Project Overview

Consumers Energy (Consumers) planning to construct a 220-megawatt single-axis tracker solar energy facility in Kalamazoo County, Michigan. The project will be comprised of photovoltaic (PV) solar arrays constructed on various connected parcels. Project limits encompass approximately 2,200 acres of rural area comprised predominantly of agricultural fields with scattered rural homes and woods. The PV arrays will be supported on steel piles and ancillary equipment will be supported on shallow foundations with spread footings, mats, slabs on grade or drilled piers.

NTH was selected by Consumers to conduct a site geotechnical investigation due to our over 50 years of geotechnical experience and familiarity with similar renewable energy projects conducted in in Barry and Calhoun Counties, Michigan. Subsurface investigation was conducted through drilled soil borings and pile load testing to develop soil profiles, driven pile and drilled shaft design parameters, and general construction recommendations.

Project Scope

As the engineering consultant NTH performed geotechnical exploration and investigation within the project area. Our services under this contract included:

44 soil borings
- 41 borings drilled to 20 feet below ground surface (bgs)
- 1 boring drilled to 30 feet bgs
- 2 borings drilled to 50 feet bgs
10 bulk soil samples tested for corrosivity, soil box electrical resistivity, and soil thermal resistivity
Laboratory soil index testing
11 in-situ soil electrical resistivity tests
1 infiltration test at the substation
1 in-situ infiltration test at the substation location using Modified Philip-Dunne (MPD) equipment
12 pile load tests performed on representative locations
Geotechnical engineering, evaluation, and recommendations/reporting

In this capacity NTH conducted the soil borings under the full-time observation of an NTH geologist or field engineer, who classified each soil sample on-site. Soil samples were then sent to the lab for further classification and soil index testing.

NTH developed a pile load testing program and provided monitoring of field pile load testing on 12 piles installed on-site. NTH used the results of the field investigation and pile load testing program to develop load-resistance curves for pile uplift, and lateral performance. Field electrical resistivity testing was also conducted by NTH.

NTH’s geotechnical engineers used subsurface soil and groundwater conditions to develop design soil profiles, advise site preparation, grading, and earthwork recommendations, temporary excavations, and groundwater control recommendations. NTH provided shallow foundation design for shallow spread footings, mats, slabs-on-grade, and drilled piers were provided with design parameters including allowable soil end bearing resistance, estimated differential settlement, lateral load resistance, and recommended factors of safety for design. NTH evaluated the pile load testing data to develop driven pile and drilled piers design recommendations included estimated ultimate skin friction and end bearing resistance values for against uplift and lateral loading.

NTH’s expertise and technical expertise continue to provide clients with efficient and budget-oriented design parameters while assisting our clients to achieve their sustainability goals.