Helical Piles For New Construction

Helical Piles For Supporting Structural Slabs

	Figure 1: Soil Boring Click on image for larger view

Supporting building loads on deeper soils can be accomplished in several ways including:

     1.    Removal of poor soil materials and replacement with properly compacted gravel. This is an economical solution when adequate soils are found within a few feet of the bottom of the footings.

     2.    Driving steel, concrete, or timber piles. “Driving” refers to the process of pounding the piles into the ground with a crane mounted hammering device. This is a very economical solution when a lot of piles are required. It may not be a very effective solution if there are other buildings or structures nearby as the ground vibrations caused by the hammering may cause damage to those nearby structures.

     3.    Drilled piers refers to the process of drilling a hole in the ground and filling it with concrete. When considering drilled piers, keep in mind that the material excavated from the hole may also have to be removed from the site. Soil condition may be poor enough that sleeving the drilled pier is required to prevent the hole from caving in. In some cases these sleeves are recovered as the concrete is placed in the hole. Drilled piers have been used for a long time with great success. Typically drilled piers become more economical as the number of piers required for the job increases and as loading requirements increase, as may be the case with multiple story steel or concrete buildings.

     4.    Geopiers are stone filled drilled holes. Holes are drilled into the ground and then  backfilled with stone which is compacted as it is placed. The placement and compaction of the stone consolidates the soil around the hole. This process may prove to be economical on larger projects. As with driven piles, ground vibrations caused by compaction of the stone fill may cause damage to nearby structures.

     5.    Dynamic compaction refers to the compaction of soil by repeatedly dropping a large weight from a crane onto the ground. No material is placed in the ground and there is no excavated material to handle. This is effective only in certain soil conditions but can be very economical. As with driven piles and Geopiers, ground vibrations caused by compaction of the soil may cause damage to nearby structures.

     6.    Helical piles are steel shafts with helixes welded to them. The Helical pile is installed by screwing it into the ground. The size of the shaft along with the size and number of helixes varies depending on the loading requirements and the soil conditions. This type of pile is very effective in areas where access is limited, where ground vibrations must be kept to a minimum, where soil conditions are very wet, and where the number of required piles can be a few as 1. Helical piles are not very effective or economical in situations where building loads are relatively high as may be the case with multiple story steel or concrete buildings. They may also not be very competitive in situations requiring a large number of piles.

We are capable and experienced with designing in all of the above discussed extended foundation systems but we install only one, the Helical pile.

In new construction we utilize the Helical pile to support foundation walls and concrete floor slabs in residential, commercial, and industrial buildings.

In existing construction where settlement has become a problem, we utilize the Helical pile to support concrete slabs but not the foundation walls. The reason for this is that the equipment required to spin the Helical piles into the ground forces the top of the Helical pile out away from the foundation wall so the pile ends up being driven into the ground at an angle under the foundation. This angle results in the building loads not acting vertically on the pile which results in bending forces being induced into the Helical pile. Because of this we prefer to utilize push piles to support existing foundations and Helical piles to support concrete slabs.

Concrete slabs supported on Helical piles must be designed and constructed as structural slabs. This requires the installation of reinforcing steel and in many cases concrete beams must be formed into the slab to transfer loads to the Helical piles.

Below are several photographs of a home supported on Helical piles. The soil boring shown in figure 1 is one of the borings taken at the site where this home was constructed. In this particular case poor soils were encountered to a depth of 7' below the surface. Because of its close proximity to the Fox River, excavating down 7' and pouring footings and foundation walls would have required extensive de-watering of the site and was not feasible. The building site was very tight with homes located to each side so getting in large equipment to drill concrete piers was also not feasible. Any type of pile driving or dynamic compaction would have risked damage to the adjacent homes and was not even considered as an option. These factors, along with competitive pricing, contributed to selecting the Helical pile as the solution to supporting the building.

Home site along Fox River. Helical Piles being installed along foundation wall locations. View image	Helical Pile sections are bolted together as the pile is driven into the ground. View image	Helical Pile driver installed to top of pile. View image

Helical Pile being turned into the ground. View image	Helical Pile cut to proper elevation. View image	Caps on Helical Piles in trench. Thin layer of concrete to be poured to allow forms to be set level. View image

Foundation walls formed over the top of the Helical Piles. View image	Reinforcing steel bars to be cast in the foundation walls so foundation wall can carry building loads from Helical Pile to Helical Pile. View image	Foundation walls completed. View image