Ductile Iron Pile Products
Ductile Iron Piles are simple, fast and highly effective modular driven pile systems utilizing high-strength ductile cast iron. Pile sections are connected by a proprietary Plug & Drive system, eliminating the need for welding and splicing while providing a high degree of stiffness. With the use of an excavator fitted with a hydraulic hammer, piles are installed in quick succession leading to fast and easy installation.
The DIP system is manufactured from ductile cast iron, which provides high-impact resistance, ultimate strength and high-elastic limit along with superior corrosion resistance, machinability and weldability when compared with traditional steel piles.
Ductile Iron Piles are well-suited for supporting loads in a variety of problematic soil conditions including both cohesive and non-cohesive soils and can also resist compression and tension loads.
Piles & Accessories
End-bearing & Friction Piles
Ductile Iron Piles are manufactured by TRM and employ a Plug & Drive connection system consisting of a tapered socket with an internal shoulder for full engagement at one end and a tapered spigot at the other end. This allows the individual pile sections to be connected together to form a pile shaft of any length without the use of special tools. The connection is formed by elastic deformation of the ductile iron and by cold welding of the friction surfaces. This joint exhibits high-compressive strength and superior resistance to bending, such that the rotational stiffness of the joint is greater than the pile material itself. This connection method eliminates the need for threads, couplers, pins and keys and welding/splicing on the job site.
End-bearing piles transfer their load onto a firm stratum located at a considerable depth below the base of the structure. They derive most of their carrying capacity from the penetration resistance of the soil at the toe of the pile.
The pile behaves as an ordinary column. Even in weak soil, an end-bearing pile will not fail by buckling and this effect need only be considered if part of the pile is unsupported.
Grouted Friction Piles
Grouted friction piles utilize a unique combination of installation speed and high capacity that results in one of the most cost-effective deep foundation systems available.
The pile transfers pressure put on it to the surrounding soil, through friction or adhesion, along the surface where pile sides interface with soil.
Ductile Iron piles are manufactured in standard lengths of 5 meters (16.4 feet). Overall pile lengths are slightly longer and range from 16.9 ft (5.15 meters) to 17.2 ft (5.25 meters). The piles are available in multiple diameters and wall thicknesses to suit the project needs. Details of the dimensional characteristics are provided below:
The same pile sections are used for both end-bearing and friction applications. However, the various accessories are specific to the type of application:
Flat End Point
Standard pile caps for end-bearing (non-friction) piles.
Alternative pile caps for end-bearing (non-friction) piles used when driving through harder material such as partially weathered rock or glacial till.
Conical Grout Shoe
Conical grout caps are used for installation of Friction piles. Grout shoes have a larger diameter than the pile, creating an annulus around the pile which enables the placement of fine-aggregate concrete (grout) over the full length of the pile shaft. Grout shoe diameters range from 220 mm (8.7 in) to 370 mm (14.6 in). Appropriate cap sizes depends on the pile size, soil conditions and desired frictional capacity.
A coupler is used to connect two partial pile sections in place of the standard spigot and socket joint. Couplers are often used when DIPs are being driven in low headroom environments where pile sections must be cut. For standard applications, deploying the Plug and Drive connections, couplers are not required.
The saddles form a load-transfer system for laying water pipes on piling. The saddle ensures uniform distribution of strain loads running from the pipeline into the pile head: for instance dead load, water load, backfilling load, surface loads and rolling loads. The saddle is a solid cast iron molded part, with a specially-calculated width and bend radius for each pipe, in order to prevent punching. A flange in the lower section facilitates laying and a corrosion-resistant rubber layer is used to fit the pipe-saddle contact correctly.
Bearing plates ensure the transfer of downward compressive loads of the superstructure into the pile head, and are an integral part of the pile-foundation connection. Bearing plates are square section steel plates drilled in the center, with variable width and thickness. Drilling enables the insertion of a reinforcement bar in the fresh concrete to ensure the plate’s horizontal alignment on the pile head or for the extension of a center reinforcing bar for added strength or tensile resistance. The bearing plate is installed straight after the pile has been driven and cut to its final length, since the pile head does not need to be trimmed.
Driving Shanks and Grout Box
A driving shank is a specialized attachment that facilitates the driving of the piles using conventional hydraulic breaker hammers. Driving shanks are specially fabricated and hardened to withstand the high driving stresses during installation. Driving shanks are available as 1) dry shanks for installation of end-bearing piles and 2) wet shanks to facilitate grout injection into the pile interior during installation of grouted Friction piles. The grout box is designed to surround the wet shank and provide a grout reservoir during friction pile installation. A wet shank and grout box are used in concert.
Ductile Iron Piles are comprised of grey cast iron, which has been used for commercial pipeline construction since the early 1800s.
The ordinary grey or lamellar graphite undergoes a sophisticated manufacturing process that transforms it into spheroidal graphite or ductile cast iron. This process drastically improves the cast iron’s impact resistance, ductility, tensile strength and flexural stiffness.
Historically, cast iron or grey cast iron was produced in a lamellar form. The material was often brittle and exhibited low strength and impact resistance. Advancements over a half-century ago led to the development of spheroidal or ductile cast iron by adding magnesium to the cast iron before pouring to produce crystallization of graphite in spheroidal form (Figure 2). The development of spheroidal graphite cast iron led to more desirable material properties including improvements in the ultimate and yield strength, tensile and flexural strength, improved impact resistance for drivability and toughness, while maintaining cast iron qualities including machinability, cast-ability and weldability.
The ductile cast iron material used in the piles contains a high recycled content and is comprised of: 90-95% scrap metal iron, approximately 3.7% carbon, and approximately 2.7% silicon. The final chemical composition of the ductile iron piles consist of the materials as shown:
Ductile Iron Piles are manufactured by Tiroler Rohre GmbH (TRM) in Austria. Ductile cast iron used in the fabrication of the piles undergoes a sophisticated centrifugal- or spun-casting manufacturing process to transform the raw recycled material into the finished product. The ductile iron piles are factory prefabricated to precise tolerances. Standardization results in the materials being subject to strict control of its chemical composition and its mechanical properties throughout the fabrication process.
The manufacturing process employs a quality assurance system that is certified in compliance with ISO 9001:2000 “Quality Management Systems”. Further, a variety of other European inspections and certifications are deployed at key stages throughout the manufacturing process to provide regular control of the product and prefabrication process:
- Standard BS EN 10204 inspection process
- ONCERT certification (ONR 22567 regulation)
- European Technical Approval (ETA-07/0169)
Installation & Equipment
How DIPs Are Implemented
Ductile Iron Piles are installed using an excavator-mounted hydraulic hammer fitted with a special drive adapter that advances the pile into the ground using a combination of excavator crowd force and the percussive energy from the hammer as necessary. Currently, two types of Ductile Iron Pile systems are available to resist applied compression and tension loads – end bearing DIPs and friction DIPs. While the same Ductile Iron Piles are used in each system, the installation process and components do vary depending on the method selected for load resistance.
1) End-bearing Ductile Iron Piles are installed by first inserting a flat or pointed driving shoe over the end of the hollow pile. 2) The pile is then driven into the ground using high-frequency impact energy (hydraulic hammer) until the belled Plug & Drive socket end is nearly at the working grade. The driving resistance (time required to drive each meter increment) is observed during driving. 3) The spigot end of the second DIP is then inserted into the socket end of the existing pile and 4) the driving process is repeated. 5) This process continues until the pile terminates on refusal or achieves a required driving criteria (typically 1 inch in 50 seconds). If interior grout is being used, the grout is placed either after the pile achieves the required set or later in the process after multiple piles have been installed.
1) Friction Ductile Iron Piles are installed by first inserting a specially-designed patented conical end cap over the end of the pile. The conical end cap is designed specifically for grouting applications and is larger diameter than the outside pile diameter to facilitate grouting exterior to the pile. 2) The pile is then driven into the ground using high-frequency impact energy (hydraulic hammer) with a specially-designed grout driving shank for the simultaneous pumping of grout. The grout fills the interior of the pile and travels out the conical end cap and alongside the DIP. The grout is pumped to maintain a grout return while creating the grout/soil interface to provide efficient skin friction along the friction DIP. 3) The pile is driven and grout is pumped continuously until the Plug & Drive socket end is nearly at the working grade. The driving resistance (time required to drive each meter increment) is observed during driving. The spigot end of the second DIP is then inserted into the existing pile and the driving / grouting process is repeated. 4) This process continues until the pile extends to a sufficient design depth in the terminating layer to develop the required capacity from a friction bond zone.
One attractive feature of the Ductile Iron Pile system is that it uses conventional earthwork equipment for installation including a medium-duty excavator, hydraulic hammer and grout pump. The amount of specialized equipment and tooling is limited to the drive tools.
1) Base Excavator Machines
Base crawler excavators used for Ductile Iron Piles are typically in the 18 to 30 ton service or operating weight range. Alternatively, vertical-mast equipment with a hydraulic hammer may also be used for installations. The primary factor for base excavator selection is the need to supply the required hydraulic power to the hammer. Therefore, compatibility of the base excavator with the hydraulic hammer is extremely important to both equipment performance and pile installation.
2) Hydraulic Hammer
The hydraulic hammer is a critical part of the Ductile Iron Pile installation process. Selection of the hammer is equally as critical to ensure 1) adequate hammer energy to drive the piles to obtain proper “set” conditions and 2) avoid overstressing and damaging the pile during driving. Factors that should be considered when selecting an appropriate hammer for DIP installation include:
- Pile diameter (98 mm, 118 mm or 170 mm)
- Grout cap diameter (if applicable) – (150 mm to 370 mm)
- Pile length
- Soil conditions (loose, dense, debris fill, etc)
- Pile capacity design:
- End-bearing with “set” criteria
- End-bearing on refusal
It is important that the hammer flow requirements are properly matched with the base excavator for adequate functionality. In addition, connection of the hammer to excavator will depend on the specifics of each piece of equipment. Specialty adaptors may be required to make the proper hammer-excavator connection and need to be investigated by the Installer.
3) Drive Shanks
Specialty drive shanks are required for installation of the Ductile Iron Piles (need link to accessories section of website). A dry drive shank is used for end-bearing installations and a wet or grout shank along with a grout box is used for friction installations. It is imperative that the wet shank only be used for Friction DIP installations to avoid tooling damage. This is largely because the combination of the high energy imparted during the driving process combined with the heating of the tooling that can occur without the presence of grout to act as a coolant during installation.
4) Grout Pump
A grout pump is required for installation of Friction Ductile Iron Piles and also following installation of end-bearing piles if the hollow annular space will be filled with grout or concrete. The pump consists of a piston-driven concrete/grout pump. Although screw pumps can deliver high rates of delivery, they are not suitable for ductile iron pile installations because of the limited discharge pressure generated.
Like hammer selection, it is important that the grout pump be selected so that it is not too small and can’t provide sufficient pressure to introduce the grout at depth in the pile nor is it too large and causes blockages in the line. Manufacturer recommendations indicate a maximum pumping pressure up to 1,000 psi (70 bars) and with a flow rate of 12 cfm (20 m3/h).
During DIP Installation, the grout pump lines are connected to the wet shank / grout box attached to the hammer. Since the connection to the wet shank is a 2 inch (50 mm) connection, hose reducers are often required from the 4 inch (100 mm) or 6 inch (150 mm) line extending from the pump.
Despite the ease of installation of the Ductile Iron Piles, successful performance of the system relies closely on the level of quality control and testing undertaken during installation. The quality control / quality assurance activities consist mostly of monitoring items such as penetration depths, penetration rate, grout pump strokes and termination depths, and also includes full-scale load testing to verify capacity.
Driving and Driving Rates
Quality control during DIP installation is largely focused on monitoring pile penetration and penetration rates (length of time to drive 1 meter increments as marked on the pile section) during driving. The rates of penetration can be used as indicators of geotechnical resistance and even pile capacity. These rates are monitored for both End-Bearing piles and also Friction Piles.
The figure below shows an illustration of driving rates with depth that is obtained for each pile.
The rate of penetration for Friction Ductile Iron Piles is used real-time during pile installation to determine the depth at which the bond layer (competent layer in which the bond zone is developed) is encountered. This is based on noting a marked increase in the driving resistance that is consistent with the anticipated depth of the bond layer.
Depth of Termination
For End-Bearing Piles, the depth of termination is determined based on either refusal on a hard layer (rock) where further penetration or advancement of the pile is not feasible. Alternatively, piles may be terminated when a “set” criteria is met. The “set” criteria is defined as a limited amount of deflection in a particular time limit. Decades of installation and verification testing indicate that a “set” criteria of 1 inch or less of penetration in 50 seconds or longer is adequate to provide the design geotechnical capacity.
Friction Ductile Iron Piles are not designed to be installed to a refusal layer or a specific “set” criteria. Instead, the grouted elements are designed to advance a particular depth into a competent strata to develop sufficient bonding length to generate the required design capacity through friction.
Load testing is an important tool for verifying capacity of both End-Bearing and Friction piles. Load testing for end-bearing applications is performed in general accordance with ASTM D-1143 for static load testing of pile foundations (see load test picture). Alternatively, load testing for Friction piles may be performed in either compression loading generally according to ASTM D-1143 or in tension in general accordance with ASTM D-3689 for axial tensile load testing of piles (see load test picture). Tension testing is an acceptable means to test the bond zone resistance for either tension or compression loads. It is often a preferred method for testing because it eliminates the need for numerous high capacity tension reactions for the load frame.
Ductile Iron Piles are often load tested to levels of 150% to 200% of the design load depending on project requirements. Following a nominal seating load, loads are applied in increments of 25% up to the maximum test load. Each load increment, except for the creep period load increment, is held for a minimum of 15 minutes and until the deflection is less than 0.01 inch/hour or 1 hour passes. The creep load is often represented by the 125% design load. The load is maintained for a minimum of one hour and is held for the minimum of 15 minutes and until the deflection is less than 0.01 inch/hour or 4 hour passes.
The results of the load tests are used to verify the design capacity of the Ductile Iron Pile. Many options for load test interpretation are used in the pile industry including the Davisson Offset, Brinch-Hansen Method and Butler-Hoy Criteria. Determination of the acceptance requirements need to rely on the project performance specifications or local code interpretation.