A construction method for softening seabed sand layers

Abstract

This application relates to the field of seabed foundation treatment technology and discloses a construction method for softening seabed sand layers, comprising the following steps: integrating a multiphysics field sensing system, an acoustic resonant module, and a torsional pulse module into a dual-wheel agitator; during construction, constructing a real-time state vector characterizing the interaction between strata through the sensing system; continuously applying high-frequency acoustic waves and functional composite fluid, and determining the triggering conditions of the stubborn barrier layer based on the state vector to conditionally apply torsional pulses; simultaneously, minimizing the total system energy consumption as the objective function, and performing closed-loop control of acoustic wave and fluid parameters. This invention achieves precise adaptive control of the construction process through real-time sensing, energy coordination, and closed-loop optimization, effectively treating stubborn barrier layers while significantly reducing total construction energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of seabed foundation treatment, in particular to a construction method for softening seabed sand layer. BACKGROUND

[0002] Dual-Wheel Deep Soil Mixing (DWDSM) is a mature seabed foundation treatment technology, which forcibly mixes solidifying agent (such as cement slurry) with in-situ soft soil through mechanical mixing to form composite soil with higher strength and stability, and is widely used in diaphragm walls, wharf foundation reinforcement and other marine engineering.

[0003] In the traditional dual-wheel stirring construction process, the equipment mainly relies on the large torque provided by the driving system to drive the milling head to rotate and penetrate, so as to realize the cutting and stirring of the soil. However, the seabed geological conditions are often complex and changeable, especially when dealing with dense sand layers or encountering stubborn obstacles such as uneven composition and density of dense interlayer, calcareous nodule, etc. The existing construction method shows its inherent limitations. When facing hard strata, the method can only use a one-size-fits-all brute force crushing method, which leads to a sharp rise in energy consumption of the driving system, significantly increasing the construction cost, and causing huge mechanical stress on the driving system and cutting components, accelerating wear and tear, and even risking damage to the equipment.

[0004] More importantly, this construction mode relying on single mechanical energy lacks self-adaptive adjustment ability to stratum changes. The operator can usually only make passive and lagging experience judgments and adjustments based on limited macro parameters such as torque and penetration speed, and cannot accurately perceive the microstate of the interaction between the milling head and the soil. Therefore, when encountering stubborn obstacles, not only is the energy utilization efficiency low, but also the quality of the composite soil formed is uneven due to uneven stirring or difficulty in effective penetration of the solidifying agent, leaving engineering hidden dangers. Therefore, there is an urgent need for a new construction method that can intelligently perceive stratum characteristics and adaptively apply multiple energies to achieve efficient and low-consumption softening treatment. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a construction method for softening seabed sand layer, which solves the problems of poor adaptability to complex geological conditions, high energy consumption, unstable construction quality and difficulty in quantitative evaluation of the process of the existing seabed sand layer treatment method.

[0006] To achieve the above purpose, the present application is implemented by the following technical scheme: a construction method for softening seabed sand layer, comprising the following steps:

[0007] S1, system preparation step: integrating a sound wave resonance module and a torsional pulse module on a dual-wheel stirring milling head, and integrating a multi-physical field sensing system on a drill pipe connected to the dual-wheel stirring milling head.

[0008] S2, real-time sensing step: during the process of the double-wheel cutterhead penetrating into the seabed sand layer, the multi-physical field sensing system continuously collects data and constructs a real-time state vector representing the current state of the stratum interacting with the equipment.

[0009] S3, energy application step: the central controller drives the acoustic resonance module, the torsional pulse module, and the functional composite fluid injection system to apply energy and inject fluid to the seabed sand layer.

[0010] S4, closed-loop regulation step: during the energy application step, the central controller adaptively adjusts the composition and flow rate of the functional composite fluid, the working parameters of the acoustic resonance module, and the triggering conditions and working parameters of the torsional pulse module according to the real-time state vector, thereby completing the treatment of softening the seabed sand layer.

[0011] In one specific embodiment, in S2, the multi-physical field sensing system collects a set of state parameters. The set of state parameters includes: the rotational torque , the rotational speed , the penetration depth , the propagation speed of acoustic waves in the soil-fluid mixed medium , the attenuation coefficient of acoustic waves in the soil-fluid mixed medium , and the pore water pressure in the mixing area , the real-time state vector can be represented as:

[0012] ;

[0013] wherein, is the real-time rotational torque of the double-wheel cutterhead; is the real-time rotational speed; is the real-time penetration depth; is the real-time propagation speed of acoustic waves in the soil-fluid mixed medium; is the real-time attenuation coefficient of acoustic waves in the soil-fluid mixed medium; is the real-time pore water pressure in the mixing area; the real-time state vector is constructed based on at least two of the set of state parameters.

[0014] Preferably, the energy application step in S3 specifically includes: the central controller continuously drives the acoustic resonance module to output high-frequency acoustic waves; when the real-time state vector satisfies a preset stubborn obstacle layer triggering condition, the central controller triggers the torsional pulse module to apply at least one low-frequency, high-amplitude torsional pulse to the double-wheel cutterhead.

[0015] In one specific embodiment, the recalcitrant disorder layer triggering condition is determined based on dynamic analysis of the real-time state vector, the triggering condition being that both the rotational torque of the dual-wheel cutterhead and the attenuation coefficient of the acoustic wave in the soil-fluid mixture medium exhibit abnormal growth significantly higher than their recent average, and the pore water pressure growth rate of the stirred zone continues to be lower than a preset effective mixing lower limit This triggering condition can be described by the following logical expression:

[0016] ;

[0017] wherein, and are the average values of the rotational torque and the attenuation coefficient within a recent time window, respectively; and are the corresponding standard deviations, respectively; and are preset sensitivity coefficients.

[0018] Preferably, the closed-loop regulation step in S4 is specifically an acoustic fluid coupling optimization process, which includes:

[0019] During the process of the dual-wheel cutterhead penetrating the seabed sand layer, the total system energy consumption consumed within each depth increment is calculated as a calculation period, and the total system energy consumption consumed within each depth increment is defined as an objective function :

[0020] ;

[0021] The central controller minimizes the objective function as the goal, and synchronously optimizes and determines the optimal acoustic wave resonance frequency and the optimal composition of the functional composite fluid and flow rate under the current working condition according to the real-time state vector , regulates the acoustic wave resonance module and the functional composite fluid injection system according to the determined optimal acoustic wave resonance frequency and the optimal composition of the functional composite fluid and flow rate .

[0022] In one specific embodiment, the total system energy consumption is the rotational cutting power consumption of the dual-wheel cutterhead Output power consumption of the acoustic resonant module Commonly constitute;

[0023] ;

[0024] Wherein,

[0025] ;

[0026] Wherein, The increment of the penetration depth The time required; The real-time output power of the acoustic resonant module; That is, a definite integral operation, the physical meaning is to accumulate all the instantaneous values of a time-varying physical quantity from the start time To the end time , So as to obtain the total amount in this period; The real-time rotating torque of the double-wheel rotary milling head; The real-time rotating speed; The product of the two divided by the constant 9550 is the instantaneous power of the milling head.

[0027] In a specific embodiment, the functional composite fluid is composed of at least two of water, water-soluble polymer and micro-bubbles, and the composition of the functional composite fluid refers to the concentration of the water-soluble polymer and the volume fraction of the micro-bubbles.

[0028] Preferably, the working parameters of the acoustic resonant module include acoustic resonant frequency and output power.

[0029] Preferably, in a specific embodiment, after S4, the method further comprises the steps of:

[0030] Logging step: record the real-time state vector of each depth in the whole construction process and the corresponding control decision output by the central controller to form a digital construction log.

[0031] In a specific embodiment, in the energy application step, the acoustic resonant module is driven to output high-frequency acoustic waves, and the frequency of the high-frequency acoustic waves is set to kilohertz level; At the same time, the torsional pulse module is triggered to apply low-frequency and high-amplitude torsional pulses, and the pulse width of the low-frequency and high-amplitude torsional pulses is set to millisecond level.

[0032] The present application provides a seabed sand layer softening construction method. It has the following beneficial effects:

[0033] 1、The present application constructs a complete perception, decision-making, execution feedback loop through the real-time perception step of S2 and the closed-loop regulation step of S4. The method can continuously obtain a real-time state vector representing the interaction state of the formation and the equipment by using a multi-physical field sensing system, and adaptively adjust the working parameters of the sound wave, fluid and torsional pulse modules according to the vector, which makes the construction process adapt to the dynamic changes of the seabed sand layer physical and mechanical properties in real time, thereby ensuring the uniformity and reliability of the treatment effect in complex and heterogeneous formations.

[0034] 2、The present application realizes strategic application of energy by synergistically applying continuously output high-frequency sound waves and low-frequency, high-amplitude torsional pulses triggered under certain conditions in the energy application step of S3. The high-frequency sound waves continuously act to reduce the solid contact number between sand particles, and the torsional pulse is only triggered to perform macroscopic shear impact when encountering stubborn barrier layers through real-time state vector judgment. This strategy significantly improves the ability and efficiency of treating specific cemented structures or dense interlayers, while avoiding continuous operation of high-energy consumption pulse modules.

[0035] 3、The present application introduces an acoustic fluid coupling optimization process targeting at minimizing the total system energy consumption in the closed-loop regulation step of S4. The method defines the total system energy consumption per unit depth as a quantifiable objective function, and drives the central controller to actively seek the combination of sound wave and fluid parameters with the lowest energy consumption under the current working condition, which makes energy utilization no longer dependent on fixed empirical settings, but realizes dynamic optimization, fundamentally reducing the energy consumption of the entire construction process and bringing significant economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a flowchart of the seabed sand layer softening treatment construction method of the present application;

[0037] Figure 2 It is a structural schematic diagram of the seabed sand layer softening treatment construction method of the present application;

[0038] Figure 3 It is a flowchart of real-time perception and state vector construction of the present application;

[0039] Figure 4 It is a synergistic control logic diagram of the energy application step of the present application;

[0040] Figure 5 It is an execution flowchart of the closed-loop regulation step of the present application;

[0041] Figure 6 It is a data structure diagram of the digital construction log of the present application. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the specification of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0043] Please refer to the drawings in the specification of the present application Figure 1 The embodiments of the present application provide a construction method for softening seabed sand layer, comprising the following steps:

[0044] Step S1: System preparation step: integrating the acoustic resonance module and the torsional pulse module on the double-wheel cutting head, and integrating the multi-physical field sensing system on the drill pipe connected to the double-wheel cutting head, which provides a hardware basis for the subsequent method execution.

[0045] Step S2: Real-time sensing step: continuously collecting data using the multi-physical field sensing system during the process of the double-wheel cutting head penetrating the seabed sand layer, and constructing a real-time state vector representing the current formation and equipment interaction state , a specific form of the real-time state vector is as follows:

[0046] ;

[0047] wherein, is the real-time rotational torque of the double-wheel cutting head; is the real-time rotational speed; is the real-time penetration depth; is the real-time propagation speed of acoustic waves in the soil-fluid mixed medium; is the real-time attenuation coefficient of acoustic waves in the soil-fluid mixed medium; is the real-time pore water pressure of the mixing area.

[0048] Step S3: Energy application step: driving the acoustic resonance module, the torsional pulse module, and the functional composite fluid injection system by the central controller to apply energy and inject fluid to the seabed sand layer,

[0049] In one specific embodiment, this step specifically includes: continuously driving the acoustic resonance module to output high-frequency acoustic waves, and at the same time, when the real-time state vector satisfies the preset stubborn obstacle layer trigger condition, triggering the torsional pulse module to apply at least one low-frequency, high-amplitude torsional pulse to the double-wheel cutting head, and a specific logical expression of the stubborn obstacle layer trigger condition is as follows:

[0050] ;

[0051] wherein, and are the average values of the rotational torque and the attenuation coefficient respectively within a recent time window;

[0052] and are the corresponding standard deviations respectively; and is a preset sensitivity coefficient; is the real-time growth rate of the pore water pressure; is a preset effective mixing lower threshold.

[0053] Step S4: Closed-loop control step: during the energy application step, the composition and flow rate of the functional composite fluid, the working parameters of the acoustic resonance module, and the triggering conditions and working parameters of the torsional pulse module are adaptively adjusted by the central controller according to the real-time state vector obtained in step S2.

[0054] In a specific embodiment, the closed-loop control step aims to minimize the total system energy consumption, and the process will preset a depth increment as a calculation period, and the total system energy consumption consumed within each depth increment is defined as the objective function ;

[0055] ;

[0056] The total system energy consumption is composed of the rotational cutting power consumption of the double-wheel agitator cutting head and the output power consumption of the acoustic resonance module :

[0057] ;

[0058] wherein, ;

[0059] wherein, i.e. a definite integral operation, the physical meaning of which is to accumulate all instantaneous values of a time-varying physical quantity (here, instantaneous power) from the start time to the end time , so as to obtain the total amount (here, total energy consumption) within the time period; is the real-time rotational torque of the double-wheel agitator cutting head; is the real-time rotational speed; the product of the two divided by the constant 9550 is the instantaneous power (unit: kilowatt) of the cutting head; by integrating the instantaneous power within the time period , the total energy consumption can be obtained;

[0060] Increment of penetration depth Time required;

[0061] ;

[0062] Wherein, Real-time output power of the acoustic resonance module; the central controller solves the minimum value of the objective function through an optimization algorithm to determine and regulate the working parameters of each module.

[0063] In one embodiment, the method of the present application can further include a logging step after step S4, which records the real-time state vector corresponding to each depth during the entire construction process and all control decisions output by the central controller, finally forming a digital construction log.

[0064] Referring to the drawings Figure 2 , Figure 2 is a schematic diagram of the system structure for implementing a seabed sand layer softening construction method according to an embodiment of the present application, and the following will describe each step in the method of the present application in detail:

[0065] Step S1 is a system preparation step: in this step, the operation of integrating the acoustic resonance module and the torsional pulse module into the double-wheel cutting head is performed, and the operation of integrating the multi-physical field sensing system into the drill pipe connected with the double-wheel cutting head is performed.

[0066] Specifically, the acoustic resonance module, for example composed of a plurality of piezoelectric ceramic transducer arrays, is fixedly installed on the outer surface of the shell of the double-wheel cutting head, and its arrangement mode enables the acoustic wave energy emitted thereby to cover the convex region in front of the cutting head. The torsional pulse module, for example an actuating unit integrated at the lower end of the drill pipe connected with the cutting head, is driven by hydraulic or electromagnetic drive, and its mechanical structure is connected with the driving shaft system of the double-wheel cutter to enable it to apply a transient torsional impact to the driving shaft system.

[0067] At the same time, the multi-physical field sensing system is integrated in a special short section of drill pipe located above the cutting head, or is fixedly installed along the outer wall of the drill pipe, and the position is selected to ensure that the measured torque, acoustic and other parameters can accurately reflect the instantaneous state of the direct action of the cutting head on the soil, while avoiding the direct impact of the severe vibration of the cutting head on the sensor.

[0068] To realize the communication and energy supply of the central controller on the ground or on the ship with the underwater modules, this step further includes laying a composite umbilical cable integrated with power cables and data transmission lines, which is connected from the central controller to the junction box on the drill pipe, and then establishes electrical connection with the acoustic resonance module, the torsional pulse module and the multi-physical field sensing system through waterproof cables respectively, to provide a path for the subsequent execution of the method steps.​

[0069] Referring to the drawings Figure 3 , Figure 3 is a flow chart of real-time sensing and state vector construction according to an embodiment of the present application, step S2 is a real-time sensing step: after the preparation work in step S1 is completed, the double-wheel cutting head is started and made to start penetrating into the seabed sand layer, in the process, step S2 is executed, step S2 continuously collects a set of state parameters reflecting the interaction of the device with the soil through the multi-physical field sensing system integrated on the drill pipe at a preset sampling frequency (for example, 100 Hz).

[0070] Specifically, the set of state parameters includes the following measurements and acquisitions:

[0071] The real-time rotational torque of the double-wheel cutting head is measured by a strain gauge torque sensor installed on the drill pipe The real-time rotational speed of the double-wheel cutting head is measured by an optical encoder installed on the driving motor or the drill pipe The real-time penetration depth of the double-wheel cutting head is measured by a depth encoder linked with the drilling penetration mechanism The real-time pore water pressure of the mixing area is measured by a diffused silicon pressure sensor installed near the cutting head .

[0072] The real-time propagation speed of sound waves in the soil-fluid mixed medium And the real-time attenuation coefficient The acquisition process is as follows:

[0073] It is performed by one or more pairs of acoustic transceiving sensors arranged at a fixed distance on the cutting head, the transmitting sensor transmits a sound wave pulse with a preset initial amplitude , the receiving sensor receives the sound wave pulse and records the arrival time and receiving amplitude The propagation speed is calculated by measuring the transit time of the sound wave pulse between the two sensors :

[0074] ;

[0075] The attenuation coefficient is calculated by measuring the amplitude attenuation of the sound wave pulse , and the calculation formula is:

[0076] ;

[0077] After obtaining the real-time measurement values of the above-mentioned set of state parameters, these data are aligned with synchronous time stamps, and a multi-dimensional real-time state vector is constructed The vector at any time The specific form is:

[0078] ;

[0079] The real-time state vector is taken as the direct input basis for judgment and control in subsequent steps S3 and S4, and is transmitted to the central controller in real time through the data transmission line established in step S1.

[0080] Referring to the accompanying Figure 4 , Figure 4 is the collaborative control logic block diagram of the energy application step according to an embodiment of the present application, and step S3 is the energy application step: in the process of the double-wheel cutting head penetrating into the seabed sand layer, this step is driven by the central controller to drive the functional composite fluid injection system, the acoustic resonance module and the torsional pulse module in parallel, and to apply fluid and composite energy to the seabed sand layer.

[0081] During the execution of this step, the central controller continuously drives the power source of the acoustic resonance module to output high-frequency sound waves into the soil body, and the frequency of the high-frequency sound waves is set to be in the order of kilohertz.

[0082] In a specific embodiment, the frequency range is 15 kHz to 40 kHz, and at the same time, the central controller also continuously drives the functional composite fluid injection system to inject fluid into the stirring area. Unlike the continuous application of sound waves and fluid, the application of torsional pulses is condition-triggered, and the central controller executes a dynamic analysis process for judging whether there is a stubborn obstacle layer in real time and periodically, which takes the real-time state vector obtained in step S2 as input, and judges whether a preset trigger condition is met.

[0083] A specific logical expression of the stubborn obstacle layer trigger condition is:

[0084] ;

[0085] wherein, is the rotational torque at the current time; and are the arithmetic mean and the standard deviation of the rotational torque in a recent time window, respectively; is the sound wave attenuation coefficient at the current time; and are the arithmetic mean and the standard deviation of the sound wave attenuation coefficient in the same recent time window, respectively; the length of the recent time window is a parameter that can be preset according to the construction speed and the stratum characteristics.

[0086] In a specific embodiment, the length of the time window is set to be 3 seconds to 10 seconds, PWP the first order derivative of time, i.e. the real-time growth rate of PWP; and is a preset dimensionless sensitivity coefficient, whose value range is for example 1.5 to 3.0; is a preset effective mixing lower threshold, which is a positive value; when and only when the judgment result of the above logical expression is true, the central controller sends a trigger instruction to the torsional pulse module, after receiving the instruction, the torsional pulse module (for example, a high-pressure hydraulic quick-release unit or an electromagnetic clutch) is driven to apply at least one low-frequency, high-amplitude torsional pulse to the drive shaft system of the double-wheel agitator cutting head, the pulse width of the torsional pulse is set to be millisecond level, the pulse width is 10 ms to 100 ms, after executing one or a preset number of pulse applications, the torsional pulse module returns to standby state.

[0087] Referring to the accompanying drawings Figure 5 , Figure 5 is the execution flowchart of the closed-loop control step according to an embodiment of the present application, step S4 is the closed-loop control step: this step is executed in parallel throughout the whole energy application process of step S3, and a closed-loop feedback control loop with the goal of minimizing energy consumption is formed by the central controller.

[0088] In a specific manner, the execution of this step takes a preset depth increment (for example 0.1 meters) as a calculation and control period, and the central controller performs an acoustic fluid coupling optimization calculation every time the depth of the double-wheel agitator cutting head increases by one .

[0089] The goal of this optimization calculation is to minimize the total system energy consumption within this depth increment , therefore, the total system energy consumption is defined as the objective function :

[0090] ;

[0091] The total system energy consumption is composed of two components: the rotational cutting power consumption of the double-wheel agitator cutting head and the output power consumption of the acoustic wave resonance module , and its calculation formula is:

[0092] ;

[0093] Among them, the rotational cutting power consumption is obtained by time integration of the real-time output power of the agitator cutting head, and the specific calculation formula is:

[0094] ;

[0095] wherein, is the real-time rotational torque (unit: N·m) acquired from step S2; is the real-time rotational speed (unit: r / min); is the time needed to complete the depth increment .

[0096] The output power consumption of the acoustic resonator module is obtained by time integration of the real-time output electric power of the module. The specific calculation formula is:

[0097] ;

[0098] wherein, is the real-time output power of the acoustic resonator module (unit: kW), which is measured by the controller of its power source.

[0099] The central controller receives the real-time state vector generated in step S2, and executes an embedded numerical optimization algorithm (for example, gradient descent method or particle swarm optimization algorithm) to solve the minimum value of the objective function , and the optimization variables of this algorithm are the working parameters of the acoustic resonator module and the injection parameters of the functional composite fluid. Through optimization calculation, the central controller determines an optimal control parameter combination that can minimize the expected total energy consumption within the next depth increment , including:

[0100] optimal acoustic resonant frequency ; optimal acoustic output power ; optimal functional composite fluid flow rate ; and optimal functional composite fluid composition .

[0101] The composition of the functional composite fluid specifically refers to two adjustable parameters: the mass concentration of water-soluble high molecular polymer (such as polyacrylamide) in water, and the volume fraction of microbubbles in the mixed fluid.

[0102] In a specific embodiment, the mass concentration of water-soluble high molecular polymer is regulated in the range of 0.01% to 0.5%, and the volume fraction of microbubbles is regulated in the range of 1% to 15%. The central controller realizes accurate regulation of these two parameters by controlling the flow rate of the polymer mother liquor injection pump and the gas production rate of the microbubble generator according to the optimization results.

[0103] After the optimal parameter combination is determined, the central controller immediately generates corresponding control instructions and sends them to the power source of the acoustic resonance module and each execution unit (e.g., a proportional pump and a mass flow controller) of the functional composite fluid injection system through the channel established in step S1, thereby completing the one-time closed-loop adaptive adjustment of the construction parameters.

[0104] Referring to the accompanying drawings Figure 6 , Figure 6 is a schematic diagram of the data structure of the digital construction log according to an embodiment of the present application. During the entire process of steps S1 to S4, the method of the present application can also include a log recording step in parallel.

[0105] The log recording step is executed by the central controller, which triggers a data recording operation at a preset time interval (e.g., every 0.5 seconds) or a preset depth interval (e.g., every 0.05 meters), which writes a set of data during the construction process to the non-volatile storage medium of the central controller to generate a digital construction log.

[0106] Each recording operation generates a data record associated with the current time stamp and the penetration depth , and each data record specifically contains the following two sets of data:

[0107] One set is the state data, i.e., the complete real-time state vector at the current time, which includes the values of the rotational torque , the rotational speed , the penetration depth , the acoustic wave propagation speed , the acoustic wave attenuation coefficient , and the pore water pressure collected and constructed by step S2.

[0108] The other set is the decision data, i.e., all the parameters output by the central controller at the current time for controlling the modules, which includes:

[0109] the set frequency and the set power sent to the acoustic resonance module, the set flow rate, the set concentration of water-soluble high polymer, and the set volume fraction of micro-bubbles sent to the functional composite fluid injection system, and a state flag bit indicating whether the torsional pulse module is triggered.

[0110] All data records are written in one or more log files in the order of time or depth, thereby establishing a traceable, depth-accurate digital archive for the entire softening treatment construction process.

[0111] The system in this embodiment can be used to execute the above algorithm embodiments, and its principle and technical effect are similar, so they will not be described again here.

Claims

1. A method of construction for softening a seabed sand layer, characterized by, The method comprises the following steps: S1: system preparation step: integrating the acoustic resonance module and the torsional pulse module on the double-wheel cutting head, and integrating the multi-physical field sensing system on the drill pipe connected with the double-wheel cutting head; S2: real-time sensing step: during the process of the double-wheel cutting head penetrating into the seabed sand layer, the multi-physical field sensing system continuously collects data, and a real-time state vector representing the current state of the stratum and the equipment interaction is constructed; S3: energy application step: the central controller drives the acoustic resonance module, the torsional pulse module and the functional composite fluid injection system to apply energy and inject fluid to the seabed sand layer; S4: closed-loop regulation step: during the energy application step, the central controller adjusts the composition and flow rate of the functional composite fluid, the working parameters of the acoustic resonance module, and the triggering conditions and working parameters of the torsional pulse module according to the real-time state vector, thereby completing the treatment of softening the seabed sand layer.

2. A method of seabed sand layer softening according to claim 1, characterized in that, In S2, the multi-physical field sensing system collects a set of state parameters, which includes: the rotation torque, rotation speed, penetration depth of the double-wheel cutting head, the propagation speed of the acoustic wave in the soil-fluid mixed medium, the attenuation coefficient of the acoustic wave in the soil-fluid mixed medium, and the pore water pressure of the mixing area; The real-time state vector is constructed based on at least two of the set of state parameters.

3. A method of seabed sand layer softening according to claim 2, characterized in that, The energy application step in S3 specifically includes: the central controller continuously drives the acoustic resonance module to output high-frequency acoustic waves; when the real-time state vector meets the preset stubborn obstacle layer triggering condition, the central controller triggers the torsional pulse module to apply at least one low-frequency, high-amplitude torsional pulse to the double-wheel cutting head.

4. A method of seabed sand layer softening according to claim 3, characterized in that, The stubborn obstacle layer triggering condition is determined based on dynamic analysis of the real-time state vector, and the triggering condition is: the rotation torque of the double-wheel cutting head and the attenuation coefficient of the acoustic wave in the soil-fluid mixed medium both show abnormal growth significantly higher than their recent average, and the growth rate of the pore water pressure of the mixing area continuously remains below the preset lower limit of effective mixing.

5. A method of seabed sand layer softening according to claim 1, characterized in that, The closed-loop regulation step in S4 is a sound-fluid coupling optimization process, which includes: during the process of the double-wheel cutting head penetrating into the seabed sand layer, the system total energy consumption consumed in each depth increment is defined as an objective function by taking a preset depth increment as a calculation period; the central controller takes minimizing the objective function as a goal, and synchronously optimizes and determines the optimal acoustic resonance frequency, and the optimal composition and flow rate of the functional composite fluid under the current working condition according to the real-time state vector; according to the determined optimal acoustic resonance frequency and the optimal composition and flow rate of the functional composite fluid, the acoustic resonance module and the functional composite fluid injection system are regulated.

6. A method of seabed sand layer softening according to claim 5, characterised in that, The system total energy consumption is composed of the rotation cutting power consumption of the double-wheel cutting head and the output power consumption of the acoustic resonance module.

7. A method of seabed sand layer softening according to claim 1, characterized in that, The functional composite fluid is composed of at least two of water, water-soluble polymer and micro-bubbles; The composition of the functional complex fluid refers to the concentration of the water-soluble polymer and the volume fraction of the micro-bubbles.

8. A method of seabed sand layer softening according to claim 1, characterized in that, The working parameters of the acoustic wave resonance module include an acoustic wave resonance frequency and an output power.

9. A method of seabed sand layer softening according to claim 1, characterized in that, After S4, further comprising steps of: A logging step: recording the real-time state vectors of each depth in the whole construction process and the corresponding control decisions output by the central controller to form a digital construction log.

10. A method of seabed sand layer softening according to claim 3, characterized in that, In the energy application step, the acoustic wave resonance module is driven to output high-frequency acoustic waves, and the frequency of the high-frequency acoustic waves is set to be in the order of kilohertz. At the same time, the torsional pulse module is triggered to apply low-frequency and high-amplitude torsional pulses, and the pulse width of the low-frequency and high-amplitude torsional pulses is set to be in the order of milliseconds.

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