TYPE OF PILE

DESCRIPTION

Driven Piles

– Concrete Driven concrete piles come in a variety of sizes, shapes and methods of construction. In cross section, they can be square, octagonal, round, solid or hollow. These piles generally vary in sizes from 10 to 60 inches. They can be either conventionally reinforced or prestressed (most common). They can also be either precast (most common) or they can be cast in driven steel shells. The types of steel shells vary from 10 to 120 inches in diameter for heavy walled pipe that are driven directly with the hammer, to thin walled or step-taper pipes which are driven with a mandrel. The steel shell may have a flat bottom or be pointed, and may be step-tapered or a uniform section.

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Caltrans has standard details for splicing precast concrete piles but it is a

difficult, time consuming, expensive procedure. Hence, this almost precludes the use of precast piles where excessively long piles are required to obtain necessary bearing.

The unit cost to furnish concrete piles is usually lower than the steel equivalent.

But this cost is often offset by the requirement for a larger crane and hammer to handle the heavier pile. This is particularly true when there are a small number of piles to drive.

Driven Piles

– Steel Steel piling includes “H” piles and pipe piles (empty or concrete filled). The pipe section is a standard alternate for the Class 45 and 70 piling, but is seldom used.

Although steel piling is relatively expensive on a “per foot” furnish basis, it has a number of advantages. The steel piles come in sizes varying from HP 8x36 to HP 14x117 rolled shapes or may consist of structural steel plates welded together.

They are available in high strength and corrosion-resistant steels. They can penetrate to bedrock where other piles would be destroyed by driving. However, even with “H” piles, care must be taken when long duration hard driving is encountered as the pile tips can be damaged or the intended penetration path of the pile can be drastically deflected. Using a reinforced point on the pile can sometimes prevent this type of damage. Due to the light weight and relative ease of splicing, they are useful where great depths of unstable material must be penetrated before reaching the desired load carrying stratum and in locations where reduced clearances require use of short sections. They are useful where piles must be closely spaced to carry a heavy load because they displace a minimal amount of material when driven.

Splice details are shown on the Standard Plans or project plans for contracts that permit the use of steel piling. Pile welding work requires the submittal and approval of a Welding Quality Control Plan. The requirements for the Welding Quality Control Plan are addressed in the contract special provisions

Sometimes “H” piles must be driven below the specified tip elevation before minimum bearing is attained. This can present an administrative problem (cost) if the length driven below the specified tip elevation is significant. Steel lugs welded to the piles are commonly used to solve this problem. This subject is covered in detail in Bridge Construction Memo 130-5.0.

Driven Piles – Wood

Untreated timber piles may be used for temporary construction, revetments, fenders and similar work; and in permanent construction where the cutoff elevation of the pile is below the permanent ground water table and where the piles are not exposed to marine borers. They are also sometimes used for trestle construction, although treated piles are preferred. Timber piles are difficult to extend, hard to anchor into the footing to resist uplift, and subject to damage if not driven carefully. Timber piles also have a maximum allowable bearing capacity of 45 Tons, whereas most structure piles are designed for at least 70 Tons.

Alternative Piles

Currently there are several alternative piles that have been approved for use by the Department. They are used on a site-specific basis. There are three (3) types of Micro-piles (DBM, Malcolm and Nicholson). The Tubex Grout Injection Pile is another alternative pile system. These systems have generalized drawings and

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have been successfully system tested by the Department. The GeoGrout

Foundation System has pile system load test results on file with the Department but no generalized drawings. Refer to Chapter 13 and Appendix D for

information, drawings and schematics of the various alternative piles.

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CHAPTER

6 Cast-In-Place Piles

Description

Few terms are as self-descriptive as the one given the Cast-In-Drilled-Hole (CIDH) pile. They are simply reinforced concrete piles cast in holes drilled to predetermined elevations. Much experience has been gained with this pile type because of their extensive use in the construction of bridge structures. While they probably are the most economical of all commonly used piles, their use is

generally limited to certain ground conditions.

CIDH piling can be grouped in two categories: the first is CIDH piling without inspection pipes (dry method), and the second is CIDH piles with inspection pipes (wet method). This chapter is applicable for both the dry and wet method of CIDH pile construction. Chapter 9 of this manual provides supplemental information on the wet method of CIDH pile construction. Note that piling dewatered with the help of a temporary casing requires inspection pipes even if the piling is poured dry.

The ground formation in which the holes for CIDH piles are to be drilled must be of such a nature that the drilled holes will retain their shape and will not cave in when concrete is placed. Because of cave-in and concrete placement difficulties, these piles are not recommended for use as battered piles. Other pile types should be considered where groundwater is present, unless dewatering can be done with a reasonable effort and unless concrete can be placed without a permanent casing.

If groundwater or caving conditions are present, the piles can be constructed by the slurry displacement method if permitted in the contract specifications. The slurry displacement method is described in detail in Chapter 9 of this manual.

A dry hole, by definition, typically contains no standing groundwater within the drilled hole, although the material at the bottom of the drilled hole may be damp or wet. However, the dry method of construction may still be used when a small amount of groundwater is present in the drilled hole. Refer to Bridge

Construction Memo 130-7.0 for information on the specific definition of a “dry”

drilled hole.

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Specifications

The Standard Specifications describe four different types of cast-in-place pile.

The first type is the cast-in-drilled-hole pile, which is described further in this chapter. The second type is the cast-in-driven-steel-shell pile. For this type of pile, a steel shell is driven to a specified tip elevation and bearing value. The ground material within the steel shell is then removed and the steel shell is filled with reinforced or non-reinforced concrete. Refer to Chapter 7 of this Manual for additional information on driven piles. The third type of pile is concrete cast within a permanently installed steel casing. For this type of pile, a steel casing is installed to a specified tip elevation using any approved means; the soil inside the casing is removed by drilling and then filled with reinforced concrete. The fourth type is a rock socket filled with concrete; which is similar to a cast-in-drilled-hole pile, but placed in rock and usually below a permanently installed steel casing that has had the rock removed and ultimately filled with reinforced concrete.

The Standard Specifications contain much of the information necessary to

administer the construction of CIDH piles. Section 49-4 contains information on the construction methods. Section 52 contains information on pile bar

reinforcement. Section 90 contains information on the concrete mix design, transportation of concrete, and curing of the concrete used for CIDH piles.

The special provisions contain job-specific requirements and revised

specifications. Because the CIDH pile specifications are continually updated and ground conditions vary from project to project, it is very important that the Engineer carefully review the special provisions and any revised specifications noted should be discussed with the Contractor.

Drilling Equipment

The drilling auger is the most commonly used drilling tool for drilling holes for CIDH piles. Augers may be used in granular and cohesive materials.

There are two basic varieties of augers—the standard short section (Figure 6-1) and continuous flight. Both have flights of varying diameter and pitch.

Continuous flight augers have flight lengths that are longer than the hole to be drilled. They are generally lead-mounted. The power unit is located at the top of the auger and it travels down the leads with the auger as the hole is drilled.

Drilling is performed in one continuous operation. As the auger moves down the hole, the drilling action of the flights forces the drill cuttings up and out of the hole. Hence, much material has to be shoveled away from around the drilled hole. Continuous flight augers are most commonly used for short piles, such as

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those used to support soundwalls or standard retaining walls, or for predrilling driven piles. They may also be used where overhead clearance is not a problem.

FIGURE 6-1