%0 Conference Proceedings %B Abstracts with Programs - Geological Society of America %D 1999 %T Factors influencing groundwater inflows in a newly constructed cross-strike tunnel, eastern Massachusetts; 3, Surface vs. subsurface fracture characteristics %A Stephen B Mabee %A Williams, Katherine W. %A Curry, Patrick J. %A Hardcastle, Kenneth C. %K #StaffPubs %K BEDROCK %K controls %K eastern Massachusetts %K factors %K fractures %K ground water %K Hydrogeology 21 %K massachusetts %K measurement %K movement %K New England %K outcrops %K spatial distribution %K tunnels %K United States %X 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. %B Abstracts with Programs - Geological Society of America %I Geological Society of America (GSA) : Boulder, CO, United States %C United States %V 31 %P 348 - 348 %8 1999/01/01/ %@ 00167592 %G eng %N 77 %! Abstracts with Programs - Geological Society of America %0 Conference Proceedings %B Abstracts with Programs - Geological Society of America %D 1999 %T Factors influencing groundwater inflows in a newly constructed cross-strike tunnel, eastern Massachusetts; 2, Fracture-supported coincident lineaments and subsurface structures %A Hardcastle, Kenneth C. %A Curry, Patrick J. %A Williams, Katherine W. %A Stephen B Mabee %K #StaffPubs %K BEDROCK %K controls %K eastern Massachusetts %K factors %K fractures %K ground water %K Hydrogeology 21 %K imagery %K lineaments %K massachusetts %K movement %K New England %K outcrops %K Structural geology 16 %K tectonics %K tunnels %K United States %X As part of the evaluation of the ability of lineaments to map subsurface structures, the coincident lineaments which intersect the tunnel (Curry et al., this volume), were evaluated to isolate those lineaments considered to be "fracture-supported". By definition, fracture-supported coincident lineaments are those which parallel nearby surface fracture sets, mapped faults, lithologic contacts, and/or primary ductile structures; features which may be influential to subsurface groundwater flow. Of the 37 coincident lineaments delineated on the three scales of imagery studied, approximately 70% are considered to be fracture-supported: 9 of the 13 on the 1:58,000 scale images, 10 of 14 on the 1:80,000, and 8 of 10 on the 1:250,000. However, the general lack of surface exposure precludes high confidence in the assignment of fracture-supported status to most lineaments. Large areas devoid of outcrops necessitated extrapolation of regional, surface fracture patterns (domains) to help define some fracture-supported coincident lineaments. There are two occurrences where fracture-supported coincident lineaments from all three scales overlap and are parallel. One occurrence successfully maps the zone of greatest fracture density and highest groundwater inflow (>560 l/min). The other occurrence maps an area of high fracture density and significant subsurface flow (95 l/min). In addition, one other high flow zone (>190 l/min) is mapped by a fracture-supported coincident lineament from the 1:80,000 scale imagery. However, many subsurface fractures and flow zones (<75 l/min) are not mapped by the coincident lineaments regardless of whether or not they are fracture-supported. When considering all fracture-supported coincident lineaments and parallel subsurface structures, the median flow (13,600 l/day) for the mapped structures is greater than the unmapped structures (6,800 liters/day). However, this difference is only significant at the 60% confidence level.Although the tunnel sections with the greatest fracture density and highest groundwater inflows are successfully mapped by fracture supported coincident lineaments, not all water-bearing zones are delineated. %B Abstracts with Programs - Geological Society of America %I Geological Society of America (GSA) : Boulder, CO, United States %C United States %V 31 %P 348 - 348 %8 1999/01/01/ %@ 00167592 %G eng %N 77 %! Abstracts with Programs - Geological Society of America