GEOPHYSICAL SITE EXPLORATION THIRD LAKE WASHINGTON FLOATING BRIDGE

A GEOPHYSICAL SURVEY IS REPORTED WHICH EMPLOYED A COMBINATION OF SEVERAL SEISMIC EXPLORATION METHODS IN THE VICINITY OF THE PROPOSED ALIGNMENT FOR THE THRID LAKE WASHINGTON FLOATING BRIDGE. THE SURVEY AREA WAS A APPROXIMATELY 7,500 FEET LONG AND COVERED THAT SECTION OF THE LAKE LOCATED BETWEEN THE CITY OF SEATTLE AND MERCER ISLAND. THE FIELD INVESTIGATION UTILIZED 3 GEOPHYSICAL METHODS FOR DEFINING SUBSURFACE CONDITIONS: (1) VERTICAL VELOCITY MEASUREMENTS IN A DRILL HOLE PENETRATING SOFT LAKE SEDIMENTS TO A DEPTH OF 50 FEET BELOW LAKE BOTTOM USING MULTI-CHANNEL SEISMOGRAPH WITH AN ARRAY OF HYDROPHONES SPACED 20 FEET APART, (2) THE COMPLETION OF A SEISMIC REFLECTION SURVEY INCLUDING 224,770 LINEAL FEET OF HIGH ENERGY SONAR SURVEY AND 193,770 LINEAL FEET OF PULSER SERVEY, AND (3) RECORDING APPROXIMATELY 10,742 LINEAL FEET OF REFRACTION SEISMIC TRAVERSE BY CONVENTIONAL OVERWATER METHODS UTILIZING HIGH EXPLOSIVES AS AN ENERGY SOURCE. THE GEOPHYSICAL SURVEY WAS SUCCESSFUL IN DEFINING THE LOCATION AND THICKNESS OF SOFT SEDIMENTS AND OUTLINING THE ORIGINAL VALLEY. IT WAS DETERMINED THAT DETAILED KNOWLEDGE OF ACTUAL SITE CONDITIONS WOULD HAVE BEEN SIGNIFICANTLY IMPROVED IF THE LOCATION OF THE BORING INFORMATION COULD BE CHANGED ON THE BASIS OF INFORMATION PRODUCED BY SUBSEQUENT GEOPHYSICAL STUDY. THE GEOPHYSICAL STUDY SHOULD HAVE BEEN COMPLETED FIRST AND THE RESULTS USED TO SELECT THE DEPTH AND LOCATION OF TEST BORINGS.

Subject/Index Terms

Filing Info

  • Accession Number: 00229602
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Aug 15 2004 2:39AM