AM-SIS proximity switch at sheet pile installation

When building earth retaining structures, it is important to install a continuous wall where no soil leaching or leakage occurs. With steel sheet pile walls or combi walls, all elements must be connected in each other's locks to ensure the soil tightness of the wall. Because the locks are in the subsurface or under water, they are often not visually verifiable. With extremely heavy pile driving, or if there are obstacles in the ground, there is a risk of the sheet piles running out of lock, resulting in possible excavation. 

Discontinuous measurement method with Dixeran™

A discontinuous measurement method consists of a sensor that verifies at one level whether the sheet wall has remained in the slot. ArcelorMittal uses the Dixeran™ system for this purpose, which consists of a shear pin placed at the bottom of the leading slot of the sheet piling. In a combi wall, these sensors are installed in the lock of the tubular piles. This lock indicator can detect whether the next plank has remained in the lock by breaking the pin of the sensor as it reaches depth. This is recorded on a measuring box connected to the sensor at the top of the sheet pile. By breaking off the pin, there is assurance that the sheet pile has reached depth in the slot. 

When no change in signal is seen on the box, the sheet pile has run out of lock. However, it is not known at what elevation this happened. If this happens in the upper gauge, it is easy to repair if this were known immediately. If it runs out of lock in the lower meter, there may be no constructive consequence at this depth. Not knowing the height at which the lock opening occurred has implications for the corrective action to be taken.

Continuous measurement method with AM-SIS

Whereas a discontinuous measurement detects at only one level whether the sheet wall is still in the lock, a continuous system measures this over the entire length of the sheet wall. The AM-SIS proximity switch uses an induction switch to detect whether the lock is still connected. This relatively new proximity switch is technically improved and more robust than comparable systems. In several works in the Netherlands and Belgium, the sensor has been successfully applied under heavy pile-driving conditions in recent years. The system gives reliable results regardless of the installation method and type of vibratory hammer and/or pile driver. 

The proximity switch is placed at the bottom of the sheet piling to be installed (also in the case of combi piling). A cable carries the signal from the sensor to the head of the sheet piling, where it is connected to a measuring box. During installation, this monitors along the entire length whether the sheet piling remains in the lock. The moment the sheet pile moves out of the lock, this is registered directly on the measuring box. In that case, the pile can be (partially) pulled out and, after any check for damage, reinstalled. 

Continuous detection

This method differs from the method using a shear pin in that any leakage from the lock is detected immediately. As a result, the exact height is also known, which is important for any corrective measures. 

The sensors are read directly at the sheet piling, but now it is also possible to monitor the installation remotely. Here a data logger is used, where the signal from the sensor becomes visible on an online dashboard. With this data logger, the course of the installation depth of the sheet piling can also be added to the signal. The dashboard thus not only helps with remote tracking of the installation, but also the results of the installation are unambiguously reported.