Compaction Profiles Research Articles

Real-time trajectory planning for asphalt compaction operator support

Operator Support Systems (OSSs) that support operators during highly time-critical asphalt compaction operations provide them with real-time sensory data. Nonetheless, the conventional asphalt compaction OSSs tend to cognitively overload operators with information that requires much human interpretation on the fly. To address the problem of OSSs' infobesity, the transition to a higher level of system automation that prescribes actions, i.e., prescriptive guidance, can be considered. To this end, this research aims to develop a novel compaction trajectory planning method that can be used to implement the Prescriptive Guidance mode in asphalt compaction OSSs. The proposed method analyzes the compaction and temperature profiles of the asphalt in real-time and suggests a compaction trajectory that ensures compaction efficiency and continuity. The proposed method is developed and compared to other types of asphalt compaction OSSs in two case studies. It is shown that while prescriptive asphalt compaction OSSs have a clear edge over more conventional OSSs in terms of improving compaction efficiency (i.e., more than 50% increase in compaction efficiency), there are still technology adoption and cultural issues that may affect the acceptance of this new technology in practice. The main contribution of this research is that it generates insights into (1) how to develop actionable and prescriptive compaction guidance, and (2) the interplay between the experience level of machine operators and the effectiveness of different support modes of asphalt compaction OSSs.

Viscosity of Crystal‐Mushes and Implications for Compaction‐Driven Fluid Flow

AbstractCentrifuge experiments on olivine, chromite, and plagioclase aggregates saturated in basaltic liquid show evidence of viscous compaction by grain‐boundary diffusion‐controlled creep. The experiments confirm that the exponential dependence of shear viscosity on melt fraction, observed at low porosities in earlier shear deformation experiments, extends to sedimentary porosities. The compaction profiles are inconsistent with the porosity‐dependence commonly ascribed to viscosity in macroscopic compaction models, which underestimate the effect of matrix disaggregation and consequently overestimate the viscosities of crystal mushes by 1–2 orders of magnitude. The time to halve the porosity of natural olivine igneous sediments by compaction is estimated from the centrifuge experiments to be O(103)y. Half‐times for plagioclase and chromite layers are O(104–105)y, suggesting that such layers compact on magmatic time scales only if they are loaded by additional sedimentation. At conditions relevant to melt flow in asthenospheric settings and trans‐crustal magmatic systems, the bulk and shear viscosities inferred for olivine and plagioclase are O(1017)Pa s, 4 orders of magnitude less than inferred from earlier experimental studies of the diffusion creep rheology. The reduced viscosities imply time‐ and length‐scales for compaction processes that are substantially shorter than previously anticipated. Our analysis serendipitously reveals that the oft‐neglected solidity term of the Carman‐Kozeny porosity‐permeability relation is essential to prevent non‐physical behavior in models of cumulate compaction.

Phase-sensitive radar as a tool for measuring firn compaction

AbstractFirn compaction models inform mass-balance estimates and paleo-climate reconstructions, but current models introduce key uncertainties. For example, models disagree on the dependence of density and compaction on accumulation rate. Observations of compaction to test these models are rare, partly because in situ methods for measuring englacial strain are time-consuming and expensive. Moreover, shallow measurements may confound strain due to compaction with strain due to ice-sheet flow. We show that phase-sensitive radio-echo sounder (pRES) systems, typically deployed to measure sub-shelf melting or ice-sheet deformation, can be used to measure firn compaction and test firn models. We present two complementary methods for extracting compaction information from pRES data, along with a method for comparing compaction models to pRES observations. The methods make different assumptions about the density structure and vary in their need for independent density measurements. Compaction profiles computed from pRES data collected on three ice rises in West Antarctica are largely consistent with measured densities and a physics-based model. With their minimal logistic requirements, new pRES systems, such as autonomous pRES, could be inexpensively deployed to monitor firn compaction more widely. Existing phase-sensitive radar data may contain compaction information even when surveys targeted other processes.

Ternary analytic porosity-reduction model of sandstone compaction trend and its significance in petroleum geology: A case study of tight sandstones in Permian Lower Shihezi Formation of Shilijiahan area, Ordos Basin, China

The tight sandstones in the Permian Lower Shihezi Formation of Shilijiahan area in the Ordos Basin was taken as study object in this research to quantitatively determine the effects of burial depth, burial time and compaction strength on porosity during densification of reservoir. Firstly, sandstone compaction profiles were analyzed in detail. Secondly, the theoretical study was performed based on visco-elasto-plastic stress–strain model. Thirdly, multiple regression and iterative algorithm were used respectively to ascertain the variation trends of Young's modulus and equivalent viscosity coefficient with burial depth and burial time. Accordingly, the ternary analytic porosity-reduction model of sandstone compaction trend was established. Eventually, the reasonability of improved model was tested by comparing with thin-section statistics under microscope and the models in common use. The study shows that the new model can divide the porosity reduction into three parts, namely, elastic porosity loss, visco-plastic porosity loss and porosity loss from cementation. And the results calculated by the new model of litharenite in He 2 Member are close to the average value from the thin-section statistics on Houseknecht chart, which approximately reveals the relative magnitudes of compaction and cementation in the normal evolution trend of sandstone porosity. Furthermore, the model can more exactly depict the compaction trend of sandstone affected little by dissolution than previous compaction models, and evaluate sandstone compaction degree and its contribution to reservoir densification during different burial and uplift processes.

Effect of Self-Microemulsifying Lipid Formulations on the Dissolution and Compaction Profiles of Tablets Containing Theophylline; A BCS Class I Compound

There is growing interest amongst formulation scientists to use self-emulsifying lipid technology as an approach to improve dissolution and hence absorption of poorly-water soluble drugs. Nonetheless, lipid based formulations requires that oil content be encapsulated in soft gelatin capsules which might exhibit some disadvantages. To overcome these limitations, solid self-micro-emulsifying drug delivery system (S-SMEDDS) is introduced as an alternative approach. The preferred dosage form for BCS class I compounds is tablets yet, some drugs which belong to this category might suffer from enzymatic degradation and gut wall efflux. The effect of converting liquid SMEDDS into compressed tablets containing a BCS class 1 compound is investigated. A SMEDDS oil formulation representing type III A lipid class was converted into S-SMEDDS using solid carrier adsorption method and compressed into tablets containing theophylline. The effect of oil loading factor on compressibility, disintegration and dissolution kinetics of theophylline from various tablet formulation was investigated. Increasing oil content in the compressed tablets ensued in progressive decrease in the hardness of tablets. Analysis of the dissolution kinetic data for tested theophylline preparations shows that it follows first-order or Higuchi kinetics. Fast dissolving tablet formulations were obtained at including an optimum oil concentration of 5% w/w.

Regularised Manova for High‐Dimensional Data

SummaryThe traditional and readily available multivariate analysis of variance (MANOVA) tests such as Wilks' Lambda and the Pillai–Bartlett trace start to suffer from low power as the number of variables approaches the sample size. Moreover, when the number of variables exceeds the number of available observations, these statistics are not available for use. Ridge regularisation of the covariance matrix has been proposed to allow the use of MANOVA in high‐dimensional situations and to increase its power when the sample size approaches the number of variables. In this paper two forms of ridge regression are compared to each other and to a novel approach based on lasso regularisation, as well as to more traditional approaches based on principal components and the Moore‐Penrose generalised inverse. The performance of the different methods is explored via an extensive simulation study. All the regularised methods perform well; the best method varies across the different scenarios, with margins of victory being relatively modest. We examine a data set of soil compaction profiles at various positions relative to a ridgetop, and illustrate how our results can be used to inform the selection of a regularisation method.

Flavored Self Microemulsifying Lipid Formulations for Masking the Organoleptic Taste of Pharmaceutical Actives

Effect of Self-Microemulsifying Lipid Formulations on the Dissolution and Compaction Profiles of Tablets Containing Theophylline; A BCS Class I CompoundNaser M.Y. Hasan, Mohammad A. Khaleel, Abdullah S. Altwairqi, Abdulmajeed G. Alqurashi, Abduallah H. Altwairqi

Comparison of drug release and mechanical properties of tramadol-hydrochloride matrix tablets prepared with selected hydrophilic polymers

This study investigates using of high molecular weight hydrophilic polymers, hypromellose and hydroxypropylcellulose, for the preparation of sustained release matrix tablets containing high dose, highly soluble drug, tramadol HCl. Proportion of polymer, type of insoluble filler, proportion of tramadol HCl, amount of drug in the tablet and compression pressure were recognized as critical formulation and process parameters and their influence on drug release and tablet mechanical properties was evaluated. Tensile strength was used as indicator of mechanical properties of the tablets. Experiments were performed with utilization of compaction simulator as a device which simulates compaction profiles of large scale rotary tablet presses. In formulations with both polymers proportion of tramadol HCl was the most critical formulation parameter wherein increasing of the tramadol HCl proportion increased its release rate in early stages of drug release. Regarding the tablet mechanical characteristics, the influence of the filler type has the most pronounced effect in formulations with both polymers. Higher tensile strengths were obtained with Avicel PH 102 as filler in formulations with both HPMC and HPC.

Predicting Tablet Strength from the Wet Granulation Conditions via the Unified Compaction Curve

Tablets make up approximately one third of all drug dosage forms which makes tablet manufacture a common process in the pharmaceutical industry. The unified compaction curve [1] is a model developed initially to look at the impact of the roller compaction conditions on the tablet strength. The tensile strength of the tablets made from formulations containing at least 50% microcrystalline cellulose produced at roller compaction pressures were measured and the profiles were collapsed into a single master “unified compaction curve” (UCC). This allowed for the tablet strength to be predicted from the roller compaction condition and formulations and target the required tablet strength criterion set by standards or specifications [1].The unified compaction curve was applied to investigate the effects of the wet granulation conditions in a 5L Key granulator on the tablet tensile strength. The study was based on a placebo formulation comprising of 50wt% microcrystalline cellulose, 50wt% lactose and a 5w/v% PVP (K90) binder solution. The effects of the liquid level (20-50wt%), wet massing time (0-10minutes), binder flow rate (130g/min and 280g/min) and impeller speed (150, 285 and 600rpm) on the tablet strength were explored. Scale-down experiments to a 1L mixer bowl were also conducted. Tablets were produced on a single station carver press with controlled force.A series of compaction profiles were created to represent the relationship between the tablet tensile strength, compaction pressure and the granulation condition. By fitting the unified compaction curve model to the data using a shifting intercept approach, the profiles exploring each granulation condition collapsed onto a single master curve which predicts the tablet strength as a function of the liquid level, wet massing time or the binder flow rate. Increasing the liquid level and/or wet massing time caused a reduction in the tablet hardness when compressed at the same compaction force, and the reduction is postulated to be proportional to the effective compaction forces experienced during granulation, PWGC. The PWGC data further collapses onto a single master curve which is solely a function of the total number of impeller revolutions. Further characterization of the granules produced at these conditions showed that the UCC intercept parameter, PWGC was inversely proportional to the granule porosity, linking the granule microstructure directly and quantitatively to the tablet strength during compaction. This is a significant finding that will allow formulators to optimize tablet hardness via a simple adjustment to the granulation conditions.

Primary welding and crystallisation textures preserved in the intra-caldera ignimbrites of the Permian Ora Formation, northern Italy: implications for deposit thermal state and cooling history

Exceptional exposure through a Permian intra-caldera ignimbrite fill within the 42 × 40 km Ora caldera (>1,290 km3 erupted volume) provides an opportunity to study welding textures in a thick intra-caldera ignimbrite succession. The ignimbrite succession records primary dense welding, a simple cooling unit structure, common crystallisation zones, and remarkably preserves fresh to slightly hydrated glass in local vitrophyre zones. Evidence for primary syn- and post-emplacement welding consists of (a) viscously deformed and sintered juvenile glass and relict shard textures; (b) complete deposit welding; (c) subtle internal welding intensity variations; (d) vitrophyre preserved locally at the base of the ignimbrite succession; (e) persistent fiamme juvenile clast shapes throughout the succession at the macroscopic and microscopic scales, defining a moderate to well-developed eutaxitic texture; (f) common undulating juvenile clast (pumice) margins and feathery terminations; (g) a general loss of deposit porosity; and (h) perlitic fracturing. A low collapsing or fountaining explosive eruption column model is proposed to have facilitated the ubiquitous welding of the deposit, which in turn helped preserve original textures. The ignimbrite succession preserves no evidence of a time break through the sequence and columnar joints cross-gradational ignimbrite lithofacies boundaries, so the ignimbrite is interpreted to represent a simple cooling unit. Aspect ratio and anisotropy of magnetic susceptibility (AMS) analyses through stratigraphic sections within the thick intra-caldera succession and at the caldera margin reveal variable welding compaction and strain profiles. Significantly, these data show that welding degree/intensity may vary in an apparently simple cooling unit because of variations in eruption process recorded in differing lithofacies. These data imply complex eruption, emplacement, and cooling processes. Three main crystallisation textural zones are identified in the ignimbrite succession: localised vitrophyre zones, widespread microcrystalline to sparsely spherulitic pseudomorphed vitriclastic textural zones, and thick granophyric zones. These zones record a typical spectrum from rapid to prolonged cooling. The non-uniform crystallisation patterns reflect variations in deposit thickness, the relative position of deposits within the larger ignimbrite succession, the type of substrate material, and the degree of confinement in the intra-caldera setting. We support previous work suggesting that traditional welding classifications (e.g. Smith, US Geological Survey Professional Paper 354-F 1960b) are most appropriate for use within altered and/or ancient ignimbrite successions.

Development and evaluation of Methocel K15M based Theophylline floating tablets

Effect of Self-Microemulsifying Lipid Formulations on the Dissolution and Compaction Profiles of Tablets Containing Theophylline; A BCS Class I CompoundNaser M.Y. Hasan, Mohammad A. Khaleel, Abdullah S. Altwairqi, Abdulmajeed G. Alqurashi, Abduallah H. Altwairqi

Understanding and optimizing the dual excipient functionality of sodium lauryl sulfate in tablet formulation of poorly water soluble drug: wetting and lubrication

Purpose: To evaluate and optimize sodium lauryl sulfate (SLS) and magnesium stearate (Mg.St) levels, with respect to dissolution and compaction, in a high dose, poorly soluble drug tablet formulation.Methods: A model poorly soluble drug was formulated using high shear aqueous granulation. A D-optimal design was used to evaluate and model the effect of granulation conditions, size of milling screen, SLS and Mg.St levels on tablet compaction and ejection. The compaction profiles were generated using a Presster© compaction simulator. Dissolution of the kernels was performed using a USP dissolution apparatus II and intrinsic dissolution was determined using a stationary disk system.Results: Unlike kernels dissolution which failed to discriminate between tablets prepared with various SLS contents, the intrinsic dissolution rate showed that a SLS level of 0.57% was sufficient to achieve the required release profile while having minimal effect on compaction. The formulation factors that affect tablet compaction and ejection were identified and satisfactorily modeled. The design space of best factor setting to achieve optimal compaction and ejection properties was successfully constructed by RSM analysis.Conclusions: A systematic study design helped identify the critical factors and provided means to optimize the functionality of key excipient to design robust drug product.

Compaction profiles of ash-flow tuffs: Modeling versus reality

Density profiles of 4 ash-flow deposits in Oregon and Idaho are simulated using the model of Riehle et al. (1995) to calculate heat flow, degassing, and compaction. The deposits are all < 45 m thick and most have well defined density reversals and lack substantial alteration or vapor-phase deposition. Model results are made to closely match the measured profiles of 3 simpler deposits by making the assumptions that density reversals represent cooling breaks between ash flows or that subtle density inflections at the base of the profiles are cooler surge deposits. The first assumption is supported by a fossil fumarole pipe truncated at a density inflection, and the second by foreset bedding at the base of the deposit. Deposit temperatures within each unit of thermally stratified deposits are assumed to be homogeneous. The Rattlesnake Tuff—a more complex ignimbrite sheet—was sampled at 3 distal sites near to one another, a medial site, and 4 proximal sites. Model results of distal profiles are similar despite more than twofold variation in thickness and comprise 3 early deposits having emplacement temperatures of 724–732 °C, followed by two hotter deposits (785–790 °C), and a cooler capping deposit of about 735 °C. One distal site has an inferred surge deposit at its base. Density reversals simulated as cooling intervals all range from 3 to 10 days. Correlated cooling intervals agree to within a factor of two, however, the duration of a cooling interval cannot be precisely hindcast owing to potential complications by rainfall or accumulation of chilled airfall ash. Thus, the seemingly wide range of model results for the cooling intervals is perhaps not surprising. Proximal profiles have more density reversals implying more deposits than the distal profiles. They also have greater overall compaction and consequential loss of detail in the density profiles. Some earlier deposits have model temperatures of 736–757 °C and may correlate with the lower distal deposits; at one site these are overlain by two hotter deposits (790–796 °C) and a cooler capping deposit (745 °C) that are almost surely correlatives of the upper distal deposits. Some sites have additional, early hotter deposits and one site has an uppermost deposit that is the coolest of all model deposits. Thus a picture emerges of thermally stratified, near-source flows during early eruptive activity and more far-travelled flows during later eruptions. Shards analyzed by Streck and Grunder (1997) show a compositional range and corresponding magma temperatures of 795–880 °C, which is permissive of thermally layered deposits and implies cooling during fallback and travel of 50–100 °C. Rare textural evidence for internal flow boundaries, as well as our consistent model results among multiple sites despite variation in deposit thickness, support the assumption that density reversals represent partial cooling breaks. If so, then modeling of density profiles can provide important evidence for how large ignimbrites are constructed. Sheridan and Wang (2004) also report stratigraphically consistent results by modeling density reversals in distal Bishop Tuff as cooling breaks. Our results contrast with those of Wilson and Hildreth (2003), who concluded that density reversals in the proximal Bishop Tuff do not represent cooling breaks but instead are evidence for thermally heterogeneous deposits. It may be that the proximal Bishop Tuff is not amenable to modeling due to its great thickness (100–200 m) and deposition on steeply dipping, rugged terrain, factors which would likely cause turbulent flow, obscure subtle stratigraphic details of flow boundaries, and complicate resulting compaction zonation.

Mechanistic investigation on pressure dependency of Heckel parameter

This work proposed to study the influence of varying compaction pressure on the plastic energy, elasticity (Young's modulus), particle yield strength, strain hardening, and applied pressures on derived Heckel parameter using material with different densification and deformation mechanisms: ibuprofen (IBN), paracetamol (PCM) (elastic behavior), methyl cellulose (Me-Cel), microcrystalline cellulose (MCC), sodium chloride (NaCl) (plastic behavior), and dicalcium phosphate (DCP) (brittle fracture). Force–displacement data were captured during in-die compaction for all materials having different deformation behavior. The apparent mean yield pressure (Py), plastic energy, Young's moduli, strain hardening parameter and rate of increase in Py were calculated from force–displacement compaction profiles obtained across a pressure range of 65–260 MPa. Materials under confined compression loading showed pressure dependent biphasic behavior in Py upon increasing pressure from 65 MPa to 260 MPa. IBN and PCM showed pressure dependency due to simultaneous elasticity and strain hardening upon increasing applied pressure. Me-Cel, MCC, and NaCl showed lower pressure dependency while DCP showed higher change in Py upon increasing pressure as a result of higher yield strength of DCP particles. Apparent mean yield pressure from Heckel analysis was significantly affected by the applied pressure, viscoelastic behavior, particle yield strength, and strain hardening. The simultaneously occurring events of elastic deformation and strain hardening give a false increase in Py at higher applied pressures.

Progress in tire rating based on soil compaction potential

The general trend in soil protection is to reduce the detrimental soil compaction by loaded wheels of power and transport equipment. This paper reports on the progress in research of soil compaction risk assessment by means of Compaction Capacity (CC) tire rating originally introduced as compaction number (CN) rating [Grečenko A. Tire load rating to reduce soil compaction. J Terramech 2003;40:97–115]. The CC rating evaluates soil dry density along a vertical column 20–50 cm below the ground surface. The unique feature of the CC approach is that it converts laboratory compaction measurements directly to soil compaction profiles under evaluated tires without touching the stresses in the ground. The laboratory soil compaction is done with round pressure plate and similarly the tire contact area is represented by a virtual plate loaded by the same mean contact pressure. This paper describes laboratory testing procedures with fundamentals of data conversion and gives examples of CC rating application.

Comparison of vibrocompaction methods by numerical simulations

AbstractSoils can be best compacted by repeated shearing. The strain amplitude plays an important role for the maximum compaction that can be reached. Experimental evidence emphasizes a vital impact of simultaneous multidirectional shear loading on the rate and magnitude of soil compaction. Two different vibrocompaction methods were analysed by the numerical simulations in the light of these findings. In an elastic finite element (FE) analysis, strain paths were determined. A strain amplitude‐dependent stiffness at small strains was introduced by multiple runs of the FE calculation to reach an appropriate stiffness for particular distances from the vibrator. Subsequently, the obtained strain paths were used to control single element simulations using hypoplasticity with intergranular strains. The calculated compaction profiles show three zones known from practical evidence: a limited compaction close to the vibrator, a zone of maximum compaction and a non‐densified zone remote from the vibrator. The deep vibrator produces a faster compaction than the top vibrator, especially in the more distant zone. The more efficient work of the deep vibrator can be attributed to a more general multidirectional shearing. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Ascent and compaction of gas rich magma and the effects of hysteretic permeability

Gas escape from volcanic conduits plays an important role in eruption dynamics and eruptive cycles. Gas volume fraction influences magma permeability, but permeability is also likely to depend on prior gas volume fraction through a hysteretic relationship. We study how this permeability behavior affects vertical segregation of gas and compaction of ascending magma. Ascent of vesiculated magma leads to compaction profiles in which gas volume fraction and permeability decrease substantially with height. Classical and hysteretic permeability functions can, however, lead to very different permeability profiles. If the magma ascent velocity is small enough, the hysteretic behavior introduces a step in the permeability profile such that a low-permeability plug sits on top of a gas-rich magma and acts as a trap for gases rising from depth. Time-dependent solutions take the form of porosity waves, although in the hysteretic case, gas is more concentrated into a thinner wave for a given amount of gas, leading to more powerful eruptions. This model shows that a highly vesicular magma can change into a degassed magma over a short distance, which has implications for phenomena such as seismicity, ground motion and eruptive behavior.

Polyols as filler-binders for disintegrating tablets prepared by direct compaction

Background: Although polyols are frequently used as tablet excipients in lozenges, chewing tablets, and orodisperse tablets, special directly compressible (DC) forms are recommended as filler-binder in common disintegrating tablets. Aim: In this article, DC types of isomalt, lactitol, mannitol, sorbitol and xylitol are evaluated. Method: Tablets of both lubricated and unlubricated DC polyols and theophylline tablets were compressed at different forces using a compaction simulator or a motorized hydraulic press. Disintegration times (without disks) and dissolution rate were measured according to Ph.Eur. Results: Compaction profiles show that the DC forms of isomalt, mannitol and sorbitol have sufficient compactibility and a low lubricant sensitivity. The crushing strengths of tablets, prepared from DC lactitol and xylitol, are too low for practical use. Because of their reduced hygroscopicity and smaller capping tendency as compared with DC sorbitol, DC types of isomalt and mannitol seem to be the most convenient filler-binders. Because of their high water solubility, tablets prepared from polyols erode rather than disintegrate. Tablet formulations with theophylline as a test drug and DC isomalt or DC mannitol as filler-binder show that both products have their own limitations: DC mannitol gives more adhesion problems than DC isomalt. On the other hand, the disintegration time and drug dissolution rate for tablets containing DC mannitol is faster than for tablets containing DC isomalt. Conclusions: Of the DC polyols investigated, both DC isomalt and DC mannitol are the most suitable filler-binders for disintegrating tablets, prepared by direct compaction.

Development of a High-Velocity Compaction process for polymer powders

The High-Velocity Compaction (HVC) process for powder polymers has been studied, with a focus on the compactibility characteristics and surface morphology of the compacted materials, with and without relaxation assists, by increasing compacting quantity and direction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain pull-out phenomena during the decompacting stage. Polyamide-11 powders with different particle size distributions have been compacted with the application of different compaction profiles, e.g. different energies and velocities. Scanning electron microscopy (SEM) and image computer board camera (IC-PCI Imaging Technology) have been used to the study the morphological characteristics, the limit of plastic deformation and particle bonding by plastic flow at contact points, and pull-out phenomena. The relative green density is influenced more by the pre-compacting (primary compaction step) than by the post-compacting (secondary compaction step). The pressure and density distribution differences between the upper and lower surface are not uniform. Projectile supports or ‘relaxation assists’ are presented as a new technique to reduce pull-out phenomenon. Experimental results for different compaction profiles are presented showing the effect of varying the opposite velocity during the decompacting stage, and how to improve the homogeneous densification between the upper and lower surface and the evenness of the upper surface of the compacted powder bed by using relaxation assists.

Cooling and welding history of the Bishop Tuff in Adobe Valley and Chidago Canyon, California

A numerical model for cooling and welding of ash-flow tuffs was developed to obtain a quantitative understanding of the welding compaction that occurs during the cooling of ash-flow sheets and to evaluate the relative effects of emplacement temperature, thickness, and emplacement histories on compaction zonation (density profiles) of large ash-flow sheets. This model includes a set of two-phase, compressible Navier–Stokes equations for the transport of mass, momentum, and energy for a variable density volatile outfluxing through a porous media (ash-flow tuff). With this model we calculated theoretical compaction profiles (density vs. elevation) to match actual data measured in sections of Bishop Tuff. Compaction profiles from the Adobe basin indicate that there were 3 periods of non-deposition (5, 10, and 40 days) separating 4 distinct rapidly emplaced packets (REP) of pyroclastic flow deposition. In contrast, the 3 periods of quiescence (400, 20, and 800 days) between the 4 REPs in Chidago Canyon were considerably longer. These data constrain models of eruption for the Bishop Tuff by implying an eruption cycle that lasted longer than 3 years. The average calculated deposition temperatures for all 4 REPs in the Adobe basin are fairly uniform at 667±33 °C. In Chidago Canyon two of the REPs had a higher deposition temperature (∼660 °C) than the other two (534 °C).