1. Purpose of construction tilt monitoring

The observed results are intended to help verify the calculation results in the design, control the impacts of construction, speed up or delay the construction progress, and handle it to prevent incidents.

Monitoring the inclination of neighboring works  and  monitoring of main works  to assess the degree of inclination of the works, thereby calculating a number of parameters to evaluate the stability of the works according to the prescribed standards.

2. Standards for application of tilt monitoring

TCVN 9364:2012: High-rise buildings - Surveying techniques for construction work

TCVN 9398-2012: Geodetic work in construction - General requirements

TCVN 9400:2012 “Houses and tower constructions – Determination of inclination by geodetic method”

TCVN 9381:2012 “Guidelines for assessing the level of danger of building structures”.

3. Inclination monitoring equipment and measures

3.1 Tilt monitoring device

3.2 Tilt monitoring method (coordinate method)

Each design position installs a mirror glued at a height suitable to the location and structure of the building to assess the best inclination and the most stable position.

The tilt value of each datum in each measurement cycle is determined based on the coordinate difference between the measurements and the next period.

The tilt monitoring method is based on the principle of coordinate difference in the X and Y axis directions.

Method and accuracy of measuring the base grid as required (Table 3, page 16, TCVN 9398:2012)

• The measurement accuracy of the basic coordinate grid, the measurement method, the permissible error limit criteria is applied according to the level 1 pass grid. The square error of the angle measurement M = 5'', the error is limited. Relatively allowable, fs/[S]≤1/15000, the limit error is 10”  n (where n is the number of angles in the pass) .
• This inclined monitoring grid is measured with an accuracy equivalent to a level 2 pass.

The monitoring points are inclined with the square error of measuring the angle M = 10'', the error is within the allowable relative limit, fs/[S]≤1/1000.

4. Report on construction tilt monitoring results

4.1 Data processing

Determine the X, Y coordinates of the tilt measurement points and use CAD MAP software to draw the construction diagram.

The cumulative component horizontal distance is calculated by the formula:

The total horizontal distance is calculated according to the formula:

Relative horizontal distance component:

The direction of inclination is calculated according to the formula:

Therefore, the total inclination is calculated by the formula:

4.2 Limits of warnings

According to TCVN 9381:2012, section 5.2.3.4 and section 5.2.5.4

- Warning level 1: When the total inclination exceeds 0.2% x H .

- Warning level 2: When the total inclination exceeds 0.5% x H .

- Warning level 3: When the total inclination exceeds 0.7% x H. 

Where: H is the height of the observation landmark above the ground

4.3 Presentation of results

5. Measure inclination by electronic inclinometer.

During construction to check the change of inclination of the building under construction and adjacent works. One can use an electronic tiltmeter Tiltmeter with an accuracy of 0.1'. Its structure consists of 3 main parts:

- Inclinometer running element unit

- Number reading unit

- Parts of the measuring head

The runner element gives a signal corresponding to the inclination of the wall mounted transducer plate. When measuring, this runner element is in contact with the 3 pins of the probe plate. The measuring head plate is made of steel, has a diameter of 150mm, on the plate there are 4 round tripods with a diameter of 13mm forming a square with a side of 75mm.

Some actual monitoring images