3800 RIVERFRONT BLVD Geotech Report 2023-05-04

July 3, 2019 HWA Project No. 2015-061-21 settlement. In addition to accommodating vertical differential settlements at this transition point, the flexible connection will also need to accommodate anticipated elongation associated with 30-inches of settlements. The magnitude of anticipated elongation at the sanitary sewer transition will be dependent on the length of the flexible connection system used. We recommend any flexible connection at this location be evaluated to verify that the joint meets elongation needs based on the joints laid length and the anticipated length after 30-inches of settlement. BSB Bentonite Sand Backfill (BSB) is a contractor manufactured mixture of sand and bentonite that can be placed in areas not accessible by compaction equipment and achieve an in-place permeability of less than l x 10^-5 cm/sec. BSB is generally used strategically to prevent gas migration along pipe bedding for utilities transitioning through LPSB, as trench damns, and around manhole/catch basins. The actual geometry and locations of BSB has been designed by Herrera. Like other gas barrier systems, BSB has a detailed acceptance and mix design procedure. This procedure includes the contractor supplying HWA with bulk samples of both the proposed sand and bentonite material. HWA takes these bulk samples and runs permeability tests on various mix ratios of the sand and bentonite. Based on the results of these tests, HWA recommends a mix design that will achieve the desired permeability of less than 1 x 10^-5 cm/sec. Once the mix design is provided to the contractor, they order the raw materials and develop a plan to generate the mix in the volumes required by the contract documents. This process is reviewed by the design team and generally involves mixing on site with a pug mill of bulk mixing within a constructed enclosure. Once the material is mixed, it must be protected from the elements to ensure that it does not take on excess moisture. The creation of BSB is time consuming and costly. Therefore, it should only be used where required to achieve the desired gas barrier. HWA has developed and provided a specification for BSB that is included in the project specification package. Utility Trench Backfill As described in our geotechnical report, the refuse materials are not suitable for reuse as trench backfill and the onsite existing fill soils are moisture sensitive and may be challenging to compact certain times of year. Therefore, imported trench backfill will be required to complete utility trench backfill. During the dry summer months, the use of onsite or imported Low Permeability Soil Barrier(LPS13) material as trench backfill may be appropriate. LPSB materials have a high fines content and are be moisture sensitive. Therefore, placement or working with LPSB during periods of wet weather will be very difficult if not impossible and is not recommended. Special care should be taken to maintain the moisture content of LPSB Riverfront Boulevard Addendum 2 2 HWA GeoSciences Inc.