Abstract: A very large percentage of bridge failures are attributed to scouring around bridge piers and this directly influences public safety. Experiments are carried out in a 12-m long rectangular open channel flume made of transparent tempered glass. A 300 mm thick bed made up of sand particles is leveled horizontally to create the test bed and a 50 mm hollow plastic cylinder is used as a model bridge pier. Tests are carried out with varying flow depths and velocities. Data points of various scour parameters such as scour depth, width, and length are collected based on different flow conditions and visual observations of changes in the stream bed downstream the bridge pier are also made as the scour progresses. Result shows that all three major flow characteristics (flow depth, Froude number and densimetric Froude number) have one way or other affect the scour profile.
Abstract: Bridge piers often fail all over the world and the whole structure may be endangered due to scouring phenomena. Scouring has been linked to catastrophic failures that lead into the loss of human lives. Various techniques have been employed to extenuate the scouring process in order to assist the bridge designs. Pier modifications plays vital role to control scouring at the vicinity of the pier. This experimental study aims at monitoring the effectiveness of pier modification and temporal development of scour depth around a bridge pier by providing a collar, a cable or openings under the same flow conditions. Provision of a collar around the octagonal pier reduced more scour depth than that for other two configurations. Providing a collar around the octagonal pier found to be the best in reducing scour. The scour depth in front of pier was found to be 19.5% less than that at the octagonal pier without any modifications. Similarly, the scour depth around the octagonal pier having provision of a cable was less than that at pier with provision of openings. The scour depth around an octagonal pier was also compared with a plain circular pier and found to be 9.1% less.
Abstract: Crossing culverts are essential element of rural roads. The paper aims to investigate failures of recently constructed wadi-crossing pipe culverts in Sennar state and provide necessary remedial measures. The investigation is conducted to provide an extensive diagnosis study in order to find out the main structural and hydrological weaknesses of the culverts. Literature of steel pipe culverts related to construction practices and common types of culvert failures and their appropriate mitigation measures were reviewed. A detailed field survey was conducted to detect failures and defects appeared on the existing culverts. The results revealed that seepage of water through the embankment and foundation of the culverts leads to excessive erosion and scouring causing sever failures and damages. The design mistakes and poor construction were detected as the main causes of culverts failures. For sustainability of the culverts, various remedial measures are recommended to be considered in urgent rehabilitation of the existing crossings.
Abstract: Sedimentation process resulting from soil erosion in
the water basin especially in arid and semi-arid where poor
vegetation cover in the slope of the mountains upstream could
contribute to sediment formation. The consequence of sedimentation
not only makes considerable change in the morphology of the river
and the hydraulic characteristics but would also have a major
challenge for the operation and maintenance of the canal network
which depend on water flow to meet the stakeholder-s requirements.
For this reason mathematical modeling can be used to simulate the
effective factors on scouring, sediment transport and their settling
along the waterways. This is particularly important behind the
reservoirs which enable the operators to estimate the useful life of
these hydraulic structures. The aim of this paper is to simulate the
sedimentation and erosion in the eastern and western water intake
structures of the Dez Diversion weir using GSTARS-3 software. This
is done to estimate the sedimentation and investigate the ways in
which to optimize the process and minimize the operational
problems. Results indicated that the at the furthest point upstream of
the diversion weir, the coarser sediment grains tended to settle. The
reason for this is the construction of the phantom bridge and the
outstanding rocks just upstream of the structure. The construction of
these along the river course has reduced the momentum energy
require to push the sediment loads and make it possible for them to
settle wherever the river regime allows it. Results further indicated a
trend for the sediment size in such a way that as the focus of study
shifts downstream the size of grains get smaller and vice versa. It
was also found that the finding of the GSTARS-3 had a close
proximity with the sets of the observed data. This suggests that the
software is a powerful analytical tool which can be applied in the
river engineering project with a minimum of costs and relatively
accurate results.
Abstract: High level and high velocity flood flows are
potentially harmful to bridge piers as evidenced in many toppled
piers, and among them the single-column piers were considered as
the most vulnerable. The flood flow characteristic parameters
including drag coefficient, scouring and vortex shedding are built into
a pier-flood interaction model to investigate structural safety against
flood hazards considering the effects of local scouring, hydrodynamic
forces, and vortex induced resonance vibrations. By extracting the
pier-flood simulation results embedded in a neural networks code,
two cases of pier toppling occurred in typhoon days were reexamined:
(1) a bridge overcome by flash flood near a mountain side;
(2) a bridge washed off in flood across a wide channel near the
estuary. The modeling procedures and simulations are capable of
identifying the probable causes for the tumbled bridge piers during
heavy floods, which include the excessive pier bending moments and
resonance in structural vibrations.
Abstract: Due to the three- dimensional flow pattern interacting with bed material, the process of local scour around bridge piers is complex. Modeling 3D flow field and scour hole evolution around a bridge pier is more feasible nowadays because the computational cost and computational time have significantly decreased. In order to evaluate local flow and scouring around a bridge pier, a completely three-dimensional numerical model, SSIIM program, was used. The model solves 3-D Navier-Stokes equations and a bed load conservation equation. The model was applied to simulate local flow and scouring around a bridge pier in a large natural river with four piers. Computation for 1 day of flood condition was carried out to predict the maximum local scour depth. The results show that the SSIIM program can be used efficiently for simulating the scouring in natural rivers. The results also showed that among the various turbulence models, the k-Ļ model gives more reasonable results.
Abstract: The purpose of this paper is to summarize the
following protection of scouring countermeasures by using
Bentonite-Enhanced Sand (BES) mixtures. The concept of
underground improvement is being used in this study to reduce the
void of the sand. The sand bentonite mixture was used to bond the
ground soil conditions surrounding the pile of integral bridge. The
right composition of sand bentonite mixture was proposed based on
previous findings. The swelling effect of bentonite also was
investigated to ensure there is no adverse impact to the structure of
the integral bridge. ScourScour, another name for severe erosion,
occurs when the erosive capacity of water resulting from natural and
manmade events exceeds the ability of earth materials to resist its
effects. According to AASHTO LRFD Specifications (Section
C3.7.5), scour is the most common reason for the collapse of
highway bridges in the United States
Abstract: Scouring around a bridge pier is a complex
phenomenon. More laboratory experiments are required to
understand the scour mechanism. This paper focused on time
development of local scour around piers and piles in semi integral
bridges. Laboratory data collected at Hydraulics Laboratory,
University of Malaya was analyzed for this purpose. Tests were
performed with two different uniform sediment sizes and five ranges
of flow velocities. Fine and coarse sediments were tested in the
flume. Results showed that scour depths for both pier and piles
increased with time up to certain levels and after that they became
almost constant. It had been found that scour depths increased when
discharges increased. Coarser sediment also produced lesser scouring
at the piers and combined piles.
Abstract: The aim of this study was to investigate the
effectiveness of anaerobic digestion for the treatment of wool
scouring wastes. The experiments design comprised three ratios of
waste (W) to seed(S) (W:S) of 25:75, 50:50 and 75:25, corresponding
to 1.9. 1.7 and 1.5g tCOD/g TS, respectively, with or without
chemicals addition. NH4Cl was added to the reactors as a source for
nitrogen to achieve C:N:P of 420:14:3. A cationic flocculent was
added at 0.5 and 0.75% to enhance flocculation of sludge. The results
showed that the reactors that received W:S at a ratio of 25:75
produced the largest volume of biogas. The final soluble COD
(sCOD) was below the limits for discharge to the sewer system.
Abstract: Permanent rivers are the main sources of renewable
water supply for the croplands under the irrigation and drainage
schemes. They are also the major source of sediment loads transport
into the storage reservoirs of the hydro-electrical dams, diversion
weirs and regulating dams. Sedimentation process results from soil
erosion which is related to poor watershed management and human
intervention ion in the hydraulic regime of the rivers. These could
change the hydraulic behavior and as such, leads to riverbed and river
bank scouring, the consequences of which would be sediment load
transport into the dams and therefore reducing the flow discharge in
water intakes. The present paper investigate sedimentation process
by varying the Manning coefficient "n" by using the SHARC
software along the watercourse in the Dez River. Results indicated
that the optimum "n" within that river range is 0.0315 at which
quantity minimum sediment loads are transported into the Eastern
intake. Comparison of the model results with those obtained by those
from the SSIIM software within the same river reach showed a very
close proximity between them. This suggests a relative accuracy with
which the model can simulate the hydraulic flow characteristics and
therefore its suitability as a powerful analytical tool for project
feasibility studies and project implementation.
Abstract: Sedimentation in reservoirs and the corresponding
loss of storage capacity is one of the most serious problems in dam
engineering. Pressurized flushing, a way to remove sediments from the reservoir, is flushing under a pressurized flow condition and
nearly constant water level. Pressurized flushing has only local
effects around the outlet. Sediment in the vicinity of the outlet openings is scoured and a funnel shaped crater is created. In this study, the temporal development of flushing cone under various
hydraulic conditions was studied experimentally. Time variations of
parameters such as maximum length and width of flushing and also
depth of scouring cone was measured. Results indicated that an
increase in flow velocity (and consequently in Froude number)
established new hydraulically conditions for flushing mechanism and
so a sudden growth was observed in the amount of sediment released
and also scouring dimenssions. In addition, a set of nondimensional
relationships were identified for temporal variations of flushing scour
dimenssions, which can eventuallt be used to estimate the development of flushing cone.