Date of Award:

5-2023

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Civil and Environmental Engineering

Committee Chair(s)

John Rice

Committee

John Rice

Committee

James Bay

Committee

Loren Anderson

Committee

Brian Crookston

Committee

Som Dutta

Abstract

Backward Erosion Piping (BEP) is an internal erosion mechanism which occurs at the down stream of dams or levees. Two conditions needed for this failure to occur: 1) head of water in the upstream of the dam or the levee to drive the seepage forces, and 2) crack in the roof or the blanket layer of the cohesionless material in the downstream of the dam or a levee. Numerous researches were performed in the past in an attempt to predict the critical gradient for BEP to initiate. Some researches are too conservative and other researches are under predicting the critical gradient. In general, the physical models were used in these researches are either one or two dimensional modelling. Due to complexity of this phenomenon and the three dimensional aspect of it as the water flowing from all directions toward the exit. Therefore, this problem needed to be simulated in a three dimensional model.

The objectives of the research are to predict the critical gradient in the sand boil throat due the suspended material which lifted in the crack. Also, calculate the local critical horizontal gradient at channels tips. A circular physical model was designed by the army corps of engineering and modified at Utah State University. This model consists of two chambers, the outer chamber is where the water applied. The inner chamber is where the soil is placed. Mariotte tube to connected to the outer chamber and used to control the differential head applied to the soil sample. Four risers with different diameters are used to simulate the sand boil throat and placed individually at the center of the model. Three different soils representing a range of grain size with different hydraulic conductivities are in the research and some one soil used for two hydraulic regimes applied to the sample. Eight differential pressure transducers are installed around the exit and in the bottom of the riser. Results of the differential transducers are used to understand the backward erosion process and to measure the head loss in the riser due to the suspension of eroded soil in the riser. Three dimensional finite element software is used to mimic the erosion occurs for each test and calibrated using the results of the experimental data. Results were used to calculate the local horizontal critical gradients at different locations from the pipe tips.

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