Technical documentation for soil pressure sensors

1. Overview

Soil pressure sensor is used to measure soilBody pressureThe specialized instrument provides pressure data support in geotechnical engineering monitoring. This document introduces its basic principles, classification, application scope, and key points of use.

2. Measurement principle

The soil pressure sensor measures the soil pressureBody pressureConversion into measurable electrical signals, common technical types include:

Piezoresistive sensorThe resistance value of strain gauges or semiconductor materials changes after being subjected to force, and a voltage signal is output through a Wheatstone bridge circuit. The structure is relatively simple, but it is sensitive to temperature.

Vibrating string typesensorThe tension of a steel string changes under pressure, resulting in a change in its natural frequency. By stimulatingvibratecoilAnd ShizhenMeasure the frequency of the coil and calculate the pressure value. Strong anti-interference ability, suitable for long-term monitoring.

Capacitive sensorPressure causes a change in the spacing between capacitor plates, resulting in a change in capacitance. High sensitivity, but greatly affected by environmental humidity.

Fiber optic sensorBased on fiber Bragg grating (FBG) technology, pressure causes the grating period to change, resulting in reflected wavesLong occurrenceDrift. It has the characteristics of anti electromagnetic interference and distributed measurement, but the cost is relatively high.

3. Product classification

Buried earth pressure gauge

1. Buried inside the soil, measure the soil's own pressure

2. Commonly used in embankment and dam filling projects

3. Consideration should be given to the disturbance impact of the installation process on the soil

Contact type soil pressure gauge

1. Installed at the contact surface between the structure and the soil

2. Used for stress monitoring of retaining walls, lining and other structures

3. The measurement results are affected by the contact surface state

Micro soil pressure gauge

1. Small size, mainly used for indoor testing

2. Not suitable for long-term field monitoring

4. Application Fields

Soil pressure sensors have practical applications in the following projects:

Monitoring the soil pressure on the retaining structure in excavation support engineering; Measurement of lining pressure in tunnels and underground engineering; Evaluating soil stability in roadbed slope engineering; Monitoring dam body and foundation pressure in water conservancy dams; Measure lateral soil pressure in bridge pile foundation.

The specific application effect depends on various factors such as engineering geological conditions, sensor selection, installation quality, etc.

5. Technical indicators

measurement range: 0.1~10 MPa, Choose according to the actual pressure level

measurement accuracy: Generally ± 0.5%~± 2% FS, affected by manufacturing process and environmental conditions

temperature range-20 ℃~+80 ℃ (regular type), expandable for special models

output methodAnalog quantity (4-20mA/0-5V) or digital quantity (RS485/Modbus, etc.)

Protection levelIP67 or IP68, meeting the requirements for field burial

long-term stabilityAnnual drift typically ranges from ± 1% to ± 3% FS

6. Installation requirements

Embedded installation

1. The excavation size should be larger than the shape of the sensor, and the backfill material should be similar to the original soil

2. The force surface of the sensor should be perpendicular to the direction of the principal stress

3. Layered backfilling and compaction to avoid overhead or local stress concentration

4. The cable should have appropriate allowance and waterproof protection

Contact installation

1． The contact surface should be flat and clean, and if necessary, a thin layer of mortar should be used for leveling

2． The fixing method should ensure that the sensor will not slip or fall off

3． Avoid point contact and ensure even force distribution

General precautions

1． Prevent impact, overload, or cable damage during construction

2． Record installation location, direction, number and other information

3． Record initial readings after installation

7. Calibration and maintenance

Factory calibrationManufacturers should provide calibration certificates, including parameters such as range, accuracy, temperature coefficient, etc. Check the calibration validity period before use.

on-site inspectionCheck if the zero reading is reasonable after installation; Regularly check data continuity and trends; Compare the data consistency of multiple sensors on the same cross-section.

Frequently Asked Questions

1. Abnormal fluctuations in readings may be due to poor contact, water ingress, or cable damage

2. Long term zeroDrifting mayRelated to temperature changes and material aging

3. Local stress concentration may lead to high readings

8. Data interpretation

The monitoring data of soil pressure is influenced by various factors:

The heterogeneity of the soil leads to significant differences between adjacent measurement points; Pressure fluctuations caused by construction disturbances, rainfall, temperature changes, etc; The size effect of sensors and the impact of installation quality on measurement representativeness; Structural deformation can alter the pressure distribution on the contact surface.

Therefore, data analysis should be combined with engineering practice, comprehensively judged, and should not rely solely on numerical values to draw conclusions. When necessary, it should be mutually verified with other monitoring methods (such as displacement, strain, etc.).

9. Limitations Explanation

The earth pressure sensor has the following limitations:

1. The measurement is of local point pressure, which may not represent the overall situation

2. The disturbance to the soil caused by the burial process is difficult to completely eliminate

3. The difference in stiffness between sensors and soil may lead to stress concentration

4. Aging phenomena such as creep and corrosion may occur during long-term burial

5. Limited response capability for dynamic fast loading

Therefore, the monitoring plan design needs to be reasonably distributed, and the data application should be carefully judged.