Laserfiche WebLink
January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 23 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />• Requires installation of a temporary grout mix plant. <br />Deep soil mixing’s advantages include the ability to improve the shear strength of all soil types <br />(including upper wood layers encountered in HWA’s explorations), reduced spoil generation <br />when compared to jet grouting, cost effectiveness when compared to jet grouting (dependent on <br />type and quantity of potential obstructions), and lack of vibrations during installation (i.e., <br />minimal disturbance to adjacent structures). In HWA’s opinion, deep soil mixing columns is a <br />feasible mitigation option for this project. <br />Jet Grout Columns: Jet grouting consists of injecting grout (water/sand/cement mix), which <br />acts as a radial hydraulic/pneumatic jet when pumped into the soil under pressure via nozzle. The <br />grout forms a zone that mixes with and solidifies the surrounding soil, thereby mitigating the <br />liquefaction potential in that soil strata. Jet grouting is a bottom-up procedure, where the jet <br />grouting nozzle is first lowered within a predrilled 6-inch-diameter borehole to the termination <br />depth of the column. Then, high-pressure grout is injected within the liquifiable soils, resulting in <br />a grouted column (i.e., soil cement column) of 4 to 6 foot in diameter. The 6-inch-diameter <br />predrill borehole allows jet grout columns to advance through woody debris and other potential <br />obstructions. The jet grouting operation typically terminates a few feet above the liquifiable <br />soils; hence, in areas where the top layer of liquefiable soils begins well below the ground <br />surface (e.g., in the area west of the proposed Effluent Pump Station), disturbance to non- <br />liquifiable crust or areas to be excavated for subgrade structures would be kept to a minimum <br />and post-excavation within the non-liquefiable crust would not be affected. <br />Jet grouting can be performed with minimal disruption to adjacent structures. The jet grouting <br />technique is intended to be used to accomplish controlled solidification to reduce the potential <br />for vertical or lateral ground movement caused by liquefaction. Additionally, jet grouting <br />equipment is often smaller and lighter than equipment used for installation of stone columns and <br />deep soil mixing columns, hence providing access to jet grout equipment within the project site <br />would be much easier than providing access to heavier equipment required for installing stone or <br />deep soil mix columns. <br />Prior to jet grout column installation, a spoils trench must be excavated to help manage the <br />jetting spoils. The trench would be approximately 3 feet wide and 3 feet deep leading from the <br />jet grout column to an appropriate spoils collection zone. During active jetting, the soil cement <br />spoils will flow into this trench for continuous removal by an excavator or a vacuum truck. <br />Limitations of using jet grouting as a mitigation option for this project include: <br />• Requires installation of a temporary grout mix plant.