One such set of the groove is placed in accordance with the expected direction of the movement, and if that is unknown, in the N-S direction. Inside the inclinometer casing, there are a string of sensors placed in a continuous array to span the movement area. These sensors successfully pick up the tilt measurement in successive segments, leading to accurate monitoring of the change in the inclinometer casing.
Each of the in-place sensors is equipped with pivoted sprung wheels, that are designed to fit perfectly inside the grooves of the inclinometer casing. Length of spacer tubing is used to estimate the distance between each sensor; the length of each segment over which the tilt is monitored.
Spacer tubing length (mm) = gauge length (mm) – 381 mm
The outside diameter of spacer tubing = 19 mm
When there is any movement in the ground, it is reflected in the displacement of the inclinometer casing. This further leads to a change in the tilt of in-place sensors. The change in tilt is reflected in the change in the output of the sensors, proportional to the tilt.
The sensors are connected to a data acquisition system for real-time monitoring of lateral movement. Keeping one end of the casing fixed, it is possible to achieve a complete profile of the access tubing by concluding the output from successive sensors. The horizontal displacement at different depths can be determined by comparing the many profiles of the tubing.
Now that we know the working of the sensor, let’s move onto the vertical in-place inclinometer components.
In-place Inclinometer Sensor Components
The number of sensors is determined by the depth of the borehole and gage length defined by the user.
Spacer tubing length is decided based on the gage length.
The placement tube length is determined with the help of the depth at which the first in-place sensor is to be placed from the tip of the borehole.
NOTE: In the following context, an SDI-12 interface is used with the sensor. You can find the horizontal and vertical sensors at Encardio Rite.
| Also Read: Inclinometer: Types, How It Works, & Uses |
Vertical In-place Inclinometer – Preparation before Installation
The first step is to install the casing as per the User’s Manual which can be found here.
The second step is to create a concrete platform in such a manner that the mouth of the inclinometer casing is placed around 25mm below the top of the concrete platform. Further, the inner diameter of the cavity of the top casing should be around 150mm.
Once you’re done, place the protective cover over the concrete platform and use the Hilti HLC-M10x80 fasteners provided to mark the location. Now remove the cover, and install the four mounting fasteners on the marked location, which will be used for the mounting of the protective cover.
There are a number of pre-installation checks that need to be carried before starting with the installation procedure.
One of the first things while installing a vertical in-place inclinometer is to check for any damage or destruction to the cable/connector of the sensors.
Each Encardio Rite sensor is marked with a serial number and has two cables attached to them. Check that everything is in place.
NOTE: Keep in mind that the bottom wheel assembly is regarded as the reference point when analysing the data.
In order to correctly lower down the sensors, mark the sensors, with the lowermost sensor to be numbered as sensor 1. You can additionally assign ID or numbers to each sensor, to ensure that no sensor has the same identification.
One end of the cable coming from the topmost sensor is connected in the junction box at the top of the borehole whereas the other end is coupling with cable connector from the lower sensor.
The next step in the installation preparation is to find the A+ side or the top wheel of the sensors, and ensure that they are all towards the direction of movement.
NOTE: The last point is very important as the wheels in the wrong directions can lead to misinterpreted output data which can have serious consequences.
Wire rope assembly that is provided with the instrument is designed with two loops. The smaller loop is attached to the lower end of the bottom wheel assembly. The other end of the wire loop is then fastened to any structure at the top of the borehole, to prevent the whole assembly from crashing down during installation/removal.
The next step is to assemble the lower end of the spacer tubing to the bottom wheel assembly as shown in the pictures.
As shown in the pictures, attach the bottom-most sensor to a wheel assembly.
Secure the spacer tubing to the other end of the wheel assembly.
Repeat the same with all the sensors except the topmost one.
The spacer tubing connected is shown in the pictures.
Top assembly/Suspension bracket:
Fix the wheel assembly to the topmost sensor.
The other end of the wheel assembly is secured with the placement tube.
To the free end of the placement tube, attach the suspension kit.
NOTE: The needed fasteners are supplied with the product mounted on the assemblies except the ones used for fixing the IPI sensors to the gage tubing. They are packed separately.
| Also Read: Digital Inclinometer System: Introduction & How does it Work |
Vertical In-place Inclinometer Installation Procedure
Seat the assemblies in a line according to their order of installation.
Place the bottom assembly into the inclinometer casing, ensuring that the safety wire rope is held securely enough to not accidentally slip the assembly down into the casing.
NOTE: The wheels in the casing grooves should be aligned in such a manner that the top/fixed wheel points towards the expected movement direction.
Enter the retaining rod in the hole which is at the top end of the spacer tubing, and then place the assembly on the top of the casing with the help of the retaining rod.
Attach the bottom-most or the first sensor assembly to the lowermost spacer tubing. Using cable ties, securely the signal cable of the sensor the wire rope to the spacer tubing.
The next step involved removing the retaining rod, lowering down the assembly into the borehole, and fixing the next sensor assembly to the lowermost sensor’s spacer tubing.
Secure the connector of the lower sensors to the one next to it using your hands, and then inject the retaining rod into the hole of the next spacer tubing.
NOTE: Be careful while fixing the connectors.
The above steps need to be repeated for all the sensors. Make sure you’re taking care of the orientation of the wheels until the suspension kit of the top assembly is successfully resting on the mouth of the inclinometer casing.
Ensure that you’re making use of the retaining rod while lowering down assemblies in every spacer tubing as it helps to prevent any accidental fall into the borehole.
Follow the order of the sensors from bottom to top, noting down the serial number/address of the sensors.
Take extra care to ensure that there is no twisting of installed sensors during the tightening of fasteners as it can lead to wheel damage and then push them out of the grooves of inclinometer casing.
This brings us to the end of the article on Vertical In-place Inclinometer. Hope this was helpful. If you have any doubts or questions, feel free to comment below.