An official website of the United States government
Gravel removal tests:Roof gravel motion initiation
destructive testing of gravel roof systems to measure the wind speed required to scour roof gravel from a flat roof with parapet.Data from this project includes pressure and shear stress measurements from the FIU WOW-EF on a square plan building.
more »
« less
- Award ID(s):
- 1760999
- PAR ID:
- 10502285
- Editor(s):
- Nigel Kaye
- Publisher / Repository:
- Designsafe-CI
- Date Published:
- Subject(s) / Keyword(s):
- gravel removal test conditions Photos of set up for removal tests Cobra probe data videos gravel removal tests Wwhr-Florida
- Format(s):
- Medium: X
- Location:
- Designsafe-CI
- Sponsoring Org:
- National Science Foundation
More Like this
-
The strength and stress-dilatancy of uniform sands has been studied extensively in geotechnical investigations, and practitioners can draw on a wealth of previously reported data for the estimation of their volumetric response. However, the suitability of accepted stress-dilatancy theory and empiricism has not been evaluated for well-graded gravelly soils. Axisymmetric, isotropically consolidated drained compression, and pure shear, plane strain quasi-K0 consolidated drained tests were performed on well-graded Kanaskat gravel using confining pressures ranging over three orders of magnitude to determine its stiffness, strength, and stress-dilatancy response. The plane strain stiffness, strength, and stress-dilatancy of Kanaskat gravel is observed from tests performed using a large cubical true-triaxial device with flexible bladders. The observed response is interpreted with a view of experimental boundary conditions and their impact on the volumetric response. The observed plane strain shear modulus and friction, and dilation angles of well-graded sandy gravel soils commonly used in practice are significantly higher than those measured in the triaxial compression stress path. Existing empirical and modified stress-dilatancy expressions proposed for low confining pressures underestimate the observed dilation response; however, another common empirical approach appears to adequately capture the dilatancy. The data reported herein should help practitioners estimate plane strain behavior of sandy gravel mixtures.more » « less
-
Gravel‐bed rivers that incise into bedrock are common worldwide. These systems have many similarities with other alluvial channels: they transport large amounts of sediment and adjust their forms in response to discharge and sediment supply. At the same time, the occurrence of bedrock incision implies behaviour that falls on a spectrum between fully detachment‐limited ‘bedrock channels’ and fully transport‐limited ‘alluvial channels’. Here, we present a mathematical model of river profile evolution that integrates bedrock erosion, gravel transport and the formation of channels whose hydraulic geometry is consistent with that of near‐threshold alluvial channels. We combine theory for five interrelated processes: bedload sediment transport in equilibrium gravel‐bed channels, channel width adjustment to flow and sediment characteristics, abrasion of bedrock by mobile sediment, plucking of bedrock and progressive loss of gravel‐sized sediment due to grain attrition. This model contributes to a growing class of models that seek to capture the dynamics of both bedrock incision and alluvial sediment transport. We demonstrate the model's ability to reproduce expected fluvial features such as inverse power law scaling between slope and area, and width and depth consistent with near‐threshold channel theory, and we discuss the role of sediment characteristics in influencing the mode of channel behaviour, erosional mechanism, channel steepness and profile concavity.more » « less
-
Abstract We calibrated an acoustic pipe microphone system to monitor bedload flux in a sandy, gravel‐bed ephemeral channel. Ours is a first attempt to test the limit of an acoustic surrogate bedload system in a channel with a high content of sand. Calibrations varied in quality; significant data subsetting was required to achieve R2values >0.75. Several data quality issues had to be addressed: (1) apparent pulses, which occur when a sensor records an impulse from sediment impacting the surrounding substrate rather than directly impacting the sensor, were frequent, especially at higher signal amplifications. (2) The impact sensors were frequently covered by gravel sheets. This prompted the development of a cover detection protocol that rejected part of the impact sensor record when at least one sensor was partially or fully covered. (3) Because of the lack of sensor sensitivity to impacts of sand‐sized particles, which was anticipated, and the considerable sand component of bedload in this channel, a grain size‐limited bedload flux was estimated. This was accomplished by sampling the bedload captured by slot samplers and evaluating the variation of grain size with increasing flow strength. This considerably improved the results when compared to attempts at estimating the flux of the entire distribution of grain sizes. This calibration is a successful first attempt, though the impact sensors required several site‐specific calibration steps. A universal set of equations using impact sensors to estimate bedload transport of fine‐gravel with a large content of sand remains elusive. Notwithstanding, our study demonstrates the utility of impact sensor data, producing relatively low root mean square errors that are independent of measurements of flow strength (i.e. discharge). These tools will be particularly useful in settings that would benefit from new methodologies for estimating bedload transport in sand‐rich gravel‐bed rivers, such as the American desert Southwest.more » « less
