An apparatus and a preparation method for preparing normally consolidated marine sedimentary soil

Abstract

The present invention discloses a device and a preparation method for preparing normally consolidated marine sedimentary soil, belonging to the field of marine geotechnical engineering. The test device includes an air compressor, a water storage cylinder, a pressure consolidation cylinder, a pneumatic control system, a water level monitoring system, a temperature control system and a soil strength testing system. Based on the hydraulic gradient, the present invention utilizes the seepage force to increase the vertical stress acting on the soil sample, realizes a pseudo-supergravity effect, and further completes the preparation of the normally consolidated soil sample in the model test. Moreover, the soil strength can be tested through the soil strength testing system, which has the advantages of strong feasibility, strong scientificity and good comprehensiveness.

Description

Technical Field

[0001] The present invention belongs to the field of marine geotechnical engineering, and relates to a device for preparing normally consolidated marine sedimentary soil, and a preparation method considering hypergravity consolidation based on hydraulic gradient. Background Technique

[0002] With the progress of science and technology, the development of offshore engineering is getting faster and faster, such as docks, offshore drilling platforms, cross-sea bridges, etc. When these offshore projects are constructed, high requirements are imposed on the marine foundation. For most marine structures, the marine foundation is crucial for the stability and safety of marine structures. And in-situ testing in the sea is relatively difficult, so some ng model tests need to be carried out in the laboratory. The so-called ng model test is to reduce the sizes of marine structures and foundation soils, etc. to 1 / n, and at the same time increase the acceleration to ng. Currently, there are two types of such tests: geotechnical centrifuge tests and hydraulic gradient model tests. In the test, it is necessary to restore the offshore field environment as much as possible, including the type, specific gravity, strength, etc. of the foundation soil. Therefore, the sample preparation link in the model test is crucial for the entire test and even for the safety and stability of subsequent projects.

[0003] Currently, for the preparation of model test marine clay, different strength soil samples can be obtained by changing the overlying pressure of the soil sample to meet the requirements of different tests. The preparation methods include loading through a consolidometer, self-weight stress consolidation, centrifuge loading, etc. In current experimental studies, the loading method by consolidometer is mostly used, which requires a large amount of counterweight for loading. For large-volume specimens, a larger-scale consolidometer is needed to complete the test, and the equipment is huge, heavy and expensive. In view of these problems, from the perspective of simplicity and practicality, based on the hypergravity field formed by the hydraulic gradient, the present invention provides a device and a preparation method for preparing normally consolidated marine sedimentary soil, which have the advantages of strong feasibility, strong scientificity and good comprehensiveness, and have good practical significance for the preparation and research of soil samples for large-scale model tests. Summary of the Invention

[0004] The purpose of the present invention is to provide a device and a preparation method for preparing normally consolidated marine sedimentary soil to overcome the deficiencies of existing research means. This method is an ng model test, and the principle is based on the hydraulic gradient, using the seepage force j (=γ w i) of water flowing downward in the soil, which is a volume force, to increase the vertical effective stress acting on the soil sample, so as to achieve that the model size is reduced by n times while the stress and strain in the soil are the same as those of the prototype:

[0005] nγ , =iγ w +γ ,

[0006] If γ , ≈γw Then the hypergravity ratio is n = i + 1, where i is the downward hydraulic gradient.

[0007] In this way, the hypergravity field is simulated, and then the preparation of soil samples in the model test is realized. It has the advantages of strong feasibility, strong scientificity and good comprehensiveness.

[0008] To achieve the above object, the technical solution of the present invention is as follows:

[0009] A device for preparing normally consolidated marine sedimentary soil, comprising an air compressor 1, a water storage cylinder 2, a pressure consolidation cylinder 3, a pneumatic control system, a water level monitoring system, a temperature control system and a soil strength testing system;

[0010] The water storage cylinder 2 includes a first upper cover 2-1, a first middle cylinder 2-2 and a first lower cover 2-3; wherein, both ends of the first middle cylinder 2-2 are respectively installed on the circular grooves of the first upper cover 2-1 and the first lower cover 2-3, and the three are connected by limit screws and sealed by a sealing rubber ring 2-11;

[0011] The top of the first upper cover 2-1 is installed with a pneumatic control valve 2-8 and a pressure gauge 2-7, and is connected to the air compressor 1 by a water pipe;

[0012] The lower part of the first lower cover 2-3 is installed with a drainage control valve 2-5, and is connected to the upper cover of the pressure consolidation cylinder 3 by a water pipe;

[0013] The first middle cylinder 2-2 is of a cylindrical structure, and its side wall is tightly fastened by a steel ring 2-6 to prevent cracking and deformation during use;

[0014] The pressure consolidation cylinder 3 includes a second upper cover 3-1, a second middle cylinder 3-2 and a second lower cover 3-3; wherein, both ends of the second middle cylinder 3-2 are respectively installed on the circular grooves of the second upper cover 3-1 and the second lower cover 3-3, and the three are connected by limit screws and sealed by a sealing rubber ring;

[0015] The top of the second upper cover 3-1 is installed with a control valve and is connected to the water storage cylinder 2 by a water pipe, and an exhaust valve is also installed;

[0016] The lower part of the second lower cover 3-3 is installed with a drain valve;

[0017] The second middle cylinder 3-2 is of a cylindrical structure, and its side wall is tightly fastened by a steel ring 2-6 to prevent cracking and deformation during use;

[0018] The pneumatic control system is used to control the air pressure of the air compressor 1 introduced into the water storage cylinder 2, and includes a pressure gauge for displaying the air pressure and a pneumatic control valve for controlling the air pressure to a required stable value;

[0019] The water level monitoring system is used to monitor the water level in the water storage cylinder 2, including a water level float sensor for monitoring the water level and an alarm device for reminding to replenish water. When the alarm device is below a certain water level, the alarm device is triggered to remind to replenish water in the water storage cylinder 2, so as to ensure that water continuously seeps into the pressure consolidation cylinder 3 under the action of air pressure;

[0020] The temperature control system is used to control the internal temperature of the pressure consolidation cylinder 3, including a heating and cooling device and a micro circulating pump, so as to control the inside of the pressure consolidation cylinder 3 to be a constant temperature and simulate the environmental temperature of the deep sea;

[0021] The soil strength testing system is used to test the strength of the soil sample in the pressure consolidation cylinder 3, including a sensing device and a testing device. The testing device can be installed with a vane or a T-bar to measure the soil sample strength.

[0022] Furthermore, a pneumatic control system is installed on the upper top cover 2-1 of the water storage cylinder 2 to control and display the air pressure of the air compressor 1 entering the water storage cylinder 2.

[0023] Furthermore, the upper top cover 3-1 of the pressure consolidation cylinder 3 has a sensor positioning hole 3-8. Under the condition of ensuring good airtightness, the temperature control system is put into the pressure consolidation cylinder 3 to realize digital regulation, or the soil strength testing device can also be put in to measure the soil sample strength.

[0024] A preparation method of a device for preparing normally consolidated marine sedimentary soil, and the testing method includes the following steps:

[0025] Step 1: Connect the device, close the control valve of the first lower top cover 2-3 of the water storage cylinder 2, close the control valve of the second upper top cover 3-1 of the pressure consolidation cylinder 3, close the drain valve of the second lower top cover 3-3 of the pressure consolidation cylinder 3, remove the second upper top cover 3-1 of the pressure consolidation cylinder 3, lay a layer of geotextile and a layer of filter paper at the bottom of the pressure consolidation cylinder 3, then pour 5 cm thick standard sand as a filter layer, lay another layer of geotextile and filter paper, and then slowly put the prepared soil sample into the pressure consolidation cylinder 3, insert the temperature control device into the soil sample, install the second upper top cover 3-1 of the pressure consolidation cylinder 3, open the exhaust valve of the second upper top cover 3-1 of the pressure consolidation cylinder 3, and then let it stand for a period of time to allow the soil sample to consolidate and settle under its own gravity stress;

[0026] Wait until the soil sample completes consolidation and settlement under its own gravity stress and then proceed to the next test;

[0027] Step 2: During the static settlement of the soil sample, remove the water injection hole valve of the first upper top cover 2-1 of the water storage cylinder 2, add water to the water storage cylinder 2, put in the water level monitoring device, and then install the water injection hole valve of the first upper top cover 2-1 of the water storage cylinder 2;

[0028] Step 3: After the static settlement is completed, turn on the air compressor 1 and adjust the pneumatic control valve on the first upper cover 2-1 of the water storage cylinder 2 until the pressure gauge reaches the test-set pressure value. Then open the control valve of the first lower cover 2-3 of the water storage cylinder 2 and the control valve of the second upper cover 3-1 of the pressure consolidation cylinder 3. When water emerges from the exhaust valve on the second upper cover 3-1 of the pressure consolidation cylinder 3, close the exhaust valve on the second upper cover 3-1 of the pressure consolidation cylinder 3 and open the drain valve on the second lower cover 3-3 of the pressure consolidation cylinder 3 to perform pressure consolidation. The introduced air pressure can increase the downward seepage force of water, thereby simulating a hypergravity environment:

[0029] nγ , =iγ w +γ ,

[0030] Assume γ , ≈γ w , then the magnification ratio of the gravitational acceleration increase is n = i + 1, where i is the downward hydraulic gradient.

[0031] Step 4: After pressure consolidation, measure the soil sample strength through the soil strength testing device. Stop pressurization after reaching the required strength; otherwise, continue pressure consolidation.

[0032] Furthermore, the described testing method is based on the hydraulic gradient method, using air pressure to increase the seepage force of water to achieve the consolidation of the soil sample.

[0033] In Steps 2 and 3, when the water volume in the water storage cylinder 2 is insufficient, the water level monitoring system issues an alarm, constantly prompting to add water through the water injection hole 2-4 without affecting the process of the pressure consolidation cylinder 3.

[0034] Advantages of the present invention: The present invention aims to provide a device and a preparation method for preparing normally consolidated marine sedimentary soil to overcome the deficiencies of existing research methods. This method is based on the hydraulic gradient, using the seepage force to increase the vertical effective stress acting on the soil sample, simulating hypergravity, and thus realizing the preparation of the soil sample in the model test. It has the advantages of high reduction degree of the deep-sea environment, strong scientificity, and good comprehensiveness. Description of the Drawings

[0035] Figure 1 is a schematic structural diagram of the sample preparation system described in the present invention.

[0036] Figure 2 is a schematic diagram of the upper cover 2-1 of the water storage cylinder 2.

[0037] Figure 3 is a schematic diagram of the lower cover 2-3 of the water storage cylinder 2.

[0038] Figure 4 is a schematic diagram of the upper cover 3-1 of the pressure consolidation cylinder 3.

[0039] Figure 5 It is a schematic diagram of the lower top cover 3-3 of the pressure consolidation cylinder 3.

[0040] Figure 6 It is the result diagram of the present invention, where (b) is the settlement diagram after standing for 24 hours, (b) is the pressure settlement diagram, (c) is the cross plate strength column diagram, and (d) is the T-bar penetration depth strength profile diagram.

[0041] In the figure: 1 air compressor; 1-1 air motor switch; 1-2 air compressor control valve; 1-3 water pipe; 1-4 pressure gauge control valve; 2 water storage cylinder; 2-1 upper top cover; 2-2 middle cylinder; 2-3 lower top cover; 2-4 water injection hole; 2-5 drainage control valve; 2-6 steel ring; 2-7 pressure gauge; 2-8 air pressure control valve; 2-9 air inlet hole; 2-10 connecting rod limit hole; 2-11 sealing rubber ring; 2-12 drainage hole; 2-13 water level detection system; 3-1 upper top cover; 3-2 middle cylinder; 3-3 lower top cover; 3-4 water inlet hole; 3-5 exhaust hole; 3-6 drainage hole; 3-7 temperature control system; 3-8 sensor positioning hole; 3-9 drainage hole; 3-10 soil strength test system. Specific embodiments

[0042] The following further explains the specific embodiments of the present invention in conjunction with the embodiments and the drawings, but is not used to limit the present invention.

[0043] As Figure 1 shown, a device for preparing normally consolidated marine sedimentary soil includes an air compressor 1, a water storage cylinder 2, a pressure consolidation cylinder 3, a pneumatic control system, a water level monitoring system, a temperature control system, and a soil strength test system.

[0044] The air compressor 1 is a device for compressing gas, which can continuously provide the required air pressure in the test to increase the water penetration force.

[0045] The water storage cylinder 2 includes an upper top cover 2-1, a middle cylinder 2-2, and a lower top cover 2-3. Among them, both ends of the middle cylinder 2-2 are respectively installed on the circular grooves of the upper top cover 2-1 and the lower top cover 2-3, and the upper top cover 2-1 and the lower top cover 2-3 are connected by limit screws.

[0046] An air pressure control valve and a pressure gauge are installed on the top of the upper top cover 2-1, and are connected to the air compressor 1 through a water pipe.

[0047] A control valve is installed at the lower part of the lower top cover 2-3, and is connected to the upper part of the upper top cover of the pressure consolidation cylinder 3 through a water pipe.

[0048] The middle cylinder 2-2 is a cylindrical structure made of plexiglass, and its side wall is tightly fastened with a steel ring to prevent cracking, deformation, etc. during use.

[0049] The pressurized consolidation cylinder 3 comprises an upper cover 3-1, a middle cylinder 3-2 and a lower cover 3-3, wherein both ends of the middle cylinder 3-2 are respectively mounted on the circular grooves of the upper cover 3-1 and the lower cover 3-3, and the upper cover 3-1 and the lower cover 3-3 are connected by a limiting screw.

[0050] A control valve is installed on the top of the upper cover 3-1 and is connected to the water storage cylinder 2 through a water pipe, and an exhaust valve is also installed.

[0051] A drain valve is installed at the lower part of the lower top cover 3-3.

[0052] The middle tube 3-2 is a cylindrical structure made of organic glass, and its side wall is tightly bound with a steel ring to prevent cracking, deformation, etc. during use.

[0053] The air pressure control system is used to control the air pressure of the air compressor 1 entering the water storage cylinder 2, and includes a barometer for displaying the air pressure and an air pressure control valve for controlling the air pressure to a desired stable value.

[0054] The water level monitoring system is used to monitor the water level in the water storage cylinder 2, including a water level float sensor for monitoring the water level and an alarm device for reminding water replenishment. When the water level is lower than a certain water level, the alarm device can be triggered to remind the water storage cylinder 2 to replenish water, so as to ensure that water continuously seeps into the pressurized consolidation cylinder 3 under the action of air pressure.

[0055] The temperature control system is used to control the internal temperature of the pressurized consolidation cylinder 3, and includes a heating refrigerator and a micro-circulation pump, so as to control the internal temperature of the pressurized consolidation cylinder 3 to be a constant temperature to simulate the ambient temperature of the deep sea.

[0056] The soil strength testing system is used to test the strength of the soil sample in the pressurized consolidation cylinder 3, and includes a sensor device and a testing device. The testing device can be installed with a cross plate or a T-bar to measure the strength of the soil sample.

[0057] Furthermore, sealing rubber rings are installed between the middle cylinders 2-2 and 3-2 and the upper and lower top covers to improve the sealing and pressure bearing properties.

[0058] A method for preparing a device for preparing normally consolidated marine sediment soil comprises the following steps:

[0059] Step 1: Connect the device, close the control valve of the lower top cover 2-3 of the water storage cylinder 2, close the control valve of the upper top cover 3-1 of the pressure consolidation cylinder 3, close the drain valve of the lower top cover 3-3 of the pressure consolidation cylinder 3, remove the upper top cover 3-1 of the pressure consolidation cylinder 3, lay a layer of geotextile and a layer of filter paper at the bottom of the pressure consolidation cylinder 3, then pour 5 cm thick standard sand as the filter layer, lay another layer of geotextile and filter paper, and then slowly pour the prepared soil sample into the pressure consolidation cylinder 3. Insert the temperature control device into the soil sample, install the upper top cover 3-1 of the pressure consolidation cylinder 3, open the exhaust valve of the upper top cover 3-1 of the pressure consolidation cylinder 3, and then let it stand for a period of time to allow the soil sample to consolidate and settle under its own gravity stress.

[0060] After the soil sample has completed consolidation and settlement under its own gravity stress, proceed to the next test.

[0061] Step 2: During the static settlement of the soil sample, remove the water injection hole valve of the upper top cover 2-1 of the water storage cylinder 2, add water to the water storage cylinder 2, insert the water level monitoring device, and then install the water injection hole valve of the upper top cover 2-1 of the water storage cylinder 2.

[0062] Step 3: After the static settlement is completed, turn on the air compressor 1, adjust the air pressure control valve on the upper top cover 2-1 of the water storage cylinder 2 until the air pressure gauge reaches the desired air pressure value for the test (apply air pressures of 50 kPa, 100 kPa, and 200 kPa respectively). Then open the control valve of the lower top cover 2-3 of the water storage cylinder 2 and the control valve of the upper top cover 3-1 of the pressure consolidation cylinder 3. When water emerges from the exhaust valve of the upper top cover 3-1 of the pressure consolidation cylinder 3, close the exhaust valve of the upper top cover 3-1 of the pressure consolidation cylinder 3, open the drain valve of the lower top cover 3-3 of the pressure consolidation cylinder 3, and perform pressure consolidation. The applied air pressure can increase the downward seepage force of water, thereby simulating a hypergravity environment:

[0063] nγ , =iγ w +γ ,

[0064] If γ , ≈γ w , then the hypergravity ratio is n = i + 1, where i is the downward hydraulic gradient.

[0065] Step 4: After pressure consolidation, measure the strength of the soil sample through the soil strength testing device. Stop applying pressure when the required strength is reached, otherwise continue pressure consolidation.

[0066] After the soil sample has completed consolidation and settlement under the hydraulic gradient, proceed to the next test.

[0067] The vane shear test for undrained shear strength S u :

[0068]

[0069] In the formula, S u is the undrained shear strength value measured by the vane; d is the diameter of the vane head; h is the height of the vane head.

[0070] The undrained shear strength S measured by the T-bar u :

[0071]

[0072] In the formula, S u is the undrained shear strength value measured by the T-bar; q net is the net penetration resistance, which is the ratio of the penetration resistance to the projected area; N c is the resistance coefficient. For medium- and low-sensitivity in-situ saturated soft cohesive soils, when N c , the value of Ball ranges from 11.6 to 13.2, and when N c , the value of T ranges from 10.9 to 12.7.

Claims

1. A method for preparing normally consolidated marine sedimentary soil, characterized in that: The device used in the method is a device for preparing normally consolidated marine sedimentary soil, comprising an air compressor (1), a water storage cylinder (2), a pressurized consolidation cylinder (3), an air pressure control system, a water level monitoring system, a temperature control system and a soil strength testing system; The water storage cylinder (2) comprises a first upper cover (2-1), a first middle cylinder (2-2) and a first lower cover (2-3); wherein two ends of the first middle cylinder (2-2) are respectively mounted on the circular grooves of the first upper cover (2-1) and the first lower cover (2-3), and the three are connected by a limiting screw and sealed by a sealing rubber ring (2-11); An air pressure control valve (2-8) and an air pressure gauge (2-7) are installed on the top of the first upper cover (2-1), and are connected to the air compressor (1) via a water pipe; A drainage control valve (2-5) is installed at the lower part of the first lower cover (2-3), and is connected to the upper cover of the pressurized consolidation cylinder (3) through a water pipe; The first middle tube (2-2) is a cylindrical structure, and its side wall is tightly bound by a steel ring (2-6) to prevent it from breaking or deforming during use; The pressurized consolidation cylinder (3) comprises a second upper cover (3-1), a second middle cylinder (3-2) and a second lower cover (3-3); wherein the two ends of the second middle cylinder (3-2) are respectively mounted on the circular grooves of the second upper cover (3-1) and the second lower cover (3-3), and the three are connected by a limiting screw and sealed by a sealing rubber ring; A control valve is installed on the top of the second upper cover (3-1) and is connected to the water storage cylinder (2) via a water pipe, and is also installed with an exhaust valve; A drain valve is installed at the lower part of the second lower top cover (3-3); The second middle cylinder (3-2) is a cylindrical structure, and its side wall is tightly bound by a steel ring (2-6) to prevent it from breaking or deforming during use; The air pressure control system is used to control the air pressure of the air compressor (1) entering the water storage cylinder (2), and includes a barometer for displaying the air pressure and an air pressure control valve for controlling the air pressure to a desired stable value; the water level monitoring system is used to monitor the water level in the water storage cylinder (2), and includes a water level float sensor for monitoring the water level and an alarm device for reminding to add water. When the water level is lower than a certain level, the alarm device is triggered to remind the water storage cylinder (2) to add water, so as to ensure that water continuously seeps into the pressurized consolidation cylinder (3) under the action of air pressure; The temperature control system is used to control the internal temperature of the pressurized consolidation cylinder (3), and includes a heating refrigerator and a micro-circulation pump, so as to control the internal temperature of the pressurized consolidation cylinder (3) to be constant, simulating the ambient temperature of the deep sea; The soil strength testing system is used to test the strength of the soil sample in the pressurized consolidation cylinder (3), and comprises a sensor device and a testing device. The testing device can be equipped with a cross plate or a T-bar to measure the strength of the soil sample; The specific steps are as follows: Step 1: Connect the device, close the control valve of the first lower cover (2-3) of the water storage cylinder (2), close the control valve of the second upper cover (3-1) of the pressurized consolidation cylinder (3), close the drain valve of the second lower cover (3-3) of the pressurized consolidation cylinder (3), remove the second upper cover (3-1) of the pressurized consolidation cylinder (3), lay a layer of geotextile and a layer of filter paper at the bottom of the pressurized consolidation cylinder (3), then pour 5 cm thick standard sand as a filter layer, and then lay a layer of geotextile and filter paper, then slowly put the prepared soil sample into the pressurized consolidation cylinder (3), insert the temperature control device into the soil sample, install the second upper cover (3-1) of the pressurized consolidation cylinder (3), open the exhaust valve of the second upper cover (3-1) of the pressurized consolidation cylinder (3), and then let it stand for a period of time to allow the soil sample to consolidate and settle under the deadweight stress; After the soil sample has completed consolidation and settlement under its own weight stress, the next test is carried out; Step 2: While the soil sample is settling, remove the water injection hole valve of the first upper cover (2-1) of the water storage cylinder (2), add water to the water storage cylinder (2), put in a water level monitoring device, and then install the water injection hole valve of the first upper cover (2-1) of the water storage cylinder (2); Step 3: After the static sedimentation is completed, the air compressor (1) is turned on, and the air pressure control valve on the first upper cover (2-1) of the water storage cylinder (2) is adjusted until the air pressure gauge reaches the air pressure value set for the test; then the control valve of the first lower cover (2-3) of the water storage cylinder (2) and the control valve of the second upper cover (3-1) of the pressurized consolidation cylinder (3) are opened, and when water emerges from the exhaust valve of the second upper cover (3-1) of the pressurized consolidation cylinder (3), the exhaust valve of the second upper cover (3-1) of the pressurized consolidation cylinder (3) is closed, and the drain valve of the second lower cover (3-3) of the pressurized consolidation cylinder (3) is opened to perform pressurized consolidation; the introduced air pressure can increase the downward penetration of water, thereby simulating a hypergravity environment: nγ , =iγ w +g , Assumption γ , ≈γ w , then the gravitational acceleration increases by a multiple of n = i + 1, where i is the downward hydraulic gradient; Step 4: After pressurization and consolidation, measure the strength of the soil sample using a soil strength testing device. Stop pressurization when the required strength is reached, otherwise continue pressurization and consolidation.

2. The method according to claim 1, characterized in that An air pressure control system is installed on the upper cover (2-1) of the water storage cylinder (2) and is used to control and display the air pressure of the air compressor (1) entering the water storage cylinder (2).

3. The method according to claim 1 or 2, characterized in that: The upper cover (3-1) of the pressurized consolidation cylinder (3) is provided with a sensor positioning hole (3-8). Under the condition of ensuring air tightness, a temperature control system is placed in the pressurized consolidation cylinder (3) to achieve digital regulation, and a soil strength testing device can also be placed in the cylinder to measure the strength of a soil sample.

4. The method according to claim 1, characterized in that: The method is based on the hydraulic gradient method, which uses air pressure to increase the seepage force of water to achieve consolidation of soil samples.

5. The method according to claim 4, characterized in that In steps 2 and 3, when the water volume in the water storage cylinder (2) is insufficient, the water level monitoring system will sound an alarm, prompting the user to add water through the water injection holes (2-4) at any time without affecting the progress of the pressurized consolidation cylinder (3).

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