Experimental Study On Pier Local Scour In Multilayer Soil

Many domestic and international experts and scholars have carried out plenty ofresearch about pier local scour, through the field observation, the model test andnumerical simulation methods and means, considering extensively each factors of thepier local scour and have put forward many empirical formulas and simi-emperical andhalf-theoretical formula about pier local scour depth calculation. However, pier localscour phenomenon are quite complex and have a lot of influencing factors, so far peopleare also not very understanding thoroughly about scour mechanism and theoreticalresearch, So further research is necessary in this aspect. And previous studies and theresearch results have lay particular stress and draw limitation on the single-layer soilstructure of geological conditions, layered soil erosion less. Due to the needs ofengineering practices, local scour problem of layered soil has been paid more and moreattention. Based on the previous studies and experimental data of the model test, pierlocal scour of layered soil were studied in the paper, and preliminary discusses somehydraulic properties. And the accomplishment of this study will be of the practicalsignificance. The main contents of the studies and achievements are as follows:1. Sand coarsening delamination phenomenon near the pier was simulatedsuccessfully by adopting fixed-point photography method on hydrodynamics flume, andreal-time observe the status of coarsening within scour hole. Provides us the detaileddynamic process coarsening layered happened before, during and after with more intuitiveand close observation, also provides to construct layered scour physical graphics. Theexperiment of sediment coarsening problems related research is worth using for reference.2. The test uses acoustic doppler velocimeters ADV to detailed measure theinstantaneous velocity of typical sections and points around the cylindrical pier in therectangle flume. Draw out the two-dimensional time-averaged velocity distribution polt,and got the vertical, horizontal and vertical three-dimensional time average velocity of thetypical sections, analyzed the evolution. As a result of this effort, we obtain therelationship between the discrete vortex around cylindrical pier and pier local scour in the layered soil.3. In the experiment, we measured the real-time vary of the local scour depth aroundpier in different thickness of sediment under each erosion stage, analyzes the functionequation about the brige local scour depth change over time in different layered soil, Sothe linear relationship between pier local scour depth and the logarithm of time isobtained.4. On the basis of experiments about pier local scour in layered soil, combiningmodel test observation data, puts forward the layered soil local scour physical model, usethe methods of the theories and dimension analysis to derive new formulas, after theactual experiment data to determine parameters is obtained after suitable for layered soilpier local scour depth, and the calculation formula of the existing scour formula of newformula is validated, and the results show that the analytic expression on basis of themodel is feasible, the new formula structure is reasonable and have certain applicability.Effect factor of piers local scouring is numerous, which including hydraulic factorsand geometric factor jointly determine the flow field hydraulic characteristics. In thispaper, Some hydraulic characteristics of sediment layer and local scour problems havebeen certain discussed, got the initial results of piers local scouring in in layered soil,which have certain reference significance. And it can be researched further combined withpractical projects and model investigation into the aspects of pier type, sedimentcharacteristics factors.