Gravity type active full-flow penetrometer with booster as well as operation method and data acquisition method of gravity type active full-flow penetrometer

Abstract

The invention discloses a gravity type active full-flow penetrometer with a booster in the technical field of ocean engineering testing, which comprises a spherical penetrometer, a connecting rod and a tail end, the lower end of the connecting rod is connected with the spherical penetrometer through a force sensor, the upper end of the connecting rod is connected with the tail end, and the tail end is connected with a mounting rope; the booster assembly comprises a middle shaft sleeve arranged on the periphery of the connecting rod in a sleeving mode, a side wing plate is arranged on the periphery of the middle shaft sleeve, a movable wing plate is hinged to the bottom of the side wing plate, and the movable wing plate can change from the vertical state to the horizontal state. And the movable wing plate at the lower end applies pressure to the surface of the seabed within a certain range around a drop point to promote immediate active formation of a shallow soil body full-flow mechanism, so that the test range and precision of the penetrometer are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ocean engineering testing, and particularly relates to a self-falling active full-flow penetrometer. Background Art

[0002] The development and utilization of ocean energy resources such as wind energy and oil and gas require the construction of a large number of underwater infrastructures (underwater oil and gas pipelines, cables, optical cables, foundation structures, etc.). The geotechnical engineering design and operation safety assessment thereof both rely on the accurate assessment of the strength of underwater sediments (seabed soft soil). Currently, the methods for surveying the strength of seabed soil mainly include: vane shear test, static cone penetration test (cone penetrometer, full-flow penetrometer), and free-falling penetrometer test.

[0003] In the static cone penetration test, the penetrometer is pressed into the seabed at a constant speed with the help of a reaction frame. The cone penetrometer (CPT) calculates the relevant parameters of the seabed soil by collecting the tip and sidewall resistance and pore pressure data. The calculation process requires the correction of pore water pressure and overburden pressure, and also requires the correct value of the end bearing capacity coefficient. The data processing process of the full-flow penetrometer (T-bar and Ball-bar) does not require the correction of pore water pressure and overburden pressure, and its bearing capacity coefficient also has a more rigorous theoretical solution. Moreover, the larger projected area of the penetrometer head improves the test accuracy of soft soil strength. The Ball-bar has a spherical penetrometer head, while the T-bar has a cylindrical penetrometer head. For uneven soil conditions, the T-bar is prone to generate a large bending moment, which affects the test accuracy. Existing research on the Ball-bar indicates that when the rod-ball area ratio is less than 0.1, the influence of the connecting rod can be ignored.

[0004] The Free-Fall Penetrometer (FFP) is a new type of in-situ marine test instrument developed based on the static cone penetrometer. Relying on the kinetic energy obtained from free fall in water, the penetrometer penetrates into the soft seabed soil at a certain initial velocity and then gradually decelerates to 0 under the action of resistance. Compared with traditional static cone penetration tests, the FFP does not require a large-scale loading instrument to be assembled and can perform rapid operations over a large area. Currently, there are mainly two types: the free-fall cone penetrometer and the free-fall spherical penetrometer. Among them, the force on the free-fall cone penetrometer during penetration into the seabed is relatively complex, and the result processing process also requires a series of complex calibrations like CPT; the shaftless free-fall spherical penetrometer proposed in the literature "Estimation of soil strength in fine-grained soils by instrumented free-fall sphere tests. Geotechnique, 2016, 66(12): 959-968" has a relatively small self-weight, resulting in a relatively small final penetration depth and a limited test range. The sphere may deflect during free fall in water and may rotate during penetration into the soil, which will increase the error of the test results; the free-fall spherical penetrometer with a thruster proposed in the literature "Interpreting strength parameters in soft clays from a new free-fall penetrometer. Computers and Geotechnics, 2021, 135: 104157" increases the penetration depth of the penetrometer through the thruster and improves the stability of the penetration process through the tail fin, but the relatively large diameter of the thruster will increase the penetration resistance and thus reduce the penetration depth.

[0005] In summary, the static cone penetration test requires the assembly of a large underwater loading device, with high time and economic costs, and is limited in application in deep-sea surveys; while the free-fall penetrometer can perform rapid operations over a large area only relying on a moving ship, but the penetration depth is relatively small and the full-flow mechanism of the soil mass in the surface penetration stage cannot be formed immediately, resulting in a limited test range and inaccurate test results for the shallow seabed soil. Summary of the Invention

[0006] Aiming at the deficiencies in the existing technology, the present invention provides a self-falling active full-flow penetrometer with a booster, its operation method and data acquisition method. The booster is used to increase the penetration depth and prevent rotation during penetration, and the movable wing plate at the lower end applies pressure to the seabed surface within a certain range around the landing point to promote the immediate and active formation of the full-flow mechanism of the shallow soil mass, so as to improve the test range and accuracy of the penetrometer.

[0007] The object of the present invention is achieved as follows: A self-falling active full-flow penetrometer with a booster, comprising a booster assembly movably sleeved on the outer periphery of a main structure assembly;

[0008] The main structure assembly includes a spherical penetrometer, a connecting rod and a tail end. The lower end of the connecting rod is connected to the spherical penetrometer through a force sensor. The upper end of the connecting rod is connected to the tail end, and the tail end is connected to an installation rope;

[0009] The booster assembly includes a central axis sleeve sleeved on the outer periphery of the connecting rod. The outer periphery of the central axis sleeve is provided with side wing plates. The bottom of the side wing plates is hinged with movable wing plates. The movable wing plates can change from a vertical state to a horizontal state. When in the vertical state, a hemispherical cavity for wrapping the bottom of the spherical penetrometer is formed between the movable wing plates. When in the horizontal state, the hemispherical cavity is opened, and at the same time, the movable wing plates form an annular plate at the bottom of the side wing plates.

[0010] Further, a laser displacement sensor is installed on the side wing plates.

[0011] Further, a movable wing plate control unit is also provided on the central axis sleeve. The movable wing plate control unit controls the movable wing plates to switch from the vertical state to the horizontal state according to the signal of the laser displacement sensor.

[0012] An operation method of a self-falling active full-flow penetrometer with a booster includes the following steps:

[0013] Step 1: Install a self-falling active full-flow penetrometer with a booster, and ensure that the center of gravity of the spherical penetrometer coincides with the axis of the booster and the tail end;

[0014] Step 2: Turn on the acceleration sensor, pore pressure sensor and related data acquisition devices inside the spherical penetrometer. Move the booster assembly to the lowermost position of the connecting rod, and embed the spherical penetrometer into the hemispherical cavity formed by the movable wing plates of the booster assembly;

[0015] Step 3: Turn on the laser displacement sensor and the movable wing plate control unit. Hang the assembled penetrometer at a certain depth below the water surface through the installation rope, and let it stand for a period of time until it is stable;

[0016] Step 4: Release the installation rope. The spherical penetrometer freely falls from rest in water, accelerates, and then penetrates into the seabed with a certain initial velocity. During the falling process, the laser displacement sensor continuously detects the distance from the seabed surface. When the distance is less than the set value, the movable vane control unit controls the movable vane to change from the vertical state to the horizontal state. The spherical penetrometer penetrates into the seabed and moves a certain distance in the soil until it comes to rest. While the spherical penetrometer penetrates into the seabed, the movable vane in the horizontal state dynamically lands on the seabed surface and applies pressure around the landing point. After the penetration is completed, the spherical penetrometer stays in the soil for a period of time to collect pore pressure data in the surrounding soil.

[0017] Step 5: After the data collection is completed, use the installation rope to recover the spherical penetrometer, export the data collected by each sensor, and perform data analysis.

[0018] A data acquisition method for a self-falling active full-flow penetrometer with a booster, including:

[0019] Step 1): Obtain the acceleration time history data of the spherical penetrometer during its movement in the seabed through an acceleration sensor, and obtain the penetration velocity and depth of the penetrometer by integrating the time.

[0020] Step 2): Invert the undrained shear strength of the seabed soil through the test results of the force sensor and the acceleration sensor.

[0021] Further, in Step 1), the penetration velocity is calculated by formula (1), and the penetration depth is calculated by formula (2).

[0022] (1)

[0023] (2)

[0024] In the formula, a is the vertical acceleration of the penetrometer measured by the acceleration sensor, v is the vertical velocity of the penetrometer, and s is the vertical displacement of the penetrometer.

[0025] Further, the process of Step 2) is as follows:

[0026] The force during the dynamic penetration process of the spherical penetrometer in the seabed is calculated by formula (3):

[0027] (3)

[0028] In the formula, m is the mass of the spherical penetrometer; a is the measured value of the acceleration sensor; F inter is the measured value of the force sensor; F ss is the buoyant weight of the spherical penetrometer in the seabed, which is obtained by subtracting the product of the volume of the spherical penetrometer immersed in the soil and the buoyant unit weight of the soil from the buoyant weight of the spherical penetrometer in water; F Dis the soil drag resistance on the spherical penetrometer; F Su-op is the soil end bearing resistance on the spherical penetrometer; m A is the additional mass of the soil, which can be calculated according to formula (4):

[0029] (4)

[0030] In the formula, C m is the additional mass coefficient; m soil is the mass of the soil displaced by the spherical penetrometer, which can be calculated according to formula (5),

[0031] (5)

[0032] In the formula, V soil is the volume of the soil displaced by the spherical penetrometer; ρ soil is the saturated density of the seabed soil;

[0033] When considering the soil rate effect during the dynamic penetration of the spherical penetrometer into the seabed, the end bearing resistance F in formula (3) Su-op can be expressed as:

[0034] (6)

[0035] In the formula, N c is the end bearing capacity coefficient of the spherical penetrometer, which is related to the friction coefficient and the soil flow mechanism and is determined by numerical simulation; s u-ref is the undrained shear strength of the soil corresponding to the reference strain rate; A p is the projected area of the spherical penetrometer; R f is the soil rate effect coefficient, which is expressed by the exponential rate effect formula as:

[0036] (7)

[0037] In the formula, is the shear strain rate of the soil, which is expressed by the ratio v / D of the spherical penetrometer velocity and diameter, is the reference shear strain rate; β is the rate effect parameter, and its value range is 0.06~0.17;

[0038] The soil drag force F on the spherical penetrometer during the penetration process in the seabed D is:

[0039] (8)

[0040] In the formula, C D is the drag resistance coefficient;

[0041] Combining equations (3) to (8), the undrained strength of the seabed soil is inversed through the acceleration a and force F measured by the sensors. inter The calculation formula is as follows:

[0042] (9)

[0043] In the above formula, F inter and a are the measured values of the force sensor and the acceleration sensor respectively. v is obtained by integrating the measured value of the acceleration sensor with respect to time once; F ss is the floating weight of the spherical penetrometer in water minus the overlying pressure of the seabed soil on the spherical penetrometer, that is, the product of the volume of the spherical penetrometer and the floating unit weight of the sphere minus the product of the volume of the soil displaced by the spherical penetrometer and the floating unit weight of the soil.

[0044] Furthermore, the undrained shear strength of the seabed soil increases linearly with depth, and s u-ref is expressed as:

[0045] (10)

[0046] In the formula, s u0 is the undrained shear strength of the soil on the seabed surface, z is the distance from the seabed surface, and k is the strength gradient; combining equations (9) and (10), using the measured data of the acceleration sensor and the force sensor, the soil strength parameters s u0 and k are inversed.

[0047] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0048] The present invention designs a self-falling active full-flow penetrometer with a booster. Its testing process does not require the assistance of other seabed loading devices. It relies on the kinetic energy obtained by the free fall of the penetrometer in water to penetrate the seabed for measurement, and the process is simple and fast; the main testing instrument is the spherical penetrometer at the lower end, which is mainly affected by soil end-bearing resistance, drag resistance, added mass force and buoyancy during the dynamic penetration process. The undrained shear strength of the soil is inversed by using the data collected by the acceleration sensor and the force sensor. The additional booster can effectively increase the penetration depth of the penetrometer, thereby increasing the testing range; the wing plates installed on the side of the booster and the tail of the connecting rod can improve the directional stability of the penetrometer during the falling process and prevent the spherical penetrometer from rotating; the movable wing plate at the lower end of the booster can apply pressure to the seabed surface within a certain range around the landing point, promoting the immediate active formation of the full-flow mechanism of the shallow soil layer, and can improve the testing accuracy of the penetrometer.

[0049] The end bearing capacity coefficient and drag resistance coefficient of the self-falling active full-flow penetrometer are key parameters for back-calculating the undrained strength of seabed soil, which are determined by the active full-flow mechanism of the soil around the spherical probe. The specific values need to be calibrated through physical experiments and numerical simulation parameter analysis. Description of the Drawings

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0051] Figure 1 It is a schematic connection diagram of the spherical penetrometer, booster, connecting rod and tail end in the present invention.

[0052] Figure 2 It is a schematic diagram of the booster before the deployment of the movable wing plate in the present invention.

[0053] Figure 3 It is a schematic diagram of the booster after the deployment of the movable wing plate in the present invention.

[0054] Figure 4 It is a schematic diagram of the spherical penetrometer and the connecting rod in the present invention.

[0055] Figure 5 (a) is the front view of the tail end in the present invention, Figure 5 (b) is the top view of the tail end in the present invention.

[0056] Figure 6 (a) is the top view of the electromagnetic fixture in the closed state in the present invention, Figure 6 (b) is the top view of the electromagnetic fixture in the open state in the present invention, Figure 6 (c) is the front view of the electromagnetic fixture in the closed state in the present invention.

[0057] Figure 7 It is the force analysis diagram of the spherical penetrometer moving in the soil in the present invention

[0058] Among them, 1. Booster, 1a. Central axis, 1b. Side wing plate, 1c. Movable wing plate control system, 1d. Underwater laser displacement sensor, 1e. Movable wing plate, 1e-1. Cylinder, 1f. Electromagnetic fixture, 1f-1. Hinge shaft, 1f-2. Arc-shaped splint, 1f-3. Electromagnet, 1g. Ring structure, 2. Spherical penetrometer, 2a. Acceleration sensor, 2b. Pore pressure sensor, 2c. Force sensor, 3. Connecting rod, 3a. Thread, 4. Tail end, 4a. Tail shaft, 4b. Tail wing, 4c. Connection groove, 4d. Mooring ring, 5. Installation rope. Detailed Embodiments

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0060] As Figures 1-6 shown, a self-falling active full-flow penetrometer with a booster includes two parts:

[0061] The first part includes a spherical penetrometer 2, a connecting rod 3, and a tail end 4; a pore pressure sensor 2b is provided in the middle of the spherical penetrometer 2 for measuring the change in the pore pressure of the soil around the spherical penetrometer; the spherical penetrometer 2 and the connecting rod 3 are connected by a force sensor 2c for measuring the interaction force between the connecting rod 3 and the spherical penetrometer 2; the connecting rod 3 passes through the inner cavity of the central axis of the booster 1, and the upper end of the connecting rod 3 is connected to the tail end 4 by a thread 3a, and the specific size of the tail fin 4b is adjusted according to actual needs; when determining the cross-sectional area of the connecting rod 3, attention should be paid to avoiding affecting the measurement accuracy of the penetrometer; the tail mooring ring 4d is connected to the installation rope (as Figure 5 shown) for releasing and recovering the instrument in each test.

[0062] The second part is a booster 1 (as Figure 2 shown) for improving the test range and accuracy of the penetrometer. The booster 1 includes a cylindrical central axis 1a, which is streamlined as a whole to reduce the resistance during penetration, and the size of the central axis 1a can be adjusted according to actual engineering needs; four side wing plates 1b are provided on the side of the central axis 1a for improving the directional stability during the falling process of the penetrometer, and the specific size of the side wing plates 1b is adjusted according to actual needs; a movable wing plate 1e is installed at the lower end of each side wing plate 1b, and it is in a vertical posture during the free fall in water; an underwater laser displacement sensor 1d is installed on the side wing plate 1b for measuring the real-time distance between the spherical penetrometer 2 and the seabed surface. When the distance is less than a certain limit value, the movable wing plate control system 1c is triggered, and each movable wing plate 1e rotates 90° to the same side and unfolds instantly to form an annular structure 1g; while the spherical penetrometer 2 penetrates into the seabed, the annular structure 1g falls on the seabed surface with power and applies pressure around the landing point to promote the active formation of the full-flow mechanism of shallow soil.

[0063] The ratio of the cross-sectional area of the connecting rod 3 to the projected area of the spherical penetrometer 2 is less than 0.1, and the length of the connecting rod 3 is determined by the test depth requirement. The control, acquisition, and storage of relevant built-in devices are wireless; the layout of external devices is as Figure 1 shown.

[0064] As shown Figures 1-6 in the figure, the self-falling active full-flow penetrometer with a booster is mainly composed of a connecting rod 3 connecting the booster 1, the spherical penetrometer 2 and the tail end 4. The booster 1 is mainly composed of a central shaft 1a, side wing plates 1b and movable wing plates 1e. The shaft body part of the central shaft 1a is cylindrical and the tail gradually shrinks to reduce the resistance during the falling process. The side wing plates 1b are evenly arranged around the shaft body to improve the directional stability during the falling process. The internal cavity of the central shaft 1a of the booster is composed of a cylinder and a hemispherical space. Before the test starts, the booster 1 is moved to the lowermost end of the connecting rod 3 and the upper hemisphere of the spherical penetrometer 2 is embedded in the cavity. Then, the four movable wing plates 1e at the lower end of the booster are respectively adjusted to be completely vertical, and the movable wing plates are fixed by the electromagnetic clamps 1f at the ends of the movable wing plates 1e. A cylinder 1e-1 matching with the electromagnetic clamp 1f is provided at the end of the movable wing plate 1e, so as to realize embedding the spherical penetrometer in the internal space formed by the movable wing plate and the booster. The tail shaft 1a of the penetrometer tail end 4 is designed to be streamlined as a whole. The tail fins 4b are evenly arranged around the shaft body and are aligned with the side wing plates 1b of the booster in the vertical plane. A mooring ring 4d is provided at the top of the tail shaft 1a for connecting the installation rope 5. A connecting groove 4c is provided at the lower end of the central shaft of the tail end 4, and the internal structure is a thread for connecting with the thread 3a at the upper end of the connecting rod 3. During the connection process, it is necessary to ensure that the axes of the booster 1, the connecting rod 3, the tail end 4 and the center of gravity of the spherical penetrometer 2 coincide to enhance the overall stability of the penetrometer and avoid large inclination angles during the free-falling process. The connecting rod 3 is connected with the spherical penetrometer 2 through a force sensor 2c, and the force sensor 2c is used to measure the resistance of the spherical penetrometer 2 during the penetration process. A pore pressure sensor 2b is provided in the middle of the spherical penetrometer 2 for measuring the pore water pressure of the surrounding soil mass. An acceleration sensor 2a, a battery and a storage card are provided inside the spherical penetrometer 2 for collecting relevant data during the movement process.

[0065] As shown Figure 2 in the figure, the movable wing plate 1e is installed at the bottom of the side wing plate 1b through a pair of hinges. At the same time, the movable wing plate 1e and the side wing plate 1b on the same side are connected by a tension spring. It should be noted that when the movable wing plate 1e is unlocked by the electromagnetic clamp 1f, it is folded under the action of the tension spring, and the movable wing plate 1e abuts against the bottom of the adjacent side wing plate 1b. When the four movable wing plates 1e are folded together and abut against the bottom of the side wing plate 1b, the four movable wing plates 1e form a complete ring structure.

[0066] As shown Figure 6As shown in the figure, the electromagnetic fixture 1f includes a pair of arc-shaped clamping plates 1f-2 hinged by a hinge shaft 1f-1. One end of the two arc-shaped clamping plates 1f-2 is hinged by the hinge shaft 1f-1, and the other end is fixedly connected through an electromagnet 1f-3. The electromagnet 1f-3 is controlled by a movable wing plate control system 1d. The through hole of the movable wing plate control system 1d controls the power-on and power-off of the electromagnet 1f-3 to realize the clamping and loosening of the electromagnetic fixture 1f. A cavity for accommodating the cylinder 1e-1 is formed between the two arc-shaped clamping plates 1f-2. The cavity is used to clamp the four cylinders 1e-1 to fix the four movable wing plates 1e.

[0067] The sizes of the connecting rod 3, the booster 1, and the tail end 4 can be determined according to the requirements of engineering measurement. If the soil to be measured is relatively deep, a booster with a larger mass and a connecting rod with a larger length need to be equipped; if the test is carried out in an area with a larger water depth, the stability of the penetration process needs to be improved by increasing the size of the tail fin 4b. An underwater laser displacement sensor 1d is installed on the side wing to measure the real-time distance between the lower end of the spherical penetrometer and the seabed surface. When the distance is less than a certain limit value, the movable wing plate control system 1c is triggered, and the movable wing plate rotates 90° to the same side to expand and instantly form an annular structure 1g; after the measurement is completed, the whole set of penetrometers is recovered by using the installation rope 5 arranged on the tail end mooring ring 4d.

[0068] An operation method of a self-falling active full-flow penetrometer with a booster includes the following steps:

[0069] Step 1: Install the booster 1, the spherical penetrometer 2, the connecting rod 3, and the tail end 4. Pass the connecting rod 3 through the central axis cavity of the booster 1. One end of the connecting rod 3 is connected to the top end of the spherical penetrometer 2 through a force sensor 2c, and the other end is connected to the tail end 4 through a thread 3a. Ensure that the center of gravity of the spherical penetrometer 2 coincides with the axes of the booster 1 and the tail end 4 to improve the directional stability of the penetrometer during the free fall in water and the dynamic penetration in the seabed soil.

[0070] Step 2: Turn on the acceleration sensor, the pore pressure sensor, and the related data acquisition device. Move the booster 1 to the lowest position of the connecting rod 3. Embed the spherical penetrometer 2 into the hemispherical cavity in the booster 1. Adjust the four movable wing plates 1e to the vertical direction and fix the movable wing plates 1e through the electromagnetic fixture 1f.

[0071] Step 3: Turn on the laser displacement sensor and its acquisition device and the movable wing plate control system 1c. Hang the assembled penetrometer at a certain depth below the water surface through the installation rope 5 and let it stand for a period of time to stabilize.

[0072] Step 4: Release the installation rope 5. The penetrometer freely falls from rest in water, accelerates, and then penetrates into the seabed with a certain initial velocity. After moving a certain distance in the soil, it comes to rest. After the penetration is completed, keep the penetrometer in the soil for a period of time to collect pore pressure data in the surrounding soil.

[0073] Step 5: After the data collection is completed, use the installation rope 5 to recover the penetrometer, export the data collected by each sensor, and perform data analysis.

[0074] A data acquisition method for a self-falling active full-flow penetrometer with a booster, comprising:

[0075] First, collect and record the acceleration data of the penetrometer through the acceleration sensor 2a, and calculate the moving speed and displacement data of the penetrometer according to formula (1) and formula (2) respectively:

[0076] (1)

[0077] (2)

[0078] In the formula, a is the vertical acceleration of the penetrometer measured by the acceleration sensor 2a, v is the vertical speed of the penetrometer, and s is the vertical displacement of the penetrometer.

[0079] The undrained shear strength of the seabed soil can be inversely obtained through the test results of the force sensor 2c and the acceleration sensor 2a. The process is as follows:

[0080] The force analysis of the spherical penetrometer 2 during the dynamic penetration in the seabed is as Figure 7 shown, and its force can be expressed by formula (3):

[0081] (3)

[0082] In the formula, m is the mass of the spherical penetrometer 2; a is the measured acceleration value of the penetrometer; F inter is the measured value of the force sensor 2c; F ss is the buoyant weight of the spherical penetrometer 2 in the seabed, which is obtained by subtracting the product of the volume of the spherical penetrometer 2 immersed in the soil and the buoyant unit weight of the soil from the buoyant weight of the spherical penetrometer 2 in water; F D is the soil drag resistance received by the spherical penetrometer 2; F Su-op is the soil end bearing resistance received by the spherical penetrometer 2; m A is the additional mass of the soil, which can be calculated according to formula (4):

[0083] (4)

[0084] In the formula, C m is the additional mass coefficient, taken as 0.5; msoil The mass of the soil displaced by the spherical penetrometer 2 can be calculated according to Equation (5).

[0085] (5)

[0086] In the formula, V soil is the volume of the soil displaced by the spherical penetrometer 2; ρ soil is the saturated density of the seabed soil;

[0087] When considering the soil rate effect during the dynamic penetration of the spherical penetrometer 2 into the seabed, the end bearing resistance F in Equation (3) Su-op can be expressed as:

[0088] (6)

[0089] In the formula, N c is the end bearing capacity coefficient of the spherical penetrometer 2, which is related to the friction coefficient and the soil flow mechanism and is determined by numerical simulation; s u-ref is the undrained shear strength of the soil corresponding to the reference strain rate; A p is the projected area of the spherical penetrometer 2; R f is the soil rate effect coefficient, which is expressed by the exponential rate effect formula as:

[0090] (7)

[0091] In the formula, is the shear strain rate of the soil, which is expressed by the ratio v / D of the velocity and diameter of the spherical penetrometer 2, is the reference shear strain rate; β is the rate effect parameter, and its value range is 0.06~0.17;

[0092] The soil drag force F on the spherical penetrometer 2 during the penetration process in the seabed D is:

[0093] (8)

[0094] In the formula, C D is the drag resistance coefficient. Morton et al. pointed out based on in-situ test and centrifuge model test results that the reasonable value of the drag resistance coefficient for the free-falling spherical penetrometer during the penetration process in soft soil is 0.26.

[0095] Combining Equations (3)~(8), the undrained strength of the seabed soil can be inverted through the acceleration a and pressure F inter data measured by the sensor, and the calculation formula is:

[0096] (9)

[0097] F in the above formula inter and a are the measured values of the force sensor 2c and the acceleration sensor 2a respectively, and v can be obtained by integrating the acceleration measurement value with respect to time once; F ss is the buoyant weight of the spherical penetrometer 2 in water minus the overburden pressure of the seabed soil on the spherical penetrometer 2, that is, the product of the volume of the spherical penetrometer 2 and the floating unit weight of the sphere minus the product of the volume of the soil displaced by the spherical penetrometer 2 and the floating unit weight of the soil.

[0098] Usually, the undrained shear strength of the seabed soil increases linearly with depth. Therefore, s u-ref is expressed as:

[0099] (10)

[0100] In the formula, s u0 is the undrained shear strength of the soil on the seabed surface, z is the distance from the seabed surface, and k is the strength gradient; combining formulas (9) and (10), using the measured acceleration sensor data and force sensor data, the soil strength parameters s u0 and k are inversely calculated.

[0101] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A self-falling active full-flow penetrometer with a booster, characterized in that: It includes a booster assembly movably mounted on the outer periphery of the main structure assembly; The main structure assembly includes a spherical penetrometer, a connecting rod and a tail end, wherein the lower end of the connecting rod is connected to the spherical penetrometer via a force sensor, the upper end of the connecting rod is connected to the tail end, and the tail end is connected to a mounting rope; The booster assembly includes a central axis sleeve sleeved on the periphery of the connecting rod, the periphery of the central axis sleeve is provided with side wing plates, the bottom of the side wing plates are hinged with movable wing plates, and the movable wing plates can realize the change from a vertical state to a horizontal state. In the vertical state, a hemispherical cavity is formed between the movable wing plates to wrap the bottom of the spherical penetrometer. In the horizontal state, the hemispherical cavity is opened, and the movable wing plates form an annular plate placed at the bottom of the side wing plates.

2. A self-falling active full-flow penetrometer with a booster according to claim 1, characterized in that: A laser displacement sensor is installed on the side wing plate.

3. A self-falling active full-flow penetrometer with a booster according to claim 2, characterized in that: The central shaft sleeve is also provided with an active wing control unit, and the active wing control unit controls the active wing to switch from a vertical state to a horizontal state according to a signal from a laser displacement sensor.

4. A method for operating a self-falling active full-flow penetrometer with a booster, characterized in that: The following steps are involved: Step 1: Install the self-falling active full-flow penetrometer with a booster, and ensure that the center of gravity of the spherical penetrometer coincides with the axis of the booster and the tail end; Step 2, turning on the acceleration sensor, pore pressure sensor and related data acquisition device in the spherical penetrometer, moving the booster assembly to the lowest position of the connecting rod, and embedding the spherical penetrometer into the hemispherical cavity formed by the movable wing plate of the booster assembly; Step 3: Turn on the laser displacement sensor and the movable wing control unit, and suspend the assembled penetrometer at a certain depth below the water surface by means of the installation rope, and let it stand for a while until it stabilizes; Step 4, release the installation rope, the spherical penetrometer falls freely from a stationary state in the water, and after acceleration, it penetrates into the seabed with a certain initial speed. During the falling process, the laser displacement sensor detects the distance to the seabed surface in real time. When it is less than the set value, the movable wing control unit controls the movable wing to change from a vertical state to a horizontal state. The spherical penetrometer penetrates the seabed and moves a certain distance in the soil before reaching a stationary state. While the spherical penetrometer penetrates the seabed, the movable wing in the horizontal state falls dynamically on the seabed surface and applies pressure around the landing point. After the penetration is completed, the spherical penetrometer stays in the soil for a period of time to collect pore pressure data in the surrounding soil. Step 5: After data collection is completed, use the installation rope to recover the spherical penetrometer, and export the data collected by each sensor and perform data analysis.

5. A data acquisition method for a self-falling active full-flow penetrometer with a booster, characterized in that: include: Step 1) obtaining the acceleration time history data of the spherical penetrometer moving in the seabed through an acceleration sensor, and obtaining the penetration speed and depth of the penetrometer by integrating the time; Step 2) The undrained shear strength of the seabed soil is obtained by inverting the test results of the force sensor and the acceleration sensor.

6. The data acquisition method of the self-falling active full-flow penetrometer with a booster according to claim 5 is characterized in that: In step 1), the penetration velocity is calculated by formula (1), and the penetration depth is calculated by formula (2). （1） （2） Where a is the vertical acceleration of the penetrometer measured by the acceleration sensor, v is the vertical velocity of the penetrometer, and s is the vertical displacement of the penetrometer.

7. The data acquisition method of the self-falling active full-flow penetrometer with a booster according to claim 6 is characterized in that: Step 2) The process is as follows: The force of the spherical penetrometer during dynamic penetration in the seabed is expressed by formula (3): （3） Where m is the mass of the spherical penetrometer; a is the measured value of the acceleration sensor; F inter F is the measured value of the force sensor; ss is the buoyant weight of the spherical penetrometer in the seabed, which is obtained by subtracting the product of the volume of the spherical penetrometer submerged in the soil and the buoyant weight of the soil from the buoyant weight of the spherical penetrometer in water; F D is the soil drag resistance of the spherical penetrometer; F Su-op is the soil end resistance of the spherical penetrometer; m A is the additional mass of the soil, which can be calculated according to formula (4): （4） In the formula, C m is the additional mass coefficient; m soil is the mass of soil displaced by the spherical penetrometer, which can be calculated according to formula (5): （5） Where V soil is the volume of soil displaced by the spherical penetrometer; ρ soil is the saturated density of seabed soil; When considering the soil velocity effect during the dynamic penetration of the spherical penetrometer into the seabed, the end bearing resistance F in formula (3) Su-op It can be expressed as: （6） Where N c is the end bearing capacity coefficient of the spherical penetrometer, which is related to the friction coefficient and soil flow mechanism and is determined by numerical simulation; s u-ref is the undrained shear strength of soil corresponding to the reference strain rate; A p is the projection area of ​​the spherical penetrometer; R f is the soil rate effect coefficient, which can be expressed using the exponential rate effect formula: （7） In the formula, is the shear strain rate of the soil, expressed by the ratio of the velocity and diameter of the spherical penetrometer v / D, is the reference shear strain rate; β is the rate effect parameter, and its value range is 0.06~0.17; The soil drag force F exerted on the spherical penetrometer during its penetration into the seabed D for: （8） In the formula, C D is the drag coefficient; Combining equations (3) to (8), the acceleration a and force F measured by the sensor inter The undrained strength of the seabed soil is inverted using the data, and the calculation formula is: （9） In the above formula, F inter and a are the measured values ​​of the force sensor and the acceleration sensor respectively, and v is obtained by integrating the measured value of the acceleration sensor over time; F ss It is the buoyant weight of the spherical penetrometer in water minus the overlying pressure of the seabed soil on the spherical penetrometer, that is, the product of the volume of the spherical penetrometer and the buoyant weight of the sphere minus the product of the volume of the soil displaced by the spherical penetrometer and the buoyant weight of the soil.

8. The data acquisition method of the self-falling active full-flow penetrometer with a booster according to claim 7 is characterized in that: The undrained shear strength of the seabed soil increases linearly with depth, s u-ref It is expressed as: （10） In the formula, s u0 is the undrained shear strength of the soil on the seabed surface, z is the distance from the seabed surface, and k is the strength gradient; Combining formulas (9) and (10), using the measured acceleration sensor data and force sensor data, the soil strength parameter s is inverted u0 and k.

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