Double-layer soil sample preparation method and system for offshore self-elevating platform puncture experiment

Abstract

The invention belongs to the technical field of offshore oil drilling engineering, and particularly relates to a double-layer soil sample preparation method and system for an offshore self-elevating platform puncture experiment. The preparation method of the double-layer soil sample for the offshore self-elevating platform puncture experiment comprises the following steps: (1) mixing kaolin, montmorillonite and water in proportion to obtain a first mixture; (2) spreading the first mixture in a drainable container, and pressing to obtain a soft-layer soil sample; (3) mixing quartz sand, quick lime and water in proportion to obtain a second mixture; and (4) spreading the second mixture on the surface of the soft-layer soil sample, and pressing to obtain the double-layer soil sample. The double-layer soil sample prepared by the method disclosed by the invention does not need to rotate at a high speed during an experiment, and is more suitable for coupling analysis experiments of soil mechanics and acoustics.

Description

Technical Field

[0001] The invention belongs to the technical field of offshore oil drilling engineering, and in particular relates to a double-layer soil sample preparation method and system for an offshore jack-up platform puncture experiment. Background Art

[0002] A jack-up platform is a mobile offshore platform. It is the most widely used engineering equipment for offshore oil field exploitation. It is the main equipment in offshore oil and gas exploration and development due to its strong positioning ability, flexible operation, good mobility and low price. According to statistics, jack-up platforms account for more than 60% of the total number of mobile drilling devices in the world, making great contributions to oil exploration and development. With the development of offshore oil development technology, the operating depth of jack-up platforms has gradually increased, and the operating scope has been continuously expanded, which has led to the need to face more complex seabed geological conditions. Punch-through, commonly known as stepping on eggshells, is a phenomenon in which the pile shoe sinks rapidly and uncontrollably when the jack-up platform encounters a hard upper and soft lower seabed stratum during the ballasting process. Punch-through accidents are one of the major risks of jack-up platform operations, which may cause damage to the platform structure and casualties, resulting in significant economic losses.

[0003] Using a reduced-scale pile shoe model to conduct puncture simulation experiments is one of the important means to study the puncture phenomenon. The most commonly used experimental method is to use a geotechnical centrifuge to generate centrifugal gravity, so that the soil is accelerated to consolidate and generate ground stress under the action of centrifugal force to simulate the actual situation of marine engineering structures.

[0004] Since geotechnical centrifuge equipment is relatively expensive and has strict weight requirements, it can usually only be used for small-scale experiments, and has high requirements for experimental sites, experimental equipment, personnel operating skills and safety. At the same time, geotechnical centrifuges produce a lot of noise when rotating, which is not conducive to the coupled analysis of soil mechanics and acoustics. Summary of the invention

[0005] The purpose of the present invention is to address the defects of the prior art and provide a double-layer soil sample preparation method and system for offshore jack-up platform penetration experiments, thereby solving the problem of poor matching between experimental soil samples and actual stratum properties.

[0006] The present invention is achieved through the following technical solutions:

[0007] A double-layer soil sample preparation method for an offshore jack-up platform puncture test comprises:

[0008] (1) mixing kaolin, montmorillonite and water according to a proportion to obtain a first mixture;

[0009] (2) spreading the first mixture in a drainable container and pressing it to obtain a soft layer soil sample;

[0010] (3) mixing quartz sand, quicklime and water according to a proportion to obtain a second mixture;

[0011] (4) Spread the second mixture on the surface of the soft soil layer and press it to obtain a double-layer soil sample.

[0012] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform puncture test, the mass ratio of the kaolin, the montmorillonite and water is (15-95): (5-85): (100-114).

[0013] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform puncture test, the mass ratio of the kaolin, the montmorillonite and water is (80-95): (5-20): (100-105).

[0014] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform penetration test, in step (2), the pressing pressure is 50 kPa to 600 kPa, and the pressing time is 2 to 12 hours.

[0015] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform puncture test, in step (2), the pressing pressure is 300 to 500 kPa, and the pressing time is 4 to 8 hours.

[0016] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform puncture test, the shear strength of the soft layer soil sample should be 2kPa to 10kPa lower than the preparation target strength.

[0017] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform puncture test, when the quartz sand particle size is 2.0-4.75 mm, the mass ratio of the quartz sand to the quicklime to the water is (92-98): (2-8): (0.7-2.6); when the quartz sand particle size is 0.425-2.0 mm, the mass ratio of the quartz sand to the quicklime to the water is (92-98): (2-8): (1-3); when the quartz particle size is 0.075-0.425 mm, the mass ratio of the quartz sand to the quicklime to the water is (91-97): (3-9): (1-3).

[0018] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform puncture test, when the quartz sand particle size is 2.0-4.75 mm, the mass ratio of the quartz sand to the quicklime and the water is (92-95): (5-8): (1.6-2.6); when the quartz sand particle size is 0.425-2.0 mm, the mass ratio of the quartz sand, the quicklime and the water is (92-95): (5-8): (2-3); when the quartz sand particle size is 0.075-0.425 mm, the mass ratio of the quartz sand, the quicklime and the water is (91-94): (6-9): (2-3).

[0019] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform penetration test, in step (4), the pressing pressure is 400kPa to 600kPa, and the pressing time is 12h to 48h.

[0020] In the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform puncture test, in step (4), the pressing pressure is 500 kPa and the pressing time is 48 hours.

[0021] On the other hand, the present invention also provides a double-layer soil sample preparation system for an offshore jack-up platform penetration test, the system is used to execute the above-mentioned double-layer soil sample preparation method for an offshore jack-up platform penetration test to prepare a double-layer soil sample, the system comprising:

[0022] Box, jack stand, hydraulic jack, constant pressure hydraulic pump and pressure plate;

[0023] The upper end surface of the box body is open, and at least one drainage hole is provided at the bottom of the box body; the jack bracket is connected to the box body to cover the open end surface of the box body; a through hole is provided on the jack bracket, the hydraulic jack is installed on the jack bracket through a flange and bolts, and the piston rod of the hydraulic jack extends out of the through hole and is connected to the pressure plate; the constant pressure hydraulic pump is connected to the hydraulic jack through a pipeline;

[0024] The constant pressure hydraulic pump injects hydraulic fluid into the hydraulic jack to drive the piston rod of the hydraulic jack to extend outward and drive the pressure plate to move downward to press and prepare soft layer soil samples and double layer soil samples.

[0025] The above-mentioned double-layer soil sample preparation system for the offshore jack-up platform puncture test further includes: permeable stones, which are laid flat on the bottom of the box body.

[0026] The above-mentioned double-layer soil sample preparation system for the offshore jack-up platform puncture test also includes: two geotextiles, one of which is fixed to the bottom of the pressure plate, and the other geotextile is laid on the permeable stone.

[0027] The technical solution of the present invention has the following beneficial effects:

[0028] (1) The method for preparing a double-layer soil sample for the offshore jack-up platform penetration test of the present invention has the following characteristics: compared with a geotechnical centrifuge, the double-layer soil sample required for the preparation is simple in configuration, the material is easy to obtain, the operation is convenient, the cost is low, and the obtained soil sample has the characteristics of stable properties and high repeatability;

[0029] (2) The double-layer soil sample preparation method for the offshore jack-up platform puncture test of the present invention can prepare multiple soil samples at the same time by increasing the number of boxes, and the overall efficiency is high;

[0030] (3) The double-layer soil sample prepared according to the method of the present invention does not need to be rotated at high speed during the experiment and is more suitable for coupled analysis experiments of soil mechanics and acoustics. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the following detailed description of the preferred embodiment.The drawings are only for the purpose of illustrating the preferred embodiments and are not to be construed as limiting the invention.

[0032] Figure 1 Structural diagram of the double-layer soil sample preparation system for the offshore jack-up platform penetration test;

[0033] Figure 2 A partial enlarged view of the double-layer soil sample preparation system for the offshore jack-up platform penetration test;

[0034] Figure 3 This is a double-layer soil sample puncture test effect diagram of Example 1;

[0035] Figure 4 This is a double-layer soil sample puncture test effect diagram of Example 2;

[0036] Explanation of symbols: 1-box; 2-jack bracket; 3-hydraulic jack; 4-constant pressure hydraulic pump; 5-pressure plate; 6-permeable stone; 7-geotextile; 8-soil sample; 11-drainage hole; 31-piston rod. DETAILED DESCRIPTION

[0037] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0038] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0039] Specifically, the present invention provides a method for preparing a double-layer soil sample for an offshore jack-up platform puncture test, comprising:

[0040] (1) mixing kaolin, montmorillonite and water according to a proportion to obtain a first mixture;

[0041] (2) spreading the first mixture in a drainable container and pressing it to obtain a soft layer soil sample;

[0042] (3) mixing quartz sand, quicklime and water according to a proportion to obtain a second mixture;

[0043] (4) Spread the second mixture on the surface of the soft soil layer and press it to obtain a double-layer soil sample.

[0044] The raw materials and equipment required for the double-layer soil sample preparation method for puncture experiments provided by the present invention are simple and easy to use, and the production cost is low. The strength of the obtained double-layer stratum soil sample can cover the common seabed stratum strength combination, and can be suitable for model experiments of marine structures under normal gravity conditions, and is particularly suitable for puncture experiments of offshore jack-up platforms.

[0045] In some preferred embodiments, the double-layer soil sample preparation method for the offshore jack-up platform puncture test of the present invention comprises:

[0046] (1) Preparation of the first mixture

[0047] The first mixture of the present invention includes kaolin, montmorillonite and water.

[0048] Preferably, the mass ratio of the kaolin, the montmorillonite and water is (15-95):(5-85):(100-114).

[0049] According to the configuration ratio of the present invention, the obtained soil shear strength is between 5kPa and 40kPa, which can cover the common soft soil strength within the range of the self-elevating platform pile insertion.

[0050] More preferably, the mass ratio of the kaolin, the montmorillonite and water is (80-95):(5-20):(100-105).

[0051] The present invention has no special requirements on kaolin and montmorillonite, and they can be obtained from the market.

[0052] (2) Pressing to obtain soft layer soil sample

[0053] Among them, the use of Figure 1 The apparatus shown compresses the first mixture.

[0054] Preferably, the pressing pressure is 50 kPa to 600 kPa, and the pressing time is 2 h to 12 h, whereby the degree of consolidation of the obtained saturated soft layer soil sample is similar to that of actual sea soil.

[0055] More preferably, the pressing pressure is 300 kPa to 500 kPa, and the pressing time is 4 to 8 hours.

[0056] More preferably, the pressing is performed in the following five ways.

[0057]

[0058] Preferably, the shear strength of the soft soil sample should be 2 kPa to 10 kPa lower than the target strength. When the difference between the shear strength of the soft soil sample and the target strength exceeds the above range, after the pressing in step (4), there will be a large error between the shear strength and the target strength.

[0059] Preferably, in order to keep the properties of the soil layer unchanged, the soil layer can be re-pressed every thirty minutes after the first pressing, wherein the pressure of the re-pressing is the same as the pressing pressure, and each re-pressing time is 5-10 minutes.

[0060] Preferably, the thickness of a single pressing does not exceed 100 mm, as thickness exceeding this value may result in uneven strength of the soft soil layer along the thickness direction.

[0061] (3) Preparation of the second mixture

[0062] The second mixture of the present invention includes quartz sand, quicklime and water.

[0063] The thickness ratio of the soft soil layer to the hard soil layer needs to be determined according to experimental requirements, and the present invention does not make any specific limitation here.

[0064] The ratio of quartz sand to quicklime varies according to the particle size of the quartz sand, thereby achieving the predetermined target strength through different ratios.

[0065] Among them, coarse sand is quartz sand with a particle size of 2.0 to 4.75 mm; medium sand is quartz sand with a particle size of 0.425 to 2.0 mm; fine sand is quartz sand with a particle size of 0.075 to 0.425 mm.

[0066] Preferably, when the quartz sand is coarse sand, the mass ratio of the quartz sand to the quicklime is (92-98):(2-8):(0.7-2.6); when the quartz sand is medium sand, the mass ratio of the quartz sand, the quicklime and the water is (92-98):(2-8):(1-3); when the quartz sand is fine sand, the mass ratio of the quartz sand, the quicklime and the water is (91-97):(3-9):(1-3).

[0067] Further preferably, the mass ratio of the quartz sand, the quicklime and the water is:

[0068]

[0069] (4) Press to obtain a double-layer soil sample

[0070] Preferably, the pressing pressure is 400 kPa to 600 kPa, and the pressing time is 12 h to 48 h.

[0071] Further preferably, the pressing pressure is 500 kPa and the pressing time is 48 h.

[0072] Preferably, in order to keep the properties of the soil layer unchanged, the soil layer can be re-pressed every thirty minutes after the first compression, wherein the re-pressing pressure is the same as the compression pressure, and each re-pressing time is 5-10 minutes until the experiment starts.

[0073] The double-layer soil sample is a double-layer soil sample with hard upper layer and soft lower layer. After the puncture test of the pile shoe model, the double-layer soil sample showed an obvious bearing capacity reversal phenomenon, that is, the shear strength of the upper layer is greater than that of the lower layer. Figure 3 As shown in the figure, a sand plug appears at the bottom of the pile shoe model, which well simulates the properties of the double-layer soil sample on the seabed.

[0074] Based on the same inventive concept, an embodiment of the present invention provides a double-layer soil sample preparation system for an offshore jack-up platform puncture experiment, the system is used to execute the above-mentioned double-layer soil sample preparation method for the offshore jack-up platform puncture experiment to prepare a double-layer soil sample, referring to Figure 1 and Figure 2As shown, the system may include: a box body 1, a jack bracket 2, a hydraulic jack 3, a constant pressure hydraulic pump 4 and a pressure plate 5; wherein, the upper end surface of the box body 1 is open, and at least one drainage hole 11 is provided at the bottom of the box body 1; the jack bracket 2 is connected to the box body 1 to cover the open end surface of the box body; a through hole is provided on the jack bracket 1, and the hydraulic jack 3 is installed on the jack bracket 2 through a flange and bolts, and the piston rod 31 of the hydraulic jack 3 extends out of the through hole and is connected to the pressure plate 5; the constant pressure hydraulic pump 4 is connected to the hydraulic jack 3 through a pipeline; the constant pressure hydraulic pump 4 injects hydraulic fluid into the hydraulic jack 3 to drive the piston rod 31 of the hydraulic jack 3 to extend outward, and drives the pressure plate 5 to move downward, so as to press and prepare soft layer soil samples and double layer soil samples.

[0075] Preferably, refer to Figure 1 and Figure 2 As shown, the system may further include: permeable stones 6 , which are laid flat on the bottom of the box body 1 .

[0076] Preferably, refer to Figure 1 and Figure 2 As shown, the system may further include: two geotextiles 7 , one geotextile 7 is fixed to the bottom of the pressure plate 5 , and the other geotextile 7 is laid on the permeable stone 6 .

[0077] Combination Figure 1 and Figure 2 As shown in the figure, the system is mainly composed of a hydraulic jack, a constant pressure hydraulic pump, a jack bracket, a box body and a pressing tool inside the box body. The hydraulic jack uses an upper flange type, which is connected to the constant pressure hydraulic pump through an oil pipe. The constant pressure hydraulic pump ensures that the pressure remains constant when pressing double-layer soil samples; the jack flange is connected to the upper end of the bracket by bolts, and the inside of the bracket is hollow (through hole), which is convenient for adding sand and soil into the box body after the jack piston rod is lifted; the box body is a cylinder, with a square plate welded on the upper side, which is connected to the lower end of the bracket by bolts, and is hollow inside. There are six drainage holes distributed around the bottom, which are convenient for draining water when pressing the simulated stratum; the inside of the box is mainly composed of permeable stone, geotextile, soil sample to be pressed, geotextile, and pressure plate from bottom to top (such as Figure 2 As shown in the figure, the bottom permeable stone is also convenient for drainage. The simulated stratum to be pressed is separated from other parts by laying geotextiles on the top and bottom. The pressure plate is connected to the piston rod of the hydraulic jack through threads. There are four circles of small holes distributed around the pressure plate to facilitate water to be discharged from the top during operation. The whole set of equipment realizes the preparation of simulated stratum through the drive of the constant pressure hydraulic pump station and the coordination of various parts.

[0078] Example

[0079] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions. The raw materials used in the following examples are all conventionally purchased.

[0080] Example 1

[0081] (1) Place permeable stones at the bottom of the box and place geotextile on the permeable stones.

[0082] (2) Kaolin and montmorillonite were mixed in a mass ratio of 55:45, placed in a dry mixer, and stirred for 30 minutes.

[0083] (3) Pour water into a blender at a mass ratio of kaolin to water of 55:109 and stir for 30 minutes to obtain a first mixture.

[0084] (4) The first mixture is stirred thoroughly and placed in a box with a thickness not exceeding 100 mm.

[0085] (5) Place geotextile.

[0086] (6) Start the constant pressure hydraulic pump, maintain the cylinder pressure at 200 kPa, press for 2 hours to obtain the soft soil layer sample, and measure the shear strength to be 12 kPa. Then, press once every 30 minutes to keep the properties of the soft soil layer unchanged. The press pressure is 200 kPa, and the press time is 5 minutes each time.

[0087] (7) Screening the fully graded quartz sand to obtain fine sand.

[0088] (8) Fine sand and quicklime were mixed in a mass ratio of 94:6, placed in a dry mixer, and stirred for 30 minutes.

[0089] (9) Take water in a ratio of fine sand to water of 94:2 and place it in a watering can.

[0090] (10) Start the mixer and spray water atomization onto the mixture of sand and quicklime during the stirring process. Continue stirring for 30 minutes after all the water is sprayed off to obtain a second mixture.

[0091] (11) The thoroughly stirred second mixture is placed on the soft soil sample obtained in step (6) with a thickness of 55 mm.

[0092] (12) Start the constant pressure hydraulic pump and maintain the cylinder pressure at 500 kPa for 48 hours.

[0093] (13) A double-layer soil sample was obtained, with the upper layer being fine sand and the lower layer being clay with a shear strength of 15 kPa.

[0094] After the puncture test of the pile shoe model, the double-layer soil sample showed an obvious bearing capacity reversal phenomenon, that is, the shear strength of the upper layer was greater than that of the lower layer. Figure 3 As shown in the figure, a sand plug appears at the bottom of the pile shoe model, which well simulates the properties of the double-layer soil sample on the seabed.

[0095] Example 2

[0096] (1) Place permeable stones at the bottom of the box and place geotextile on the permeable stones.

[0097] (2) Kaolin and montmorillonite were mixed in a mass ratio of 90:10, placed in a dry mixer, and stirred for 30 minutes.

[0098] (3) Take water in a ratio of kaolin to water of 90:102 by mass, pour the mixture into a blender and stir for 30 minutes to obtain a first mixture.

[0099] (4) The first mixture is stirred thoroughly and placed in a box with a thickness not exceeding 100 mm.

[0100] (5) Place geotextile.

[0101] (6) Start the constant pressure hydraulic pump and maintain the cylinder pressure at 400 kPa. Press for 10 hours to obtain the soft soil sample. The shear strength of the soil sample is measured by an electric cross plate and is about 30 kPa. Then, press once every 30 minutes to keep the properties of the soft soil layer unchanged. The press pressure is 400 kPa and the press time is 5 minutes each time.

[0102] (7) Repeat steps (1) to (6) to obtain a soft layer soil sample with a thickness of 200 mm.

[0103] (8) Screening the fully graded quartz sand to obtain coarse sand.

[0104] (9) Mix coarse sand and quicklime in a mass ratio of 95:5, place in a dry mixer and stir for 30 minutes.

[0105] (9) Take water in a ratio of fine sand to water of 95:1.6 and place it in a watering can.

[0106] (10) Start the mixer and spray water atomization onto the mixture of sand and quicklime during the stirring process. Continue stirring for 30 minutes after all the water is sprayed off to obtain a second mixture.

[0107] (11) The thoroughly stirred second mixture is placed on the soft soil sample obtained in step (7) with a thickness of 28 mm.

[0108] (12) Start the constant pressure hydraulic pump and maintain the cylinder pressure at 500 kPa for 48 hours to obtain a double-layer soil sample.

[0109] (13) A triaxial shear test was conducted on a hard layer soil sample at a location that would not affect the experiment, and the internal friction angle was measured to be approximately 25°.

[0110] (14) After the puncture test of the pile shoe model, the double-layer soil sample showed an obvious bearing capacity reversal phenomenon, that is, the shear strength of the upper layer was greater than that of the lower layer. Figure 4 As shown in the figure, a sand plug appears at the bottom of the pile shoe model, which well simulates the properties of the double-layer soil sample on the seabed.

[0111] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A method for preparing double-layer soil samples for offshore jack-up platform puncture test, characterized in that: include: (1) mixing kaolin, montmorillonite and water according to a proportion to obtain a first mixture; (2) spreading the first mixture in a drainable container and pressing it to obtain a soft layer soil sample; (3) mixing quartz sand, quicklime and water according to a proportion to obtain a second mixture; (4) Spread the second mixture on the surface of the soft soil layer and press it to obtain a double-layer soil sample.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the kaolin, the montmorillonite and water is (15-95):(5-85):(100-114).

3. The preparation method according to claim 2, characterized in that: The mass ratio of the kaolin, the montmorillonite and water is (80-95):(5-20):(100-105).

4. The preparation method according to claim 1, characterized in that: In step (2), the pressing pressure is 50 kPa to 600 kPa, and the pressing time is 2 to 12 hours.

5. The preparation method according to claim 4, characterized in that: In step (2), the pressing pressure is 300 kPa to 500 kPa, and the pressing time is 4 to 8 hours.

6. The preparation method according to claim 1, characterized in that: The shear strength of the soft soil sample should be 2 kPa to 10 kPa lower than the preparation target strength.

7. The preparation method according to claim 1, characterized in that: When the particle size of quartz sand is 2.0-4.75 mm, the mass ratio of the quartz sand, the quicklime and the water is (92-98): (2-8): (0.7-2.6); when the particle size of quartz sand is 0.425-2.0 mm, the mass ratio of the quartz sand, the quicklime and the water is (92-98): (2-8): (1-3); when the particle size of quartz is 0.075-0.425 mm, the mass ratio of the quartz sand, the quicklime and the water is (91-97): (3-9): (1-3).

8. The preparation method according to claim 1, characterized in that: When the particle size of quartz sand is 2.0-4.75 mm, the mass ratio of the quartz sand to the quicklime and the water is (92-95):(5-8):(1.6-2.6); when the particle size of quartz sand is 0.425-2.0 mm, the mass ratio of the quartz sand to the quicklime and the water is (92-95):(5-8):(2-3); when the particle size of quartz sand is 0.075-0.425 mm, the mass ratio of the quartz sand to the quicklime and the water is (91-94):(6-9):(2-3).

9. The preparation method according to claim 1, characterized in that: In step (4), the pressing pressure is 400 kPa to 600 kPa, and the pressing time is 12 h to 48 h.

10. The preparation method according to claim 9, characterized in that: In step (4), the pressing pressure is 500 kPa and the pressing time is 48 h.

11. A double-layer soil sample preparation system for an offshore jack-up platform penetration test, the system being used to execute the double-layer soil sample preparation method for an offshore jack-up platform penetration test as claimed in any one of claims 1 to 10 to prepare a double-layer soil sample, characterized in that: The system comprises: Box, jack stand, hydraulic jack, constant pressure hydraulic pump and pressure plate; The upper end surface of the box body is open, and at least one drainage hole is provided at the bottom of the box body; the jack bracket is connected to the box body to cover the open end surface of the box body; a through hole is provided on the jack bracket, the hydraulic jack is installed on the jack bracket through a flange and bolts, and the piston rod of the hydraulic jack extends out of the through hole and is connected to the pressure plate; the constant pressure hydraulic pump is connected to the hydraulic jack through a pipeline; The constant pressure hydraulic pump injects hydraulic fluid into the hydraulic jack to drive the piston rod of the hydraulic jack to extend outward and drive the pressure plate to move downward to press and prepare soft layer soil samples and double layer soil samples.

12. The system according to claim 11, characterized in that The system further comprises: permeable stones, which are laid flat on the bottom of the box.

13. The system according to claim 12, characterized in that The system further comprises: two geotextiles, one of which is fixed on the bottom of the pressure plate, and the other is laid on the permeable stone.

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