Caisson construction method

Abstract

The invention relates to a caisson construction method, which adopts a technical solution that inclination sensors are pre—embedded in opposite corners of an inner wall of a caisson and a bottom high—pressure water spray pipe system is provided, six groups of mounting bases arranged in an equilateral triangle are distributed at caisson, a steel spray pipe having an axis at an included angle of 30° with a horizontal plane is provided, mud is formed to assist sinking combined with 2.5 MPa high-pressure water, a water pressure is dynamically adjusted by monitoring inclination data of four corners, an inclination difference is controlled within 0.30, and peripheral gravel throwing and filling and layered clay rolling backfilling are implemented after sinking. The invention ensures precise control of a sinking attitude of caisson, is suitable for rapid and accurate mounting of the caisson structure in hydraulic engineering, and improves construction efficiency and structural stability.

Description

TECHNICAL FIELD The present invention relates to the technical eld of caisson construction of hydraulic engineering. More particularly, the present invention relates to a . BACKGROUND In hydraulic engineering, a caisson structure is widely used in river regulation, wharf foundation and other scenes, and the verticality control of caisson sinking construction is directly related to the structural stability and engineering safety. Traditional caisson sinking construction mainly depends on a self-weight or an additional ballast, but under complex geological conditions, especially when there is hardness unevenness or local obstacle on a surface of a river bed, the caisson is prone to deection due to a stress difference at a bottom portion. In the prior art, an attitude is usually monitored by manual measurement or a simple inclinometer, but a number of measuring points is limited and data feedback is delayed, so that it is difcult to capture a dynamic inclination change in a sinking process in time. For example, according to conventional methods, single-point inclination monitoring devices are only arranged on four side surfaces of a top portion of the caisson, so that an actual stress state of a bottom contact surface cannot be accurately reected, resulting in insufcient basis for rectication. In addition, when the deection is detected, the deection is often rectied by locally increasing the ballast, adjusting a hoisting rigging or manually digging the river bed, and such method not only has low efciency, but also may aggravate the uncertainty of a sinking trajectory due to damage of a formed mud lubrication layer by repeated adjustment. In a high-pressure water jet assisted sinking technology, spray pipes are usually circumferentially arranged at an equal distance along the bottom portion of the caisson, but an angle of a nozzle is mostly a horizontal or single xed elevation angle, so that mud regions formed by scouring are unevenly distributed. For example, when an axis of the spray pipe is parallel to a horizontal plane, a scouring range of a water ow to the river bed is limited to an edge of the caisson, and mud displacement efciency in a central region is low, which is easy to cause increased resistance in a middle section of the bottom portion of the caisson, thus inducing whole inclination. Moreover, when a number of existing spray pipes is insufcient (for example, only 34 groups of spray pipes are provided), a ow adjustment accuracy of each spray pipe is limited, so that it is difcult to effectively balance a local resistance difference through water pressure distribution. Meanwhile, highpressure water pumps mostly adopt a constantpressure output mode, and cannot dynamically adjust a water pressure according to a sinking stage. At an initial stage, a high water pressure may lead to excessive scouring to the river bed to form a deep pit, and at a later stage, an insufcient water pressure cannot maintain effective mud suspension, resulting in the stopping of the caisson or the aggravation of inclination. In traditional rectication methods, an operator needs to manually adjust an opening degree of each spray pipe valve according to a phased measurement result. However, due to the inertia of owing of the mud, there is a time difference between water pressure adjustment and caisson attitude change, and it often takes many times of trial and error operation to reach a balanced state. In this process, the continuous deection of the caisson may lead to a shear stress on a contact surface between the bottom portion and the river bed, resulting in local structural damage. In addition, the prior art lacks systematic control over a backlling technology after sinking, such as directly backlling an ungraded earth and stone mixture or adopting a single rolling parameter, which is easy to cause a lateral displacement of the caisson due to uneven compactness of a backlled body, especially in an environment of water ow scouring, so that a caisson foundation may be followed out, thus affecting the long-term stability. Fundamental reasons for the above problems are as follows: existing monitoring methods cannot realize the real-time accurate perception of a three-dimensional caisson attitude, leading to the lack of data support for a rectication decision; a spray pipe layout and a water pressure control strategy fail to match with a dynamic response characteristic of the river bed, so that it is difcult to form a uniform and controllable mud lubrication layer; and a relationship between technological parameters of backlling and a nal caisson attitude is not fully considered, and subsequent construction may offset an accuracy control effect on previous sinking. The difculty in solving these problems lies in how to synchronously acquire highprecision attitude data and convert the data into a real-time control instruction in a dynamic self-weight sinking process of the caisson. Meanwhile, a spray pipe system capable of adapting to different geological conditions and accurately distributing scouring energy is designed, and it is necessary to ensure that all control actions will not interfere with the stability of the caisson itself, which puts forward extremely high requirements for sensor distribution, hydraulic model construction and construction collaborative control. SUMMARY One objective of the present invention is to solve at least the above problems, and to provide at least the advantages that will be described hereinafter. Another objective of the present invention is to provide a , which solves the technical problems of insufcient verticality control accuracy caused by lagged monitoring means and unreasonable spray pipe layout, and poor structural stability caused by the lack of ne control over a backlling technology in a traditional caisson sinking process in the claims. Another objective of the present invention solves the technical defect in the prior art that an annular gap between a caisson and a backlled body is not tightly lled and an anchoring reliability of a top plate connecting structure is insufcient, which easily causes foundation leakage and structural instability. Another objective of the present invention solves the technical problem in the prior art that the zero calibration of a sensor relies on manual operation, which leads to error accumulation, and the lack of dynamic calibration validity verication affects the reliability of monitoring data. Another objective of the present invention solves the technical problem in the prior art that water pressure adjustment lacks a subsection control strategy, and an abrupt pressure change easily causes caisson Vibration, so that it is difcult to balance rectication efciency and system stability. Another objective of the present invention solves the technical problem in the prior art that the stage conversion of water pressure adjustment lacks a quantitative judgment standard, and the lack of reverse pressure synchronous control leads to a secondary offset in a rectication process. Another objective of the present invention solves the technical problem in the prior art that the asymmetry of throwing and lling construction and the inaccurate control over a thickness of a backlled layer cause the unbalance of a lateral earth pressure of the caisson, which affects a nal positioning accuracy. Another objective of the present invention solves the technical problem in the prior art that technological parameters of layered rolling are not matched with a detection method, so that a weak interlayer is easily formed, resulting in insufcient integrity of the backlled body. Another objective of the present invention solves the technical problem in the prior art that a starting impact of a high-pressure water pump and continuous spraying cause pipeline vibration, and the lack of dynamic feedback of a mud concentration affects the scouring efciency. Another objective of the present invention solves the technical problem in the prior art that a pressure uctuation and an unstable ow velocity in a grouting process lead to uncompacted lling of the gap, and a vertical displacement difference is not effectively monitored. Another objective of the present invention solves the technical problem in the prior art that elongation control and stress relaxation compensation in a tensioning process of a steel strand are insufcient, and there is a hidden danger in a longterm reliability of an anchorage system. In order to achieve these objectives and other advantages according to the present invention, a is provided, which comprises the following steps: rst step: prefabricating a reinforced concrete caisson, pre-embedding inclination sensors in four opposite corner positions of an inner wall of the caisson, annularly and uniformly welding six groups of high-pressure water nozzle mounting bases at a bottom portion of the caisson, wherein each group of bases comprises three mounting holes arranged in an equilateral triangle, and an axis of the mounting hole forms an included angle of 25350 with a horizontal plane, xing a steel spray pipe with a diameter of 50 mm in the mounting hole, and butting the spray pipe with a water outlet of a high-pressure water pump through a quick connector; second step: hoisting the caisson to a design positioning point, keeping a distance of 0.3-0.7 m between the bottom portion of the caisson and a surface of a river bed, turning on the high-pressure water pump to inject water and exhaust air in a pipeline and then turning off the water pump, mounting a verticality monitoring system, and connecting a signal line of the inclination sensor into the system to complete zero calibration; third step: turning on the highpressure water pump to supply water to the spray pipe at an initial water pressure of 2.03.0 MPa, so that a water ow impacts the river bed at an elevation angle of 30° to form mud and the caisson sinks by self-weight, and displaying inclination data of four corners in real time by the monitoring system; fourth step: judging a caisson attitude according to monitoring data: if an inclination difference between two opposite comers in any direction is greater than 0.5 °, executing pressure adjustment to restore the initial water pressure after the inclination difference is less than 0.30; and if the inclination difference does not exceed a limit, maintaining a current water pressure to make the caisson sink continuously; and fth step: repeating the third step to the fourth step until the caisson bottoms out to a design elevation, symmetrically throwing and lling gravel with a particle size of 5-10 mm around the caisson to a thickness of 1.8-2.2 m immediately after turning off the water pump, then backlling clay in layers, wherein a thickness of each layer is 0.5 m, and rolling the backlled body six times by a Vibration roller with an exciting force of 280 kN, wherein an overlapping width of adjacent wheel tracks is one third of a wheel width. Preferably, the of the present invention further comprises the following steps: sixth step: when backlling to an elevation of 1.2 m from a top portion of the caisson, inserting a grouting pipe into a bottom portion of a 200 mm annular gap between the inner wall of the caisson and the backlled body, injecting a cement slurry with a water-cement ratio of 0.45 through a grouting pump, controlling a grouting ow rate at 50 L / min, and when the slurry continuously ows out from an overow port at a top portion of the gap, maintaining a grouting pressure for 10 minutes and then stopping grouting; and seventh step: 24 hours after grouting, mounting a steel connecting ange on a top surface of the caisson, evenly distributing eight anchor bolt holes around the ange, allowing two prestressed steel strands with a diameter of 32 mm to penetrate into each hole, anchoring lower ends of the steel strands in a pre-embedded sleeve of a top plate of the caisson, tensioning the steel strands to 30%, 80% and 100% of a design value in three times, wherein a time interval of each tensioning is 4 hours, and nally xing an anchor head by a hydraulic lock nut. Preferably, according to the of the present invention, in the second step, the connection of the signal line and the zero calibration specically comprise: connecting RS485 signal lines of four inclination sensors in parallel to channels 1-4 of a data acquisition card of the verticality monitoring system, arranging a laser level in a center of a top plane of the caisson, and adjusting a hoisting attitude of the caisson to make a cross datum line emitted by the laser level coincide with a cross positioning mark pre-embedded in the top surface of the caisson, so that the caisson is in a theoretical vertical state at this time; starting a calibration mode of the monitoring system, reading initial output values of the four inclination sensors at the same time, and if an absolute value of an output angle of any sensor is greater than 0.050, sending a zero offset compensation instruction to a corresponding sensor through software of the monitoring system, with a compensation amount of A0=(01+02+03+04) / 4, wherein 04 is a current reading number of the sensor; and after compensating through the software, operating the caisson to make three lateral micro-displacements at an amplitude of 0.3 m, allowing the caisson to stand for 2 minutes after each displacement, and then collecting sensor data, wherein, when a variation standard deviation of angles output by the four sensors is less than 0.02", it is judged that the calibration is effective. Preferably, according to the of the present invention, in the fourth step, the water pressure adjustment specically comprises: in a rst stage, increasing a water pressure of a high-pressure water nozzle in a corresponding region in an inclination direction to 2.8 MPa at a rate of 0.3 MPa / s, and detecting an attitude variation of the caisson after maintaining the pressure for 120 seconds; in a second stage, linearly adjusting the water pressure to 3.3 MPa according to the attitude variation, wherein an adjustment rate is not greater than 0.5 MPa / s; in a third stage, stabilizing the water pressure to 3.8 Mpa at a rate of 0.2 MPa / s; and repeating the three-stage adjustment until a verticality deviation of the caisson is less than 03°. Preferably, according to the of the present invention, during the water pressure adjustment, the operation is suspended for 2 minutes after each stage of adjustment to verify the data of the inclination sensors, and when a verticality deviation difference between two adjacent verications is less than 005°, the next stage is executed; and a water pressure reduction process of a high-pressure water nozzle in an opposite direction is implemented synchronously with the three stages, and a pressure change rate remains the same numerical value. Preferably, according to the of the present invention, in the fth step, two barges carrying the gravel with the particle size of 5-10 mm are symmetrically distributed on two sides of the caisson, distances between the two barges and a center of the caisson are the same and kept at 25 m, the two barges synchronously throw the gravel at a rate of 2 m3 per minute during throwing and lling, and a thickness distribution of a gravel layer is scanned in real time by a multi-beam echo sounder; and When scanning data show that a minimum thickness of the gravel layer in any 10 m>< 10 m region reaches 1.8 m, clay backlling is started, a plasticity index of the backlling clay is controlled between 12 and 18, and two parallel operation lines are formed by combining a longarm excavator with a dump truck, wherein, for a rst operation line, a clay layer with a thickness of 0.3 m is paved around the caisson, and for a second operation line, a clay layer with a thickness of 0.2 m is supplementarily paved to form a single-layer backlled body after rolling the previous operation line. Preferably, according to the of the present invention, when each layer of backlled body is constructed, the backlled body is rolled for twice without vibration by a Vibration roller with an exciting force of 180 kN rst, and then rolled for four times under strong vibration by a roller with an exciting force of 280 kN, wherein a rolling speed is kept at 2 km / h, an overlapping width of adjacent wheel tracks is 40 cm, and after rolling, a compactness degree is detected by a sand lling method, and the next layer is constructed when the compactness degree is 296%. Preferably, according to the of the present invention, in the third step, the high-pressure water pump runs at no-load for 30 seconds before being turned on, and then a working water pressure is established in three stages: in a stage A, the water pressure is increased to 1.0 MPa at a rate of 0.5 MPa / s and maintained for 60 seconds, in a stage B, the water pressure is increased to 2.0 MPa at a rate of 0.3 MPa / s and maintained for 90 seconds, and in a stage C, the water pressure reaches 2.5 MPa at a rate of 0.2 MPa / s; the spraying of the spray pipe adopts an intermittent pulse mode, the operation is suspended for 15 seconds after every 120 seconds of spraying, a mud concentration is detected by a turbidity sensor pre-embedded in the bottom portion of the caisson during the suspension, and when the mud concentration is lower than 180 g / L, the water pressure is increased by 0.2 MPa in the next cycle of spraying, wherein a maximum water pressure is not greater than 3.0 MPa; and the monitoring system collects the inclination data of the four corners at a sampling frequency of 5 times per second, the data are processed by a moving average ltering algorithm, an inclination display value is updated every 10 seconds, and an audible and visual alarm is triggered when a variation between two adjacent display values is greater than 0. 1 °. Preferably, according to the of the present invention, in the sixth step, when the slurry continuously ows out from the overow port, the grouting process comprises: continuously grouting at a constant pressure of 0.8 MPa for 5 minutes, wherein a ow velocity of the slurry at the overow port is detected every 30 seconds, and when a uctuation range of the ow velocity is greater than i10%, an automatic compensation pressure deviation value is AP=0.05><(Vmeasurement'Vreference) / Vreference MPa, wherein Vreference is 50 L / min; gradiently reducing the pressure to 0.6 MPa and then maintaining the pressure for 3 minutes, synchronously monitoring a rising velocity of the slurry through an ultrasonic owmeter pre-embedded in a middle portion of the gap, and controlling the rising velocity within a range of 20-25 cm / min; and recovering the pressure to 0.8 MPa and maintaining the pressure for 2 minutes, symmetrically mounting four displacement sensors at the top portion of the caisson at the same time, and when a vertical displacement difference of the caisson displayed by each sensor is greater than 05 mm, terminating the grouting and releasing the pressure. Preferably, according to the of the present invention, in the seventh step, the tensioning of the steel strand is specically implemented as follows: when primary tensioning is carried out, a tensioning force is applied to 30% of a design value by a center hole jack at a rate of 2 mm per minute, an elongation of the steel strand is measured after the load is maintained for 5 minutes, and when an elongation deviation is greater than i5% of a theoretical value, a subsequent tensioning force is adjusted according to AF=0. 15><(Lmeasurement-Ltheory) / Lthe0ry><F design, wherein Fdesign is a design tensioning force; secondary tensioning is carried out 4 hours after the primary tensioning, the tensioning force is applied to 80% of the design value at a rate of 3 mm per minute, a concrete strain value in a region where the preembedded sleeve of the top plate of the caisson is monitored synchronously, and a strain growth rate is controlled in a range not greater than 5 us, / min; tertiary tensioning is implemented 4 hours after the secondary tensioning, and when the tensioning force is applied to 100% of the design value, the load is maintained for 10 minutes, wherein a tension loss caused by the relaxation of the steel strand is compensated once every 2 minutes, and a compensation amount is 0.3% of a primary tensioning force; and after the tensioning is completed, the hydraulic lock nut is used for anchoring, a tightening torque of the nut is 850 N-m, a 304 stainless steel anti-loosening lock sheet with a thickness of 8 mm is mounted at an exposed end of an anchorage device, and a contact surface between the lock sheet and the anchorage device is applied with special anti-slip grease with a friction coefcient of 0. 12. The present invention comprises at least the following benecial effects. According to the present invention, through the inclination sensors of the four corners and the six groups of spray pipes arranged in equilateral triangles, the realtime monitoring of a three-dimensional caisson attitude and the balanced distribution of a bottom scouring force are realized, and by combining the staged water pressure adjustment with the standardized backlling technology, the verticality deviation is controlled within 0.3°, a symmetry deviation of gravel throwing and lling is reduced to i5%, and a compactness degree of the clay layer is improved to above 96%, thus effectively avoiding the common problems of deection accumulation and uneven foundation settlement in traditional construction. Furthermore, the gradient pressure control over gap grouting is combined with the graded steel strand tensioning technology, so that a lling fullness degree of the annular gap reaches above 98%, an anchorage efciency coefcient of the prestressed steel strand is increased to 0.95, a connection reliability between the caisson and an upper structure is signicantly improved, and a foundation impermeability is improved by 40%. According to the present invention, based on a physical standard of the laser level and a dynamic compensation algorithm of the software, a zero drift error of the sensor is reduced to be within 0.020, and a micro-displacement verication mechanism ensures that the calibrated sensor maintains a measurement accuracy of i0.01° in a dynamic construction environment, thus providing a reliable data basis for a rectication decision. A three-stage pressure adjustment mechanism is combined with linear pressure boost control, so that response time of caisson attitude adjustment is shortened to be within 180 seconds, and a pressure uctuation amplitude in a rectication process is controlled within i015 MPa, thus avoiding system oscillation caused by traditional single-stage pressure adjustment, and improving the rectication efciency by 60%. Through a quantitative judgment standard for stage switching and two-way pressure synchronous control, a secondary offset in the rectication process is limited within 0.05°, so that a system stability index is increased by 35%, thus realizing accurate closed-loop control over the rectication. According to the present invention, a thickness uniformity of the gravel layer reaches $0.15 through the synchronous throwing and lling of the double barges and the real-time sounding monitoring, singlelayer construction time is shortened by 40% through a layered backlling technology, and an imbalance coefcient of the lateral earth pressure is reduced to below 1.05. According to the present invention, a doubleexciting force combined rolling strategy is matched with the sand lling method for detection, which eliminates an internal porosity difference in the backlled body, so that an overall stiffness variation coefcient is £0.08, thus effectively preventing an interlayer stripping phenomenon under water ow scouring. According to the present invention, the hydraulic pressure is constructed in stages and an intermittent pulse spraying mode is adopted, so that a pipeline impact load is reduced by 65%, a proportion of effective scouring time is increased to 85% by feedback control over the mud concentration, and energy consumption of the system is reduced by 20%. Through dynamic pressure compensation and cooperative control over the rising velocity, a compactness degree of the lled gap reaches above 97%, a risk of unbalanced load of the structure is reduced by 90% through a displacement difference monitoring mechanism, and a qualication rate of grouting is improved to 100%. According to the present invention, through closed-loop elongation correction and a relaxation compensation mechanism, an effective prestress retention rate of the steel strand is 295%, and a displacement of the anchorage system is control within 0.2 mm through an antiloosening lock structure, thus ensuring a longterm stability of the structure in a service period. Other advantages, objectives and features of the present invention will be partially reected by the following description, and will be partially understood by those skilled in the art through researching and practicing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a technological ow chart of a according to the present invention. DETAILED DESCRIPTION The present invention is further described in detail hereinafter with reference to the embodiments, so that those skilled in the art can implement according to the text of the specication. It should be understood that the terms such as "having," "including," and "comprising" as used herein do not exclude the presence or addition of one or more other elements or combinations thereof. It should be noted that experimental methods described in the following embodiments are all conventional methods unless otherwise specied. All the reagents and materials can be obtained commercially unless otherwise specied. In the description of the present invention, the orientation or position relationships indicated by the terms such as " transverse", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like, refer to the orientation or position relationships shown in the drawings, which are only intended to facilitate describing the present invention and simplifying the description, and do not indicate or imply that the indicated devices or elements must have a specic orientation, be constructed and operated in a specic orientation, and therefore cannot be understood as a limitation of the present invention. The present invention provides a , which comprises the following steps: rst step: prefabricating a reinforced concrete caisson, pre-embedding inclination sensors in four opposite corner positions of an inner wall of the caisson, annularly and uniformly welding six groups of high-pressure water nozzle mounting bases at a bottom portion of the caisson, wherein each group of bases comprises three mounting holes arranged in an equilateral triangle, and an axis of the mounting hole forms an included angle of 25~35° with a horizontal plane, xing a steel spray pipe with a diameter of 50 mm in the mounting hole, and butting the spray pipe with a water outlet of a high-pressure water pump through a quick connector; second step: hoisting the caisson to a design positioning point, keeping a distance of 0.3~0.7m between the bottom portion of the caisson and a surface of a river bed, turning on the high-pressure water pump to inject water and exhaust air in a pipeline and then turning off the water pump, mounting a verticality monitoring system, and connecting a signal line of the inclination sensor into the system to complete zero calibration; third step: turning on the high-pressure water pump to supply water to the spray pipe at an initial water pressure of 2.03.0 MPa, so that a water ow impacts the river bed at an elevation angle of 30° to form mud and the caisson sinks by self-weight, and displaying inclination data of four corners in real time by the monitoring system; fourth step: judging a caisson attitude according to monitoring data: if an inclination difference between two opposite corners in any direction is greater than 05°, executing pressure adjustment to restore the initial water pressure after the inclination difference is less than 03°; and if the inclination difference does not exceed a limit, maintaining a current water pressure to make the caisson sink continuously; and fth step: repeating the third step to the fourth step until the caisson bottoms out to a design elevation, symmetrically throwing and lling gravel with a particle size of 5-10 mm around the caisson to a thickness of 1.82.2 m immediately after turning off the water pump, then backlling clay in layers, wherein a thickness of each layer is 0.5 m, and rolling the backlled body six times by a Vibration roller with an exciting force of 280 kN, wherein an overlapping width of adjacent wheel tracks is one third of a wheel width. In the above technical solution, in terms of pre-embedding the structure and conguring the spray pipe system in the caisson prefabrication stage, SICK CKS36 inclination sensors may be used, which have a measurement accuracy of i0.01o and a protection level of IP67, and when the sensors are pre-embedded in the opposite comer positions of the inner wall of the caisson, a stainless steel mounting box is arranged at a height of 1.2 m from the bottom portion. The mounting base is formed by welding a Q345 steel plate, a ratio of an annular distribution diameter of the bases to an outer diameter of the caisson is 0.85: l, and a center distance between adjacent bases is controlled within a range of 600-800 mm. The spray pipe is an ASTM A106 Gr.B seamless steel pipe, which has an outer diameter of 50 mm and a wall thickness of 6 mm, and the included angle between the axis of the mounting hole and the horizontal plane may be 25°, 30° or 35°, preferably 30°; and when the included angle is 30°, a tail end of the spray pipe is 150 mm away from an outer edge of the caisson. The quick connector is a Parker H series plane sealing connector, which has a nominal pressure of 4.0 MPa, and a distance between the quick connector and a discharge ange of the high-pressure water pump is kept within 1.2 m. In terms of attitude monitoring and dynamic pressure adjustment control in a sinking process of the caisson, when the caisson is hoisted and positioned, a distance between the bottom portion and the river bed may be set to be 0.3 m, 0.5 m or 0.7 m, preferably 0.5 m, and a Trimble SPS986 GNSS positioning system is used to ensure a plane deviation of <50 mm. The verticality monitoring system may be integrated with Siemens SIMATIC S71200 PLC, a sampling frequency is set to be 5 Hz or 10 Hz, and an emission wavelength of the laser level may be 635 nm or 650 nm during zero calibration. The high-pressure water pump is a Grundfos CR series vertical multi-stage pump, which has a rated ow rate of 120 m3 / h, and an initial water pressure setting range of 2.0-3.0 MPa, preferably 2.5 Mpa, and a pressure difference between adjacent spray pipe groups is not greater than 0.5MPa during pressure adjustment A rectication judgment threshold is set to be 05°, and a corresponding recovery threshold is 0.3°. In terms of a peripheral backlling construction technology after the caisson is positioned, the particle size of the thrown and lled gravel may be 5-10 mm, and the throwing and lling thickness of the gravel is controlled at 1.8 m, 2.0 m or 2.2 m. A water content of the backlled clay layer is controlled at l8%-22%, and a liquid limit range corresponding to a plasticity index of 1218 is 3845. Rolling equipment may be a Dynapac CA250 vibration roller, which has an exciting force set at 280 kN and a rolling speed kept at 1.52.5 km / h. The overlapping width of the wheel tracks may be set to be 1 / 3 of the wheel width, and when the roller has the steel wheel width of 800 mm, the corresponding overlapping width is 267mm. Specic implementation mode of workow of caisson construction First stage: prefabrication of caisson A steel formwork combination system is constructed in a prefabrication site, and a distance between an internal formwork and an external formwork is controlled at 450 mmi5 mm according to a design wall thickness. After the formworks are assembled, the SICK CKS36 inclination sensors are pre-embedded in four inner angle positions at a height of 1.2 m from a top surface of a bottom plate, a sensor mounting box is welded and xed with 304 stainless steel, and the signal line penetrates through a 20 mm galvanized steel pipe to be led to a top junction box. Six groups of high-pressure water nozzle bases are welded on the bottom plate of the caisson, the base is made of the Q345 steel plate, each group of bases are arranged in an equilateral triangle with a side length of 200 mm, and the axis of the mounting hole forms an included angle of 30°il° with the horizontal plane. The spray pipe is the ASTM A106 Gr. B seamless steel pipe, which has an outer diameter of 50 mm, and a port of the spray pipe is provided with a chamfer of 30°, which is welded with the base by a twin llet weld seam, wherein a height of the weld seam is 6 mm. Concrete pouring is carried out in three stages: in a rst stage, the bottom plate is formed by concrete pouring to reach a bottom elevation of the base and compacted by vibration, and then the spray pipe system is mounted; in a second stage, a side wall is formed by concrete pouring to reach a mounting position of the sensor, and the concrete pouring is continued after pre-embedded members are xed; and in a third stage, a top structure is completed. During curing, a temperature is kept at 20-25°C and a humidity is kept at 290%, a strength is detected by a rebound apparatus after the formworks are removed, and the caisson may be transported when the strength reaches 80% of a design strength. Second stage: hoisting and positioning of caisson A 2000 t oating crane is used for hoisting, a rigging is provided with four groups of (p CD80 mm steelcored steel wire ropes, and a hoisting point is arranged on a lifting lug pre-embedded in the top portion of the caisson. Before the caisson enters water, a counterweight is calculated to ensure that a draft is 3 / 5 of a total height when the caisson is in a self-oating state in the water. During positioning, a plane position deviation is controlled at <50 mm by the Trimble SPS986 GNSS system, and the distance between the bottom portion and the river bed is controlled at 0.5 mi0.l m. When the verticality monitoring system is mounted, the signal lines of four groups of sensors are connected to Siemens SIMATIC S7-l200 PLC, the zero calibration is carried out by a Leica LS10 laser level, and an initial angle deviation of each sensor is $0.030 after calibration, Third stage: control over sinking process A Grundfos CR45-6 high-pressure water pump is turned on, and a working water pressure is established by gradient pressure boost: after no-load running for the rst 30 seconds, the working water pressure is increased to 1.0 MPa at a rate of 0.5 MPa / s and then maintained for 60 seconds; subsequently, the working water pressure is increased to 2.0 MPa at a rate of 0.3 MPa / s and then maintained for 90 seconds; and nally, the working water pressure is increased to 2.5 MPa at a rate of 0.2 MPa / s. In a spraying process, the operation is suspended for 15 seconds after every 120 seconds of spraying, the mud concentration is detected by a HACH 2100Q turbidimeter, and when the concentration is lower than 180 g / L, the water pressure is automatically increased by 0.2 MPa. The monitoring system displays the inclination data of the four corners in real time, and if the inclination difference between two opposite corners is greater than 0.50, a pressure adjustment program is started immediately: pressures of three groups of spray pipes on an inclined side are increased to 2.8 MPa at 0.3 MPa / s and then maintained for 120 seconds, subsequently increased to 3.3 MPa at 0.5 MPa / s, and nally stabilized at 3.8MPa; and pressures of spray pipes on the opposite side are reduced synchronously at consistent pressure change rates. Fourth stage: precise backlling construction The throwing and lling operation is started within 2 hours after the caisson is in place, two 800 m3 barges simultaneously throw 5-10 mm gravel in positions 25 m away from two sides of the caisson, and a throwing and lling thickness is monitored in real time by an R2Sonic 2024 multi-beam echo sounder. After the gravel layer reaches a design thickness of 2.0 m, a Caterpillar 336 excavator is combined with a Shaanxi Automobile Delong dump truck for clay backlling. Each clay layer with a thickness of 0.5 m is paved in two stages: rstly, an initial layer with a thickness of 0.3 m is paved by a Komatsu PC360-8 excavator, and rolled twice without vibration by a Dynapak CA250 roller; and then, a sub-layer with a thickness of 0.2 m is supplementarily paved, and rolled four times under strong vibration with an exciting force of 280 kN, and the overlapping width of the wheel tracks is 40 cm. After each layer is rolled, a compactness degree is detected by a sand lling method, and a qualication standard is 296%. In the technical solution, a sinking verticality deviation of the caisson is £0.30, a water ow coverage uniformity of the spray pipe system is improved by 40%, a symmetry deviation of gravel throwing and lling is <5%, and a compactness degree of clay backlling is 296%. Through the adjustable sensor arrangement and the modular spray pipe system, caisson construction requirements of different diameters ranging from 6 m to 15 m are met, and energy consumption of the high-pressure pump is reduced by 15%-20%. A standardized backlling technology improves a bearing capacity of a foundation by 30%, and a post-construction settlement amount is controlled within 80% of a design value. In another technical solution, the further comprises: sixth step: when backlling to an elevation of 1.2 m from a top portion of the caisson, inserting a grouting pipe into a bottom portion of a 200 mm annular gap between the inner wall of the caisson and the backlled body, injecting a cement slurry with a water-cement ratio of 0.45 through a grouting pump, controlling a grouting ow rate at 50 L / min, and when the slurry continuously ows out from an overow port at a top portion of the gap, maintaining a grouting pressure for 10 minutes and then stopping grouting; and seventh step: 24 hours after grouting, mounting a steel connecting ange on a top surface of the caisson, evenly distributing eight anchor bolt holes around the ange, allowing two prestressed steel strands with a diameter of 32 mm to penetrate into each hole, anchoring lower ends of the steel strands in a pre-embedded sleeve of a top plate of the caisson, tensioning the steel strands to 30%, 80% and 100% of a design value in three times, wherein a time interval of each tensioning is 4 hours, and nally xing an anchor head by a hydraulic lock nut. In the above technical solution, according to the grouting technology for the gap between the caisson and the backlled body, a width of the annular gap may be set to be 200 mm, the grouting pipe may be a CD25 mm 304 stainless steel pipe, and an insertion depth of the pipe is 2 / 3 of a height of the gap. The grouting pressure may be 0.6 MPa, 0.8 MPa or 1.0 MPa, preferably 0.8 MPa, and the corresponding water-cement ratio may be adjusted to be 0.45. The grouting pump may be a SANY HEAVY INDUSTRY SY93OOJQZ model, which has a grouting ow rate controlled at 50 L / min and a ow rate control accuracy of i2 L / min, and a high-pressure rubber hose of HIROSS brand may be connected between the grouting pipe and the pump body, which has a bursting pressure of 212 MPa. The overow port may be a pre-embedded PVC pipe arranged in a position 50 mm away from the top portion of the caisson, which has an inner diameter of 38 mm, and a pipe port is 100 mm higher than a backlled plane. The pressure maintenance stage is set to last for 10 minutes, a rising velocity of the slurry is monitored by a Geokon BGK3D ultrasonic owmeter, the equipment may measure a ow velocity in a range of 20-30 cm / min at an accuracy of il 5%. In a graded tensioning technology for a prestressing anchorage system of the top plate, a ange plate may be made of Q355B steel, which has a thickness of 40 mm, and 8 anchor bolt holes may be evenly distributed circumferentially, which have a diameter of 42 mm. The prestressed steel strand may have a specication of 1X715.2 mm in accordance with a GB / T5224 standard, and a single-strand breaking force is 2260 kN. Tensioning equipment may be a YCW250B center hole jack produced by Liuzhou OVM Company, which has a rated tensioning force of 2500 kN and a stroke of 200 mm. The prestressed steel strand is tensioned in three stages to 30%, 80% and 100% of the design value, and the time interval may be adjusted to be 4 hours. The hydraulic lock nut may be a high-strength nut of a DIN6914 standard, a surface of the nut is galvanized, and a locking torque of the nut may be set to be 850 Nm. An antiloosening lock sheet may be made of a 316 stainless steel plate with a thickness of 8 mm, and antislip grease may be Krupp Tribolm series, which has a friction coefcient of 0.10-0.15. In a construction process, the grouting may be carried out after the strength of the backlled body reaches 15 MPa, and a hardness degree of a clamping sheet of an anchorage device should be detected and controlled at HRC5862 before the steel strand is tensioned. After the gap is grouted, a curing temperature is kept at 535°C and a relative humidity is kept at 275%. During tensioning, an environmental temperature difference should be controlled within iIOOC, and an accuracy grade of an oil pressure gauge of the jack should not be lower than 0.4. An acceptance standard of the anchorage system is that: a residual deformation of a single steel strand is 52mm, and a levelness deviation of the ange plate is 50.5%o. In the technical solution, a lling fullness degree of the annular gap may reach above 95%, a slurry loss rate is reduced to be within 3%, and an effective prestress retention rate of the steel strand is 293%. Through graded tensioning control, a peak value of a local compressive stress of concrete is reduced by 40%, and a displacement of the anchorage system is 5 0.3 mm. Through a dynamic compensation mechanism for the grouting pressure, a standard deviation of a compactness degree of lling is 508%, a dispersion coefcient of elongation of steel strand is 55%, and an overall construction qualication rate is improved to above 98%. In another technical solution, according to the , in the second step, the connection of the signal line and the zero calibration specically comprise: connecting RS485 signal lines of four inclination sensors in parallel to channels 1-4 of a data acquisition card of the verticality monitoring system, arranging a laser level in a center of a top plane of the caisson, and adjusting a hoisting attitude of the caisson to make a cross datum line emitted by the laser level coincide with a cross positioning mark preembedded in the top surface of the caisson, so that the caisson is in a theoretical vertical state at this time; starting a calibration mode of the monitoring system, reading initial output values of the four inclination sensors at the same time, and if an absolute value of an output angle of any sensor is greater than 0.05°, sending a zero offset compensation instruction to a corresponding sensor through software of the monitoring system, with a compensation amount of A0=-(01+02+03+04) / 4, wherein 04 is a current reading number of the sensor; and after compensating through the software, operating the caisson to make three lateral microdisplacements at an amplitude of 0.3 m, allowing the caisson to stand for 2 minutes after each displacement, and then collecting sensor data, wherein, when a variation standard deviation of angles output by the four sensors is less than 0.02°, it is judged that the calibration is effective. In the above technical solution, sensor signal line connection and data channel conguration adopt an RS485 or CAN bus communication protocol, and the data acquisition card may be an SM1231 module of Siemens S7-1200 or an Advantech USB-4716 module. The signal line may be an AWG18 shielded twisted pair, which penetrates through a CD25 mm galvanized steel pipe and is pre-embedded and laid along the inner wall of caisson, and the junction box is mounted at a height of 1.5 m in a southeast corner of the top portion of the caisson. When the channels are allocated, the channels 14 may correspond to the sensors at four opposite corners in the northeast, northwest, southwest and southeast of the caisson, and the sampling frequency may be set to be 10 Hz. A signal line shielding layer may be grounded at a single point in a control box, and a grounding resistance is required to be 54 Q. In the above technical solution, in a physical standard establishment process of the laser level, a Leica LSlO or Topcon LS-B3 instrument may be used and mounted on a prefabricated 150><150 mm concrete base on the top surface of the caisson. The cross positioning mark may be formed by cutting a stainless steel sheet with a thickness of 2 mm through laser, and embedded in a 200X200 mm region in a center of the top surface. When the attitude is adjusted, the attitude may be nely adjusted by four 50 t hydraulic jacks, and each jacking amount may be set to be 0.2 m. A deviation between a center of a laser spot and a center of the cross mark may be controlled within i2 mm, and a corresponding angular deviation is 0.02o respectively. During the dynamic compensation and verication test of the software, in a calculation formula for the compensation amount of the zero offset, a denominator may be a mean of 4 points, 6 points or 8 points, and a compensation threshold may be set to be 0.05°. A lateral microdisplacement may be realized by a hydraulic jacking device, a jacking stroke may be set to be 0.3 m, and rest time may be adjusted to be 2 minutes. During data acquisition, each group of micro-displacement tests may be repeated 5 times, and a standard deviation judgment threshold may be set to be 0.02°. After the verication is qualied, the system may automatically generate a calibration certicate and record zero offset values of each sensor before and after compensation. Through the technical solution, a zero drift error of the sensor is reduced to be within 0.02°, an establishment accuracy of laser datum reaches i0.01°, and a repeatability error of micro-displacement verication test is 50.005°. Through multi-channel synchronous calibration, a dispersion coefcient of a measured value of each sensor is 51.5%, and time spent for calibration is shortened to be within 45 minutes. Through a dynamic compensation algorithm, an inuence of temperature drift is reduced by 70%, measurement stability is kept at i0.015° in an ambient temperature range of -10°C to 50°C, and an overall calibration effectiveness of the system is improved to above 98%. In another technical solution, according to the , in the fourth step, the water pressure adjustment specically comprises: in a rst stage, increasing a water pressure of a highpressure water nozzle in a corresponding region in an inclination direction to 2.8 MPa at a rate of 0.3 MPa / s, and detecting an attitude variation of the caisson after maintaining the pressure for 120 seconds; in a second stage, linearly adjusting the water pressure to 3.3 MPa according to the attitude variation, wherein an adjustment rate is not greater than 0.5 MPa / s; in a third stage, stabilizing the water pressure to 3.8 Mpa at a rate of 0.2 MPa / s; and repeating the three-stage adjustment until a verticality deviation of the caisson is less than 0.3°. In the above technical solution, when the graded pressure adjustment is divided in stages, in the rst stage, a target pressure may be set to be 2.8 MPa, and a pressure boost rate may be 0.3 MPa / s. Maintenance time may be adjusted to be 120 seconds, and a detection interval of the attitude variation of the caisson is set to be 60 seconds. In the second stage, a linearly adjusted terminal pressure may be 3.3 MPa, and an upper limit of the pressure change rate may be set to be 0.5 MPa / s. In the third stage, a nally stabilized pressure may be congured as 3.8 MPa, and a stabilization rate may be controlled at 0.2 MPa / s. In the above technical solution, pressure control equipment may be a Danfoss MBS3000 pressure transmitter, which has a measuring range of 06 MPa and an accuracy of 0.5% FS, and is mounted in a position 1.2 m downstream an outlet ange of the high-pressure water pump. An electric control valve may be a Wuzhong Instrument ZDLP model, which has a diameter of DN50, and is connected with the spray pipe, and the pipe is the ASTM A106 Gr.B seamless steel pipe, which has a wall thickness of 6 mm. A pressure adjustment system may be integrated with Siemens S7-1500 PLC, an analog quantity output module may be SM1232, and a signal cable may be a BELDEN 8761 shielded twisted pair, which penetrates through a (D32 mm galvanized steel pipe and is laid along an outer wall of the caisson. In the above technical solution, in a dynamic monitoring process, the operation may be suspended for 2 minutes for data verication before the switching of each pressure adjustment stage. An adjustment threshold of a verticality deviation difference may be set to be 005°, and a time interval between two adjacent verications may be set to be 60 seconds. A pressure synchronous control system may be congured with a proportionalintegral adjustment algorithm, an integral time constant may be set to be 3 seconds, and a proportional band may be adjusted to be 15%. When reverse pressure adjustment is implemented, a pressure release rate keeps a synchronous accuracy of i0.05MPa / s with the pressure boost rate. Through the technical solution, a pressure overshoot in a pressure adjustment process is controlled within i015 MPa, and response time of attitude adjustment of the caisson is shortened to be less than 150 seconds. Through a three-stage pressure adjustment mechanism, an oscillation amplitude of the system is reduced by 60%, and a uctuation range of the verticality deviation difference is reduced to 0.02°-0.04°. Dynamic feedback control improves a pressure synchronization accuracy to i0.8%, a success rate of rectication is improved to above 95%, and overall energy consumption of the system is reduced by l8%-22%. In another technical solution, according to the , during the water pressure adjustment, the operation is suspended for 2 minutes after each stage of adjustment to verify the data of the inclination sensors, and when a verticality deviation difference between two adjacent verications is less than 0.05°, the next stage is executed; and a water pressure reduction process of a highpressure water nozzle in an opposite direction is implemented synchronously with the three stages, and a pressure change rate remains the same numerical value. In the above technical solution, when a quantitative judgment standard for stage switching is set, suspension time after the pressure adjustment stage may be set to be 2 minutes. A threshold of the verticality deviation difference between two adjacent verications may be 0.05°, and a data acquisition interval may be congured as 60 seconds. A number of verication times may be set to be 3 consecutive acquisitions, and a standard deviation calculation window may be set to be a moving average of 7 points. When the deviation difference is less than 0.05o for two consecutive times, the next stage is allowed to be executed. In the above technical solution, when reverse pressure synchronous control is implemented, an initial pressure of a spray pipe group in an opposite direction may be set to be 2.2 MPa, and the pressure release rate may be kept at the same value of 0.4 MPa / s as the pressure boost rate. A Yokogawa EJA430A differential pressure transmitter may be used for pressure balance detection, which has a measuring range of 0-2 MPa, and is mounted between main pipelines of spray pipe groups on the inclined side and the opposite side at a distance of 1.8 m from an outlet of the control valve. A synchronous control algorithm may be congured with a feedforwardfeedback compound control mode, a feedforward compensation coefcient may be set to be 01.0, and a feedback adjustment period may be set to be 3 seconds. In the above technical solution, when the system is executed in linkage, a pressure adjustment instruction may be sent to four groups of spray pipe controllers at the same time, and a response time difference is controlled within 0.8 seconds. An electric actuating mechanism may be an Actuators AUMA SAR model, and stroke time may be set to be 20 seconds / whole stroke. A pressure uctuation suppression module may be integrated in Siemens S71500 PLC, and a ltering time constant may be set to be 1.0 second. A dynamic balance detection frequency may be congured as 2 times per second, and a pressure matching tolerance may be set to be 10.08 MPa. Through the technical solution, a stage switching judgment error is reduced to be within 0.02°, and a system response delay is shortened to below 0.7 second. Through reverse pressure synchronous control, a secondary offset is limited in a range of 0.05°, and pressure balance time is reduced by 40%. Through a compound control algorithm, a pressure uctuation amplitude is reduced by 55%, a system stability index is increased by 35%, and hydraulic impact energy during operation is reduced to below 120 kJ / m3. In another technical solution, according to the , in the fth step, two barges carrying the gravel with the particle size of 5-10 mm are symmetrically distributed on two sides of the caisson, distances between the two barges and a center of the caisson are the same and kept at 25 m, the two barges synchronously throw the gravel at a rate of 2 m3 per minute during throwing and lling, and a thickness distribution of a gravel layer is scanned in real time by a multibeam echo sounder; and when scanning data show that a minimum thickness of the gravel layer in any 10 m><10 m region reaches 1.8 m, clay backlling is started, a plasticity index of the backlling clay is controlled between 12 and 18, and two parallel operation lines are formed by combining a longarm excavator with a dump truck, wherein, for a rst operation line, a clay layer with a thickness of 0.3 m is paved around the caisson, and for a second operation line, a clay layer with a thickness of 0.2 m is supplementarily paved to form a single-layer backlled body after rolling the previous operation line. In the above technical solution, in symmetrical throwing and lling control, the barge may be an 800-ton or lOOO-ton dump barge, wherein a hull length may be set to be 45 m, and a distance from a center of the caisson may be controlled at 25 m. A distance between the barges may be set to be 50 m, and a throwing and lling rate may be congured as 2 m3 per minute. A synchronous dropping control system may be a BDStar Navigation BD982 positioning terminal, which has a plane positioning accuracy of i0.1 m, and is mounted at a height of 1.8 m on a top portion of a barge cab. During throwing and lling, a ship draft difference needs to be controlled within 10.5 m. In the above technical solution, an R2Sonic 2024 or Kongsberg EM2040 multi-beam echo sounder may be used for monitoring the thickness of the gravel layer, and a transducer may be mount in a middle portion of a bottom of a surveying ship at a depth of 0.6 m from a water surface. A scanning region may be divided into a 10 mXlO m grid, and a thickness adjustment threshold may be set to be 1.8 m. When a minimum thickness in a single grid reaches a threshold, the control system may automatically trigger an audible and visual alarm, and an alarm signal delay is not greater than 3 seconds. In the above technical solution, when a layered backlling technology is implemented, the plasticity index of the clay may be controlled in a range of 1218, and a corresponding optimal moisture content range is l8%-24%. The long-arm excavator may be a Caterpillar 336 model or a Komatsu PC3608 model, and an arm span may be set to be 18 m. The dump truck may be a Shaanxi Automobile Delong X3000 model or a Jiefang J6P model, and a load capacity may be congured as 25 tons. A paving thickness of the rst operation line may be set to be 0.3 m, and a thickness of a second supplementary layer may be 0.2 m, so that a total thickness of a single layer formed is 0.5 m. Through the technical solution, a symmetry deviation of gravel throwing and lling is controlled within 14%, and a thickness uniformity reaches an accuracy of 10.12 m. Through multibeam realtime monitoring, a misjudgment rate is reduced to below 3%, and response time of starting the backlling is shortened to 15 seconds. Through the layered backlling technology, a standard deviation of a compactness degree of the clay is 512%, a single-layer construction period is reduced to 2.5 hours, an unbalance coefcient of the lateral earth pressure is reduced to below 1.03, and an overall foundation settlement amount is reduced by 35%. In another technical solution, according to the , when each layer of backlled body is constructed, the backlled body is rolled for twice without vibration by a vibration roller with an exciting force of 180 kN rst, and then rolled for four times under strong vibration by a roller with an exciting force of 280 kN, wherein a rolling speed is kept at 2 km / h, an overlapping width of adjacent wheel tracks is 40 cm, and after rolling, a compactness degree is detected by a sand lling method, and the next layer is constructed when the compactness degree is 296%. In the above technical solution, when parameters of a layered rolling technology are congured, in an initial rolling stage, the Vibration roller with the exciting force of 180 kN is adopted, a number of Vibrationfree rolling times may be set to be 2, and the rolling speed may be controlled at 2.0 km / h. In a re-rolling stage, the roller with the exciting force of 280 kN may be provided, a number of strong-vibration rolling times may be 4, and the overlapping width of adjacent wheel tracks may be set to be 40 cm. In the transitional rolling region, a rolling-free belt with a width of 1.5 m may be reserved for joint treatment. In the above technical solution, the compactness degree may be detected by the sand lling method or a nuclear densimeter method, a diameter of a sand lling cylinder may be 200 mm, and measuring sand may be standard quartz sand with a particle size of 0.250.5mm. Detection points may be arranged according to 3 detection points per 800 m2, and positions of the detection points may be distributed into a quincunx or a grid. A qualication standard of the compactness degree may be set to be 96%, and an allowable deviation of a single detection point is -l.0%. Detection data may be uploaded to a project management platform in real time, and outofgauge data trigger a red early warning sign. In the above technical solution, in the quality control of a construction process, a backlling thickness of each layer may be veried by an inserting drill rod or a laser rangender, and a verication frequency may be set to be one section every 30 m. The moisture content of the clay may be detected by a quick tester, and a number of detection times per operation shift may be set to be 5. A rolling track may be recorded by a GPS positioning system, and a track coverage rate is required to reach 97%. A treatment plan for abnormal working conditions comprises supplementarily rolling twice, changing the lling or adding lime for improvement, and a treatment scope may be limited to a range of 1.5 m outside a defective region. Through the technical solution, a qualication rate of a compactness degree of clay backlling is improved to above 98.5%, and a shear strength of an interlayer bonding surface is increased by 40%. Through a twostage rolling technology, the construction efciency is improved by 30%, and an overlapping control accuracy of wheel tracks reaches 15 cm. A dispersion coefcient of quality detection data is 535%, response time of defect treatment is shortened to be within 20 minutes, and a permeability coefcient of a whole backlled body is reduced to a magnitude of 1><106 cm / s. In another technical solution, according to the , in the third step, the high-pressure water pump runs at no-load for 30 seconds before being turned on, and then a working water pressure is established in three stages: in a stage A, the water pressure is increased to 1.0 MPa at a rate of 0.5 MPa / s and maintained for 60 seconds, in a stage B, the water pressure is increased to 2.0 MPa at a rate of 0.3 MPa / s and maintained for 90 seconds, and in a stage C, the water pressure reaches 2.5 MPa at a rate of 0.2 MPa / s; the spraying of the spray pipe adopts an intermittent pulse mode, the operation is suspended for 15 seconds after every 120 seconds of spraying, a mud concentration is detected by a turbidity sensor pre-embedded in the bottom portion of the caisson during the suspension, and when the mud concentration is lower than 180 g / L, the water pressure is increased by 0.2 MPa in the next cycle of spraying, wherein a maximum water pressure is not greater than 3.0 MPa; and the monitoring system collects the inclination data of the four corners at a sampling frequency of 5 times per second, the data are processed by a moving average ltering algorithm, an inclination display value is updated every 10 seconds, and an audible and visual alarm is triggered when a variation between two adjacent display values is greater than 0. 1 °. In the above technical solution, in the turn-on control of the high-pressure water pump, no-load running time may be set to be 30 seconds, and pressure boost rates in the three stages may be congured as 0.5 MPa / s respectively. In the stage A, a target pressure may be 1.0 MPa, and maintenance time may be adjusted to be 60 seconds. In the stage B, a nally boosted pressure may be set to be 2.0 MPa, and maintenance time may be congured as 90 seconds. In the stage C, a nal working pressure may be controlled at 2.5 MPa or 2.7 MPa, and pressure stabilization time may be set to be 150 seconds. In the above technical solution, a spraying mode may be a cyclic combination of spraying for 150 seconds and suspending for 20 seconds. The turbidity sensor may be a HACH 2100Q model or an E+H CUS71 model, which has a measuring range of 0-500 g / L, and is mounted in a center position of the bottom portion of the caisson at a distance of 1.2 m from the nearest outlet of the spray pipe. A step size of water pressure boost may be set to be 0.2 MPa, and a maximum pressure limit may be congured as 3.0 MPa. A mud concentration adjustment threshold may be set to be 180 g / L, and a response delay of triggering water pressure adjustment is not greater than 8 seconds. In the above technical solution, the data acquisition of the monitoring system may be carried out at a sampling frequency of 5 Hz, and a moving average ltering window may be set to have 10 points. An update interval of an inclination display value may be 10 seconds, and a triggering threshold of the audible and visual alarm may be set to be 0.1°. A data storage module may be an Advantech USB-4716 acquisition card, and a storage interval may be congured as 2 seconds. A signal transmission line may be a BELDEN 8761 shielded twisted pair, which penetrates a (D25mm galvanized steel pipe and is laid along a maintenance channel of the caisson. Through the technical solution, a turn-on impact load of the high-pressure water pump is reduced by 65%, and a vibration amplitude of the pipe is controlled within 10.12 mm. Through mud concentration feedback control, a proportion of effective scouring time is increased to 82%-85%, and response time of water pressure adjustment is shortened to be within 7 seconds. A data drift amount of the monitoring system is 50.015°, an alarm triggering accuracy reaches 97%, and overall energy consumption of the system is reduced by l8%-22%. In another technical solution, according to the , in the sixth step, when the slurry continuously ows out from the overow port, the grouting process comprises: continuously grouting at a constant pressure of 0.8 MPa for 5 minutes, wherein a ow velocity of the slurry at the overow port is detected every 30 seconds, and when a uctuation range of the ow velocity is greater than 110%, an automatic compensation pressure deviation value is AP=0.05><(Vmeasurement'Vreference) / Vreference MPa, wherein Vreference is 50 L / min; gradiently reducing the pressure to 0.6 MPa and then maintaining the pressure for 3 minutes, synchronously monitoring a rising velocity of the slurry through an ultrasonic owmeter pre-embedded in a middle portion of the gap, and controlling the rising velocity within a range of 2025 cm / min; and recovering the pressure to 0.8 MPa and maintaining the pressure for 2 minutes, symmetrically mounting four displacement sensors at the top portion of the caisson at the same time, and when a vertical displacement difference of the caisson displayed by each sensor is greater than 0.5 mm, terminating the grouting and releasing the pressure. In the above technical solution, in the dynamic compensation control over the grouting pressure, the pressure may be set to be 0.8MPa in a constant pressure stage, and maintenance time may be 5 minutes. A uctuation amplitude threshold of a ow velocity may be congured as 10%, and a corresponding pressure compensation coefcient may be set to be 0.05. A reference ow rate may be set to be 50 L / min, and an Emerson Rosemount 8712 electromagnetic owmeter may be used for realtime ow rate detection, which is mounted in a position 0.8 m downstream of an outlet ange of the grouting pump. A denominator in a pressure deviation compensation formula may also be 90% or 110% of the reference ow rate as a calculation base. In the above technical solution, when the rising velocity of the slurry is collaboratively adjusted, a target pressure in a pressure release stage may be 0.6 MPa, and maintenance time may be adjusted to be 3 minutes. The ultrasonic owmeter may be a Geokon BGK-3D model, which has a measuring range of 15-30 cm / min, and is mounted in the preembedded sleeve at a height of 1 / 2 of the gap, and the sleeve is a PVCU pipe. A velocity control algorithm may be congured with a proportional-integral adjustment mode, an integration time constant may be set to be 2 seconds, and a proportional gain may be adjusted to be 0.8. A step size of pressure correction may be set to be 0.03 MPa when the slurry rises at an excessive velocity. In the above technical solution, in a displacement difference monitoring and grouting termination mechanism, a displacement sensor may be an Omron ZXLD40 laser displacement meter, which has a measuring range of 110 mm and an accuracy of 101%, and the displacement sensors are symmetrically mounted on 100><100 mm steel plate bases pre-embedded in four corners of a top surface of the caisson. A vertical displacement difference threshold may be set to be 0.5 mm, and a data acquisition frequency may be congured as 3 times per second. An electric ball valve may be used in a pressure relief process, which has a diameter of DN50, and a pressure relief rate may be controlled at 0.2 MPa / s. After the grouting is terminated, the pressure is stabilized for 20 minutes, during which a displacement resilience is not greater than 0.2 mm. Through the technical solution, a compactness degree of lling of a grouting gap reaches 96%-98%, and a loss of the slurry is controlled within 2.5 m3. Through dynamic pressure compensation, a uctuation amplitude of the ow velocity is reduced to below 17%, and a control accuracy of the rising velocity reaches 11.2 cm / min. Through displacement difference monitoring, a risk of unbalanced load of the structure is reduced by 85%, a grouting termination judgment accuracy is improved to above 98%, and an overall construction qualication rate reaches 99.2%. In another technical solution, according to the , in the seventh step, the tensioning of the steel strand is specically implemented as follows: when primary tensioning is carried out, a tensioning force is applied to 30% of a design value by a center hole jack at a rate of 2 mm per minute, an elongation of the steel strand is measured after the load is maintained for 5 minutes, and when an elongation deviation is greater than 15% of a theoretical value, a subsequent tensioning force is adjusted according to AFZO.15X(Lmeasurement'Ltheory) / LtheoryXFdesign, wherein Fdesign is a design tensioning force; secondary tensioning is carried out 4 hours after the primary tensioning, the tensioning force is applied to 80% of the design value at a rate of 3 mm per minute, a concrete strain value in a region where the preembedded sleeve of the top plate of the caisson is monitored synchronously, and a strain growth rate is controlled in a range not greater than 5 us, / min; tertiary tensioning is implemented 4 hours after the secondary tensioning, and when the tensioning force is applied to 100% of the design value, the load is maintained for 10 minutes, wherein a tension loss caused by the relaxation of the steel strand is compensated once every 2 minutes, and a compensation amount is 0.3% of a primary tensioning force; and after the tensioning is completed, the hydraulic lock nut is used for anchoring, a tightening torque of the nut is 850 N-m, a 304 stainless steel antiloosening lock sheet with a thickness of 8 mm is mounted at an exposed end of an anchorage device, and a contact surface between the lock sheet and the anchorage device is applied with special anti-slip grease with a friction coefcient of0. 12. In the above technical solution, in graded tensioning parameter control, a proportion of a design value of primary tensioning may be set to be 30%, and a loading rate may be 2 mm per minute. Load maintenance time may be congured as 5 minutes, and an allowable range of an elongation deviation may be set to be 15%. A loading rate of secondary tensioning may be adjusted to be 3 mm per minute, and a threshold of a concrete strain growth rate monitored synchronously may be set to be 5 pts / min. Maintenance time of tertiary tensioning may be 10 minutes, and a frequency of tension loss compensation may be congured as once every 2 minutes. In the above technical solution, a Geokon BGK4850 vibration wire strain gauge may be used for monitoring a tensioning process, which has a measuring range of 11500 us, and is mounted in a range of 150 mm around the preembedded sleeve of the top plate of the caisson. An Omron ZW7000 laser length measuring instrument may be used for elongation measurement, which has an accuracy of 10.05 mm, and is mounted on an outer side of a piston rod of the jack. An adjustment coefcient in a compensation formula may be set to be 0.15, and a design tensioning force reference value may be taken according to 70% of a breaking strength of the steel strand. In the above technical solution, in the antiloosening treatment of the anchorage system, the hydraulic lock nut may adopt an M36 specication of a DIN 6914 standard, and the tightening torque may be set to be 850 N~m. The anti-loosening lock sheet may be made of a 304 stainless steel plate with a thickness of 8 mm, and an outer diameter of the lock sheet is 110 mm. Special anti-skid grease may be a Krupp KLUBER Tribolm NW12 model, which has a friction coefcient ranges from 0.10 to 0.15, and a coating thickness of the antiskid grease may be controlled at 0.3 mm. The anticorrosion treatment for the exposed end of the anchorage device may adopt a hot-dip galvanizing or Dacromet technology, and a plating thickness may be 60 um. Through the technical solution, an elongation control accuracy of the steel strand reaches 11.8 mm, and an effective prestress retention rate is 295%. Through the graded tensioning technology, the peak value of the local compressive stress of concrete is reduced by 30%, and a response delay of strain monitoring is 50.5 second. Through anti-loosening structure treatment, a displacement of the anchorage system is controlled within a range of 0.15-0.25 mm, and after 106 fatigue loading tests, a prestress loss rate is 52.5%, and a sliding displacement of a clamping sheet of the anchorage device is 50.08 mm. Application example of In a certain river regulation project, 12 reinforced concrete caissons need to be mounted, wherein a single weight is 800 t, and a design sinking depth is 9 m. The river bed is a layer of silty clay mixed with sand in geology, and an underground water ow velocity is 0.8 m / s. As shown in FIG. 1, the operation is implemented by the technical solution: S100: prefabrication of caisson and mounting of equipment When the caisson is manufactured in a prefabrication plant, the SICK CKS36 inclination sensors (with an accuracy of 10.01°) are embedded in four opposite corners of the inner wall at a distance of 1.2 m from the bottom plate, and the signal line penetrates through the $20 galvanized steel pipe and is led to a top junction box. 6 groups of highpressure water nozzle bases are welded on the bottom plate, there are 3 (1)50 spray pipes in each group, which are arranged in an equilateral triangle (with a side length of 200 mm), and the axis of the spray pipe forms the included angle of 30° with the horizontal plane. The spray pipe is the ASTM A106 Gr.B seamless steel pipe, which is connected with a Grundfos CR456 highpressure water pump (with a ow rate of 120 m3 / h) through a Parker H series quick connector. 8200: precise positioning and system calibration The caisson is hoisted by a 2000 t oating crane, the plane deviation is controlled at 540 mm by a Trimble SPS986 positioning system, and a distance between the bottom portion and the river bed is kept at 0.5 m. After a Siemens S7-1200 monitoring system is connected, the zero calibration is carried out by a Leica LSlO laser level: four 50 t hydraulic jacks are adjusted to make a laser crosshair coincide with a prefabricated mark, and the software automatically compensates the zero offset (with a maximum compensation amount of 0.03°) of the sensor. After three 0.3 m lateral microdisplacement tests, a standard deviation of inclination data of the four corners is stabilized at 0.018°. S300: controllable sinking The water pressure of the high-pressure water pump is established in stages: the water pressure is increased to 1.0 MPa at 0.5 MPa / s (60 seconds)>increased to 2.0 MPa at 0.3 MPa / s (90 seconds)>increased to 2.5 MPa at 0.2 MPa / s. The spraying adopts an intermittent mode of working for 120 seconds / suspending for 15 seconds, and the mud concentration is detected by the HACH 2100Q turbidimeter in real time. When an inclination difference between northeast and southwest opposite corners reaches 0.52°, the system starts a pressure adjustment program: pressures of 3 groups of spray pipes on the inclined side are increased to 2.8 MPa at 0.3 MPa / s (120 seconds)>increased to 3.3 MPa at 0.5 MPa / s>stabilized at 3.8 MPa; and pressures of spray pipes on the opposite side are reduced synchronously, and the inclination difference is reduced to 0.27o after 180 seconds. The whole sinking takes 6.5 hours, and the verticality deviation is 0.28°. S400: intelligent backlling construction After the caisson is in place, two 800 m3 barges throw and ll 5-10 mm gravel at a distance of 25 m synchronously, and the R2Sonic 2024 echo sounder generates a thickness cloud diagram in real time. The gravel layer of 2.0 m (with a thickness deviation of 10.12 m) is completed after 2.2 hours. The clay is backlled by a combination of a Caterpillar 336 excavator and a Dynapac CA250 road roller: each layer is paved in two stages according to 0.3 m+0.2 m, and rolled twice with the exciting force of 180 kN without vibration and rolled four times with the exciting force of +280 kN under strong vibration (at a speed of 2 km / h and an overlapping width of 40 cm). Compactness degrees of 10 points detected by the sand lling method are 96.2%97.8%. 8500: gap grouting and anchoring When backlling to an elevation of 1.2 m from the top, a CD25 grouting pipe is inserted to inject a cement slurry with a water-cement ratio of 0.45. When the Geokon BGK-3D monitors that the rising velocity of the slurry is 23 cm / min, the grouting pressure is dynamically compensated 3 times (a maximum value is AP=0.04 MPa). When the displacement sensors show that a maximum vertical difference is 0.42 mm, the grouting is terminated. After 24 hours, a Q355B ange is mounted, and the steel strand is tensioned in three stages: 30% (2 mm / min), 80% (3 mm / min) and 100% by an OVM YCW250B jack, during which the tension loss is compensated by 0.3%><3 times. Finally, the 850 N-m hydraulic nut is tightened, and an 8 mm 304 lock sheet is provided. Relevant parameter data in whole construction process 1. Verticality control: in the whole process, a maximum inclination difference is 0.52°>0.27° after adjustment, and a nal sinking deviation is 0.28° (1.2°-2.5° in a traditional technology). 2. Backlling quality: the thickness deviation of the gravel layer is 0.24 m (allowing to be 0.5 m in the specication); an average compactness value of the clay is 97.1% (295% in the specication). 3. Grouting effect: the ultrasonic detection shows that a lling degree of the gap is 98.2% (85-90% in the traditional technology). 4. Anchorage performance: 72 hours after tensioning, the prestress retention rate is 96.3% (89-92% in the traditional technology). 5. Construction efciency: a construction period of a single caisson is 78 hours (120-150 hours in the traditional technology). This example veries that the provided by the present invention signicantly improves the verticality control, the backlling compactness, the structural connection reliability and other aspects, wherein all indicators are superior to industry standards, thus effectively solving the key technical problems such as deection accumulation and foundation leakage in traditional caisson construction. The equipment quantity and the processing scale described herein are used to simplify the description of the present invention. The application, modication and variation of the present invention are obvious to those skilled in the art. Although the implementation of the present invention has been disclosed above, it is not limited to the applications listed in the specication and the embodiments, and can be fully applied to various elds suitable for the present invention, and additional modications can be easily implemented by those skilled in the art. Therefore, the present invention is not limited to the specic details and illustrations shown and described herein without departing from the general concept dened by the claims and the equivalent scope.

Claims

l. Construction method for a caisson, comprising the following steps: first step: prefabricating a reinforced concrete caisson, pre-embedding tilt angle sensors in Four opposite corner positions of an inner wall of the caisson, the annular and even welding of six groups of high-pressure water nozzle mounting bases to a base portion of the caisson, each group of bases comprising three mounting holes which are arranged in an equilateral triangle, and an axis of the mounting hole forms a included angle of 25 - 35° with a horizontal plane, fixing a steel injection pipe with a diameter of 50 mm in the mounting hole, and the knob of the spray pipe with a water outlet of a high pressure water pump via a quick connection piece; second step: hoisting the caisson to a design positioning point, holding a distance of 0.3 - 0.7 mm between the bottom part of the caisson and a surface of a riverbed, switching on the high pressure water pump to perform water injection and air evacuation in a to run the pipeline and then turn off the water pump, install a verticality monitoring system, and connecting a signal line from the tilt sensor in the system to complete zero calibration; third step: turning on the high pressure water pump to supply water to the spray pipe at a to provide an initial water pressure of 2.0 - 3.0 MPa so that a water flow flows down the riverbed at an elevation angle of 30° influences to form mud and the caisson by its own weight sinks, and displaying slope data of Four Corners in real time by the monitoring system; fourth step: assessing a caisson's posture based on monitoring data: if the difference in slope between two opposite angles in a given direction is greater than 0.50, performing pressure adjustment to restore the initial water pressure after the slope difference is less than 0.30; and if the slope difference does not exceed a limit, the maintain a current water pressure to continuously sink the caisson; and Fifth step: Repeating the third step to the Fourth step until the caisson reaches the bottom reaches a design elevation, the symmetrical throwing and filling of gravel with a particle size of 5-10 mm around the caisson to a thickness of 1.8-2.2 m immediately after the switching off the water pump, then backfilling the clay in layers, with a thickness of each layer is 0.5 m, and rolling the back-filled body six times by a vibratory roller with a generating force of 280 kN, with an overlapping width of adjacent Wheel tracks are one third of a wheel width.

2. Construction method for a caisson according to claim 1, further comprising: next steps: sixth step: when backfilling up to an elevation of 1.2 m from a top part of the caisson, the insertion of an injection pipe into a bottom portion of a 200 mm annular space between the inner wall of the caisson and the backfilled body, the injection of a cement slurry with a water-cement ratio of 0.45 through an injection pump, the controlling an injection flow rate at 50 L / min, and when the slurry is continuously discharged from a overflow gate on a top portion of the interspace flows, maintaining a injection pressure for 10 minutes and then stop the injection; and seventh step: 24 hours after injection, mounting a steel connection sensor on a top surface of the caisson, evenly distributing eight anchor bolt holes around the enceinte, allowing two prestressed steel strands of 32 mm diameter to be inserted into each hole penetrating, anchoring the lower ends of the steel strands in a pre-embedded sleeve of a caisson top plate, tensioning the steel strands to 30%, 80% and 100% of a design value in three times, where a time interval of each stress is 4 hours, and the finally securing an anchor head by means of a hydraulic lock nut.

3. Construction method for a caisson according to claim 2, characterized in that in the second step the connection of the signal line and the zero calibration specifically include: connecting RS485 signal lines of four tilt sensors in parallel to channels 1 4 of a verticality monitoring system data collection map, arranging of a welding level gauge in the middle of a top surface of the caisson and adjusting a lifting position of the caisson to a cross datum line radiated by the welding level gauge to coincide with a cross positioning mark pre-embedded in the top surface of the caisson, so that the caisson is currently in a theoretical vertical state; starting a calibration mode of the monitoring system, reading initial output values ​​of the four tilt sensors simultaneously, and as an absolute value of a exit angle of a sensor is greater than 0.050, transmitting a zero offset compensation instruction to a corresponding sensor via software of the monitoring system, with a compensation amount of A0=-(01+02+03+04) / 4, where 04 is a current sensor reading number is; and After compensating by the software, operating the caisson to perform three lateral to create micro-displacements at an amplitude of 0.3 m, allowing the caisson to to stand still for 2 minutes after each movement, and then collect sensor data, where when a variation standard deviation of the angles passed through the four If the sensors are performed less than 0.020, the calibration is considered effective.

4. Construction method for a caisson according to claim 1, characterized in that in the fourth step the water pressure adjustment specifically includes: in a first phase, increasing the water pressure of a high-pressure water nozzle in a corresponding area in a slope direction up to 2.8 MPa at a rate of 0.3 MPa / s, and detecting a postural variation of the caisson after maintaining pressure for 120 seconds; in a second phase, linearly adjusting the water pressure to 3.3 MPa according to the postural variation, with an adjustment rate not exceeding 0.5 MPa / s; in a third stage, stabilizing the water pressure to 3.8 Mpa at a rate of 0.2 MPa / s; and repeating the three-phase adjustment until a verticality deviation of the caisson is less than 0.3°.

5. Construction method for a caisson according to claim 4, characterized in that during water pressure adjustment, turn off the control after each adjustment phase for 2 minutes is paused to verify the data from the tilt sensors, and when a verticality deviation difference between two adjacent verifications is less than 0.05°, the next phase carried out; and that a process of water pressure reduction of a high pressure water nozzle in an opposite direction synchronously with the three phases performed, and a pressure change rate remains the same numerical value ft.

6. Construction method for a caisson according to claim 1, characterized in that in the fifth step two aches carrying the gravel with a particle size of 5 10 mm, symmetrical are distributed on two sides of the caisson, with distances between the two barges and a center of the caisson are level and kept at 25 m, with the two barges touching the gravel synchronous throwing at a speed of 2 m3 per minute during throwing and filling, and where a thickness distribution of a gravel layer is scanned in real time by a multi-beam echo sounder; and that scanning data shows that a minimum thickness of the gravel layer in a When the area of ​​10 m X 10 m reaches 1.8 m, the backfilling of clay is started, with a plasticity index of clay backfill is controlled between 12 and 18, where two parallel operating lines are formed by a long-arm excavator combine with a dump truck, where a clay layer with a first operating line thickness of 0.3 m is paved around the caisson, and for a second operating line, a clay layer with a thickness of 0.2 m is additionally added after rolling the previous operating line paved to form a single-layer backfilled body.

7. Construction method for a caisson according to claim 6, characterized in that when each layer of back-filled body is constructed, the back-filled body is first rolled twice without vibration by a vibrating roller with an exciting force of 180 kN, and then rolled four times under strong vibration through a roller with an exciting force of 280 kN, maintaining a roller speed of 2 km / h, with an overlapping width of adjacent wheel tracks is 40 cm, whereby after rolling, a degree of compaction is achieved by a sand filling method is detected, and the next layer is constructed when the degree of compactness is 2 96%.

8. Construction method for a caisson according to claim 1, characterized in that in the third step the high pressure water pump runs for 30 seconds without load before is switched on, and then a working water pressure is determined in three stages: in a In phase A the water pressure is increased to 1.0 MPa at a rate of 0.5 MPa / s and maintained for 60 seconds, in phase B the water pressure is increased to 2.0 MPa at a rate of 0.3 MPa / s and maintained for 90 seconds, and in a phase C the water pressure reaches 2.5 MPa at a rate of 0.2 MPa / s; that an intermittent pulse mode is used for spraying the spray pipe, where the operation is paused for 15 seconds after every 120 seconds of the spraying, where a mud concentration is detected by a turbidity sensor that is pre-embedded in the bottom section of the caisson during the break, and when the mud concentration is less than 180 g / L, the water pressure is increased by 0.2 MPa in the subsequent spray cycle, where a maximum water pressure is not greater than 3.0 MPa; and that the monitoring system collects the slope data from the four corners with a sampling rate of 5 times per second, with the data being processed by a moving average filter algorithm, where a slope display value is displayed every 10 seconds is updated, and an audible and visual alarm is activated when a variation between two adjacent display values ​​is greater than 0.1°.

9. Construction method for a caisson according to claim 1, characterized in that in the sixth step, when the slurry flows continuously from the overflow port, the injection process includes: continuous injection at a constant pressure of 0.8 MPa for 5 minutes, whereby every 30 seconds a flow rate of the slurry at the overflow port is detected, and where when a flow rate uctuation range is greater than i10%, a automatic compensation pressure deviation value AP=0.05X(Vmeasurement'Vreference) / Vreference Mpa is, where Vreference is 50 L / min; gradually reducing the pressure to 0.6 MPa and then maintaining the press for 3 minutes, synchronously monitoring the increasing speed of the slurry by means of an ultrasonic flow meter pre-embedded in a central section of the spacing, and adjusting the rising speed within a range of 20 - 25 cm / min; and restoring the pressure to 0.8 MPa and maintaining the pressure for 2 minutes, the symmetrical mounting of four displacement sensors on the top section of the caisson on the same time, and when a vertical displacement difference of the caisson is shown by each sensor is greater than 0.5 mm, stopping the injection and releasing the Busy.

10. Construction method for a caisson according to claim 1, characterized in that in the seventh step the tensioning of the steel strand is carried out specifically as follows: when a primary tension is applied, a tension force is applied at 30% from a design value by a center hole jack at a speed of 2 mm per minute, where an elongation of the steel strand is measured after the load has been applied for 5 minutes is maintained, and when an extension deviation is greater than i5% of a theoretical value, a subsequent tension force is adjusted according to AF=0.15X(Lmeasurement-Ltheory) / LtheoryXFdesign, where Fdesign is a design tension force; a secondary voltage is applied 4 hours after the primary voltage, where the tension force is applied at 80% of the design value at a rate of 3 mm per minute, where a concrete stress value is applied in an area where the pre-embedded sleeve of the caisson top plate is monitored synchronously, and where a voltage growth rate is controlled in a range of not more than 5 ts / min; a tertiary voltage is applied 4 hours after the secondary voltage, where when the tension force is applied at 100% of the design value, the load for 10 minutes is maintained, with a loss of tension caused by the relaxation of the steel string is compensated once every 2 minutes, and a compensation amount 0.3% of a primary tension force; and after tensioning is completed, the hydraulic lock nut is used for anchoring, where the tightening torque of the nut is 850 N°m, where a 304 stainless steel anti-loosening lock blade with a thickness of 8 mm is mounted at an exposed end of an anchoring device, and in which a contact surface between the lock blade and the anchoring device is applied with special anti-slip grease with a friction coefficient 5 of 0.12.