Karst region pile foundation intelligent positioning and accurate construction method

Abstract

The present application relates to geotechnical engineering and underground concealed engineering construction technology field, disclose a kind of karst area pile foundation intelligent positioning and accurate construction method, comprising: the establishment of drill string dynamics model and inversion drill bottom mechanical impedance and mechanical equivalent aperture;Based on mechanical parameter mapping generates preset hydraulic impedance boundary model;In the pouring stage, the measured equivalent flow resistance is analyzed and the effective hydraulic aperture is back calculated;The flow resistance deviation and aperture deviation of measured parameters and reference model are calculated, and the deviation combination is used to identify the geological defect types such as lateral communication karst cave, plastic shrinkage and hole wall collapse, and the corresponding adaptive control instruction is generated.The present application converts the drilling mechanical characteristics into pouring flow reference, uses the double deviation analysis of mechanical and hydraulic aperture, realizes the accurate identification of concealed karst defect and the closed-loop adaptive control of construction process, and guarantees the pile quality and construction safety under complex karst geological environment.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering and underground concealed engineering construction technology, specifically to a method for intelligent positioning and precise construction of pile foundations in karst areas. Background Technology

[0002] The geological structure of karst areas is highly heterogeneous and anisotropic. The presence of underground caverns, fracture zones, and weak infill materials poses technical challenges to deep-hole pile foundation construction, such as uncontrollable borehole geometry and loss of grouting medium. Achieving precise monitoring and closed-loop control throughout the construction process is crucial to ensuring the integrity of the pile foundation structure.

[0003] Existing pile foundation construction monitoring technologies typically treat drilling and fluid grouting as two separate operational phases. During the drilling phase, measurement-while-drilling (MWD) technology primarily collects mechanical parameters such as drill pressure, torque, and rotational speed through surface monitoring units to identify lithological interfaces or optimize mechanical efficiency. However, when dealing with deep-hole long drill string systems, existing methods often employ simplified lumped parameter models or rigid body assumptions, neglecting the delay, attenuation, and dispersion effects caused by stress wave propagation in slender drill strings. This leads to discrepancies between the inverted bottom-hole forces and displacement responses. Furthermore, existing technologies only focus on the macroscopic mechanical strength characterization of the rock, failing to establish a physical mapping relationship between the mechanical energy dissipation characteristics during rock fracturing and hydraulic properties such as formation pore structure and permeability. This prevents the effective transfer of geological information acquired during the drilling phase to the grouting phase.

[0004] During the grouting phase, construction control primarily relies on real-time collected pumping pressure and flow data, comparing them with preset empirical thresholds to determine the grouting status. However, due to the lack of theoretical rheological benchmarks specific to the geological characteristics of the current pile boreholes, this single fluid monitoring model struggles to analyze the physical causes of abnormal data. Fluid pressure or flow fluctuations can be triggered by a variety of distinct geological defects. For example, nonlinear attenuation of grouting pressure can originate from grout leakage caused by laterally connected karst caves, or from plastic expansion of weak strata under pressure. Without prior information on borehole geometry and stratum permeability as a reference, the monitoring system cannot accurately distinguish between different types of conditions, such as laterally connected karst caves, elastic rebound of the strata causing diameter reduction, and borehole wall collapse and blockage. Consequently, it is difficult to match targeted grouting adjustments or pressure control measures, limiting the accuracy of pile foundation construction quality control under complex geological conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an intelligent positioning and precise construction method for pile foundations in karst areas. This method solves the problem that the data on drilling machinery characteristics and grouting rheological behavior are fragmented during pile foundation construction in karst areas, making it difficult to accurately distinguish and implement targeted control of geological defects such as lateral hidden karst caves, plastic diameter reduction, and borehole wall collapse.

[0006] To achieve the above objectives, the present invention provides a method for intelligent positioning and precise construction of pile foundations in karst areas, mainly comprising the following steps: First, establishing a discretized dynamic model describing the frequency domain response characteristics of the drilling rig's drill string system, and correcting the boundary parameters of the dynamic model through no-load operation testing; Second, acquiring vibration and force signals at the top of the drill string, using the dynamic model for decoupling and inversion to obtain the true response at the bottom of the drill bit, calculating the transient mechanical impedance of the contact surface between the drill bit and the rock, and extracting the mechanical damping coefficient. Simultaneously, calculating the mechanical specific energy dissipation value based on the drilling mechanical parameters, and reconstructing the mechanical equivalent aperture along the depth; Subsequently, establishing a mapping relationship between mechanical parameters and hydraulic parameters, and predicting the permeability of the soil and rock mass based on the mechanical damping coefficient and the mechanical specific energy dissipation value. The process involves generating a baseline pressure-flow characteristic curve that varies with depth, based on the mechanical equivalent orifice diameter. Next, a pulsating pressure wave is applied during fluid injection, and pressure and flow data at the pipe inlet are collected to construct a pressure-flow hysteresis loop. The measured equivalent flow resistance is then analyzed, and the current effective hydraulic orifice diameter is inferred using the pressure wave propagation characteristics. Finally, the flow resistance deviation between the measured equivalent flow resistance and the baseline flow resistance corresponding to the baseline pressure-flow characteristic curve, as well as the orifice diameter deviation between the mechanical equivalent orifice diameter and the effective hydraulic orifice diameter, are calculated. Based on the combination of the positive and negative values ​​of the flow resistance deviation and orifice diameter deviation with threshold ranges, the current geological defect type is identified from laterally connected karst caves, plastic narrowing, orifice wall collapse, or pipe blockage. Corresponding adaptive control commands are then generated based on the identification results to adjust the operating mode of the injection equipment.

[0007] Furthermore, when constructing the drill string dynamics model, the drill string system is divided into several finite element nodes along the axial direction. A one-dimensional wave equation is used to establish an element transfer matrix describing the frequency domain transformation relationship between the top and bottom states of the drill string elements. The overall drill string state transfer matrix is ​​then constructed through matrix cascading. During system initialization, the drilling rig is controlled to rotate under no-load conditions. The measured natural frequencies are extracted from the collected background noise spectrum. Minimizing the residual between the theoretical and measured natural frequencies is used as the objective to iteratively correct the equivalent stiffness coefficient and equivalent damping coefficient of the top boundary of the overall drill string state transfer matrix, ensuring that the model boundary conditions match the actual equipment conditions.

[0008] Furthermore, during the inversion stage of the drilling process, the inverse matrix of the overall drill string state transfer matrix is ​​used to calculate the frequency domain signal at the top of the drill string, eliminating the elastic wave delay and attenuation effects caused by the slender drill pipe, and solving for the true displacement and force data at the bottom of the drill bit. The transient mechanical impedance spectrum is obtained by calculating the ratio of the vibration velocity corresponding to the true force data to the true displacement data in the frequency domain. Subsequently, a rheological model using a parallel linear spring and linear damper is employed to identify the parameters of the transient mechanical impedance spectrum, extracting the equivalent transient stiffness reflecting the rock's elastic modulus and the mechanical damping coefficient reflecting the degree of rock fracture. Simultaneously, based on the true bottom-hole torque, drill pipe rotation speed, true bottom-hole drilling pressure, and mechanical drilling speed during the drilling process, the mechanical specific energy dissipation required for rock fracturing per unit volume is calculated. The mechanical specific energy dissipation value is compared with the standard specific energy threshold of bedrock. When the mechanical specific energy dissipation value is lower than the standard specific energy threshold, it is determined that there is a risk of enlargement. The mechanical equivalent hole diameter greater than the nominal diameter of the drill bit is calculated based on the ratio of the difference between the two, thereby quantifying the geometric dimensions of the physical hole formation.

[0009] Furthermore, this invention relates to a parameter mapping mechanism across physical fields. When generating a preset hydraulic impedance boundary model, a nonlinear mapping function is constructed, in which the estimated permeability of the soil and rock mass is positively correlated with the mechanical damping coefficient (characterizing increased permeability due to fracture development) and negatively correlated with the mechanical specific energy dissipation value (characterizing decreased permeability due to rock density). Based on the radial flow model in fluid mechanics, combined with the estimated permeability and mechanical equivalent pore size, the theoretically required baseline flow resistance is calculated; and the baseline volumetric stiffness of the grouting system is estimated using the equivalent transient stiffness of the rock. Based on the baseline flow resistance and baseline volumetric stiffness, a baseline pressure-flow characteristic curve describing the dynamic relationship between grouting pressure and grouting flow rate under ideal conditions is generated, serving as a digital template for subsequent grouting construction.

[0010] Furthermore, during the rheological fingerprinting process in the injection phase, an unsteady rheological dynamic equation was established, incorporating fluid inertia, flow resistance, and system volumetric stiffness terms. A pressure-flow hysteresis loop was constructed based on real-time acquired pressure and flow data. Regression analysis was used to solve the unsteady rheological dynamic equation, extracting the measured equivalent flow resistance that characterizes the actual permeability of the current formation. Simultaneously, correlation analysis was performed on the acquired pressure signals to identify the propagation time delay of pressure waves in the downhole fluid, thus calculating the actual propagation velocity. Based on the wave velocity theory model, the correlation between the actual propagation velocity and the fluid bulk modulus, surrounding rock elastic modulus, and channel cross-sectional dimensions was established. Utilizing the physical property that wave velocity decreases with increasing lateral constraint stiffness, the effective hydraulic aperture under fluid pressure was obtained through inverse calculation.

[0011] Furthermore, this invention employs an adaptive control strategy based on multi-source deviation. When the measured equivalent flow resistance is lower than the reference flow resistance and the flow resistance deviation exceeds the first threshold, while the mechanical specific energy dissipation value is within the normal bedrock range, it is determined that there is a hidden karst cave that is not touched by the drilling tool but is laterally connected to the borehole wall. The control system generates a command to adjust the grouting equipment to switch to intermittent grouting mode and increase the proportion of quick-setting agent or flocculant. When the effective hydraulic aperture is smaller than the mechanical equivalent aperture and the aperture deviation exceeds the second threshold, while the measured equivalent flow resistance is higher than the reference flow resistance, it is determined that a diameter reduction has occurred due to formation elastic rebound or plastic extrusion. The control system generates a command to control the grouting equipment to increase the pumping static pressure to the target pressure value and use the hydrostatic pressure to expand the diameter reduction area. When the measured equivalent flow resistance is higher than the reference flow resistance and the flow resistance deviation exceeds the third threshold, and the deviation amplitude is significantly greater than the deviation caused by the diameter reduction, it is determined that a borehole wall collapse or pipeline blockage has occurred. The control system generates a command to suspend continuous pumping and start a high-frequency pressure pulse oscillation program to clear the blockage using water hammer wave energy.

[0012] This invention provides a method for intelligent positioning and precise construction of pile foundations in karst areas. It has the following beneficial effects:

[0013] 1. This invention establishes a nonlinear mapping function between mechanical damping coefficient, mechanical specific energy dissipation, and hydraulic permeability, and utilizes lithological characteristics obtained during the drilling stage to generate a baseline pressure-flow characteristic curve for the grouting stage in advance. This mechanism breaks the data silo effect between drilling and grouting in traditional pile foundation construction, transforming the physical cutting response of the formation during drilling into a prediction of rheological behavior during grouting. This provides a digital template reflecting the integrity of the borehole wall that varies with depth for subsequent grouting operations, solving the technical problems of traditional methods lacking theoretical reference standards and struggling to identify minute rheological anomalies.

[0014] 2. This invention introduces a comparative dimension between the mechanical equivalent aperture (physical hole geometry) and the effective hydraulic aperture (fluid constraint geometry), and combines it with flow resistance deviation to construct a two-dimensional fault diagnosis logic. This allows for the accurate differentiation of geological defects with different physical natures, such as laterally concealed karst caves (manifested as normal mechanical aperture but low flow resistance) and plastic diameter reduction (manifested as normal mechanical aperture but small hydraulic aperture). This improves the accuracy of risk identification for connected karst caves, stratum rebound, and borehole wall collapse in complex karst geological environments, and effectively avoids misjudgments caused by single monitoring methods.

[0015] 3. This invention utilizes pulsating pressure waves to construct a pressure-flow hysteresis loop in real time and invert the wave velocity, achieving millisecond-level monitoring of downhole fluid flow resistance and orifice status. Based on the real-time diagnosed geological defect type, the system can automatically match and execute differentiated control strategies, such as intermittent grouting and thickening control for cavern leakage, static pressure expansion control for diameter reduction, and high-frequency pulse oscillation control for blockage. This proactive closed-loop regulation mechanism ensures the stability of the grouting process under varying geological conditions, effectively preventing construction accidents such as concrete segregation, pile breakage, or excessive consumption during diameter expansion. Attached Figure Description

[0016] Figure 1 This is an overall flowchart of the method in the embodiments of the present invention;

[0017] Figure 2 This is a schematic diagram of the drill string dynamics discretization model and signal acquisition in an embodiment of the present invention;

[0018] Figure 3 This is a schematic diagram illustrating the mapping of mechanical parameters to hydraulic parameters and the generation of reference curves in an embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the pressure-flow hysteresis loop and wave velocity inversion during the injection stage in an embodiment of the present invention;

[0020] Figure 5 This is a logic diagram for two-dimensional geological defect identification based on flow resistance deviation and aperture deviation in an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This embodiment first introduces the hardware architecture and operating environment required to implement the method of the present invention. The system's physical architecture mainly includes a drilling sensing subsystem, a rheological injection subsystem, and a central control and processing subsystem.

[0023] Drilling Sensing Subsystem: Responsible for acquiring dynamic response data during the drilling phase. A highly sensitive triaxial vibration acceleration sensor is installed on the non-rotating component below the drill rig's power head (top drive) to collect longitudinal and lateral vibration signals at the top of the drill string; a torque-speed composite sensor and a tension-compression sensor are installed at the power output shaft to monitor drill pipe speed, drive torque, and axial drilling pressure in real time.

[0024] The rheological grouting subsystem is responsible for performing pulsating pressure excitation and rheological data acquisition during the grouting phase. It includes a variable frequency grouting pump (or concrete delivery pump) and an intelligent additive injection pump. The variable frequency grouting pump is equipped with a programmable controller, capable of superimposing adjustable frequency pressure pulsations into the continuously pumped fluid according to instructions. A high-frequency dynamic pressure transmitter and an electromagnetic flowmeter are installed in series at the orifice where the grouting pipeline enters the pile hole.

[0025] Central Control and Processing Subsystem: Serving as the core computing platform, this subsystem employs an industrial control computer equipped with a multi-channel high-speed data acquisition card. Internally, it stores the drill string dynamics transfer model and control algorithms. These algorithms are used to receive sensor signals, perform parameter inversion, calculate deviation vectors, and send control commands to the drilling rig and grouting pump via an industrial bus, forming a closed-loop control system.

[0026] See attached document Figure 1 This invention provides a method for construction control of karst pile foundations based on drilling mechanical impedance inversion and rheological feedback, which may include:

[0027] S100: Construct the drill string dynamics transfer model and perform system initialization.

[0028] Based on the physical parameters of the drilling rig drill string system, a discretized dynamic model is established. The drill string is divided into multiple finite element nodes with distributed mass, stiffness, and damping. A drill string state transfer matrix is ​​defined to describe the frequency domain relationship between the excitation at the top of the drill string and the response at the bottom.

[0029] During the system initialization phase, the drilling rig is controlled to perform an unloaded operation test. Vibration signals from the drilling rig system are collected to obtain background noise data and natural frequency data. Based on the background noise data and natural frequency data, the boundary parameters of the drill string state transfer matrix are corrected, completing the system initialization.

[0030] S200: Implement bottom mechanical impedance inversion and lithological feature extraction during drilling.

[0031] During drilling, sensors are used to collect vibration acceleration and driving force signals from the top of the drill pipe in real time. The collected vibration acceleration and driving force signals are processed using the inverse operation of the drill string state transfer matrix to eliminate the elastic effect of the drill pipe and friction interference along the drill line, and to calculate the true displacement and true force data at the bottom of the drill bit.

[0032] Based on actual displacement and force data, the transient mechanical impedance at the drill bit-rock contact surface is calculated. The transient mechanical impedance is then fitted to extract the equivalent transient stiffness and mechanical damping coefficient of the rock at the current depth.

[0033] Simultaneously, data on rotational speed, torque, drilling pressure, and drilling speed during the drilling process are acquired. Based on these data, the mechanical energy dissipation value per unit volume of rock breaking is calculated. Based on this mechanical energy dissipation value, the mechanical equivalent aperture along the depth is reconstructed. When the mechanical energy dissipation value is lower than a preset void threshold, the mechanical equivalent aperture is larger than the drill bit diameter.

[0034] S300: Generates a preset hydraulic impedance boundary model based on mechanical parameters.

[0035] Establish a mapping function between the mechanical damping coefficient and the hydraulic permeability. Based on the mechanical damping coefficient and mechanical specific energy dissipation value extracted in step S200, predict the estimated permeability of the soil and rock mass at the current depth using the mapping function.

[0036] Based on the estimated permeability and the mechanically equivalent pore size reconstructed in step S200, the theoretically required baseline flow resistance and baseline volumetric stiffness for fluid injection at this depth are calculated. Based on the baseline flow resistance and baseline volumetric stiffness, a baseline pressure-flow characteristic curve varying with depth is generated. This baseline pressure-flow characteristic curve is used to characterize the theoretical rheological behavior when the pore wall is intact and there are no hidden caverns.

[0037] S400: Collects rheological fingerprints and performs parameter inversion during the infusion stage.

[0038] During concrete or slurry pouring, the pumping equipment is controlled to apply periodic pulsating pressure waves. Real-time inlet pressure and flow data are acquired. A real-time pressure-flow hysteresis loop is constructed based on the inlet pressure and flow data.

[0039] The pressure-flow hysteresis loop was analyzed, and the measured equivalent flow resistance was calculated. Cross-correlation analysis was performed using pulsating pressure waves to calculate the propagation velocity of the pressure waves in the downhole fluid. The current effective hydraulic orifice size was then deduced based on the propagation velocity.

[0040] S500: Implement construction control based on the deviation between measured parameters and the benchmark model.

[0041] Calculate the flow resistance deviation between the measured equivalent flow resistance and the reference flow resistance generated in step S300. Calculate the aperture deviation between the reconstructed mechanical equivalent aperture in step S200 and the back-calculated effective hydraulic aperture in step S400. Determine the geological defect type based on the distribution of flow resistance and aperture deviations, and output control commands.

[0042] When the measured equivalent flow resistance is lower than the reference flow resistance and the flow resistance deviation exceeds the preset first threshold, while the mechanical specific energy dissipation value is within the normal bedrock range, it is determined that a laterally connected karst cave exists. At this time, a first control command is generated to control the grouting equipment to switch to intermittent grouting mode and increase the grout yield stress.

[0043] When the effective hydraulic aperture is smaller than the mechanical equivalent aperture and the aperture deviation exceeds a preset second threshold, it is determined that a narrowing has occurred due to formation elastic rebound or plastic extrusion. At this time, a second control command is generated to control the injection equipment to increase the pumping static pressure to the target pressure value to expand the aperture.

[0044] When the measured equivalent flow resistance is higher than the reference flow resistance and the flow resistance deviation exceeds the preset third threshold, it is determined that orifice wall collapse or pipeline blockage has occurred. At this time, a third control command is generated to control the injection equipment to execute a high-frequency pressure pulse oscillation program.

[0045] In one embodiment of the present invention, the process of constructing a drill string dynamics transfer model and performing system initialization specifically includes the following:

[0046] Based on the physical structural parameters of the drilling rig and drilling tools, a discretized distributed parameter model of the drill string system is established. The drill string system is divided into several finite element nodes along the axial direction, each node corresponding to a drill rod element, drill collar element, or connector element with uniform cross-sectional properties. For the slender drill rod used in deep-hole pile foundation construction in karst areas, it is regarded as a one-dimensional viscoelastic waveguide, and its longitudinal vibration modes and axial transmission characteristics are analyzed in detail. A frequency domain state vector is defined at any cross-sectional position in the drill string system. This state vector consists of two physical quantities: the longitudinal displacement component and the longitudinal force component at that cross-section.

[0047] Based on the one-dimensional wave equation, a cell transfer matrix describing the dynamic transmission characteristics of a drill pipe element is established. For a length of... The elastic modulus is The material density is And the cross-sectional area is A single uniform drill pipe element, whose element transfer matrix This describes the linear transformation relationship between the top and bottom state vectors of this unit in the frequency domain. The mathematical expression for the unit's transfer matrix is:

[0048] ;

[0049] in, The wave number is represented by the angular frequency. Divide by the speed of sound propagation in the drill pipe material Calculated; The characteristic impedance of a drill pipe element is equal to the cross-sectional area of ​​the drill pipe. Multiply by material density With the speed of sound wave propagation The product of the two forces. The cosine terms in this matrix represent the in-phase components of the inertial and elastic forces, while the sine terms represent the orthogonal components of the inertial and elastic forces. This provides a complete description of the phase delay and amplitude attenuation of the wave signal in a continuous medium.

[0050] A comprehensive drill string state transfer matrix is ​​constructed through matrix cascading operations. Following the actual drill string assembly sequence, starting from the surface top drive system, the unit transfer matrices of each drill pipe section, drill collar, and connector are multiplied sequentially from top to bottom to obtain the overall transfer matrix describing the entire drill string system. This overall transfer matrix establishes the frequency domain analytical relationship between the displacement and force responses at surface measuring points and the displacement and force responses at the bottom hole drill bit. During the construction process, the complex form of the elastic modulus is used. To characterize the structural damping of drill pipe materials, among which As a material loss factor, it can quantify the dissipation effect of energy during propagation along a long drill string in the model.

[0051] After model construction is completed, the system initialization program is executed to correct the model boundary parameters. The drilling rig is controlled to lift the drill string, so that the drill bit is completely detached from the rock at the bottom of the hole and suspended in the air. The drilling rig is then controlled to rotate unloaded within a preset operating speed range. Time-domain signals are synchronously acquired by vibration acceleration sensors and force sensors installed below the drive unit on top of the drilling rig. The acquired time-domain signals are then converted into frequency-domain signals using a fast Fourier transform to obtain the background noise spectrum of the drilling rig system. The peak frequency with concentrated energy is extracted from the background noise spectrum and determined as the measured natural frequency of the drill string system.

[0052] The top boundary conditions of the dynamic model are iteratively calibrated using measured natural frequencies. The drilling rig top drive system is simplified into a lumped parameter model boundary with equivalent mass, equivalent stiffness, and equivalent damping. Using minimizing the residual between the theoretical and measured natural frequencies calculated by the model as the objective function, a numerical optimization algorithm is employed to correct the equivalent stiffness and damping coefficients of the top boundary. The corrected boundary parameters are then substituted into the overall transfer matrix to generate a benchmark transfer model for subsequent construction monitoring, ensuring that the mathematical model stored in the control unit accurately matches the actual physical state of the current construction equipment.

[0053] See attached document Figure 2 In one embodiment of the present invention, the process of performing bottom mechanical impedance inversion and lithological feature extraction during drilling specifically includes the following:

[0054] During the rotary cutting drilling operation, the vibration acceleration time-domain signal at the top of the drill string is synchronously acquired by a multi-channel data acquisition unit located on the top of the drilling rig. and longitudinal driving force time domain signal The data acquisition unit continuously samples at a sampling rate more than 10 times higher than the drilling rig's highest rotational frequency to capture high-frequency information containing rock fracturing characteristics. The acquired time-domain sequence is processed using a Fast Fourier Transform algorithm, converting it into a top displacement spectrum in the frequency domain. and apex force spectrum .in It is obtained by integrating the acceleration spectrum twice in the frequency domain.

[0055] Using a pre-built and boundary-corrected global state transfer matrix of the drill string Perform inverse decoupling operations on the top-level frequency domain data. This is done by transferring the inverse matrix of the matrix. This method eliminates elastic wave delay, amplitude attenuation, and phase distortion introduced during signal transmission by long drill pipes, and reconstructs the true displacement response at the interface between the drill bit bottom and the rock. and the response of real forces The inversion calculation is based on the following matrix transformation relationship:

[0056] ;

[0057] in, The angular frequency is used to calculate the frequency range that includes the main longitudinal resonant frequency of the drill string and the excitation frequency of rock breaking.

[0058] Based on the calculated bottom-hole physical quantities, the transient mechanical impedance spectrum of the drill bit-rock interface is calculated. This index is defined as the ratio of the bottom-hole force to the bottom-hole vibration velocity in the frequency domain, and is used to characterize the dynamic resistance of rock to drill bit cutting action. The calculation formula is:

[0059] ;

[0060] in, The imaginary unit, Frequency domain representation of the vibration velocity at the bottom of the well.

[0061] To extract physically meaningful lithological parameters from complex impedance spectra, the Kelvin-Voigt rheological model was used to identify and fit the calculated transient mechanical impedance spectrum. The interaction between the drill bit and the rock was equivalent to a mechanical system consisting of a linear spring and a linear damper in parallel. Within the local depth range, a least-squares optimization algorithm was used to fit the imaginary and equivalence parts of the measured impedance spectrum within the effective frequency band, thereby extracting the equivalent transient stiffness of the rock. and mechanical damping coefficient These two parameters directly reflect the mechanical properties of the formation: equivalent transient stiffness. Characterizing the rock's elastic modulus and roof support capacity, when the drill bit approaches the cave ceiling... It will exhibit a non-linear decreasing trend; mechanical damping coefficient Characterizing the energy dissipation characteristics and fracture development degree during rock fracturing, fracture-developed zones or fracture zones The value is significantly higher than that of intact bedrock.

[0062] Simultaneously acquire macroscopic mechanical parameters during the drilling process, including the actual torque at the bottom of the well. Drill rod speed Actual drilling pressure at the bottom of the well and mechanical drilling speed These parameters are used to calculate the mechanical energy dissipation required to break a unit volume of rock. This index combines the energy density of rotary cutting work and axial propulsion work. The calculation formula is:

[0063] ;

[0064] in, This represents the cross-sectional area of ​​the drill bit. Mechanical energy dissipation. The magnitude of the value is positively correlated with the rock strength. When encountering cave filling or cavities, It will drop sharply to near zero.

[0065] Based on the calculated mechanical specific energy dissipation Constructing a mechanically equivalent aperture that varies with depth This parameter quantifies the actual physical borehole diameter range formed by the drill bit under the current mechanical energy input, especially in soft formations where the borehole enlargement effect can occur due to drill string oscillation or erosion. It sets the standard specific energy threshold for the bedrock. When calculated in real time Below this threshold, an expansion risk is identified. The reconstruction model for the mechanical equivalent aperture is as follows:

[0066] ;

[0067] in, This is the nominal diameter of the drill bit. This is the formation enlargement factor, which is statistically determined from historical construction data and used to characterize the lateral failure sensitivity of a specific formation under low-energy fracturing conditions. When At that time, take directly The mechanical equivalent aperture curve generated in this step provides a geometric reference for fluid wave velocity calibration in the subsequent injection stage.

[0068] See attached document Figure 3 In one embodiment of the present invention, the process of generating a preset hydraulic impedance boundary model based on mechanical parameters specifically includes the following:

[0069] A nonlinear mapping model is established to connect drilling mechanical parameters with formation hydraulic parameters. Based on geotechnical mechanisms, the mechanical damping coefficients extracted in the preceding steps are... Compared to mechanical energy dissipation As an input variable, predict the hydraulic permeability of the soil and rock mass at the current depth. This mapping logic is based on the following physical correlations: an increase in the mechanical damping coefficient usually corresponds to an increase in the density of fractures in the rock mass or enhanced interparticle friction, which in turn leads to an increase in fluid permeation channels; a decrease in mechanical specific energy dissipation usually corresponds to a decrease in the cementation strength of the rock or an increase in porosity, which in turn leads to a decrease in fluid flow resistance.

[0070] Construct specific mapping functions This multiphysics coupling relationship is characterized by a combination of power law and exponential function. For depth... The stratigraphic unit at that location has an estimated permeability. The calculation formula is:

[0071] ;

[0072] In the formula, The standard reference damping value for intact bedrock. These are the standard reference specific energy values ​​for intact bedrock, and these two reference values ​​are determined through field core sampling tests or pile test data. Based on the basic penetration coefficient, The damping sensitivity index, These three model parameters represent the energy consumption degradation index. , , The calibration was performed based on historical geological survey data of the construction area. This function realizes the numerical conversion from discrete mechanical fracturing characteristics to continuous fluid permeability characteristics, providing a medium property basis for subsequent rheological behavior prediction.

[0073] Based on Darcy's law in fluid mechanics and its application in radial flow, combined with the estimated permeability The mechanical equivalent aperture reconstructed by the aforementioned steps Calculate the theoretically expected reference flow resistance when fluid is injected at this depth. Assuming the fluid during the grouting process permeates radially from the borehole axis into the surrounding soil and rock mass, the calculation model for the baseline flow resistance is as follows:

[0074] ;

[0075] in, The dynamic viscosity of the grout is represented by its viscosity. The axial height of the fluid computing unit. The radius of influence represents the radial distance at which the fluid pressure decays to the formation hydrostatic pressure.

[0076] Simultaneously, the reference volumetric stiffness of the formation and borehole wall system is calculated. This parameter reflects the grouting system's ability to contain fluid under pressure, and is mainly determined by the compressibility of the grout and the elastic modulus of the rock and soil surrounding the borehole. The equivalent transient stiffness of the rock obtained through the aforementioned steps is used for inversion. Estimate the reference volumetric stiffness:

[0077] ;

[0078] In the formula, To calculate the slurry volume within the calculation unit, This is the bulk modulus of the grout. This formula shows that when the surrounding rock stiffness... At higher temperatures, the volumetric deformation of the system is mainly controlled by fluid compression; when the surrounding rock stiffness is low (such as in soft soil or karst caves), the contribution of borehole wall deformation to volumetric stiffness increases significantly.

[0079] The reference flow resistance obtained based on the above calculations and reference volumetric stiffness A baseline pressure-flow characteristic curve as a function of depth is generated. This curve describes the injection pressure under ideal conditions assuming intact borehole walls, no lateral hidden caverns, and no additional plastic deformation. With infusion flow rate The dynamic relationship that should be followed between them The baseline characteristic curve is stored in the database of the control system, serving as a digital template for identifying abnormal geological conditions in subsequent real-time construction monitoring. This achieves the technical effect of using the mechanical fingerprint of the drilling stage to calibrate the hydraulic fingerprint of the grouting stage.

[0080] See attached document Figure 4 In one embodiment of the present invention, the process of acquiring rheological fingerprints and performing parameter inversion during the perfusion stage specifically includes the following:

[0081] In concrete or slurry pumping and grouting operations, the output of the pumping equipment is superimposed with periodic, minute pulsations of fluid pressure waves. High-frequency pressure sensors and electromagnetic flowmeters installed at the grouting pipe inlet are used to synchronously and sequentially acquire the time-domain signal of the inlet pressure in real time. and flow time domain signal Within each monitoring cycle, a dynamic pressure-flow hysteresis loop is constructed on the phase plane based on the collected pressure and flow data sequences. The area and shape characteristics of this hysteresis loop directly reflect the energy dissipation (flow resistance effect) and energy storage (volume effect) in the injection system.

[0082] Unsteady rheological dynamic equations were established to analyze the hysteresis loop characteristics and extract the measured equivalent flow resistance. Considering the inertia and compressibility of the fluid within the pipe and orifice, the kinetic equation is described as follows:

[0083] ;

[0084] In the formula, The fluid inertial inductance coefficient mainly depends on the pipe length and cross-sectional area; This represents the measured volumetric stiffness of the system (the reciprocal of the capacitance coefficient). By performing multiple linear regression analysis or elliptic fitting algorithms on the hysteresis loop data, the unknown parameters in the above equations are solved, thereby obtaining the measured equivalent flow resistance that characterizes the actual permeability of the current formation. .

[0085] Downhole wave velocity inversion is performed using pressure wave signals generated by pulsating pumping. The acquired pressure signals... Perform autocorrelation or cross-correlation analysis with the pump source signal to identify the characteristic time delay of pressure wave reflection and propagation at the bottom of the well. Based on the known pipe length Calculate the actual propagation speed of the pressure wave within the fluid-filled pile borehole. The calculation formula is: The propagation speed is not a constant, but is affected by the fluid's own sound speed, the pipe wall constraint stiffness, and the effective flow channel cross-section.

[0086] Based on Korteweg's wave speed theory formula, the actual propagation speed is calculated. Back-calculation of the current effective hydraulic aperture The theory states that the wave velocity of fluid within a pipe decreases with increasing pipe wall elasticity. In karst pile foundation environments, changes in pore size directly alter the lateral constraint stiffness experienced by the fluid. The inversion calculation model is as follows:

[0087] ;

[0088] in, The speed of sound of the fluid itself. For fluid bulk modulus, The elastic modulus of the surrounding rock (which can be taken from the modulus value corresponding to the equivalent transient stiffness in step S200) This represents the equivalent pipe wall thickness. By transforming this formula, the measured wave velocity can be... Converted to effective hydraulic aperture This parameter reflects the diameter of the fluid cross section that actually participates in wave propagation under fluid pressure, and can sensitively detect lateral expansion or contraction caused by the rebound of plastic formations that mechanical drilling tools cannot reach.

[0089] See attached document Figure 5 In one embodiment of the present invention, the process of performing construction control based on the deviation between measured parameters and the benchmark model specifically includes the following:

[0090] Construct a deviation vector to quantify the differences between the drilling machinery model and the grouting hydraulic model. Calculate the measured equivalent flow resistance. With reference flow resistance relative flow resistance deviation between This index reflects the degree of deviation between the actual permeability of the formation and the permeability predicted based on mechanical fracturing characteristics. Simultaneously, the mechanical equivalent pore size is calculated. With effective hydraulic aperture relative aperture deviation This metric reflects the difference between the physical hole geometry and the fluid-constrained geometry. Deviation vector The definition is as follows:

[0091] ;

[0092] The control system is based on the deviation vector The quadrant distribution in a two-dimensional plane coordinate system identifies potential geological defect types and automatically executes corresponding closed-loop control strategies.

[0093] When relative flow resistance deviation is detected The value is negative and its absolute value exceeds a preset first threshold, while the relative aperture deviation is... When the depth is close to zero or within the preset normal tolerance range, the system determines that there is a laterally connected karst cave at the current depth. The physical characteristics of this condition are: normal specific energy dissipation during mechanical drilling indicates that the drill bit is cutting intact bedrock and has not directly encountered a cavity; however, the flow resistance during grouting is significantly lower than the theoretically predicted value, indicating that the fluid, under pressure, has breached the thin wall on the side of the borehole and entered a hidden karst cave or fracture network not reached by the drill bit. Based on this determination, the control system automatically generates a first control command, adjusting the grouting pump to switch to intermittent grouting mode, i.e., using a pulse cycle of grouting followed by a pause, and controlling the additive pump to increase the proportion of quick-setting agent or flocculant to improve the yield stress and thixotropy of the grout, promoting rapid sealing of the lateral flow channels.

[0094] When aperture deviation is detected The value is positive and exceeds the preset second threshold, meaning the mechanical equivalent aperture is significantly larger than the effective hydraulic aperture, and the flow resistance deviation is also positive. When the value is positive, the system determines that plastic reduction in diameter has occurred. This condition corresponds to high-stress soft rock or cohesive soil layers, where the drill bit undergoes elastic rebound or rheological creep after passing through the borehole wall, resulting in the actual fluid channel cross-section being smaller than the mechanical cutting cross-section. Based on this determination, the control system automatically generates a second control command to gradually increase the pumping static pressure of the grouting pump until the target pressure is reached. The target pressure is set slightly higher than the passive earth pressure or yield stress of the stratum. Hydrostatic pressure is used to reopen the rebounding and constricted borehole wall, ensuring that the pile diameter meets the design requirements.

[0095] When the flow resistance deviation is monitored When the value is positive and significantly exceeds the preset third threshold, and its value is much greater than the increase in flow resistance caused by the narrowing of the borehole, the system determines that borehole wall collapse or pipeline blockage has occurred. Under this condition, fluid flow is severely impeded by the physical barrier. Based on this determination, the control system automatically generates a third control command to suspend continuous pumping and initiate a high-frequency pressure pulse oscillation program. High-frequency water hammer waves are generated through the control valve group, using the wave energy to loosen the blockage or compact the collapsed material. If the flow resistance does not return to normal after oscillation, a shutdown alarm is issued to prompt manual intervention for borehole cleaning.

Claims

1. A method for intelligent positioning and precise construction of pile foundations in karst areas, characterized in that, Includes the following steps: S100. Establish a discretized dynamic model describing the frequency domain response characteristics of the drilling rig drill string system, and correct the boundary parameters of the dynamic model through no-load operation test; S200. Collect vibration and force signals at the top of the drill string, use the dynamic model to decouple and invert to obtain the true response at the bottom of the drill bit, calculate the transient mechanical impedance of the contact surface between the drill bit and the rock, and extract the mechanical damping coefficient; at the same time, calculate the mechanical specific energy dissipation value based on the drilling mechanical parameters, and reconstruct the mechanical equivalent aperture along the depth. S300. Establish the mapping relationship between mechanical parameters and hydraulic parameters, predict the permeability of the soil and rock mass based on the mechanical damping coefficient and mechanical specific energy dissipation value, and generate a reference pressure-flow characteristic curve that varies with depth by combining the mechanical equivalent pore size. S400: During the fluid injection process, a pulsating pressure wave is applied, and the pressure and flow data at the pipe inlet are collected to construct a pressure-flow hysteresis loop. The measured equivalent flow resistance is obtained by analysis, and the current effective hydraulic aperture is inferred by using the pressure wave propagation characteristics. S500: Calculate the flow resistance deviation between the measured equivalent flow resistance and the reference flow resistance corresponding to the reference pressure-flow characteristic curve, and the aperture deviation between the mechanical equivalent aperture and the effective hydraulic aperture. Based on the combination relationship between the positive and negative values ​​of the flow resistance deviation and the aperture deviation and the threshold range, identify the current geological defect type from laterally connected karst caves, plastic narrowing, and pore wall collapse or pipeline blockage, and generate corresponding adaptive control commands to adjust the operation mode of the grouting equipment according to the identification results.

2. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 1, characterized in that, The S100 step specifically includes: The drill string system is divided into several finite element nodes along the axial direction. The element transfer matrix describing the frequency domain transformation relationship between the top and bottom states of the drill string unit is established using the one-dimensional wave equation. The overall drill string state transfer matrix is ​​constructed by matrix cascading. During system initialization, the drilling rig is controlled to rotate under no-load, and the measured natural frequency is extracted by collecting the background noise spectrum. The equivalent stiffness coefficient and equivalent damping coefficient of the top boundary of the overall drill string state transfer matrix are iteratively corrected with the goal of minimizing the residual between the theoretical natural frequency and the measured natural frequency.

3. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 2, characterized in that, The S200 step specifically includes: The inverse matrix of the overall drill string state transfer matrix is ​​used to calculate the frequency domain signal at the top of the drill string to eliminate the drill pipe elastic effect and solve for the true displacement data and true force data at the bottom of the drill bit. The transient mechanical impedance spectrum is obtained by calculating the ratio of the vibration velocity corresponding to the actual force data and the actual displacement data in the frequency domain. The transient mechanical impedance spectrum was fitted using a rheological model of a linear spring and a linear damper in parallel, and the equivalent transient stiffness reflecting the rock's elastic modulus and the mechanical damping coefficient reflecting the degree of rock fracture were extracted.

4. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 1, characterized in that, In step S200, the step of reconstructing the mechanical equivalent aperture along the depth specifically includes: Based on the actual bottom torque, drill pipe speed, actual bottom drilling pressure, and mechanical drilling speed during the drilling process, calculate the mechanical specific energy dissipation value required for rock breaking per unit volume. The mechanical specific energy dissipation value is compared with the standard specific energy threshold of the bedrock; when the mechanical specific energy dissipation value is lower than the standard specific energy threshold, it is determined that there is a risk of enlargement, and the mechanical equivalent hole diameter greater than the nominal diameter of the drill bit is calculated based on the ratio of the difference between the two.

5. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 1, characterized in that, The S300 step specifically includes: A nonlinear mapping function is constructed, in which the estimated permeability of the soil and rock mass is positively correlated with the mechanical damping coefficient and negatively correlated with the mechanical specific energy dissipation value; Using a radial flow hydrodynamic model, the theoretically required baseline flow resistance is calculated based on the estimated permeability and the mechanical equivalent pore size. The reference volumetric stiffness of the grouting system is estimated using the equivalent transient stiffness of the rock; based on the reference flow resistance and reference volumetric stiffness, a reference pressure-flow characteristic curve describing the dynamic relationship between grouting pressure and grouting flow rate under ideal operating conditions is generated.

6. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 1, characterized in that, In step S400, the analytical method for obtaining the measured equivalent flow resistance specifically includes: Establish unsteady rheological dynamic equations that include fluid inertia terms, flow resistance terms, and system volumetric stiffness terms; Based on the pressure and flow hysteresis loop constructed from real-time collected pressure and flow data, the unsteady rheological dynamic equation is solved by regression analysis, and the measured equivalent flow resistance that can characterize the actual permeability characteristics of the current formation is extracted.

7. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 6, characterized in that, In step S400, the current effective hydraulic aperture is deduced by utilizing the pressure wave propagation characteristics. Specifically, this includes: Correlation analysis is performed on the collected pressure signals to identify the propagation time delay of pressure waves in downhole fluids and calculate the actual propagation speed. Based on the wave velocity theory model, the correlation between the actual propagation velocity and the fluid bulk modulus, the elastic modulus of the surrounding rock, and the cross-sectional dimensions of the flow channel is established; the correlation shows that the wave velocity decreases with the increase of the lateral constraint stiffness. The effective hydraulic aperture under fluid pressure is obtained by using the actual propagation speed to solve in reverse.

8. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 1, characterized in that, In step S500, identifying the current geological defect type from the laterally connected cavern includes: When the measured equivalent flow resistance is lower than the reference flow resistance and the flow resistance deviation exceeds the first threshold, and the mechanical specific energy dissipation value is within the normal bedrock range, it is determined that there is a hidden karst cave that is not touched by the drilling tool but is laterally connected to the borehole wall. The control system generates instructions to adjust the grouting equipment to switch to intermittent grouting mode and increase the proportion of quick-setting agent or flocculant added.

9. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 1, characterized in that, In step S500, identifying the current geological defect type from plastic necking includes: When the effective hydraulic aperture is detected to be smaller than the mechanical equivalent aperture and the aperture deviation exceeds the second threshold, and the measured equivalent flow resistance is higher than the reference flow resistance, it is determined that the diameter reduction is caused by formation elastic rebound or plastic extrusion. The control system generates instructions to control the injection equipment to increase the pumping static pressure to the target pressure value, and uses the fluid static pressure to expand the narrowed area.

10. The intelligent positioning and precise construction method for pile foundations in karst areas according to claim 1, characterized in that, In step S500, identifying the current geological defect type from borehole wall collapse or pipeline blockage includes: When the measured equivalent flow resistance is higher than the reference flow resistance and the flow resistance deviation exceeds the third threshold, and the deviation is greater than the deviation caused by the diameter reduction, it is determined that the hole wall collapse or the pipeline blockage has occurred. The control system generates a command to pause continuous pumping and start a high-frequency pressure pulse oscillation program to utilize the energy of water jet waves for unblocking.

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