A kind of based on field direct grouting microbial reinforcement pile test device and loading test method

Abstract

The present application relates to a kind of based on field direct grouting microbial reinforcement pile test device and loading test method, fill test soil body in test site, vertical implantation single pile in test soil body, with single pile as symmetry center, steel frame structure is respectively arranged in its two sides, one side steel frame can slip installation jack, the other side steel frame can slip installation exciter, the output end of jack and exciter all bear single pile wall;Strain gauge is pasted in single pile body different height, force sensor is installed in the output end of jack, exciter, eddy current displacement meter is installed in the output end of jack, exciter near acting point position;The steel frame structure of installation jack side is provided with slurry tank, bacteria solution and cementing solution are contained in slurry tank, one end of conveying pipe is inserted in slurry tank, the other end is inserted into test soil body by grouting pump.The present application simulates ocean dynamic load by standardization loading process, in experiment, using the method of grading loading and repeated test, can provide scientific basis for the engineering application of microbial reinforcement pile, with significant practical value and popularization prospect.

Description

Technical Field

[0001] This invention relates to a test device and loading test method for microbial reinforced piles based on direct grouting in the field, belonging to the field of pile foundation dynamic characteristic testing technology. Specifically, it is applied to the cyclic loading characteristic test of microbial reinforced piles based on direct grouting in the field, and is suitable for pile foundation testing scenarios in marine engineering such as offshore wind power and cross-sea bridges. Background Technology

[0002] In offshore wind power and other marine engineering projects, large-diameter monopile foundations need to withstand the horizontal cyclic loads coupled by wind, waves and currents for a long time. Softening of the soil around the pile can easily lead to fatigue failure of the pile foundation. Microbial induced carbonate deposition (MICP) technology has become the preferred technical solution for soil reinforcement around piles due to its advantages of low disturbance, low carbon emissions and good reinforcement effect. Microbial reinforced piles with direct grouting in place have therefore been widely used in marine engineering pile foundation projects. The cumulative deformation, stiffness attenuation, microscopic damage of the reinforced soil and pile-soil interface under long-term cyclic loads have become the core research contents of engineering design and safety monitoring.

[0003] To study the cyclic mechanical response of microbially reinforced pile foundations, key mechanical parameters need to be obtained through indoor / field cyclic loading tests. However, existing pile foundation cyclic loading test equipment and methods have many technical limitations when adapted to field tests of microbially reinforced piles, and can no longer meet the needs of engineering research. Specifically, these include the following issues: The cyclic loading test apparatus suffers from insufficient adaptability and accuracy. Traditional cyclic loading test devices are mainly divided into two categories. One category is pulley loading devices based on the torque principle. Although these devices are simple in structure and easy to operate, they have low loading accuracy and large test result errors. They can only achieve cyclic loading in a single direction and cannot quickly switch between unidirectional and bidirectional load conditions, making it difficult to simulate complex marine dynamic load environments. The other category is servo hydraulic loading systems. Although they can ensure loading accuracy, they are bulky, expensive, and uneconomical. They are only suitable for small indoor model tests and cannot meet the large-scale test requirements of on-site direct grouting microbial reinforced piles.

[0004] Significant structural defects exist in reaction devices: Traditional reaction devices are mostly independent heavy structures with an integral welded design. They are bulky, complex to install and dismantle, and cannot be moved or reused, resulting in extremely low construction efficiency in field testing. At the same time, the simple fixing method of traditional reaction devices makes them prone to vibration and loosening during cyclic loading, which can cause the loading direction to shift and further reduce the accuracy of the test.

[0005] The experimental methods lack standardized procedures: existing cyclic loading tests for microbially reinforced piles lack unified loading specifications, and loading parameters (load amplitude, number of cycles, loading sequence) are set arbitrarily without considering the long-term cyclic characteristics of marine loads. Furthermore, the on-site grouting process of microbially reinforced soil is not integrated with the experimental procedure, resulting in a disconnect between the experimental conditions and actual engineering conditions. At the same time, the tests only obtain a single indicator of the ultimate bearing capacity of the pile foundation, without quantitatively analyzing the long-term cyclic damage evolution of the reinforced soil and the stiffness decay law of the pile foundation. The tests also do not include repeated testing after the reinforced soil is damaged, making it impossible to capture key damage nodes such as cementation surface slippage. The experimental data cannot provide comprehensive and reliable theoretical support for engineering design.

[0006] The data acquisition and observation system is incomplete: the sensor layout of traditional tests lacks specificity, and the acquisition equipment such as strain gauges and displacement gauges are evenly distributed, which cannot accurately capture the mechanical response of key parts such as the mud surface; at the same time, only macroscopic data such as load and displacement are collected, and no microscopic observation equipment is set up, which cannot capture the microscopic deformation and damage law of microbial reinforced soil around the pile, and it is difficult to establish a collaborative deformation model of pile foundation and reinforced soil.

[0007] To address the aforementioned issues, an integrated and highly adaptable testing device, coupled with standardized testing methods, is needed to achieve a systematic study of the cyclic mechanical response of microbially reinforced piles directly injected in the field. Summary of the Invention

[0008] This invention provides a test device and loading test method for microbial reinforced piles based on direct grouting in the field. It is an integrated and highly accurate cyclic loading test device adapted to direct grouting microbial reinforced piles in the field, and a standardized test method with comprehensive working condition coverage is developed to achieve a systematic and accurate study of the mechanical response of microbial reinforced piles under long-term marine cyclic loading.

[0009] The technical solution adopted by this invention to solve its technical problem is: A test device for microbial-reinforced piles based on direct in-situ grouting. Test soil was filled into the test site, and a single pile was vertically driven into the test soil. With the single pile as the center of symmetry, steel frame structures were set up on both sides of it. A jack could be slidably installed on one side of the steel frame, and a vibrator could be slidably installed on the other side. The output ends of the jack and the vibrator were both pressed against the wall of the single pile. It also includes a data acquisition system, which includes force sensors, eddy current displacement gauges, strain gauges and a data acquisition instrument. Several strain gauges are attached to different heights of the single pile body. Force sensors are installed at the output ends of the jacks and vibrators. Eddy current displacement gauges are installed at the output ends of the jacks and vibrators near the point of action. Force sensors, eddy current displacement gauges and strain gauges are all connected to the data acquisition instrument. A slurry storage tank is installed on the steel frame structure on one side of the jack. The slurry storage tank contains bacterial solution and cementing solution. One end of the delivery pipe is inserted into the slurry storage tank, and the other end is inserted into the test soil through a grouting pump. Furthermore, the steel frame structure includes a steel frame body, which includes columns, diagonal braces, and transverse reinforcing beams. The columns and transverse reinforcing beams are arranged perpendicularly. One end of the diagonal brace is fixed to the column, and the other end is fixed to the transverse reinforcing beam. The three form a triangular stable structure. The bottom of the steel frame body is fixed by ground anchors. The two steel frame bodies arranged opposite each other are connected by two horizontally arranged slide rails to form a closed frame, that is, two slide rails are vertically fixed between the two columns. Furthermore, the jacks and vibrators are both hung on the slide rails via sliding brackets. Guide sliders are installed on the side of the brackets that contact the jacks and vibrators, allowing the jacks and vibrators to slide on the slide rails. The base of the jack is connected to the column by a ball joint, and the base of the vibrator is covered with a rubber pad and then fixed to the column by a rigid bracket. Furthermore, the slurry storage tank has a double-cavity structure, and a double-blade agitator is installed inside the slurry storage tank; Furthermore, the test soil includes sand and clay, with the clay layer located above the sand in the test site. Furthermore, a high-resolution digital camera was installed on one side of the test site. Furthermore, when several strain gauges are attached to the pile body, they are arranged differently, with the interval between strain gauges near the mud surface of the test soil being less than the interval between strain gauges at the bottom of the pile. A loading test method based on a field-direct grouting microbial reinforced pile test device, comprising the following steps: Step S1: Prepare the bacterial solution and the cementing solution, and place them in the two chambers of the slurry storage tank respectively; Step S2: Fill the test site with layers of sand and clay and compact them. Continue to install symmetrically distributed steel frame structures on the test site. After attaching several strain gauges at different heights of the single pile, vertically implant the single pile into the test soil. Step S3: Connect the jack and vibrator to the slide rail respectively, then install the slide rail on the symmetrically arranged steel frame structure, install force sensors at the output ends of the jack and vibrator respectively, and fix eddy current displacement gauges at positions close to the point of action. Step S4: Start the grouting pump, first inject a quantitative bacterial solution into the test soil, let it stand for a preset time, then inject a quantitative cementing solution into the test soil, and continue to let it stand for a preset time. Repeat the cementing and standing process three times until the test soil is stable. At this time, the grouting range is 4 to 5 times the pile diameter, and the reinforcement depth is 1 to 2 times the pile diameter. Step S5: Connect the data acquisition instrument to the computer, start the high-resolution digital camera, adjust the output parameters of the exciter, and verify all equipment before proceeding to the next step; if a unidirectional cyclic loading test is to be performed, proceed to step S6; if a bidirectional cyclic loading test is to be performed, proceed to step S11. Step S6: Start the vibrator to apply force to the single pile. Symmetrical bidirectional cyclic load with a cycle number of cycles Adjust the peak value of the loading to be consistent with the peak value of the pre-applied unidirectional cyclic load, and record the load, displacement and pile strain data during the bidirectional cyclic loading process; Step S7: Stop the vibrator, start the jack to apply static load, adjust the load size to half of the peak value of the pre-applied load, and after the load stabilizes, record the load, displacement and pile strain parameters during the static loading process. Step S8: Keeping the static load stable, restart the exciter to apply a bidirectional cyclic load. The two loads are superimposed to form a unidirectional cyclic load. At this time... Set the number of loops Data is collected synchronously during the cycle and the deformation of the test soil is recorded using a high-resolution digital camera; Step S9: After completing the current loading, stop the jack, remove the static load, and repeat steps S6-S8 to apply different load amplitude parameters in sequence. One-way cyclic loading test; Step S10: After all unidirectional cyclic loading sets are completed, perform a horizontal static load test, slowly increase the load until the displacement of the mud surface at the top of the single pile reaches 0.1 times the pile diameter, record the ultimate bearing capacity at this time, and complete the unidirectional cyclic loading test. Step S11: Set the load amplitude parameters of the exciter. Start the vibrator to apply force to the single pile. Symmetrical bidirectional cyclic load with a cycle number of cycles , =-1, Record the data during the loading process and the deformation of the test soil; Step S12, add load amplitude parameters Repeat step S11 to obtain the values ​​of different load amplitude parameters. Bidirectional cyclic loading test; Step S13: After all bidirectional cyclic loading sets are completed, perform a horizontal static load test, slowly increase the load until the displacement of the mud surface at the top of the single pile reaches 0.1 times the pile diameter, record the ultimate bearing capacity at this time, and complete the bidirectional cyclic loading test.

[0010] Furthermore, if the cemented surface of the test soil detaches and slips under bidirectional cyclic loading, steps S6 to S8 should be repeated to compare the changes in the mechanical properties of the pile foundation under bidirectional cyclic loading after cementation failure. Furthermore, in steps S9 and S12, the load amplitude parameters are set. The expected range is 0.1 to 0.7.

[0011] By employing the above technical solutions, the present invention has the following beneficial effects compared to the prior art: 1. The on-site direct grouting microbial reinforced pile test device provided by this invention integrates support, reaction force, and loading adjustment functions in the double steel frame sliding rail support reaction system. The grouting system also serves as the counterweight of the device. The entire device has a compact structure and moderate size. It adopts a detachable design with bolt connection and ground anchor fixation, which is convenient to disassemble and reassemble and can be reused. It adopts layered filling and compaction of bottom sand and top clay to truly restore the actual environment of the soil around the marine engineering pile. It can be adapted to indoor model tests and large-scale on-site tests, solving the problems of traditional devices being bulky and unable to be moved, and greatly improving the efficiency of test construction. 2. The on-site direct grouting microbial reinforced pile test device provided by this invention solves the problems of static loading eccentricity and dynamic loading vibration interference by using a spherical hinge and a rubber pad composite buffer device, ensuring that the load is accurately applied to the pile top in the horizontal direction. The strain gauges are arranged differently, and the sensors are laid out according to key parts. Combined with a synchronous data acquisition and microscopic observation system, the macroscopic mechanical parameters and microscopic soil deformation are captured synchronously, which greatly improves the accuracy and comprehensiveness of the test data. Compared with the traditional pulley block device, the test error is significantly reduced. 3. The on-site direct grouting microbial reinforced pile test device provided by the present invention can quickly achieve flexible switching between unidirectional and bidirectional cyclic loading through the combination of jacks and vibrators. The load amplitude parameter is adjustable in the range of 0.1 to 0.7. It can accurately simulate various dynamic load conditions of marine wind, wave and current coupling. Compared with the traditional single-direction loading device, the adaptability is greatly improved. One device can complete multi-condition tests without the need for additional equipment replacement. 4. The loading test method based on the on-site direct grouting microbial reinforced pile test device provided by the present invention clarifies the matching relationship between the grouting range, depth and test soil, so that the preparation of microbial reinforced soil is consistent with the on-site grouting process, the test conditions are more in line with the actual project, and the problem of the disconnect between traditional test and project is solved. The test results can truly reflect the mechanical characteristics of the on-site direct grouting microbial reinforced pile. 5. The loading test method based on the on-site direct grouting microbial reinforced pile test device provided by this invention clarifies key requirements such as loading sequence, load parameters, number of cycles, and static verification standards. The number of cycles ≥1000 times conforms to the long-term load characteristics of the ocean. After loading, the ultimate bearing capacity is obtained through static loading as a benchmark, solving the problems of arbitrary test parameters and lack of unified verification standards in traditional tests. The repeatability of the test is greatly improved, and the test data of different testers and different test sites are comparable. 6. The loading test method based on the on-site direct grouting microbial reinforced pile test device provided by this invention, through comparative tests of unidirectional / bidirectional cyclic loading and repeated tests after cementation failure of reinforced soil, can comprehensively study the cumulative deformation and stiffness attenuation law of pile foundation under different dynamic loads, as well as the long-term cyclic damage evolution of microbial reinforced soil and the pile-soil interface interaction law. At the same time, the standardized secant stiffness extraction process realizes the quantitative analysis of pile foundation stiffness evolution. Compared with traditional tests that only obtain the ultimate bearing capacity, it provides a multi-dimensional data system of load-displacement-strain-stiffness-microscopic damage, providing more comprehensive theoretical support for engineering design. Attached Figure Description

[0012] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0013] Figure 1 This is a schematic diagram of a preferred embodiment of the test device for microbial reinforcement of piles based on direct on-site grouting provided by the present invention; Figure 2 This is a perspective view of a preferred embodiment of the on-site direct grouting microbial reinforced pile test device provided by the present invention; Figure 3 This is a top view of a preferred embodiment of the on-site direct grouting microbial reinforced pile test device provided by the present invention; Figure 4 This is a schematic diagram of the steel frame structure, jacks, and vibrator in the on-site direct grouting microbial reinforced pile test device provided by the present invention; Figure 5 This is a schematic diagram of the grout storage tank in the on-site direct grouting microbial reinforced pile test device provided by the present invention.

[0014] In the diagram: 1 is sand, 2 is clay, 3 is test soil, 4 is a single pile, 5 is a jack, 6 is a sliding rail, 7 is a steel frame structure, 8 is a ground anchor, 9 is a vibrator, 10 is a rubber pad, 11 is a force sensor, 12 is a stress plate, 13 is an eddy current displacement meter, 14 is a data acquisition instrument, 15 is a computer, 16 is a grout storage tank, 17 is a grouting pump, 18 is a mixer, 19 is a bacterial solution, 20 is a cementing solution, and 21 is a high-resolution digital camera. Detailed Implementation

[0015] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "left side," "right side," "upper part," "lower part," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. "First," "second," etc., do not indicate the importance of the components, and therefore should not be construed as a limitation of the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the scope of protection of the present invention.

[0016] In offshore wind power and other marine engineering projects, microbial-induced carbonate deposition technology has become the preferred solution for fatigue resistance of large-diameter monopile foundations. However, this solution still has several drawbacks: the test results are not accurate enough and cannot meet the requirements for rapid switching between different working conditions, or the accuracy can be met but the economy is low; the traditional structure is bulky and inconvenient to install, making it difficult to apply to various working conditions; the traditional test method lacks standardized procedures, the loading parameters are set arbitrarily, and the evolution of long-term cyclic damage of the reinforced soil cannot be fully considered.

[0017] To address the aforementioned issues, this application provides a test device for microbial-reinforced piles based on direct in-situ grouting. This device also includes a matching loading test method. The test device is comprehensive, capable of both unidirectional and bidirectional circulation to simulate complex marine dynamic load conditions. Furthermore, the entire device incorporates a series of testing functions, including grouting, loading, and recording, adaptable to different test requirements. The loading test method is highly standardized, with controllable loading parameters. Repeated tests ensure data reliability, and static tests after loading provide a reference for ultimate bearing capacity, thus improving the data system. The test results accurately reflect the evolution of the dynamic characteristics of microbial-reinforced piles under long-term cyclic loading.

[0018] For the experimental setup, the entire system is as follows: Figure 1 , Figure 2 as well as Figure 3 As shown, test soil 3 is filled in the test site, and a single pile 4 is vertically inserted into the test soil. With the single pile as the center of symmetry, steel frame structures 7 are arranged on both sides of it. A jack 5 can be slidably installed on one side of the steel frame, and a vibrator 9 can be slidably installed on the other side of the steel frame. The output ends of the jack and the vibrator are both against the pile wall of the single pile. The test soil includes sand 1 and clay 2. In the test site, the clay is located on top of the sand. The clay and sand are prepared by layered compaction to ensure that the real environment is fully simulated.

[0019] The system also includes a data acquisition system comprising a force sensor 11, an eddy current displacement meter 13, strain gauges 12, and a data acquisition instrument 14. Several strain gauges are attached to different heights on the single pile. Force sensors are installed at the output ends of the jacks and vibrators, and eddy current displacement meters are installed near the point of application at the output ends of the jacks and vibrators. All force sensors, eddy current displacement meters, and strain gauges are connected to the data acquisition instrument. It is particularly important to emphasize that the strain gauges are arranged differently on the single pile, with the spacing between strain gauges near the mud surface of the test soil being less than the spacing at the bottom of the single pile. The placement of the force sensor and eddy current displacement meter further demonstrates this meticulous layout. Simultaneously, a high-resolution digital camera 21 is installed on one side of the test site, enabling simultaneous acquisition of load, displacement, strain, and microscopic soil deformation. Compared to the single data acquisition mode of traditional devices, this allows for the complete capture of the coordinated deformation patterns of the pile foundation and the reinforced soil.

[0020] A slurry storage tank 16 is installed on the steel frame structure on one side of the jack. The slurry storage tank contains bacterial solution 19 and cementing solution 20. One end of the delivery pipe is inserted into the slurry storage tank, and the other end is inserted into the test soil through a grouting pump 17. Regarding the slurry storage tank... Figure 5 As shown, it features a double-cavity structure, with a double-blade agitator 18 installed inside the grout storage tank. Initially, it is positioned on the side where the jack is installed to increase counterweight and optimize the device's center of gravity distribution. Compared to the traditional design where the grouting system and loading device are separate, this significantly improves the device's compactness and eliminates the need for additional counterweight structures. The double-cavity structure of the grout storage tank ensures that the bacterial solution and cementing solution are stored separately, preventing premature mixing and potential pipe blockage. The agitator uses a double-blade configuration to ensure thorough mixing of the test solution. In actual working conditions, on-site microbial grouting reinforcement is achieved by uniformly covering the perimeter of a single pile using a two-phase, multiple-stage grouting process.

[0021] The entire testing setup requires integration and high precision; therefore, regarding the steel frame structure, Figure 4As shown, the structure includes a steel frame body, comprising columns, diagonal braces, and transverse reinforcing beams. The columns and transverse reinforcing beams are arranged perpendicularly. One end of each diagonal brace is fixed to a column, and the other end is fixed to a transverse reinforcing beam, forming a stable triangular structure. The bottom of the steel frame body is fixed by ground anchors 8. Two opposing steel frame bodies are connected by two horizontally arranged slide rails 6 to form a closed frame, i.e., two slide rails are vertically fixed between two columns. This serves as both a support frame for the test device and a reaction frame. The uprights are made of I-beams, and when fixed to the diagonal braces and transverse reinforcing beams, they are welded from angle steel, and then combined with high-strength horizontal slide rails to form a closed frame, taking into account the three functions of support, reaction force, and load adjustment. Compared with the torque structure of traditional pulley loading devices and the large independent reaction frames of servo hydraulic loading systems, the steel frame structure provided in this application has high rigidity, a clear disassembly and assembly boundary, and can be reused, solving the problems of bulky, complex installation, and poor adaptability of traditional reaction devices.

[0022] Since the jacks and vibrators require adaptive fine-tuning, they are both suspended on slide rails via sliding brackets. Guide sliders are installed on the side of the brackets that contact the jacks and vibrators, allowing them to slide on the slide rails. The base of the jack is connected to the column via a spherical hinge, which can adapt to minor deformations of the device, offset assembly errors and directional deviations caused by dynamic load disturbances, ensuring that the static load is applied horizontally and accurately to the pile top, avoiding pile torsion caused by eccentric loads, and improving loading accuracy. The base of the vibrator is covered with a rubber pad 10 and fixed to the column by a rigid bracket. The rubber pad and the rigid bracket form a composite buffer device, achieving both vibration isolation and stable support, preventing the steel frame from being affected by cyclic loading vibration and ensuring the accuracy of test data, thus solving the problem of vibration interference in traditional loading devices.

[0023] In addition to the meticulous design of the test apparatus, a corresponding test method is also required. The loading test method provided in this application is an innovative design based on standardization and closed-loop system. It clarifies the fixed process of unidirectional / bidirectional cyclic loading, first calibrating the parameters through a small amount of bidirectional cyclic preloading, then applying cyclic loads of different amplitudes in stages (the number of cycles ≥1000 to simulate long-term marine loads). After loading, horizontal static loading is performed until the displacement of the mud surface at the top of the pile reaches 0.1 times the pile diameter, and the ultimate bearing capacity is obtained as a reference benchmark. This solves the problems of arbitrary setting of loading parameters and lack of unified verification standards in traditional tests, and significantly improves the repeatability of the test. Specifically, a loading test method based on a field-directly grouted microbial reinforced pile test device includes the following steps: Step S1: Prepare the bacterial solution and the cementing solution, and place them in the two chambers of the slurry storage tank respectively; Step S2: Fill the test site with layers of sand and clay and compact them. Continue to install symmetrically distributed steel frame structures on the test site. After attaching several strain gauges at different heights of the single pile, vertically implant the single pile into the test soil. Step S3: Connect the jack and vibrator to the slide rail respectively, then install the slide rail on the symmetrically arranged steel frame structure, install force sensors at the output ends of the jack and vibrator respectively, and fix eddy current displacement gauges at positions close to the point of action. Step S4: Start the grouting pump, first inject a quantitative bacterial solution into the test soil, let it stand for a preset time, then inject a quantitative cementing solution into the test soil, and continue to let it stand for a preset time. Repeat the cementing and standing process three times until the test soil is stable. At this time, the grouting range is 4 to 5 times the pile diameter, and the reinforcement depth is 1 to 2 times the pile diameter. Steps S1 to S4 integrate the microbial reinforced soil with the test, clarifying the process requirements for direct on-site grouting. Compared with the traditional test mode that separates the preparation of reinforced soil from the loading test, this approach is more in line with engineering practice and can accurately reflect the true mechanical properties of the pile foundation after on-site grouting reinforcement.

[0024] Step S5: Connect the data acquisition instrument to the computer 15, start the high-resolution digital camera, adjust the output parameters of the exciter, verify all equipment, and then proceed to the next step; if a unidirectional cyclic loading test is to be performed, proceed to step S6; if a bidirectional cyclic loading test is to be performed, proceed to step S11. Step S6: Start the vibrator to apply force to the single pile. Symmetrical bidirectional cyclic load with a cycle number of cycles Adjust the peak value of the loading to be consistent with the peak value of the pre-applied unidirectional cyclic load, and record the load, displacement and pile strain data during the bidirectional cyclic loading process; Step S7: Stop the vibrator, start the jack to apply static load, adjust the load size to half of the peak value of the pre-applied load, and after the load stabilizes, record the load, displacement and pile strain parameters during the static loading process. Step S8: Keeping the static load stable, restart the exciter to apply a bidirectional cyclic load. The two loads are superimposed to form a unidirectional cyclic load. At this time... Set the number of loops Data is collected synchronously during the cycle and the deformation of the test soil is recorded using a high-resolution digital camera; Step S9: After completing the current loading, stop the jack, remove the static load, and repeat steps S6-S8 to apply different load amplitude parameters in sequence. One-way cyclic loading test; Step S10: After all unidirectional cyclic loading sets are completed, perform a horizontal static load test, slowly increase the load until the displacement of the mud surface at the top of the single pile reaches 0.1 times the pile diameter, record the ultimate bearing capacity at this time, and complete the unidirectional cyclic loading test. Step S11: Set the load amplitude parameters of the exciter. Start the vibrator to apply force to the single pile. Symmetrical bidirectional cyclic load with a cycle number of cycles , =-1, Record the data during the loading process and the deformation of the test soil; Step S12, add load amplitude parameters Repeat step S11 to obtain the values ​​of different load amplitude parameters. Bidirectional cyclic loading test; Step S13: After all bidirectional cyclic loading sets are completed, perform a horizontal static load test, slowly increase the load until the displacement of the mud surface at the top of the single pile reaches 0.1 times the pile diameter, record the ultimate bearing capacity at this time, and complete the bidirectional cyclic loading test.

[0025] Traditional tests cannot capture the key nodes of microscopic damage in reinforced soil. Therefore, in this application, if the cemented surface of the test soil detaches and slips under bidirectional cyclic loading, steps S6 to S8 should be performed again to compare the changes in the mechanical properties of the pile foundation under bidirectional cyclic loading after cementation failure. This allows for a complete study of the long-term cyclic damage evolution law of microbially reinforced soil.

[0026] The loading test method clearly defines key requirements such as loading sequence, load parameters, number of cycles, and static verification standards. Unidirectional cyclic loading is achieved through the combined superposition of jacks (static load) and vibrators (bidirectional cyclic load), while symmetrical bidirectional cyclic loading is achieved directly through the vibrator. The data acquisition system synchronously acquires load, displacement, and strain data at a sampling frequency of 20Hz, and the observation system captures the microscopic deformation of the soil around the pile. The selection of at least 1000 loading cycles better reflects the characteristics of long-term marine loads. After loading, the ultimate bearing capacity is obtained through static loading as a benchmark, solving the problems of arbitrary test parameters and lack of unified verification standards in traditional tests. The repeatability of the test is greatly improved, thus ensuring the accuracy of the test data even with different test personnel and different test sites.

[0027] Simultaneously, in steps S9 and S12, the load amplitude parameters are set. The expected range is 0.1 to 0.7. Setting this critical range allows for precise simulation of unidirectional or bidirectional dynamic load conditions involving the coupling of ocean wind, waves, and currents, significantly improving adaptability and enabling comprehensive research on the mechanical response of pile foundations under different marine dynamic loads.

[0028] In summary, the on-site grouting microbial reinforced pile test device and loading test method provided in this application are the first to integrate the on-site grouting process of microbial reinforced soil with the cyclic loading test of pile foundations, constructing a standardized unidirectional / bidirectional cyclic loading test system for microbial reinforced piles. This solves the technical problems of traditional tests being unable to capture microscopic damage in reinforced soil and quantitatively analyze stiffness decay. Furthermore, the device is easy to assemble and disassemble, enabling rapid testing at various marine engineering construction sites, facilitating large-scale application, and possessing excellent prospects for engineering promotion.

[0029] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0030] The meaning of "and / or" as used in this application includes situations where each exists alone or both exist simultaneously.

[0031] The term "connection" as used in this application can mean a direct connection between components or an indirect connection between components through other components.

[0032] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A test device for microbial-reinforced piles based on direct on-site grouting, characterized in that: Test soil was filled into the test site, and a single pile was vertically driven into the test soil. With the single pile as the center of symmetry, steel frame structures were set up on both sides of it. A jack could be slidably installed on one side of the steel frame, and a vibrator could be slidably installed on the other side. The output ends of the jack and the vibrator were both pressed against the wall of the single pile. It also includes a data acquisition system, which includes force sensors, eddy current displacement gauges, strain gauges and a data acquisition instrument. Several strain gauges are attached to different heights of the single pile body. Force sensors are installed at the output ends of the jacks and vibrators. Eddy current displacement gauges are installed at the output ends of the jacks and vibrators near the point of action. Force sensors, eddy current displacement gauges and strain gauges are all connected to the data acquisition instrument. A slurry storage tank is installed on the steel frame structure on one side of the jack. The slurry storage tank contains bacterial solution and cementing solution. One end of the delivery pipe is inserted into the slurry storage tank, and the other end is inserted into the test soil through a grouting pump.

2. The experimental device for microbial-reinforced piles based on direct on-site grouting as described in claim 1, characterized in that: The steel frame structure includes a steel frame body, which includes columns, diagonal braces, and transverse reinforcing beams. The columns and transverse reinforcing beams are arranged perpendicularly. One end of the diagonal brace is fixed to the column, and the other end is fixed to the transverse reinforcing beam. The three form a triangular stable structure. The bottom of the steel frame body is fixed by ground anchors. The two steel frame bodies arranged opposite each other are connected by two horizontally arranged slide rails to form a closed frame, that is, two slide rails are vertically fixed between the two columns.

3. The test device for microbial-reinforced piles based on direct on-site grouting as described in claim 1, characterized in that: The jack and vibrator are both hung on the slide rail via sliding brackets. Guide sliders are installed on the side of the bracket that contacts the jack and vibrator, allowing the jack and vibrator to slide on the slide rail. The base of the jack is connected to the column by a ball joint, and the base of the vibrator is covered with a rubber pad and then fixed to the column by a rigid bracket.

4. The test device for microbial-reinforced piles based on direct on-site grouting as described in claim 1, characterized in that: The slurry storage tank has a double-cavity structure, and a double-blade agitator is installed inside the slurry storage tank.

5. The test device for microbial-reinforced piles based on direct on-site grouting as described in claim 1, characterized in that: The test soil includes sand and clay, with the clay layer located on top of the sand in the test site.

6. The test device for microbial-reinforced piles based on direct on-site grouting as described in claim 1, characterized in that: A high-resolution digital camera was installed on the outside side of the test site.

7. The test device for microbial-reinforced piles based on direct on-site grouting as described in claim 1, characterized in that: When several strain gauges are attached to the pile body, a differentiated arrangement is adopted, with the interval between strain gauges near the mud surface of the test soil on the pile body being less than the interval between strain gauges at the bottom of the pile.

8. A loading test method based on a field-direct grouting microbial reinforced pile test device, using the field-direct grouting microbial reinforced pile test device as described in any one of claims 1-7, characterized in that: Includes the following steps: Step S1: Prepare the bacterial solution and the cementing solution, and place them in the two chambers of the slurry storage tank respectively; Step S2: Fill the test site with layers of sand and clay and compact them. Continue to install symmetrically distributed steel frame structures on the test site. After attaching several strain gauges at different heights of the single pile, vertically implant the single pile into the test soil. Step S3: Connect the jack and vibrator to the slide rail respectively, then install the slide rail on the symmetrically arranged steel frame structure, install force sensors at the output ends of the jack and vibrator respectively, and fix eddy current displacement gauges at positions close to the point of action. Step S4: Start the grouting pump, first inject a quantitative bacterial solution into the test soil, let it stand for a preset time, then inject a quantitative cementing solution into the test soil, and continue to let it stand for a preset time. Repeat the cementing and standing process three times until the test soil is stable. At this time, the grouting range is 4 to 5 times the pile diameter, and the reinforcement depth is 1 to 2 times the pile diameter. Step S5: Connect the data acquisition instrument to the computer, start the high-resolution digital camera, adjust the output parameters of the exciter, and verify all equipment before proceeding to the next step; if a unidirectional cyclic loading test is to be performed, proceed to step S6; if a bidirectional cyclic loading test is to be performed, proceed to step S11. Step S6: Start the vibrator to apply force to the single pile. Symmetrical bidirectional cyclic load with a cycle number of cycles Adjust the peak value of the loading to be consistent with the peak value of the pre-applied unidirectional cyclic load, and record the load, displacement and pile strain data during the bidirectional cyclic loading process; Step S7: Stop the vibrator, start the jack to apply static load, adjust the load size to half of the peak value of the pre-applied load, and after the load stabilizes, record the load, displacement and pile strain parameters during the static loading process. Step S8: Keeping the static load stable, restart the exciter to apply a bidirectional cyclic load. The two loads are superimposed to form a unidirectional cyclic load. At this time... Set the number of loops Data is collected synchronously during the cycle and the deformation of the test soil is recorded using a high-resolution digital camera; Step S9: After completing the current loading, stop the jack, remove the static load, and repeat steps S6-S8 to apply different load amplitude parameters in sequence. One-way cyclic loading test; Step S10: After all unidirectional cyclic loading sets are completed, perform a horizontal static load test, slowly increase the load until the displacement of the mud surface at the top of the single pile reaches 0.1 times the pile diameter, record the ultimate bearing capacity at this time, and complete the unidirectional cyclic loading test. Step S11: Set the load amplitude parameters of the exciter. Start the vibrator to apply force to the single pile. Symmetrical bidirectional cyclic load with a cycle number of cycles , =-1, Record the data during the loading process and the deformation of the test soil; Step S12, add load amplitude parameters Repeat step S11 to obtain the values ​​of different load amplitude parameters. Bidirectional cyclic loading test; Step S13: After all bidirectional cyclic loading sets are completed, perform a horizontal static load test, slowly increase the load until the displacement of the mud surface at the top of the single pile reaches 0.1 times the pile diameter, record the ultimate bearing capacity at this time, and complete the bidirectional cyclic loading test.

9. The loading test method based on the on-site direct grouting microbial reinforced pile test device according to claim 8, characterized in that: If the cemented surface of the test soil detaches and slips under bidirectional cyclic loading, steps S6 to S8 should be repeated to compare the changes in the mechanical properties of the pile foundation under bidirectional cyclic loading after cementation failure.

10. The loading test method based on the on-site direct grouting microbial reinforced pile test device according to claim 8, characterized in that: In steps S9 and S12, the load amplitude parameters are set. The expected range is 0.1 to 0.7.

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