How long to install combi walls? For heavy Marine construction and deep foundation applications, constructions usually require high bearing capacity and stiffness. In the absence of conventional sheet pile walls, combi wall systems may be just what is needed to achieve the desired performance.
Methods to install combi walls
How to choose suitable piles when installing
How long to install combi walls
For the installation of permanent combi walls like underground parking lots or basements, panel driving is a prefered choice. The method includes erection of a panel in a rigid template (preferably a two-layer template) prior to driving the sheet pile. Typically, each element of the panel is pushed a few meters into the ground in a specific order. This method of mounting is accurate for tolerances (i.e. interlocks with the sealing system) and can be used in soft soils, effectively preventing sheet piling from leaning. However, this process takes more time to process and penetrate the pile, which requires a longer crane boom to lift the piles.
Pitching and driving this method is very simple: each sheet pile is threaded and driven directly into its final depth. So, it's pretty fast and cheap. Mainly suitable for temporary combi walls whose shape tolerance is not the main problem. Most of these buildings have short sheet piles and leaning is not a predictable problem. Please note that some driving equipment like hydraulic presses can only handle such installations. The use of leader guided piling equipment can greatly improve the installation tolerance.
In cases where heavy equipment or vibration and noise reduction are not available, and in very compact soils, consideration should be given to providing driving assistance: waterjetting, pre-drilling or pre-drilling or blasting. Low-pressure sprays (up to 20 bar) work well in dense granular soils, whereas in hard clays, waterjetting require special equipment capable of withstanding pressures up to 200 bar. Water reduces the friction on the steel surface and, therefore, the drive resistance. In addition, pre-drilling reduces soil resistance.
There are many choice of piles when installing combi walls so we should choose a better one according to the project requirements. Firstly, the connector is welded to the pipe pile so that the pipe and sheet pile are interlocked. Usually, the pipe is driven first. Wall alignment is better achieved by using framework during pipe installation and it is easier to obtain precise spacing between each pipe so that the middle sheet pile portion fits between the two pipes. A variety of pipes and sheet piles can be used to achieve the required minimum wall strength.
Instead of using pipe piles, combi wall designs may specify wide flange king piles with sheet piles. King piles are also equipped with sheet pile interlock device to make it compatible. In places where pipe sizes may sometimes be too large to install, wide flanged king piles can remain relatively compact and drivable while still providing the desired wall performance.
High wall strength and stiffness can be achieved by using only pipe pile or wide flange beam. This wall requires extensive welding of the connectors and is only suitable for very specific situations. High wall strength is especially needed when the height of the soil or water level on either side of the wall varies greatly.
The installation of the combi walls is determined by specific project requirements and is divided into permanent walls and temporary walls. Generally, the higher the accuracy of the installation, the lower the shape tolerance, the higher the load bearing capacity, the longer the installation time is. As short projects only need a couple of weeks, long ones need many months or even a year.
The introducyion of combi walls is as described above. As a reminder, sheet piles, as a vital elemnet in combi walls, can be driven into any type of soil except rock. The selection of mounting methods and piling equipment shall take into account the entire project system. Furthermore, piling can be successful only on the basis of extensive soil surveys.