Proposed stratigraphic nomenclature and macroscopic identification of lithostratigraphic units of the Paintbrush Group exposed at Yucca Mountain, Nevada

Compaction and gas loss in welded pyroclastic deposits as revealed by porosity, permeability, and electrical conductivity measurements of the Shevlin Park Tuff

“…The main processes involved in porosity (and permeability) change include: (1) compaction (brittle or viscous), which causes porosity reduction, (2) expulsion or resorption of gas that once fi lled pore space (Sparks et al, 1999), (3) dissolution of water vapor (and N 2 from entrained air at higher pressures) into glass (Sparks et al, 1999; note: throughout this paper, the word glass is also taken to include material at or above the glass transition; cf. Dingwell 1996), (4) vaporphase precipitation, which can fi ll pore space and decrease porosity, (5) vapor-phase corrosion, which can increase porosity (e.g., Buesch et al, 1996), (6) devitrifi cation, which can slightly increase porosity (due to the negative volume change of the glass-crystal transition), and (7) fracture/crack formation (more common in more highly welded deposits), which can increase local porosity along specifi c planes (and thereby create zones of elevated permeability). Because these changes are nonlinear, porosity and permeability must be known as a function of time and location within the deposit in order to predict time scales of gas loss due to permeable gas migration, and conditions that initiate resorption welding.…”

“…Flint, 1998;Flint et al, 2006;Smyth and Sharp, 2006;Wright et al, 2011). Conversely, corrosion of glass by a vapor phase creates pore space and therefore increases porosity (and commonly permeability; e.g., Buesch et al, 1996). Furthermore, the presence of microfractures can increase permeability without substantially affecting porosity (e.g., Flint, 1998;Flint et al, 2006;Smyth and Sharp, 2006).…”

Stochastic analysis and prioritization of the influence of parameter uncertainty on the predicted pressure profile in heterogeneous, unsaturated soils

“…Non-welded units have higher matrix porosities (about 30%) and low fracture densities [11]. The hydrogeologic units that are considered in most unsaturated flow analyses as well as in this study are, from top to bottom: the Tiva Canyon welded (TCw) with a thickness of 81 m, the Paintbrush nonwelded (PTn) with a thickness of 39 m, the Topopah Spring welded (TSw) with a thickness of 299 m, the Topopah Spring vitrophyre (TSv) with a thickness of 15 m, the Calico Hills nonwelded-vitric (CHnv) with a thickness of 64 m, and the Calico Hills nonwelded-zeolitic (CHnz) with a thickness of 127 m [12,13]. The units exhibit significant differences in their properties [14] and hydraulic behaviors, and data that were available for this study included the thickness of layers, the means and standard deviations, and the range of the parameters.…”

Observations on the influence of lithophysae on elastic (Young's) modulus and uniaxial compressive strength of Topopah Spring Tuff at Yucca Mountain, Nevada, USA

“…The rock matrix consists of euhedral crystals of tridymite, sanidine and possibly magnetite and hornblende with various inclusions such as pumice. The porosity of rock matrix ranges from 8% to 14% [4][5][6].…”

“…Abundant inter-lithophysal fracturing with sparse thoroughgoing fractures was also reported. Lithophysae vary from 1 to 180 cm and are smooth and spherical to irregular and jagged [4,5].…”