Deep Soil Mixing (DSM) Ground Improvement Design: Port of Vancouver USA Terminal 1 Dock Improvements

Abstract: The Port of Vancouver USA is in the process of replacing the original 1920’s dock structure at Terminal 1 with a new dock structure which will eventually support a new public Marketplace Building and provide public access to the Columbia River. The next phase of the project will include the installation of a combi-wall bulkhead to replace an existing concrete bulkhead wall, the installation of upland ground improvements to reduce liquefaction-induced lateral spreading deformations and kinematic loading on the future dock piles, and grading the over-steepened slope on the river side of the bulkhead.
In the upland area, subsurface conditions at the site typically consist of dredge sand fill underlain by alluvial silt and sand to a depth of about 40 to 50 feet. These materials, when encountered below the river level, are susceptible to liquefaction during the design level earthquake. One of the explorations for the project encountered a 25-foot thick layer of very soft, high-plastic, organic silt below the alluvial sands and silts and over the underlying gravel. To better characterize the extent of the clayey silt, an offshore geophysical survey and additional upland explorations were completed. The offshore geophysical study identified a paleochannel in the footprint of the proposed dock structure.
Geotechnical engineering analysis indicated the potential for large lateral spreading deformations necessitating a deep soil mixing (DSM) ground improvement buttress. As a result of environmental permitting restrictions and property constraints, the DSM buttress width was limited to a 30-foot wide zone behind the proposed bulkhead. To estimate the required composite shear strength of the DSM buttress, numerical modeling calibrated to the site-specific cyclic direct simple shear laboratory data was used to better evaluate the seismic performance of the narrow and tall buttress and wall system. The numerical model was subjected to representative ground motions with a series of parametric studies conducted on ground improvement configurations and the variability in subsurface conditions along the length of the wall including the presence of the paleochannel.
Historical photographs and as-built records for the project site were reviewed. A historical dock structure associated with World War I shipbuilding was formerly located at the site prior to construction of the 1920’s dock. Remnant timber piling from the historical dock structure, which are located greater than 20 feet below the ground surface and below the average water level of the Columbia River are present within the zone of ground improvement. To 111allow installation of the DSM ground improvement buttress, the project specifications were selected to require that all of the areas that will receive ground improvement be predrilled to remove potential timber pile obstructions. Construction of the bulkhead wall and ground improvement buttress is planned for late-2024. This paper will provide additional discussion regarding the unique subsurface conditions at the site, the ground improvement design completed using numerical modeling, and the selection of predrilling to mitigate against potential timber pile obstruction risk within the limited project footprint.

How does this project / topic contribute to the advancement of the industry and profession?: This project offers valuable insights into the design and analysis of seismic mitigation strategies for port and waterfront structures, particularly those susceptible to liquefaction-induced lateral spreading during seismic events. The findings presented herein are beneficial for both project owners and designers, offering practical solutions and addressing common challenges encountered in ground improvement construction within industrial waterfronts.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: Yes, the subsurface investigation included a marine geophysical survey in the Columbia River where the boring data showed inconsistencies in the layering profile. Cyclic direct-simple shear testing was completed on the highly-plastic, organic silt in order to estimate the seismic susceptibility and strength of these materials. The results were used in numerical modeling to develop multiple profiles which enabled the project team to investigate the effects of variation in soil profile on the ground improvement performance. Predrilling of 100% of the ground improvement zone was included in the specifications to limit the risk of construction change orders.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: This project presented several notable challenges. The geophysical survey highlighted significant variations in gravel depths along the wall, rendering a simple model inadequate to capture this variability. In addition, the ground improvement layout was constrained to a narrow width along the wall which posed the design and construction to considerable challenges. Furthermore, the presence of existing timber piles in the ground further complicated the ground improvement installation process. To address these complexities, we employed sophisticated constitutive models in our numerical simulations which required robust calibration to properly simulate the soil and structure behavior.

Who is the target audience for this paper?: The observations from the numerical modeling results in this paper may serve as practical lessons for designers of ground improvement buttresses in port and waterfront structures with significant historical site use.