UMass Sesquicentennial

Factors influencing groundwater inflows in a newly constructed cross-strike tunnel, eastern Massachusetts; 3, Surface vs. subsurface fracture characteristics

TitleFactors influencing groundwater inflows in a newly constructed cross-strike tunnel, eastern Massachusetts; 3, Surface vs. subsurface fracture characteristics
Publication TypeConference Proceedings
Year of Publication1999
AuthorsMabee, SB, Williams, KW, Curry, PJ, Hardcastle, KC
Conference NameAbstracts with Programs - Geological Society of America
Volume31
Pagination348 - 348
Date Published1999/01/01/
PublisherGeological Society of America (GSA) : Boulder, CO, United States
Conference LocationUnited States
ISBN Number00167592
Keywords#StaffPubs, BEDROCK, controls, eastern Massachusetts, factors, fractures, ground water, Hydrogeology 21, massachusetts, measurement, movement, New England, outcrops, spatial distribution, tunnels, United States
Abstract

Major fracture sets (dip >45 degrees ), their geographic distributions (domains), and their characteristics (spacing, trace length, and planarity) were measured in surface outcrops and in a 9 km section of the tunnel (Curry et al., this volume) to determine how well fracture data collected at widely-spaced surface exposures can be extrapolated to a depth of 70 to 90 meters. For the surface fracture data set, fracture sets and domains were determined from 1513 measurements collected at 21 outcrops located within 3 km of the trace of the tunnel. Spacing, trace length, and planarity were determined from scanline measurements (n = 899). For the tunnel data set, 413 fracture measurements were made to determine major sets and domains and a smaller subset (n = 156) was used to estimate fracture characteristics.Five fracture sets (14, 38, 86, 117, and 171) were identified in the outcrops and seven sets (13, 29, 41, 62, 132, 159, and 175) in the tunnel. The 14 and 171 sets correspond well with the 13 and 175 sets in the tunnel. The 38 set observed at the surface includes parts of the 29 and 41 sets in the tunnel. The 86 set does occur in the tunnel but is undersampled because it is aligned with the tunnel. The 62 and 159 sets occur in the tunnel but are not seen at the surface. Although large areas are devoid of outcrops, comparison of surface and subsurface fracture domains indicates that only the 14 and 171 sets show a reasonable overlap with the 13 and 175 domains in the tunnel. These latter sets are the fractures generating most of the groundwater inflow into the tunnel. Median fracture spacing and trace lengths for the 13 and 175 sets in the tunnel are significantly wider and longer than the corresponding 14 and 171 sets at the surface. Fracture planarities showed no significant differences between any of the surface and subsurface fracture sets.

Short TitleAbstracts with Programs - Geological Society of America
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