A Spreadsheet for Estimating Soil Water Characteristic Curves (SWCC)

SWCC can be measured in the lab; however, due to the cost, time, and high variability in the results, empirical equations were developed using multiple regression approaches on databases consisting of a large number of measured SWCCs. The spreadsheet presented herein utilizes different methods that use basic soil properties, such as grain size distribution and Atterberg limits, to calculate the input parameters for van Genuchten and Fredlund and Xing equations. These parameters are required by numerical models, such as SEEP/W, to perform transient seepage analysis. The spreadsheet allows copying the generated curve data points as well as an input into the numerical model. The spreadsheet calculates the SWCCs using seven different methods for comparison. It also compares four closed form models, Gardner (1958), Brooks and Corey (1964), van Genuchten (1980), and Fredlund and Xing (1994), given the model parameters are known

Case Study: Unsaturated Embankment Failure on Soft Soils

This paper describes the application of unsaturated soil mechanics to an interstate connecting-ramp embankment that failed during construction. Specifically, matric suction is incorporated into the calculation of the tension crack (TC) depth induced by desiccation and strain incompatibility and the contribution of matric suction to embankment shear strength. The results are compared with field observations to assess the viability of unsaturated soil mechanics in modeling compacted embankments in stability analyses. Results from this study suggest that using unsaturated shear strength parameters while introducing a TC in the compacted fill yields a reasonable inverse analysis of this interstate embankment. This may be preferred in slope stability analyses to the current practice of using an undrained shear strength (i.e., cohesion) for the unsaturated compacted fill and including a TC to generate a reasonable factor of safety

Using Machine Learning in Estimating Changing Bed Shear over a Flume Test Box

A dam or levee breach caused by overflow erosion is difficult to evaluate during an overtopping event due to difficulty in accessibility and quickly changing conditions. However, for assessment of risk associated with breach time and ensuing downstream consequences, the erosion rate of embankment soils during this process needs to be evaluated. Soil erosion and water depth measurements were taken during flume tests using a Shallow Water Lidar (SWL) system scans. The tests were conducted in a 1-m-wide tilting flume on three cleans and gravel soil mixes with a median grain size D50of 2, 5,and 20 mm. The box measured 0.45-m-wide ×1.2-m-long ×0.25-m-deep. Due to the confined environment of the flow in the flume, the acting bed shear changes with hydrodynamics of the flow differently from under a uniform flow. The scour hole generated in the test box reaches equilibrium when the acting bed shear is equal to the critical shear. Standard machine learning techniques were used to image soil and water profiles from noisy Lidar data. First, the data are filtered using zonal-averaging and then based on the filtered data; the methodology selects the best profiles from a competing set based on the minimum error each profile produces on the data. Once the profiles are obtained, erosion rates and bed shear are computed, and a qualitative assessment is carried out to understand the relationship between temporal and spatial dependence of erosion rate on bed shear and soil particle size. Erosion rate and shear stress reached their maximum value within the first 60–70 seconds of the test and spatially within 0.3 m from the upstream end of the test box. The erosion rate decreased by about 4 times from 0.13 cm/s to 0.03 cm/s as D50increased from 2 mm to 20 mm at the same acting bed shear. The erosion rate for both mixes is reduced over time; however, the rate of reduction for D50of 20 mm is much higher over the same test duration. The erosion rate was shown to be strongly correlated to the acting bed shear nonlinearly. The results indicate that the calculated spatial variation of shear stress over the duration of the tests is consistent with the formation of maximum depth of scour hole

Integrating Field Monitoring and Numerical Modeling to 3 Evaluate Performance of a Levee under 4 Climatic and Tidal Variations

Several short-duration and extreme hydraulic loadings impose time-dependent variably saturated seepage conditions on earthen 7 slopes and embankments. Difficulty assigning appropriate input parameters and lack of full-scale validation are among the main factors 8 introducing uncertainty and lack of confidence when performing numerical transient seepage analysis. This case study demonstrates how 9 to effectively use field-monitoring data to improve the numerical analysis of a levee under climatic and tidal variations. The case study 10 includes a silty sand setback levee located near Seattle. An array of tensiometers and soil moisture sensors installed within the levee’s embank11 ment and foundation, along with a nearly real-time data acquisition system, were used to collect and process the in situ data for a period of 12 about 15 months. Climatic and weather data, including precipitation, temperature, humidity, and wind speed, were collected from a weather 13 station at the site, and tidal water fluctuations were monitored using a water level sensor. The field-measured matric suction and water content 14 were used along with a suction stress–based representation of effective stress to compute suction stress and effective stress profiles versus time. 15 A finite-element model of transient seepage under saturated-unsaturated conditions was developed. The numerical model was calibrated and 16 then validated using the measured pore-water pressures and the piezometric surface. The application of the numerical model was illustrated by 17 modeling the seepage and stability of the levee during a 100-year flood event. The results highlight the need to consider climatic variables and 18 soil–atmosphere interaction when performing transient seepage analysis. DOI: 10.1061/(ASCE)GT.1943-5606.0002134. © 2019 American 19 Society of Civil Engineers

Erosion Rate Equations for Coarse- Grained Materials Using a Small Flume Testing

Erosion rate of soils during a levee or dam overtopping event is a major component in risk assessment evaluation of breach time and consequently in determining the downstream consequences. There is uncertainty in estimation of the erosion rate especially for coarsegrained materials that comprise the outer shell layer of dams as well as homogenous levees that are constructed of such materials. In this paper, erosion rate results are presented on three soil mixes that share the same median grain size D50 of 2 mm, the fines content varies between zero and 20%, and the gravel content between zero and 30%. Each of the three mixes is compacted in the box at optimum or near optimum moisture content as determined from standard Proctor test. The box measures 0.3 m wide x 0.6 m long x 0.15 m deep. Each material is tested several times at varying hydraulic loading to determine the erosion rate after equal time intervals. The water depth, velocity are measured at each hydraulic loading and the acting bed shear is calculated. The validity of the excess shear stress equation is discussed as well as other bilinear and nonlinear models that could fit the erosion rate of such materials as it relates to the acting bed shear stress. The effect of fines content and level of acting shear stresses are presented in the paper

Using Microbial Induced Calcite Precipitation (MICP) to stabilize degraded soils

In nature ureolytic bacteria will use Urea as a carbon source. In the presence of Calcium, the ureolytic reaction will form Calcium Carbonate. This pathway is of interest because Calcium Carbonate will function as a bio-cementing molecule, stabilizing the soil in a process known as Microbial-Induced Calcite Precipitation (MICP). This study hypothesizes that amendment of soil with Urea will enrich the natural population of ureolytic bacteria which upon the addition of Calcium Chloride will result in the stabilization of the soil. For this purpose, burned and unburned soil will be treated with microbiological media to promote the growth of native ureolytic populations. We will then measure the enriched soil urease activity using a colorimetric assay, calcite precipitation with a gravimetric method after the acid dissolution of the calcite, and the compaction and stabilization of soil using ASTM standard methods. We will also isolate and identify ureolytic bacteria to be applied in future MICP experiments. This is a collaborative effort between students and faculty of the Aerospace Physiology and Civil Engineering programs

Monte Carlo Simulations of Coupled Transient Seepage Flow and Compressive Stress in Levees

The purpose of this research is to compare the results from two different computer programs of flow analyses of two levees at Port Arthur, Texas where rising water of a flood from Hurricane Ike occurred on the levees. The first program (Program 1) is a two-dimensional (2-D) transient finite element program that couples the conservation of mass flow equation with accompanying hydraulic boundary conditions with the conservation of force equations with accompanying x and y displacement and force boundary conditions, thus yielding total head, x displacement, and y displacement as unknowns at each finite element node. The second program (Program 2) is a 2-D transient finite element program that considers only the conservation of mass flow equation with its accompanying hydraulic boundary conditions, yielding only total head as the unknown at each finite element node. Compressive stresses can be computed at the centroid of each finite element when using the coupled program. Programs 1 and 2 were parallelized for high performance computing to consider thousands of realisations of the material properties. Since a single realisation requires as much as one hour of computer time for certain levees, the large realisation computation is made possible by utilising HPC. This Monte Carlo type analysis was used to compute the probability of unsatisfactory performance for under seepage, through seepage, and uplift for the two levees. Respective hydrographs from the flood resulting from Hurricane Ike were applied to each levee. When comparing the computations from the two programs, the most significant result was the two programs yielded significantly different values in the computed results in the two clay levees considered in this research

A Spreadsheet for Estimating Soil Water Characteristic Curves (SWCC)

SWCC can be measured in the lab; however, due to the cost, time, and high variability in the results, empirical equations were developed using multiple regression approaches on databases consisting of a large number of measured SWCCs. The spreadsheet presented herein utilizes different methods that use basic soil properties, such as grain size distribution and Atterberg limits, to calculate the input parameters for van Genuchten and Fredlund and Xing equations. These parameters are required by numerical models, such as SEEP/W, to perform transient seepage analysis. The spreadsheet allows copying the generated curve data points as well as an input into the numerical model. The spreadsheet calculates the SWCCs using seven different methods for comparison. It also compares four closed form models, Gardner (1958), Brooks and Corey (1964), van Genuchten (1980), and Fredlund and Xing (1994), given the model parameters are known

Interface load: Deformation behavior of landfill liner systems over subsurface cavities.

The leachate collection system and the double liner required by the EPA for solid and hazardous waste landfills consist typically of a combination of geosynthetics materials and natural or processed soils. This research is conducted to study the load-deformation behavior of a multi layered landfill liner system under stresses imposed by the waste fill. Experimental and analytical work achieved in this research is summarized as follows: (1) Experimental Evaluation of the shear stress-shear deformation characteristics of seven geosynthetic interfaces encountered in landfill lining systems in addition to four geosynthetic materials and three soils. The investigated materials included: Ottawa sand, kaoline clay, and limestone gravel. These soils represent the clay liner, drainage material, and cover soil, respectively, in a landfill. The four geosynthetics included: smooth and textured HDPE geomembrane, Polypropylene nonwoven geotextiles, and solid rib extruded geonet. (2) Development of two constitutive models for the shear stress-shear deformation behavior of the tested interfaces. Parameters of both models are obtained for all interfaces tested in the experimental work. The effect of degree of saturation and compacted soil structure on these parameters is also evaluated and implemented in the model. Furthermore, verification of the two models was achieved. (3) Finite Element (FE) simulation of the load-deformation behavior of a liner system over a trough subsidence. The FE simulations included a study of the effect of subsidence on the mobilized interface shear resistance and associated shear deformations and strains

Case Study: Unsaturated Embankment Failure on Soft Soils

This paper describes the application of unsaturated soil mechanics to an interstate connecting-ramp embankment that failed during construction. Specifically, matric suction is incorporated into the calculation of the tension crack (TC) depth induced by desiccation and strain incompatibility and the contribution of matric suction to embankment shear strength. The results are compared with field observations to assess the viability of unsaturated soil mechanics in modeling compacted embankments in stability analyses. Results from this study suggest that using unsaturated shear strength parameters while introducing a TC in the compacted fill yields a reasonable inverse analysis of this interstate embankment. This may be preferred in slope stability analyses to the current practice of using an undrained shear strength (i.e., cohesion) for the unsaturated compacted fill and including a TC to generate a reasonable factor of safety