PURPOSE OF INCLINOMETER MONITORING
Monitoring the value and state of horizontal displacement of the fin pile, diaphragm wall or soil in the area affected by the construciton. It is the basis for the Consultant and the Owner to assess the extent and to forecast the development of the displacement. From there, there are handling solutions for horizontal displacement problems.
METHOD OF INCLINOMETER MONITORING
Inclinometer casing is a special-purpose, grooved pipe used in inclinometer installation. It performs three functions:
- It provides access for the inclinometer probe, allowing it to obtain subsurface measurements;
- It deforms with the diaphragm wall or ground, so that inclination measurements of the casing accurately present displacement of walls or ground;
- Its internal grooves control the orientation of the wheeled inclinometer probe.
Casing will be installed in the near – vertical borehole that is drilled through suspected zones of displacement or in the diaphragm wall.
The initial position of the casing is established in a survey taken with the inclinometer probe. Displacement of ground or diagphram wall causes the casing to move from its initial position. The speed, depth, and magnitude of this displacement are calculated by comparing data from the initial survey with data from next survey.
The wheeled inclinometer probe tracks the longitudinal grooves in the casing. It contains two force-balanced servo-accelerometers. One accelerometer measures tilt in a plane of the inclinometer wheels. This plane is known as the A axis. The other accelerometer measures tilt in a plane perpendicular to that of the wheels. This plane is known as the B axis. Tilts reading are typically obtained at 0.5m intervals as the probe is drawn from the bottom to the top of the casing.
Control cable is used to control the depth of the inclinometer probe. It also conducts power and signals between the probe and the readout. Cables are graduated at 0.5-meter intervals.
The screen of digital readout unit displays displacement measurement results obtained from the wheeled inclinometer probe. The results are stored in memory or on a minute record. Digital readout unit model GK-603 or GK-604 manufactured from Geokon Inc. will be used to save data.
The wheeled inclinometer probe is placed in the inclinometer casing. For easy detection of displacement, the displacement measurements are often taken at regular distances 1/2 m or 2 feet from the bottom to the top of the inclinometer casing. In all cases, the record relates with depth or elevation.
When the record of the probe is computed, the tilt is converted to a horizontal distance. Deviation at each distance is called incremental distance deviation. Total distance deviation is called total deviation shows the inclination of the inclinometer casing.
The deviation shows the location of the inclinometer casing.
Displacement shows a change of the location of the inclinometer casing, ie a deviation change. Displacement is calculated by taking the current deviation minus the first deviation. The distance deviation is a change at a distance. Total displacement is the sum of the displacement distance.
- AASHTO T254-80 “Standard Method of Test for Installing, Monitoring, and Processing Data of the Traveling Type Slope Inclinometer”.