Browsing by Author "Labuz, Joseph"
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Item Cone Penetration Testing in Pavement Design(Minnesota Department of Transportation, 2007-09) Dehler, William; Labuz, JosephThe objective of this work was to show that cone penetration testing (CPT) can be used for pavement applications, specifically estimating resilient modulus and organic content. A series of undisturbed samples were obtained from borings directly adjacent to CPT soundings. These samples underwent both laboratory resilient modulus and bender element testing. A statistical analysis was then performed on these results in conjunction with the data obtained from the CPT soundings to determine the feasibility of developing correlations between field and laboratory measurements of moduli. A relationship was developed between Young's modulus determined by bender element testing and that determined by resilient modulus testing. However, the correlation did not apply to the field-based seismic measurements of stiffness from the CPT soundings. The analysis presented with respect to the identification of highly organic soils via CPT testing shows that at this point the model identified using the discriminate analysis method is not currently sufficient to use in practice. The 10% increase in correctly classified soils, however, holds promise for the future, and the introduction of additional independent parameters within a significantly larger data set can be easily analyzed using the methods and tools presented here.Item Cracking of Asphalt Concrete at Low Temperatures(Center for Transportation Studies, University of Minnesota, 1994-10) Labuz, Joseph; Dai, ShongtaoThe objectives of this research are (1) to characterize the fracture resistance of asphalt concrete at low temperatures and (2) to develop a simple test method for laboratory testing. Cracking of asphalt concrete at low temperatures is a major problem in the Upper Midwest. The cold temperatures in the winter months impart a brittle behavior to an otherwise ductile (viscous) material. The formation of cracks in the pavement provides a pathway for the migration of water, which may refreeze and cause more damage. The conventional three-point-bend (3PB) load configuration is proposed for conducting fracture tests. The entire 3PB fixture is placed in an environmental chamber, where the temperature is controlled and maintained at -18° (0°) and -34°C (-30°F). The experimental apparatus and test procedure are described in detail, and the corresponding formulae are derived. Following linear fracture mechanics, the fracture toughness of a particular asphalt concrete at 10% air voids is about 0.5 MPa-m° s at both temperatures, although the nonlinear response is more pronounced at -18"C. This means that less energy is needed to initiate a crack at -34°C compared to -18"C. Furthermore, it appears that the toughness of the asphalt concrete is increased with an increase in compactive energy, which is indicated by a decrease in air voids content.Item Data for Response of a large, low porosity rock sample to hydromechanical loading(2024-10-22) Asem, Pouyan; Detournay, Emmanuel; Voller, Vaughan; Labuz, Joseph; pasem@umn.edu; Asem, Pouyan; University of MinnesotaA unique laboratory framework is developed for measuring hydromechanical parameters in a 6025 mL confined specimen of Westerly blue granite. Tracking the water uptake in the sample shows that infiltration over a length scale of 230 mm is effectively modeled by assuming a sharp front separating saturated and dry regions. Through matching the movement of this front with the experimental data, an estimate of the sample permeability is obtained. In addition, following full saturation, Skempton coefficient B, drained bulk modulus K, unjacketed bulk modulus Ks′, and unjacketed pore modulus Ks'' are determined. Thus, we demonstrate that a single experimental framework for measuring the infiltration and saturation of a large, tight rock specimen provides a significant array of reliable parameters for use in modeling and characterizing critical hydrogeological processes.Item Data for Saturating a Tight Rock and Measuring Its Hydromechanical Response(2023-08-21) Asem, Pouyan; Detournay, Emmanuel; Huang, Haiying; Labuz, Joseph; pasem@umn.edu; Asem, PouyanInvestigation of hydromechanical behavior of fluid-saturated tight rock is motivated by the need to quantify the effect of changes of fluid pressure p and mean stress P on rock deformation, hydrothermal fluid, and mass transport. In particular, hydromechanical properties of low porosity crystalline rock are required for analysis of geological processes including areal hydration or dehydration, mineral weathering, and fault mechanics. In this study, poroelastic parameters – drained bulk modulus K, and Biot coefficient α – governing the volumetric response of Westerly blue granite, a typical crystalline rock of low porosity are measured. Three additional hydromechanical properties, unjacketed bulk modulus Ks , expansion modulus H, and permeability k, are also measured. For the Terzaghi effective mean stress of 1.0 < P′ = P −p < 25.0 MPa, the unjacketed bulk modulus Ks = 57.5 GPa is constant within the range of mean stresses investigated but other poroelastic coeff icients exhibit effective mean stress dependency; the ranges are 13.2 < K < 32.3 GPa, 19.0 < H < 60.0 GPa, 0.83 > α > 0.38, and 20 > k > 5 nanodarcy. The agreement between poroelastic coefficients determined from various methods suggests that the underlying linear elastic assumption in Biot’s theory of poroelasticity is applicable to Westerly blue granite over small increments of effective mean stress.Item Detecting Foundation Pile Length of High-Mast Light Towers(Minnesota Department of Transportation, 2022-08) Kennedy, Daniel; Guzina, Bojan; Labuz, JosephThe goal of the project is to establish a non-destructive field testing technique, including a data analysis algorithm, for determining in-place pile lengths by way of seismic waves. The length of each pile supporting a high-mast light tower (HMLT) will be identified through a systematic sensing approach that includes (i) collection and classification of the pertinent foundation designs and soil conditions; (ii) use of ground vibration waveforms captured by a seismic cone penetrometer; (iii) three-dimensional visco-elastodynamic finite element analysis (FEA) used as a tool to relate the sensory data to in situ pile length; (iv) use of machine learning (ML) algorithms, trained with the outputs of FEA simulations, to solve the germane inverse problem; (v) HMLT field testing; and (vi) analysis-driven data interpretation. Several hundred HMLTs throughout Minnesota have foundation systems, typically concrete-filled steel pipe piles or steel H-piles, with no construction documentation (e.g., pile lengths). Reviews of designs within current standards suggest that some of these foundations may have insufficient uplift capacity in the event of peak wind loads. Without knowledge of the in situ pile length, an expensive retrofit or replacement program would need to be conducted. Thus, developing a screening tool to determine in situ pile length - as compared to a bulk retrofit of all towers with unknown foundations - would provide significant cost savings.Item Development of a Rock Strength Database(Minnesota Department of Transportation, 2018-06) Folta, Brian; Sharpe, Jacob; Hu, Chen; Labuz, JosephRock 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.Item Implementation of Ground Penetrating Radar(Local Road Research Board, Minnesota Department of Transportation, 2007-08) Cao, Yuejian; Dai, Shongtao; Labuz, Joseph; Pantelis, JohnThe objective of this project was to demonstrate the capabilities and limitations of ground penetrating radar (GPR) for use in local road applications. The effectiveness of a GPR survey is a function of site conditions, the equipment used, and experience of personnel interpreting the results. In addition, not all site conditions are appropriate for GPR applications. GPR is a nondestructive field test that can provide a continuous profile of existing road conditions. GPR utilizes high-speed data collection at speeds up to 50 mph, thus requiring less traffic control and resulting in greater safety. GPR has the potential to be used for a variety of pavement applications, including measuring the thickness of asphalt pavement, base and sub-grade; assisting in the analysis of rutting mechanisms; calculating and verifying material properties; locating subsurface objects; detecting stripping and/or layer separation; detecting subsurface moisture; and determining depth to near-surface bedrock and peat deposits. These applications are discussed in reference to 22 projects completed throughout the State of Minnesota. Three reports were produced. (1) A technical summary report provides an overview of the project. (2) A comprehensive review of GPR applications for use on local roads is also available. (3) The final report describes the results of the GPR surveys.Item Implementation of Pavement Evaluation Tools(Minnesota Department of Transportation, 2013-11) Tang, Shuling; Guzina, Bojan; Labuz, JosephThe objective of this project was to render the Falling Weight Deflectometer (FWD) and Ground Penetrating Radar (GPR) road assessment methods accessible to field engineers through a software package with a graphical user interface. The software implements both methods more effectively by integrating the complementary nature of GPR and FWD information. For instance, the use of FWD requires prior knowledge of pavement thickness, which is obtained independently from GPR.Item Mechanical Response of a Composite Steel, Concrete-Filled Pile(Minnesota Department of Transportation, 2018-06) Hu, Chen; Sharpe, Jacob; Labuz, JosephA steel pipe-pile section, filled with concrete, was instrumented and tested under axial load. Two types of strain gages, resistive and vibrating wire, were mounted to the steel-pipe pile and checked by determining the known Young’s modulus of steel E^s. The steel section was filled with concrete and a resistive embedment gage was placed in the concrete during the filling process to measure axial strain of the concrete. The axial load – axial strain responses of the steel (area A^s) and concrete (area A^c) were evaluated. The stiffening of concrete, related to curing, was also studied. Assuming the boundary condition of uniform axial displacement, i.e., equal axial strain in the steel and concrete, εz^s = εz^c = εz, the sum of the forces carried by the two materials, F^s + F^c, where F^s = εz * E^s * A^s and Fc = εz * E^c * A^c, provides a reasonable estimate – within 3% – of the pile force. For the particular specimen studied (12 in. ID, 0.25 in. wall thickness), the stiffness of the composite section of steel and concrete was about three times larger compared to the steel section without concrete. Further, the concrete carried about 70% of the load, but the axial stress in the concrete, at an applied force of 150,000 lb, was less than 20% of the compressive strength of the concrete.Item Pavement Rehabilitation Selection(Minnesota Department of Transportation, 2008-01) Dai, Shongtao; Skok, Eugene; Westover, Thomas; Labuz, Joseph; Lukanen, ErlandThe objective of the project was to outline best practices for the selection of asphalt pavement recycling techniques from the many choices that are available. The report specifically examines cold-in-place recycling (CIR), plain full depth reclamation (FDR), and mill & overlay (M&O). Interviews, surveys, and site visits were conducted at both Mn/DOT districts and counties, where relevant rehabilitation information was supplied on over 120 projects. A database was constructed to organize the details of these projects, and the parameters in the database included (1) cracking, (2) ride, (3) rutting, (4) age, and (5) traffic volume. From studying the existing rehabilitation projects in the State, Ride Quality Index (RQI) and Surface Rating (SR) were selected as the descriptors of pavement surface condition. A decision procedure based on the analysis of all available projects was developed. The decision procedure included (1) consideration of road geometrics; (2) pavement condition survey; and (3) structural adequacy evaluation. Furthermore, a step-by-step checklist was developed to provide local engineers with a simple and useful tool to follow the decision procedures. The procedure includes selection of rehabilitation method, pavement thickness design, materials mixture design, and construction.Item Resilient Modulus And Strength Of Base Course With Recycled Bituminous Material(Minnesota Department of Transportation, Research Services Section, 2007-01) Kim, Woosung; Labuz, JosephThe objective of the research was to determine the strength and deformation characteristics of base material produced from recycled asphalt pavement (RAP) and aggregate. Various samples with different ratios of RAP and aggregate base were mixed (% RAP/aggregate): 0/100, 25/75, 50/50, 75/25. Laboratory compaction testing and field monitoring indicated that gyratory compacted specimens were closer to the densities measured in the field. Resilient modulus (MR) tests were generally conducted following the National Cooperative Highway Research Program 1-28A test protocol. MR increased with increase of confining pressure, but MR showed little change with deviator stress. The specimens with 65% optimum moisture contents were stiffer than the specimens with 100% optimum moisture contents at all confining pressures. Cyclic triaxial tests were conducted at two deviator stresses, 35% and 50% of the estimated peak stress, to evaluate recoverable and permanent deformation behavior from initial loading to 5000 cycles. The specimens with RAP exhibited at least two times greater permanent deformation than the 100% aggregate material. As %RAP increased, more permanent deformation occurred. In summary, the base material produced with various %RAP content performed at a similar level to 100% aggregate in terms of MR and strength when properly compacted.Item Resilient Modulus Development of Aggregate Base and Subbase Containing Recycled Bituminous and Concrete for 2002 Design Guide and Mn/Pave Pavement Design(Minnesota Department of Transportation, 2007-06) Westover, Thomas; Labuz, Joseph; Guzina, BojanThe primary objective of this study was to quantify stiffness (resilient modulus) of aggregate base containing recycled asphalt and concrete pavements. After a survey of other state's specifications and implementation guidelines, Minnesota recycling projects were selected based on the availability of laboratory resilient modulus (MR) tests and field measurements from FWD. The projects were County State Aid Highway 3, Trunk Highway 23 and Trunk Highway 200. Based on the results of a parametric study, it was found that traditional peak-based analysis of FWD data can lead to significant errors in elastostatic backcalculation. A procedure for extracting the static response of the pavement was formulated and implemented in a software package called GopherCalc. Laboratory resilient modulus measurements were compared with moduli backcalculated from the FWD data. The FWD data was analyzed using conventional (peak-based) and modified (FRF-based) elastostatic backcalculation (Evercalc) as well as a simplified mechanistic empirical model called Yonapave. Laboratory values from sequences in the MR protocol that produced a similar state-of-stress were used. Additionally, a seasonal analysis of FWD test data revealed a significant increase in stiffness when the pavement is in the frozen state.Item TH 241 Column-Supported Embankment(University of Minnesota Center for Transportation Studies', 2008-06) Wachman, Gregory; Labuz, JosephA pile-supported embankment constructed on TH 241 near St. Michael, MN was instrumented with 48 sensors, including strain gages on the piles and on the geogrid, as well as earth pressure cells and settlement systems near the base of the embankment. Pile supported embankments are relatively novel structures employed largely at bridge approaches and highway expansions where soft soils would otherwise lead to unacceptably large differential settlements. The structure typically consists of a number of capped piles, well-compacted gravel, and one or more layers of geogrid reinforcement above the piles. Analyses of the data suggest that the redistribution of the embankment load to the piles occurs within and above the so-called load transfer platform, a 1 m layer of geogridreinforced gravel. Arching seemed to take place within the embankment, such that the stress at the top of the platform was concentrated above the piles.