Measurement of scour in cohesive soils around a vertical pile - simplified instrumentation and regression analysis
TL;DR: In this article, an instrumentation system has been developed for measuring scour depth with time, considering the complexity of the problem, an experimental laboratory techniques used to measure scour around pile foundations in silty-clay sediments.
Abstract: The flow-structure interaction in an ocean environment, for a pile placed in an erodible bed where currents and waves are of prime concern, changes the bed elevation due to scour in the vicinity of the obstruction. There are certain difficulties in predicting the scour depth, as the particulate movement of sediments due to scour is time-dependent. Considering the complexity of the problem, an instrumentation system has been developed for measuring scour depth with time. This paper outlines the experimental laboratory techniques used to measure scour around pile foundations in silty-clay sediments. Detailed laboratory testing on model piles having a diameter of 50-110 mm was carried out in a wave flume having a length of 30 m and a width of 2.0 m. The motivation of these studies is to obtain observational experience of scour rate in silty-clay soil. Scour depths were monitored continuously for different combinations of wave characteristics and current velocities, and scour-time history is measured. Based on the measurements, a relationship for the scour depth in terms of duration of flow, soil properties, model characteristics, and fluid parameters is presented.
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TL;DR: In this article, a 3D finite element numerical model was developed for simulating local scour around submerged vertical cylinders in steady currents, and the effect of the height-to-diameter ratio on the scour depth was investigated.
165 citations
TL;DR: In this article, two types of real-time monitoring systems for bridge scour, using fiber Bragg grating (FBG) sensors, have been developed and tested in the laboratory.
Abstract: Local scour is one of the major factors for bridge failure. Scour failures tend to occur suddenly and without prior warning or sign of distress to the structure. Two types of real-time monitoring systems for bridge scour, using fiber Bragg grating (FBG) sensors, have been developed and tested in the laboratory. These FBG scour-monitoring systems can measure both the processes of scouring/deposition and the variations of water level. Several experimental runs have been conducted in the flume to demonstrate the applicability of the FBG systems. The experimental results indicate that the real-time monitoring system has the potential for further applications in the field.
78 citations
TL;DR: In this article, an innovative scour monitoring system using button-like fiber Bragg grating (FBG) sensors was developed and applied successfully in the field during the Aere typhoon period in 2004.
Abstract: The exposure and subsequent undermining of pier/abutment foundations through the scouring action of a flood can result in the structural failure of a bridge. Bridge scour is one of the leading causes of bridge failure. Bridges subject to periods of flood/high flow require monitoring during those times in order to protect the traveling public. In this study, an innovative scour monitoring system using button-like fiber Bragg grating (FBG) sensors was developed and applied successfully in the field during the Aere typhoon period in 2004. The in situ FBG scour monitoring system has been demonstrated to be robust and reliable for real-time scour-depth measurements, and to be valid for indicating depositional depth at the Dadu Bridge. The field results show that this system can function well and survive a typhoon flood.
71 citations
TL;DR: In this paper, microelectro-mechanical system (MEMS) pressure sensors are integrated with the wireless Zigbee network on a sensor board for real-time bridge scour monitoring.
Abstract: Scour failures tend to occur suddenly and without warning. Hydraulic scouring is one of the major factors in bridge failure. Bridges that are subject to periodic flooding should be monitored during high‐flow seasons for the safety of the public. Wireless sensor networks have been applied widely, and in many fields. In this study, micro‐electro‐mechanical system (MEMS) pressure sensors are integrated with the wireless Zigbee network on a sensor board for real‐time bridge scour monitoring. A wireless MEMS scour monitoring system has been developed and tested in the laboratory. This system can measure the scouring/deposition process and the variations of water levels at a bridge pier. A scour model is employed to calculate the scour‐depth evolution and validated with real‐time measured data. The results indicate that the proposed system has potential applicability to monitor scour evolution in the field.
46 citations
Cites methods from "Measurement of scour in cohesive so..."
...…methodologies adopting various instruments have been developed for measuring and monitoring, such as sonar, radar, and time-domain reflectometry (TDR), etc. (Yankielun et al., 1999; Cuevas et al., 2002; Babu et al., 2003; Lin et al., 2005; Lin et al., 2006; Lynch et al., 2006; Yuan et al., 2006)....
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TL;DR: In this article, the lateral capacity of a pile is reduced due to scour and bending moments and deflection are increased due to the scour, which results in a reduction in lateral capacity and increase in bending moments.
Abstract: Pile foundations are used to transmit both vertical and horizontal loads. Many of offshore and coastal structures are founded on piles and these piles are subjected to significant amounts of lateral loads due to wind, wave and currents. Piles in shallow water regions are subjected to scour and there can be loss of soil support around these pile foundations. Bending moments and deflections are increased due to scour. In this investigation, it has been brought out that the lateral capacity of foundation is reduced due to scour. Tests on model piles of PVC and Aluminum embedded in soft marine clay bed formed at different consistency indices and load eccentricity ratios were conducted with and without scour. These pile materials are chosen such that there is a good variation in the rigidity of piles. From the model tests, it is noticed that scour results in the reduction in lateral capacity and increase in bending moments. In the second set of tests, cyclic loading is applied on PVC and Aluminum piles for a time period of 12 seconds. This time period represents the time period of storm wave in across the Indian seas. Considerable increase in deflection occurred due to scour in cyclic load tests for different consistency conditions of soil.
39 citations
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TL;DR: In this article, the divergent concepts of a stability analysis, as compared with a load-deformation approach to soil mechanics, are shown to be compatible within the framework of a hyperbolic stress-strain relation.
Abstract: The divergent concepts of a stability analysis, as compared with a load-deformation approach to soil mechanics, are shown to be compatible within the framework of a hyperbolic stress-strain relation. The two-constant hyperbolic form of the stress-strain response is such that the ultimate shear strength of the soil is contained within the general formulation and appears in the mathematical limit of the stress as the strain becomes excessive. This is quantiatively demonstrated for a remolded cohesive soil tested in consolidated-undrained triaxial compression. The variables contained in the hyperbolic stress-strain relation include the preconsolidation pressure, rebound stress, lateral pressure during the test, vertical normal stress, strain, and rate of strain. History effects are included in terms of the overconsolidation ratio. The general formulations obtained for the consolidated-undrained triaxial tests are compared with the results reported in the literature by other investigators for both drained and undrained consolidated triaxial tests under various conditions.
919 citations
TL;DR: In this paper, a review of literature on model and field data is presented, and the empirical data are compared with theoretical considerations, together with a set of design suggestions together with possibilities for protection against scour.
Abstract: A “state of the art“ report on the subject of local scour around cylindrical piers is given here. After a description of the scouring process, a critical review of literature on model and field data is presented, and the empirical data are compared with theoretical considerations. The final result is a set of design suggestions together with possibilities for protection against scour.
608 citations
TL;DR: In this paper, a design method for the estimation of equilibrium depths of local scour at bridge piers is presented, based upon envelope curves drawn to experimental data derived mostly from laboratory experiments.
Abstract: A design method for the estimation of equilibrium depths of local scour at bridge piers is presented. The method is based upon envelope curves drawn to experimental data derived mostly from laboratory experiments. The laboratory data include wide variations in flow velocity and depth, sediment size and gradation, and pier size, shape, and alignment. Local scour depth estimation is based upon the largest possible scour depth that can occur at a cylindrical pier, which is 2.4D, where D=thepierdiameter. According to the method, this depth is reduced using multiplying factors where clear‐water scour conditions exist, the flow depth is relatively shallow, and the sediment size is relatively coarse. In the case of nonrectangular piers, additional multiplying factors to account for pier shape and alignment are applied. The method of estimation of local scour depth is summarized in a flow chart.
565 citations
TL;DR: In this article, an experimental procedure involving layer by layer erosion under a range of bed shear stresses, τb, of successively increasing magnitude was utilized to investigate the erosion behavior of soft cohesive sediment deposits.
Abstract: Erosion behavior of soft cohesive sediment deposits has been investigated in laboratory experiments. Such deposits are representative of the top, active layer of estuarial beds. An experimental procedure involving layer by layer erosion under a range of bed shear stresses, τb, of successively increasing magnitude was utilized. Interpretation of the resulting concentrationtime data together with bed density profiles yielded a description of the variation of the bed shear strength, τs, with depth as well as an expression for the rate of surface erosion. In general, τs increased with depth and was also influenced by the type of sediment, bed consolidation period and salinity. The rate of erosion was found to vary exponentially with (τb-τs)1/2. In modeling estuarial bed erosion, it is essential to take these characteristics of τs and the rate of erosion into account.
471 citations
Additional excerpts
...the works of Kamphuis and Hall [7], Parchure and Mehta [ 8 ], and Shaik et al. [9]....
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TL;DR: In this article, a new method called SRICOS is proposed to predict the scour depth z versus time t around a cylindrical bridge pier of diameter D founded in clay.
Abstract: A new method called SRICOS is proposed to predict the scour depth z versus time t around a cylindrical bridge pier of diameter D founded in clay. The steps involved are: (1) taking samples at the bridge pier site; (2) testing them in an erosion function apparatus to obtain the scour rate z versus the hydraulic shear stress applied τ; (3) predicting the maximum shear stress τmax, which will be induced around the pier by the water flowing at vo before the scour hole starts to develop; (4) using the measured z versus τ curve to obtain the initial scour rate zi corresponding to τmax; (5) predicting the maximum depth of scour zmax for the pier; (6) using zi and zmax to develop the hyperbolic function describing the scour depth z versus time t curve; and (7) reading the z versus t curve at a time corresponding to the duration of the flood to find the scour depth that will develop around that pier. A new apparatus is developed to measure the z versus t curve of step 2, a series of advanced numerical simulations ...
321 citations
"Measurement of scour in cohesive so..." refers methods or result in this paper
...As an illustration, for field conditions, scour depth versus time generated for a bridge pier in clay (as reported by Briaud et al. [ 25 ]) is shown in Fig. 7(a) and the corresponding transformed plot is shown in Fig. 7(b)....
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...These results of long duration laboratory test results and field observations carried out by Briaud et al. [ 25 ] confirm the applicability of the hyperbolic relationship....
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...Some of the geotechnical applications of this law are demonstrated [ 25 ]....
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