Finite element temperature calculation and detection method for pile forming effect of jet grouting pile

Abstract

The invention discloses a finite element temperature calculation and detection method for the pile forming effect of a jet grouting pile, and relates to the technical field of jet grouting pile construction quality detection and monitoring. The hydration heat based on the curing material is obtained before guniting, after a pile is formed, temperature measuring devices are reasonably arranged according to the size of a jet grouting drill rod and the range of the inner side and the outer side of the detected pile diameter, temperature informatization collection is conducted on the arranged temperature measuring devices, and due to the fact that the hydration heat of the curing material is obviously different from the temperature of the surrounding soil body, the temperature of the pile can be accurately measured. A temperature field prediction model is established by analyzing heat transfer parameters of solidified soil, and parameters used for judging the pile diameter of a formed pile, the uniformity of cemented soil and the use amount of cement are obtained to judge the pile forming effect of the jet grouting pile. The pile forming effect and the construction quality can be guaranteed; the method is high in detection precision, flexible, lossless and suitable for engineering popularization and application; a finite element temperature calculation technology is introduced into detection of the jet grouting pile, a multidisciplinary cross research means is provided for scientific research of the jet grouting pile, and informatization detection and monitoring data collection are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of jet grouting pile construction quality detection and monitoring, and in particular to a finite element temperature calculation detection method for the jet grouting pile forming effect. Background Art

[0002] The rotary jet pile method is a new technology used for foundation reinforcement and water-stop curtain. It has the advantages of wide application range, convenient construction, high efficiency and simple operation. It is suitable for foundation anti-subsidence, anti-seepage and foundation reinforcement. The principle of this technology is to use a drilling rig to drill the rotary jet drill rod to a predetermined design depth, and then spray out the configured high-pressure cement slurry. At the same time, the grouting pipe is slowly and uniformly lifted, and can also rotate or swing to shear and disturb the soil and fill it with cement slurry. After the cement slurry solidifies, a pile body that meets the requirements can be formed underground. Obviously, whether the diameter of the rotary jet pile, the uniformity of cement soil and the amount of cement can meet the design requirements is the focus of construction quality control, and the rotary jet pile belongs to an underground hidden project and is not directly measurable. The construction process and parameter setting of the rotary jet pile are closely related to the foundation conditions. The process parameters need to be determined through typical construction before construction. Rapid determination of the process and parameters can shorten the construction period. Therefore, it is very important to develop a short-term, non-destructive and indirect detection method for the quality process control of the rotary jet pile.

[0003] Conventional methods for testing the effect of pile formation are only excavation inspection, core drilling, standard penetration test, dynamic penetration test and static penetration test. The jet grouting pile adopts the core drilling method, standard penetration test, dynamic penetration test and static penetration test. It can only be tested after reaching the specified strength, which generally takes 28 days. Within 3 days after the dry construction of the cement soil mixing method, the uniformity of the upper body can be checked by light dynamic penetration test. After 7 days of pile formation, the pile head is inspected by shallow excavation. The load test should be carried out 28 days after the pile is formed. For projects with strict requirements on deformation, the cement soil compressive strength test should be carried out by drilling and coring 28 days after the pile is formed. It cannot meet the typical construction and process quality control requirements under tight construction period conditions; the core drilling method is a destructive test; the electromagnetic method is not widely used at present due to the complexity of the detection method and the low data accuracy.

[0004] Therefore, in order to scientifically and accurately test whether the diameter of jet grouting piles can meet the design requirements, it is urgent to find a quality testing method for jet grouting piles to judge the compliance of the pile diameter, cement soil uniformity and cement dosage. Summary of the invention

[0005] The purpose of the present invention is to address the problems existing in the above-mentioned prior art and to provide a short-term, non-destructive, indirect detection method and system for the pile diameter, cement soil uniformity and cement dosage compliance of jet grouting piles. The method adopts a mathematical model based on finite element temperature calculation prediction-actual measurement, and finally judges the pile diameter, cement soil uniformity and cement dosage through a temperature monitoring system and digital modeling decision-making. This not only makes the detection results more accurate and reliable, but also easier to operate, and completes information data collection and result judgment through a temperature acquisition system and a digital modeling decision-making system.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a finite element temperature calculation detection method for the pile forming effect of jet grouting pile, characterized in that it comprises the following steps: Step A, 13 temperature measuring rods are arranged crosswise according to the size of the jet grouting drill rod and the inner and outer ranges of the detection pile diameter: 1 rod is arranged at the center point, 4 rods are arranged at 1 / 2 of the pile diameter, at the pile boundary and at 1 / 2 of the pile diameter from the pile boundary, 3 temperature detectors are installed in each temperature measuring rod, and the total number of temperature detectors is 39; Step B: collect temperature from the deployed temperature detectors to realize online information collection of the temperature at each measuring point, and establish and draw temperature rise and temperature difference change diagrams based on the real-time on-site temperature data obtained; Step C, through the previous similar physical test and numerical simulation, and based on the heat transfer algorithm of hydration exothermicity of solidified materials, obtain the pile characteristic parameters under multivariable conditions and the characteristic values ​​that can highlight the abnormal information of grouting; Step D, by comparing the established and drawn temperature rise and temperature difference change diagram with the real-time detection temperature data result, determining the temperature boundary value; Step E: adopt a mathematical model based on finite element temperature calculation prediction and actual measurement, use a temperature monitoring system, make a digital model decision, use the second-order derivative to derive the temperature change rate, and determine the temperature and temperature difference boundary values ​​through the temperature change slope. Finally, determine the pile quality process control through the predicted temperature field model established based on the hydration heat of the solidifying material and the heat transfer parameters of the solidifying soil obtained before spraying.

[0007] In step C, the aforementioned preliminary similar physical test and numerical simulation are carried out according to the following steps to obtain characteristic parameters that can highlight the abnormal grouting information: (1) The materials used and their thermal properties; the specific heat, thermal conductivity, convection coefficient, thermal expansion coefficient, heat release coefficient function, and Poisson's ratio characteristic value parameters are derived by fitting the measured temperature field values; (2) Test the hydration heat of the solidified material and the heat transfer parameters of the solidified soil; (3) Establish the temperature field under different curing materials through finite element temperature calculation and collect numerical simulation process; (4) Based on the numerical simulation results, the sensitivity parameters under different grouting conditions are obtained, and the pile characteristic parameters under multivariate conditions and the characteristic values ​​that can highlight the grouting anomaly information are obtained based on statistical methods.

[0008] In step A, the center point of the pile should be marked immediately after each pile is constructed.

[0009] In step B, the total collection time is 72 hours, and the temperature measuring rod is taken out in time after the collection is completed.

[0010] The real-time detection system involved in the present invention mainly consists of two parts: an underground detection device and an above-ground detection system; the underground detection device mainly consists of a temperature measuring device and a temperature measuring rod; the above-ground detection system mainly consists of a data transmission harness, a temperature measurement data collector and a data processing platform.

[0011] The present invention realizes real-time detection of the pile-forming effect of jet grouting piles based on the heat transfer algorithm of hydration exothermic heat of solidifying materials to obtain pile-type characteristic parameters under multivariable conditions and the characteristic value technology that can highlight the abnormal grouting information. The detection principle is as follows: the hydration heat based on the solidifying material is obtained before grouting, and after the pile is formed, the temperature detectors are reasonably arranged according to the size of the jet grouting drill rod and the inner and outer sides of the detection pile diameter, and the temperature information of the arranged temperature detectors is collected. Since there is a significant difference between the hydration heat of the solidifying material and the temperature of the surrounding soil, the predicted temperature field model established by analyzing the heat transfer parameters of the solidifying soil can be used to obtain parameters for judging the pile diameter, cement soil uniformity and cement dosage to judge the pile-forming effect of the jet grouting pile.

[0012] The present invention can realize the process control detection and information data collection of the jet grouting pile quality, so as to ensure the pile forming effect and the construction quality; and the detection method has the characteristics of high detection accuracy, flexibility and non-destructiveness, and is suitable for engineering promotion and application; in addition, by introducing the finite element temperature calculation technology into the detection of the jet grouting pile, a multidisciplinary cross-research method is provided for the scientific research of the jet grouting pile, and information detection and monitoring data collection are realized, which has great scientific significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0014] Figure 1 It is a flow chart of the detection method of the present invention.

[0015] Figure 2 It is a schematic diagram of the detection system of the present invention.

[0016] Figure 3 This is the main view of the temperature detector layout.

[0017] Figure 4 This is a top view of the temperature sensor layout.

[0018] Figure 5 It is a finite element model diagram of cement soil according to an embodiment of the present invention.

[0019] Figure 6 It is a temperature field cloud diagram at the highest temperature moment of an embodiment of the present invention.

[0020] Figure 7 The temperature field of the embodiment of the present invention is divided into Figure 1 .

[0021] Figure 8 4 is a temperature curve diagram of a simulation analysis of an embodiment of the present invention.

[0022] Fig. 9 4 is a trend diagram of the second-order derivative of temperature difference according to an embodiment of the present invention.

[0023] In the figure: 1-pile body; 2-temperature detector; 3-temperature measuring rod; 4-data transmission harness; 5-temperature measurement data collector; 6-data processing platform. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings, and each embodiment does not constitute a limitation on the embodiments of the present invention.

[0026] Example 1

[0027] like Figure 1 As shown, the finite element temperature calculation detection method for the jet grouting pile forming effect includes the following steps: Step A, 13 temperature measuring rods are arranged crosswise according to the size of the jet grouting drill rod and the inner and outer ranges of the detection pile diameter: 1 rod is arranged at the center point, 4 rods are arranged at 1 / 2 of the pile diameter, at the pile boundary and at 1 / 2 of the pile diameter from the pile boundary, 3 temperature detectors are installed in each temperature measuring rod, and the total number of temperature detectors is 39; Step B: collect temperature from the deployed temperature detectors to realize online information collection of the temperature at each measuring point, and establish and draw temperature rise and temperature difference change diagrams based on the real-time on-site temperature data obtained; Step C, through the previous similar physical test and numerical simulation, and based on the heat transfer algorithm of hydration exothermicity of solidified materials, obtain the pile characteristic parameters under multivariable conditions and the characteristic values ​​that can highlight the abnormal information of grouting; Step D, by comparing the established and drawn temperature rise and temperature difference change diagram with the real-time detection temperature data result, determining the temperature boundary value; Step E: adopt a mathematical model based on finite element temperature calculation prediction and actual measurement, use a temperature monitoring system, make a digital model decision, use the second-order derivative to derive the temperature change rate, and determine the temperature and temperature difference boundary values ​​through the temperature change slope. Finally, determine the pile quality process control through the predicted temperature field model established based on the hydration heat of the solidifying material and the heat transfer parameters of the solidifying soil obtained before spraying.

[0028] In step C, the aforementioned preliminary similar physical test and numerical simulation are carried out according to the following steps to obtain characteristic parameters that can highlight the abnormal grouting information: (1) The materials used and their thermal properties; the specific heat, thermal conductivity, convection coefficient, thermal expansion coefficient, heat release coefficient function, and Poisson's ratio characteristic value parameters are derived by fitting the measured temperature field values; (2) Test the hydration heat of the solidified material and the heat transfer parameters of the solidified soil; (3) Establish the temperature field under different curing materials through finite element temperature calculation and collect numerical simulation process; (4) Based on the numerical simulation results, the sensitivity parameters under different grouting conditions are obtained, and the pile characteristic parameters under multivariate conditions and the characteristic values ​​that can highlight the grouting anomaly information are obtained based on statistical methods.

[0029] In step A, the center point of the pile should be marked immediately after each pile is constructed.

[0030] In step B, the total collection time is 72 hours, and the temperature measuring rod is taken out in time after the collection is completed.

[0031] Example 2

[0032] The foundation design of a certain project adopts jet grouting for reinforcement. The project is under tight schedule. Comprehensive consideration is given to the rapid determination of pile forming process parameters after typical construction and the rapid detection of pile diameter, cement soil uniformity and cement dosage parameters after large-scale construction to ensure the close connection of the next process to shorten the construction period. Therefore, it is very important to develop a short-term, non-destructive, indirect detection method for the quality process control of jet grouting. This embodiment adopts the method described in Example 1. The real-time detection system used in the above method is as follows: Figure 2-Figure 4As shown, it is mainly composed of two parts: underground detection device and ground detection system; the underground detection device is mainly composed of temperature measuring device 2 and temperature measuring rod 3; the ground detection system is mainly composed of data transmission harness 4, temperature measurement data collector 5 and data processing platform 6. The specific implementation steps are as follows: 1. Determine the basic conditions of the foundation and soil sample parameters In this embodiment, the project foundation is a soft foundation of silty clay with a bearing capacity of 80kN. The CBR value of the soil sample is 1.5% in the 90th zone, 2.6% in the 92nd zone, and 3.3% in the 94th zone; the liquid limit is 48.2% and the plastic limit is 24.8%.

[0033] 2. Simulation analysis of temperature field of cement-solidified silt soil 1. Environmental parameters: The average temperature used in simulation calculations is the air temperature during the test.

[0034] 2. The cement-soil reference mix ratio is the construction mix ratio and shall be implemented according to Table 1.

[0035] Table 1 Cement-soil mix ratio (kg / m3)

[0036] 3. Material thermal property values: The materials and thermal property values ​​used in this project are shown in Table 2. Among them, the characteristic value parameters such as specific heat, thermal conductivity, convection coefficient, thermal expansion coefficient, heat release coefficient function, Poisson's ratio, etc. are derived by fitting the measured temperature field values.

[0037] Table 2 Calculation parameter values

[0038] 4. Simulation size: The cement soil is a cylinder with a diameter of 50 cm and a height of 60 cm; the outside is a cubic silt soil base with a length, width and height of 100 cm and a height of 60 cm. The simulation time is 48 hours.

[0039] 5. Simulation calculation: The finite element simulation analysis model is established. The temperature calculation is carried out using MIDAS / FEA3.60 finite element software. The finite element model is as follows Figure 5-Figure 7 shown.

[0040] According to the results of temperature simulation analysis, when the temperature of cement soil entering the mold is 14°C, the internal temperature of cement soil reaches the highest temperature of 28.8°C at 26 hours after pouring, and the maximum temperature rise is 14.8°C; the highest temperature at the boundary is 20.76°C, and the maximum temperature difference is 1.88°C at 2cm on both sides of the boundary. The maximum temperature difference is 4.04°C at 5cm on both sides of the boundary.

[0041] Table 3 Temperature difference at the highest temperature

[0042] According to the above temperature difference data, the second-order derivative is used to determine the temperature difference boundary, and then the parameters used to judge the pile diameter, cement soil uniformity and cement dosage are obtained. The second-order derivative of temperature difference is shown in Table 4. Fig. 9 As shown, the boundary temperature rise data is shown in Table 5, and the temperature difference control data is shown in Table 6.

[0043] Table 4 Second-order derivative values ​​at the highest temperature

[0044] Table 5 Boundary temperature rise data table

[0045] Table 6 Temperature difference control data table ;

[0046] 3. Temperature monitoring after the technological test pile is completed Before the construction of cement-soil mixing piles, process test piles should be carried out according to the design. The designed pile length is 21m and the pile diameter is 0.5m. After the test pile construction is completed, temperature monitoring should be carried out after the pile is completed.

[0047] 1. After the pile is formed, a 4CM diameter detection hole is drilled to the bottom of the pile within 2 hours using a drilling rig. According to the size of the jet-jet drill rod and the inner and outer ranges of the detection pile diameter, 13 temperature measuring rods are cross-crossed, with 1 at the center, 1 / 2 of the pile diameter, 4 temperature measuring rods 3 at the pile boundary and 1 / 2 of the pile diameter outside the pile. Three temperature measuring devices 2 are installed in each temperature measuring rod, and the total number of temperature measuring devices is 39. After completion, the temperature measuring rods 3 and temperature measuring devices 2 are buried, and connected to the temperature measuring data collector 5 through the data transmission harness 4; the temperature measuring data collector 5 transmits the collected data to the data processing platform 6 in real time through the network.

[0048] 2. After the scheduled collection time is reached (determined according to the temperature rise change, generally 48h-72h), the data obtained through the data processing platform 6 is analyzed for temperature rise and temperature difference.

[0049] 3. Plot the temperature rise change and temperature difference curves through the collected temperature data to preliminarily judge the conformity of the pile diameter and cement soil uniformity; then fit the temperature rise, temperature difference and second-order derivative temperature difference data graphs with the finite element simulation analysis data graphs to judge the parameters of the pile diameter, cement soil uniformity and cement dosage. The temperature measurement data at the singular point depth of this embodiment is shown in Table 9, and the fitting comparison of the experimental data and the measured temperature rise data at the singular point depth is shown in Table 7; the temperature difference data at the highest temperature moment at different pile depths of this embodiment is shown in Table 10; the fitting comparison of the experimental data and the measured temperature difference data at the singular point depth is shown in Table 8.

[0050] 4. Through the temperature rise and temperature difference data curves drawn, it is preliminarily determined that there is an abnormality at 1m above the pile bottom. The possible reason is uneven mixing of cement soil or insufficient cement slurry spraying at this location. Secondly, the simulation model is used to perform curve fitting and comparative analysis with the actual temperature difference and temperature rise data of the pile body to determine whether the curve change is abnormal.

[0051] 5. The quality of the piles was determined by the core sampling method. By drilling core samples, it was finally determined that the jet grouting pile depth was 90 degrees, the boundary was 15 cm from the center of the pile, and there was insufficient grouting at a depth of 19.5 to 21 m.

[0052] Table 7 Comparison of experimental data and measured temperature rise data

[0053] Table 8 Comparison of experimental data and measured temperature difference data

[0054] Table 9 Temperature measurement data at the depth of the singular point

[0055] Table 10 Temperature difference data at the highest temperature at different pile depths ;

[0056] Conclusion, the purpose of the present invention is to observe the temperature rise and temperature difference after the rotary jet grouting pile is formed to judge the pile diameter, cement soil uniformity and cement dosage of the short-term non-destructive indirect detection method and system. The method adopts a mathematical model based on finite element temperature calculation prediction-actual measurement, and finally judges the pile diameter, cement soil uniformity and cement dosage through the temperature monitoring system and digital model decision-making. Not only can the detection result be more accurate and reliable, but also easier to operate, and the information data collection and result judgment are completed through the temperature acquisition system and the digital model decision-making system. Therefore, the present invention meets the quality inspection of whether the rotary jet grouting pile can meet the design requirements, and is used to judge the compliance of the pile diameter, cement soil uniformity and cement dosage.

[0057] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description, and it is impossible to list all the implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A finite element temperature calculation and detection method for the effect of jet grouting piles, characterized in that: The following steps are involved: Step A, 13 temperature measuring rods are arranged crosswise according to the size of the jet grouting drill rod and the inner and outer ranges of the detection pile diameter: 1 rod is arranged at the center point, 4 rods are arranged at 1 / 2 of the pile diameter, at the pile boundary and at 1 / 2 of the pile diameter from the pile boundary, 3 temperature detectors are installed in each temperature measuring rod, and the total number of temperature detectors is 39; Step B: collect temperature from the deployed temperature detectors to realize online information collection of the temperature at each measuring point, and establish and draw temperature rise and temperature difference change diagrams based on the real-time on-site temperature data obtained; Step C, through the previous similar physical test and numerical simulation, and based on the heat transfer algorithm of hydration exothermicity of solidified materials, obtain the pile characteristic parameters under multivariable conditions and the characteristic values ​​that can highlight the abnormal information of grouting; The aforementioned similar physical test and numerical simulation are carried out according to the following steps to obtain characteristic parameters that can highlight the abnormal grouting information: (1) The materials used and their thermal properties; the specific heat, thermal conductivity, convection coefficient, thermal expansion coefficient, heat release coefficient function, and Poisson's ratio characteristic value parameters are derived by fitting the measured temperature field values; (2) Test the hydration heat of the solidified material and the heat transfer parameters of the solidified soil; (3) Establish the temperature field under different curing materials through finite element temperature calculation and collect numerical simulation process; (4) Obtain sensitivity parameters under different grouting conditions based on numerical simulation results, and obtain pile characteristic parameters under multivariate conditions and characteristic values ​​that can highlight grouting abnormality information based on statistical methods; Step D, by comparing the established and drawn temperature rise and temperature difference change diagram with the real-time detection temperature data result, determining the temperature boundary value; Step E: adopt a mathematical model based on finite element temperature calculation prediction and actual measurement, use a temperature monitoring system, make a digital model decision, use the second-order derivative to derive the temperature change rate, and determine the temperature and temperature difference boundary values ​​through the temperature change slope. Finally, determine the pile quality process control through the predicted temperature field model established based on the hydration heat of the solidifying material and the heat transfer parameters of the solidifying soil obtained before spraying.

2. The finite element temperature calculation detection method for the jet grouting pile effect according to claim 1 is characterized in that: In step A, the center point of the pile should be marked immediately after each pile is constructed.

3. The finite element temperature calculation detection method for the jet grouting pile effect according to claim 1 is characterized in that: In step B, the total collection time is 72 hours, and the temperature measuring rod is taken out in time after the collection is completed.

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