45 research outputs found
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
Axial behavior of drilled shafts in soft rock
Get PDFShallow foundations are commonly not suitable to support the load of heavy structures such as tall buildings or bridges because the resulting contact pressures far exceeds the allowable pressure of the near-surface soils leading to bearing capacity failure or excessive settlements. Therefore, deep foundations are normally used to support heavy structures where loads are transferred to the more competent strata. Drilled shaft foundations are among the most commonly used types of deep foundations. Drilled shafts are often socketed into soft rock formations between near-surface residual soils and the unweathered bedrock that is commonly encountered at greater depths. Socketing drilled shaft foundations into soft rocks has increased in the recent years because it leads to safer and more economical designs. Therefore, a better understanding of the axial behavior of drilled shafts in soft rock is necessary.
Field evidence is collected for study of the axial resistance and deformational properties of rock sockets in soft rock masses. These include six databases: i) back-calculated side and tip resistances from axial load tests on drilled shafts and back-calculated base resistances from plate load tests, all in soft rocks, ii) a database for shear strength and deformational properties of rock/concrete interfaces that are tested in the laboratory, iii) a database for in situ shear strength and deformational properties of soft rock masses, iv) a database for near-surface measurements of in situ horizontal stresses in soft rock masses, v) a database for the mode of failure for side and tip of drilled shafts in soft rock, and vi) a database of measured in situ values of socket wall roughness height.
A predictive model is proposed for the peak shear strength for the side resistance of drilled shafts in soft rock. The back-calculated shear stress-shear displacement (t-z) relationships from drilled shaft load tests are used to develop a framework for prediction of t-z relationships for rock sockets in soft rock masses. The tip resistance database is used to develop design equations for prediction of the yield and fracture initiation pressures and a framework for prediction of the tip pressure-displacement (q-z) behavior of rock sockets in soft rocks.
A probabilistic Limit State Design (LSD) framework is adopted. Two limit states are evaluated, namely axial resistance (strength limit state) and settlement (serviceability limit state). The theory of probability is used to calibrate the Load and Resistance Factor Design (LRFD) resistance factors for the proposed models for prediction of peak side resistance and the fracture initiation pressure. The strength limit state may be evaluated using the proposed design equations (peak shear strength and fracture initiation pressure) and the corresponding LRFD resistance factors. The serviceability limit state is assessed using the proposed q-z and t-z relationships in combination with the load-transfer approach and tolerable values of settlement from the structural engineering literature.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2020-05-01The student, Pouyan Asem, accepted the attached license on 2018-01-25 at 15:51.The student, Pouyan Asem, submitted this Dissertation for approval on 2018-01-25 at 16:16.This Dissertation was approved for publication on 2018-01-30 at 14:21.DSpace SAF Submission Ingestion Package generated from Vireo submission #12023 on 2018-08-31 at 17:24:38Made available in DSpace on 2018-09-04T20:46:45Z (GMT). No. of bitstreams: 3
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Previous issue date: 2018-01-30Embargo set by: Seth Robbins for item 107336
Lift date: 2020-09-04T20:47:38Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107336
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Geochemical-hydromechanical couplings during water-serpentinized harzburgite interactions at 20°C and 30 bars
No full textInteraction of groundwater with the serpentinized harzburgites of the upper mantle plays an important role in the geologic carbon cycle and serpentinization processes. In this study, an intact serpentinized harzburgite with more than 60% lizardite from the Semail ophiolite in Oman was reacted with water at near neutral pH and low PCO2 to observe its dissolution behavior and reaction path within the CaO-MgO-SiO2-CO2-H2O system at 20 °C and 30 bars. In the experiment, mass (i.e. H2O, ions) transfer is by diffusion and the selected temperature and pressure conditions mimic water-rock interactions at the shallow portions of most ultramafic rock hosted aquifers. Equilibrium activity-activity diagrams and thermodynamic data were used to compare the experimentally determined reaction path with the theoretical stability boundaries for minerals involved to investigate the evolution of bulk chemical composition, mineralogy, and water composition. The experiments demonstrated that (i) the water-rock interactions increased the pH of the aqueous phase from 5.9 to 7.5 over a period of 18 weeks; (ii) the dissolution of lizardite, orthopyroxene (enstatite), and clinopyroxene (diopside and augite) increased the concentration of Mg, Ca, and Si in the aqueous phase; (iii) the dissolution was incongruent with respect to Mg and Si, favoring Si release at pH > 6 due to (a) breaking of more reactive cation‑oxygen bonds that is consistent with the stoichiometry of magnesium for proton exchange reaction which favors a surface that is enriched in Mg at basic conditions, and (b) preferential dissolution of clinopyroxene Mg1.30Ca0.52Fe0.06Si2O6; (iv) the aqueous phase was undersaturated with respect to carbonate (e.g. calcite, magnesite, and hydromagnesite) and hydrous (e.g. lizardite, chrysotile, brucite, and talc) minerals; (v) the bulk chemical composition and mineralogy of the intact serpentinized harzburgite matrix did not change; (vi) the thermodynamic data can successfully predict water-intact serpentinized harzburgite behavior if the water chemical composition can be constrained; and (vii) no detectable macroscopic form of damage (e.g. microcracks forming as a result of differential stress fields due to changes in volume during chemical reaction) was observed
Evaluation of the peak side resistance for rock socketed shafts in weak sedimentary rock from an extensive database of published field load tests: a limit state approach
Get PDFThis paper presents the analyses of the measured peak side resistance of rock sockets constructed in weak claystone, shale, limestone, siltstone, and sandstone. The peak side resistance is obtained from the in situ axial load tests on drilled shafts, anchors, and plugs. The parameters that affect the development of the peak side resistance are determined using the in situ load test data. It is found that the peak side resistance increases with the unconfined compressive strength and the deformation modulus of the weak rock, and decreases with increase in the length of the shear surface along the rock socket sidewalls. The increase in the socket diameter also slightly decreases the peak side resistance. Additionally, it is found that the initial normal stresses do not significantly affect the measured peak side resistance in the in situ load tests. The in situ load test data are used to develop an empirical design equation for the determination of the peak side resistance. The proposed model for the peak side resistance, and the reliability analysis are used to determine the corresponding resistance factors for use in the load and resistance factor design framework for the assessment of the strength limit state.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Axial behavior of drilled shafts in soft rock
No full textShallow foundations are commonly not suitable to support the load of heavy structures such as tall buildings or bridges because the resulting contact pressures far exceeds the allowable pressure of the near-surface soils leading to bearing capacity failure or excessive settlements. Therefore, deep foundations are normally used to support heavy structures where loads are transferred to the more competent strata. Drilled shaft foundations are among the most commonly used types of deep foundations. Drilled shafts are often socketed into soft rock formations between near-surface residual soils and the unweathered bedrock that is commonly encountered at greater depths. Socketing drilled shaft foundations into soft rocks has increased in the recent years because it leads to safer and more economical designs. Therefore, a better understanding of the axial behavior of drilled shafts in soft rock is necessary.
Field evidence is collected for study of the axial resistance and deformational properties of rock sockets in soft rock masses. These include six databases: i) back-calculated side and tip resistances from axial load tests on drilled shafts and back-calculated base resistances from plate load tests, all in soft rocks, ii) a database for shear strength and deformational properties of rock/concrete interfaces that are tested in the laboratory, iii) a database for in situ shear strength and deformational properties of soft rock masses, iv) a database for near-surface measurements of in situ horizontal stresses in soft rock masses, v) a database for the mode of failure for side and tip of drilled shafts in soft rock, and vi) a database of measured in situ values of socket wall roughness height.
A predictive model is proposed for the peak shear strength for the side resistance of drilled shafts in soft rock. The back-calculated shear stress-shear displacement (t-z) relationships from drilled shaft load tests are used to develop a framework for prediction of t-z relationships for rock sockets in soft rock masses. The tip resistance database is used to develop design equations for prediction of the yield and fracture initiation pressures and a framework for prediction of the tip pressure-displacement (q-z) behavior of rock sockets in soft rocks.
A probabilistic Limit State Design (LSD) framework is adopted. Two limit states are evaluated, namely axial resistance (strength limit state) and settlement (serviceability limit state). The theory of probability is used to calibrate the Load and Resistance Factor Design (LRFD) resistance factors for the proposed models for prediction of peak side resistance and the fracture initiation pressure. The strength limit state may be evaluated using the proposed design equations (peak shear strength and fracture initiation pressure) and the corresponding LRFD resistance factors. The serviceability limit state is assessed using the proposed q-z and t-z relationships in combination with the load-transfer approach and tolerable values of settlement from the structural engineering literature.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste
Assessment of the modulus of elasticity at a triaxial stress state for rocks using gene expression programming
Get PDFRocks were subjected to the deformation test under five different confining stresses (0, 5, 10, 15, and 20 MPa) using the Hoek cell to determine changes in the elastic properties of the rocks under confining stress, and the results were evaluated based on density, porosity, Schmidt hardness, and compressive strength. A total of nine different rocks, two granites, two andesites, two limestones, one tuff, one diorite, and one marble, were used. When the confining stress was increased from 0 MPa to 5 MPa and from 5 MPa to 10 MPa, elasticity increased by approximately 20%. When the confining stress was increased from 10 MPa to 20 MPa, the increase was 7% in comparison with the previous value. Then, to formulate the modulus of elasticity for rocks under the triaxial stress conditions, a new and intelligent approach to gene application, gene expression programming was utilized. The success of the model was thoroughly assessed based on measurable criteria such as the root mean square error, mean absolute percentage error, and coefficient of determination. Furthermore, the success of the model was comprehensively assessed based on the model testing, and 0.88 and 0.81 R2 values were obtained for training and validation, respectively. The performance of the gene expression programming-based formulation was compared with the formulae previously proposed in the literature. The gene expression method exhibited the best performance, and it was identified to calculate the modulus of elasticity under triaxial stress conditions more effectively. © 2020 The Author. Published by Pouyan Press
Probabilistic Model and LRFD Resistance Factors for the Tip Resistance of Drilled Shafts in Soft Sedimentary Rock Based on Axial Load Tests
No full text
Coupled Fracture Mechanics‐Geochemical Model of Reaction‐Driven Cracking
No full textAbstract Reaction‐driven cracking has been discussed for decades. One mechanism is the extension of a microcrack resulting from precipitation. This mechanism can create porosity, permeability and reactive surface area in low‐permeability rock. We model this problem as a fracture loaded over a fraction of its length by a vein. The loading causes crack propagation when the stress intensity factor reaches its critical value. We calculate the conditions for the onset of crack growth, the time required, pressure distribution around the vein, and the crack surface displacements. These results are relevant to many problems. One application is to geological storage of CO2 by mineralization. Results depend strongly on rock parameters but using representative values from experiments, our calculations suggest an initiation time within tens of years at low temperature and dilute fluid conditions. Lower critical stress intensity factor, higher reaction rate, and greater carbonate filling ratio reduce the time to initiation
