3,183 research outputs found
Experimental data on pore moduli of porous rock
No full textDeposited here are Excel spreadsheets containing all figure data except for figures 1 and 2. Descriptions of each file can be found in "Tarokh-Labuz-Readme.txt".These data address two key questions: (i) is Ks'' a constant and (ii) under what conditions does Ks'' = Ks hold. We present unique laboratory experiments that enable the direct measurement of Ks'', for the first time, for ideal and natural porous solids.Partial support from the MSES/Miles Kersten ChairTarokh, Ali; Labuz, Joseph F. (2018). Experimental data on pore moduli of porous rock. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/D6RX0J
Experimental data on poroelastic moduli of transversely isotropic rock
No full textDeposited here are Excel spreadsheets containing data for figures 3 to 9. Descriptions of each file can be found in Readme.txtThese data present volumetric and deviatoric poroelastic moduli from a series of drained, undrained, and unjacketed tests in uniaxial, hydrostatic, and axisymmetric compression for a porous sandstone. These data enable the direct and independent measurement of all eight parameters that fully describe the mechanical response of a transversely isotropic rock.Sponsorship: Partial support from the MSES/Miles Kersten ChairTarokh, Ali; Labuz, Joseph F. (2021). Experimental data on poroelastic moduli of transversely isotropic rock. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/s9ce-z534
Inelastic Strain and Damage in Surface Instability Tests
No full textSpalling near a free surface in laboratory experiments on two sandstones was characterized using acoustic emission and digital image correlation. A surface instability apparatus was used to reproduce a state of plane strain near a free surface in a modeled semi-infinite medium subjected to far-field compressive stress. Comparison between AE locations and crack trajectory mapped after the test showed good consistency. Digital image correlation was used to find the displacements in directions parallel (axial direction) and perpendicular (lateral direction) to the free surface at various stages of loading. At a load ratio, LR = current load/peak load, of approximately 30 %, elastic deformation was measured. At 70–80 % LR, the free-face effect started to appear in the displacement contours, especially for the lateral displacement measurements. As the axial compressive stress increased close to peak, extensional lateral strain started to show concentrations associated with localized damage. Continuum damage mechanics was used to describe damage evolution in the surface instability test, and it was shown that a critical value of extensional inelastic strain, on the order of -10-3 for the virgin sandstones, may provide an indicator for determining the onset of surface spalling
Opening and mixed mode fracture processes in a quasi-brittle material via digital imaging
No full textFracture tests were performed on sandstone specimens under three-point bending with a
variety of notch positions to achieve KII/KI = 0???12%. At peak load, the maximum crack opening
displacement measured by digital image correlation was 45 lm under mixed mode
loading and 30 lm under mode I, and these values were used to determine the length of
the cohesive zone: 10???12 mm for mixed mode and 5???7 mm for mode I. For mixed mode
fracture, the displacement in the cohesive zone was identified to be opening only, while
sliding and opening were detected along the remaining length
Fabric for Reinforcement and Separation in Unpaved Roads
No full textResearchers performed laboratory experiments on soil-fabric-aggregate systems to evaluate the effect of a geotextile on unpaved road performance. Direct shear tests performed on gravel indicated a 42-degree friction angle. Similar tests performed on soil-fabric-aggregate systems resulted in an interface friction value for the nonwoven geotextile system similar to that of the gravel alone. The slit film and heavy weight woven systems generated friction angles about 20 percent lower.
Observations of model tests showed that in terms of rut depths, the nonwoven performed better than the slit film woven geotextile for all gravel thickness', most likely because of the nonwoven's higher frictional characteristics. The rut diameters for the slit film and nonwoven reinforced systems tended to be larger than those observed for the unreinforced systems indicating an increased load-spread angle through the gravel. Based on rutting alone, the unreinforced model with 200 mm (8 in.) gravel was equivalent to that of the slit film in reinforced model with 150 mm (6 in.) gravel and the nonwoven model with 100 mm (4 in.) gravel. A so-called bearing capacity factor for the unreinforced models was approximately 50 percent less than the nonwoven reinforced models, in reasonable agreement with theory.Local Road Research BoardBearden, Julie; Labuz, Joseph F.. (1998). Fabric for Reinforcement and Separation in Unpaved Roads. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/675
A problem of scaling in fracture of damaged rock
No full textPre-existing inhomogeneities such as micropores and microcracks dictate the mechanical and physical
properties of rock. Overloading, weathering, changing temperatures, and exceptional events can increase
this damage, usually by microcracking, and as a consequence, modify the effective properties of the rock.
To examine the problem of a structure composed of rock with various stages of damage, three point
bending tests on sandstone specimens exposed to elevated temperatures are presented, with a detailed
evaluation of process-zone size. Both virgin rock, with pre-existing damage and heat-treated rock, with
further damage, were tested by conducting experiments at ambient conditions after exposure to the high temperature. For virgin and heat-treated specimens, high resolution interferometric measurementswere used to characterize the evolution of the process zone as a function of the applied load.
The size and shape of the localized damage zone due to increased microcracking are the significant
factors influencing the strength and post-peak response of quasi-brittle materials. One of the aspects of this phenomenon is that structural scaling evolves with damage, which is explained by the increase of the process-zone size, and a decreasing influence of the scaling problem on nominal strength. As a result, a rigorous interpretation of the experimental data requires an identification of fracture parameters, and a
convenient indirect method is proposed
Earth Pressure Behind A Retaining Wall
No full textEarth pressure cells, tiltmeters, strain gages, inclinometer casings, and survey reflectors were installed in fall 2002 during construction of a 26-ft (7.9-m) high Minnesota Department of Transportation (Mn/DOT) reinforced concrete cantilever retaining wall. A data acquisition system with remote access monitored some 60 sensors on a continual basis. Analyses of the data indicated the development of active earth pressure at the end of backfilling, with a resultant at about one-third of the backfill height. Translation of 0.45 in. (11 mm), or about 0.1% of the backfill height, was responsible for development of the active condition. The wall also rotated 0.03 degrees into the backfill as a rigid body, while the top of the stem deflected 0.16 in. (4 mm) away from the backfill. Sensor readings showed the earth pressure distribution to be quite complex during the backfilling process. Evidence was found for residual lateral stresses from compaction. Translation of the wall overnight following the construction workday reduced the compaction-induced lateral stresses. Changes in earth pressure and wall deflection weeks after backfilling were attributed to changes in temperature and rainfall. The data showed that the wall design, while reasonable, could be made more efficient by removing the shear key, which was ineffective.Minnesota Department of TransportationBentler, Joseph G.; Labuz, Joseph F.; Schultz, Arturo E.. (2005). Earth Pressure Behind A Retaining Wall. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/830
Resilient Modulus and Strength cf Base Course With Recycled Bituminous Material
No full textThe 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.Minnesota Department of TransportationKim, Woosung; Labuz, Joseph. (2007). Resilient Modulus and Strength cf Base Course With Recycled Bituminous Material. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/5567
Data for Saturating a Tight Rock and Measuring Its Hydromechanical Response
No full textInvestigation 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 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.Research was supported by the (i) Center on Geoprocess in Mineral Carbon Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award # DE-SC0023429 (ED, HH, JFL: synthesis; HH: analysis and interpretation of permeability tests), and (ii) J.S. Braun/Braun Intertec Visiting Chair at the Department of Civil, Environmental, and Geo- Engineering, University of Minnesota (PA: experiments, analyses).Asem, Pouyan; Detournay, Emmanuel; Huang, Haiying; Labuz, Joseph. (2023). Data for Saturating a Tight Rock and Measuring Its Hydromechanical Response. Retrieved from the Data Repository for the University of Minnesota (DRUM), https://doi.org/10.13020/1vh3-sa45
Calibration of An Earth Pressure Cell
No full textIn this study, researchers devised a scheme for calibration of earth pressure cells to observe their response to various loading configurations and to recommend a procedure for field installation. Transducers designed to provide an estimate of normal stress within a soil, earth pressure cells have provided readings that conflict with known loading conditions. Initial calibration tests used hydraulic oil as the pressurizing medium in both hydrostatic and uniaxial pressure conditions, which mimic the manufacturers' procedure for pressure cell calibration. Researchers designed a new testing device to permit the application of uniaxial soil pressure to the earth pressure cells using various types of soil and load configurations. As a result of calibration tests, a field installation procedure was developed and recommended. In the laboratory, a thin-walled steel cylinder with a geotextile bottom was filled with uniform silica sand of a known density, and the earth pressure cell was placed within the sand. The entire apparatus was carried into the field and installed in the desired locations. Once in place, the steel cylinder was pulled up out of the ground, leaving the cell and geotextile behind. Preliminary field data indicate that soil calibration and placement procedure provide reasonably accurate measurements.Minnesota Department of TransportationTheroux, Brent; Labuz, Joseph F.; Drescher, Andrew. (2000). Calibration of An Earth Pressure Cell. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/700
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