The Northtown Mall Expansion Project involved the partial demolition of the northern side of a mall in Spokane, Washington.  120,000 square feet of store space in the corridor between Macy’s and Kohl’s were demolished, and 63,000 square feet of new store and restaurant space will be added.

Team Members

General Growth Properties

Vandervert Construction Inc.

Crux Subsurface

Crux’s Role

Crux was contracted to design and install nine micropiles to retrofit existing foundation columns.  The additional capacity was required to support higher building loads accompanying the new retail space.  Micropiles were installed from within the existing structure, and in close proximity to offices and businesses, requiring compact installation equipment.

Access to pile locations required installation equipment to fit through a 37-inch by 84-inch doorway.  Overhead clearance during drilling operations was as low as 8.5 feet.  Crux’s fleet of micropile drills are specially modified to break down into small components and access these confined spaces.  The drill was brought into the mall through staff entrances and positioned at pile locations.  The power unit was stationed outside the building and connected using approximately 150 feet of hydraulic hose to accommodate size restrictions and ensure air quality during indoor operations.

Soil conditions consisted primarily of medium-dense to coarse sand, increasing the potential for dusty conditions.  A dust curtain was established prior to drilling, and a portable air scrubber was used to prevent dust from entering the main portion of the mall.  Crux also used a specially designed water injection pump to inject water into the compressed air system.

Hard rock was not encountered at any of the nine piles, necessitating pressure grouting to reach capacity.  Micropile operations were completed outside of business hours, typically between 9:00pm and 7:00am, to ensure that customers and employees were not disturbed during the busy post-Christmas shopping season.  All piles were successfully installed and proof tested.

Equipment needed to fit through a 37” by 84” doorway and operate with as little as 8.5 feet of overhead clearance

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