2007/11/21 Council Agenda Packet

I? • 5 Sievc Analysis Tests (ASTiVI-D422) • 2 H ydrometer Tests (.'ASTM -D422) • 1 Soil Organic Content -fest (ASTM -D2974) • 3 Atterberg Limits (AS INel-0431 S) • 3 Consolidation Tests (AS- IVI-D243>) The sieve, hydrometer and Atterberg results will be used for obtaining basic soil design parameters needed for design related to bearing capacity, liquefaction, soil loads and stability. The soil organic content and consolidation results will be used for estimating the settlement of the existing pipelines and soils under the proposed development loads. Task 70200: Pipeline Impact Evaluation: The pipeline impact evaluation swill focus on estimating the maxinurm allowable till height that will not impact the existing pipelines based oil the limited known subsurface geotechnical and ground water conditions, pipeline properties and assumed till properties. Two criteria will be used to estimate the maximum allowable till height over the top of existing pipelines. 0.01 -inch. D -load based on ASTM Designation C76-05 Existinu capacity of the pile supports of the 72 -inch pipeline A 0.01 -inch D -load is a three -edge pipe bearing test load that will generate a maxii-nu[n 0.01 - inch -wide crack around a concrete pipe. ASTM considers a 0.01 -inch -wide crack is the maximum allowable under normal pipe service conditions. By comparing estimated D -loads at different fill heights with the ASTM allowable D -load, a maximum allowable till height is determined. There is no geotech-nical information north of where the two borings were drilled, which is an area more than 2,000 feet long_ It is too far to extrapolate the geotechnical information from the south end to the north end of the development area. Therefore, additional geotechnical investigations will be required along the central and northern parts of the development area. "Task 70300: Pipeline Protection Options: The pipeline impact evaluation will estimate till heights that will not impact the pipelines. It higher tills are planned, additional analyses will be needed to quantity the impacts to the pipelines and develop design concepts to protect the pipelines. If necessary, URS will develop conceptual - level options and cost estimates to protect the pipelines from the higher fill loads. Using the known soil conditions and pipe details, URS compared the feasibility of supporting tills over the pipelines with holding up the pipeline themselves. It was found to be more technically feasible and cost effective to support the fill over the pipelines with a combined structure for two parallel pipelines. URS will consider the following conceptual -level pipeline protection options: Shalloxv looting supported cover that involves constructin« a continuous footing atom, both edges of the pipeline corridor and spanning a structure between the footings. Deep pile supported cover that involves driving piles along both edges of the pipeline corridor and spanning a structure between the piles. Lightweight fill that involves balancing the removal of overlying soil with the placement of lighter material to produce an acceptable fill load. 104 URS Page 9 of 10