What should be paid attention to in the monitoring of deep foundation pits 5

Monitoring items: monitoring of the displacement (horizontal and settlement) of the top of the supporting structure; monitoring of surrounding surface pipelines and building settlement; lateral displacement of soil; Groundwater level monitoring around the foundation pit.

In addition to the above monitoring items, it is necessary to carry out manual inspections around the foundation pit every day to observe the emergence and development of surface cracks, changes and damage of surrounding underground pipelines and buildings, cracks in supporting structures, water leakage, and overload around the foundation pit.

It is also necessary to increase the vertical displacement of the support system.

The principle of selecting monitoring points for deep foundation pits.

1) The monitoring point should be able to fully reflect the stable state of the slope, that is, the monitoring point should be selected at the maximum position of the expected movement (settlement);

2) The deformation law of the slope should be reflected in a section, that is, the deformation curve should be able to be made on the same section;

3) The movement value of the monitoring point is convenient for the stress analysis of the supporting structure;

4) Important parts (dangerous parts) should be encrypted monitoring points;

The characteristics of deep foundation pit construction monitoring are:

1. Timeliness Ordinary engineering measurements generally have no obvious time effect. Foundation pit monitoring is usually combined with precipitation and excavation process, and has a distinct temporality. The measurement results are dynamic, and the measurement results of a day ago (or even a few hours ago) will lose their direct meaning, so the monitoring in the construction of deep foundation pits needs to be carried out at any time, usually 1 time, and may need to be carried out several times a day during the critical period when the measurement object changes rapidly.

The timeliness of foundation pit monitoring requires that the corresponding methods and equipment have the ability to collect data quickly and work around the clock, and even adapt to harsh environmental conditions such as night or foggy weather.

2. High precision The error limit in ordinary engineering measurement is usually in a few millimeters, for example, the error limit in the height difference measured by the building below 60m on the measuring station is, and the environmental deformation rate in the foundation pit construction may be below under normal circumstances, to measure such deformation accuracy, the ordinary measurement method and the instrument department can not be competent, so the measurement in the foundation pit construction usually adopts some special high-precision instruments.

3. Accuracy The monitoring in foundation pit construction usually only requires the measurement of the relative change value, but does not require the measurement of the absolute value. For example, the general survey requires the building to be positioned on the ground, which is an absolute measurement of coordinates and elevation, while in the foundation pit side wall deformation measurement, it is only required to determine the displacement of the side wall relative to the original datum position, and the original position of the edge wall (coordinates and elevation) may not need to be known at all.

Due to this distinctive feature, the construction monitoring of deep foundation pit has its own rules. For example, ordinary leveling requires the front and rear sight distances to be equal to clear the earth curvature, atmospheric refraction, and the non-parallel axis of the level alignment axis and the horizontal tube axis, but in foundation pit monitoring, limited by environmental conditions, the front and rear sight distances may not be equal at all. Such measurement results are not allowed in ordinary measurements, but in foundation pit monitoring, as long as the measurement position is consistent each time, even if the front and rear sight distances are very different, the results are still fully usable.

Therefore, foundation pit monitoring requires as much accuracy as possible. The same instrument is used, in the same location, and by the same observer according to the same scheme.

Yes. The construction monitoring unit is entrusted by the construction unit to monitor the engineering structure itself and the surrounding environment according to the design requirements, and the work content should meet the design requirements, including point layout, instrument monitoring and inspection according to the design or specification requirements.

The third-party monitoring should be entrusted by the construction party (there are also cases where the actual third-party monitoring fee is paid by the construction unit), and the third-party monitoring work is usually carried out according to the contract requirements, which is different from the construction monitoring

1. The third party is not the main unit of the monitoring point layout, and generally checks the monitoring point laid by the construction monitoring unit to see whether it meets the design and site needs (there are also those that are distributed in advance because the construction monitoring unit has not yet entered the site);

2. The on-site monitoring work of third-party monitoring is mainly aimed at checking the quality of construction monitoring, and the monitoring frequency is reduced compared with construction monitoring, and the general workload is about 30 of construction monitoring, but important parts and important nodes are generally required to be monitored according to the design frequency; The third-party monitoring data is compared with the construction monitoring data to determine whether it meets the requirements.