An indoor test method for scour protection of pile foundation solidified soil

Abstract

The present invention discloses an indoor test method for scour protection of pile foundation solidified soil, comprising: erecting a transparent model pile in a grit chamber of a water flume, laying a soil layer around the model pile; placing an ADV flow velocity sensor in front of the model pile and a video recorder inside the model pile to record flow velocity data and image data during the test; preparing solidified soil; slowly injecting water into the water flume until a corresponding water level is reached, adjusting the water flume flow generating equipment to ensure that the water flow reaches a designed flow velocity, and scouring the soil until a scour pit develops in equilibrium at the corresponding flow velocity; blowing solidified soil into the scour pit according to the range and depth of the scour pit; observing and measuring the development of scour during the solidified soil curing process until the scour pit develops in equilibrium, and recording the scour depth and scour range at each measuring point around the model pile. The present invention overcomes the drawback that on-site testing cannot fully meet the requirements of research work for environmental conditions, test conditions, and test accuracy.

Description

Technical Field

[0001] The invention relates to a scour protection test method, in particular to an indoor test method for scour protection of pile foundation solidified soil. Background Art

[0002] Against the backdrop of carbon peak and carbon neutrality, offshore wind power construction has developed rapidly. Many offshore wind farms that have been built are also facing problems such as scouring causing submarine cables to dangle and exceeding the designed reserved depth. In severe cases, it may even affect the vibration frequency of the wind turbine foundation or lead to insufficient bearing capacity. In the future, there will be good market prospects for the repair of offshore pile foundation scour pits and foundation anti-scour. The effects of traditional scour protection methods such as riprap and sand blankets vary. In recent years, the concepts of ex situ silt solidification technology, in situ silt solidification technology and bionic aquatic grass protection technology that have emerged are relatively new and have better results so far. However, their related protection effects, action mechanisms, design standards, construction processes, etc. are not yet mature. The project relies on physical projects and conducts experimental tests on the engineering site to provide measured data for the study of offshore pile foundation scour mechanisms and anti-scour measures.

[0003] Currently, the research on pile foundation scour protection mechanisms and scour protection simulation technologies in complex marine environments is still in the exploratory research stage. The scour mechanism of marine foundations is relatively complex and requires consideration of the influence of hydraulic characteristics, tidal reciprocating flow, sediment conditions, foundation structure form and layout under sea conditions. Since the wave and current environment at the engineering site varies greatly over time and across regions, on-site tests cannot fully meet the research requirements for environmental conditions, test conditions, and test accuracy. At this stage, it is necessary to use indoor model tests to control variables such as flow rate and scour time to study and demonstrate the feasibility of scour protection design schemes in stable wave and current environments, obtain reliable development laws, and provide scientific support for scour protection mechanism research and scheme optimization. Summary of the Invention

[0004] The purpose of the present invention is to provide an indoor test method for pile foundation solidified soil scour protection, which overcomes the defect that on-site test tests are difficult to fully meet the requirements of research work on environmental conditions, test conditions, test accuracy, etc.

[0005] The technical solution to achieve the above purpose is:

[0006] An indoor test method for scour protection of pile foundation stabilized soil, comprising:

[0007] Step S1: Setting up a test model based on the prototype site hydrogeological conditions, erecting transparent model piles in the grit chamber of the water tank, and laying soil around the model piles;

[0008] Step S2: an ADV flow velocity sensor is arranged in front of the model pile, and a video recorder is arranged inside the model pile to record the flow velocity data and image data during the test;

[0009] Step S3, manufacturing solidified soil;

[0010] Step S4: slowly add water to the water tank until the water level reaches the corresponding level, adjust the water tank flow generating equipment to make the water flow reach the designed flow rate, and flush the water until the scouring pit develops in equilibrium at the corresponding flow rate;

[0011] Step S5: Blowing solidified soil into the scouring pit according to the scope and depth of the scouring pit, and controlling the scope and elevation to meet the test design requirements;

[0012] Step S6: Observe and measure the development of scouring during the solidification process of the solidified soil until the scouring pit develops into equilibrium, and record the scouring depth and scouring range of each measuring point around the model pile.

[0013] Preferably, in step S1, the soil layer is laid in layers and compacted layer by layer. After laying to a preset elevation, water is slowly injected to submerge the surface of the soil layer and soaked for 24 hours to saturate it.

[0014] Preferably, the sand particle size used in the soil layer is 0.15 mm, and the material is quartz sand.

[0015] Preferably, an ADV flow velocity sensor is arranged 10 to 20 cm in front of the model pile, and a probe of the ADV flow velocity sensor is 3 to 5 cm away from the bottom surface of the water tank.

[0016] Preferably, six depth measurement points are provided around the model pile, with a spacing of 60° between the measurement points.

[0017] Preferably, manufacturing the stabilized soil comprises:

[0018] Use a cement mixer to mix the weighed soil, cement and water. Before starting mixing, pour the weighed water into the mixing pot first, then pour in the mixed cement soil powder, stir slowly for 120 seconds, pause for 15 seconds, scrape the soil off the pot wall and mixing head of the cement mixer, and then stir quickly for 120 seconds to obtain a uniform solidified soil slurry.

[0019] Preferably, the scour pit develops in equilibrium, which means that when the scour depth no longer changes or changes by less than 1 mm within 1 hour, the scour pit is considered to have reached equilibrium.

[0020] Preferably, the Froude numbers between the test model and the prototype are equal,

[0021]

[0022] Where g is the acceleration due to gravity; V and L are the velocity and size of the object, respectively. The subscripts m and p represent the test model and prototype, respectively. The length of the model is L. p / L m =λ L .

[0023] The beneficial effects of the present invention are: the present invention follows the gravity similarity criterion design, that is, the Froude number (Fr) between the model and the prototype is equal. By controlling single-factor variables, the scour protection effect of solidified soil in a stable wave and flow environment is studied and demonstrated, and a reliable development law is obtained, providing scientific support for the research on scour protection mechanism and scheme optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is an elevation view of the overall layout of the test model in the present invention;

[0025] Figure 2 It is a cross-sectional view of the overall arrangement of the test model in the present invention;

[0026] Figure 3 It is a layout diagram of the test model test equipment in the present invention;

[0027] Figure 4 This is a diagram of the test point arrangement of the test model in the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] like Figure 1-4 The indoor test method for pile foundation solidified soil scour protection of the present invention comprises the following steps:

[0030] Step S1: A test model is constructed based on the prototype site's hydrogeological conditions. Transparent model piles are erected in the grit chamber of the flume. Soil is laid around the model piles in layers, compacted layer by layer, and laid to a predetermined elevation (generally around 30 cm). Ensure that scouring does not penetrate the soil layer. Water is slowly added to submerge the soil surface and allowed to soak for 24 hours to saturate it.

[0031] Specifically, the test often focuses on the main contradiction and is designed according to the gravity similarity criterion, that is, the Froude number (Fr) between the test model and the prototype is equal:

[0032]

[0033] Where g is the acceleration due to gravity; V and L are the velocity and size of the object, respectively; the subscripts m and p represent the model and prototype, respectively; and the model length ratio is Lp / Lm=λL.

[0034] The similarity principle described above can be used to design a typical flume model test. However, because the presence of flume walls can disrupt the flow structure in the surrounding area, this similarity principle alone cannot be used effectively for all similarity designs. To avoid this effect on the model in the test section, the full sand model similarity law can be used for design. The calculation of the various similarity scales is as follows:

[0035] The geometric scale of the test model is calculated according to formula (2), the scale is calculated to be 100, and the scale is selected to be 100;

[0036] λ L =λ H (2)

[0037] The test model test velocity scale is calculated according to the calculation formula (3), and the scale is 10, so the scale 10 is selected;

[0038]

[0039] The sand particle scale was used in the experimental model test and calculated according to formula (4);

[0040]

[0041] Calculate the ratio of the model diameter to the median sediment particle size using a scale of 2.13 and a scale of 0.5, i.e. D / d 50 When it is greater than 25, the median particle size of the model sand has little effect on the equilibrium scour depth. Considering the operability and test effect of the test, the sand particle size used in the soil layer of the model is 0.15mm, and the material is quartz sand, which meets the D / d 50 >25;

[0042] The test time of the test model is calculated according to the calculation formula (5), and the scale is 22.01. The scale is 22.01;

[0043]

[0044] In the above calculation formula, λ L is the horizontal length scale, λ H is the vertical length scale, representing the proportional relationship between the prototype (p) and the test model (m) in the horizontal and vertical directions respectively. γ0 is the dry bulk density of the material, γ s is the bulk density of the material, γ is the bulk density of water, and this criterion is adopted for all model scale problems involved in this experiment.

[0045] Step S2, such as Figure 3 , an ADV flow velocity sensor is placed 10 to 20 cm in front of the model pile. The probe of the ADV flow velocity sensor is 3 to 5 cm away from the bottom of the water tank. A video recorder is placed in the center of the model pile to record the flow velocity data and image data during the test. According to the characteristics of the local flow field around the foundation during the scouring process, a total of 6 depth measurement points are set, with a spacing of 60°. Through these 6 measurement points, the depth of the scouring pit can be basically reflected. Figure 4 shown.

[0046] Step S3, making solidified soil: according to the experimental design working conditions, a certain amount of soil, cement and water are measured. The determination of the water content of the solidified soil should ensure the workability of the sample so that the sample is easy to shape. Specifically, a cement mixer is used to mix the weighed soil, cement and water. Before starting to mix, first pour the weighed water into the mixing pot, then pour in the mixed cement soil powder, stir slowly for 120 seconds, pause for 15 seconds, scrape the soil on the pot wall and the mixing head of the cement mixer, and then stir quickly for 120 seconds to obtain a uniform solidified soil slurry. Among them, the reinforced soil sample for the test can be silt clay, and the solidified soil strength is designed according to the test.

[0047] In step S4, water is slowly added to the water tank according to the test working condition design until the corresponding water level is reached. The water tank flow-generating equipment is adjusted to make the water flow reach the designed flow rate. The water is flushed at the corresponding flow rate until the scouring pit develops equilibrium. When the scouring depth does not change or changes by less than 1 mm within 1 hour, it can be considered that the scouring pit has reached equilibrium.

[0048] Step S5: Determine the amount of solidified soil required based on the scope and depth of the scour pit and the type of solidified soil placement specified in the test conditions. Blow the solidified soil into the scour pit based on the scope and depth of the scour pit, controlling the scope and elevation to meet the test design requirements.

[0049] Step S6: Observe and measure the development of scour during the solidification process. Record the depth of the scour pit at regular intervals. If the scour pit depth does not change or changes by less than 1 mm within 1 hour, the scour pit is considered balanced and the test is terminated. Record the scour depth and scour range at each measuring point around the model pile.

[0050] The above embodiments are only used to illustrate the present invention, rather than to limit the present invention. Those skilled in the art may make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also fall within the scope of the present invention and should be defined by the claims.

Claims

1. A method for indoor testing of pile foundation solidified soil scour protection, characterized in that: include: Step S1: A test model is constructed based on the hydrogeological conditions of the prototype site. Transparent model piles are erected in the sedimentation tank of the water tank, and a soil layer is laid around the model piles. The sand particle size of the soil layer is 0.15 mm and the material is quartz sand. Step S2: an ADV flow velocity sensor is arranged in front of the model pile, and a video recorder is arranged inside the model pile to record flow velocity data and image data during the test; the ADV flow velocity sensor is arranged 10 to 20 cm in front of the model pile, and the probe of the ADV flow velocity sensor is 3 to 5 cm away from the bottom of the water tank; 6 depth measurement points are set around the model pile, and the measurement points are spaced 60 degrees apart; Step S3, producing solidified soil: using a cement mixer to mix the weighed soil, cement, and water. Before starting the mixing, first pour the weighed water into the mixing pot, then pour the mixed cement soil powder into it. Stir slowly for 120 seconds, pause for 15 seconds, scrape the soil off the pot wall and the mixing head of the cement mixer, and then stir rapidly for another 120 seconds to obtain a uniform solidified soil slurry. Step S4: Slowly add water to the water tank until the water level reaches the desired level. Adjust the water flow generator to achieve the designed flow rate. The water is flushed until the scour pit reaches equilibrium at the desired flow rate. The scour pit is considered to be in equilibrium when the scour depth does not change or changes by less than 1 mm within 1 hour. Step S5: Blowing solidified soil into the scouring pit according to the scope and depth of the scouring pit, and controlling the scope and elevation to meet the test design requirements; Step S6: Observe and measure the development of scouring during the solidification process of the solidified soil until the scouring pit develops into equilibrium, and record the scouring depth and scouring range of each measuring point around the model pile.

2. The indoor test method for scour protection of pile foundation stabilized soil according to claim 1, characterized in that: In step S1, the soil layer is laid in layers and compacted layer by layer. After laying to a preset elevation, water is slowly injected to submerge the surface of the soil layer and soaked for 24 hours to saturate it.

3. The indoor test method for scour protection of pile foundation solidified soil according to claim 1, characterized in that: The Froude numbers between the test model and the prototype are equal, Where g is the acceleration due to gravity; V and L are the velocity and size of the object, respectively. The subscripts m and p represent the test model and prototype, respectively. The length of the model is L. p / L m =λ L .

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