Full-flow penetrometer with T-shaped spindle-shaped cross section and penetration resistance coefficient calculation method of full-flow penetrometer

Abstract

The invention relates to the technical field of ocean engineering equipment, and particularly discloses a full-flow penetrometer with a T-shaped spindle-shaped section and a penetration resistance coefficient calculation method. The full-flow penetrometer innovatively adopts a spindle-shaped probe and is composed of a probe rod, a tension and compression sensor and the spindle-shaped probe. Wherein the spindle-shaped touch probe is connected with the tension and compression sensor through threads, and the tension and compression sensor is connected with the spindle-shaped touch probe through threads. The spindle-shaped probe penetrates into a soil body through the hydraulic driving device, and the numerical value of the tension and compression sensor is measured in real time. And performing real-time inversion on undrained shear strength parameters of the soil layer based on an analytic solution of the penetration resistance coefficient of the spindle-shaped probe. Compared with a traditional T-shaped sounding structure, the fusiform design can effectively reduce the penetration resistance, the probe rod is prevented from being bent and damaged, and meanwhile the influence of the cavity effect on the measurement result is effectively avoided. The obtained parameter error of the undrained shear strength of the soil body is smaller, and the method has important application value in ocean in-situ survey.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore engineering equipment, and particularly to a spindle-shaped cross-section T-type full-flow penetrometer and a method for calculating its penetration resistance coefficient. Background Art

[0002] With the development of China's marine resource development strategy towards the deep sea, offshore engineering structures are undergoing a paradigm shift from shallow water near the shore (<50m) to ultra-deep water (>1500m). This process poses important challenges to the strength assessment of seabed foundations. During the penetration process of the full-flow penetrometer from shallow to deep, an open cavity mechanism, a closed cavity mechanism, and a full-flow mechanism will appear in sequence. However, only when the full-flow penetrometer enters the full-flow mechanism, the plastic analytical solution of the penetration resistance coefficient Nt = 10.5 is accurate. Both the open cavity and the closed cavity will cause the penetration resistance coefficient to be less than Nt = 10.5, resulting in an underestimated undrained shear strength of the soil mass. Therefore, in order to overcome the influence of the closed cavity mechanism generated by the traditional full-flow penetrometer on the calculation result of soil strength, a spindle-shaped cross-section full-flow penetrometer is proposed. The relevant research reports of the prior art are as follows:

[0003] Chinese invention patent "A spherical full-flow piezocone penetrometer and its consolidation coefficient evaluation method" (Patent No.: CN201610546164.3) innovatively introduces a spherical geometric configuration into the field of marine geotechnical exploration. The device adopts a modular integrated design of a spherical full-flow piezocone penetrometer and a probe rod. Its core feature is that by optimizing the hydrodynamic profile of the probe head, a complete circumferential backflow is generated in the soil around the probe head during the penetration process, effectively eliminating the local soil disturbance caused by the traditional conical probe head. It is particularly suitable for obtaining in-situ parameters of soils with different degrees of consolidation. Compared with the conventional static cone penetration test (CPT) technology, the test error of the soil shear strength can be reduced to within ±3 kPa.

[0004] Chinese invention patent "A device for measuring soil strength based on full-flow penetration test" (Patent No.: CN202010689523.7) proposes an improvement scheme for the technical bottleneck of traditional geotechnical exploration equipment. Although the device innovatively adopts a triaxial confining pressure loading system and can synchronously collect the anisotropic strength parameters of the soil, its system integration needs to be optimized. Experimental data shows that using the T-shaped penetration system results in an average tip resistance deviation of ±15 kPa, and the probe contact area ratio is only 0.65, which is significantly lower than the 0.95 required by the full-flow penetration test technology, resulting in a soil backflow rate of less than 82%.

[0005] The Chinese invention patent "A device for measuring the strength and strain softening parameters of saturated clay specimens based on full-flow penetrometer" (Patent No.: CN201811023958.7) proposes an innovative solution to the problem of characterizing the strain-softening behavior of cohesive soils. The technical features of this device are as follows: ① It first creates an annular-constrained cylindrical rigid box and real-time monitors the radial deformation of the soil through a three-dimensional displacement sensor array; ② It integrates a dual-mode loading system; ③ It develops a parameter inversion algorithm based on the improved Strain-Space plasticity theory.

[0006] The Chinese invention patent "A device and method for testing the early thixotropic strength of soft clay based on FBG and full-flow penetrometer" (Patent No.: CN201911049027.9) proposes a device for testing the early thixotropic strength of soft clay based on FBG and full-flow penetrometer, which is specifically composed of a base and fixing device, heightening struts, ball screw linear guide rails, a motor, a slider, etc. It has many advantages such as small volume, light weight, and corrosion resistance, and can more accurately measure the shear strength of undisturbed soil with as little disturbance as possible.

[0007] The Chinese invention patent "A device and method for testing the early thixotropic strength of soft clay based on FBG and full-flow penetrometer" (Patent No.: CN201911049027.9) innovatively integrates fiber Bragg grating sensing technology with a micro full-flow penetrometer system. This device consists of the following core modules: ① An aerospace-grade aluminum alloy base integrated with a three-point positioning fixture system; ② High-rigidity carbon fiber heightening struts; ③ Precision ball screw linear guide rails; ④ A brushless servo drive unit; ⑤ A silicon nitride ceramic slider assembly. Its breakthrough technical feature is that through the collaborative measurement of a distributed fiber Bragg grating array and a full-flow penetrometer probe, real-time inversion of the thixotropic strength is achieved.

[0008] It can be seen that most of the probes of existing full-flow penetrometers are cylindrical, and there are few beneficial attempts in the prior art to change the cross-sectional shape of the T-shaped penetrometer probe to reduce the penetration resistance and prevent the generation of the closed cavity mechanism. There is no report on achieving easy penetration and easy extraction by changing the cross-sectional shape of the T-shaped penetrometer probe. Therefore, it is particularly important to develop a spindle-shaped cross-section T-type full-flow penetrometer and its calculation method for penetration resistance coefficient.

[0009] The information disclosed in this background art section is only intended to increase the understanding of the overall background of the present invention and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art already known to those of ordinary skill in the art. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a spindle-shaped cross-section T-type full-flow penetrometer and a method for calculating its penetration resistance coefficient. The purpose is to reduce the insertion and extraction resistance by changing the shape of the penetrometer tip, and to provide a T-type penetrometer tip with a spindle-shaped cross-section that has less resistance and is convenient for insertion and extraction for accurate measurement of soil strength. Moreover, the traditional method for determining the penetration resistance coefficient of a full-flow penetrometer is not suitable for the present invention. Therefore, through the derivation of plastic mechanics theory, a method for calculating the penetration resistance coefficient of a spindle-shaped cross-section T-type full-flow penetrometer is obtained to accurately interpret the undrained shear strength of the soil.

[0011] To solve the above problems, the technical solution of the present invention is a spindle-shaped cross-section T-type full-flow penetrometer and a method for calculating its penetration resistance coefficient: A spindle-shaped cross-section T-type full-flow penetrometer, characterized in that it includes a drill rod, a tension-compression sensor, and a spindle-shaped probe;

[0012] The drill rod is a thin-walled cylindrical structure, and the signal line of the tension-compression sensor is passed through the inside of the cylinder; the outer diameter of the drill rod is the same as the diameter of the tension-compression sensor, and the inner diameter of the drill rod is larger than the outer diameter of the signal line of the tension-compression sensor; a vertical driving device is provided at the upper part of the drill rod, the drill rod is threadedly connected to the vertical driving device, and the bottom of the drill rod is threadedly connected to the tension-compression sensor;

[0013] The tension-compression sensor is a cylindrical structure, and connecting threaded columns are provided at both the upper and lower ends of the tension sensor. The upper part of the tension sensor is axially connected to the drill rod through the connecting threaded column, and the lower part of the tension sensor is threadedly connected to the spindle-shaped probe through the connecting threaded column;

[0014] The cross-section of the spindle-shaped probe is a spindle-shaped cross-section, and the upper and lower apex angles of the spindle-shaped cross-section are 90 degrees, and both sides of the upper and lower apex angles are tangent to two arc lines respectively.

[0015] Furthermore, the drill rod is made of a hollow cylindrical steel pipe, and multiple drill rods can be threadedly connected and spliced; the outer diameter of the drill rod is equal to the diameter of the spindle-shaped probe.

[0016] Furthermore, the diameter of the tension-compression sensor is 4 cm, and connecting threaded columns with a diameter of 2 cm are respectively provided at the upper and lower ends of the tension sensor.

[0017] Furthermore, the cross-sectional dimension diameter of the spindle-shaped probe tip is 4 cm, and the upper and lower apex angles are 90 degrees; the length of the spindle-shaped probe tip is 25 cm, and the vertical projection area of the entire spindle-shaped probe is 100 cm 2 .

[0018] Furthermore, it also includes a method for using a spindle-shaped cross-section T-type full-flow penetrometer, which includes the following steps:

[0019] Step 1. Assemble the spindle-shaped cross-section T-type full-flow penetrometer: According to the design requirements, connect the probe rod and the tension-compression sensor by threads; connect the tension-compression sensor and the spindle-shaped probe by threads; according to the seawater depth, connect multiple single-section probe rods by threads to ensure that the spindle-shaped probe can touch the seabed mud surface.

[0020] Step 2. Insert into the soil: Fix the upper part of the assembled spindle-shaped cross-section T-type full-flow penetrometer on the upper hydraulic telescopic device by threads; through the upper hydraulic telescopic device, press the spindle-shaped cross-section T-type full-flow penetrometer into the soil at a uniform speed; during the process of pressing into the soil, connect the probe rod to ensure that the pressing process continues without interruption, and finally reach the designed detection depth; record the values of the tension-compression sensor during the entire penetration process, and calculate the undrained shear strength of the soil through the penetration resistance coefficient.

[0021] Furthermore, the calculation method of the penetration resistance coefficient of a spindle-shaped cross-section T-type full-flow penetrometer includes the following steps:

[0022] Let the average stress on ox be p0. According to the properties of stress characteristics, the average stresses of the stress characteristic lines ce, ln, and bu can be obtained as follows:

[0023] p ce = p cd + 2(π / 2 - η)s u = p0 + (π - 2η)s u

[0024] p ln = p cd + 2(π / 2 - η + θ)s u = p0 + (π - 2η + 2θ)s u

[0025] p bu = p cd + 2(π / 2 - η + π / 4)s u = p0 + (3π / 2 - 2η)s u

[0026] The normal stresses of the stress characteristic lines ab and bc are respectively:

[0027] σ ab = p bu + s u sin2η = p0 + (3π / 2 - 2η + sin2η)s u

[0028] σ bc = p ln + s u sin2η = p0 + (π - 2η + 2θ + sin2η)su ,

[0029] The total penetration resistance of the spindle-shaped T-type full-flow penetration tester is composed of the normal stress component and the shear stress component in the vertical direction. The shear stress component on each interface ab and bc is:

[0030]

[0031] The normal force components on each section ab and bc are:

[0032]

[0033] Based on the force balance of the probe in the vertical direction, the penetration resistance coefficient Nt can be obtained:

[0034]

[0035] The advantages of the present invention compared with the existing technology are:

[0036] 1. The present invention offers the advantages of simple manufacturing, quick installation, buckling resistance, and quick and safe plugging and unplugging, significantly improving construction safety. Furthermore, based on plasticity theory, a method for calculating the penetration resistance coefficient compatible with the present invention's spindle-shaped T-type full-flow penetrometer has been developed, enabling accurate interpretation of data obtained from the present invention's spindle-shaped T-type full-flow penetrometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a front view of a new type of full-flow probe of the present invention

[0038] Figure 2 This is a three-dimensional schematic diagram of a new type of full-flow penetrometer of the present invention;

[0039] Figure 3 Figure 2 is a stress characteristic line field diagram of the spindle-shaped cross-section full-flow probe of the present invention. (a) is the geometric shape diagram of the characteristic line field grid, and (b) is the stress diagram of the T-bar edge.

[0040] Reference numerals: 1. probe rod; 2. tension and compression sensor; 3. spindle-shaped probe. DETAILED DESCRIPTION

[0041] The specific embodiments of the present invention are further described below with reference to the accompanying drawings, wherein the same parts are represented by the same reference numerals.

[0042] It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to directions in the accompanying drawings, and the words "inside" and "outside" refer to directions toward or away from the geometric center of a specific component, respectively.

[0043] In order to make the content of the present invention easier to be clearly understood, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention.

[0044] A spindle-shaped cross-section T-type full-flow penetrometer, comprising a sounding rod 1, a tension-compression sensor 2, and a spindle-shaped penetrometer head 3;

[0045] The sounding rod 1 is of a thin-walled cylindrical structure, and a signal wire of the tension-compression sensor 2 is passed through the inside of the cylinder; the outer diameter of the sounding rod 1 is the same as the diameter of the tension-compression sensor 2, and the inner diameter of the sounding rod 1 is larger than the outer diameter of the signal wire of the tension-compression sensor 2; a vertical driving device is provided at the upper part of the sounding rod 1, the sounding rod 1 is threadedly connected to the vertical driving device, and the bottom of the sounding rod 1 is threadedly connected to the tension-compression sensor 2; the sounding rod 1 is made of a hollow cylindrical steel pipe, and a plurality of the sounding rods 1 can be threadedly connected for splicing; the outer diameter of the sounding rod 1 is equal to the diameter of the spindle-shaped penetrometer head 3.

[0046] The tension-compression sensor 2 is of a cylindrical structure, and connecting threaded columns are provided at both the upper and lower ends of the tension-compression sensor. The upper part of the tension-compression sensor 2 is axially connected to the sounding rod 1 through the connecting threaded column, and the lower part of the tension-compression sensor 2 is threadedly connected to the spindle-shaped penetrometer head 3 through the connecting threaded column; the diameter of the tension-compression sensor 2 is 4 cm, and connecting threaded columns with a diameter of 2 cm are respectively provided at both the upper and lower ends of the tension-compression sensor 2.

[0047] The cross-section of the spindle-shaped penetrometer head 3 is of a spindle-shaped cross-section, the upper and lower apex angles of the spindle-shaped cross-section are 90 degrees, and both sides of the upper and lower apex angles are respectively tangent to two arc lines. The cross-section size diameter of the spindle-shaped penetrometer head 3 is 4 cm, and the upper and lower apex angles are 90 degrees; the length of the spindle-shaped penetrometer head 3 is 25 cm, and the vertical projection area of the entire spindle-shaped penetrometer head 3 is 100 cm 2 .

[0048] An installation method of a spindle-shaped cross-section T-type full-flow penetrometer, comprising the following steps:

[0049] Step 1: Assemble the spindle-shaped cross-section T-type full-flow penetrometer: According to the design requirements, threadedly connect the sounding rod 1 and the tension-compression sensor 2; threadedly connect the tension-compression sensor 2 and the spindle-shaped penetrometer head 3; according to the seawater depth, threadedly connect a plurality of single-section sounding rods 1 to ensure that the spindle-shaped penetrometer head can contact the seabed mud surface.

[0050] Step 2: Insert into the soil mass; fix the upper part of the assembled T-shaped full-flow penetrometer with a spindle-shaped cross-section onto the upper hydraulic telescopic device through threads; use the upper hydraulic telescopic device to press the T-shaped full-flow penetrometer with a spindle-shaped cross-section into the soil mass at a uniform speed; during the process of pressing into the soil mass, connect the sounding rod 1, and ensure that the pressing process continues without interruption until the final designed detection depth is reached; record the values of the tension and compression sensor 2 during the entire penetration process, and calculate the undrained shear strength of the soil mass through the penetration resistance coefficient.

[0051] A method for calculating the penetration resistance coefficient of a T-shaped full-flow penetrometer with a spindle-shaped cross-section includes the following steps:

[0052] Assume that the average stress on ox is p0. According to the properties of stress characteristics, the average stresses of the stress characteristic lines ce, ln, and bu can be obtained as follows:

[0053] p ce = p cd + 2(π / 2 - η)s u = p0 + (π - 2η)s u

[0054] p ln = p cd + 2(π / 2 - η + θ)s u = p0 + (π - 2η + 2θ)s u

[0055] p bu = p cd + 2(π / 2 - η + π / 4)s u = p0 + (3π / 2 - 2η)s u

[0056] The normal stresses of the stress characteristic lines ab and bc are as follows:

[0057] σ ab = p bu + s u sin2η = p0 + (3π / 2 - 2η + sin2η)s u

[0058] σ bc = p ln + s u sin2η = p0 + (π - 2η + 2θ + sin2η)s u ,

[0059] The total penetration resistance of the T-shaped full-flow penetrometer with a spindle-shaped cross-section consists of the normal stress component and the shear stress component in the vertical direction. The shear stress components on each interface ab and bc are:

[0060]

[0061] The normal stress components on each cross-section ab and bc are as follows:

[0062]

[0063] All terms containing s u are summed up, and all terms containing p0 cancel each other out. Based on the force balance of the probe in the vertical direction, the penetration resistance coefficient Nt can be obtained:

[0064]

[0065] The present invention and its embodiments have been described above. Such description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. In general, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural modes and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A spindle-shaped cross-section T-type full-flow penetrometer, characterized in that: It includes a sounding rod (1), a tension-compression sensor (2), and a spindle-shaped touch probe (3); The sounding rod (1) is of a thin-walled cylinder structure, and the signal line of the tension-compression sensor (2) is threaded through the inside of the cylinder; the outer diameter of the sounding rod (1) is the same as the diameter of the tension-compression sensor (2), and the inner diameter of the sounding rod (1) is larger than the outer diameter of the signal line of the tension-compression sensor (2); a vertical driving device is provided at the upper part of the sounding rod (1), the sounding rod (1) is threadedly connected to the vertical driving device, and the bottom of the sounding rod (1) is threadedly connected to the tension-compression sensor (2); The tension-compression sensor (2) is of a cylindrical structure, and connecting threaded columns are provided at both the upper and lower ends of the tension-compression sensor. The upper part of the tension-compression sensor (2) is axially connected to the sounding rod (1) through the connecting threaded column, and the lower part of the tension-compression sensor (2) is connected to the spindle-shaped touch probe (3) through the connecting threaded column; The cross-section of the spindle-shaped touch probe (3) is a spindle-shaped cross-section, and the upper and lower apex angles of the spindle-shaped cross-section are 90 degrees, and the two sides of the upper and lower apex angles are respectively tangent to two arc lines.

2. The spindle-shaped cross-section T-type full-flow penetrometer according to claim 1, characterized in that: The sounding rod (1) is made of a hollow cylindrical steel pipe, and multiple sounding rods (1) can be threadedly connected for splicing; the outer diameter of the sounding rod (1) is equal to the diameter of the spindle-shaped touch probe (3).

3. A spindle-shaped cross-section T-type full-flow penetrometer according to claim 1, characterized in that: The diameter of the tension-compression sensor (2) is 4 cm, and connecting threaded columns with a diameter of 2 cm are respectively provided at the upper and lower ends of the tension-compression sensor (2).

4. A spindle-shaped cross-section T-type full-flow penetrometer according to claim 1, characterized in that: The cross-sectional dimension of the spindle-shaped touch probe (3) is 4 cm in diameter, and the upper and lower apex angles are 90 degrees; the length of the spindle-shaped touch probe (3) is 25 cm, and the vertical projection area of the entire spindle-shaped touch probe (3) is 100 cm 2 .

5. A method for using a spindle-shaped cross-section T-type full-flow penetrometer according to any one of claims 1-4, characterized in that: It includes the following steps: Step 1: Assemble the spindle-shaped cross-section T-shaped full-flow penetrometer: According to the design requirements, threadedly connect the sounding rod (1) and the tension-compression sensor (2); threadedly connect the tension-compression sensor (2) and the spindle-shaped touch probe (3); according to the seawater depth, threadedly connect multiple single-section sounding rods (1) to ensure that the spindle-shaped touch probe can contact the seabed mud surface. Step 2: Insert into the soil; fix the upper part of the assembled spindle-shaped cross-section T-shaped full-flow penetrometer on the upper hydraulic telescopic device through threads; through the upper hydraulic telescopic device, evenly press the spindle-shaped cross-section T-shaped full-flow penetrometer into the soil; during the process of pressing into the soil, connect the sounding rod (1), and ensure that the pressing process continues without interruption until the designed detection depth is finally reached; record the values of the tension-compression sensor (2) during the entire penetration process, and calculate the undrained shear strength of the soil through the penetration resistance coefficient.

6. A method for calculating the penetration resistance coefficient of a spindle-shaped cross-section T-type full-flow penetrometer according to any one of claims 1-4, characterized in that: It includes the following steps: Let the average stress on ox be p0. According to the properties of stress characteristics, the average stresses of the stress characteristic lines ce, ln, and bu can be obtained as follows: p ce = p cd + 2(π / 2 - η)s u = p0 + (π - 2η)s u p ln = p cd + 2(π / 2 - η + θ)s u = p0 + (π - 2η + 2θ)s u p bu = p cd + 2(π / 2 - η + π / 4)s u = p0 + (3π / 2 - 2η)s u The normal stresses of the stress characteristic lines ab and bc are respectively: σ ab = p bu + s u sin 2η = p0 + (3π / 2 - 2η + sin 2η)s u σ bc = p ln + s u sin2η = p0 + (π - 2η + 2θ + sin2η)s u , The total penetration resistance of the spindle-shaped cross-section T-shaped full-flow penetrometer consists of the normal stress component and the shear stress component in the vertical direction. The shear stress components on each interface ab and bc are: The normal stress components on each section ab and bc are: Based on the force balance of the probe in the vertical direction, the penetration resistance coefficient Nt can be obtained:

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