The project includes the design and construction of an approximately 17.5-mile long interceptor pipeline, as well as improvements to portions of the existing Sand Creek Interceptor System.  The inside diameter of the proposed interceptor pipeline will range in size from 8-inches at its upstream end near Denver International Airport to 66-inches at its downstream end near MWRD’s South Platte Interceptor.  The pipeline will be relatively deep, with invert depths in excess of 4 feet.  For this reason, construction dewatering, trench stability, and bedrock excavation are key geotechnical considerations for the project. 

Shannon & Wilson’s scope of services includes multiple phases of field explorations consisting of nearly 200 geotechnical borings, groundwater monitoring wells, and test pits at the proposed tunnel crossings.  We are also performing laboratory testing on soil and rock samples collected during the field exploration program for both index and engineering properties.  In addition, we will perform two aquifer pumping tests in Winter 2019 to evaluate hydraulic conductivity in support of groundwater modeling and dewatering design.  

Shannon & Wilson has completed a preliminary Geotechnical Data Report (GDR) summarizing the results of our field and laboratory studies, and is updating this report throughout the design process until field investigations are completed.  Shannon & Wilson is also performing a wide variety of geotechnical analyses in support of project design, and will present our recommendations in a Geotechnical Interpretative Report (GIR) which will be submitted at several key milestones.

The GIR will address the following design considerations, many of which are anticipated as part of this on-call services contract with utilities:

• Soil and rock parameters, groundwater and geologic hazards, corrosion potential, and seismic hazards and design criteria
• Construction dewatering
• Excavation and trench support, settlement, uplift, site grading and earthwork, pipe bedding and backfill and compaction
• Design and construction considerations for both foundations, including spread footings and mat foundations
• Lateral earth pressures and resistance to lateral loads