Rammed Aggregate Pier Specifications

Types

• Commonly used reinforcements to prepare the soil of piers include silt, soft to stiff clay, rocks and sand. Potable water is also used to raise aggregate moisture composition within the soil stratus. RAP elements are integrated to soft, weak soil by ramming, not vibration. This means that technicians dig a hole in predetermined locations and literally ram silt, rock or sand to compact the soil.

RAP Footing

• Construction footings, together with a foundation, ensure that a structure will stay on the location it is to be erected. In RAP systems, footings should be continuous and linked together between RAP elements. As for weak soil types, footings can be fashioned as a beam with an elastic base to easily incorporate stiffness of the RAP element to unimproved soil to create spring stiffness.

Design

• Following generally accepted engineering practice, the RAP system must comply with criteria for differential settling and service load-carrying pressure. This means that each RAP element should be uniform on how much weight it can handle, as well as how long it can last before the rammed rocks and sand start to loosen. A life of 50 years is a normal design requirement.

Construction

• The first step in creating RAP is to drill holes or cavities in the area being improved. The locations of these cavities depend on the size of the structure being supported, as well as the size of the structure that will be built on top of it. Once the cavities are drilled, RAP elements, such as rock and sand, are poured into the cavity.
  A heavy machinery then rams the rocks to form “bulbs” to strengthen the surrounding soil. The heavy machinery usually uses a minimum of 15 tons of force to ram the rocks in place. This process is repeated, until the cavity has been filled with rammed rock aggregates. The same process is repeated on all cavities, and the footing, usually concrete, is poured on top.