each other. Additionally, their bond behavior can be improved by using concrete mortar to fill the joints between the stones. Although such structures are now widely used, there is still a need for research concerning their inner stability and the structural design of such protective stone structures. In this study, experimentally, investigations were made to determine the force transmission and the interaction between rock and concrete mortar by deriving characteristic values of the adhesion strength and friction angle at different scales. A method for the determination of shear parameters from direct shear testing is used, considering the interaction between vertical and horizontal forces in the joint. In the course of these investigations, the roughness of the rock surface was recorded using conventional visual methods using the joint roughness coefficient (JRC) as well as via laser imaging. By applying laser scanning, a theoretical roughness factor could be derived. Furthermore, the properties of the rocks of the concrete mortar (fresh and hardened concrete mortar properties as well as a durability characteristic) were investigated in detail. It could be shown that different types of concrete mortar result in different bond strengths—expressed as tensile and shear strengths—when applied to a stone surface. The roughness of the stone surface has a positive influence on the tensile and shear strength between the stone and the mortar. Based on the test results, a failure description based on the Mohr–Coulomb fracture criterion could be determined, which can be used to calculate characteristic parameters for the design of stone support bodies. It was also shown that the stone’s compressive strength is being exceeded through load due to very punctual contact areas. Moreover, concrete mortar differs significantly from conventional concrete in terms of its mechanical properties due to the on-site installation conditions, which allow no dynamic compaction.

Multi-objective optimization of pressure sensor location for burst detection and network calibration

This paper proposes a methodology to determine the optimal location of pressure sensors for the simultaneous calibration of the hydraulic network model and the detection of pipe bursts. The methodology considers a search space reduction process and aims at maximizing nodal pressure sensitivities to both pipe roughness coefficients and pipe burst sizes. A multi-objective optimization problem is formulated for a given number of sensors and multiple optimal configurations of pressure sensors are obtained. Three different optimal configurations are selected and compared: one solution that individually maximizes each objective function (two solutions) and one trade-off solution. The methodology is applied to a real water distribution network with hourly consumption data. Results demonstrate that (i) the optimal location of pressure sensors hardly changes with the perturbation values used to numerically compute the sensitivities and (ii) minor differences can be found in the performance of pipe roughness calibration and pipe burst location by using either a solution that individually maximizes each objective function or the trade-off solution considering the high number of pressure sensors (26) and the oversized pipe diameters to comply with firefighting conditions, being pressure less sensitive to friction and flow rate changes.

A Hybrid Approach to Improve Flood Forecasting by Combining a Hydrodynamic Flow Model and Artificial Neural Networks

Climate change is driving worsening flood events worldwide. In this study, a hybrid approach based on a combination of the optimization of a hydrodynamic model and an error correction modeling that exploit different aspects of the physical system is proposed to improve the forecasting accuracy of flood water levels. In the parameter optimization procedure for the hydrodynamic model, Manning’s roughness coefficients were estimated by considering their spatial distribution and temporal variation in unsteady flow conditions. In the following error correction procedure, the systematic errors of the optimized hydrodynamic model were captured by combining the input variable selection method using partial mutual information (PMI) and artificial neural networks (ANNs), and therefore, complementary information provided by the data was achieved. The developed ANNs were used to analyze the potential non-linear relationships between the considered state variables and simulation errors to predict systematic errors. To assess the hybrid forecasting approach (hydrodynamic model with an ANN-based error correction model), performances of the hydrodynamic model, two ANN-based water-level forecasting models (ANN1 and ANN2), and the hybrid model were compared. Regarding input candidates, ANN1 considers the historical observations only, and ANN2 considers not only the historical observations that used in ANN1 but also the prescribed boundary conditions required for the hydrodynamic forecast model. As a result, the hybrid model significantly improved the forecasting accuracy of flood water levels compared to individual models, which indicates that the hybrid model is able to take advantage of complementary strengths of both the hydrodynamic model and the ANN model. The optimization of the hydrodynamic model allowing spatially and temporally variable parameters estimated water levels with acceptable accuracy. Furthermore, the use of PMI-based input variable selection and optimized ANNs as error correction models for different sites were proven to successfully predict simulation errors in the hydrodynamic model. Hence, the parameter optimization of the hydrodynamic model coupled with error correction modeling for water level forecasting can be used to provide accurate information for flood management.

Effect of joint roughness coefficient and size on shear and characteristic strengths of structural planes.

Joint roughness coefficients (JRCs) influence the shear and characteristic strengths of structural planes; however, the relationship model of this influence is yet to be derived. This study investigates 11 numerical simulation programs using a realistic failure process analysis software. The influence of size and JRC on the shear strengths of the structural planes was studied. The stress-strain curves of different JRCs and their sizes were analyzed. Mathematical models of the shear strength of structural planes and JRC and sizes were formulated and proposed, and their expressions were obtained. Moreover, mathematical models of JRC and the characteristic size and strength of the structural planes were established.

Experimental study on stress wave propagation in jointed rock coupling the effect of JMC & JRC

The objective of this study is to experimentally investigate how the rough joints effect the stress wave propagation through jointed rocks coupling the effect of the joint matching coefficient (JMC) and joint roughness coefficient (JRC). The Split Hopkinson Pressure Bar (SHPB) apparatus was adopted to conduct uniaxial compression experiments on jointed specimens. The joint matching coefficient (JMC) and joint roughness coefficient (JRC) are introduced as morphology parameters to estimate joint roughness. Based on SHPB experiments, we found out that the joint matching coefficient (JMC) has a greater influence on the transmission and reflection coefficient than the joint roughness coefficient (JRC). Jointed specimens with lower JMC and JRC make less energy transmitted through it and have a smaller transmission coefficient and bigger reflection coefficients. Also, the joint with lower JMC and JRC has less initial stiffness and greater maximum closure.

A New Approach to Solving Linear Fractional Programming Problem with Rough Interval Coefficients in the Objective Function

This paper presents a linear fractional programming problem (LFPP) with rough interval coefficients (RICs) in the objective function. It shows that the LFPP with RICs in the objective function can be converted into a linear programming problem (LPP) with RICs by using the variable transformations. To solve this problem, we will make two LPP with interval coefficients (ICs). Next, those four LPPs can be constructed under these assumptions; the LPPs can be solved by the classical simplex method and used with MS Excel Solver. There is also argumentation about solving this type of linear fractional optimization programming problem. The derived theory can be applied to several numerical examples with its details, but we show only two examples for promising.

Flow Resistance in Lowland Rivers Impacted by Distributed Aquatic Vegetation

This study addressed a research concern that employing a fixed value for the bed roughness coefficient in lowland rivers (mostly sand-bed rivers) is deemed practically questionable in the presence of a mobile bed and time-dependent changes in vegetation patches. Accordingly, we set up 45 cross-sections in four lowland streams to investigate seasonal flow resistance values within a year. The results revealed that the significant sources of boundary resistance in lowland rivers with the lower regime flow were bed forms and aquatic vegetation. The study then used flow discharge as an influential variable reflecting the impacts of the above-mentioned sources of resistance to flow. The studied approach ended up with two new flow resistance predictors which simply connected the dimensionless unit discharge to flow resistance factors, Darcy-Weisbach (f) and Manning (n) coefficients. A comparison of the computed and measured flow resistance values also indicated that 87–89% of the data sets were within ± 20% error bands. The flow resistance predictors were also verified against large independent sets of field and flume data. The obtained predictions using the developed predictors might overestimate flow resistance factors by 40% for other lowland rivers. Based on a different view, according to the findings of this research, seasonal variation of vegetation abundance could show the augmentation in flow resistance values, both f and n, in low summer flows when vegetation covers river bed and side banks. The highest amount of flow resistance was observed during the summer period, during the July–August period.

Global sensitivity analysis in hydrodynamic modeling and flood inundation mapping

Flood simulation with two-dimensional hydrodynamic models is subject to different sources of uncertainties in model configuration, boundary conditions, and model parametrization. HEC-RAS 2D is a widely used hydrodynamic model. Here, we assess the sensitivity of the HEC-RAS 2D to its configuration factors and parameters. We evaluate the impacts of different model configuration factors, including the floodplain and channel roughness coefficients, terrain and mesh size, as well as river boundary conditions on the dynamic of water levels, maximum water level, and flood extent, and determine the importance of these contributing factors for reliable flood inundation modeling using both variogram and variance-based analyses. For our case study, we found that depending on the perturbation scale, the performance measure, and the predicted output, the sensitivity to input factors changes. While for simulation of water level dynamics, the DEM and mesh resolutions are the most important factors, for flood extent mapping the floodplain roughness coefficient and the upstream boundary condition are the key factors. In addition, our analyses indicated that for a reliable simulation of maximum flood water level, modelers need to spend resources on the calibration of floodplain roughness coefficient while using fine DEM and mesh resolutions. Here, we also investigate the role of computational time interval and mesh resolution on the model's run time and accuracy. Our results suggested that reducing the computational time interval has minimum impact, as it increases the model run time without much improving the model accuracy.

Simulation of Poyang Lake water levels and outflow under historical extreme hydrological scenarios

AbstractDue to an intensification of anthropogenic activities and climate change in recent decades, the hydrological connections and relationships between rivers and lakes have been significantly modified globally. Poyang Lake is one of the largest freshwater lakes globally and is one of the few that remain naturally connected to the Yangtze River. To investigate the full hydrological conditions (extreme high and low discharge) of Poyang Lake outflow under current bathymetric conditions, a large‐scale 1D‐ and 2D‐coupled high‐resolution hydrodynamic model of the Poyang Lake basin–Yangtze River system was developed. We simulated the outflow and water levels of Poyang Lake under nine different extreme hydrological scenarios with high precision and computational efficiency. We propose (1) a novel partition calibration method to characterize the roughness coefficient of large water bodies in complicated geographical terrain both for wet and dry seasons; (2) a new method for setting initial conditions for hydrodynamic simulation of large water bodies subject to strong hydrological regulation. Results indicated that (1) maximum outflow and water levels will reach 37,200 m3/s and 22.28 m when Poyang Lake basin floodwater coincides with flooding on the Yangtze River; (2) precipitation over the lake has increased outflow but this has had very limited influence on its changing hydrological pattern; (3) the effect of hydrological conditions within the system differs for both the lake outflow and water level. The research provides important reference conditions for the application of the InfoWorks ICM model in future applications and studies of large river–lake systems.

Evaluation of water supply reliability improvement enabled by on-site greywater reuse systems

Water utilities are under enormous pressure to provide a continuous supply of potable water under the presence of an increasing supply-demand deficit. The deteriorating condition of our centralized water distribution infrastructure exacerbates this uncertainty due to the growing number of main breaks and the associated supply interruptions. Distributed water supply systems leveraging treated household and industrial greywater or blackwater are currently being explored as a sustainable alternative in many arid regions to reduce their dependence on conventional freshwater resources. While the sustainability benefits of such alternate water resources have been established, the reliability improvement benefits have seen limited research. To address this need, the objective of this study is to evaluate the reliability improvement when on-site greywater reuse systems complement existing centralized water distribution infrastructure. This paper presents a computational water supply reliability model adapted to suit both centralized and on-site supply scenarios. This model is applied to a small water distribution system to evaluate the reliability improvement benefits and further assess their sensitivity to a variety of adoption scenarios and infrastructure characteristics. The results reveal that when on-site greywater reuse systems supplement existing water supply systems, the supply reliability improved up to 195% and 65% for the least cost and the reasonable design scenarios, respectively. However, the reliability improved only up to 31% and 23% for the least-cost and reasonable scenarios, respectively, when the centralized system was merely retrofitted with on-site freshwater storage. The subsequent sensitivity analyses found that the improvement in supply reliability decreased with the increase in system age and pipeline failure growth rate, whereas it increased with an increase in maximum usable reclaimed water, treatment efficiency, and the pipeline roughness coefficient. Overall, the results encourage the adoption of on-site greywater reuse systems from the perspective of infrastructure supply reliability.

Influences of rock fragments on the hydraulics and erosion of concentrated runoff in steep spoil heaps on the Loess Plateau of China

The soil–rock mixed spoil heaps are prone to severe soil erosion during heavy rain, causing severe land degradation and ecological and environmental damage. Nevertheless, past research on the erosion on spoil heaps has focused on soil particles that were readily eroded and disregarded the rock fragments (RF) that were not readily eroded. To explore the effect of the RF embedded in spoil heaps on the hydraulics of and erosion caused by concentrated runoff, scour-erosion experiments were implemented on three types of spoil heaps: RF = 7%, RF = 45%, and RF = 69%. The RF clearly reduced runoff and erosion on steep spoil heaps. As the RF increased from 7% to 69%, the runoff intensity and runoff coefficient decreased by 72.9%–79.1% and 83.2%–84.1% respectively, and the sediment concentration, soil denudation rate, and total soil loss decreased by 36.0%–47.8%, 83.7%–87.1%, and 87.0%–92.3%, respectively. Narrow rills were generated during the experiments, and the RF distinctly influenced the rill characteristics. High contents of RF restrained rill retreating and undercutting, and promoted rill widening. With an increase in RF, the flow shear stress and stream power gradually decreased, and the Darcy–Weisbach roughness coefficient increased. These findings imply that the RF dissipated the flow energy and reduced soil detachment capacity and sediment transport capacity. Soil detachment is strongly related to the Darcy–Weisbach roughness coefficient, Reynolds number, and runoff intensity, which may be the preferred descriptors of soil detachment. The current findings indicate that embedded rock fragments could effectively reduce soil loss on steep spoil heaps.

Application of the Harmony Search Algorithm for Optimization of WDN and Assessment of Pipe Deterioration

The relevance of the optimal design of water distribution networks lies in its applicability. Thus, the design must be as efficient and affordable as possible, meaning that it achieves a minimum level of serviceability using an appropriate amount of resources. In this context, an ideal water network requires the use of minimum-size elements to reach the minimum head pressure required for each node of the system with the lowest energy consumption. For this purpose, a relatively new meta-heuristic algorithm, called Harmony Search, was used in this study to optimize the water distribution network of Cheongna International City, Korea, in terms of the pipe diameter. Furthermore, using the same algorithm under a different approach, an assessment of the deterioration of conduits over time was conducted by analyzing the optimal roughness coefficient for the original pipe material, which provides a useful tool for decision making. Other heuristic and meta-heuristic algorithms have been applied to this type of problem; however, Harmony Search provides a convenient implementation at a reasonable computational cost. In this study, Harmony Search is demonstrated to be a valuable tool for water distribution network optimization as well as for pipe aging assessment.

Remote Sensing Methodology for Roughness Estimation in Ungauged Streams for Different Hydraulic/Hydrodynamic Modeling Approaches

This study investigates the generation of spatially distributed roughness coefficient maps based on image analysis and the extent to which those roughness coefficient values affect the flood inundation modeling using different hydraulic/hydrodynamic modeling approaches ungauged streams. Unmanned Aerial Vehicle (UAV) images were used for the generation of high-resolution Orthophoto mosaic (1.34 cm/px) and Digital Elevation Model (DEM). Among various pixel-based and object-based image analyses (OBIA), a Grey-Level Co-occurrence Matrix (GLCM) was eventually selected to examine several texture parameters. The combination of local entropy values (OBIA method) with Maximum Likelihood Classifier (MLC; pixel-based analysis) was highlighted as a satisfactory approach (65% accuracy) to determine dominant grain classes along a stream with inhomogeneous bed composition. Spatially distributed roughness coefficient maps were generated based on the riverbed image analysis (grain size classification), the size-frequency distributions of river bed materials derived from field works (grid sampling), detailed land use data, and the usage of several empirical formulas that used for the estimation of Manning’s n values. One-dimensional (1D), two-dimensional (2D), and coupled (1D/2D) hydraulic modeling approaches were used for flood inundation modeling using specific Manning’s n roughness coefficient map scenarios. The validation of the simulated flooded area was accomplished using historical flood extent data, the Critical Success Index (CSI), and CSI penalization. The methodology was applied and demonstrated at the ungauged Xerias stream reach, Greece, and indicated that it might be applied to other Mediterranean streams with similar characteristics and flow conditions.

Shearing Performance of Natural Joints with Different Roughnesses under Direct Shearing Tests

Roughness is one of the major characteristics of natural fracture in hydrocarbon and geothermal reservoirs, which has a significant influence on the activation of fractures during hydraulic stimulation. The main purpose of this study is to investigate the effect of different roughnesses and high normal stresses on shear behaviors of rock joints. To do this, replicas of natural rock joint surfaces were constructed using the 3D optical scanning and 3D rigid engraving technique. Direct shear tests were performed on rock joint replicas with three joint roughness coefficient (JRC) indices (i.e., 1.42, 4.98, and 7.96) at two high normal load conditions (i.e., 15 and 30 MPa). The results show that the shear strength dependence on surface roughness is similar at normal stresses of 15 and 30 MPa. In addition, JRC-JCS shear strength criterion can reasonably describe the peak shear strengths that obtained from experimental curves, and the peak shear stresses have a positive correlation with JRC values at both normal stresses. Moreover, at normal stresses of 15 and 30 MPa, the shearing mechanism of joints with different JRC values is asperity shearing off. Results also show that the friction coefficient of joint surface increases as joint roughness increases, and higher normal loads may lead to a decrease of apparent cohesion, which weakens the residual strength during the slip. The results of this study improve insight into the natural fracture activation behavior during hydraulic fracturing.

The hydraulic characteristics of Roman lead water pipes: An experimental investigation

An experimental investigation was conducted on two lengths of Roman lead water pipe excavated near Corbridge, Northumberland, England. The pipes date from approximately AD 80. One length of pipe contained a sleeve joint. The pipes were linked to a pump system using 3 D-printed connectors, and the hydraulic head loss along the pipe was measured. The pipe without a joint was used to determine a value for the wall roughness height, fitting the results to the Darcy-Weisbach equation. The wall roughness height obtained was assumed to apply to the pipe with the joint, and the additional head loss observed was then assumed to be due to the joint, allowing determination of a local loss coefficient. The pipes have a sinter encrustation, indicating that they had typically flowed partially full. Using this as an indication of water depth and deriving topographical information from the excavation report, the likely flow the pipes carried during their operational life was estimated. It was concluded that the pipe wall roughness coefficient ks was 0.9 mm, the joint local loss coefficient was 1.159, and that during operation the pipe probably carried around 17 litres/minute.

Flow resistance and velocity distribution in a smooth triangular channel

Abstract This study investigates the flow resistance and velocity distribution in a smooth triangular channel under varying slope conditions in a laboratory environment. For this purpose, two triangular cross-sectional shaped channels with 30° and 45° sidewall slopes were made. In various hydraulic conditions, bed slopes were carried out at different flow discharges and channels. The results have been used to test the stage-discharge curve, Manning roughness coefficient, n, the Darcy-Weisbach friction factor, f, and flow velocity profiles. By increasing the channel bed slope and flow discharge, the water surface fluctuation increased simultaneously. The fluctuation of flow surface profile in the triangular cross section (TCS) at 45° is more than in TCS 30° cases. The stage-discharge rating curve has less curvature with increasing channel bed slope. The Darcy-Weisbach f obtained from TCS 30° is higher than for TCS 45°, which means that TCS 30° has more resistance against flowing water passing through the channel than the 45° cross-section. Examination of the velocity contours shows that the maximum velocity occurred in the 30° triangular cross-section. Practical-sound findings from this research might be helpful for hydraulic engineers to design cost-effective open channels and other similar hydraulic structures.

Analisis Kekasaran Dan Kapasitas Penampang Sungai Galang-Galang Kabupaten Polewali Mandar

Galang-Galang River or Binanga Karaeng River is a research site where this river is a border river between polewali mandar regency and Pinrang regency. In April 2020 there was a flood that damaged irrigation buildings on the right side of the bend downstream of the Galang-Galang River. This research aims to analyze the roughness and cross-sectional capacity of the Galang-Galang River. The data used consists of primary data and secondary data. The methods used in survey methods and location points are determined based on observation points that can represent the upstream, middle, and downstream sections. Analysis of roughness coefficients using manning equations. The coefficient of the galang-galang river upstream is 0.037, the middle is 0.015, and the downstream is 0.037. The difference in the coefficient value of roughness is influenced by cross-sectional irregularities, the size of the sediment grains that differ from each point, and the narrowing of the channel. Cross-sectional capacity in segments 1-1, 2-2, and 3-3 is unable to accommodate Q50 and Q100 flood discharges.

АНАЛІЗ ПРОБЛЕМ ЗАБЕЗПЕЧЕННЯ НАДІЙНОСТІ ТА ДОВГОВІЧНОСТІ ГІДРОТЕХНІЧНИХ СПОРУД ТРАНСПОРТНОГО БУДІВНИЦТВА З ДОРОЖНІХ ВОДОПРОПУСКНИХ ТРУБ В УМОВАХ ЕКСПЛУАТАЦІЇ

Abstract. Introduction. Failure to ensure the reliability and durability of hydraulic structures of transport construction of road culverts in operating conditions due to static and dynamic loads from vehicles and temperature and climatic influences, the destructive force of water flow, abrasive destruction, corrosion of metal. The reason for the lack of efficiency of design solutions of road culverts is the fundamental difference in the conditions of water flow through the road culvert, at the outlet of the pipe a two-dimensional flow is formed, and and, as a consequence, the destruction of the structure of the lower reaches, landslides, the destruction of the culvert as a whole. Problems. From the literature analysis it is established that road culverts are in difficult operating conditions, which causes their premature destruction. Goal. It consists in the analysis of problems of ensuring reliability and durability of hydraulic structures of transport construction from road corrugated metal culverts. Results. The analysis of problems of ensuring reliability and durability of hydraulic structures of transport construction from road culverts in operating conditions is carried out. Proposals for calculating the initial sections of the structure to ensure its reliability are given. Conclusions. To date, the issue of ensuring the reliability and durability of hydraulic structures of transport construction of road culverts is not fully studied - alternating changes in the modes of flooding of culverts, including the operation of road culverts in part in the pressure mode; change and influence of the roughness coefficient due to the presence of corrugations, their placement; the effect of metal corrosion on the durability of the structure; abrasive wear of corrugated walls. The question of the kinetics of the initial sections of the corrugated metal culvert is insufficiently studied. Key words: highways, culverts, hydraulic stru