Deep cement mixing pile construction model test method and system

Abstract

The invention discloses a deep cement mixing pile construction model test method and system. The method comprises the steps that a soil pressure box, a pore pressure sensor, a resistivity test device, a three-dimensional laser scanner, a vertical displacement meter and a CT scanning system are adopted for monitoring a test, and G = alpha R + beta (au + b sigma) + gamma ne-delta Z is adopted for evaluating the construction effect; g is an evaluation index, R is an average value of increment of the resistivity of the radial section at different depths, u is an average value of increment of pore pressure sensors at different depths, sigma is an average value of increment of soil pressure cells at different depths, ne is a porosity reduction value, measured by a CT scanning system, of a grouting area, and Z is an average value of upheaval quantity, measured by a comprehensive three-dimensional laser scanner and a vertical displacement meter, of a soil body; alpha, beta, gamma and delta are the influence coefficients of the resistivity, the soil layer stress, the porosity and the upheaval amount respectively, and a and b are the influence weight ratios of the stress parameters respectively.

Description

Technical Field

[0001] The present application relates to the technical field of building test equipment, and in particular to a deep cement mixing pile construction model test method and system. Background Art

[0002] Deep cement mixing pile technology is a method widely used in foundation treatment. Its main principle is to fully mix cement slurry with in-situ soil through special mixing equipment, so that cement and soil undergo a series of physical and chemical reactions, thereby improving the bearing capacity of the foundation and reducing foundation settlement. In my country's infrastructure construction, deep cement mixing piles play an important role in the field of foundation treatment. However, due to the complexity of geological conditions and the diversity of construction technologies, the construction quality and effect of deep cement mixing piles are often difficult to accurately evaluate. Therefore, conducting a construction model test of deep cement mixing piles has important engineering significance. By simulating the geological conditions and construction process in actual projects, its working mechanism can be better revealed, providing a reference for optimizing design and construction.

[0003] The existing deep cement mixing pile construction model test has the following defects: (1) The monitoring of the grouting process is mostly based on conventional indicators such as quality and soil stress changes, and lacks accurate characterization and description of the internal conditions of the soil layer during the grouting process; (2) The drill bit and the matching model box need to be replaced to switch the working conditions under different mixer parameters. The adjustment method is not flexible enough and is costly, time-consuming and labor-intensive; (3) The evaluation of the construction effect needs to be determined after the composite foundation is tested after a certain number of days of maintenance, and there is a lack of rapid evaluation methods; (4) The underwater environment has an adverse effect on the mixing and grouting process, and the existing model test does not take this effect into consideration.

[0004] In summary, the existing deep cement mixing pile construction model test system and method have problems such as lack of effective observation and evaluation of the grouting diffusion process, time-consuming and labor-intensive switching between different working conditions, and ignoring the adverse effects of the actual underwater environment on the grouting process. Summary of the invention

[0005] The present application aims to solve at least one of the above-mentioned technical problems in the prior art to a certain extent. To this end, the first embodiment of the present application provides a deep cement mixing pile construction model test method, which can monitor the grouting diffusion process of cement liquid in the soil and realize quantitative evaluation of the construction effect.

[0006] The deep cement mixing pile construction model test method according to the first aspect of the present application includes: using an earth pressure box, a pore pressure sensor, a resistivity test device, a three-dimensional laser scanner, a vertical displacement meter and a CT scanning system to monitor the grouting diffusion process during the construction process;

[0007] After the model test, the following formula is used to evaluate the construction effect of deep cement mixing piles:

[0008] G=αR+β(au+bσ)+γn e -δZ

[0009] Among them, G is the evaluation index of deep cement mixing pile grouting effect, R is the average value of the increase in radial section resistivity at different depths, u is the average value of the increment of pore pressure sensors buried at different depths, σ is the average value of the increment of earth pressure boxes buried at different depths, and n is the average value of the increment of the earth pressure box buried at different depths. e is the porosity reduction value of the grouting area measured by the CT scanning system, Z is the average vertical uplift of the soil measured by the integrated three-dimensional laser scanner and the vertical displacement meter; α, β, γ, δ are the influence coefficients of resistivity, soil stress, porosity and uplift, respectively, and a and b are the influence weight ratios of each stress parameter, respectively.

[0010] Based on the above technical scheme, the first aspect of the present application has at least the following beneficial effects: First, the deep cement mixing pile construction model test method proposed in the present application introduces a resistivity test device and a CT scanning system on the basis of a soil pressure box and a pore pressure sensor to comprehensively monitor the grouting diffusion process of the deep cement mixing pile, and takes into account the influence of the grouting diffusion process on the pile forming effect. Secondly, the deep cement mixing pile construction effect evaluation formula proposed in the present application can be directly calculated based on the observation of the cement grouting process, without the need to wait for the cement mixing pile construction to be completed and maintained for a certain period of time before taking a composite foundation sample for testing and determination, and the evaluation of the cement mixing pile construction effect is simpler and more direct. In addition, the construction effect evaluation formula proposed in the present application takes into account the changes in multiple physical parameters such as internal components, stress, pores, and displacement deformation of the soil body, avoiding the errors that may be caused by measuring a single physical quantity in the past, making the evaluation results more accurate and comprehensive.

[0011] According to the deep cement mixing pile construction model test method of the first aspect of the present application, after the test barrel is filled with soil, water is added to the soil surface. At the same time, the test barrel is designed as a closed structure and gas is pumped into the test barrel. By adjusting the internal air pressure of the test barrel, the water pressure effect of cement mixing pile construction in water bodies of different depths is simulated.

[0012] According to the deep cement mixing pile construction model test method of the first aspect of the present application, a mixing blade is arranged inside the test barrel, and the operating parameters of the mixer during different cement mixing pile construction processes are simulated by adjusting the barrel diameter of the test barrel and the radial size of the mixing blade.

[0013] According to the deep cement mixing pile construction model test method of the first aspect of the present application, the process of measuring the porosity reduction value of the grouting area by the CT scanning system is:

[0014] The data collected by the CT scanning system was input into commercial software to realize the three-dimensional reconstruction of the grouting area, and the change value of soil porosity at different times was obtained through the three-dimensional reconstruction results.

[0015] A deep cement mixing pile construction model test system according to the second embodiment of the present application includes: a gantry, a cement mixer, a test barrel and a monitoring system;

[0016] The cement mixer is fixed to the middle part of the gantry, and the test bucket is located directly below the cement mixer;

[0017] The monitoring system includes a resistivity test device, a CT scanning system, an earth pressure box, a pore pressure sensor, a vertical displacement meter, a three-dimensional laser scanner and a data acquisition control system;

[0018] The three-dimensional laser scanner is fixed directly above the gantry, and there are multiple soil pressure boxes and pore pressure sensors, which are buried at different depths in the test barrel.

[0019] According to the deep cement mixing pile construction model test system of the second aspect of the present application, the deep cement mixing pile construction model test system also includes an air pressure pump, the air pressure pump is provided with an air intake pipe, and the air pressure pump is sealed and connected to the upper part of the test barrel through the air intake pipe.

[0020] According to the deep cement mixing pile construction model test system of the second aspect embodiment of the present application, the cement mixer includes a transmission connection, a drill rod main shaft, a drill rod housing, mixing blades and a drill bit, the first end of the drill rod main shaft is connected to the transmission connection, the second end of the drill rod main shaft is connected to the drill bit, the drill rod housing is arranged on the outside of the drill rod main shaft, and the middle section of the drill rod main shaft is provided with a plurality of mixing blades, and the mixing blades extend out of the drill rod housing by a first distance along the radial direction of the drill rod main shaft.

[0021] According to the deep cement mixing pile construction model test system of the second aspect of the present application, the resistivity testing device includes a resistivity tester and a plurality of testing components, and the plurality of testing components are fixedly arranged at different heights on the side wall of the test barrel.

[0022] According to the deep cement mixing pile construction model test system of the second aspect of the present application, the test barrel includes a side wall, an upper cover and a bottom plate, and the bottom plate and the upper cover are fixedly connected to the side wall through a sealing ring;

[0023] The upper cover is provided with a first through hole, and the first through hole is used for the drill rod housing to extend into the test barrel.

[0024] According to the deep cement mixing pile construction model test system of the second aspect of the present application, the upper cover is made of a transparent material.

[0025] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is a structural schematic diagram of a deep cement mixing pile construction model test system in an embodiment of the second aspect of the present application;

[0028] Figure 2 This is a structural schematic diagram of a cement mixer in an embodiment of the second aspect of the present application;

[0029] Figure 3 This is a schematic diagram of the structure of the test barrel in the embodiment of the second aspect of the present application;

[0030] Reference numerals:

[0031] Gantry 100, support column 110, crossbeam 120, cement mixer 200, transmission connector 210, drill pipe main shaft 220, drill pipe housing 230, mixing blade 240, drill bit 250, test barrel 300, upper cover 310, first perforation 311, side wall 320, bottom plate 330, three-dimensional laser scanner 410, support rod 411, support plate 412, guide rail 413, laser rangefinder 414, vertical displacement meter 420, resistivity tester 431, test component 432, X-ray source 441, detector 442, soil pressure box 450, pore pressure sensor 460, data acquisition and control system 470, air pressure pump 500, air intake pipe 510. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0033] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0034] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0035] In addition, the terms "installed", "set", "provided with", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0036] In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, "plurality" means two or more.

[0037] The technical solution of the present application will be further described below in conjunction with embodiments and drawings.

[0038] The embodiment of the present application provides a deep cement mixing pile construction model test method, which can monitor the grouting diffusion process of cement liquid in soil and realize quantitative evaluation of construction effect. The deep cement mixing pile construction model test method includes:

[0039] The grouting diffusion process during construction was monitored using earth pressure cells, pore pressure sensors, resistivity test devices, 3D laser scanners, vertical displacement meters and CT scanning systems;

[0040] After the model test, the following formula is used to evaluate the construction effect of deep cement mixing piles:

[0041] G=αR+β(au+bσ)+γn e -δZ

[0042] Among them, G is the evaluation index of deep cement mixing pile grouting effect, R is the average value of the increase in radial section resistivity at different depths, u is the average value of the increment of pore pressure sensors buried at different depths, σ is the average value of the increment of earth pressure boxes buried at different depths, n e is the porosity reduction value of the grouting area measured by the CT scanning system, Z is the average vertical uplift of the soil measured by the integrated three-dimensional laser scanner and the vertical displacement meter; α, β, γ, δ are the influence coefficients of resistivity, soil stress, porosity and uplift, respectively, and a and b are the influence weight ratios of each stress parameter, respectively.

[0043] It should be noted that in the existing deep cement mixing pile construction model test, the monitoring of the cement grouting process is usually based on conventional indicators such as quality and soil layer stress changes, and the monitoring and description of the internal conditions of the soil layer during the cement grouting process are not accurate enough. Therefore, in the deep cement mixing pile construction model test proposed in this application, a resistivity test device and a CT scanning system are introduced to assist in the monitoring of the cement grouting process.

[0044] The resistivity test device can measure the cross-sectional resistivity of the soil, and the cross-sectional resistivity can reflect the pile formation effect of cement mixing piles. The principle is that before the cement liquid is injected, the soil pores below the liquid surface are basically filled with water. As an excellent conductor, water has a high conductivity, which is much greater than the conductivity of cement. Therefore, as the cement penetrates into the soil, the cross-sectional resistivity will gradually increase. Therefore, by monitoring the average cross-sectional resistivity of different depths at each time, the overall injection of cement slurry can be evaluated.

[0045] CT scanning system has been widely used in geotechnical field and is often used to scan the pores and skeleton structure of geotechnical samples. Therefore, it is feasible and has good expected effect to introduce it into the deep cement mixing pile construction model test to monitor the cement injection process in the soil. The CT scanning system can capture the micro-structural characteristics of the pores and cracks in the grouting area in real time. The data collected by the CT scanning system can be input into commercial software such as AVIZO to perform three-dimensional reconstruction of the grouting area and realize the visual monitoring of the soil grouting process.

[0046] It can be understood that in the deep cement mixing pile construction model test provided by the present application: an earth pressure box, a pore pressure sensor, a resistivity testing device, a three-dimensional laser scanner, a vertical displacement meter and a CT scanning system are used to carry out multi-information monitoring of the grouting diffusion process during the construction process, wherein, by using an earth pressure box to monitor the grouting diffusion process during the construction process, the average value σ of the increment of the earth pressure box buried at different depths can be calculated; by using a pore pressure sensor to monitor the grouting diffusion process during the construction process, the average value u of the increment of the pore pressure sensor buried at different depths can be calculated; by using a resistivity testing device to monitor the grouting diffusion process during the construction process, the average value R of the resistivity increment of the radial section at different depths can be calculated; by using a CT scanning system to monitor the grouting diffusion process during the construction process, the porosity reduction value n of the grouting area can be calculated. e ; The grouting diffusion process during construction is monitored using a three-dimensional laser scanner and a vertical displacement meter, and the average value Z of the vertical uplift of the soil can be calculated.

[0047] Based on the test results of the above-mentioned deep cement mixing pile construction model test, this application proposes a comprehensive evaluation formula for the construction effect of deep cement mixing piles: G = αR + β (au + bσ) + γn e -δZ, where G is the evaluation index of deep cement mixing pile grouting effect. The positive and negative signs are determined according to the correlation of the above evaluation parameters to the grouting effect. In addition to the evaluation parameters involved in the above test results, α, β, γ, and δ are the influence coefficients of resistivity, soil stress, porosity, and uplift, respectively. a and b are the influence weight ratios of various stress parameters, respectively. The influence coefficients and influence weight ratios can be calibrated according to multiple test results, or selected by reference to standards.

[0048] It should be noted that the construction effect of the deep cement mixing pile proposed in this application can be directly calculated based on the observation of the cement grouting process, without the need to wait for the cement mixing pile construction to be completed and maintained for a certain period of time before taking the composite foundation sample for testing and determination, and the evaluation of the construction effect of the cement mixing pile is simpler and more direct. In addition, the construction effect evaluation formula proposed in this application takes into account the changes in multiple physical parameters such as soil internal components, stress, porosity, displacement and deformation, avoiding the errors that may be caused by measuring a single physical quantity in the past, making the evaluation results more accurate and comprehensive.

[0049] As an example, the reduction in porosity in the grouting area can be measured through a CT scanning system. The specific process is: the data collected by the CT scanning system is input into commercial software to achieve three-dimensional reconstruction of the grouting area, and the change in soil porosity at different times is obtained through the three-dimensional reconstruction results.

[0050] It is understandable that when deep cement mixing pile construction is carried out underwater at a certain depth, the actual underwater environment will have an adverse effect on the formation mixing and grouting process, such as cement slurry dilution, uneven distribution, prolonged curing time and other problems. Therefore, the adverse effect of the actual underwater environment on the formation mixing and grouting process also needs to be considered in the deep cement mixing pile construction model test.

[0051] Optionally, in the deep cement mixing pile construction model test proposed in the present application, water is added to the surface of the soil after the test barrel is filled with soil. At the same time, the test barrel is designed as a closed structure and gas is pumped into the test barrel. The air pressure inside the test barrel is adjusted to simulate the water pressure effect of cement mixing pile construction in water bodies of different depths. It is understandable that adding a certain amount of water that is the same as the site to the surface of the soil after the test barrel is filled with soil can simulate the actual underwater environment. After ensuring that the test barrel is in a sealed environment, the water body exerts pressure on the soil layer by pumping gas into the test barrel, thereby restoring the actual underwater pressure environment, making the model test results more valuable for reference to actual projects.

[0052] In actual deep cement mixing pile construction, the operating parameters of the mixer will be adjusted according to construction requirements. Therefore, in order to simulate the actual construction scene, the drill bit and the matching test bucket are usually replaced in the deep cement mixing pile construction model test. The test process is cumbersome, costly, time-consuming and labor-intensive.

[0053] As an example, in the deep cement mixing pile construction model test method provided by the present application, a mixing blade is provided inside the test barrel, and the working parameters of the mixer during different cement mixing pile construction processes are simulated by adjusting the barrel diameter of the test barrel and the radial size of the mixing blade. By providing a test barrel with adjustable barrel diameter and a mixing blade with adjustable radial size, there is no need to replace the drill bit and the matching test barrel during the model test, which can meet the current demand for flexible adjustment of mixing parameters during the deep cement mixing pile model test.

[0054] Optionally, the radial size of the mixing blades can be adjusted by designing a retractable mixing blade, and the diameter of the test barrel can be adjusted by designing a test barrel with an adjustable diameter, so as to facilitate the test under various technical parameters, and flexibly simulate the parameters of the mixer under different working conditions, avoid the extra work caused by replacing the drill bit and the test barrel, simplify the steps of the deep cement mixing pile construction model test method, and save time and effort. At the same time, the optimal replacement rate and the recommended length of the empty pile under different construction parameters can be determined through a large number of test results, so as to directly guide the on-site construction.

[0055] It is understandable that when designing and constructing cement mixing piles under different formation conditions, it is crucial to accurately evaluate the quantitative relationship between the grouting volume and the heave volume, as well as the optimal replacement rate and the recommended length of the empty pile under different construction parameters. The deep cement mixing pile construction model test method provided in this application can obtain the real-time changes in the heave deformation of the soil layer and the cement grouting volume and the quantitative relationship between the two, thereby assisting in determining the above parameters and providing a reference for determining the actual construction parameters.

[0056] The second aspect of the present application also provides a deep cement mixing pile construction model test system, including: a gantry 100, a cement mixer 200, a test barrel 300 and a monitoring system; the cement mixer 200 is fixed to the middle part of the gantry 100, and the test barrel 300 is located directly below the cement mixer 200; the monitoring system includes a resistivity testing device (not shown in the figure), a CT scanning system (not shown in the figure), an earth pressure box 450, a pore pressure sensor 460, a vertical displacement meter 420, a three-dimensional laser scanner 410 and a data acquisition control system 470; the three-dimensional laser scanner 410 is fixed directly above the gantry 100, and there are multiple earth pressure boxes 450 and pore pressure sensors 460, which are buried at different depths of the test barrel 300.

[0057] refer to Figure 1 -to Figure 3 In the deep cement mixing construction model test system, the gantry 100 includes two support columns 110 and a crossbeam 120 erected between the two support columns 110 , and the cement mixer 200 is suspended and fixed on the crossbeam 120 of the gantry 100 .

[0058] refer to Figure 2 The cement mixer 200 includes a transmission connector 210, a drill rod main shaft 220, a drill rod housing 230, a mixing blade 240 and a drill bit 250, wherein the first end of the drill rod main shaft 220 is connected to the transmission connector 210, and the second end of the drill rod main shaft 220 is connected to the drill bit 250. The transmission connector 210 fixes the cement mixer 200 to the middle of the crossbeam 120 of the gantry 100 on the one hand, and transmits the torque of the motor to the drill rod main shaft 220 on the other hand, driving the mixing blade 240 and the drill bit 250 to rotate. The drill rod housing 230 is arranged on the outside of the drill rod main shaft 220, and a plurality of mixing blades 240 are arranged in the middle section of the drill rod main shaft 220, and the mixing blades 240 extend out of the drill rod housing 230 by a first distance along the radial direction of the drill rod main shaft 220.

[0059] refer to Figure 3The test barrel 300 includes a side wall 320, an upper cover 310 and a bottom plate 330. The bottom plate 330 and the upper cover 310 are fixedly connected to the side wall 320 through a sealing ring. The upper cover 310 is provided with a first through hole 311. The first through hole 311 is used for the drill pipe housing 230 to extend into the test barrel 300. Figure 1 The test barrel 300 is placed directly below the gantry 100 , and the drill pipe housing 230 of the cement mixer fixed on the crossbeam 120 of the gantry 100 extends downward into the interior of the test barrel 300 .

[0060] It is understandable that after the drill rod housing 230 extends downward into the interior of the test barrel 300, the drill rod housing 230 and the first perforation 311 of the upper cover 310 are designed to be sealed, which can be achieved by designing a sealing ring or other forms, and the present application does not make specific limitations here.

[0061] The monitoring system includes a resistivity testing device, a CT scanning system, an earth pressure box 450, a pore pressure sensor 460, a vertical displacement meter 420, a three-dimensional laser scanner 410 and a data acquisition control system 470. The monitoring system is arranged inside or around the test barrel 300 to monitor and collect data on the cement grouting area in the test barrel 300.

[0062] As an example, refer to Figure 1 The resistivity test device includes a resistivity tester 431 and a plurality of test components 432, and the plurality of test components 432 are fixedly arranged at different heights of the side wall 320 of the test barrel 300. Optionally, the plurality of test components 432 are implemented by copper nails, and the plurality of copper nails are fixed at different heights of the side wall 320 of the test barrel 300, so that the cross-sectional resistivity at different positions can be obtained, thereby reflecting the filling condition of the cement slurry inside the soil layer. It is understandable that the test component 432 can also use conductive contacts made of other metals, which is not specifically limited in this application.

[0063] As an example, refer to Figure 1 The CT scanning system includes an X-ray source 441 and a detector 442, wherein the X-ray source 441 is arranged in front of the test barrel 300, and the detector 442 is arranged in the rear of the test barrel 300. The X-ray source 441 and the detector 442 are both electrically connected to the data acquisition control system 470, and transmit the data collected by the CT scanning system to the data acquisition control system 470. The data collected by the CT scanning system can realize the three-dimensional reconstruction of the grouting area through commercial software such as AVIZO. This method can accurately depict the changes of the three-dimensional contour after the slurry is injected with time, and at the same time realize the visual monitoring of the soil layer during the shotcrete process, and can obtain the soil porosity at different times.

[0064] As an example, refer to Figure 1There are multiple soil pressure boxes 450 and multiple pore pressure sensors 460, and the multiple soil pressure boxes 450 and multiple pore pressure sensors 460 are buried at different depths inside the test barrel 300, so as to obtain the soil stress and pore pressure at different positions in the soil layer in real time.

[0065] As an example, refer to Figure 1 , the three-dimensional laser scanner 410 is fixed on the top of the gantry 100. Optionally, the three-dimensional laser scanner 410 is fixed on the crossbeam 120 of the gantry 100 through two support rods 411. The three-dimensional laser scanner 410 includes a support plate 412 and a laser rangefinder 414 that can move relative to the support plate 412. Optionally, a guide rail 413 is provided on the support plate 412, and the laser rangefinder 414 slides relative to the guide rail 413 to achieve movement relative to the bottom plate 330. As an example, in the present application, two horizontal and vertical cross-guide rails 413 are provided on the support plate 412, and the laser rangefinder 414 can move arbitrarily along the guide rails 413 in two directions, and finally realizes the collection of deformation information of the soil surface inside the test barrel 300.

[0066] As an example, in the present application, the upper cover 310 is made of a transparent material, and the upper cover 310 is designed to be a transparent material to ensure that the three-dimensional laser scanner 410 can more accurately obtain the position and fluctuation of the soil surface. Optionally, the upper cover 310 can be made of a transparent acrylic material or a glass material, which is not specifically limited in the present application.

[0067] It is understandable that in the present application, the three-dimensional laser scanner 410 and the vertical displacement meter 420 are used simultaneously to collect the undulation information of the soil layer surface in real time, thereby making the test result of the uplift amount more accurate.

[0068] As an example, the deep cement mixing pile construction model test system in the present application also includes an air pressure pump 500, which is provided with an air intake pipe 510. The air pressure pump 500 is sealed and connected to the upper part of the test barrel 300 through the air intake pipe 510. In the deep cement mixing pile construction model test, the air pressure pump 500 pumps gas into the test barrel 300 through the air intake pipe 510, so that the water body produces a pressure on the lower soil layer similar to that of the construction site, thereby restoring the actual underwater pressure environment.

[0069] It can be understood that by controlling the volume of gas pumped by the air pressure pump 500, different water pressure environments can be simulated, and the control pressure value of the air pressure pump 500 can be determined by the soil pressure box 450 and the pore pressure sensor 460 buried in the soil layer, making the model test results more valuable for reference to actual projects.

[0070] As an example, refer to Figure 2The cement mixer 200 includes a retractable mixing blade 240, and the extension length of the mixing blade 240 is adjusted by controlling the knob on the top of the drill rod main shaft 220 to change the mixing diameter; optionally, inner and outer ring locks are provided in the transmission connection 210, and the lower drill rod main shaft 220 can be driven to rotate by manually rotating the inner ring bearing, so that the mixing blade 240 can be adjusted to extend the first distance of the drill rod housing 230 along the radial direction of the drill rod main shaft 220, thereby changing the telescopic length of the blade and changing the mixing diameter.

[0071] It should be understood that after the stirring diameter of the stirring blade 240 changes, the size of the test barrel 300 needs to be adjusted accordingly to meet the test requirements. As an example, in the present application, the test barrel 300 uses a pull ring to adjust the diameter of the test barrel 300 to adapt to the change in the radial size of the stirring blade 240. Figure 3 In the present application, the pull ring controls the extension and retraction size of the side wall 320 of the test barrel 300 through the telescopic opening, thereby changing the barrel diameter of the test barrel 300.

[0072] The process of conducting a deep cement mixing pile construction model test using the above-mentioned deep cement mixing pile construction model test system is described as follows:

[0073] (1) Open the inner and outer ring locks of the cement mixer 200 and manually adjust the mixing blades 240 to a predetermined working condition.

[0074] (2) Determine the diameter of the test barrel 300 according to the extended length of the stirring blade 240, control the diameter of the test barrel 300 to be about 3 times the stirring diameter, adjust the diameter to a preset diameter through the pull ring of the test barrel 300, and then fix the sealing ring between the side wall 320 and the bottom plate 330 of the test barrel 300.

[0075] (3) The soil collected on site is filled in layers into the test barrel 300 until it reaches 2 / 3 of the height of the test barrel 300, and the on-site water is added to the surface of the soil.

[0076] (4) The upper cover 310 is fixed to the top surface of the side wall 320 of the test barrel 300 through a sealing ring. Then, the air pressure pump 500 is turned on to apply air pressure into the test barrel 300, so that the water body generates a pressure on the lower soil layer similar to that at the engineering site, and the control pressure value of the air pressure pump 500 is determined by the soil pressure box 450 and the pore pressure sensor 460 buried in the soil layer.

[0077] (5) The control module in the data acquisition control system 470 is used to carry out deep cement mixing tests under different factors such as mud dosage (18%, 20%), mixing speed (30-50r / min), and grouting volume. After turning on the cement mixer 200, the CT scanning system, resistivity test device, three-dimensional laser scanner 410, and data acquisition module in the data acquisition control system 470 are turned on. The data obtained by the CT scanning system can be processed by AVIZO software to monitor the three-dimensional structure and porosity of the soil in the grouting area in real time. The three-dimensional laser scanner 410 will collect information once within 2 minutes. Since the upper cover 310 and the water body above the soil layer are both transparent materials, the three-dimensional laser scanner 410 will accurately obtain the position and fluctuation changes of the soil surface.

[0078] (6) The resistivity of each cross-section is tested and recorded every 2 minutes. The data collected by the soil pressure box 450 and the pore pressure sensor 460 at different depths and the test results of the vertical displacement meter 420 will be transmitted to the data acquisition control system 470 in real time.

[0079] (7) Based on the test results, the following formula can be used to evaluate the construction effect of deep cement mixing piles:

[0080] G=αR+β(au+bσ)+γn e -δZ

[0081] Among them, G is the evaluation index of deep cement mixing pile grouting effect, R is the average value of the increase in radial section resistivity at different depths, u is the average value of the increment of pore pressure sensors buried at different depths, σ is the average value of the increment of earth pressure boxes buried at different depths, and n is the average value of the increment of the earth pressure box buried at different depths. e is the porosity reduction value of the grouting area measured by CT, and Z is the average value of the vertical uplift of the soil measured by the integrated three-dimensional laser scanning and vertical displacement meter. α, β, γ, and δ are the influence coefficients of resistivity, soil layer stress, porosity, and uplift, respectively, and a and b are the influence weight ratios of each stress parameter, respectively.

[0082] The embodiments of the present application are described in detail above in conjunction with the accompanying drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present application.

Claims

1. A deep cement mixing pile construction model test method, characterized in that: include: The grouting diffusion process during construction was monitored using earth pressure cells, pore pressure sensors, resistivity test devices, 3D laser scanners, vertical displacement meters and CT scanning systems; After the model test, the following formula is used to evaluate the construction effect of deep cement mixing piles: G=αR+β(au+bσ)+γn e -δZ Among them, G is the evaluation index of deep cement mixing pile grouting effect, R is the average value of the increase in radial section resistivity at different depths, u is the average value of the increment of pore pressure sensors buried at different depths, σ is the average value of the increment of earth pressure boxes buried at different depths, and n is the average value of the increment of the earth pressure box buried at different depths. e is the porosity reduction value of the grouting area measured by the CT scanning system, and Z is the average value of the vertical uplift of the soil measured by the integrated three-dimensional laser scanner and the vertical displacement meter; α, β, γ, and δ are the influence coefficients of resistivity, soil stress, porosity, and uplift, respectively, and a and b are the influence weight ratios of each stress parameter, respectively.

2. The deep cement mixing pile construction model test method according to claim 1 is characterized in that: After the test barrel is filled with soil, water is added to the soil surface. At the same time, the test barrel is designed as a closed structure and gas is pumped into the test barrel. By adjusting the internal air pressure of the test barrel, the water pressure effect of cement mixing pile construction in water at different depths is simulated.

3. The deep cement mixing pile construction model test method according to claim 1 is characterized in that: A stirring blade is arranged inside the test barrel, and the working parameters of the mixer during the construction of different cement mixing piles are simulated by adjusting the barrel diameter of the test barrel and the radial size of the stirring blade.

4. The deep cement mixing pile construction model test method according to claim 1 is characterized in that: The process of measuring the porosity reduction value of the grouting area by the CT scanning system is as follows: The data collected by the CT scanning system was input into commercial software to realize the three-dimensional reconstruction of the grouting area, and the change value of soil porosity at different times was obtained through the three-dimensional reconstruction results.

5. Deep cement mixing pile construction model test system, characterized by: include: gantries, cement mixers, test barrels and monitoring systems; The cement mixer is fixed to the middle part of the gantry, and the test bucket is located directly below the cement mixer; The monitoring system includes a resistivity test device, a CT scanning system, an earth pressure box, a pore pressure sensor, a vertical displacement meter, a three-dimensional laser scanner and a data acquisition control system; The three-dimensional laser scanner is fixed directly above the gantry, and there are multiple soil pressure boxes and pore pressure sensors, which are buried at different depths in the test barrel.

6. The deep cement mixing pile construction model test system according to claim 5 is characterized in that: The deep cement mixing pile construction model test system also includes an air pressure pump, which is provided with an air intake pipe. The air pressure pump is sealed and connected to the upper part of the test barrel through the air intake pipe.

7. The deep cement mixing pile construction model test system according to claim 5 is characterized by: The cement mixer includes a transmission connection, a drill rod main shaft, a drill rod housing, stirring blades and a drill bit. The first end of the drill rod main shaft is connected to the transmission connection, the second end of the drill rod main shaft is connected to the drill bit, the drill rod housing is arranged on the outside of the drill rod main shaft, and the middle section of the drill rod main shaft is provided with a plurality of stirring blades. The stirring blades extend out of the drill rod housing by a first distance along the radial direction of the drill rod main shaft.

8. The deep cement mixing pile construction model test system according to claim 5 is characterized by: The resistivity testing device comprises a resistivity tester and a plurality of testing components, and the plurality of testing components are fixedly arranged at different heights of the side wall of the test barrel.

9. The deep cement mixing pile construction model test system according to claim 7, characterized in that: The test barrel comprises a side wall, an upper cover and a bottom plate, wherein the bottom plate and the upper cover are fixedly connected to the side wall via a sealing ring; The upper cover is provided with a first through hole, and the first through hole is used for the drill rod housing to extend into the test barrel.

10. The deep cement mixing pile construction model test system according to claim 9, characterized in that: The upper sealing cover is made of transparent material.

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