CN103091471A - Model for promoting solidification of hydraulic fill and test method for model - Google Patents

Abstract

A model for promoting solidification of hydraulic fill comprises a model barrel, a load plate and a simulation material, wherein the bottom and the body of the model barrel are sealed integrally; the top of the model barrel serves as the only drainage path; the load plate is matched with the top surface of the barrel in size so as to prevent the soil mass in the simulation material from overflowing from the slit between the edge of the load plate and the barrel wall; a plurality of drill holes are formed in the load plate along the radial direction; and the simulation material comprises test soil and a drainage plate 3D grid, and is arranged in the model barrel. The model provided by the invention can be used for studying the influence of the grid parameters of the plastic drainage plate on the drainage solidification effect so as to obtain the optimized method for promoting drainage solidification of the hydraulic fill. The invention further discloses the specific content of the method.

Description

A Model of Accelerated Consolidation of Scouring Fill and Its Test Method

technical field

The invention belongs to the technical field of geotechnical engineering, and relates to a model for consolidation of flushing fill soil and a test method thereof.

Background technique

Flush fill (also known as dredging fill) is the sedimentary soil formed by hydraulic flushing and filling of sand, that is, when dredging and dredging river channels, dredgers are used in a planned way to enclose a large amount of water in the sand and sand through mud pumps, and blow them away. A kind of fill formed on both sides of the river. In recent years, with the rapid development of my country's economy, the pace of urbanization has been accelerating, and the demand for land resources has become increasingly urgent. In coastal areas and rivers and lakes, the dredged silt and sand have been used to make land, which has become a relief land for coastal cities. An efficient approach to resource constraints. At present, the utilization scale of flushing land areas is increasing. For example, the construction of Lingang New City in Shanghai is mostly carried out on flushing land, and coastal cities such as Tianjin, Zhuhai, Guangzhou, and Shenzhen are all using flushing land. Carry out municipal construction and port construction.

The formation method of flush fill is special, and it has the characteristics of large void ratio, high natural water content, high compressibility, and low permeability. Therefore, the engineering properties of flush fill have obvious individuality. The specific performance is that its self-weight consolidation time is long, the consolidation settlement of the soil filling is large after construction, and the deformation of the filling soil is obvious under the action of external loads. How to accelerate the drainage and consolidation of the filling soil, reduce the consolidation settlement after construction, and avoid The engineering geological hazards caused by the consolidation, deformation and failure of the filled foundation are currently an important issue facing the areas of flushing and filling.

Regarding the drainage and consolidation treatment of the flushing and filling soil foundation, some work has been carried out at home and abroad, such as: Strip drains in dredged material placement areas.International Conference on Dredging and Dredged Material Placement, 1, pp.420–429); Sato’s cylindrical self-weight consolidation test in 2001 used plastic drainage boards to accelerate drainage consolidation (Acceleration of self-weight consolidation for dredged clay using plastic board drainage. Proceedings of the International Offshore and Polar Engineering Conference, 2, pp.715–721.); Nagaoka also applied the vertical drainage body of plastic drainage board to the self-weight consolidation of dredging fill (Accelerated self- weight consolidation mechanism for dredged clay using dewatering method and plastic board drains. Proceedings of the International Offshore and Polar Engineering Conference, pp. 703–708.). In addition, there are also methods such as horizontal plastic drainage belt consolidation fluid state blowing, vertical drainage body combined with surcharge, and strong calendar combined with vacuum preloading.

The above method has played a certain role in the drainage and consolidation of flushing and filling soil, but there are also some shortcomings, such as well resistance effect and smearing effect will reduce the permeability number, and the insertion of drainage boards will cause disturbance to the soil, which will affect Drainage effect, the shape of the plastic drainage board will also affect the drainage effect. At the same time, the above-mentioned treatment methods often require the flushing soil to have a certain bearing capacity, which seems powerless for the freshly filled flushing soil.

Contents of the invention

In view of the above-mentioned technical defects and adverse effects during application, the purpose of the present invention is to provide a model and a test method for accelerating the consolidation of flushing fill through the three-dimensional grid of the pre-embedded plastic drainage board.

Technical scheme of the present invention is as follows:

A model for accelerating the consolidation of flushing fill through the three-dimensional grid of the pre-embedded drainage board. The model includes a model bucket, a load plate and simulation materials; the bottom and body of the bucket are completely sealed, and the top of the bucket is the only drainage channel , the size of the load plate is consistent with the top surface of the barrel, so that the soil in the simulated material cannot overflow from the gap between the edge of the load plate and the wall of the barrel, and the load plate is provided with a number of boreholes in the radial direction; The simulation materials include test soil and three-dimensional grids of drainage boards, which are placed in the model bucket.

The barrel wall of the model barrel is provided with a barrel wall support, and the barrel wall support is provided with a fixed support along the diameter direction of the barrel top.

The model barrel is a cylinder, and the height of the cylinder is 0.6 to 2 times the diameter.

The test soil is sandy silt.

The three-dimensional grid of the drainage board is fixedly connected with the horizontal grid formed by the drainage board and the vertical drainage board, and the drainage board in the three-dimensional grid of the drainage board has multiple drainage channels.

The present invention also proposes a test method for accelerating filling soil consolidation through pre-embedded plastic drainage board three-dimensional grid, which includes the following steps: step 1, according to the size and spacing of the simulated drainage board and the plane size of the model bucket, determine each Similarity constant; step 2, prepare model materials, including test soil, drainage board grid; step 3: make model box, prepare simulation materials, measurement equipment and data acquisition equipment; step 4, conduct model test, including the following steps: (1 ) Preparation of backfill soil and loading into model buckets in layers; (2) Pre-embedded three-dimensional grid of drainage board; (3) Installation of measuring equipment; (4) Loading and measurement.

Step 1 also includes determining the influencing factors that need to be studied, and determining the geometric similarity constants according to the consolidation theory, the size and spacing of the simulated drainage boards, and the plane size of the model bucket.

The measuring equipment includes an earth pressure gauge, a pore pressure gauge, a subsidence scale, and a dial indicator. The pore pressure gauge and the earth pressure gauge are respectively arranged at the bottom and the middle of the model barrel, and the faces of the two directly in contact with the medium are facing upwards. The earth pressure gauge or the upper and lower ends of the pore pressure gauge are all laid with a fine sand cushion.

The dial indicators are respectively placed on the load plate and layered settlement rods to record the settlement deformation of the soil surface and the deformation of the soil layer located in the middle of the test barrel.

Further, the filling soil is obtained by adding water to the test soil and fully mixing, and the water content of the filling soil is determined according to the requirements of the experiment.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

The invention can carry out experimental research on the consolidation of the three-dimensional grid of the pre-embedded plastic drainage board to accelerate the flushing and filling, reduces the uncertainty of actual construction, has the characteristics of wide versatility and high accuracy, and creates good economic benefits and scientific research value .

Description of drawings

Fig. 1 is a schematic structural diagram of the test model of the embodiment of the present invention.

Among them: 1-upper heap load; 2-diameter support; 3-top sand cushion; 4-settlement mark; 5-earth pressure gauge (or hole pressure gauge); 6-three-dimensional grid of plastic drainage board; 7- Loading plate; 8-model iron drum; 9-dynamic strain gauge.

Fig. 2 is a schematic diagram of the three-dimensional grid of the plastic drainage board shown in Fig. 1 . Among them: 10-vertical grid; 11-horizontal grid.

Detailed ways

Embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

Please refer to Figures 1, 2, and 3. This embodiment is a model device for pre-embedded plastic drainage board three-dimensional grids to accelerate the consolidation of flushing and filling soil. It includes a model bucket, simulation materials, measuring equipment and data acquisition equipment. Placed in the model bucket Simulate materials, and set measuring equipment in the model bucket for parameter measurement. The data acquisition equipment is connected to the measuring equipment, and the parameters measured by the measuring equipment are collected and processed.

Model barrel 8 is irony, is made of barrel body, barrel wall support 2, load plate 7. The bottom of the barrel is completely sealed, and the top of the barrel is the only drainage channel. The barrel wall support 2 has two iron frames that protrude along the diameter direction, and is used for fixing the dial indicator. After loading the soil, it is necessary to use a load plate 7 whose size matches the size of the top surface of the bucket to cover, and use the upper part of the load plate 7 to load with static weights. There are two load plates 7 in the radial direction, left and right, each with a diameter of about 5 cm. The drilled holes are respectively used for pre-embedded pressure gauge winding and settlement rods for layered settlement mark 4. The settlement mark 4 is connected with the dial indicator, and parameters such as earth pressure and layer drop can be read from the dial indicator.

The simulated materials include test soil, drainage board and geotextile. The test soil is sandy silt. According to the size of the model bucket, choose to use the corresponding size of the drainage board, in order to enhance the drainage capacity of the device, each drainage board is equipped with three drainage channels, and each drainage board is wrapped with a geotextile that matches its size, and then bound, and then made Three-dimensional grid of drainage board6. When the three-dimensional grid 6 has many layers, use geotextile strips to tie the horizontal grid and the vertical drainage board tightly.

In order to monitor the growth of earth pressure inside the soil mass and the dissipation law of pore water pressure during the drainage and consolidation process of flush fill soil, the measuring equipment should include earth pressure gauge 5 and pore pressure gauge. When burying the earth pressure gauge 5, the working surface should be facing up (the so-called working surface is the surface in direct contact with the medium). Since the earth pressure gauge 5 may sink or deflect a small amount in the model soil, a fine sand cushion 3 is laid on its upper and lower ends in the test, and attention should also be paid to the protection of the cables. A total of two dial gauges were installed to record the settlement deformation of the soil surface and the deformation of the soil layer in the middle of the test barrel respectively. One was placed on the load plate, and the other was placed on the settlement bar, which penetrated into the soil. About 35cm.

Through multiple tests, it can be concluded that the length, width and height of the three-dimensional grid 6 of the drainage board can be changed to obtain the most favorable size combination for the drainage and consolidation of the backfill. Therefore, it is particularly important to strictly control other test conditions. Fixing the amount of water and soil can improve the comparability of experimental results. The model bucket should be the same as the actual engineering situation as much as possible to reduce the soil confinement.

The present invention also proposes a test method for accelerating the consolidation of flushing and filling soil through the three-dimensional grid of the pre-embedded plastic drainage board, which includes the following steps:

The first step is to determine the influencing factors required for the research according to the purpose of the research. According to the consolidation theory, considering the size and spacing of the simulated drainage board and the plane size of the model bucket, the similarity theory is used to determine the geometric similarity constants. When determining the geometric similarity constant, the following requirements are mainly met:

(1) The size of the drainage board should be compatible with the size of the model bucket;

(2) The size of the drainage board shall meet the requirements of boundary conditions;

(3) The size of the drainage board should meet the requirements of the treatment depth;

(4) When determining the size of the drainage board, the convenience of the test operation should also be considered;

(5) The size of the model should be coordinated with the actual soil thickness and simulation time of the project.

The second step is to determine the model materials, including test soil, drainage board and geotextile; the model soil is sandy silt, in order to obtain the effect of filling soil, add water to fully stir. The moisture content requirements of each barrel of soil are similar to ensure that the tests are neat and comparable. The moisture content of the model soil configured in the test was controlled above 38%. The soil sample with a moisture content of 38% has a weight of about 17.7kg/m ³ , the calculated void ratio is about 1.11, and the specific gravity of soil particles is 2.7, so the saturation is about 0.924, which is considered saturated. The plastic drainage board is a common 10cm wide drainage board on the construction site, and the drainage board used in the model test is 1cm wide. The specific production method is as follows:

(1) Cut the purchased 10cm wide drainage board into about 1cm wide, and control each drainage board to have three drainage channels.

(2) Each drainage board is wrapped with a geotextile matching its size and stapled together.

(3) Use staples to make the grid of the drainage board. When encountering a network frame with many layers, use geotextile strips to tie the horizontal grid and the vertical drainage board tightly.

The third step: pre-preparation for the model test, including making model boxes, preparing test instruments, simulation materials, measuring equipment and data acquisition equipment;

The fourth step is to conduct model tests, including the following steps:

(1) Prepare the flush fill soil and put it into the model bucket and pre-embed the three-dimensional grid of the drainage board; (2) Bury the pressure gauge; (3) Level the surface of the model soil and spread sand; (4) Install the dial gauge; (5) Load and measurement.

The following is an example to set forth the test method of the present embodiment with the specific test scheme:

1. Considering that the width of the plastic drainage board in the actual project is mostly 10cm and the size of the model bucket, the similarity constant n of this test is determined to be 10. That is, the width of the plastic drainage belt is set at 1cm. Determine the test parameters as follows:

Table 1 Test parameter list

parameter similarity ratio Model prototype unit drain board width 1/n 1 10 cm Surface area of flushing soil 1/n ² 0.228 22.9 m ² Fill soil thickness 1/n 0.75 7.5 m Preload 1/n ³ 0.392 392 kN

After the above similar scale is determined, the soil range of the actual project that can be represented by the model test can be determined and the time required for its drainage consolidation process to be roughly stable can be estimated

2. uniform design

The drainage consolidation test of the pre-embedded three-dimensional grid in the flushing soil carried out by the present invention includes three factors, that is, the length, width and height of the three-dimensional grid of the drainage plate. Considering the size of the model bucket, the drainage board and the time required for the test, five levels are proposed for each factor. The test index is the duration of consolidation deformation stability. Since the number of trials in an orthogonal experiment is at least the square of the number of levels, it is more reasonable to use a uniform design for multifactorial multilevel experiments. At the same time, when performing regression analysis on the test results, the uniform design can not only calculate the main effect and interaction effect of the factors in the regression model, but also predict the level value of each factor when the test has the best effect, and provide a more optimized reference value.

Table 2 Test schedule

serial number x ₁ /m x ₂ /m x ₃ /m T(min) 1 0.40 0.20 0.23 2 0.35 0.12 0.35 3 0.20 0.35 0.65 4 0.12 0.17 0.70 5 0.08 0.09 0.175

The above is the arrangement of the five conventional experiments. In order to better compare and analyze the effect of the three-dimensional grid of the drainage board on the filling soil foundation, and to make the experiment more complete, a blank test was added, that is, the model soil without the drainage board was under load. Under the drainage consolidation test.

3. Test layout: model making; layout of earth pressure gauges and pore pressure gauges; layout of settlement observation points.

(1) Model making

When making the model, it is necessary to ensure that the filling height of each test is the same. The cylindrical model iron barrel in the test is composed of the barrel body, the barrel wall support, and the load plate. The bottom of the barrel is completely sealed, and the top of the barrel is the only drainage channel. There are two protruding iron frames along the diameter of the barrel wall, which are used to fix the dial indicator. After the soil is loaded, it is necessary to use a load plate whose size matches the size of the top surface of the barrel to cover. The load plate has two holes with a diameter of about 5 cm along the radial direction, which are used for pre-embedded pressure gauge winding and layered settlement. pole.

(2) Arrangement of earth pressure gauge and pore pressure gauge

According to the consolidation theory, during the drainage consolidation process, the pore water pressure will gradually decrease, while the earth pressure will gradually increase. In order to further clarify the change of stress in the soil and help determine the settlement stability time, a hole piezometer and an earth pressure gauge are arranged at the bottom and middle of the model bucket. When the earth pressure is buried at 5 hours, the working surface is facing up, and fine sand cushions 3 are laid on its upper and lower ends. There are permeable stones at both ends of the piezometer. After the pore water seeps into the piezometer, the corresponding sensitivity data is transmitted to the strain gauge 9 . According to the measured micro-strain, the actual value of the pore pressure can be obtained. The burial and installation process of the piezometer is the same as that of the earth pressure gauge.

(3) Layout of settlement observation points

In this test, the immediate settlement value of the soil was measured with a dial indicator after loading, and layered settlement rods were installed to obtain the settlement of the soil layer at 1/2 depth, which provided a reference for the final settlement and stability duration.

4. Preparation of test materials: test soil, plastic drainage board

In order to obtain the effect of flushing and filling soil, add water to fully stir the test soil. The moisture content requirements of each barrel of soil are similar to ensure that the tests are neat and comparable. The moisture content of the model soil configured in the test was controlled above 38%.

5. Pre-embedded plastic drainage boards, piezometers, and earth pressure gauges.

(1) Pre-embedded three-dimensional grid of plastic drainage board

The diameter of the bottom surface of the test barrel is 54cm, and the height is about 85cm. The three-dimensional grid 6 volume of the drainage board is generally determined as 40*35*70cm. First, add the prepared test soil evenly into the model bucket, and add the bottom plastic drainage board when the model soil is about 5cm away from the bottom of the bucket. With the addition of the model soil, the three-dimensional grid of the drainage board is completed. Add soil until it submerges the grid of the horizontal drainage board, and the vertical drainage board needs to protrude a little. In order to optimize its drainage effect and prevent the soil from being squeezed, a sand layer about 0.5cm thick is evenly laid on the soil surface, and then the excess length of the vertical drainage board is cut off with scissors. After completion, slowly cover the load plate on it. The size of the load plate should be slightly smaller than the size of the top of the barrel. If the control is not done properly, the soil will easily overflow from the gap between the edge of the load plate and the barrel wall.

(2) Embedding of pore pressure gauges and earth pressure gauges

Water pressure gauges and earth pressure gauges were respectively buried at two depths of 10cm and 40cm from the bottom of the barrel. The pre-embedded pressure gauge requires its pressure surface to be pressurized horizontally, and a small amount of sand can be spread under it to help it stabilize its position.

6. Test monitoring: Consolidation deformation monitoring, pore water pressure and earth pressure monitoring:

Consolidation deformation monitoring:

The consolidation and drainage of the model soil is a slow and long-term process, and the settlement deformation of the model soil is observed by using a dial indicator. In this test, two dial gauges were installed to record the settlement deformation of the soil surface and the deformation of the soil layer in the middle of the test barrel respectively. That is, one is connected with the load plate 7, and the other is connected with the layered settlement rod, and the layered settlement rod penetrates into the soil about 35cm. The settlement observation starts after loading. Due to the rapid drainage in the early stage, the settlement is relatively fast, and the measurement and reading interval is one minute, and then gradually becomes longer. Each trial lasted approximately one week.

Pore water pressure and earth pressure monitoring: monitor the pore water pressure and earth pressure to obtain the actual pressure value. In order to compare the consolidation drainage effect and obtain the strength index of the model soil after treatment, samples were taken at three different depths each time the model bucket was disassembled, and indoor soil tests were carried out, including moisture content test, fast shear test and standard consolidation test.

Those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described here to other embodiments without creative effort. Therefore, the present invention is not limited to the embodiments herein. Improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims (10)

1. A model for accelerating the consolidation of flush fill, characterized in that: The model includes model buckets, load plates and simulated materials; The bottom and body of the model bucket are completely sealed, and the top of the bucket is the only drainage channel. The size of the load plate is consistent with the top surface of the bucket, so that the soil in the simulated material cannot be separated from the edge of the load plate and the wall of the bucket. The gap between overflows, and the load plate is provided with a number of boreholes along the radial direction; The simulated materials include test soil and three-dimensional grids of drainage boards, which are placed in the model bucket. 2. The model according to claim 1, characterized in that: the barrel wall of the model barrel is provided with a barrel wall bracket, and the barrel wall bracket is provided with a fixed bracket along the diameter direction of the barrel top. 3. The model according to claim 1, characterized in that: the model barrel is a cylinder, and the height of the cylinder is 0.6 to 2 times the diameter. 4. The model according to claim 1, characterized in that: said test soil is sandy silt. 5. The model as claimed in claim 4, characterized in that: the three-dimensional grid of the drainage plate is fixedly connected with the vertical drainage plate by the horizontal grid formed by the drainage plate, and the drainage in the three-dimensional grid of the drainage plate The board has multiple drainage channels. 6. A test method for accelerating the consolidation of flushing fill, comprising the following steps: Step 1, according to the size and spacing of the simulated drainage board and the plane size of the model bucket, determine the similarity constants; Step 2, preparing model materials, including test soil and drainage board grid; Step 3: Make the model box, prepare simulation materials, measuring equipment and data acquisition equipment; Step 4, carry out model test, including the following steps: (1) Prepare the flushing soil and put it into the model bucket layer by layer; (2) Pre-embedded three-dimensional grid of drainage board; (3) Install measuring equipment; (4) Loading and measurement. 7. The test method as claimed in claim 6, characterized in that: step one also includes determining the influencing factors of the required research, and determining each geometric similarity constant; the model material described in step 2 is the model described in claim 1. 8. test method as claimed in claim 7 is characterized in that: described measuring equipment comprises earth pressure gauge, hole piezometer, subsidence scale, dial gauge, respectively arranges described hole piezometer and middle part at model barrel bottom and As for the earth pressure gauge, the faces of the two directly in contact with the medium face upward, and the upper and lower ends of the earth pressure gauge or the pore pressure gauge are laid with fine sand cushions. 9. The test method according to claim 8, characterized in that: said dial indicator is respectively placed on the load plate and on the layered settlement bar for recording the settlement deformation of the soil surface and the soil in the middle of the test bucket. layer deformation. 10 . The test method according to claim 7 , characterized in that: the filling soil is fully mixed with water for testing, and the water content of the filling soil is determined according to the requirements of the experiment. 11 .

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