Engineering Properties of Coquina: An Interesting and Historic Building Stone

Coquina is a weak sedimentary limestone composed of shell and shell fragments that have been cemented together. It is most often found in coastal regions, such as the Anastasia Formation along the east coast of Florida. Coquina is a historically significant building material, with the best-known example being the Spanish Castillo de San Marcos in St. Augustine, Florida. It has withstood cannonball fire during battles and centuries of weathering yet is still structurally sound. Although coquina is very important historically, not much is known about its properties. Preliminary studies have shown the orientation of the shells impacts tensile strength. Additionally, larger specimens tended to have lower tensile strength. Building on previously performed tests, I will further investigate how the orientation of shells impacts coquina’s tensile strength, as well as how specimen size affects tensile strength. I predict the specimens cored in the vertical direction will have a higher tensile strength because the shells will be oriented horizontally. The larger specimens will have a lower tensile strength because there is a greater number of existing fractures within the larger specimens. Indirect tension testing will be performed on the specimens. Compression on the top of the puck-shaped specimens will cause failure in tension. I will use acoustic emission monitoring to measure microcracking events during testing, specifically looking for the beginning of unstable crack growth. Unstable crack growth is a precursor to ultimate failure, where microcracks coalesce and form a macroscopic failure plane

Studying the Relationship Between Indigenous Microbial Communities, Urease Activity, and Calcite Precipitation in Artificial Mixes of Clay and Sand

Microbial-induced calcium carbonate precipitation (MICP) is evolving as a new method of improving the mechanical properties of soil. This environmentally friendly technique is a bio-geo-chemical process where microbes play a key role in increasing soil strength through precipitating calcium carbonate. Past studies at Boise State University have indicated that MICP via bio-stimulation could be a viable alternative for expansive clayey soil treatments. However, these studies raised a new question about the relationship between soil composition, urease activity, and calcite precipitation. To answer this question, batch studies were conducted using autoclaved-sterilized sand mixed with different percentages of non-sterile natural clay and tested for urease activity. Moreover, to investigate the difference in urease activity between sand and clay bacterial communities, experiments were repeated on samples with different amounts of non-sterile sand and autoclaved-sterilized clay. MICP-treated clay/sand mixes were then evaluated for calcite precipitation. Our results showed that soil mixes with higher clay content have more urease activity and higher levels of calcite precipitation for both sand-autoclaved and clay-autoclaved soil mixes. Test results indicate that urease activity could potentially be used as an indicator of MICP performance in different soil compositions

Influence of lithophysal porosity on stress-strain properties of Topopah Spring Tuff - numerical analysis

The purpose of the numerical analysis effort of Task 27 of cooperative agreement DE-FC08-98NV12081 was to investigate the effect of lithophysal porosity on the elastic stress-strain properties of the tuff rock mass. Rock mass properties without lithophysal cavities are designated matrix properties. Rock mass properties with lithophysal cavities are designated effective properties. The analysis will be performed for a 6 by 6 square cross-section with a uniform distribution of lithophysal cavities for a variety of porosities. The analyses will be performed using FLAG 2D version 3.5, a Department of Energy qualified software. The analyses will compare the matrix properties to the effective properties

WIP: Halting Attrition in Civil Engineering Programs Through Lower-Division Engagement Course Implementation

This work in progress paper will describe how a department of civil engineering has built 1-credit engagement courses into the first two years of a new curriculum design to increase retention rates, create a sense of belonging, showcase civil engineering principles and practicality to non-majors, and begin engaging alumni and local civil engineering professionals. Retention is a core issue for academic departments in the STEM fields. In civil engineering, we have seen a large number of students depart the major each fall and spring semester for various, preventable reasons. This is true for traditional, non-traditional, and transfer students alike. Students have cited a lack of community and support systems as well as a high degree of difficulty in foundational courses without an understanding of how the knowledge gained in these foundational courses will be used in civil engineering specific courses as reasons they have left the program. When students switch majors, they often switch to programs with a lower difficulty level in the required foundational coursework (math, chemistry, physics, etc.). We have also seen them begin to pursue programs where it is simple to see connections between lower division coursework and their intended field of study early in their academic career. Many students initially choose civil engineering as a career path with a limited view of the field’s breadth and interdisciplinary nature which, when not conveyed early, has led to attrition. Students desire a community of peers and faculty and a sense of belonging (Marra et al., 2012) in their major. Belonging can be developed in many ways, but a core piece of belonging is knowing what you belong to. When students understand what they are studying, they can connect their input to an output that reflects their values and self-identity now and in the future (Matusovich, Streveler, and Miller, 2010). A large contributing factor to programs not being able to help students make connections is a lack of major-specific courses available where students can find and spend structured time with peers/faculty in their major during the first two years of academic study. The lower division of a traditional civil engineering curriculum is largely made up of mathematics, physics, and chemistry coursework. At a majority of universities these courses cannot be modified to engage specific majors due to the nature of “service courses” that are taught by centralized departments outside the purview of engineering programs. These courses tend to be very large and students may have a difficult time finding peers from their own major. Students need time to develop a connection to peers as well as to the content of their coursework and neither of these goals are easily met in large-format courses that serve all majors (Hoit & Ohland, 1998). To begin addressing these issues, a new type of 1-credit, non-prerequisite course has been developed. Students in civil engineering will be required to take three Civil Engineering Engagement Courses (CE-EC or phonetically, “seek”) during the first two years of study and these courses aim to develop a sense of community amongst civil engineering students, introduce students to faculty in a non-intimidating fashion, and allow students to explore the different focus areas of civil engineering early in their academic career. Students outside of civil engineering will also be welcome into these courses to gain an understanding of the field and learn about potential interdisciplinary collaborations. Courses will also help students become acquainted with the local area and challenges faced by civil engineering professionals. In order to determine if these courses will help solve some of the ongoing retention and sense of belonging issues experienced by many civil engineering programs, we will look at historical attrition rates going back five years, survey alumni about their experiences, and survey students as they graduate. We will also be looking at internal markers that denote a student is thriving (Schreiner et al., 2012). This will occur in tandem with research determining the overall effectiveness of the full curriculum redesign. Through the implementation of CE-EC courses we anticipate that students, even those who struggle with connection making, will be able to build a connection with peers, faculty, staff, and the civil engineering program in general. We also expect lower attrition rates and possibly a larger student population due to the new visibility civil engineering will have across majors

A New Apparatus for Analog Modeling of Clay Smears

An apparatus has been developed for analog modeling of clay smears. This rather simple apparatus compliments the more sophisticated but less common geotechnical engineering ring shear apparatus that has been used in previous studies of clay smear formation. The new apparatus provides analog modelers with the ability to view and record soil deformation and formation of clay smears. The laboratory produced deformations and clay smears are very similar to those found in nature. A complete deformation history and clay smear formation process is documented

Ultra-Close Range Photogrammetry for Imaging Rock Surfaces

It is well known that microscopic or macroscopic porosity controls the strength of rock specimens. Many researchers have presented relationships between porosity and tensile strength based on the assumption that the porosity on the failure plane is representative of the porosity of the entire specimen. Our goal was to investigate and compare the relationship between total specimen macroporosity and tensile strength and failure plane macroporosity porosity and tensile strength. Indirect tension testing was conducted on twenty-two cylindrical mortar specimens to determine tensile strength. Styrofoam balls were mixed into the mortar mix to simulate macroporosity, and any uneven surfaces were ground using prior to testing. A load cell measured the compressive force applied by the loading frame; the maximum force was recorded and used to calculate the tensile strength of the specimen. The total specimen porosity was determined using the mass, diameter, and thickness of the specimens. The failure plane macroporosity was determined by taking overlapping pictures of the failure plane and stitching them together to create a high-definition digital image of the failure plane. Digital measurements of the styrofoam balls were taken and used to calculate the failure plane macroporosity. The results of this study concluded that specimens with higher porosities have lower tensile strengths. However, the failure plane macroporosity and total specimens macroporosity of some specimens were vastly different for the same tensile strength. This demonstrates that while failure plane porosity can be generally representative of the total specimen macroporosity, one must be careful when creating a direct correlation between the two

Influence of Schistosity Orientation on Failure Mode and Indirect Tensile Strength of Mica Schist

The indirect tension test is an important laboratory test for rock characterization. The presence of rock fabric, such as schistosity, complicates the assessment of test results. One hundred and forty-five indirect tension tests were conducted on mica schist specimens to investigate the effect of schistosity orientation on failure mode and tensile strength. Tensile strength results did not provide a clear relationship between schistosity orientation and tensile strength, so the failure patterns were investigated. A new naming scheme for failure modes was developed, incorporating fracture patterns observed in the specimen faces and edges. The Single Mode failure group specimens had only one failure pattern that appeared on both specimen faces, either axial failure (seventy-three specimens), schistosity failure (six specimens), or out-of-plane failure (seven specimens). The Mixed Mode failure group had thirty-two specimens that exhibited one failure pattern on one face and another on the other. The Hybrid Mode failure group had twenty-seven specimens with multiple failure patterns on both specimen faces. It was noted that Mixed Mode and Hybrid Mode specimens with components of axial failure had higher indirect tensile strengths than specimens without elements of axial failures. Statistical analyses of the tensile strength data using Levene’s Test for equal variances and two-sample t-tests showed no statistical difference between the Mixed Mode and Hybrid Mode failure groups. However, there was a statistical difference between the tensile strengths of the Single Mode axial failure specimens and the combined Mixed Mode and Hybrid Mode failure groups. These results clearly emphasize that indirect tensile strength should be assessed using schistosity orientation and failure mode

Porosity dependence of the elastic modulus of lithophysae-rich tuff: Numerical and experimental investigations

The influence of porosity on the mechanical properties of rock has received much research attention. Portions of the Yucca Mountain high-level nuclear waste repository may be placed in tuff units containing lithophysal cavities, which are large, generally noninterconnected cavities that can be considered a form of macroscopic porosity. This paper presents the results of numerical modeling and uniaxial compression testing of analog models and tuff rock, in order to assess the relationships between elastic modulus and porosity. The first part of the paper presents numerical simulation of uniaxial compression testing to calculate the elastic modulus of two-dimensional models containing randomly distributed circular holes in plane strain. The range of porosities investigated is approximately 5–40%. In the second part, the elastic modulus determined from the uniaxial compression testing of analog models and tuff specimens is presented. The analog specimens were made of plaster of Paris containing varying amounts of spherical shaped Styrofoam® inclusions to simulate a cavity structure similar to tuff. The results from the numerical analysis and analog material testing show an exponential decrease in elastic modulus with increasing porosity, whereas the elastic moduli of tuff show a linear decrease. The difference in the two behaviors can be attributed to the nonuniform cavity shapes in the tuff specimens

Northeast Florida-A New Hotspot for Hurricane Damage?

Until recent Hurricanes Matthew and Irma struck northeast Florida, Hurricane Dora had been the first and only hurricane-strength storm in recorded history to strike the region. The area had gradually become regarded as a safe spot as storms at that latitude generally curved away from Jacksonville and northeast Florida, and turned north to make landfall in the Carolinas. Unknown to most, Vilano Beach had been experiencing steady yet chronic beach erosion and was already in a highly vulnerable state in many places when the recent storms struck. The cause of the ongoing background erosion continues to be a source of contention among residents and some experts. This paper presents prestorm historic beach conditions, the potential causes and progression of erosional events surrounding Hurricanes Matthew and Irma at three locations in northeast Florida, and an assessment of protection measures implemented by homeowners. Observations made during field investigations show that bulkheads constructed to protect single or multiple houses exacerbate erosion at the ends of the bulkheads. This results in both failure of the bulkheads as well as increased erosion for neighboring properties

Evolution of filling system design for an A356-T6 aluminum housing casting

The results of a student project to produce two housing halves for an engine dynamometer are presented in this paper. The filling systems were designed to minimize turbulence and damage to the metal. The results of small changes in the filling system design are discussed. A new method of using different parts of the filling system (rigging) to evaluate the results of quality improvement efforts is introduced