What Is an Inclinometer?

Inclinometer is a kind of instrument used to measure the apex angle and azimuth angle of engineering structures such as drilling, foundation pit, foundation, wall and dam slope ^[1] .

Divided into portable inclinometer and fixed inclinometer, portable inclinometer is divided into portable vertical inclinometer and portable horizontal inclinometer, fixed type is divided into single-axis and dual-axis inclinometer, currently the most widely used is Portable inclinometer. Inclinometer is an in-situ monitoring instrument that determines the horizontal displacement by measuring the inclination angle of a borehole ^[3]

Inclinometers are usually installed in vertical boreholes that pass through unstable soil to lower stable formations. Use digital vertical mobile inclinometer probes, control cables, pulleys, and readers to observe the deformation of the inclinometer tube. The first observation can establish the initial section of the oblique pipe displacement. Subsequent observations will show changes in section displacements as the ground surface moves. When observing, the probe moves from the bottom of the oblique tube to the top, pauses at a half-meter interval and performs tilt measurement. The inclination of the probe is measured by two force-balanced servo accelerometers. An accelerometer measures the longitudinal position of the incline tube groove, that is, the inclination of the plane on which the measuring wheel is located on the inclinometer probe. The other accelerometer measures the inclination perpendicular to the plane of the wheel. Inclination can be converted into lateral displacement. Comparing the current and initial observation data, the amount of lateral offset change can be determined, showing the movement displacement of the formation. Plotting the change of the offset can get a high-resolution displacement profile. This section view helps determine the magnitude, depth, direction, and velocity of ground motion displacement.

Excellent performance: The portable digital vertical inclinometer has won worldwide praise for its durability, high accuracy and fast response.

Repeatable detection: In order to ensure the same detection on various inclinometer tubes, the inclinometer probe is equipped with a sturdy wheel frame, a sealed axle and a specially designed measuring wheel.

Long service life: The probe has a compact structure that allows it to pass through small radius curves, and the installation life span exceeds that of all other manufacturers' inclinometers.

Computer calibration: Each inclinometer probe is strictly calibrated by a specially designed computer calibration table.

Reliable control cable: The control cable is very durable and easy to handle, and it can remain flexible and durable even at low temperatures. The control cable is also resistant to chemical corrosion and abrasion, and provides excellent spatial stability. The flexible rubber depth marker is permanently and reliably hardened on the cable jacket. The markings are not loose, and there are no burrs that could damage the cable jacket and wires.

Depth control is consistent: The pulley device is a recommended auxiliary device, which helps the operator to achieve unified depth control. Cable clamps, which can only move in one direction, ensure consistent probe positions.

System integrity: The inclinometer system includes high-quality inclinometer tubes, vertical and horizontal active inclinometers, vertical and horizontal fixed inclinometers, recording reading devices, chart analysis software, and special accessories.

The workflow of different inclinometers is similar. GN-1A fixed inclinometer produced by Nanjing Genan Enterprise Co., Ltd. is used to introduce its working process ^[2]

There are five misunderstandings in the use of inclinometers ^[4]

Notes on the use of inclinometer:

1. Use within working temperature, prevent vibration, do not hit the bottom of the hole, prevent the probe from accelerating suddenly, and do not swing the probe with the cable;

2. It is strictly forbidden to use iron wire and metal when bundling cables, and it is better to use winches or ropes to take up the wires;

3. Wipe the probe in time, clean and dry the joints, lubricate the measuring wheel and o-ring, pay attention to moisture, and clean the socket and panel;

4. After use, it is strictly forbidden to keep each connection apart for a long time. This will cause long-term moisture residue in the probe to corrode the connector;

5. After the test is completed, dry the probe and cables, cover the protective cover, and place the probe in the protective box;

6. Return to the room, dry the reader and charge the battery;

7. It is best to allow all joints to air dry indoors.

After decades of theoretical research and application practice, inclinometers have become more and more portable, simple, and automated, and the resulting effects have become more and more obvious. In order to ensure the safety of geotechnical engineering design, construction and operation, various inclinometers play an important role. It is believed that with the informatization construction of geotechnical engineering, various monitoring methods will receive widespread attention ^[6] .

Project Overview

LNG power plant next to the Shell Oil Project in Daya Bay, Huizhou City, Guangdong Province. The plant faces the sea to the east and the hills to the north. The ground treatment area is about 360,600 square meters. The monitoring and testing area of this test area is about 900m ² . According to the engineering geological survey report provided by the Shenzhen Institute of Surveying and Mapping, no weak underlying soil layer such as muddy soil was exposed in the site. The treatment method of dynamic compaction and roller compaction is adopted in the test area. The main purpose of inclinometer monitoring is to monitor the lateral displacement of soil caused by dynamic compaction.

Design layout

According to the design and specification requirements, a total of 3 monitoring points (near the seaside) are arranged, and the locations are arranged according to the requirements of the designer. Inclination monitoring is performed at about 1.5, 2.5, 4.5, and 5.5m below the ground, respectively. After the oblique pipe is buried, observe once a day before the dynamic compaction construction, and make intensive observations during the dynamic compaction construction, and observe once a day thereafter. The total monitoring time is one month.

Monitoring data acquisition and processing

The instrument used for monitoring is the GN-1A fixed inclinometer produced by Nanjing Genan Enterprise Co., Ltd. Through the automatic data acquisition and processing system, the monitoring result table of the inclinometer can be obtained.

Monitoring significance

During the dynamic compaction of the site, the structure and properties of the soil on the site changed. On the one hand, the soil in the center of the site was densified, and even some of the soil was uplifted. Too much energy); on the other hand, the soil in the center of the site will squeeze the surrounding soil, especially the soil near the sea has a volcanic surface with a height of 4-6m. Significant changes occurred, and even a small amount of soil collapse occurred in some areas. Three monitoring holes are arranged at equal distances near the sea. After monitoring the 3 holes arranged, the lateral displacement of the soil caused by the dynamic compaction of the site can be obtained, which provides timely monitoring information for the dynamic compaction of the site, so as to modify the dynamic compaction point distance and compaction energy in time. By monitoring the test area with an area of about 900m ² , the optimal dynamic compaction point distance is 6-7m, and the compaction energy is 2000kN · m. This can not only meet the design value of the bearing capacity of the site foundation, but also prevent the soil near the seashore from tilting or collapsing.