- Serving Northern California
- Geopier FAQ
- What is Impact pier?
- What is a Geopier infosheet (pdf)
- Geopier at BART (pdf)
- Geopier at Regent Hotel (pdf)
- Geopier @ HWY 880-92 (pdf)
Farrell installing uplift Geopier at the Regent Hotel in Stockton, CA.
Geopier - Uplift RAP bottom plate
Geopier - CALTRANs installation
Geopier - DSA approved high school
School of Engineering installation
ANSWER: a Geopier System is a ground improvement method that prestrains and prestresses the soil using soil "replacement" and soil "displacement" technology to strengthen soft soil and loose soil with very dense, stiff, rock columns constructed by heavy equipment crowd force and vertical impact ramming.
Geopier® RAP improves poor soil and uncontrolled urban fill by increasing the soil strength and stiffness. RAP improved soil supports conventional shallow foundations (spread and strip footings) as an alternate to deep foundations. A Geopier Intermediate Foundation does two things at once: first, it vertically reinforces the soil around the Geopier RAP element and second, it supports structures built on top of it. In other words, it makes the soil around the RAP stronger to withstand foundation loads. The depth and quantity of RAPs are determined by geotechnical conditions and structural load cases of the project. Most RAPs are 7 to 15 feet deep and occupy between 30% to 50% of the footing plan area. No complicated steel or concrete connections, only conventional shallow spread footings over Geopier RAP reinforced soil. Hence the name "intermediate foundation system" ... as deep foundations are usually at least 30 feet deep and often 50 to 100 feet deep, while conventional shallow foundations are normally no deeper than 4 to 6 feet.
A Geopier RAP is constructed by drilling a hole in the soil, referred to as the Geopier shaft. After drilling, 2 to 4 inch crushed rock is poured into the shaft and then rammed into the bottom of the shaft with a hydrualic hammer and the specially designed Geopier rammer tool. The rammer tool is shaped with 45-degree beveled sides to press the rock laterally during construction. This pre-consolidation technique vertically pre-strains and pre-stresses the soil below the drilled bottom, creating the Geopier "bottom bulb.". Once the bottom bulb is constructed, layers of well-graded crushed rock are successively rammed to the top of the Geopier shaft (averaging a 12 inch compacted lift thickness). This ramming effect creates a very dense, stiff, rock pier that expands the drilled shaft and reinforces the soil. The RAP pre-consolidation technique, also pre-strains and pre-stresses the soil laterally at the drilled shaft edge adding lateral stress to the soil - the key to Geopier success.
The total construction process is characterized by a transient, high frequency, high energy ramming action utilizing heavy equipment crowd for maximum hammering efficiency. The rated energy of ramming equipment ranges from 1.0 million to 2.0 million ft-lb. per minute, while the ramming frequency generally varies between 4hz to 6hz. Typical RAP construction performance exceeds 400 to 600 feet per day.