Browsing by Subject "Drill core analysis"
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Item A facies-scale chemo-lithostratigraphic composite profile of Del Rio claystone through Austin Chalk deposition, late Cretaceous, central Texas, USA(2016-05) Gabb, Kyle Christopher; Fisher, W. L. (William Lawrence), 1932-; Rowe, Harry; Hentz, Tucker FLate Cretaceous deposition (Comanche/Gulfian Series) across the San Marcos Arch of central Texas is characterized by both aluminosilicate- and carbonate-dominated mudrock successions. Twelve drill cores were recovered from the 2-acre construction site of the AT&T Executive Education and Conference Center on The University of Texas at Austin main campus. Thirteen detailed chemo-lithofacies were defined through a combination of visual description and elemental analysis utilizing energy-dispersive X-ray fluorescence (ED-XRF). Elemental analysis was undertaken at a 0.25-ft sampling interval to provide a record of facies-scale variability. A composite profile from two cores was created by identifying the boundary between the top of the Buda Limestone and bottom of the Eagle Ford Group and then splicing the records together, thus maximizing the length of the composite core to 174 ft and incorporating the Del Rio Claystone, Buda Limestone, Eagle Ford Group, and Austin Chalk formations. Lithofacies within the four formations were defined based on Dunham’s (1962) carbonate and Potter’s (1980) shale classifications. Important sedimentary structures and mineralogical compositions were identified and added as modifiers to the facies description. The shifts between the carbonate formations and the clay-rich formations are caused by changes in sea level, productivity, anoxia, and reworking by bottom currents. The Buda Limestone and Austin Chalk are identified to range in composition from limestone to marl, as the matrixes of the formations are composed of alumo-siliceous mud. Covariance of silicon with aluminum and titanium (proxies for detrital inputs) suggests that the silica is dominantly of terrigenous origin, rather than of biogenic origin. The enrichment of redox elements (molybdenum and vanadium) indicates the occurrence of anoxia during deposition of the Eagle Ford Group. The increased presence of volcanic ash beds within fossil-rich section of the Eagle Ford Group indicates that nutrients supplied by volcanism led to increased primary productivity, triggering depleted oxygen levels and anoxic bottom waters. Whereas sea level was likely the driving force that caused changes within the Del Rio Claystone, Buda Limestone, and Austin Chalk, productivity and anoxia are the drivers of transitions within the Eagle Ford Group.Item Effect of verification core hole on the point bearing capacity of drilled shafts(2008-12) Youn, Heejung, 1976-; Tonon, FulvioFor many projects involving drilled shafts, cores are required to be taken below the shaft base for visual identification of the underlying material. For example, the Texas Department of Transportation (TxDOT) requires a core length of at least 1.5 m (5 ft) or equal to the shaft diameter, whichever is greater, at the shaft base. Although the verification cores are to be extracted at the shaft base, The Department of Transportation of many states do not provide guidance to eliminate the effect of the verification core on the point bearing capacity. A recent study shows that the verification core hole is either filled with concrete in dry condition or with sand-gravel mixture in wet pour (Raibagkar, 2008). This finding is crucial because the point bearing capacity of drilled shafts with an empty hole at the base should be significantly lower than that of drilled shafts without verification core. Although the materials that fill in the verification core remove the risk of losing large point bearing capacity, the exposure of the core holes to air-drying may have an adverse effect on the point bearing capacity tipped in clay shales, especially when the basal material is susceptible to weathering. Therefore, the effect of the verification core on the point bearing capacity has been thoroughly investigated with emphasis on changes in the material properties of four clay shales (Del Rio Clay, Eagle Ford Shale, Taylor Marl, and Navarro Shale) in central Texas. The effect of verification core on the point bearing capacity of drilled shafts was investigated using finite element method (FEM) software, PLAXIS. The results from laboratory tests were converted to input material parameters for Mohr-Coulomb failure criterion, and the thickness of degraded zone around the core was interpreted from fullscale condition degradation tests. The load-displacement curves at the shaft base were created from PLAXIS analyses, and the point bearing capacities were obtained at 5%D and 10%D displacement from load-displacement curves. These capacities were used to calculate reduction factors that relate the point bearing capacity of the reference model (without a verification core) with that of the “core models” (with a verification core). The reduction factors are good indicators to determine if verification core had a positive or negative effect on the point bearing capacity. It was found that the reduction in point bearing capacity of “core models” is typically within 10% capacity of the reference model, and a maximum reduction of 14% was found for the Taylor Marl that was dried for 48 hours.Item Petrographical, petrophysical, and biostratigraphical investigation of the Caddo Limestone (Pennsylvanian) Stephens County, Texas(Texas Tech University, 2001-12) Miller, Matthew CThe Pennsylvanian Caddo Limestone (Desmoinesian) of Stephens County, Texas, is a thick-hydrocarbon bearing carbonate unit. The uppermost Caddo is an algal-mound structure formed by the sediment-baffling effect of phylloid algae. Two cores south and southeast of Breckenridge, Texas were investigated petrographically and using geophysical logs. Within the cored intervals, multiple shallowing-upward mounding cycles can be recognized. Six depositional lithofacies were recognized and were associated with six depositional environments. These associations are: (1) Sponge Spiculite - Deep Water, (2) Fusulinid - Crinoid - Komia Packstone/Grainstone - Debris Bed or Capping Unit, (3) Phylloid Algal Wackestone - Mound Core, (4) Skeletal Wackestone - Near Flank Beds, (5) Carbonate Clast - Wackestone - Intermound, and (6) Skeletal Ooid Grainstone and Fusulinid - Crinoid – Komia Packstone/Grainstone - Capping Unit. The Caddo algal mounds follow a typical mounding pattern: (1) Deep Water, (2) Debris (stabilization of the deep water substrate), (3) Mound Core - Near Flank- Intermound (upward mound growth and lateral mound migration, and (4) a Capping Environments (termination of mound growth). The algal mounds original depositional fabric is heavily modified by four stages of diagenesis: (1) syndiagensis, (2) marine, (3) multiple phases of meteoric, and (4) deep (burial). Meteoric diagenesis had the largest modifying effect in the original depositional fabric. Three major relative sea level fluctuations occurred within the Caddo algal mounds, producing three mounding cycles. Correlation of cored wells and geophysical logs in the studied area lead to the determination of a progressive step wise westward termination of the Caddo algal mounds were a result the migration of the fore bulge (Bend Arch) associated with tectonic loading of the Ouachita Thrust Belt. Progradation of prodeltaic and basinal terrigenous sediments derived from the Ouachita thrust belt across the Caddo algal mounds in one event. The termination of the Caddo algal mounds, by drowning is time transgressive getting progressively younger in the westward direction.