CN113959842A - Indoor model test device and method for bearing characteristics of composite foundation under salt expansion and salt dissolution - Google Patents
Indoor model test device and method for bearing characteristics of composite foundation under salt expansion and salt dissolution Download PDFInfo
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- 238000012360 testing method Methods 0.000 title claims abstract description 46
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- 238000004090 dissolution Methods 0.000 title claims abstract description 17
- 239000002689 soil Substances 0.000 claims abstract description 131
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- 238000005485 electric heating Methods 0.000 claims abstract description 35
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- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims abstract description 8
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- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
- G01B5/30—Measuring arrangements characterised by the use of mechanical techniques for measuring the deformation in a solid, e.g. mechanical strain gauge
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract
The invention discloses an indoor model test device for bearing characteristics of a composite foundation under salt swelling and salt dissolution, which comprises a model box, a composite foundation model, a loading system and a measuring system. The composite foundation model comprises a plurality of reinforcing piles arranged in foundation soil, wherein the foundation soil is saline soil, and electric heating pipes are arranged in the saline soil; the loading system comprises a broken stone reinforced cushion layer, embankment filling soil and a loading plate, and vertical loading equipment is arranged on the loading plate; the upper part of the model box is provided with a spraying device; the measuring system comprises a displacement dial indicator, a soil pressure cell, a signal acquisition device and the like. The temperature of the saline soil can be raised through the electric heating pipe in the test process by using the device, so that the aim of salt expansion is fulfilled; and spraying water to the composite foundation model in a circulating manner through a spraying device to achieve the purpose of salt dissolution. The method can be used for researching the bearing deformation characteristic of the composite foundation under the conventional and salt swelling and salt solution conditions, the test method is simple, the result is more consistent with the actual engineering, and the problem that the conventional test equipment cannot simulate the salt swelling and salt solution effect is solved.
Description
Technical Field
The invention belongs to the technical field of foundation treatment and geotechnical tests, and particularly relates to a system and a method for simulating the bearing characteristic of a composite foundation under the action of salt swelling and salt dissolution.
Background
The composite foundation treatment technology of different pile types is widely applied in China, and the bearing deformation characteristic of the composite foundation treatment technology is deeply known. However, the bearing deformation characteristic in the high salt region is not clear: because of factors such as natural environment, large amount of hydration heat generated by the reaction of cement and saturated soft soil, the solubility of soluble salt in soil is influenced by the increase and decrease of temperature, and further the phenomenon of salt expansion and salt dissolution is generated, and the bearing deformation characteristic of the composite foundation is influenced. The phenomenon directly causes the reduction of engineering quality, but related research methods are deficient. Therefore, a composite foundation bearing characteristic indoor model test device and method capable of considering the salt swelling and salt dissolving effects are needed to measure the bearing deformation characteristic change rule of the composite foundation under the influence of the factors such as salt swelling and salt dissolving.
Disclosure of Invention
Aiming at the prior art, the invention provides a system and a method for simulating the bearing characteristic of a composite foundation under salt swelling and salt dissolving, which are used for researching the change rule of the bearing characteristic of the composite foundation under the influence of factors such as salt swelling and salt dissolving through an indoor model test and providing a theoretical basis for the actual engineering of the composite foundation.
In order to solve the technical problem, the invention provides an indoor model test device for the bearing characteristic of a composite foundation under salt expansion and salt dissolution, which comprises a model box, wherein a composite foundation model, a loading system and a measuring system are arranged in the model box; the composite foundation model comprises N reinforcing piles arranged in foundation soil, the foundation soil is saline soil arranged indoors, and electric heating pipes are arranged in the foundation soil; the loading system comprises a broken stone reinforced cushion layer, embankment filling soil and a loading plate which are arranged in a certain range at the top of the reinforced pile and are sequentially arranged from bottom to top, and a vertical load loading unit is arranged on the loading plate; a spraying device is arranged at the upper part of the model box, the spraying range of the spraying device covers the gravel reinforcement cushion layer, and the area of the gravel reinforcement cushion layer covers the foundation soil; the measuring system comprises 2 displacement dial indicators, 2N soil pressure boxes, N pore pressure sensors and signal acquisition equipment; the 2 displacement dial indicators are arranged on the upper surface of the load bearing plate, the 2N soil pressure boxes are respectively arranged at the bottom and the top of each reinforcing pile, and the N pore pressure sensors are arranged in the foundation soil and are respectively positioned right below each soil pressure box; and the displacement dial indicator, the pore pressure sensor and the soil pressure box are all connected to the signal acquisition equipment.
Further, the invention relates to an indoor model test device for the bearing characteristic of a composite foundation under salt swelling and salt dissolution, wherein:
the vertical load loading unit has one of the following two structures: adopting a load weight or a vertical load loading unit which comprises a counter-force beam and servo motor loading equipment supported at the top of the model box; the vertical load is applied step by utilizing load weights or servo motor loading equipment so as to simulate the stress condition of piles and soil.
The 2 displacement dial indicators are respectively arranged at two opposite angle points of the load plate.
The signal acquisition equipment is externally connected to computer equipment, and the computer equipment automatically reads and stores the acquired signals and converts the acquired signals into foundation settlement and pile/soil pressure data.
The mass percentage of the salt content in the foundation soil is 0-15%, and 0 is not included.
The reinforcing pile is any one of a powder-sprayed pile, a gravel pile and a scattered pile, and is cast in situ in foundation soil or is installed in the foundation soil after being prefabricated; the reinforcing piles are reduced in size from 1:20 to 1:100 in terms of pile diameter, length and pile spacing according to the size of the actual project.
Dissolving salt in the foundation soil in the model box by circularly and regularly sprinkling water through the spraying device so as to simulate a salt dissolving process; the water content of the soil body of the foundation soil is reduced through the heating effect of the electric heating pipe, and salt particles in the foundation soil are crystallized, so that the aim of salt expansion is fulfilled.
The area ratio of the load plate to the broken stone reinforced cushion layer is 1:3, so that vertical load is uniformly distributed on the foundation soil.
Meanwhile, the invention provides a method for testing by using the indoor model test device for the bearing characteristic of the composite foundation under salt swelling and salt dissolution, which comprises the following steps:
step 1) before the test is started, vertically arranging the electric heating pipes in a model box in advance; using indoor prepared salinized soil as foundation soil, fully washing salt, airing and crushing soil body of the foundation soil, calculating water adding amount and salt adding amount according to test requirements, uniformly stirring, and then filling in a model box in layers; in the filling process, soil pressure boxes with the same number as the reinforcing piles are respectively placed at the positions corresponding to the bottom surfaces and the top surfaces of the reinforcing piles, and a pore pressure sensor is placed under each soil pressure box; the materials of the reinforced pile comprise fly ash, gypsum, mineral powder and cement, wherein the mass fraction of the cement is 20%, and the mass fractions of the fly ash, the gypsum and the mineral powder are selected according to actual engineering requirements; preparing a reinforcing pile in foundation soil by stirring the materials, and maintaining for 28 days under the conditions of constant temperature and constant humidity; placing a broken stone reinforcement cushion layer in a certain range of the pile top of the reinforcing pile, paving embankment filling soil on the broken stone reinforcement cushion layer, simulating the load condition borne by a real embankment, placing a load plate on the embankment filling soil, wherein the area ratio of the load plate to the broken stone reinforcement cushion layer is 1: 3; respectively placing 2 displacement dial indicators at two diagonal points of the load plate;
step 2) starting a test, preloading the foundation through servo motor loading equipment, and then loading step by step; in the step-by-step loading process, the electric heating pipe is used for heating the foundation soil to reduce the water content in the soil body of the foundation soil, so that the aim of salt expansion is fulfilled, and the heating temperature is determined according to the test requirement; meanwhile, the foundation soil is infiltrated by sprinkling water through the upper spraying device, so that the salt dissolving effect is realized;
and 3) recording the changes of stress, strain and settlement of the foundation soil body and the reinforcing piles in the salt solution and salt expansion processes, and further analyzing the influence of the salt expansion and salt solution effect on the bearing deformation characteristic of the composite foundation.
Further, in the step 1) of the method, when the electric heating pipes are arranged, 2 electric heating pipes are respectively arranged on the left side and the right side of the area of the N reinforcing piles, the diameter of each reinforcing pile is D, the distance between each two electric heating pipes on each side and the reinforcing pile on the outer side is D, and D is larger than 3D; the length of the electric heating pipe is the same as the thickness of foundation soil filled in the model box.
Compared with the prior art, the invention has the beneficial effects that:
by simulating the stress condition of the composite foundation under the action of different stresses and salt-soluble salt expansion cycle times and measuring parameters such as load plate settlement and soil body stress at different depths under the action of different salt-soluble salt expansion, the information such as pile-soil stress ratio and foundation settlement can be clearly obtained, and the load transfer mechanism and the long-term deformation characteristic of the composite foundation are disclosed.
Drawings
FIG. 1 is a schematic view of a model test apparatus according to the present invention;
fig. 2 is a schematic layout view of the electric heating pipe and the reinforcing piles and the soil pressure cell shown in fig. 1.
In the figure: 1-load plate, 2-embankment filling, 3-broken stone reinforced cushion layer, 4-displacement dial indicator, 5-foundation soil, 6-reinforced pile, 7-soil pressure box, 8-model box, 9-counterforce beam, 10-servo motor loading equipment, 11-spraying device, 12-electric heating pipe, 13-pore pressure sensor and 14-ceramic thermal insulation material.
Detailed Description
The invention will be further described with reference to the following figures and specific examples, which are not intended to limit the invention in any way.
As shown in fig. 1 and fig. 2, the indoor model test device for the bearing characteristics of the composite foundation under salt expansion and salt solution provided by the invention comprises a model box 8, wherein a composite foundation model, a loading system and a measuring system are arranged in the model box 8.
The composite foundation model comprises N reinforcing piles 6 arranged in foundation soil 5, the foundation soil 5 is saline soil arranged indoors, and the salt content in the foundation soil 5 is 0-15% by mass and does not include 0. An electric heating pipe 12 is arranged in the foundation soil 5. The reinforcing pile 6 is any one of a powder-blasting pile, a gravel pile and a scattered pile, and is cast in situ in the foundation soil 5 or is installed in the foundation soil 5 after being prefabricated; the reinforcing piles 6 are scaled down in a ratio of 1:20 to 1:100 in terms of pile diameter, length and pile spacing according to the size of the actual project.
The loading system comprises a broken stone reinforced cushion layer 3, embankment filling 2 and a load plate 1 which are arranged in a certain range at the top of the reinforced pile 6 and are sequentially arranged from bottom to top, and the area ratio of the load plate 1 to the broken stone reinforced cushion layer 3 is 1:3, so that vertical load is uniformly distributed on foundation soil 5. The load carrying plate 1 is provided with a vertical load loading unit; the vertical load loading unit has one of the following two conditions: firstly, adopting a load weight; secondly, the vertical load loading unit comprises a counterforce beam 9 and a servo motor loading device 10 which are supported on the top of the model box 8, as shown in fig. 1. The vertical load is applied step by utilizing load weights or servo motor loading equipment so as to simulate the stress condition of piles and soil. And a spraying device 11 is arranged at the upper part of the model box 8, the spraying range of the spraying device 11 covers the gravel reinforcement cushion layer 3, and the area of the gravel reinforcement cushion layer 3 covers the foundation soil 5. Salt in the foundation soil 5 in the model box 8 is dissolved by circularly and regularly sprinkling water through the spraying device 11, so that a salt dissolving process is simulated; the water content of the soil body of the foundation soil 5 is reduced through the heating effect of the electric heating pipe 12, and salt particles in the foundation soil are crystallized, so that the purpose of salt expansion is achieved.
The measuring system comprises 2 displacement dial indicators 4, 2N soil pressure boxes 7, N pore pressure sensors 13 and signal acquisition equipment; the 2 displacement dial indicators 4 are arranged on the upper surface of the load bearing plate 1 and are respectively arranged at two diagonal positions of the load bearing plate 1. 2N soil pressure boxes 7 are respectively arranged at the bottom and the top surface of each reinforcing pile 6, and N pore pressure sensors 13 are arranged in the foundation soil 5 and are respectively positioned right below each soil pressure box 7; and the displacement dial indicator 4, the pore pressure sensor 13 and the soil pressure box 7 are connected to the signal acquisition equipment. The signal acquisition equipment is externally connected to computer equipment, and the computer equipment automatically reads and stores the acquired signals and converts the acquired signals into foundation settlement and pile/soil pressure data.
In this embodiment, the number of the reinforcing piles 6 is 6, and the reinforcing piles are arranged in two rows and three columns; the number of the electric heating pipes 12 is 4; the vertical load loading unit adopts the following structure: comprising a reaction beam 9 supported on top of the mold box 8 and a servo motor loading device 10. The test carried out by using the indoor model test device for the bearing characteristics of the composite foundation under the salt swelling and salt dissolution shown in the figure 1 and the figure 2 comprises the following steps:
step 1, before the test begins
4 electric heating pipes 12 are vertically arranged in a model box 8 in advance; as shown in fig. 1, when the electric heating pipes 12 are arranged, 2 electric heating pipes 12 are respectively arranged on the left side and the right side of the area of the 6 reinforcing piles 6, the front and back positions of the two electric heating pipes 12 on each side are basically consistent with the front and back positions of the two rows of reinforcing piles 6, the diameter of each reinforcing pile 6 is D, the distance between each two electric heating pipes 12 on each side and the outer reinforcing pile 6 is D, and D is greater than 3D; the length of the electric heating pipe 12 is substantially the same as the thickness of the foundation soil 5 filled in the mold box 1, as shown in fig. 1, the distance between the bottom end of the electric heating pipe 12 and the bottom of the mold box 8 is substantially the same as the diameter d of the reinforcing pile 6, the top end of the electric heating pipe 12 is exposed out of the upper part of the gravel reinforcement mat 3, and the top of the electric heating pipe 12 is connected with a heat source. And a layer of ceramic heat-insulating material 14 is wrapped outside the model box 8 to prevent heat loss in the test process.
Using indoor saline soil as foundation soil 5, fully washing salt, airing and crushing soil body of the foundation soil 5, calculating water adding amount and salt adding amount according to test requirements, uniformly stirring, and then filling in a model box 8 in layers;
in the filling process, the soil pressure boxes 7 are fixed at the bottom of the model box 8 in advance, after the dry salinized soil of the foundation is tamped in layers to reach a specified height, the soil pressure boxes 7 with the same number as the number of the reinforcing piles 6 are respectively placed at the corresponding positions of the bottom surface and the top surface of each reinforcing pile 6, and a pore pressure sensor 13 is placed under each soil pressure box 7.
The reinforcing piles 6 can be scattered piles, powder spraying piles and the like, can be prepared by field stirring and maintenance, can also be prefabricated, and are reduced in size according to the actual engineering size by 1: 20-1: 100 according to parameters such as the diameter, the length, the pile spacing and the like of the reinforcing piles. The material of the reinforcing pile 6 comprises fly ash, gypsum, mineral powder and cement, wherein the mass fraction of the cement is 20%, and the mass fractions of the fly ash, the gypsum and the mineral powder are selected according to actual engineering requirements; the reinforcing piles 6 are made in the foundation soil 5 by stirring the above materials and maintained for 28 days under the conditions of constant temperature and humidity.
Placing a broken stone reinforced cushion layer 3 in a certain range on the pile tops of the reinforcing piles 6, paving embankment filling 2 on the broken stone reinforced cushion layer 3 to simulate the load condition of a real embankment, placing a load plate 1 on the embankment filling 2, wherein the area of the load plate 1 can cover the area where all the reinforcing piles 6 are located (namely the area of the load plate 1 is larger than the area where all the reinforcing piles 6 are distributed); placing 2 displacement dial indicators 4 at two positions of the diagonal point of the load plate 1 respectively; through placing a load weight on the load carrying plate 1, or as shown in the embodiment shown in fig. 1, a reaction beam 9 is supported at the top of the model box 8, and a servo motor loading device 10 is utilized to gradually apply vertical load so as to simulate the stress condition of piles and soil. According to the invention, the load bearing plate 1 is arranged above the gravel reinforcement cushion layer 3 to directly bear the upper load, and the area ratio of the load bearing plate 1 to the gravel reinforcement cushion layer 3 is 1:3, so that the vertical load can be uniformly distributed on the composite foundation, and the composite foundation is prevented from being locally damaged due to overlarge local stress.
The spray device 11 is arranged on the reaction beam 9 at the upper part of the model box 8, and when the spray device 11 is installed, the spray range is ensured to cover the whole region of the foundation soil 5 in the model box 8 by adjusting the number and the positions of the nozzles.
Step 2, start of the test
Firstly, the displacement dial indicator 4, the hole pull sensor 13 and the soil pressure box 7 are all connected to the signal acquisition equipment, and the signal acquisition equipment, the electric heating pipe 12, the spraying device 11 and the servo motor loading equipment 10 are connected to a computer.
The servo motor loading equipment 10 is used for loading the composite foundation step by step, and preloading is needed before actual engineering loading, so that settlement errors caused by partial loose contact are eliminated. Preloading is carried out on the foundation through the servo motor loading equipment 10, and then loading is carried out step by step; in the step-by-step loading process, as the electric heating pipes 12 are arranged in the soil body of the foundation soil 5, the foundation soil 5 is heated through the heating effect of the electric heating pipes 12, so that the water content in the soil body of the foundation soil 5 is reduced, the salt particles in the soil body are crystallized, the salt expansion purpose is achieved, and the heating temperature is determined according to the test requirement; meanwhile, the upper spraying device 11 sprays water circularly and regularly to infiltrate the foundation soil 5, so that salt in the foundation soil 5 in the model box 8 is dissolved, and a simulated salt dissolving process is realized; in the test process, the ceramic heat-insulating material 14 is wrapped outside the model box to insulate the test system, so that the influence of heat loss on the test result is reduced.
Information such as foundation settlement, pile soil pressure and the like is collected through an external computer, the computer equipment automatically reads and stores collected signals, changes of stress, strain and settlement of the soil body of the foundation soil 5 and the reinforcing piles 6 in the salt solution and salt expansion processes are recorded, the influence of the salt expansion salt solution effect on the bearing deformation characteristic of the composite foundation is further analyzed, and the test result can be displayed through the computer.
In conclusion, the invention develops research on the composite foundation failure mode, the load transmission mechanism and the deformation characteristic under the conventional salt expansion and salt solution conditions through model tests, and the research result can provide a theoretical basis for the composite foundation design method under the salt expansion and salt solution effects. The test method is simple, the result is more consistent with the actual engineering, and the problem that the conventional test cannot simulate the salt swelling and salt dissolving effect is solved.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.
Claims (10)
1. An indoor model test device for bearing characteristics of a composite foundation under salt expansion and salt dissolution is characterized by comprising a model box (8), wherein a composite foundation model, a loading system and a measuring system are arranged in the model box (8),
the composite foundation model comprises N reinforcing piles (6) arranged in foundation soil (5), the foundation soil (5) is saline soil arranged indoors, and an electric heating pipe (12) is arranged in the foundation soil (5);
the loading system comprises a broken stone reinforced cushion layer (3), embankment filling soil (2) and a load plate (1) which are arranged in a certain range at the top of the reinforced pile (6) and are sequentially arranged from bottom to top, and a vertical load loading unit is arranged on the load plate (1); a spraying device (11) is arranged at the upper part of the model box (8), the spraying range of the spraying device (11) covers the gravel reinforcement cushion layer (3), and the area of the gravel reinforcement cushion layer (3) covers the foundation soil (5);
the measuring system comprises 2 displacement dial indicators (4), 2N soil pressure boxes (7), N pore pressure sensors (13) and signal acquisition equipment; the 2 displacement dial indicators (4) are arranged on the upper surface of the load bearing plate (1), the N soil pressure boxes (7) are respectively arranged at the bottom of each reinforcing pile (6), and the N pore pressure sensors (13) are arranged in the foundation soil (5) and are respectively positioned right below the soil pressure boxes (7) at the bottom of each reinforcing pile (6); and the displacement dial indicator (4), the pore pressure sensor (13) and the soil pressure box (7) are connected to the signal acquisition equipment.
2. The indoor model test device for bearing characteristics of the composite foundation under salt swelling and salt dissolving condition according to claim 1, wherein the vertical load loading unit has one of the following two structures:
firstly, adopting a load weight;
the device comprises a reaction beam (9) supported at the top of the model box (8) and servo motor loading equipment (10);
the vertical load is applied step by utilizing load weights or servo motor loading equipment so as to simulate the stress condition of piles and soil.
3. The salt swelling and salt dissolving lower composite foundation bearing characteristic indoor model test device according to claim 1, wherein 2 displacement dial indicators (4) are respectively arranged at two opposite corners of the bearing plate (1).
4. The indoor model test device for bearing characteristics of a composite foundation under salt swelling and salt dissolution according to claim 1, wherein the signal acquisition device is externally connected to a computer device, and the computer device automatically reads and stores the acquired signals and converts the acquired signals into foundation settlement and pile/soil pressure data.
5. The indoor model test device for bearing characteristics of the composite foundation under salt swelling and salt dissolution according to claim 1, wherein the mass percentage of salt content in the foundation soil (5) is 0% -15%, and 0 is not included.
6. The indoor model test device for bearing characteristics of the salt swelling and salt dissolving composite foundation according to claim 1, wherein the reinforcing pile (6) is any one of a powder-blasting pile, a gravel pile and a scattered pile, and is cast in situ in the foundation soil (5) or is installed in the foundation soil (5) after being prefabricated; the reinforcing piles (6) are reduced in size from 1:20 to 1:100 in terms of pile diameter, length and pile spacing according to the size of the actual project.
7. The indoor model test device for bearing characteristics of the composite foundation under salinization and salt dissolution of claim 1, characterized in that salt dissolution process is simulated by dissolving salt in foundation soil (5) in the model box (8) through cyclic and timed watering of the spraying device (11); the water content of the soil body of the foundation soil (5) is reduced through the heating effect of the electric heating pipe (12), and salt particles in the foundation soil are crystallized, so that the purpose of salt expansion is achieved.
8. The indoor model test device for the bearing characteristics of the composite foundation under salt swelling and salt dissolution according to claim 1, wherein the area ratio of the load plate (1) to the broken stone reinforced cushion layer (3) is 1:3, so that the vertical load is uniformly distributed on the foundation soil (5).
9. A simulation test method for bearing characteristics of a composite foundation under salt swelling and salt dissolving conditions, which is characterized in that the indoor model test device for the bearing characteristics of the composite foundation under salt swelling and salt dissolving conditions, as claimed in any one of claims 1 to 8, is used, and comprises the following steps:
step 1) arranging the electric heating pipe (12) vertically in a model box (8) in advance before the test is started;
using indoor saline soil as foundation soil (5), fully washing salt, airing and crushing soil body of the foundation soil (5), calculating water adding amount and salt adding amount according to test requirements, stirring uniformly, and then filling in a model box (8) in a layered mode;
in the filling process, soil pressure boxes (7) with the same number as the reinforcing piles (6) are respectively placed at the corresponding positions of the bottom surfaces and the top surfaces of the reinforcing piles (6), and a pore pressure sensor (13) is placed under each soil pressure box (7);
the material of the reinforcing pile (6) comprises 20% of fly ash, gypsum, mineral powder and cement, wherein the mass fraction of the cement is selected according to the actual engineering requirement; stirring the materials in foundation soil (5) to prepare a reinforcing pile (6), and maintaining for 28 days under the conditions of constant temperature and constant humidity;
placing a broken stone reinforcement cushion layer (3) in a certain range of the pile top of a reinforcing pile (6), laying embankment filling soil (2) on the broken stone reinforcement cushion layer (3), simulating the load condition of a real embankment, placing a load plate (1) on the embankment filling soil (2), wherein the area ratio of the load plate (1) to the broken stone reinforcement cushion layer (3) is 1: 3; placing 2 displacement dial indicators (4) at two diagonal points of the load plate (1) respectively;
step 2) starting a test, preloading the foundation through servo motor loading equipment (10), and then loading step by step; in the step-by-step loading process, the foundation soil (5) is heated through the electric heating pipe (12), so that the water content in the soil body of the foundation soil (5) is reduced, the salt expansion purpose is achieved, and the heating temperature is determined according to the test requirement; meanwhile, the foundation soil (5) is infiltrated by sprinkling water through the upper spraying device (11) to realize the salt dissolving effect;
and 3) recording the changes of stress, strain and settlement of the soil body of the foundation soil (5) and the reinforcing piles (6) in the salt solution and salt expansion processes, and further analyzing the influence of the salt expansion and salt solution effect on the bearing deformation characteristic of the composite foundation.
10. The method for the simulation test of the bearing characteristics of the composite foundation under salt swelling and salt dissolution according to claim 9, wherein when the electric heating pipes (12) are arranged in the step 1), 2 electric heating pipes (12) are respectively arranged on the left side and the right side of the area of N reinforcing piles (6), the diameter of each reinforcing pile (6) is D, the distance between each two electric heating pipes (12) on each side and the outer reinforcing pile (6) is D, and D is more than 3D; the length of the electric heating pipe (12) is the same as the thickness of foundation soil (5) filled in the model box (1).
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