Sheet pile installation techniques

Vibration

Vibration is the most commonly used technique for installing and extracting sheet pile through the use of a vibratory hammer. When sheet pile are vibrated, a sinus-shaped vertical pressure is exerted on the top of the sheet pile by a vibratory hammer. The mass of this hammer also acts as a static load on the sheet pile.

The harmonic pressure exerted on the sheet pile by the vibratory hammer creates stress waves in the sheet pile wall elements. When the sheet pile are vibrated into the ground, the soil resistance is exceeded by the stress waves. The breakdown of the ground resistance due to the large number of stress changes is more important here than with pile-driving, because the size of the particle velocities occurring in a cross-section of the sheet pile is considerably smaller than with driving.

Advantages of vibration are:

- the high speed at which the sheet pile can be inserted to the required depth for the appropriate combination of soil, sheet pile and vibratory hammer.

- The ground breaks down, so that the sheet pile encounters significantly reduced resistance and much less force is required. This greatly reduces the risk of deformation or declutching.

- The possibility of making corrections during the vibrating process, so that placement can be more accurate.

- The speed of the work means that the disruption to the environment is of short(er) duration.

Driving

When sheet pile is driven, an extremely high, pulsating load is applied repeatedly to the top of the sheet pile. This can be done through the free fall of the driving hammer, which can be driven by steam, diesel or hydraulically. With driving, a sufficiently high stress wave can temporarily exceed the ground resistance along the shaft and at the point. The sheet pile will sink permanently. The following types of hammer are fairly common in the Netherlands: impact hammers, drop hammers, hydraulic hammers and diesel hammers.

Pressing

An increasingly important method of installing sheet pile is to press them in. Both driving and vibrating cause vibrations and environmental noise disturbance. Vibrations are often forbidden in busy urban environments or in the vicinity of sensitive adjacent structures. In these cases, static pressing can be used to install or extract the sheet pile.

The pressure force exerted by conventional machines is generally between 600 and 1500 kN. The pressure force is supplied by a hydraulic cylinder. Single piles or quadruple unpunched piles are used for all systems. If the installation is difficult, it can be facilitated by fluidation. The shape and unique interlock shape of the PZC section means it is eminently suitable for this installation method. No soil enters the interlock, and therefore no lumps can arise.

This article comes from gooimeer edit released