Equipment and method for measuring buoyancy borne by assembly type circular open caisson structure through centrifugal machine

Abstract

The invention discloses equipment and a method for measuring buoyancy borne by an assembly type circular open caisson structure through a centrifugal machine, and belongs to the technical field of civil engineering. The device comprises a centrifugal machine, a circular open caisson structure and a buoyancy measuring device, the circular open caisson structure is arranged in a hanging basket of the centrifugal machine; the buoyancy measuring device is installed on the centrifugal machine and connected with a data acquisition port of the centrifugal machine through a sensor signal line. According to the embodiment, the stress conditions of the soil layer and the structure of the assembly type circular open caisson under various working conditions are effectively simulated through centrifugal machine tests, meanwhile, the researched and developed buoyancy measuring device has universality, and the buoyancy measuring device can be suitable for all centrifugal machine facilities needing to measure the buoyancy borne by the underground structure by properly modifying the structure of the reaction frame.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, and particularly relates to a device and method for measuring the buoyancy force on an assembled circular caisson structure by a centrifuge. Background Art

[0002] At present, several cities in China have carried out pilot projects on underground multi-storey car parks. However, when using traditional construction methods such as open cut method and caisson method to build underground multi-storey car parks in the central urban areas, there are problems such as large floor area occupation, traffic congestion, long construction period, and even possible hazards such as tilting and cracking of ground buildings. Therefore, it is urgent to explore a method for building underground multi-storey car parks in complex and crowded central urban areas with little environmental impact, fast construction speed and small construction floor area. Compared with traditional methods, the caisson construction method that realizes simultaneous tunneling and assembly with a new type of equipment, the vertical shaft tunneling machine, has obvious advantages and can effectively avoid the above problems. In recent years, there have been engineering application examples in China.

[0003] In the non-drainage excavation mode, during the sinking process of the caisson, it is affected by the water buoyancy force, which is part of the sinking resistance. The value of the water buoyancy force is relatively small and can generally be calculated according to Archimedes' principle. After the caisson is sealed at the bottom to form a well and the water in the well is pumped out, the caisson may float under the action of the groundwater buoyancy force. Therefore, anti-floating checking calculations / designs need to be carried out in the design. However, although the current design specifications require that anti-floating checking calculations should be carried out for all underground structures during design, no specific design method is stipulated. Due to the lack of unified regulations on the anti-floating checking calculation method and the selection of the design water level, many unreasonable designs have been caused.

[0004] Centrifuge tests can use small-scale geometric models to simulate the deformation characteristics of prototypes. It can, under the condition of greatly saving manpower and material resources, conduct comparative studies on multiple different design schemes for the same complex problem under the same test conditions, conduct comparative analysis from multiple angles, obtain a deeper understanding and general laws, and provide references for future similar projects.

[0005] In different strata, due to differences in soil permeability coefficients and the interaction modes between water and soil particles, etc., the magnitude of the groundwater buoyancy force acting on underground structures may vary. Therefore, it is necessary to provide a device and method for measuring the buoyancy force on an assembled circular caisson structure by a centrifuge. Summary of the Invention

[0006] The purpose of the present invention is to provide a device and method for measuring the buoyancy force on an assembled circular caisson structure by a centrifuge, so as to monitor the buoyancy force suffered during the construction process of the assembled circular caisson.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A device for measuring the buoyancy force on an assembled circular caisson structure by a centrifuge, comprising: a centrifuge, a circular caisson structure, and a buoyancy force measuring device;

[0009] The circular caisson structure is arranged in the hanging basket of the centrifuge;

[0010] The buoyancy force measuring device is installed on the centrifuge and is connected to the data acquisition port of the centrifuge through a sensor signal line.

[0011] Furthermore, the circular caisson structure includes: segments designed and processed by 3D printing technology.

[0012] Furthermore, a plurality of sidewall earth pressure sensors and a plurality of circumferential joint strain gauges are arranged at intervals on the surface of the circular caisson structure, and a plurality of vertical earth pressure sensors are arranged at intervals on the bottom plate of the circular caisson structure.

[0013] Furthermore, the buoyancy force measuring device includes:

[0014] A reaction frame welded by steel plates, the top of the reaction frame has a cross beam, and the feet have brackets; slots are provided on both the cross beam and the brackets;

[0015] A force transfer rod, one end of which is connected to the reaction frame, and the other end is connected to a force measuring sensor;

[0016] A cover plate, one end of which is connected to the force measuring sensor, and the other end is arranged at intervals above the circular caisson structure.

[0017] A method for measuring the buoyancy force on an assembled circular caisson structure by a centrifuge, applied to the device for measuring the buoyancy force on an assembled circular caisson structure by a centrifuge, the method comprising:

[0018] S1, Preparation of the model box;

[0019] S2, Preparation of the soil sample;

[0020] S3, Precast segments are assembled into a circular caisson structure, and sensors are installed on the wall surface of the circular caisson structure;

[0021] S4, Placing the specimen in the box

[0022] S41, Embed the prepared soil sample into the model box, and synchronously bury the sensors and the prefabricated assembled circular caisson structure;

[0023] S42, Install the buoyancy force measuring device;

[0024] S43, Drive the drainage channels;

[0025] S5, Wiring of the centrifuge

[0026] S51. Weigh the model box as a whole and calculate the required counterweight.

[0027] S52. Lift the model box into the centrifuge basket and install the corresponding counterweight blocks.

[0028] S53. Connect all sensors to the centrifuge data acquisition port through aviation plugs.

[0029] S6. Test preparation

[0030] Connect the centrifuge main system, servo control system, and numerical control system to the power supply, put them in a standby state, and turn on the video monitoring system and data acquisition system.

[0031] S7. Start the test

[0032] Enable dynamic data acquisition, start the centrifuge, gradually increase the centripetal acceleration to the set value, then keep running, and read and collect sensor parameters in real time.

[0033] S8. End of the test

[0034] Gradually reduce the speed of the centrifuge until it stops completely, remove the data cable, lift out the model box and clean it.

[0035] Furthermore, step S4 specifically includes:

[0036] Fill the prepared undisturbed soil samples into the model box in multiple layers. Among them, when filling to a height of 8 cm, place the first pore pressure sensor; when filling to a height of 16 cm, place the second pore pressure sensor; when filling to a height of 24 cm, place the third, fourth, fifth, and sixth pore pressure sensors; when filling to a height of 25 cm, place the circular caisson structure into the model box; finally, fill the soil sample to a height higher than 63 cm; pour the pre-prepared sodium silicate solution with a specific concentration into the circular caisson structure and determine the liquid level height.

[0037] Furthermore, step S7 specifically includes:

[0038] S71. Consolidation

[0039] Gradually increase the centrifuge speed by 10g for each centripetal acceleration. After reaching a centripetal acceleration of 50g, keep the centrifuge stable for more than 5 hours to consolidate the soil sample in the model box; wait until the readings of the piezometers around the circular caisson structure are basically stable, and the consolidation is completed.

[0040] S72. Stop the machine and drain the liquid

[0041] After the centrifuge stops running, use a pumping device to pump out the sodium silicate solution to simulate the pumping condition after the caisson construction is completed, and ensure that the circular caisson structure can float after starting again.

[0042] S73, Buoyancy measurement

[0043] Enable dynamic data acquisition, start the centrifuge, gradually increase the centripetal acceleration to 50g, then keep running until the readings of the pore pressure sensor, earth pressure sensor, and force sensor are stable, and collect the data of the force sensor;

[0044] S74, Loading measurement

[0045] Stop the centrifuge, inject sand into the inside of the circular caisson structure to keep the internal and external pressures balanced, enable dynamic data acquisition, start the centrifuge, gradually increase the centripetal acceleration to 50g, and then keep running until the readings of the pore pressure sensor and earth pressure sensor are stable.

[0046] The present invention has the following beneficial effects:

[0047] In this embodiment, the centrifuge test effectively simulates the stress conditions of the soil layer and the structure of the prefabricated circular caisson under various working conditions. At the same time, the developed buoyancy measurement device is universal, and it can be applied to all centrifuge facilities that need to measure the buoyancy force on underground structures by appropriately modifying the structure of the reaction frame. Moreover, the device is easy to operate and can quickly adjust its own installation position, providing convenience for buoyancy measurement. Description of the drawings

[0048] Figure 1 It is an enlarged three-dimensional structure schematic diagram of the reaction frame in this embodiment;

[0049] Figure 2 It is an enlarged front view structure schematic diagram of the segment in this embodiment. Specific implementation manners

[0050] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention.

[0051] This embodiment provides a device for measuring the buoyancy force on a prefabricated circular caisson structure by a centrifuge, including: a centrifuge, a circular caisson structure, and a buoyancy measurement device; the circular caisson structure is arranged in the hanging basket of the centrifuge; the circular caisson structure includes: segments designed and processed by 3D printing technology.

[0052] Among them, the segment is designed and processed by using the aluminum alloy 3D printing technology. The size of the segment is scaled down to 1 / 50 of the prototype according to the determined similarity ratio. However, the thickness of the segment and the bolts for the connection of the caisson should be converted with reference to the modulus of the prototype and model materials, referring to the similar relationship between the flexural stiffness and the tensile yield strength of the model and the prototype. In addition, considering the feasibility of the prefabricated model connection, in this model, every two rings of the segment are combined into one ring, that is, the length of the single lining ring of the model along the caisson direction is 48 mm instead of 24 mm. Each caisson lining ring is composed of 6 segments, namely 1 segment with an angle of 16°, 4 segments with an angle of 65° and 1 segment with an angle of 84°. According to this similarity ratio relationship, the thickness of the segment of the tunnel model should be 5.56 mm. Considering the need for sensor layout and tunnel model connection, the width of the single lining ring of the tunnel model is changed to 2 times that of the prototype, that is, 48 mm, and the prototype is 2.4 m.

[0053] 7 M1 bolts are required for a single ring section; 1 M1 bolt is required for the longitudinal joint of a single lining ring.

[0054] During the test, six side wall earth pressure sensors and six circumferential joint strain gauges are arranged at intervals on the surface of the circular caisson structure, and three vertical earth pressure sensors are arranged at intervals on the bottom plate of the structure.

[0055] In this embodiment, the buoyancy measuring device is installed on the centrifuge and connected to the data acquisition port of the centrifuge through the sensor signal line.

[0056] The buoyancy measuring device includes: a reaction frame welded by steel plates, the top of the reaction frame has a cross beam, and the feet have brackets; slots are provided on both the cross beam and the brackets.

[0057] A force transfer rod, one end of which is connected to the reaction frame and the other end is connected with a force measuring sensor.

[0058] A cover plate, one end of which is connected to the force measuring sensor and the other end is arranged at intervals above the circular caisson structure.

[0059] It can be understood that the reaction frame is welded by steel plates, and slots are provided on both the top cross beam and the feet brackets. It is connected to the force transfer rod and the model box by bolts and can move freely to facilitate the alignment of the buoyancy measuring device with the center of the structure.

[0060] The force transfer rod is a metal rod with a through-thread, one end of which is connected to the cross beam of the reaction frame by bolts and can move back and forth to facilitate the alignment of the buoyancy measuring device with the center of the structure, and the other end is connected to the upper side screw hole of the force measuring sensor.

[0061] The force measuring sensor is S-shaped, with an outer dimension of 50.8 mm (length) × 25.4 mm (width) × 76.2 mm (height). There are internal threads of M12 level with a height of about 20 mm at the upper and lower parts, which are used to connect the force transfer rod and the lower cover plate respectively.

[0062] One end of the cover is connected to the load cell, while the other end is suspended above the underground structure model, slightly away from it. Its diameter is 16 cm, its thickness is 1 cm, and its planar dimensions are slightly larger than the structure to ensure that the cover can completely cover the structure.

[0063] This embodiment provides a method for measuring the buoyancy of an assembled circular caisson structure using a centrifuge, which is applied to a device for measuring the buoyancy of an assembled circular caisson structure using a centrifuge. The method includes:

[0064] S1, model box preparation

[0065] The contact area between the partition and the model box was sanded smooth and wiped clean. After installing the partition, waterproof glue was applied and air-dried to ensure that the soil sample and water would not leak during the test. To prevent friction between the soil and the side walls of the model box from affecting the experimental results, a layer of Teflon film was attached to the inner wall of the model box.

[0066] S2, soil sample preparation

[0067] Take a small amount of soil sample to measure its moisture content, then cut it into small pieces. Considering that some water will be expelled during the consolidation process, add water corresponding to the mass of the remolded soil sample at 103% saturation. Use a handheld blender to mix evenly in multiple passes. Store the prepared soil sample in a covered bucket to prevent the surface soil from drying out.

[0068] S3, prefabricated segments are assembled into a circular caisson structure, and sensors are installed on the well wall surface of the circular caisson structure;

[0069] Specifically, the segments (seven rings in total) are bolted together, then coated internally with a barely-there waterproof paint. Once the paint dries, a base plate is attached to the bottom of the caisson, and waterproof glue is applied to the joints between the base plate and the inside and outside of the caisson. Once assembled, strain gauges and earth pressure gauges are attached to the exterior of the caisson model at predetermined locations, and then connected to a centrifuge to test the sensors for proper function.

[0070] S4, sample packing

[0071] S41. Embed the prepared soil sample into the model box, and synchronously embed the sensors and the prefabricated circular caisson structure. Specifically, fill the prepared undisturbed soil sample into the model box in multiple layers. Among them, when filling to a height of about 8 cm, place the first pore pressure sensor; when filling to a height of about 16 cm, place the second pore pressure sensor; when filling to a height of about 24 cm, place the third, fourth, fifth, and sixth pore pressure sensors; when filling to a height of about 25 cm, place the circular caisson structure into the model box; finally, fill the soil sample to a height slightly higher than 63 cm. During the process, pay attention to the smooth routing of the sensors. The routing of the sensors in the soil body extends from the corners of the model box, and is fixed with cable ties, fixed on the surface of the box with geotextile tape, and finally connected to the centrifuge data acquisition port; the sensors on the structure are firmly attached to the well wall with glue, extend from directly above the structure, and are fixed with cable ties, and finally connected to the centrifuge data acquisition port.

[0072] Pour the pre-prepared sodium silicate solution with a specific concentration into the circular caisson structure to ensure that the water pressure at the bottom of the caisson sealing position is consistent with the actual water pressure at this depth, and determine the liquid level height.

[0073] S42. Install the buoyancy measurement device;

[0074] S43. Drive the drainage channel

[0075] Specifically, ensure that the bottom of the drainage pipe is also sealed with gauze and fixed with cable ties. Drive the drainage pipe at a suitable position in the soil body (avoiding the routing of the sensors), and at the same time pay attention not to affect the structure position.

[0076] The drainage channel is a PVC pipe with a length of one meter. A pair of through holes with a diameter of 4 mm are driven every 2 cm, and the surface is wrapped with gauze and finally fixed with cable ties.

[0077] S5. Connect the centrifuge

[0078] S51. Weigh the model box as a whole and calculate the required counterweight;

[0079] S52. Lift the model box into the centrifuge hanging basket and install the corresponding counterweight blocks;

[0080] S53. Connect all the sensors to the centrifuge data acquisition port through aviation plugs.

[0081] Specifically, install the buoyancy measurement device, weigh the total mass of the model box and the buoyancy measurement device, and then carefully lift the model box into the centrifuge hanging basket with a laboratory crane, trying to avoid bumps. After lifting in place, adjust the counterweight at the counterweight end of the centrifuge according to the total mass of the model box to ensure the safe and stable operation of the equipment. Connect the sensor signal wire to a special aviation plug and connect it to the centrifuge data acquisition port.

[0082] S6. Test preparation

[0083] Connect the main centrifuge system, servo control system, and numerical control system to the power supply, put them in the standby state, and turn on the video monitoring system and data acquisition system.

[0084] Specifically, turn on the power supply of the centrifuge data acquisition channel, start the data acquisition software, check and debug the connection of each channel. After the data of each channel is displayed normally, clean the sundries in the centrifuge room and prepare to start the centrifuge.

[0085] Close the door of the centrifuge room and turn on the centrifuge video monitoring system. After the video signal is normal, turn on the centrifuge power supply, oil pump, and fan switches in sequence, set the centrifuge speed, start the centrifuge driving device, and the centrifuge starts to rotate.

[0086] S7, Start the test

[0087] Enable dynamic data acquisition, start the centrifuge, gradually increase the centrifugal acceleration to the set value, then keep running, and read and collect the sensor parameters in real time. Specifically as follows:

[0088] S71, Consolidation

[0089] Increase the centrifuge speed step by step by 10g of centrifugal acceleration. After reaching a centrifugal acceleration of 50g, keep the centrifuge stable for more than 5 hours to consolidate the soil sample in the model box. Wait until the readings of the pore water pressure gauges around the caisson are basically stable, and consider that the first-stage consolidation is completed.

[0090] S72, Stop the machine and drain the liquid

[0091] After the centrifuge stops running, use the pumping device to pump out the sodium silicate solution to simulate the pumping condition after the caisson construction is completed, and ensure that the structure can float up after starting again.

[0092] S73, Buoyancy measurement

[0093] Enable dynamic data acquisition, start the centrifuge, gradually increase the centrifugal acceleration to 50g, then keep running until the readings of the pore pressure, soil pressure sensors, and force measuring sensors are stable, and consider that the structure no longer floats up. Collect the data of the force measuring sensor.

[0094] It should be noted that in the initial stage, the acceleration is small, the structure does not float up, and the reading of the force measuring sensor is the self-weight of the cover plate, which is a positive number; after the centrifuge runs stably, affected by the floating up of the structure, the reading of the force measuring sensor is negative. The actually measured buoyancy should be added with the self-weight of the cover plate and is greater than the image peak value.

[0095] S74, Loading measurement

[0096] The centrifuge is shut down, sand is injected into the interior of the circular caisson structure to maintain the internal and external pressure balance, data dynamic acquisition is started, the centrifuge is started, and the centrifugal acceleration is gradually increased to 50g, and then it is kept running until the readings of the pore pressure and earth pressure sensors are stable.

[0097] S8, the test is completed

[0098] Gradually reduce the speed of the centrifuge until it comes to a complete stop, remove the data cable, lift out the model box and clean it up.

[0099] In this embodiment, the centrifuge test effectively simulates the stress conditions of the soil layer and the structure of the assembled circular caisson under various working conditions. At the same time, the developed buoyancy measurement device is universal. By appropriately modifying the structure of the reaction frame, it can be applied to all centrifuge facilities that need to measure the buoyancy force on underground structures. And the device is easy to operate and can quickly adjust its own installation position, providing convenience for buoyancy measurement.

[0100] The embodiments described above are only used to describe the preferred mode of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. An equipment for measuring the buoyancy force received by an assembled circular caisson structure of a centrifuge, characterized in that, Comprising: A centrifuge, a circular caisson structure, and a buoyancy measurement device; The circular caisson structure is arranged inside the hanging basket of the centrifuge; The buoyancy measurement device is installed on the centrifuge and connected to the data acquisition port of the centrifuge through a sensor signal line.

2. The device for measuring the buoyancy force on the assembled circular caisson structure by the centrifuge according to claim 1, wherein The circular caisson structure includes: segments designed and processed using 3D printing technology.

3. The device for measuring the buoyancy force on the assembled circular caisson structure by the centrifuge according to claim 1, characterized in that, A plurality of sidewall earth pressure sensors and a plurality of circumferential joint strain gauges are arranged at intervals on the surface of the circular caisson structure, and a plurality of vertical earth pressure sensors are arranged at intervals on the bottom plate of the circular caisson structure.

4. The device for measuring the buoyancy force on the assembled circular caisson structure by the centrifuge according to claim 1, wherein The buoyancy measurement device includes: A reaction frame welded by steel plates, the top of the reaction frame has a cross beam, and the feet have brackets; slots are provided on both the cross beam and the brackets; A load transfer rod, one end of which is connected to the reaction frame and the other end is connected to a force measurement sensor; A cover plate, one end of which is connected to the force measurement sensor and the other end is arranged at intervals above the circular caisson structure.

5. A method for measuring the buoyancy force on an assembled circular caisson structure by a centrifuge, characterized in that, Equipment applied to a centrifuge for measuring the buoyancy received by an assembled circular caisson structure, the method includes: S1, Preparation of the model box; S2, Preparation of the soil sample; S3, Precast segments are assembled into a circular caisson structure, and sensors are installed on the wall surface of the circular caisson structure; S4, Loading the specimen S41, Embed the prepared soil sample into the model box, and synchronously bury the sensors and the precast assembled circular caisson structure; S42, Install the buoyancy measurement device; S43, Drive drainage channels; S5, Wiring of the centrifuge S51, Weigh the model box as a whole and calculate the required counterweight; S52, Lift the model box into the hanging basket of the centrifuge and install the corresponding counterweight blocks; S53, Connect all sensors to the data acquisition port of the centrifuge through aviation plugs; S6, Test preparation Connect the main system of the centrifuge, the servo control system, and the numerical control system to the power supply, be in a standby state, and turn on the video monitoring system and the data acquisition system; S7, Start the test Enable dynamic data acquisition, start the centrifuge, gradually increase the centrifugal acceleration to the set value, then keep running, and read and collect sensor parameters in real time; S8, End of the test Gradually reduce the speed of the centrifuge until it stops completely, remove the data cable, lift out the model box and clean it.

6. The method for measuring the buoyancy force on the assembled circular caisson structure by the centrifuge according to claim 5, characterized in that, Step S4 specifically includes: Fill the prepared undisturbed soil sample into the model box in multiple layers. Among them, when filling to a height of 8 cm, place the first pore pressure sensor; when filling to a height of 16 cm, place the second pore pressure sensor; when filling to a height of 24 cm, place the third pore pressure sensor, the fourth pore pressure sensor, the fifth pore pressure sensor, and the sixth pore pressure sensor; when filling to a height of 25 cm, place the circular caisson structure into the model box; finally fill the soil sample to a height higher than 63 cm; pour a pre-prepared sodium silicate solution with a specific concentration into the circular caisson structure and determine the liquid level height.

7. The method for measuring the buoyancy force on the assembled circular caisson structure by the centrifuge according to the claim, characterized in that, Step S7 specifically includes: S71, Consolidation Gradually increase the speed of the centrifuge by 10g for each centrifugal acceleration. After reaching a centrifugal acceleration of 50g, keep the centrifuge stable for a duration greater than 5 hours to consolidate the soil sample in the model box; wait until the readings of the pore water pressure gauges around the circular caisson structure are basically stable, and the consolidation is completed; S72, Stop the machine and drain the liquid After the centrifuge stops running, use a water pumping device to pump out the sodium silicate solution, simulating the water pumping condition after the caisson construction is completed, to ensure that the circular caisson structure can float after starting to rotate again; S73, Buoyancy measurement Turn on the dynamic data acquisition, start the centrifuge, gradually increase the centrifugal acceleration to 50g, and then keep running until the readings of the pore pressure, earth pressure sensors and force measuring sensors are stable, and collect the data of the force measuring sensors; S74, Loading measurement Stop the centrifuge, fill the inside of the circular caisson structure with sand to keep the internal and external pressures balanced, turn on the dynamic data acquisition, start the centrifuge, gradually increase the centrifugal acceleration to 50g, and then keep running until the readings of the pore pressure and earth pressure sensors are stable.

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