CN110987507A - Buoyancy model test device - Google Patents

Buoyancy model test device Download PDF

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Publication number
CN110987507A
CN110987507A CN201911398526.9A CN201911398526A CN110987507A CN 110987507 A CN110987507 A CN 110987507A CN 201911398526 A CN201911398526 A CN 201911398526A CN 110987507 A CN110987507 A CN 110987507A
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China
Prior art keywords
box body
buoyancy
inner barrel
test box
underground structure
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CN201911398526.9A
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Chinese (zh)
Inventor
王宇博
徐永亮
庞炜
王伟
周玉凤
黄溯航
郭红梅
孙常青
秦新
陈璐璐
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Beijing Urban Construction Exploration and Surveying Design Research Institute Co Ltd
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Beijing Urban Construction Exploration and Surveying Design Research Institute Co Ltd
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Priority to CN201911398526.9A priority Critical patent/CN110987507A/en
Publication of CN110987507A publication Critical patent/CN110987507A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M99/00—Subject matter not provided for in other groups of this subclass
    • G01M99/005—Testing of complete machines, e.g. washing-machines or mobile phones
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M99/00—Subject matter not provided for in other groups of this subclass
    • G01M99/007—Subject matter not provided for in other groups of this subclass by applying a load, e.g. for resistance or wear testing

Abstract

The invention belongs to the technical field of geotechnical engineering, and particularly relates to a buoyancy model test device. The device comprises a test box body, an underground structure unit and a water inlet pipe; the top of the test box body is open, and a foundation soil layer is arranged inside the test box body; the underground structure unit is arranged inside the foundation soil layer, and the top of the underground structure unit and the top of the test box body are positioned on the same horizontal line; the underground structure unit comprises an inner barrel and an outer sleeve, the inner barrel is a cylindrical barrel body with an open top, the outer sleeve is a sleeve which is vertically penetrated and sleeved outside the inner barrel, and a gap is formed between the outer sleeve and the inner barrel; the inlet tube sets up in the inside of experimental box, along the vertical setting of direction of height of experimental box. The device eliminates the vertical stress on the side wall, so that the device is only subjected to the gravity, the buoyancy and the counter force of the bottom soil body, and the measuring result is more accurate.

Description

Buoyancy model test device
Technical Field
The invention belongs to the technical field of geotechnical engineering, and particularly relates to a buoyancy model test device.
Background
The calculation of buoyancy in liquid can be generally simply applied to the Archimedes' law, while the buoyancy in solid-liquid two-phase media cannot be well applied to partial solid media, and particularly the calculation of buoyancy in saturated clay, namely the problem of pore water pressure of a weak permeable layer, is always under controversial debate. The debate view is basically divided into two groups, some scholars think that even under the condition of no seepage, the pore water pressure needs to be reduced due to the poor connectivity of the weak permeable layer caused by the bound water and other reasons, and some scholars can measure the maximum reduction coefficient to be 65 percent through model tests; the other part of scholars thinks that even the cohesive soil has small reduction coefficient of pore water pressure, and almost no consideration is taken in engineering application, and model test researches prove that the saturated cohesive soil can completely transmit the pore water pressure under a long-term stable state.
The vertical stress of the lateral wall of the underground structure module device is mainly frictional resistance and cohesive force, and the above scholars generally adopt two modes when eliminating the vertical stress of the lateral wall of the simulated underground structure module device when carrying out the model test: the first is to adopt smooth and flat materials for the side wall of the underground structure module as much as possible or to paint lubricants such as vaseline and the like at the same time, but the treatment mode can only reduce the frictional resistance and the cohesive force by a certain amount generally and can not completely eliminate the frictional resistance and the cohesive force, and the effect is not good when the soil body tamping effect around the underground structure module is good. And the other method is to firstly carry out a damage experiment of the frictional resistance and the cohesive force, measure the force required by the upward sliding of the module without the action of the buoyancy, namely the sum of the maximum static friction force, the cohesive force and the self gravity of the module, and further regard the sum as the lateral stress of the device after the gravity is reduced. However, the maximum static friction force in the maximum stress values measured by the processing method is not consistent with the actual sliding friction force, and is obviously influenced by the tamping effect of the surrounding soil body. The vertical stress on the side wall in the test process is actually a variable value, is different under different conditions and side wall pressure states, and obviously has large error when a uniform value is used for substitution.
Throughout the above experimental study, due to the limitation of the underground structure buoyancy measurement and calculation test device, each researcher has a great divergence in the measurement and calculation results of all buoyancy effects of the underground structure modules in the cohesive soil. Therefore, it is necessary to design a subsurface structure buoyancy measuring and calculating device with more detailed measurement and calculation and closer to an objective value, so as to develop more intensive experimental research work, taking into account the advantages and disadvantages of the above-mentioned testing device.
Disclosure of Invention
Technical problem to be solved
Aiming at the existing technical problems, the invention provides a buoyancy model test device, which eliminates the vertical stress on the side wall, so that the device is only subjected to the gravity, the buoyancy and the counter force of the bottom soil body, and the measurement result is more accurate.
(II) technical scheme
The invention provides a buoyancy model test device, which comprises a test box body, an underground structure unit and a water inlet pipe, wherein the test box body is provided with a water inlet pipe;
the top of the test box body is open, and a foundation soil layer is arranged inside the test box body;
the underground structure unit is arranged inside the foundation soil layer, and the top of the underground structure unit and the top of the test box body are positioned on the same horizontal line;
the underground structure unit comprises an inner barrel and an outer sleeve, the inner barrel is a cylindrical barrel body with an open top, the outer sleeve is a sleeve which is vertically penetrated and sleeved outside the inner barrel, and a gap is formed between the outer sleeve and the inner barrel;
the water inlet pipe is arranged in the test box body and is vertically arranged along the height direction of the test box body;
when buoyancy is calculated, water enters a foundation soil layer through the water inlet pipe, and the underground structure unit is subjected to stress analysis according to the static balance principle:
the underground structure unit can bear the structure dead weight G and the bottom soil body counterforce F in the foundation soil layer1Buoyancy of groundwater F2Sidewall soil reaction force F3Side wall water pressure F4Side wall frictional resistance F5And sidewall cohesion force F6；
Sidewall soil reaction force F3And side wall water pressure F4Cancel each other out in the horizontal direction;
in the vertical direction, the static equilibrium equation is calculated as follows:
F1+F2＝G+F5+F6(1)
side wall friction force F borne by underground structural units when the underground structural units are in a critical floating state5And sidewall cohesion force F6Acting only on the side wall of the outer sleeve and the bottom soil body reaction force F borne by the inner barrel1And because the floating critical state is equal to zero, the static equilibrium equation of the inner barrel at the moment is calculated as follows:
F2＝G (2)
obtaining the buoyancy F of the groundwater2。
Further, the gap is 3-5 mm.
Further, a waterproof layer is arranged outside the underground structure unit.
Further, still include a plurality of water level observation holes, the water level observation hole sets up in the inside of experimental box, along the vertical setting of direction of height of experimental box, and the bottom of a plurality of water level observation holes is located the different degree of depth of experimental box.
Further, the foundation soil layer comprises a coarse sand layer and a clay layer which are sequentially arranged in the height direction from the bottom of the test box body to the horizontal line where the top of the underground structural unit is located.
Further, the thickness of the coarse sand layer is 15-20cm, and the thickness of the clay layer is 95-100 cm.
Further, still include the delivery port, the delivery port sets up the bottom at least one side of experimental box.
Further, the outer sleeve is made of a rigid material.
Further, the test box body is 100cm long, 100cm wide and 120cm high.
Further, the distance between the top of the foundation soil layer and the top of the test box body is 4-6 cm.
(III) advantageous effects
(1) The underground structure unit of the invention adopts the combination of the inner barrel and the outer sleeve, thereby effectively eliminating the side wall friction and cohesive force. Wherein, a proper gap is ensured between the inner barrel and the outer sleeve to ensure that the inner barrel can not contact with the outer sleeve when freely floating and rotating.
(2) Waterproof layers are wrapped at the bottom and the side part of the underground structural unit, water in a foundation soil layer cannot enter a gap between the inner barrel and the outer sleeve, so that the side wall of the inner barrel is not subjected to water pressure, and the inner barrel is ensured to be only subjected to vertical structural dead weight G and buoyancy F2And bottom soil reaction force F1And the measurement result is more accurate.
Drawings
FIG. 1 is a front view of a buoyancy model test device provided by the present invention;
FIG. 2 is a top view of a buoyancy model test device provided by the present invention;
FIG. 3 is a front view of an underground structural unit of the present invention;
FIG. 4 is a force analysis diagram of a subsurface structural unit of the present invention.
[ description of reference ]
1: a test box body; 2: an underground structural unit; 3: a water inlet pipe; 4: a water outlet; 5: a coarse sand layer; 6: a clay layer; 7: a water level observation hole; 8: a waterproof layer; 21: an inner barrel; 22: an outer sleeve.
Detailed Description
For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.
Example 1
As shown in fig. 1 to 3, the buoyancy model test device provided in this embodiment includes a test box 1, an underground structure unit 2, a foundation soil layer, a water inlet pipe 3, a water outlet 4, and a water level observation hole 7.
The test box body 1 is of a cubic structure with an open top and is made of an iron sheet with the thickness of 3mm, and the length, the width and the height of the test box body are respectively 100cm, 100cm and 120 cm. The bottom of at least one side of the test box body 1 is provided with a water outlet 4, the diameter of the water outlet 4 is about 5cm, and a valve switch is arranged on the water outlet 4 and used for discharging water in the test box body 1.
The inside of experimental box 1 is provided with the foundation soil layer, and the foundation soil layer includes from supreme setting gradually down and has laid 20cm thick coarse sand layer 5 and 95cm thick clay layer 6. Specifically, the test box 1 is filled with foundation soil layers in a layered manner: filling medium coarse sand with the thickness of 20cm at the bottom so as to facilitate water drainage and water injection; and then filling the powdery clay layers 6 on the coarse sand layer 5 in a layered manner, wherein each layer is 20cm, tamping in a layered manner, sampling and detecting indexes such as density, water content and the like to ensure that the error with the simulated actual stratum is within a controllable range.
Further, the water inlet pipe 3 is arranged at the angular position of the test box 1 along the height direction of the test box 1, and the bottom of the water inlet pipe 3 and the bottom of the clay layer 6 are positioned at the same horizontal line. The water inlet pipe 3 is a PVC pipe with the diameter of 10cm, holes with the distance of 5cm are drilled at the position with the length of 20cm at the bottom, and 2 layers of wire winding filter screens are wrapped outside the holes to be used as a filter of the water inlet pipe 3.
PVC pipes with the diameter of 5cm and the lengths of 90cm, 80cm, 70cm, 60cm, 50cm, 40cm and 30cm are sequentially placed in the filling process to serve as water level observation holes 7, three corner points except a triangle where the water inlet pipe 3 is located are placed at first, then middle points of four side faces are placed, holes with the distance of 5cm are formed in the position with the length of 20cm at the bottom of each PVC pipe, 2 layers of wire winding filter screens are wrapped outside the holes to serve as filters of the water level observation holes 7, and the filters are used for preventing foundation soil layers from entering the water level observation holes 7 and affecting test results. Meanwhile, the top of the water level observation hole 7 and the top of the test box body 1 are ensured to be positioned on the same horizontal line, so that the water level can be conveniently measured and calculated.
When the clay layer 6 is filled to about 40cm from the top opening of the test tank 1, the upper surface of the soil is carefully leveled and placed into the underground structural unit 2. The top of the underground structure unit 2 and the top of the test box body 1 are positioned on the same horizontal line. When the underground structural unit 2 is placed, the smoothness of the clay layer 6 contacted with the bottom of the inner barrel 21 needs to be ensured, and then the bottom of the inner barrel 21 is completely attached to the clay layer 6, so that the influence of uneven bottom stress on the accuracy of a measuring result is prevented.
The underground structure unit 2 comprises an inner barrel 21 and an outer sleeve 22, wherein the inner barrel 21 is a cylindrical barrel body with an open top, the diameter of the bottom surface of the inner barrel is 30cm, the height of the inner barrel is 40cm, the outer sleeve 22 is a sleeve barrel which is communicated up and down, the outer sleeve 22 is sleeved outside the inner barrel 21, and a gap of about 4mm is formed between the outer sleeve 22 and the inner barrel 21 so as to ensure that the inner barrel 21 does not generate friction with the side wall of the outer sleeve 22 when the inner barrel freely floats up or rotates. Preferably, the outer sleeve 22 is made of a rigid material. Waterproof layers 8 are wrapped at the bottom and the side parts of the underground structural unit 2, and the waterproof layers 8 can prevent water in a foundation soil layer from entering a gap between the inner barrel 21 and the outer sleeve 22. The underground structural unit 2 was placed and then clay was continuously charged to a distance of 5cm from the top of the test chamber 1.
Principle of operation
Fill water in the bucket after foundation soil layer loads and finishes in order to ensure to can not take place the come-up to interior bucket when the water injection in the experimental box, then through the inlet tube to the internal water injection of experimental box and survey the water level come-up condition simultaneously through the water level observation hole, water gets into coarse sand layer through the inlet tube, again by coarse sand layer make up supply clay layer to saturation, treat that the water level reaches the take the altitude and stabilizes the back, underground structure unit atress as follows:
as shown in fig. 4, the underground structural unit receives a structural dead weight G and a bottom soil reaction force F in a clay layer1Buoyancy F2Sidewall soil reaction force F3Side wall water pressure F4Side wall frictional resistance F5And sidewall cohesion force F6. Wherein the side wall has frictional resistance F5And sidewall cohesion force F6Depending on the tendency of the underground structural units to move. During the buoyancy estimation test, the underground structural unit usually has upward movement tendencyTherefore, the side wall friction force F in the force balance relation5And sidewall cohesion force F6Is considered to be downward. Because the underground structure unit is in a barrel shape, the underground structure unit is subjected to the counterforce F of the soil body on the side wall3Side wall water pressure F4The horizontal direction and the horizontal direction are mutually offset, and the stress balance equation of the whole underground structural unit is as follows:
F1+F2＝G+F5+F6(1)
slowly reducing water in the inner barrel until the inner barrel is about to float, namely when the underground structural unit is in a critical state about to float, the side wall friction force F borne by the underground structural unit5And sidewall cohesion force F6Acting only on the side wall of the outer sleeve and the bottom soil body reaction force F borne by the inner barrel1And because the upper floating critical state is equal to zero, the inner barrel only bears the structural dead weight G and the buoyancy F2Therefore, the stress balance equation of the inner barrel is as follows:
F2＝G (2)
at the moment, the weight of the inner barrel (including the water body in the barrel) is accurately measured, and then the buoyancy F borne by the underground structural unit can be calculated2I.e. the magnitude of the pore water pressure. In addition, according to the water level in the water level observation hole, the depth of the inner barrel actually entering the water can be inversely calculated by utilizing the Archimedes principle, the liquid buoyancy theoretical value received by the inner barrel is calculated, and the actually measured buoyancy F2The reduction degree of the pore water pressure can be determined by comparing the sizes.
Furthermore, when the device is used, the liquid buoyancy theoretical value is calculated by measuring the water level through the water level observation holes, and the water level is stable and slow after the clay layer is injected with water, so that the test can be carried out only after the water levels of the observation holes at the periphery are completely consistent, namely the water level is completely stable.
The technical principles of the present invention have been described above in connection with specific embodiments, which are intended to explain the principles of the present invention and should not be construed as limiting the scope of the present invention in any way. Based on the explanations herein, those skilled in the art will be able to conceive of other embodiments of the present invention without inventive efforts, which shall fall within the scope of the present invention.

Claims (10)

1. A buoyancy model test device is characterized by comprising a test box body (1), an underground structure unit (2) and a water inlet pipe (3);
the top of the test box body (1) is open, and a foundation soil layer is arranged inside the test box body;
the underground structure unit (2) is arranged inside the foundation soil layer, and the top of the underground structure unit (2) and the top of the test box body (1) are positioned on the same horizontal line;
the underground structure unit (2) comprises an inner barrel (21) and an outer sleeve (22), the inner barrel (21) is a cylindrical barrel body with an open top, the outer sleeve (22) is a sleeve which is vertically penetrated and sleeved outside the inner barrel (21), and a gap is formed between the outer sleeve (22) and the inner barrel (21);
the water inlet pipe (3) is arranged inside the test box body (1) and is vertically arranged along the height direction of the test box body (1);
when buoyancy is calculated, water enters a foundation soil layer through the water inlet pipe, and the underground structure unit is subjected to stress analysis according to the static balance principle:
the underground structure unit can bear the structure dead weight G and the bottom soil body counterforce F in the foundation soil layer1Buoyancy of groundwater F2Sidewall soil reaction force F3Side wall water pressure F4Side wall frictional resistance F5And sidewall cohesion force F6；
Sidewall soil reaction force F3And side wall water pressure F4Cancel each other out in the horizontal direction;
in the vertical direction, the static equilibrium equation is calculated as follows:
F1+F2＝G+F5+F6(1)
side wall friction force F borne by underground structural units when the underground structural units are in a critical floating state5And sidewall cohesion force F6Acting only on the side wall of the outer sleeve and the bottom soil body reaction force F borne by the inner barrel1Also, since the floating critical state is equal to zero, the static equilibrium equation of the inner barrel at the moment is calculated as follows：
F2＝G (2)
Obtaining the buoyancy F of the groundwater2。
2. The buoyancy model test device of claim 1, wherein the gap is 3-5 mm.
3. The buoyancy model test device according to claim 1, characterized in that the exterior of the underground structural unit (2) is provided with a waterproof layer (8).
4. The buoyancy model test device according to claim 1, further comprising a plurality of water level observation holes (7), wherein the water level observation holes (7) are arranged inside the test box body (1) and are vertically arranged along the height direction of the test box body (1), and the bottoms of the water level observation holes (7) are located at different depths of the test box body (1).
5. The buoyancy model test device according to claim 1, characterized in that the foundation soil layer comprises a coarse sand layer (5) and a clay layer (6) which are arranged in sequence in the height direction from the bottom of the test box body (1) to the horizontal line of the top of the underground structure unit (2).
6. The buoyancy model test device according to claim 5, wherein the thickness of the coarse sand layer (5) is 15-20cm and the thickness of the clay layer (6) is 95-100 cm.
7. The buoyancy model test device according to claim 1, further comprising a water outlet (4), wherein the water outlet (4) is arranged at the bottom of at least one side of the test box body (1).
8. The buoyancy model test device according to claim 1, wherein the outer sleeve (22) is made of a rigid material.
9. The buoyancy model test device according to claim 1, wherein the test tank (1) has a length of 100cm, a width of 100cm and a height of 120 cm.
10. The buoyancy model test device according to claim 1, characterized in that the top of the foundation soil layer is 4-6cm from the top of the test tank (1).
CN201911398526.9A 2019-12-30 2019-12-30 Buoyancy model test device Pending CN110987507A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115389182A (en) * 2022-08-17 2022-11-25 武汉地铁集团有限公司 Simulation test device for measuring buoyancy of bottom plate of underground station, installation method and test method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115389182A (en) * 2022-08-17 2022-11-25 武汉地铁集团有限公司 Simulation test device for measuring buoyancy of bottom plate of underground station, installation method and test method

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