Press-in piling: a construction solution for cut ; cover tunnels

Abstract

Pile driving is potentially the greatest source of ground vibrations and noise generated from piling machines used during construction of a cut and cover tunnel. Design codes place limits on the ground vibrations and noise created by these piling activities. These limits are intended to prevent disturbance to humans and damage (both cosmetic and structural) to nearby buildings. Conventional designs and construction methods are easily applicable to areas that have no environmental restraints. However in an urban environment, the number of restrictions can turn a simple project into one that is virtually impossible. Conventional pile driving has all but disappeared from urban construction arenas, not because of limitations in performance, but because of the emissions of deafening noise and earth shattering vibrations, both of which would not be accepted by even the most tolerant community. Drilled shafts, slurry walls and other cast-in-place foundation or retaining wall systems alleviate some of these problems but add additional problems of their own with large bulky machines and reliance on dusty concrete plants and urban trucking grief. The Press-in Method using Silent Piler has been used to install vast majority of hot-rolled steel sheet piles throughout Japan to form temporary and permanent retaining wall system for cut and cover tunnels but they are still virtually unknown worldwide. This piling method allows construction to proceed at sites where conventional vibratory techniques would cause excessive settlement and in cities where noise regulations limit the use of pile hammers. Initially, the system was designed for sheet piling operation but subsequently technological advancements has allowed the Silent Piler to press-in various piles in different shapes and materials, such as U, Z, H, tubular steel sheet piles and concrete sheet piles. Obvious advantages can be seen as there is no perceived vibration and the noise levels are often quieter than ambient traffic levels. Through its ability to self-move over installed pile heads without crane support and followed by a pile pitching crane that clamps on reaction piles (the GRB System), it enables sheet piling works to be carried out easily on slopes, above water and narrow access areas. This system has advantages over conventional piling techniques in other areas too. For example, the Silent Piler can lay piles accurately around curves and corners as sharp as 90 degrees and, because of its low centre of gravity, the machine can infiltrate restricted spaces like under bridges or between railway tracks -situations under which major disruption would be necessary using established practice. For pressing-in a pile into hard and difficult sub soils, Giken has developed a simultaneous auguring procedure that loosens the rock sufficiently for the Press-in Method to work. Another development incorporates a water jetting that lubricates the movement of piles in the ground. Savvy readers will have noticed that the Silent Piler uses piles that have been installed to anchor the machine to provide reaction for the hydraulic pressure. They will ask themselves the classic chicken and egg question: which comes first? The solution is that when the first pile is ready to be installed, the Silent Piler must be anchored to the ground by sufficient weight to stop it from rising. This counter weight is often provided by the stack of piles waiting to be installed. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.