Bank foundation settlement deformation monitoring method based on pore pressure measurement

Abstract

The invention relates to an embankment foundation settlement deformation monitoring method based on pore pressure measurement, which comprises the following steps: S1, carrying out site survey before embankment construction, determining the length of a communication hose, fixing a pore water pressure gauge into the communication hose, and laying the communication hose at the positions of a to-be-monitored section and a datum point; s2, water pressure P of the monitoring points and the datum points is collected and obtained; s3, converting the water pressure P obtained in the step S2 into a corresponding water column height h; s4, calibrating a water column height difference between the reference point and the monitoring point before construction; s5, calculating the settlement amount si of the monitoring point at the Ti moment in the construction process, namely, the settlement amount si is the difference value between the water column height difference between the monitoring point at the Ti moment and the reference point and the initial water column height difference calibrated in the step S4; the method has the advantages that underwater real-time settlement monitoring including the early stage of causeway construction can be achieved, the process is efficient and economical, and meanwhile the precision of monitored data meets the engineering requirement.

Description

Technical Field

[0001] The invention belongs to the field of water conservancy engineering, relates to the technical field of water conservancy engineering monitoring, and in particular to a method for monitoring embankment foundation settlement deformation based on pore pressure measurement. Background Art

[0002] There are a large number of deep soft soils distributed in my country's coastal areas. The foundation soil has high water content, high compressibility, low strength and poor permeability. Not only is the bearing capacity very low, but also under the action of embankment load, it will produce considerable settlement, deformation and differential settlement. The settlement and deformation last for a long time. Settlement monitoring is one of the important technical indicators to ensure the safety of embankment construction and project quantity prediction.

[0003] The settlement of the embankment project includes two parts: one is the settlement before the embankment is out of water, and the other is the settlement after the embankment is out of water. For the settlement monitoring of this type of project, the manual leveling observation method has relatively high site requirements, and observation can only be carried out after the embankment is out of water. Compared with some automated settlement observation methods, although the settlement measurement of the underwater part can be realized, it is usually necessary to set up a steel platform to place the monitoring equipment. The cost of burying the steel platform and the equipment is often high. The stability of the platform will be greatly affected by the on-site environment, and the maintenance difficulty and cost are also high. In addition, before the embankment is out of water, the settlement that occurs during the underwater construction process cannot be observed by traditional optical measurement methods, and is often missing data. The above has brought considerable challenges to the settlement and deformation prediction of embankment projects, the formulation of construction plans, and the control of potential risks.

[0004] Therefore, the existing direct acquisition method has obvious technical defects in adapting to the real-time settlement monitoring of the embankment foundation during the underwater construction period, and cannot meet the actual needs of the embankment project. Based on this, it is of great significance to study indirect means to make up for the lack of settlement data in such projects and explore new methods for underwater settlement monitoring of embankment foundation that are both efficient and economical. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems existing in the prior art and to provide a method for monitoring embankment foundation settlement and deformation based on pore pressure measurement.

[0006] To achieve the above object, the technical solution adopted by the present invention is: A method for monitoring embankment foundation settlement deformation based on pore pressure measurement comprises the following steps: S1. Conduct on-site survey before dike construction to determine the length of the connecting hose, fix the pore water pressure gauge into the connecting hose, and lay the connecting hose at the section to be monitored and the reference point; S2, collecting and obtaining the water pressure P at the monitoring point and the reference point; S3, converting the water pressure P obtained in step S2 into the corresponding water column height h; S4. Before construction, calibrate the water column height difference between the benchmark point and the monitoring point; S5. Calculation during construction T i The settlement amount si at the monitoring point at time Ti is the difference between the water column height difference between the monitoring point and the reference point at time Ti and the initial water column height difference calibrated in step S4.

[0007] Preferably, in step S2, the calculation formula of the water pressure P is as follows:

[0008] Where P is water pressure, unit is kPa; K is pore water pressure gauge calibration coefficient, unit is MPa / Hz 2 ; f 0 is the initial reading of the pore water pressure gauge, in Hz; f i It is the pore water pressure gauge observation reading, unit is Hz.

[0009] Preferably, in step S3, the conversion formula of the water column height h is: in, Indicates the density of seawater in kg / m 3 , g represents the acceleration due to gravity, unit is m 2 / s.

[0010] Preferably, in step S4, the calibration method of the initial water column height difference is: the initial water column height at the reference point is H0, and the initial water column height after the water pressure gauge at the monitoring point is buried is H m0 ; The initial water column height difference between the two is the position difference between the two measuring points after the initial pore water pressure gauge is installed. :

[0011] Preferably, in step S5, the calculation formula of the settlement amount si at time Ti is: Among them, H 0i for T i The height of the water column at the reference point at that moment; H mi is the water column height obtained at the monitoring point, is the initial water column height difference calibrated in step S4.

[0012] Preferably, in step S1, the reference point is set in a stable stratum outside the construction embankment, and the reference point fixing piles need to penetrate into the hard soil layer; the pore water pressure gauge of the monitoring point is buried in the shallow soft soil layer below the embankment, directly reflecting the soil compression settlement caused by the embankment load.

[0013] Preferably, the measurement accuracy of the pore water pressure gauge is not less than 0.01 Hz, and the corresponding settlement calculation error range is ±0.28 mm, meeting the accuracy requirement of engineering settlement monitoring error less than 3 mm.

[0014] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention include: The present invention is based on pore pressure theory and pore pressure measurement technology, which converts settlement changes into water pressure changes. Through technical innovations such as pore pressure-water column height conversion, tidal level linkage offset, and low-cost hose laying, it achieves high-precision, full-cycle, and low-cost underwater settlement monitoring of embankment foundations, solves the technical bottleneck of missing settlement data for embankment projects in deep soft soil areas, and provides a reliable tool for safe construction and risk control of similar water conservancy projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the embankment foundation settlement deformation monitoring method based on pore pressure measurement of the present invention.

[0016] Figure 2 It is a schematic diagram of the principle of burial of the piezometer and initial settlement calculation of the present invention.

[0017] Figure 3 It is a schematic diagram of the position change of the piezometer at the monitoring point and the principle of settlement calculation during the implementation of the project of the present invention.

[0018] Figure 4 It is a schematic diagram of the water column height results of the benchmark point and the monitoring point measured during the observation period of the present invention.

[0019] Figure 5 It is a schematic diagram of the dike load loading during the observation period of the present invention.

[0020] Figure 6 It is a comparison result diagram of the dike settlement monitoring values ​​using different methods during the observation period of the present invention. DETAILED DESCRIPTION

[0021] like Figure 1 As shown, the present invention provides a method for monitoring embankment foundation settlement and deformation based on pore pressure measurement, comprising the following steps: S1. Before the construction of the dike, after the site survey, determine the length of the connecting hose according to the actual needs of the project, then fix the pore water pressure gauge to a fixed position in the connecting hose, and then lay the hose at the section to be monitored and the reference point, and bury the system in relative position; Figure 2 As shown in the figure, specifically: the location of the benchmark point should be a certain distance away from the construction embankment, and the fixed piles of the benchmark point erection platform need to penetrate into the harder soil layer to ensure the safety of the benchmark point and the validity of the on-site data; according to the monitoring plan, the piezometer at the monitoring point is buried in the shallow soil layer below the embankment to be monitored, so that the settlement data is the embankment settlement.

[0022] S2. Collect and obtain the water pressure P at the monitoring point and the reference point. The calculation formula of the water pressure P obtained by the water pressure gauge is as follows: in, P is the water pressure, unit is kPa; K is the pore water pressure gauge calibration coefficient, unit: MPa / Hz 2 ; f 0 is the initial reading of the pore water pressure gauge, in Hz; f i It is the pore water pressure gauge observation reading, unit is Hz.

[0023] S3. Use the following formula to convert the water pressure P into the corresponding water column height h : in, Indicates the density of seawater in kg / m 3 , g represents the acceleration due to gravity, unit is m 2 / s.

[0024] In this embodiment, the accuracy of the method of observing settlement using a water pressure gauge mainly depends on the accuracy of the pore water pressure gauge; the accuracy of a conventional pore water pressure gauge is 0.01 Hz, and the accuracy of the converted settlement calculation is about ±0.28 mm, which meets the accuracy requirements for monitoring the embankment project.

[0025] S4. Before construction, calibrate the water column height difference between the benchmark point and the monitoring point (theoretically, the buried elevation of the benchmark point and the monitoring point should be consistent, but there is still an error in reality, so calibration is required before construction). Figure 2 As shown in the figure, the monitoring point is determined according to the specific monitoring plan, and the pore water pressure gauge is buried in the shallow soil layer below the planned monitoring embankment to better monitor the settlement changes of the embankment during construction and use. Among them, the initial water column height at the reference point is H0, and the initial water column height of the water pressure gauge at the monitoring point after being buried is Hm0. Both are affected by the tide level and are variables; and the difference in the initial water column height between the two is the initial position difference between the two measuring points after the pore water pressure gauge is installed. : .

[0026] S5. The water column height difference between the reference point and the monitoring point during the construction process is as follows: Figure 3 As shown in the figure, it can be seen that after the linkage water pressure adjustment, the influence of tide level on the observation point and the reference point is consistent, that is, it can be automatically offset during the calculation process; based on this, T i The height of the water column at the reference point at that moment is H 0i ; The water column height obtained at the monitoring point is H mi , at this time, the embankment settlement caused by the increase of additional load s iCalculated by the following formula: .

[0027] The feasibility of the present invention can be verified by comparing different types of data on site: Figure 4 This is a schematic diagram of the water column height results of the benchmark point and the monitoring point during a certain observation period (December 26, 2018 to January 15, 2019); Figure 4 It can be seen that the shapes of the water column height curves at the benchmark point and the monitoring point are consistent, and the water column height at the monitoring point and the benchmark point gradually increase, indicating that after the linkage water pressure adjustment, the two monitoring points are affected by tidal changes, and the phase difference is basically the same, that is, the influence of this variable can be basically eliminated.

[0028] Figure 5 This application mainly reflects the schematic diagram of the dike load during the observation period (December 26, 2018 to March 1, 2019); Figure 6 Summarize the settlement monitoring data obtained by the present invention in the underwater construction section and compare them with the settlement monitoring data obtained by the conventional settlement plate method after the dike is out of water; Figure 6 It can be seen that compared with the traditional settlement plate monitoring data, the monitoring error of the present invention after the water is discharged from the dike is only 0.1-2.4mm, the curve trend is completely consistent, and it has a certain reliability; among them, the initial value of the settlement plate monitoring data is -62.7mm, which is the settlement value measured by the present invention on the same day; it can be seen that in the same time period, the curves of the two methods can basically match, and the maximum difference is 0.1mm~2.4mm, which can basically meet the needs of this type of engineering.

[0029] It should be noted that: when the present invention performs pore pressure measurement, the fixed platform column can be initially buried in the foundation soil 2 on the seabed for fixation (such as Figure 2 As shown), then fix the pore water pressure gauge into the connecting hose so that the connecting hose is fixed to the fixed platform column, and then select the position according to the laid parts; The present invention realizes for the first time the real-time monitoring of the settlement during the underwater construction phase before the dike emerges from the water, and completely obtains the settlement data of the entire construction cycle (from underwater to above water), solving the problem of missing key data in soft soil foundation engineering. In addition, through the dynamic conversion mechanism of pore pressure-water column height, the high-frequency collection of settlement data at the minute level (compared with the day / week cycle of manual leveling) is realized, which significantly improves the timeliness of construction safety warning. The present invention is based on pore pressure theory and pore pressure measurement technology, which converts settlement changes into water pressure changes. Through water level linkage adjustment, the influence of tidal water level changes on settlement is offset. It can realize real-time underwater settlement monitoring including the initial stage of dike construction, making the process efficient and economical. At the same time, the accuracy of the monitored data meets engineering requirements.

[0030] The above-mentioned related explanations and descriptions of the embodiments are for the convenience of those skilled in the art to understand and apply the present invention. It is obvious that those familiar with the art can easily make various modifications to these contents and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above-mentioned related explanations and descriptions of the embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for monitoring embankment foundation settlement and deformation based on pore pressure measurement, characterized in that: The following steps are involved: S1. Conduct on-site survey before dike construction to determine the length of the connecting hose, fix the pore water pressure gauge into the connecting hose, and lay the connecting hose at the section to be monitored and the reference point; S2, collecting and obtaining the water pressure P at the monitoring point and the reference point; S3, converting the water pressure P obtained in step S2 into the corresponding water column height h; S4. Before construction, calibrate the water column height difference between the benchmark point and the monitoring point; S5. Calculation during construction T i The settlement amount si at the monitoring point at time Ti is the difference between the water column height difference between the monitoring point and the reference point at time Ti and the initial water column height difference calibrated in step S4.

2. The method for monitoring embankment foundation settlement and deformation based on pore pressure measurement according to claim 1 is characterized in that: In step S2, the calculation formula of the water pressure P is as follows: Where P is water pressure, unit is kPa; K is pore water pressure gauge calibration coefficient, unit is MPa / Hz 2 ; f 0 is the initial reading of the pore water pressure gauge, in Hz; f i It is the pore water pressure gauge observation reading, unit is Hz.

3. The method for monitoring embankment foundation settlement and deformation based on pore pressure measurement according to claim 1 is characterized in that: In step S3, the conversion formula of the water column height h is: in, Indicates the density of seawater in kg / m 3 , g represents the acceleration due to gravity, unit is m 2 / s.

4. The method for monitoring embankment foundation settlement and deformation based on pore pressure measurement according to claim 1 is characterized in that: In step S4, the initial water column height difference is calibrated as follows: the initial water column height at the reference point is H0, and the initial water column height after the water pressure gauge at the monitoring point is buried is H m0 ; The initial water column height difference between the two is the position difference between the two measuring points after the initial pore water pressure gauge is installed. : .

5. The method for monitoring embankment foundation settlement and deformation based on pore pressure measurement according to claim 1, characterized in that: In step S5, the calculation formula of the settlement amount si at time Ti is: Among them, H 0i for T i The height of the water column at the reference point at that moment; H mi is the water column height obtained at the monitoring point, is the initial water column height difference calibrated in step S4.

6. The method for monitoring embankment foundation settlement and deformation based on pore pressure measurement according to claim 1 is characterized in that: In step S1, the reference point is set in a stable stratum outside the construction dike, and the reference point fixing pile needs to penetrate into the hard soil layer; the pore water pressure gauge of the monitoring point is buried in the shallow soft soil layer below the dike, directly reflecting the soil compression settlement caused by the dike load.

7. The method for monitoring embankment foundation settlement and deformation based on pore pressure measurement according to any one of claims 1 to 6, characterized in that: The measurement accuracy of the pore water pressure meter is not less than 0.01 Hz, and the corresponding settlement calculation error range is ±0.28 mm, which meets the accuracy requirement of engineering settlement monitoring error less than 3 mm.

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