Quantifying Rock Strength from River Channel Morphology
Abstract
The technical objective of the proposed effort is to test the hypothesis that as a river flows over different rock types, changes in channel morphology can be quantitatively related to material properties. The proposed effort seeks to achieve the stated technical objective using a combined approach: (1) quantifying channel morphology and characteristics as it flows over different rock types, (2) quantifying the geotechnical properties of the rock types, and (3) performing a series of controlled laboratory experiments to quantify the susceptibility of the different rock types to abrasion and damage accumulation/fatigue. To achieve (1), remote and field surveys will be conducted to measure channel slope and width along streams that cross lithologic boundaries. Channel longitudinal profiles and slopes will be measured remotely using flow routing algorithms on a 10-m digital elevation model (DEM). In the field, exposed bedrock and sediments will be characterized to assess erosional processes and the potential influence of sediment cover at each site. Structure-from-motion photogrammetry will be used to develop fine-scale (1 m) three-dimensional surface representation. To achieve (2), each rock type will be analyzed in the field using indirect Brazilian tensile tests, and P-wave velocities will be measured both in the field on river beds and in the laboratory. Samples will be extracted using a 16-inch cut-off saw from both the stream bed and nearby outcrops. Slake durability tests will be performed to assess the durability of each rock unit. Field observations of fracture and joint spacing, width and orientation will be made. The data acquired by (2) will be compared those acquired by (1) as a first test of the study hypothesis. To achieve (3), the efficiency of grain-by-grain abrasion versus damage accumulation and microscopic failure will be distinguished using fatigue tests performed on a MTS810 machine with a Flex Test SE system that allows cyclical loading down to 1 Hz or a predetermined stress onto the prepared sample. Also, experiments will be performed using bedrock slabs in a large (2 m by 20 m, slopes up to 10%) flume to mimic natural abrasion and sediment cover effects. Sediment from sand-size to 30 mm will be fed from a system of hoppers upstream. Experiments will be performed using a raised-bed platform, and nine 15 cm x 15 cm bedrock slabs will be place along the flume centerline, spaced ~ 1 m apart. A series of six runs will be performed in which grain size or the total boundary shear stress is varied. Slabs will be weighed before and after each run. Finally, slabs will be dried and weighed. Data from (3) will be compared with those from (1) and (2) to test the research hypothesis.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 12, 2017
- Source ID
- W911NF1510380
Entities
People
- Brian J Yanites
Organizations
- Army Contracting Command
- United States Army
- University of Idaho