Geopier® Rammed Aggregate Pier® Elements
Our engineer and builder partners often ask us, “Could you give us a ballpark figure for ground improvement costs?” To provide a meaningful estimate, it’s important to first assess some fundamental, project-specific cost factors, even for rough estimates.
The primary cost drivers for ground improvement are:
- Geotechnical Conditions
- Structural Loading Demand
- Proposed vs. Existing Grading
Geotechnical Conditions
Geotechnical conditions, such as soil consistency, density, and depth, significantly affect the feasibility, stiffness, capacity, and depth of ground improvement (GI) elements, all of which impact GI costs. Differing geotechnical conditions can lead to drastically different costs for the same structure. For example, a six-story building on 10 feet of granular fill may only require short Rammed Aggregate Pier (RAP) elements, resulting in lower costs. In contrast, the same building on 40 feet of granular fill and compressible organic material would require a more robust (and more expensive) solution, such as deeper GeoConcrete Column® (GCC) rigid inclusions.
Structural Loading Demand
Ground improvement costs can also vary based on the structural demand, even if the underlying soil profile is the same. The loads from columns, walls, and slabs impact the demand on the soil and the GI system. For example, a one-story retail building with 100-kip column loads puts much less demand on the underlying soils than a 10-story office building with 1,000-kip column loads. The 10-story building will have a much higher GI element concentration (and associated costs) than the one-story building, even though the soil conditions are the same.
Proposed vs. Existing Grading
Changes to existing grading, particularly grade-raise-fill (GRF), are often an overlooked but significant cost driver in GI projects. For example, if the existing grade is at an elevation of 10 feet and the finish floor elevation is set at 15 feet, the GI design must account for the additional 4-5 feet of GRF. This added load, along with the structural column, wall, and slab loads, increases the demand on GI elements and can significantly affect GI costs.
