Underground Infrastructure Project Descriptions

Colorado School of Mines

1: Development of an ASTM Standard for Biochar Use in Concrete

Project Number: 1

Faculty Mentors: Dr. Lori E. Tunstall


Our lab has demonstrated a nearly 40% increase in the compressive strength of cement mortars through replacement of 15% of the cement with wood biochar—a carbon rich, renewable additive made from pyrolysis of pine. We estimate that this innovation will offset the CO2 emissions associated with concrete by over 48%, when compared to traditional cementitious materials. However, before this technology is viable for widescale adoption, we need to develop a standard for biochar use in concrete. This will require a deeper understanding of which biochar properties control the performance of cementitious materials and how widely these biochar characteristics can vary before adverse performance in biochar mortars (Figure 1) is observed.

Preliminary results indicate that biochar characteristics of surface area and water sorption are the most strongly correlated variables to the performance of biochar mortars; however, this conclusion is based on a limited data set. Additional characterization of distinct biochars and biochar mortars are required to develop a comprehensive understanding of not only which biochar characteristics are critical to control, but also what are the tolerable variations in these characteristics. These data will be necessary for beginning the process of material standardization for the highly regulated concrete industry.

The objective of this REU project is twofold: 1) to improve our understanding of the effect of various biochar characteristics on mortar properties and 2) to determine the tolerable variation of these properties without sacrificing the performance of cementitious materials. The research activities for the REU student will include the following: (a) review and finalize the specific research objective in collaboration with faculty mentor; (b) make mortars with varying types and quantities of biochar; (c) test mortars for compressive strength; (d) characterize biochar for surface area, surface acidity, chemical composition, and water sorption; (d) conduct sensitivity analysis to determine critical biochar characteristics to control; (e) develop a hypothesis to explain results; and (f) discuss results and hypothesis with faculty mentor and develop a research plan for future work.


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2: Tunnel induced building deformation


Project Number: 2

Faculty Mentors: Michael Mooney

This research will involve evaluating tunnel construction-induced settlement and potential damage to structures along the alignment of an actual urban tunnel project. As-built building information will be used along with ground conditions (soil profile, soil properties) to explore why existing estimation techniques are inaccurate. Some modeling of the ground-structure interaction will be pursued to better match the observed behavior and to assess how to improve simplified estimation techniques.


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3: Study of clogging of clay in soft ground tunneling

Project Number: 3

Faculty Mentors: Dr. Jamal Rostami

Earth Pressure Balanced (EPB) Tunnel Boring Machines are the most common tunneling machines in the world. In particular they are the best choice of machines in soft ground tunnels involving Clay formations. To improve the machine performance and reduce the possibility of clogging, often foam is injected at the face, to condition the soil.  The behavior of Soil-Foam mixture is not fully explored and in particular a proper mixing of clay and foam for evaluating the behavior of the mixture has been an obstacle. The proposed research is experimental work that involves looking at various ways that clay and foam can be mixed to develop a uniform material for testing. The work involves reading background information, conducting tests on various soil types to see the impact of soil conditioning on soil behavior and measurement of proper parameters on a recently developed soil rheology testing unit shown in the picture below. The student will receive proper introduction and will be trained on operating the testing unit.




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4: Evaluation of Fiber Reinforced Concrete for Underground Structures Subject to Fire Events

Project Number: 4

Faculty Mentors: Dr. Spencer Quiel and Dr. Clay Naito

Figure 1: Tensile test setup for UHPC specimens

Figure 1: Tensile test setup for UHPC specimens

Steel fiber reinforced concrete has been gaining traction in the U.S. construction industry for use in bridges, buildings, and tunnels. The use of steel fibers at addition rates of up to 2% by volume allows concrete element to have a stable and reliable tension capacity. In conventional reinforced concrete design, the portion of the concrete in tension is assumed to have no resistance and instead reinforcing bars are used to provide the tension strength. The tension capacity of fiber reinforced concrete mixes facilitate the removal of conventional steel reinforcement from flexural elements. Depending on the type and amount of fiber used, the fiber reinforced concrete (FRC) can provide idealized elastic brittle, elastic-plastic, or elastic-hardening constitutive properties. These tensile properties can be determined using flexural beam tests or direct tension coupon tests (Figure 1).

Figure 2: Oven for high temperature exposure testing

Figure 2: Oven for high temperature exposure testing


Fire effects on FRC members pose a potential risk to the long-term performance of these materials. To provide fire resistance, conventional reinforced concrete requires a minimum distance from the surface of the concrete to the tension reinforcement (concrete cover), structural steel utilizes fire protective coatings or materials to resist the effects of fire. Minimal research has been conducted on the fire resistance of FRC systems. Unlike conventional concrete, the fibers are present throughout the section and have no cover protection in the event of a fire event. Furthermore, recommended protection layers, similar to what is done for structural steel, have not been developed.


The research effort will examine different FRC mixes and determine the mechanical and thermal properties. These results will be used to assess the performance of the material under both conventional loads and fire events in tunnel systems. The experimental program will consist of fabrication of FRC mixes, tension and compression testing of materials, high temperature exposure of samples and determination of residual strengths.

The research activities for two REU students will include the following: (a) review and finalize the research objectives in collaboration with the faculty mentors; (b) collect information on conventional FRC mix designs; (c) design lab tests to investigate the performance of FRC during and after fire exposure; (d) define failure mechanism of FRC exposed to heat; (e) utilize the experimental results to propose recommended designs for tunnel applications. One student will focus on thermal performance of FRC over a range of temperature conditions, and the other will focus on thermo-mechanical response to applied loading and restraint of thermal expansion.

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5: Examination of Limestone Calcined Clay Cements for Underground Concrete Construction

Project Number: 5

Faculty Mentors: Dr. Clay Naito and Dr. Spencer Quiel

Concrete is one of the most common construction materials used in the world. In general, concrete is comprised of cement, coarse and fine aggregates, water and admixtures. The most common cement used is Portland cement which is produced by an energy intensive process in which limestone and other raw materials are heated at temperatures ranging from 1400 to 1550ºC to form clinker. Clinker is then ground and combined with gypsum to form Portland cements. Though the cement content of conventional concretes is typically only on the order of 10% of the concrete volume, the production methods result in significant CO2 generation. In most years the CO2 generated by the cement industry exceeds that generated by the entire airline industry. These emissions are mainly due to the large amount of fossil fuel needed to reach the high temperatures needed for clinker. To help reducing the amount of carbon emissions from concrete production, alternative cements have been developed. A material which has recently gained interest in Europe is Limestone Calcined Clay Cement or LC3. Unlike clinker production, calcination of clays can be conducted at 800°C. This lower temperature can significantly reduce the amount of carbon emissions thus improving the environmental sustainability of concrete production.

The research effort will examine LC3 for use in ready mix and precast concrete production. The formulations will target the requirement of the various industry needs. Issues like strength gain, the rheology of the mixes and the long-term performance will be examined.

The research activities for one to two REU students will include the following: (a) review and finalize the research objectives in collaboration with the faculty mentors; (b) collect information on conventional ready mix and precast mix designs; (c) design lab tests to investigate the performance of LC3 concrete; (d) utilize the experimental results to propose recommended designs for use in transportation infrastructure applications.

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6: Tunnels in modern tools for risk assessment and resilience analysis

Project Number: 6

Faculty Mentor: Dr. Paolo Bocchini

The results of previous REU students who contributed to this program confirmed that the damage on tunnels can have catastrophic effects on transportation networks and severely hinder the post-disaster recovery phase, with large losses. Moreover, federal and local agencies are moving toward judging investment in transportation infrastructure through benefit-cost analyses at the system level, which include the vulnerability of all the assets in the region, including tunnels. Yet, while road/railway segments and bridges are always included in risk and resilience analysis tools, tunnels appear to be an afterthought.

In this sense, Hazus is an exception, being a software tool for natural hazard analysis that incorporate the analysis of tunnels, even though to a lesser extent than bridges and other infrastructure components. In the past years, REU students have used Hazus to study the role of tunnels in transportation networks subjected to natural disasters. This new project will generalize the investigation, study how other, more modern, software tools incorporate tunnels and how they can be used for regional resilience studies. In particular, the research activities for the REU student will include the following: (a) review of the state-of-the-art and the state-of-practice on software for tunnel risk assessment under multiple hazards, to finalize the research objectives in collaboration with the faculty mentor; (b) perform a survey of the relevant software tools and platforms for risk and resilience analysis, to determine how tunnels are considered, starting with the RDR tool that the US DOT has released just two months ago; (c) identify at least one of these software tools, and conduct a risk or resilience analysis for a test region including important tunnels; (d) report on their findings and compare the results with what could be obtained with Hazus. Depending on the level of experience of the student, task (c) may or may not include a benefit-cost analysis to compare the outcomes of a number of potential investment in risk mitigation for tunnels. During this effort, the REU student will be supervised by the faculty advisor and mentored by graduate students and postdocs who worked extensively in the field.

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California State University – Los Angeles

7: Establish liquefaction capacity curves at various PD levels

Project Number: 7

Faculty Mentors: Welson Kwan

A series of PD cyclic simple shear tests will be performed with the PD filter and actual pore ware pressure measurements. We will consider three PD levels: low, medium, and high, and create families of liquefaction capacity curves (Fig. 1) at two sand densities: loose and dense.


Such data is currently unavailable, and the generated information will be valuable for numerical modelers to calibrate their constitutive models for liquefaction designs in PD conditions.

Preliminary testing plan for Project#1

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8: Validating Drained Tests under Constant Vertical Loads

Project Number: 8

Faculty Mentors: Welson Kwan

The constant-volume condition was validated in simulating undrained conditions (Dyvik et al. 1987) and is now widely adopted in engineering standards for static and uni-directional cyclic undrained tests (ASTM D6528 and D8296). However, it remained unclear for controlling boundaries to simulate the drained tests. Conceptually, drained conditions (constant-normal-load) oppositely mirror undrained conditions (constant-volume). Most commercial simple-shear devices can maintain a constant-vertical-load during the shearing phase. The recorded change in specimen’s height possibly reflects the volumetric change in drained conditions. There are limited studies to examine this simulation (El Mohtar et al. 2018), and the PI proposes a comprehensive analysis including sand and clay specimens to examine the simulations.

Preliminary testing plan for Project#2 (NC = normally consolidated; OC = overly consolidated)


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9: Detecting underground infrastructure surface defects using machine learning

Project Number: 9

Faculty Mentors: Dr. Mohammad Pourhomayoun

The integrity of materials in infrastructure is essential to ensure durability and safety. Concrete is a common construction material due to its performance, durability, and cost-effectiveness. Concrete structures are prone to develop surface cracking during their lifetime. Identifying and assessing these defects is important for decision-makers to take any necessary maintenance actions to prevent further deterioration and potential failure. Machine Learning is an effective tool that have been applied to this and many other fields to automatically obtain meaningful information instead of manually developing complicated analytical models.Infrastructure Defect Monitoring and Forecasting with Artificial Intelligence

This study proposes a machine learning method to predict the growth pattern of cracks on the concrete surface. The REU student will work with the faculty mentor to a) analyze the images for capturing the partial propagation of individual cracks with the aim of producing a series of frames that predict the continuation of the growth sequence over time, b) Employ various machine learning algorithms to achieve the best prediction performance, and c) Implement transfer learning and data augmentation to deal with a limited dataset.


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