Aggregate piers/vibro stone columns

Q. What are aggregate piers/vibro stone columns?

A. Aggregate piers, also called vibro stone columns or vibroreplacement, are installed by excavating a hole via a high-frequency vibratory tool called a vibroflot. Once the hole has been excavated, clean stone is placed into the hole in lifts, and each lift is compacted with vibration and crowd pressure. This process densifies the adjacent soil and allows for pore water pressure to dissipate from the ground, thus improving the overall bearing capacity and settlement characteristics of the soil.

Q. How are Subsurface’s stone columns different than other aggregate pier systems?

A. Subsurface installs vibro stone columns with a stratacaster vibro rig that combines crowd pressure with high frequency vibration in order to excavate the column hole, thus usually eliminating the need for pre-drilling. Since pre-drilling is not typically required with our service, no spoils are generated. The stone is placed in lifts compacted to design stiffness via the vibro flotation method, and the soil around the outside of the column is densified, thus increasing the overall bearing capacity of the ground.

Q. Who designs and installs the stone columns?

A. Unlike other aggregate pier systems, Subsurface designs AND installs the stone columns themselves. The owner/contractor will only have one company to work with during the design and construction of the ground improvement system.

Q. What are typical structures that can benefit from the use of stone columns?

A. All different types of structures can be suitable candidates for ground improvement, depending on their load and settlement criteria. The installation of stone columns is a means to improve the overall performance capability of the existing ground. Bearing capacities in the range of 6,000psf can be achieved while remaining within required settlement tolerance.


Augercast pile

Q. What is an augercast pile?

A. An augercast pile is a deep foundation element that is constructed by using a continuous flight auger to advance a hole to its design depth. Once at the design depth, concrete is pumped through the hollow stem of the augers to the bottom of the hole as the augers are slowly removed from the hole. After the pile has been constructed, or the concrete has reached the surface and the augers have been removed from the hole, a reinforcing steel cage can be placed in the upper portion of the pile. Augercast piles are typically used in wet silty or sandy soils where loading conditions are such that a deep foundation system is required.

Q. What diameters of augercast pile can Subsurface construct?

A. Typical augercast pile diameters are 14”, 16”, and 18”; however, Subsurface can also install pile diameters of 24”, 30”, and 36”.

Q. What is the load bearing capability of augercast piles?

A. Depending on the soil structure and size of the pile, augercast pile capacities range from 40 ton to 200 ton.



Q. What is a micropile?

A. Micropiles, also sometimes referred to as pin piles, are small diameter, drilled and grouted steel piles that are typically reinforced. Micropiles are often used where difficult soil conditions are present and the work space has low headroom and/or restricted access.

Q. What is the lowest headroom required for Subsurface to install micropile?

A. For low headroom micropile installation, Subsurface uses a rig that requires 9 feet of overhead room and can fit through a 3-foot wide opening.

Q. What are the typical diameters of micropile?

A. Typical diameters of micropile range from about 5” diameter to 9” diameter.

Q. What loads can be put on micropile?

A. Depending on soil structure and size of pile, micropile typically carry loads ranging from 25 tons to 250 tons.