Mehrad Kamalzare

Numerical Study of Behavior of Anchor Plates in Clayey Soils

AbstractThis paper presents numerical models and mathematical formulations to predict the pullout capacity of anchor plates with different inclination angles embedded in clay. The models were developed based on the failure mechanism deduced from laboratory testing and utilize the Mohr-Coulomb yielding criteria. Expression was given to estimate the maximum pullout resistance of plates with different dimensions and inclination angles embedded in various clayey soils. A comparison between results of finite-element analyses has been performed to find out the effect of different parameters. New two-variable functions have been presented to show the relationship between pullout resistance and embedment ratio with different inclination angles. In addition, an interesting relationship among pullout capacities of anchor plates at different inclination angles was found, and a new concept, ellipse of pullout capacity, has been pronounced. Finally, a new theory has been introduced to predict the pullout capacity of a...

Computer Simulation of Levee Erosion and Overtopping

Improved computer models of erosion have been developed, considering soil hydraulic conductivity. The models deal with erosion of levees, dams and embankments due to overtopping. The simulations trace the formation of rills and gullies, beginning with initial overtopping and continuing to final breaching. Physical models performed at “1-g” and high “g” using a geotechnical centrifuge have been used to calibrate the models. Previous models did not consider soil hydraulic conductivity, and although results were quite good for the formation of rills and gullies and sediment quantities, breach times were underestimated. Essentially the water flow was treated as if passing over a solid surface, not entering the soil, and the total water flow was available for erosion. Thus, breach times were underestimated. Soil erodibility parameters had to be adjusted in order to achieve good agreement with breach times. The new models developed consider soil hydraulic conductivity, and produce good agreement with the performance of the physical modeling, including breach times and the use of proper soil erodibility parameters.

Correlation between Cα/Cc ratio and index parameters of soils

There is a general acceptance of constant Cα/Cc ratio (secondary compression index/ compression index) after many investigations made with different soil specimens. Therefore it should be possible to find useful correlations between soil properties and a soil’s unique Cα/Cc ratio. In this paper the secondary compression behaviour of Iranian soils was investigated through the performance of a series of conventional and long duration 1D consolidation tests conducted on undisturbed samples from 11 sites in different parts of Iran. The characteristics of the secondary compression index were examined and the relationship between the coefficient of secondary compression, Cα, and compression index, Cc, was established for each site. Single and multiple regression models to estimate the ratio of Cα/Cc were investigated based on soil properties (liquid limit (LL), plasticity limit (PL), plasticity index (PI) and natural water content (ω0)), and various equations are presented to predict the value of the Cα/Cc ratio of soils.

VALIDATION OF EROSION MODELING: PHYSICAL AND NUMERICAL

The overall intent of this research is to develop numerical models of erosion of levees, dams and embankments, validated by physical models. The physical model tests are performed at 1-g and at high g’s using a geotechnical centrifuge facility. The erosion is modeled in detail, from beginning to end, that is from the time the levee is overtopped until the levee is breached. Typical quantities measured as a function of time including the depth, width and volume of rills, number of junction points, rills shape (straight or meandering), sediment transport quantities, and time to breach. This data can be obtained from the numerical modeling, but is difficult to obtain from the physical tests in real life. Video images indicate that the physical modeling results which have been tested in this research agree with the numerical modeling results. A comparison has also been made between observed breaching width and the FEMA (Federal Emergency Management Agency) new levee breach formula for both 1-g and higher g’s centrifuge tests. Results also show that at small water flows, seepage plays a significant roll in controlling erosion. Although long-term seepage may eventually cause failure, in the short term low flows tend to reduce erosion by reducing the amount of overtopping.

New Visualization Method to Evaluate Erosion Quantity and Pattern

The objective of this research is to develop tools that would improve the understanding of the process of levee failure because of erosion and reduce the risk of failure. Hydraulic erosion is a complicated phenomenon and depends on many different parameters. To improve design criteria for levees, embankments, and earthen structures, the development of realistic computer models that can simulate the erosion process is necessary. Verification of these computer simulations, as with any simulation, is a necessity. In this research, a large number of physical levee erosion tests were performed at 1g and at high gs using a geotechnical centrifuge. Centrifuge tests were performed to simulate real (prototype) size levees, and thus to obtain a more realistic model. The erosion was modeled physically in detail. Conventional three-dimensional scanning was used to precisely verify the calculated dimensions of initial and final computer model geometries, but did not yield interim data or measurements of the quantity of eroded soil during the tests. A Kinect device was used to scan and evaluate the volume of eroded soil and variation of the shape of the channels as a function of time. Three-dimensional images were obtained, and variations of different parameters were plotted. Various quantities were measured as a function of time. Based on recorded videos and pictures taken during the tests, it was discovered that the Kinect results agreed well with the physical models. The Kinect is a low-cost sensor, and enables the measurement of the rate of soil erosion, which, if done at all, usually requires expensive equipment. The Kinect device was also used in the centrifuge experiments, and functioned well in the high g environment. It is believed to be the first use of a Kinect device in a centrifuge. The application of this method in other laboratory experiments was also investigated.