The performance of retaining structures is often a key requirement for the design and construction of any significant retention wall. This is often carried out using an inclinometer, an instrument that measures the deflection at various depths within specialised casing installed in, or near, the wall.
The Roads and Maritime Service (RMS) Technical Direction GTD 2012/001 “Excavation adjacent to RMS infrastructure“ requires instrumentation and monitoring of cantilevered walls with a retained height greater than 3 m and of propped or anchored walls with a retained height greater than 6 m. The instrumentation is to include a minimum of two inclinometers installed to at least 3 m below the toe level of the excavation.
The inclinometer casing is essentially a PVC pipe with grooves in the sides to allow the inclinometer to run along two axes (often referred to as an ‘x’ and ‘y’ axis that is perpendicular to each other). The casing can be installed within a boreholes drilled behind the retaining wall. Where the retaining wall is constructed using bored or Continuous Flight Auger (CFA) piles, the casing can be installed directly into the pile by tying it to the reinforcing cage (prior to installation and carefully inserted into the pile hole. Once installed, baseline readings are taken with the inclinometer . Subsequent readings are then compared to the baseline data. The RMS requires readings to be taken at several critical stages during excavation. When threshold limits, established by the RMS, are exceeded then various actions need to be followed. Examples of the type of data obtained from inclinometer are shown
Care must be taken during excavation and anchor drilling not to damage the inclinometer casing. If the casing is damage then reinstallation is generally required (often difficult and expensive). If the damage is not too extensive, sometimes smaller casing can be installed inside the damaged original casing, however, this is generally a difficult and expensive exercise.
Douglas Partners has extensive experience with inclinometers and is able to assist with the installation and monitoring on your project.