Thomas F. Wolff

Effect of Deterministic and Probabilistic Models on Slope Reliability Index

Many deterministic and probabilistic models can be applied to reliability analysis of earth slopes. This paper investigates the effect of commonly used models by a set of comparative studies based on three prototype embankments. The deterministic models considered are the simplified Bishop method, the modified Swedish method, and Spencers method. For Spencers method, both circular and non-circular failure surfaces are considered. The probabilistic models considered are the mean-value first order second moment method (MFOSM), the point estimate method (PEM), and the advanced first order second moment method (AFOSM). The results indicate that the effect of these different models on the calculated slope reliability index varies with slope geometry and soil strength parameters. The effect of deterministic slope stability method is not significant; but the shape of the failure surface can significantly affect the slope reliability, especially for layered embankments. No practical difference was observed between the results of reliability analyses done by the mean-value First Order Second Moment method (MFOSM) and Point Estimate Method (PEM). For the cases studied the AFOSM gave a more conservative reliability index, but it requires more computational effort due to the iterative nature of slope stability problems and numerical problems may occur.

Effects of particle size distribution and water content at compaction on saturated hydraulic conductivity and strength of high sand content root zone materials

Athletic field root zones are built with high sand content materials primarily to maintain drainage and macroporosity with compaction. However, these materials can also create problems due to their lack of strength. The objective of this study was to develop a better understanding of how particle size distribution and water content at compaction affect the strength and the hydraulic conductivity of high sand content root zones. One sand and one sandy loam textured soil were mixed in various proportions to produce seven mixtures. The sand/soil mixtures were subjected to four tests: standard Proctor compaction test, modified California bearing ratio, saturated hydraulic conductivity, and pore size distribution. The sand/soil mixtures were compacted at three water contents (5%, 9%, 13% kg kg−1) for mixes containing 2%, 5%, 7%, 8% silt + clay and at five water contents (5%, 7%, 9%, 11%, 13% kg kg−1) for mixes containing 10%, 12%, 15%, 19% silt + clay. For mixes containing 10% and 12% silt + clay, compacted at 5% water content, more than 100% increase in strength was observed over sand alone while maintaining hydraulic conductivity values of 19.0 and 8.5 cm h−1, respectively.

DETECTING SEGREGATION IN BITUMINOUS PAVEMENTS

Field and laboratory studies were conducted to determine the feasibility of detecting and quantifying segregation in hot-mix asphalt pavements. The study involved extensive testing at 19 field sites in Michigan. Areas of apparent segregation were classified as light, medium, and heavy. At the selected sampling areas, 1-min nuclear density measurements were made, cores were taken and incinerated, asphalt contents and air voids were determined, and gradation tests were performed. Statistical comparisons were made by using t-tests to characterize the differences between the measured nuclear density and percent passing various sieves. More than 80% of the nuclear density measurements supported the visual observations of a heavy degree of segregation when the significance of the differences (the p-value) between the areas compared was less than 10-3. Moreover, for areas with medium or heavy segregation, the probability that significant differences in nuclear density between segregated and nonsegregated areas with p-values less than 10-3 corresponded to significant differences (p-values less than 10-2) in aggregate gradation was .88. On the basis of the results, a spreadsheet, mbitseg2, was developed to perform statistical tests with the nuclear density measurements obtained during the paving operation. After 6 months of trial testing, the program has been accepted and implemented by the Michigan Department of Transportation, the Michigan Asphalt Paving Association, and the asphalt industry. The program is available on a web page (http://www.egr.msu.edu/prce) in Excel (mbitseg2.xls) and QuattroPro (mbitseg2.wb3) formats.

USING PAVEMENT DISTRESS DATA TO ASSESS IMPACT OF CONSTRUCTION ON PAVEMENT PERFORMANCE

Most state highway agencies specify incentives, disincentives, or acceptance criteria based on one or more attributes that can be measured during or immediately after construction (smoothness, early completion of construction, and nuclear density). In many scenarios in which contractors were awarded incentives, the pavement showed premature distress after construction. Furthermore, the magnitude of the incentive or disincentive is typically determined on the basis of intuition and past practice, without assessing the effect of the incentive’s attribute on pavement performance. In a study sponsored by the Michigan Department of Transportation (MDOT) and conducted by the Pavement Research Center of Excellence at Michigan State University, the impact of segregation on pavement performance was assessed, and an expedient test to detect segregation was developed so that MDOT could establish incentives, disincentives, or acceptance criteria. The study included 17 segregated pavement projects and 2 nonsegregated projects. Two types of segregation-related distress were observed: raveling, which was observed on 11 projects, and cracking, which was observed on 7 projects. Three projects showed both raveling and cracking. For each project, the raveled areas and the length of the cracks were measured over time, and their rates of growth were assessed. On the basis of the results, the reductions in the pavement service life due to raveling and cracking were estimated. It is shown that areas with heavy and medium degrees of segregation experience on average 73 and 56 percent reduction in pavement service life, respectively, due to raveling and 46 percent due to segregation-related cracks.

Underseepage analysis of levees on two-layer and three-layer foundation

Abstract A simplified numerical model for the analysis of levee underseepage is developed and presented. Idealization of the subsurface hydrogeologic conditions was achieved using two-layer and three-layer representation of the flow domain. Data from Magnolia levee, located in Magnolia, Ohio, were used to demonstrate the model applicability by comparing exit hydraulic gradient (i) values from the simplified model to predictions from 2-D finite element analysis (FEA). Results from the simplified model indicated that i values were merely dependent on the ratio of the foundation permeability (Kfx) to the blanket permeability (Kby). The i values from the FEA closely matched those from the simplified model for Kfx/Kby ratios less than 2000 and assuming permeability anisotropic ratio (rk) = 1. Piezometer data from the Sny Island levee, located in Quincy, Illinois, were used to demonstrate the applicability of the three-layer model.

Aligning Computing Education with engineering workforce computational needs: New curricular directions to improve computational thinking in engineering graduates

In this global economy, the preparation of a globally competitive U.S. workforce with knowledge and understanding of critical computing concepts is essential. Our CPACE (Collaborative Process to Align Computing Education with Engineering Workforce Needs) vision is to revitalize undergraduate computing education within the engineering and technology fields. Our objective is to design and implement a process to engage stakeholders from multiple sectors and identify the computational tools and problem-solving skills and define how these skills-directly informed by industry needs-can be integrated across disciplinary curricula. By explicitly integrating computing concepts and disciplinary problem solving, engineering graduates will enter the workforce with improved and practice-ready computational thinking that will enhance their problem-solving and design skills. We present the analysis of the computational skills and the strategies that we are using to map the workforce problem-solving requirements onto the foundational computer science principles. We outline the framework that we are using to identify opportunities for curricular integration between computer science concepts and the disciplinary engineering curricula. By documenting, evaluating, and making the process explicit, this process can serve as a model for national efforts to strengthen undergraduate computing education in engineering.

Engaging Early Engineering Students (EEES)

Undergraduate STEM student enrollment has declined substantially over the last decade. Specifically there has been a steady decline in retention of early engineering students working through the first half of their degree programs. Student “leavers” typically fall into two categories (i) those facing academic difficulties and (ii) those that perceive the education environment of early engineering as hostile and not engaging. The Engaging Early Engineering Students Project (EEES) is a collaborative effort between Michigan State University (MSU) and Lansing Community College (LCC). EEES functions through the integration of four component programs designed to ease the transition of high school students into engineering undergraduate programs, and, by making the transition smoother, to increase retention at the College of Engineering (COE). The programs are: (a) Peer-Assisted Learning, (b) Connector Faculty, (c) Diagnostic-driven Early Intervention and (d) Cross Course linkages.

Work in progress - computing and undergraduate engineering: A collaborative process to align computing education with engineering workforce needs (CPACE)

This NSF-funded community-building (CB) project brings together Michigan State University (MSU), Lansing Community College (LCC), and the Corporation for a Skilled Workforce (CSW) to design and implement a process to create a collaboratively defined undergraduate computing education within the engineering and technology fields in alignment with the computational problem-solving abilities needed to transform mid-Michiganpsilas economy and workforce. In this WIP we outline the process we are developing to ensure that a wide variety of stakeholders - business, community leaders and post secondary educators - collaborate to identify workforce computational skills, define how these skills can be integrated across a curriculum, and develop revised curricula that integrate computational problem-solving across engineering departmental courses. By documenting, evaluating and making the process explicit, this process can serve as a model for national efforts to revitalize undergraduate computing education in engineering, and should be extensible to other computing education reform efforts.

Quantitative Relationship of Grouting to the Reduction of Groundwater Flow through Rock Foundations

A unique and extensive test grout program, with both stage and stop-grouted holes on 5-ft centers, was conducted in fractured and solutioned dolomite at the Meramec Park Lake damsite, Sullivan, Missouri. Pre-grouting and postgrouting pumping tests from water wells completely surrounded by a 50-ft square grout curtain provided quantitative data on the amount of seepage actually occurring through a completed grout curtain. A 97 percent reduction in the specific capacity of the test well after grouting showed that grouting is a positive method of reducing groundwater flow. Optimum grout take was achieved using thin mixes of neat cement with a small amount of bentonite injected at a total pressure of 1f times foot of depth. Grout take was not influenced by hole diameter. Grout movement was joint controlled, and most grout injected did not spread more than 5 ft. Overcoring showed grout was penetrating all openings around hole perimeters. Test results showed that criteria developed to indicate the relative effectiveness of grouting do provide a real method to assess the quality of grouting.