Foundations

The variations in electromagnetic and electric properties with the moisture content of several geomaterials were assessed in this report to demonstrate their viability in estimating the moisture content of compacted geomaterials. A prototype device was also designed and fabricated to estimate the moisture content of compacted geomaterials by measuring the complex resistivity (amplitude and phase shift between the voltage and current) of geomaterials over numerous frequencies. Two fine-grained soils, two sandy soils, and two coarse-grained geomaterials were selected as a baseline for laboratory measurements. These soils were compacted and tested to measure their dielectric constants, traditional resistivities, and their complex resistivities using the developed prototype. The dielectric constants were less sensitive and more uncertain to the moisture content variations than the resistivity values. The traditional and complex resistivity measurements showed promise in the laboratory. The same soils’ seismic moduli, unconfined compressive strengths, and lightweight deflectometer moduli were also established. For field implementation, a rolling four-electrode equatorial array was created and tested within the laboratory and MnROAD facility. Field polarization and deviation from expected voltages and currents occurred frequently. These results suggested that resistivity or complex-resistivity measurements with rolling four-electrode arrays may need significant improvement for controlling moisture content.

Current research focuses on advancing the existing capabilities for stability analysis of pile foundations. To this end, researchers developed a continuum model and a structural model. In the continuum model, three-dimensional solid finite elements and mapped infinite elements are employed for modeling the three-dimensional geometry, pile-soil-pile interaction, and unbounded domain whereas three dimensional thin-layer interface elements are used for modeling interaction behavior between the pile and the soil. In contrast, thin-walled structural elements and flat shell elements are used for the piles and pile cap in the structural model. Nonlinear soil springs are adopted for modeling the lateral and axial pile-soil interaction. The continuum model is capable of accounting for pile-soil interaction and pile-soil-pile interaction appropriately whereas the structural model is efficient and simple to implement. To include pile-soil-pile interaction for groups of closely spaced piles, the group-reduction factor is introduced in an approximate fashion in the structural model. Both the continuum model and structural model developed in the current study are used together for some representative but simpler pile configurations to obtain the group-reduction factor.

The Minnesota Department of Transportation (Mn/DOT) currently uses the Engineering News Record (ENR) formula to monitor pile driving. This formula, first developed in 1893, uses an oversimplified model of the pile driving system to predict the pile capacity in the field. Since the beginning of this century, however, engineers have known that this formula neglects many complexities involved in the pile driving system including wave action, hammer energy loss, pile flexibility, and different soil resistance factors. This report is a record of the initial use of the Pile Driving Analyzer (PDA) by Mn/DOT. A sophisticated analog/digital device with high computational speed, the PDA uses one-dimensional wave propagation theory to calculate the forces acting on the pile that resist penetration. The PDA gives the test engineer immediate soil resistance, pile or shaft stress, and hammer efficiency results during pile driving, restriking, or impact testing. More than two-thirds of state transportation departments use the PDA, currently in worldwide use on more than 2,500 projects each year. For this project, we planned to receive training on the PDA and use it to monitor pile driving on selected projects in hopes of incorporating this more modem method of measuring pile capacity into Mn/DOT's pile driving program.

This Technical Summary pertains to Reports 2018-19, “Development of a Rock Strength Database,” and 2018-20, “Mechanical Response of a Composite Steel, Concrete-Filled Pile,” both published June 2018.

This Technical Summary pertains to Report 2014-37, “Scour Monitoring Technology Implementation,” published September 2014. The research being implemented via this project can be found mainly in Report 2010-14, “Bridge Scour Monitoring Technologies: Development of Evaluation and Selection Protocols for Application on River Bridges in Minnesota,” published March 2010.

This Technical Summary pertains to Report 2014-16, “Load and Resistance Factor Design (LRFD) Pile Driving Project—Phase II Study,” published April 2014.

This Technical Summary pertains to Report 2012-01, “Best Value Granular Material for Road Foundations,” published January 2012.

Rock strength and elastic behavior are important for foundations such as spread footings resting on rock and drilled shafts socketed into rock. In addition to traditional rock quality information; stiffness and failure parameters are helpful for design. MnDOT has previously used a low-capacity load frame for routine rock testing but this apparatus does not generate sufficient force for testing hard rock. The report provides a comprehensive suite of results from 134 specimens tested under uniaxial compression and 33 specimens tested under triaxial compression on a wide variety of rock; including hard rock; which frequently is of interest for high-capacity foundation systems. Thus; an economic benefit is realized if the strength of the rock is measured; as opposed to correlated with an index parameter; due to the potential to reduce foundation size and construction time. Information from the testing was used to expand the MnDOT database of rock properties and allow for improved designs based on accurate measurements of Young's modulus; uniaxial compressive strength; and friction angle.

Bridge scour is the removal of sediment around bridge foundations and can result in the failure of the bridge. Scour monitoring is performed to identify unacceptable scour on bridges considered to be scour critical and determine when scour reaches elevations that could cause potential bridge failure. Two types of monitoring are available: portable monitoring and fixed monitoring. Prior to this project, MnDOT was only using portable monitoring devices, which requires the deployment of personnel to make physical measurements of scour depths. For some scour critical bridges, especially during high-water events, fixed instrumentation capable of continuous scour monitoring was preferred, but MnDOT lacked the experience or expertise to install this type of equipment. This project installed fixed monitoring equipment at two bridge sites and monitored them for three years to determine the effectiveness and reliability of fixed scour monitoring deployments. Several device options were installed to allow MnDOT to analyze the installation and performance of different types of sensors. Both systems operated for the three years with some outages due to various causes but overall performance was acceptable. The outages were mostly related to power issues and communication issues. Valuable lessons were learned through the deployment, which may be applied to future installations. The deployment executed in this project has provided the confidence to deploy other fixed scour monitoring equipment at key bridges around the state of Minnesota. In addition, the data collected during deployment of the scour monitoring equipment has been stored and provides insight into scour processes. This data can be used by other research groups for design or research purposes.

Driven piles are the most common foundation solution used in bridge construction (Paikowsky et al., 2004). Their safe use requires to reliable verification of their capacity and integrity. Dynamic analyses of driven piles are methods attempting to obtain the static capacity of a pile, utilizing its behavior during driving. Dynamic equations (aka pile driving formulas) are the earliest and simplest forms of dynamic analyses. The development and the examination of such equation tailored for MnDOT demands is presented. In phase I of the study reported by Paikowsky et al. (2009, databases were utilized to investigate previous MnDOT (and other) dynamic formulas and use object oriented programming for linear regression to develop a new formula that was then calibrated for LRFD methodology and evaluated for its performance. This report presents the findings of phase II of the study in which a comprehensive investigation of the Phase I findings were conducted. The studies lead to the development of dynamic formulae suitable for MnDOT foundation practices, its calibrated resistance factors and its application to concrete and timber piles. Phase II of the study also expanded on related issues associated with Wave Equation analyses and static load tests, assisting the MnDOT in establishing requirements and specifications.