Lateral support monitoring
Lateral support monitoring
(OP)
We undertake regular monitoring/survey of targets during installation of lateral support (as well as for a certain time period after completion to check that there is not movement, although we all know that with any form of excavation, some form of movement will occur). It has become practice that when monitoring readings of say 5 to 10 mm are recorded, many geotech chaps ignore these results and relate the result to thermal differences and instrument error. What I wanted to know from others out there, what would you accept as thermal or instrument error on say a 200mm thick, shotcreted, mesh reinforced wall? Is 10mm acceptable?





RE: Lateral support monitoring
One can choose an initial point (to remain more or less stable) as reference and then refer everything happening to it; it would be surmised that point doesn't move even if it does, and at any time t all coordinates would be referred to that purportedly fixed poing. Later analysis of the evolution of the shapes will help in deciding what movement to adjudicate to that point itself, and so the evolution of the shape.
RE: Lateral support monitoring
Typically, we would see a 3 to 6 mm change; occasionally a few locations might move on the order of 10 to 12 mm. Same thing - the geotechs didn't seem worried. Movements were always attributed to thermal changes. In our case water wasn't an issue becuase these types of walls drain through the open joints.
I agree with Ishvaaag's approach. Another method is to place sensors on the wall. This gives continuous real-time monitoring.