Seabed clay slope sample structure for large-scale vibration table model test and preparation method of seabed clay slope sample structure

Abstract

According to the preparation method of the seabed clay slope sample structure for the large-scale vibration table model test, a real seabed clay sample is air-dried and crushed, so that impurities such as shells and gravels in the seabed clay sample are removed, and the mass of dry soil required by a model is conveniently and accurately calculated; increasing a proper degree according to the natural moisture content to enable the moisture content of the model to be close to the natural moisture content after the model is manufactured and formed in air, and fully stirring for 2 hours by using a vacuum stirrer to enable the moisture content of the soil sample to be uniform; a layer-by-layer tamping method is adopted to ensure that the density and the uniformity degree are the same in the model manufacturing process, water is injected from a slope toe during water injection, and the flow is controlled to be 5 L / min to 10 L / min to ensure that disturbance suffered by the model is minimum; and finally, the consolidation completion time is judged according to a pore water pressure sensor embedded in the soil body, so that the preparation of the seabed clay slope sample in the large-scale vibration table model test, which is simple and convenient to operate, is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering mechanics, and particularly relates to a submarine clay slope specimen structure for large-scale shaking table model tests and a preparation method thereof. Background Art

[0002] Seismic-triggered submarine landslides are a common disaster type developed on continental margins. They often have huge scales, extremely long movement distances, and significant disaster-causing effects. However, due to the limitations of current in-situ observation and geophysical technologies as well as the suddenness of submarine landslides, there are very few submarine slope instability phenomena that can be truly monitored and captured so far, which makes the instability mechanism of seismic-triggered submarine landslides still lack key evidence and data support. Indoor tests have gradually become an effective means for studying the mechanical properties of submarine slopes under seismic dynamic actions due to their high controllability, low cost, and good repeatability. Among them, shaking table tests are carried out in a 1g gravity environment, which can set up models with larger sizes and consider the effects of earthquakes and the hydrodynamic pressures generated by earthquakes on slope models, and have advantages in studying the movement process of submarine slope instability.

[0003] However, there are few current tests using large-scale shaking table tests to simulate the evolution process of submarine slopes under seismic actions. Most tests only use small-scale flumes, shaking tables or centrifuge tests, and use artificially prepared sand or clay to simulate submarine slopes. This not only cannot restore the real complex dynamic environment where submarine slopes are located, but also cannot simulate the real physical and mechanical properties of marine soils. Currently, the methods for carrying out large-scale submarine landslide shaking table model tests are still very limited. Summary of the Invention

[0004] The purpose of the present invention is to provide a submarine clay slope specimen structure for large-scale shaking table tests and a preparation method thereof, which have a simple process, are easy to operate, are used for large-scale shaking table test simulation, can effectively ensure uniform soil preparation, restore the real submarine clay characteristics, reduce the disturbance to the soil body, and accurately judge the consolidation degree of the soil sample.

[0005] To achieve the above purpose, the present invention is realized through the following technical solutions: A preparation method of a submarine clay slope specimen structure for large-scale shaking table model tests includes the following steps: S1) Take real submarine clay soil samples from the engineering site, air-dry them naturally in the air, crush them with a ball mill, and sieve out larger gravels, shells and other impurities; S2) According to conventional geotechnical tests, measure the natural water content of the undisturbed soil samples obtained from boreholes at the engineering site, as well as the water content of the soil samples obtained in step S1). Then, after increasing the natural water content to a certain extent, obtain the sample preparation water content, calculate the mass of water required for the soil samples in step S1), mix the soil samples with water, and stir them thoroughly in a vacuum mixer for 2 hours to remove the gas in the soil, and configure the remolded soil samples for testing; S3) Fix the pore water pressure sensor at the designated position in the shaking table model box in advance, and fill the remolded soil samples made in step S2) into the model box by the method of tamping layer by layer until the entire moist clay slope is formed in the air; S4) Lift and install the model box and fix it on the shaking table with special bolts. Slowly inject water from the toe of the slope model of the water pipe connected with a flowmeter to reach the designated water depth, and start the consolidation of the soil samples; S5) Determine whether the slope model is completed in consolidation through the values of the pore water pressure sensors buried. After the initial excess pore water pressure is completely dissipated, the model can start the subsequent shaking table test.

[0006] Further, in step S3), the method of tamping layer by layer is as follows: Each time of stacking starts from one side of the slope top; first stack the soil samples to form a platform with a thickness of 5 - 10 cm, and the thickness of each layer of soil samples is the same, then continuously extend from the end of the platform to the toe of the slope; during the process, repeatedly cut with a trowel until the shape conforms to the design, and so on until the entire moist clay slope is formed in the air; after the stacking is completed, gently tamp the slope with tools such as shovels, and finally level the surface with a small shovel.

[0007] The method of tamping layer by layer should be strictly controlled based on the target density, and the controlled density is the same as the density of the undisturbed soil measured by conventional geotechnical tests; calculate the mass of soil and water required for each layer of soil samples in advance, and strictly control its filling height.

[0008] Further, the sample preparation water content of the remolded soil samples is 5% - 8% higher than the natural water content.

[0009] Further, the remolded soil samples are placed in a moist container for use.

[0010] Further, the aperture of the sieve mesh for sieving is 3 mm - 5 mm.

[0011] A submarine clay slope specimen structure for large-scale shaking table model tests, which is filled in a large model box. The large model box is connected and fixed to a large shaking table by special bolts. A number of pore water pressure sensors are regularly arranged in the large model box, and the remolded soil samples are filled into the large model box layer by layer until the shape of the soil samples conforms to the design requirements; an injection water pipe is also provided in the large model box, and the injection water pipe is equipped with a flowmeter by itself. The injection water pipe slowly injects water from the toe of the slope model to the set depth.

[0012] Further, the remolded soil samples filled in layers are 10 layers, with each layer having a thickness of 5 - 10 cm. Each time of piling starts from one side of the slope top. First, a platform with a thickness of 5 - 10 cm is piled up with the remolded soil samples, and then it extends from the platform end to the slope foot. During the process, a trowel is used to repeatedly cut until the shape meets the design requirements; this is repeated until the entire slope sample model is formed in the air.

[0013] Further, the water injection flow rate of the water injection pipe is 5 - 10 L / min, and the water valve is closed when the water injection depth reaches 1.2 m.

[0014] Compared with the prior art, the present invention has the following advantages: A subsea clay slope sample structure for large-scale shaking table model tests and a preparation method thereof according to the present invention have a simple process and convenient operation. When used for large-scale shaking table tests for simulation, it can effectively ensure the uniform preparation of the soil body, restore the characteristics of real subsea clay, reduce the disturbance to the soil body, and accurately judge the consolidation degree of the soil sample.

[0015] Specifically, in the present invention, the real subsea clay soil samples are air-dried and crushed to remove internal impurities such as shells and gravels, which is convenient for accurately calculating the mass of dry soil required for the model. According to the natural water content, an appropriate amount is increased so that the water content of the model is close to the natural water content after being formed in the air, and the soil samples are fully stirred by a vacuum mixer for 2 hours to make the water content of the soil samples uniform; the method of tamping layer by layer is adopted to ensure the same density and uniformity during the model making process, and when injecting water, it is injected from the slope foot, and the flow rate is controlled at 5 L / min - 10 L / min to ensure the minimum disturbance to the model; finally, according to the pore water pressure sensors buried in the soil body, the time for consolidation completion is judged, realizing a simple operation for the preparation of subsea clay slope samples in large-scale shaking table model tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic flow chart of the preparation method of the present invention.

[0017] Figure 2 is a schematic diagram of the structure of the subsea clay slope sample of the present invention.

[0018] Figure 3 is a schematic diagram of the effect of tamping layer by layer of the structure of the subsea clay slope sample of the present invention.

[0019] Reference numerals: 1. Large shaking table; 2. Special bolts; 3. Large model box; 4. Remolded soil sample; 5. Flowmeter; 6. Water injection pipe; 7. Water body; 8. Pore water pressure sensor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following will further describe in detail the embodiments of the present invention with reference to the drawings.

[0021] As shown Figures 1 - 3 in the figure, a preparation method for the structure of a submarine clay slope specimen for large-scale shaking table model tests includes the following steps: Step S1), preliminarily crush a large amount of clay and place it in a place where sunlight can directly shine and air can circulate to naturally air-dry for 1-2 weeks. After air-drying, the soil sample is crushed again by a ball mill and passed through a 3-mm sieve; Step S2), open the original soil sample barrel, and test its natural water content to be 44.3% and natural density to be 17.5 g / cm 3 ³. The water content of the soil sample obtained in Step S1) is 0%. By increasing the natural water content by 5%, the water content for sample preparation can be obtained as 49.3%. Then, the mass of water required for every 100 kg of soil sample is 49.3 kg. Weigh the required soil sample and water and fully stir them in a vacuum mixer for 2 hours to remove the gas in the soil, and configure the remolded soil sample 4 for the test. Place it in a moist plastic barrel for later use; Step S3), pre-fix the pore water pressure sensor 8 at the key positions of the model preset in the large model box 3 as shown Figure 2 in the figure. Layer the remolded soil sample 4 prepared in Step S2) into the large model box 3. The method is as shown Figure 3 in the figure. The thickness of each layer is 5 cm, and there are 10 layers in total. Each time of piling starts from one side of the slope top. First, pile up the remolded soil sample 4 to form a platform with a thickness of 5 cm, and then continuously extend from the platform end to the slope foot. During the process, repeatedly cut with a trowel until the shape conforms to the design. Repeat this process until the entire moist cohesive soil remolded soil sample 4 is formed in the air. Gently pat the piled slope with tools such as a shovel, and finally level the surface with a small shovel. The amount of soil and water for each layer of the remolded soil sample 4 needs to be strictly calculated according to the natural density of 17.5 g / cm³ to ensure the same density of the entire slope; Step S4), use the laboratory crane to hoist the large model box 3 onto the large shaking table 1 and fix the two with special bolts 2. Slowly inject water from the slope foot of the slope model into the large model box 3 through the water injection pipe 6 with a built-in flow meter 5 until the water depth reaches 1.2 m, then close the water valve. At this time, there is water body 7 in the large model box 3, and the water injection flow rate is controlled at about 5 L / min; Step S5), through the monitoring of the pore water pressure sensor 8, when its value remains stable and no longer changes, it is judged that the model consolidation is completed, the initial excess pore water pressure dissipates, and the model can start the subsequent shaking table test.

[0022] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the concept of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as within the protection scope of the present invention.

Claims

1. A preparation method for the structure of a submarine clay slope specimen used in large shaking table model tests, characterized in that The steps include: S1) Take a real seabed clay sample from the project site, dry it naturally in the air, crush it with a ball mill, and sieve out larger gravel, shells and other impurities; S2) According to conventional geotechnical tests, the natural moisture content of the original soil sample obtained by drilling at the engineering site and the moisture content of the soil sample obtained in step S1) are measured, and the moisture content of the sample is obtained by increasing the natural moisture content to a certain extent, and the water mass required for the soil sample in step S1) is calculated. The soil sample and water are mixed and fully stirred in a vacuum mixer for 2 hours to remove the gas in the soil, and a reshaped soil sample for the test is prepared; S3) pre-fixing the pore water pressure sensor at a designated position of the shaking table model box, and filling the reshaped soil sample prepared in step S2) into the model box by compacting layer by layer until the entire moist clay slope is formed in the air; S4) Lift the model box and fix it on the vibration table with special bolts, and slowly inject water from the foot of the slope model to the specified water depth using a water pipe connected to a flow meter to start consolidation of the soil sample; S5) The values ​​of the buried pore water pressure sensors are used to determine whether the slope model has been consolidated. When the initial excess pore water pressure is completely dissipated, the model can start the subsequent shaking table test.

2. The preparation method of a submarine clay slope specimen structure for large shaking table model tests according to claim 1, characterized in that: In step S3), the layer-by-layer compaction method is as follows: each accumulation starts from one side of the top of the slope; first, the soil sample is piled up to form a platform with a thickness of 5 to 10 cm, and each layer of soil sample has the same thickness, and then it is continuously extended from the end of the platform to the foot of the slope; the spatula is used to repeatedly cut until the shape meets the design, and this is repeated until the entire moist clay slope is formed in the air; after the accumulation is completed, the slope is gently patted with a shovel or other tool, and finally the surface is smoothed with a small shovel.

3. The preparation method of a submarine clay slope specimen structure for large-scale shaking table model tests according to claim 1, characterized in that: The moisture content of the remolded soil sample is 5% to 8% higher than the natural moisture content.

4. The preparation method of a submarine clay slope specimen structure for large shaking table model tests according to claim 1, characterized in that: The remolded soil samples were placed in moist containers ready for use.

5. The preparation method of a submarine clay slope specimen structure for large shaking table model tests according to claim 1, characterized in that: The aperture of the sieve mesh is 3mm~5mm.

6. A subsea clay slope specimen structure for large shaking table model tests, which is filled in a large model box. The large model box is fixedly connected to a large shaking table through special bolts, and is characterized in that: A number of pore water pressure sensors are regularly arranged in the large model box, and the reshaped soil samples are filled into the large model box in layers until the shape of the soil samples meets the design requirements; a water injection pipe is also provided in the large model box, and the water injection pipe is equipped with a flow meter, and the water injection pipe slowly injects water from the foot of the slope model to a set depth.

7. A submarine clay slope specimen structure for large shaking table model tests according to claim 6, characterized in that: There are 10 layers of reshaped soil samples filled in layers, and each layer is 5~10cm thick. Each stacking starts from the top of the slope. First, the reshaped soil samples are piled up to form a platform with a thickness of 5~10cm, and then extended from the end of the platform to the foot of the slope. Repeated cutting with a spatula in the middle until the shape meets the design requirements; this process is repeated until the entire slope specimen model is formed in the air.

8. The structure of a submarine clay slope specimen for large shaking table model tests according to claim 7, characterized in that: The water injection flow rate of the water injection pipe is 5-10L / min, and the water valve is closed when the water injection depth reaches 1.2m.

Images