Installation of Sheet Piles

One of the important characteristics of the vibratory technology of pile driving in contrast to the impact method consists in the fact that, in most cases, it is necessary to fasten the sheet pile rigidly with the vibrating driver, and this operation is carried out in the horizontal position at ground level or on special supports with subsequent raising of the vibrating driver with the pile.

The choice of vibrator or impact-vibration hammer for pile driving or extraction is made as a function of the geological conditions, the type of pile, its length, the depth of installation, and also the technological scheme used for effecting the operations. The pile should be driven using self-propelled cranes or pile drivers.

The cranes or pile drivers should satisfy the following requirements:

• •  The height of the crane boom should permit the lifting of the sheet pile arrangement with the vibrating driver fastened to it into the interlock of the sheet pile previously driven;
• •  The outreach of the crane boom should be sufficient to bring the vibrating driver to the sheet pile and permit placement of the raised sheet pile with vibrating driver on the site of installation without moving the crane;
• •  The load-lifting capacity of the crane or pile driver should be sufficient to lift the sheet pile to be driven with the vibrating driver fastened to it.

The preparatory work, performed prior to beginning the pile driving, includes levelling of the land, the layout of the plan of the pile structure, establishment of the guides (templates) for pile driving (if necessary,) and delivery of the piles to the site and their preparation for driving.

The driving of a pile with vibrating drivers is divided into the following basic operations:

• •  Servicing and fastening of the sheet pile in the head of the vibrating driver;
• •  Raising and placement of the sheet pile at the driving site;
• •  Driving the sheet pile;
• •  Detachment of the vibrating driver from the driven sheet pile.

During the vibratory driving of the sheet pile, its connection with the vibrating driver should have an assured immobility; this is accomplished with the aid of a hydraulic head or wedge clamp.

During servicing, the sheet pile is placed near the site of the operations on a support (cross beam) with a height of 1—1.5 m so that the upper end projects 1—1.2 m beyond the cross beam.

During the driving of the sheet pile, it is necessary to keep track of the state of the cable and the hook of the crane, to which the vibrating driver is suspended.

The rate of lowering of the crane hook should be such that the crane does not inhibit the installation of the sheet pile; in addition, there should not be excessive free cable because with a great length of the sheet pile it is possible that it could buckle under the weight of the vibrating driver fastened on it. The cable is fully slackened in the final stage of the driving.

The following deviations from the planned position are possible during the driving of the pile:

• •  Deviation of the pile from the vertical in the plane of the alignment;
• •  Deviation of the pile perpendicular to the alignment;
• •  Installation of the sheet pile below the planned mark due to its withdrawal with the adjacent driven sheet pile;
• •  Not driving the sheet pile to the planned elevation.

Elimination of fanning in the case of a slight deviation is achieved by drawing out the pile during installation in a direction opposite the deviation, and with a substantial deviation and the impossibility of its correction by drawing out, by the installation of wedge-like sheet piles. Deviation of the pile from the line of direction is eliminated by drawing out the sheet pile in the opposite direction.

If the drawing out of the sheet pile does not straighten its position, the sheet pile is pulled out and again driven in, using the necessary measures for maintenance of its projected position. Passage of the sheet pile below the projected mark is corrected by its building up or plating.

Incomplete installation of the pile to the projected mark is eliminated by one-two-fold raising of the sheet pile by 0.5-0.8 m and its subsequent reinstallation. Extraction of the pile with the application of vibration is usually effected with cranes.

In a tentative selection of the load-lifting capacity of the crane for the vibro-extraction of a pile that has been in the ground for a short time (less than one month), it is necessary that the force at its hook exceed the weight of the system (the vibrating driver and pile) driven into the ground by at least 2 times.

When the pile has been in the ground for a prolonged period, the force at the crane hook should exceed the weight of the system driven by vibration by 3-4 times. To reduce the force transfered to the crane boom, it is permissible to use vertical props (outriggers,) joined to the crane boom in an articulated manner and based on the ground with the aid of a plate or slab. Prior to vibro-extraction, the vibrator should be rigidly fastened on the sheet pile with the aid of a wedge or hydraulic head. The rigid connection should be assured during the entire process of vibro-extraction.

If the pile has been in the ground for a long time, a preliminary vibration (prior to lifting) is indispensable, the time of which is determined by testing on each object. The crane cable should not be taut in this case. In the following stage it is necessary with the force of the crane to tension the springs until the coils almost touch and continue the vibration up to the beginning of the vibro-extraction under the action of the force of the opening springs.

Further vibro-extraction is effected with the minimum lifting rate of the crane hook, not allowing the complete compression of the shock absorber springs here. In the final stage the extraction of the pile is carried out without vibration.

This article comes from vulcanhammer edit released