Click above [Big Buffalo Surveying and Mapping] to follow us 1. Overview Deep horizontal displacement monitoring in foundation pit projects is carried out for the retaining wall or other retaining structures of the foundation pit. It can describe the horizontal displacement curve

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1. Overview

Foundation pit engineering Medium and deep Horizontal displacement monitoring is carried out for the retaining wall or other retaining nodes of the foundation pit, and can describe the edge of the retaining wall Horizontal displacement curves in different depth directions can be used to determine the maximum horizontal displacement and its position in a timely manner, which plays an important role in analyzing the stability and deformation of retaining walls and other enclosure structures.

2. Principles for laying out inclinometer points

Since the deep horizontal displacement is reflected by the deformation of the inclinometer tube, the inclinometer point is a point on the plane and a line on the profile. The following factors should be considered when laying out ∶

① Lay out at the position with the largest calculated horizontal displacement on the foundation pit plane:

② There are key monitoring objects around the foundation pit, such as buildings (structures), and the support section closest to them;

③ There is a pair of measured inclined pipes The notch should always be perpendicular to the edge of the foundation pit from top to bottom to ensure that the maximum horizontal displacement of the deep layer of the retaining wall can be measured.

④ Since the probe of inclinometer measures a reading every 0.5m in the tube, the interface position of the inclinometer tube should be accurately calculated to avoid the interface stopping at the probe pulley.

⑤The depth of the inclinometer tube in the wall of the enclosure structure should not be less than the depth of the enclosure wall. The inclinometer pipes in the pile wall of the enclosure structure are buried in the form of binding. During installation, the guide grooves of the upper and lower pipe sections should be aligned with each other smoothly, and the joints should be sealed. The inclinometer pipes should use steel casings within the crown beam range. For protection, the bottom of the pipe should be sealed.

3. Burial of inclinometer tubes

(1) In order to truly reflect the deep horizontal displacement of the retaining wall, the inclinometer tubes should be buried in the piles or walls that constitute the retaining wall as much as possible. When designing the pile position of the measuring point or the groove section of the diaphragm wall, the inclinometer pipe is generally fixed on the steel cage by binding method and sunk into the hole (trough) together with it. Due to the buoyancy of the mud, the binding and positioning of the inclinometer must be firm and reliable to avoid floating or lateral movement when pouring concrete.

When the structure is deep and the inclinometer tube is long, attention should also be paid to avoiding the axial rotation of the inclinometer tube itself to ensure that the measured data truly reflects the deflection in the vertical plane of the edge of the foundation pit. When connecting inclinometer pipe sections, the chutes of the upper and lower pipe sections must be aligned with each other so that the inclinometer probe can run smoothly in the pipe. The joints should be sealed, and flexible sealing materials or sealing strips should be applied.

(2) During specific operations, the following points should be noted:

① The inclinometer tube should be buried and kept vertical;

② There are two pairs of inclinometer tubes. Orientation grooves with directions perpendicular to each other, one pair of which need to be perpendicular to the edge of the foundation pit;

③ When measuring, it must be ensured that the temperature of the inclinometer and the inside of the pipe are basically consistent, so that the display reading is stable before the measurement can be started;

Since the inclinometer measures The relative displacement between the two pairs of rollers (500mm height), so the fixed point (bottom of the tube or top of the tube) in the inclinometer must be selected as the reference point for measurement. Generally, the bottom of the tube is the fixed point.

(3) When the inclinometer cannot be buried in the pile (wall) in time during the construction of the retaining wall, or when measuring the deep horizontal displacement of steel sheet piles, composite soil nail walls, etc., drilling can be used cannot be buried.

Use a small drill to drill holes in the soil layer immediately behind the pile (wall) to be measured. The hole depth is greater than or equal to the depth of the supporting structure to be measured, and the hole diameter is 5~ larger than the selected inclinometer tube. 10cm. When drilling holes in strata with poor soil quality, mud wall protection should be used. While drilling, connect the inclinometer pipes on the ground with special joints, and seal the joints. Then fill the pipe with clean water, and sink it into the hole immediately after drilling. Then fill the gap between the inclinometer pipe and the drill hole with mortar mixed with fine sand or cement and bentonite . The mix ratio depends on the soil layer. physical mechanics performance and geological conditions. Within a few days after burying, the filling material in the hole will solidify and sink, so it must be replenished in time to keep it higher than the hole opening. The

pipe mouth is generally about 20cm above the ground. A protection well is built around it and a sign is erected to avoid damage.The deep horizontal displacement of the retaining wall measured by the inclinometer buried in the soil has a lag process in time, and the actual value is numerically smaller.