Portland Area Super Market


The overall project included the construction of a supermarket to serve as the anchor amenity of a 2 million-square feet mixed-use development.  Helical Drilling provided ground improvement services on the supermarket site by using Geopier GeoConcrete® Column (GCC) Rigid Inclusion elements that extended through the unsuitable fill and soft/sensitive clay layer. Given the challenges with the installation of rigid inclusion ground improvement in thick/sensitive clays, the project included a state-of-the-art pre-production testing program.

Geotechnical Challenges:

The soil profile included unsuitable fill material underlain by a thick, soft, sensitive clay layer that extended up to about 70 feet below the ground surface.  Furthermore, the project required up to about 5(+) feet of filling to achieve the proposed ground floor elevation.  Constructing grade-raise-fill, footings, and slabs-on-grade, over the existing soil profile would result in excessive settlement, leading the design team to consider ground improvement or deep foundations.

Geotechnical Design Solution:

Helical and Geopier Foundation Company designed a rigid inclusion ground improvement solution consisting of a network of GeoConcrete Column (GCC) Rigid Inclusions that extended through the unsuitable fill and soft/sensitive clay layer.  The design included finite element modeling of the GeoConcrete Column (GCC) Rigid Inclusion system to help ensure proper support of the grade-raise fill and slab-on-grade.   

Ground Improvement Construction:

Helical installed over 1,300 GCC Rigid Inclusions to depths up to ~ 70 feet below ground surface.  Production was completed ahead of schedule with two rigs/crews and allowed the Developer to expedite building pad delivery to the supermarket tenant.

Quality Assurance and Control:

Installation of rigid inclusion ground improvement though thick/sensitive clays is somewhat rare in the Northeast due to challenges with ensuring proper rigid inclusion shaft integrity which is paramount for proper performance. As such, a thorough pre-production testing program was implemented. The pre-production testing program included installing and testing sacrificial rigid inclusions as single elements and in groups.  The testing included six full-scale load tests to 200% design load, non-destructive sonic echo tests, and “proof” load tests on production elements.  The full-scale load tests consistently resulted in <1/2” of deflection at the design load.   Test and production elements were observed by Helical’s full-time Quality Control employee, the Developer’s geotechnical representative, and the Tenant’s geotechnical representative.  Concrete installation volumes were checked through careful monitoring of concrete pump strokes and mandrel extrusion pressures.