“Geotechnical

Frequently Asked Questions about Auger Piles

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Auger Piles – Answers

Auger Cast Pile (Continuous Flight Auger Pile, Auger Grouted Pile, CFA Pile, Auger Grouted Cast in Place Pile)

How is the Installation of an Auger Piles done?

The installation of an Auger Cast in Place Grouted Piles is done by using a rotating hollow shaft auger. Keeping it in continuous motion, it is buried till refusal or a specified depth is achieved. As the hollow auger shaft is rotated in a clockwise direction, high strength sand cement grout is pumped into the hollow shaft while it is being slowly withdrawn.

The top of the pile is cleared of spoil and a galvanized can of metal measuring up to 18 inches in depth is placed on the pile's top. Once this is done, removal of contaminants is done by screening the pile. If necessary, the pile is dipped and if required, reinforced steel is inserted in the pile through the still fluid grout.

The grout columns produced through this technique are what form the Auger Cast in Place Grouted Piles once they harden.

How is an Auger Cast in Place Grout cut off or built up if the grade is below or above the design top of the elevation of the pile when it is time to drill?

If a situation arises where the design top of the pile or pile cut off elevation is below the surface of the ground when it is time to drill, it is possible to dip the grout from the top of the pile if the conditions of the soil allow it.

If soil conditions are favorable, piles can be dipped to an accurate measurement ranging from three to four feet. As the depth to pile cut off increases, the accuracy involved in dipping decreases. It is possible to perform dipping by air lifting if the dipping required is of a large amount. Please note that dipping should always be performed immediately after the casting of the pile.

Dipping should be stopped if any caving begins from the sides of the hole. In some cases soil conditions can prevent dipping. In such scenarios, chipping guns, hydraulic cutters or concrete saws can be utilized after the excavation of the pile cap.

If the cutoff of elevation of the pile is above the working grade at the time of installation, it is possible to build up the pile with the help of a round/circular form. If there is a buildup of 8 inches or less then the use of standard 18 inch is commonly utilized.

For buildups that are greater than that, sonatube or longer cans may be utilized. Once it is firmly positioned, fluid grout is used to fill the form in order to create the proper level of the top of the pile.

What happens when the level of the grout drops or when an Auger Cast in Place Grouted Pile settles?

Owing to some soil conditions, settlement in grout is considered a normal occurrence in the installation process of Auger Cast in Place Grouted Piles. This largely occurs due to pressure on the soil caused by the column of grout or pile, particularly when the grout is still in its fluid form.

It is possible to add fresh grout to the top (top off a pile). However, care must be taken to ensure that no contamination is occuring and grout at the top is still in fluid form.

How is reinforcement installed in an Auger Cast in Place Grouted Pile?

When required, reinforcement is installed into the pile when the cement grout is still in a fluid form. If considered necessary a single reinforcement bar can also be installed through the hollow auger preceding the grouting process and withdrawal of the auger. In cases where reinforcement is installed once the pile has been grouted, centralizes are utilized to give the necessary clearances.

What are the reinforcement requirements typically utilized in the placement process of Auger Cast in Place Grouted Piles?

In accordance with 2009 IBC 1810.3.9.2 No reinforcing is required except where subject to uplift or where required due to the moment strength determined using the load combinations of Section 1810.3.9.1.

When carrying seismic or lateral loads in the top 20 to 15 feet of a pile, it is typical to use cage reinforcing. However, it is considered to be more economical to opt for a single center bar to bear uplift loads. The longer a reinforcing cage is, the more expensive and difficult the installation becomes.

What type of reinforcement centralizers are utilized for Auger Cast in Place Grouted Piles?

The most commonly utilized centralizers are either made of PVC material or plastic. They are specifically designed to help maintain a (minimum coverage) clearance distance of a minimum between the bars and the surrounding soil.

The most commonly utilized cage centralizer is a spacer wheel with a diameter up to 6 inches. It has a central groove which can be snapped on to #3 ties. The wheel placements in the groove allows the placement of the wheel in a manner that enables 3 inches of a wheel to gain access to the inside of the cage while clearance is maintained with the help of 3 inches of the wheel outside. The attachment of the wheels is made in a manner to enable rotation about the tie #3 while the cage is being lowered in the pile.

When considering reinforcement of the bars in the center the plastic collar, also known as the PVC "football" is best choice for a centralizer. The strap centralizer that can be tied in place or slide over the bar is also a good option. The diameter of the centralizer is smaller towards each of its ends while the diameter widens out towards the center in order to ascertain proper clearance while aiding in installation.

What is the minimum requirement for concrete covers in cast in place piles that are uncased?

IBC Table 1808.8.2 requires a minimum cover of 2.5 inches; However, the industry standard cover is measured 3 inches which greatly simplifies the installation process of the cage.

When working next to an Auger Cast in Place Grouted Pile that is newly completed, how close can you drill?

Unless approved by the building official, the IBC table 1810.3.3 requires a minimum spacing of at least 6 pile diameters center to center for piles installed within 12 hours of each other.

How are Auger Cast in Place Grouted Piles Utilized? Do Auger Cast in Place Grouted Piles qualify as piles that are end bearing or friction piles?

Auger Cast in Place Grouted Piles can be utilized in a variety of ways including the following:

• Can function as friction piles – Through friction between the soil and the surface of the pile, it is possible to transfer the load on to the soil.

• Can also function as end bearing piles – The tip of the pile can transfer the load into a solid stratum of rock or soil.

• Can function as a combination of end bearing piles and friction piles – Either of the two combinations described above can transfer the load.

• Can function as a Soil Anchor or Uplift Anchor – Uplift or tension forces can be resisted by the means of the contact created between the soil and the grout along the complete surface area of the pile and is transferrable through the full length tendon which is embedded in the center of a column of grout.

• If placed adjacently a series of Auger Cast in Place Grouted Piles can form a continuous wall of auger cast to function as a permanent or temporary below grade wall and shoring system.

• Can also function as a permanent or temporary tie-back that is diagonal in an auger cast curtain wall, lagging walls, walls of sheet pile and lagging walls.

What advantages does one get if using Auger Cast in Place Grouted Piles

Reduced noise – Auger Cast in Place Grouted Piles are pumped and drilled pile. This eliminates the chances of heavy noise pollution created by hammer impacts when driving piles.

No unpleasant vibrations – The exclusion of working with a pile installation hammer enables the installation of Auger Cast in Place Grouted Piles next to present structures without endangering or weakening existing walls, footings and other structural elements by vibrations.

Auger Cast in Place Grouted Piles can be utilized as an economical and cost effective alternative to other pile types in various situations.

Auger Cast in Place Grouted Piles are completely flexible in length up to the maximum lengths that can be installed with the mobilized pile rig. On projects that have variable lengths, waste of material can be drastically reduced owing to the fact that the placement of material is halted at the drilling grade. The pile contractor does not have to select the accurate length of the pile for each location prior to installation.

The Auger Cast in Place Grouted Pile is also much more flexible in size with dimensions that can be changed quickly by simply changing the guide devices and auger flighting using the same pile rig, allowing freedom of installation of a range of sizes for load testing that can help determine the most competent size or the installation of diverse sizes for various capacities on one project.

An Auger Cast in Place Grouted Pile can have a very irregular shape. This greatly boosts friction capacity of the pile in various soil conditions.

Seeing as an Auger Cast in Place Grouted Pile is cast in place, concerns about shipment like the length of the material or the handling and moving of piles at the jobsite are non-existent.

Casing is not required – In its installation, pile auger is filled with earth that maintains the pile hole's shape during the drilling phase. The pressures produced by the head of grout in the auger during the grouting phase and withdrawal can exceed the pressures exerted laterally by the soil. While the grout is present in a fluid state, the pressures per foot of depth of the soil are lower than the lateral pressures per foot of depth of the grout.

Installation is possible with restricted headroom condition – Auger sections can be assembled to accommodate the installation of Auger Cast in Place Grouted Piles particularly inside existing buildings that have a clearance limit of 7 feet to 10 feet.

Inspection of soil can be done at each pile hole – Displacement of soil occurs while drilling and pumping grout and is available for testing or inspection.

When faced with different conditions in the soil, before installing a test pile, it is possible to drill probe holes at various locations on the site. This enables the inspecting engineer to successfully and accurately appraise the conditions of the soil and work out the most efficient location for the placement of a test pile. Since no material is wasted the cost is economical compared to other types of probe piles.

What are the load bearing qualities of different Auger Cast Piles?

Pile loads:

  • Diameter (Inches)
  • Load Range (Tons)
  • 12
  • 10-75
  • 14
  • 50-90
  • 16
  • 75-150
  • 18
  • 100-175
  • 24
  • 125-200

Note: Pile capacity is largely dependent on the conditions of the surrounding soil. Piles diameters that are also available but less frequently used include 20", 36", and 42". 36 inch and 42 inch auger cast piles are very heavily reliant on the soil conditions.

What is typical Grout Strength for Auger Cast Piles?

The most common grout strengths in Auger Cast in Place Grouted Piles range from 3000 psi to 5000 psi. The 6000 psi grout has become more commonly utilized in several locations. Grout strengths that are higher like the 7000 psi are limited for use in few locations. Particular attention is needed when curing speciments of grout especially before delivering them to the controlled environment of the testing laboratory.

What procedure is used for Auger Cast in Place Grouted Piles when testing for compression?

Normally an Auger Cast in Place Grouted Pile that is being tested is installed in a centered position between four Auger Cast in Place Grouted Piles laid out in a rectangular format. These four piles hold down the beams for testing by acting as reaction piles. If four reaction piles are not adequate to successfully carry the compression load applied in the test pile, you might require extra reaction piles or replace them with rock anchors.

ASTM D1143 Standard Test Methods for Deep Foundations Under Static Axial Compressive Load applies to Auger Cast in Place Grouted Pile compression tests. It calls for a minimum clear space of five times the largest pile diameter between the reaction piles and the test pile but in no case less than eight feet.

The test is conducted by placing a reaction beam on either side of the test pile on top of the test beam. These reaction beams are each connected to two reaction piles by threaded rods, nuts, and plates. The Test beam is a wide flange beam with gusset plates designed to carry the load of the test pile to the reaction piles. The test beam runs above the test pile and is held down by two or more reaction beams.

During this test, compression load is applied by placing the hydraulic jack under the test beam and on top of the test pile. The compression load is then conveyed to the reaction beams through the test beams and reaches the rock anchors or the reaction piles.

The applied load in the compression test is measured with the help of a load cell that is positioned between the test beam and the test jack in accordance with ASTM D1143-07 when test is 100 tons or more. If the test load is less than 100 tons, the load may be measured with a calibrated jack or a load cell.

Two methods must be utilized to measure movement of the test pile. The main measurement is normally assessed by placing dial guages on two sides of the pile between a connection to the test pile and a reference beam. This reference beam is supported independently of the load test frame. Its supports must be no less than five times the largest pile diameter or 8 feet, whichever is greater from test or reaction piles.

The secondary method typically is a scale attached to the test pile that is read, either by a surveyor's level or a wire that is independent of the load test frame and is supported not less than five times the largest pile diameter or 8 feet, whichever is greater from test or reaction piles.

When should I avoid using Cast in Place Grouted Piles? When may I expect problems with Auger Cast in Place Grouted Piles?

In the following situations, it is better to seek out advice and stay away from Cast in Place Grouted Piles:

If layers of rock are present at the site, that will not support the load of the pile and if the rock is too near the ground surface to allow for use of friction. Unless you can successfully pre-drill the layer of rock, you should avoid using Auger Cast in Place Grouted Piles. In such scenarios, Geotech gladly reviews all the information submitted about the soil and offers you their professional opinion on how to proceed. Since we have experience working with almost every kind of pile, you can rest assured that you will get advice that is beneficial and economical for your project.

You may want to stay away from Auger Cast in Place Grouted Piles if there is an abundance of material that has N values of 3 or lower. In such scenarios, you might want to avoid using Auger Cast in Place Grouted Piles. In such scenarios, Geotechnical gladly reviews all the information submitted about the soil and offers you sound opinion on how to proceed. Since we have experience working with almost every kind of pile, you can rest assured that you will get advice that is beneficial and economical for your project.

If the soil is weak or granular and you are trying to install piles close to or against a structure that has no pile support. It is possible that the installation process of the Auger Cast in Place Grouted Piles could remove material and weaken the existing structure. In such scenarios, Geotech gladly reviews all the information submitted about the soil and offers you sound opinion on how to proceed. Since we have experience working with almost every kind of pile, you can rest assured that you will get advice that is beneficial and economical for your project.

If only a small number of piles are required, it is possible to get rid of the load test and opt to have driven piles installed since the mobilization may be less expensive and the load can be ascertained with the help of the hammer blow count.

If the chosen area is covered with water and you have been unsuccessful in the removal of water either by filling above it or lowering it. In such scenarios using Auger Cast in Place Grouted Piles can be highly impractical. Geotech gladly reviews all the information submitted about the soil and offers you sound opinion on how to proceed. Since we have experience working with almost every kind of pile, you can rest assured that you will get advice that is beneficial and economical for your project.

If the surrounding soil contains pollutants – and you would rather not risk bringing contamination up to the surface. In such scenarios, using Auger Cast in Place Grouted Piles can be highly impractical. Geotech gladly reviews all the information submitted about the soil and offers you sound opinion on how to proceed. Since we have experience working with almost every kind of pile, you can rest assured that you will get advice that is beneficial and economical for your project.


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