{precast concrete elements )——T Design-related

bored pile walls |

f methods and tools I excavations supported by casings rexcavations supported by fluids ■-boring with contiguous flight augers Nunsupported excavation ^enlargements /joints f bending of reinforcement -assembly of cages ^ spacers installation /concreting in dry conditions concreting in submerged conditions extraction of casings permanent casings or linings concreting of contiguous flight auger piles -prepacked piles uoss of immersion of tremie or casing piles containing precast concrete elements, reinforcement tubes or permanent casings external grouting of cast in place piles supervision } —-[monitoring of pile construction")-pile testing 1—loading tests

Figure 15.3. Scope of EN 1536, Execution of... bored piles

EN 1536 restricts itself to bored piles with shaft diameters between 0.3m and 3m. Smaller diameter piles are classified as micropiles (see Section 15.2.3).

The structural design of bored piles is governed by European Standards ENs 1990, 1992-1-1, and 1994-1-1 and no further guidance on this subject is provided in EN 1536. Bored piles may be designed as unreinforced concrete elements provided the various actions upon them produce only compressive stresses in the pile (and the foundation is not in a seismic area).

The recommended design strength of concrete for bored piles is between grades C20/25 and C30/37 and the cement content should not be less than 325kg/m3 using dry placement and 375kg/m3 using submerged. Specific requirements for water/cement ratio, fines content, and concrete slump are also given.

The plan deviation of a bored pile from its required position should be < 100mm for piles < 1000mm in diameter and < 150mm for piles > 1500mm in diameter. Linear interpolation may be used for diameters between these limits. The inclination of piles raked less than 1:15 from the vertical should deviate no more than 2% from that specified and that of piles raked between 1:15 and 1:4 no more than 4%.

EN 1536 gives detailed recommendations for monitoring bored pile construction, including subjects in the following general areas: setting out (11 subjects), stabilizing fluid (3), reinforcement (8), fresh concrete (6), concrete placement in dry or submerged conditions (11), continuous flight auger piles (5), pre-packed piles (6), external grouting and shaft-base grouting (3), and cutting-off (11).

For example, the eight subjects covered for reinforcement include delivery of materials, dimensions, fabrication of cages, spacers, and installation of cases. For each subject, guidance is given on control (what should be monitored?), purpose (why should it be monitored?), and frequency (when should it be monitored?).

EN 1536 was published by CEN in 1999, confirmed in 2002 for a further five years, and in 2007 was scheduled for revision by TC 288 following a systematic review.

15.2.2 Displacement piles

Figure 15.4 summarizes the scope of EN 12699,4 which deals with the execution of displacement piles including driven cast-in-place, screwed cast-

in-place, prefabricated concrete (round or square), steel (round or H), and prefabricated concrete conical (round or square) piles with or without enlarged bases.

EN 12699 restricts itelf to displacement piles with diameters greater than 150mm. Smaller diameter piles are classified as micropiles (see Section 15.2.3).

Displacement piles are classified according to how they are fabricated (prefabricated or cast-in-place) and then according to material type (concrete, steel, or timber) for prefabricated piles or casing type (temporarily cased concrete pile or permanently concrete- or steel-cased) for cast-in-place piles.

The structural design of displacement piles is governed by European Standards ENs 1991-1, 1992-3, 1993-5, 1994-1-1, and 1995-1-1 and no further guidance is provided on this subject in EN 12699.

The plan deviation of a displacement pile from its required position must be < 100mm on land but may be higher over water. The inclination of vertical and raked piles must deviate no more than 4% from the specified inclination.

During driving the maximum calculated stress in the pile must not exceed 80% of the characteristic compressive strength of the concrete or timber and 90% of the characteristic yield stress for steel piles. Particular requirements are also given to govern the reinforcement in driven cast-in-place piles, including: 0.5% minimum longitudinal reinforcement; 100mm clear distance between bars; 5mm minimum diameter for transverse reinforcement; and 50mm cover for piles with temporary casing, rising to 75mm for high exposure risks.

For all displacement pile types useful lists are provided for factors that need to be considered as part of the construction process. Specific guidance is given for driven cast-in-place piles to control the driving of tubes adjacent to piles already constructed which states that piles may not be installed within six pile diameters until the concrete has reached the desired resistance. Further limits are also placed depending on the strength of the soil.

Amongst the special requirements discussed for displacement piles are site safety (security of the site, operational safety of driving and auxiliary equipment and tools, and safety of the working practices), noise and vibration hindrance, environmental damage (noise pollution), and impact on surrounding structures and slopes.


-[^formative references I Terms and definitions^-

-[^formative references I Terms and definitions^-

■j equipment and methods

Id c prefabricated piles


■[cast in place displacement piles -(grout j-

{paints, coatings ard other shaft protections}-

■[geometrical construction deviations j-[ sequence of installation ^ {protection of piles j-■[needs for driving assistance^

prefabricated concrete piles steel piles timber piles reinforcement of cast in place piles \ pile shoe pile joint pile enlargement spacing of piles combined piles

Scope of EN 12699 Execution of special geotechnical work — displacement piles

design for impact driving of prefabricated elements

L{Supervision, monitoring and testing ]—^

Figure 15.4. Scope of EN 12699, Execution of... displacement piles

-I cast in place piles

impact hammer vibrating hammer equipment for screw piles equipment for jacked piles auxiliary equipment drive tube , prefabricated concrete piles 1 L- steel piles ' t-timber piles ^■combined piles ^temporary cased piles [handling and installation of -^reinforcement r- concreting

^■permanently cased piles grouting during driving grouting after driving trimming of concrete piles }

driving assistance methods ground movement limiting methods working from floating platform cast in place base enlargements additional methods for special cases design for impact driving of prefabricated elements

L{Supervision, monitoring and testing ]—^

monitoring of pile construction

{testing ]

Specific requirements i noise and vibration hindrance

—(environmental damage (pollution)

impact on the surrounding structures and slopes

Figure 15.4. Scope of EN 12699, Execution of... displacement piles

EN 12699 was published by CEN in 2000 and re-confirmed for a further five years in 2005.

15.2.3 Micropiles

Figure 15.5 summarizes the scope of EN 14199,5 which deals with the execution of micropiles including bored micropiles with diameters not exceeding 300mm and driven micropiles with diameters not exceeding 150mm. Micropiles can be constructed of steel, reinforced concrete, grout, or mortar and are particularly useful where there is restricted access or difficult drilling conditions (obstructions, rock, etc.), but may also be used for standard foundation applications.

The structural design of micropiles is governed by European Standards ENs 1991-1, 1992-3, 1993, 1994-1-1, and 10138-4.

EN 14199 provides guidance on the information required for execution of the works and associated geotechnical investigations. In particular, it requires additional investigations to be carried out if the available information is deemed insufficient. Since the installation of micropiles may require special tools to overcome obstructions, the geotechnical investigation report must record their presence if encountered.

EN 14199 makes no specific requirements relating to the steel used either for reinforcement or as bearing elements, but instead refers to related European standards. For cement grouts, mortars, and concrete used for micropiles, the following specific requirements are stated: minimum unconfined compressive strength of 25MPa at 28 days; a water cement ratio less than 0.55 for grouts and 0.6 for mortar/concrete; and cement content at least 375kg/m3.

EN 14199 contains no details on the structural design of micropiles but refers to other standards particularly the codes dealing with structural materials and EN 1997-1.

A load testing regime incorporating preliminary piles is recommended where conditions are not well known. For micropiles working in compression, at least 2% of the first 100 piles should be tested and then 1% of every 100 piles above. For micropiles working in tension, at least 8% of the first 100 piles should be tested and then 4% of every 100 piles above.

The use of dynamic load testing and integrity testing of micropiles should only be used where there is relevant experience or comparison with static load tests to demonstrate that these methods are suitable.

EN 14199 was published by CEN in 2005 and is due for systematic review by TC 288 in 2010.

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