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V <br />4 <br />Task 60100: Geotechnical lnvestication: <br />This geotechnical imcstigatiinr task originally planned to include explorations by drilling and test <br />pits. I lowcver. because of the difficulties in coordinatinga drill rig and BNSF flagg.er on the same <br />da}. and in order to not delay the 13NSI: construction schedule, the originally planned drilling <br />program was reduced in scope by eliminating the drilling. It was agreed to complete the design by <br />completing test pits and relying on geotecimical information from other nearby projects <br />(hc test pit explorations were completed in September 2007 by the City. Two test pits were <br />excavated by a track -mounted vacuum suction machine (Vector 2100 Series). The purpose of this <br />work was to contirrn the pipeline location. pipeline and casing conditions, soil and ground water <br />conditions. and other underground structures that may be present. The City corrfintted the richt- <br />of"-\vay. checked for underground utilities, and marked the test pit locations on the :ground. <br />The first test pit was excavated on September 6. 2007 to a depth of approximately 13.5 feet at a <br />location that was believed to be near the southeast end of. the pipe casing. TWO 2 -inch fiber <br />optical lines were encountered at depths of about 4.5 feet, but the casing and pipeline were not <br />encountered. It was later determined by the City that test pit was about 20 feet south of the <br />pipeline_ Therefore, a second test pit was planned. <br />The second test pit was excavated on September 10, 2007 to a depth of approximately 7 feet on <br />the % est side of the existing track and close to the southeast end of the pipe casing. The 60 -inch <br />steel casing pipe was encountered. The ground water table was at about 2 feet deep arid the <br />distance from the ground surface to the top of the casing was about 6.3 feet. <br />Task 60200: Enyineerint! and Design: <br />The em-oncering analysis will include a geotechn►cal evaluation of data from previous nearby <br />projects, the test pit explorations, modeling of track and subsurface conditions. and structural <br />analysis of the pipeline support system and its foundations ro protect the pipeline. <br />A critical aspect ol'thc engineering analysis mill be to provide a design that will support Nle <br />pipeline jog, but will remain independent of the truck, yet be compatible ���ith the track design. It <br />is important that the pipeline and track be separately maintained without impacting each other. <br />The analysis will consider the use of various types and combinations of support structures that <br />could include: underpinning by battered pilings with the pipeline tied to the piles; soil compaction <br />densification under and around the pipeline; replacement of the underlying soils with granular <br />fill; and grouting of the underlying, soils. <br />Designs concepts and very conceptual -level cost estimates will be prepare([ for lite methods that <br />appear to be the most reasonable, constructible and reliable. URS, in collaboration with the City, <br />will select a method that is considered to be the most cost effective and teclvtically feasible. <br />As discussed above, URS will design the pipeline support without geotechnical drilling at the site, <br />and will assume the worst case of original native soils still being under the pipeline. [f different <br />site conditions such as replaced or improved soils or shallower or deeper soft soils are <br />encountered, change orders will be needed for construction, and maybe for design modifications_ <br />U RS <br />f'a-e 3 of 19 8 <br />1I <br />