CN109931861B - Soil frost heaving force testing method and device - Google Patents
Soil frost heaving force testing method and device Download PDFInfo
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Abstract
The invention relates to a soil frost heaving force test method and a device, wherein the method comprises the steps of calibrating a frost heaving force test rod of each test unit, and establishing a functional relation between a strain value and a load of the frost heaving force test rod; assembling each test unit in a target test scene; connecting the assembled test unit to a static resistance strain gauge; after the balance of the data acquisition channel is adjusted, strain data of each test unit are acquired, the axial force of the frost heaving force test rod is obtained according to the calibration relation, and the corresponding frost heaving force value is obtained through conversion; the device comprises a fitting pipe and at least one test unit arranged in the fitting pipe, wherein the test unit comprises a deformation coordination anchor plate assembly and a test rod assembly. The invention can coordinate with the deformation of the surrounding soil to the greatest extent, thereby describing the time course change condition of the frost heaving force field of the soil in each test unit relatively finely, setting the acquisition frequency according to the need by adopting an automatic data acquisition mode and reducing the manual workload.
Description
Technical Field
The invention relates to the field of geotechnical engineering field experiment monitoring and measuring, in particular to a soil frost heaving force testing method and device, which are suitable for testing horizontal and vertical frost heaving forces of soil bodies of supporting structures such as ditches, retaining walls, foundation pits and the like in a frozen soil area.
Background
Engineering structures such as ditches, retaining walls, foundation pits and the like in frozen soil areas and seasonal frozen soil areas bear great loads due to frost heaving of soil bodies, and the safety, durability and operation of the structures are all serious tests. Therefore, the research on the distribution mode and the extreme value of the horizontal and vertical frost heaving force of the supporting structure is of great significance to the design, reinforcement and protection of the supporting structure. At present, the influence of frost heaving force is not considered in the design and construction of the supporting structure in the industry, and a mature testing device and a technical means are lacked to test the frost heaving force.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a soil frost heaving force testing method and device, which can automatically monitor soil frost heaving force fields (horizontal and vertical) after supporting structures such as ditches, retaining walls, foundation pits and the like in a frozen soil area.
The technical scheme adopted by the invention for achieving the purpose is as follows:
a soil frost heaving force testing method comprises the following steps:
step 1: calibrating the frost heaving force test bars of each test unit, and establishing a functional relation between the strain value of the frost heaving force test bars and the load;
step 2: assembling each test unit in a target test scene;
step 3: connecting the assembled test unit to a static resistance strain gauge;
step 4: and after the balance of the data acquisition channels is adjusted, strain data of each test unit are acquired, the axial force of the frost heaving force test rod is obtained according to the calibration relation, and the corresponding frost heaving force value is obtained through conversion.
Calibrating the frost heaving force test rod of each test unit comprises the following steps:
and fixing an anchor plate of the test unit, connecting a bridge circuit formed by the strain gauges to a static resistance strain acquisition instrument, carrying out channel balance under the condition that the frost heaving force test rod is not loaded, applying load step by step along the axial direction of the frost heaving force test rod at the other end of the frost heaving force test rod relative to the anchor plate, and calibrating the response value and the load value of the frost heaving force test rod.
After calibrating the frost heaving force test bars of each test unit, calibrating the reading change of the frost heaving force test bars of the test units under different temperature environments.
The step of assembling each test unit in the target test scene comprises the step of performing horizontal test assembly when the target test scene is a free face; and when the target test scene is a non-free surface, performing non-horizontal test assembly.
The horizontal test assembly comprises:
1) Filling gaps between adjacent anchor plates with the prepared soil samples according to the target density;
2) And (3) opening a hole at a target test position on the free surface, wherein the hole has the same outer diameter as the horizontal test auxiliary assembly kit, placing the assembled test kit into the hole, and filling the outside with soil to complete horizontal test assembly.
The non-horizontal test assembly comprises:
1) Fixing the test unit at a target test position, and backfilling according to target density until the backfill height reaches the position of an anchor plate at the upper part of the test unit;
2) Arranging the test units according to the process of 1) upwards in sequence, and enabling the upper anchor plate of the uppermost test unit to be positioned below the ground surface structural layer to finish non-horizontal test assembly.
And setting a temperature correction probe at the position of the frost heaving force test rod of the test unit, which is close to the strain gauge, collecting the ambient temperature of the strain gauge, and correcting the test data according to the calibrated temperature value.
The test data is corrected according to the calibrated temperature value:
ε ti ＝ε′ ti +(T 0 -T ti )*Δε
wherein ε' ti The strain value is acquired by a static resistance strain acquisition instrument; epsilon ti The temperature is a true value after temperature correction; t (T) 0 The temperature is the temperature when the static resistance strain acquisition instrument channel is balanced; t (T) ti Is the temperature at a certain momentA degree; delta epsilon is the bridge strain change per unit change in ambient temperature.
The soil frost heaving force testing device comprises a mounting pipe 8 and at least one testing unit arranged in the mounting pipe 8, wherein the testing unit comprises a deformation coordination anchor plate assembly and a testing rod assembly, deformation coordination anchor plate assemblies arranged on the mounting pipe 8 are arranged at two ends of the testing rod assembly, the testing rod assembly comprises a testing sensor 5, a frost heaving force testing rod 6 and an external protection cylinder 7, two ends of the frost heaving force testing rod 6 are respectively hinged with the deformation coordination anchor plate assemblies at two ends of the testing rod assembly, the external protection cylinder 7 is sleeved outside the frost heaving force testing rod 6, and the part of the frost heaving force testing rod 6 positioned in the external protection cylinder 7 is provided with the testing sensor 5 for monitoring the strain of the frost heaving force testing rod 6; the assembly pipe 8 is provided with an opening 14, and the soil body 13 to be tested is backfilled into the assembly pipe 8 through the opening 14.
The deformation coordination anchor plate assembly comprises an anchor plate 1, a gasket 2, a fixing nut 3 and a connecting rod 4, wherein the anchor plate 1 is arranged in the assembly pipe 8, a through hole for the connecting rod 4 to pass through is formed in the anchor plate 1, one end of the connecting rod 4 is connected with the anchor plate 1, and the other end of the connecting rod 4 is hinged with the frost heaving force testing rod 6; fixing nuts 3 are symmetrically arranged on two sides of the anchor plate 1, the fixing nuts 3 on each side are connected with one end of the connecting rod 4 in a threaded mode, and gaskets 2 sleeved on the connecting rod 4 are arranged between the fixing nuts 3 on each side and the anchor plate 1;
temporary fixing bolts 10 are arranged on two sides of the anchor plate 1, the temporary fixing bolts 10 are inserted into the assembly pipes 8 and are abutted against the anchor plate 1, and two adjacent anchor plates 1 are positioned according to a set target distance through the temporary fixing bolts 10;
the horizontal two sides of the through hole on the anchor plate 1 are symmetrically provided with data wire preformed holes 9 for the wires of the test sensor 5 to pass through;
the inner diameter of the assembly pipe 8 is equal to the outer diameter of the anchor plate 1, and the outer diameter of the anchor plate 1 is five to ten times of the diameter of the frost heaving force test rod 6;
the other end of the connecting rod 4 is provided with a hole and hinged with the frost heaving force testing rod 6 through a hinge 12; the distance between the arrangement area of the test sensor 5 on the frost heaving force test rod 6 and the opening at the other end of the connecting rod 4 is more than or equal to three times of the diameter of the frost heaving force test rod 6;
the connecting rod 4, the frost heaving force testing rod 6, the external protection cylinder 7, the anchor plate 1 and the assembly pipe 8 are coaxially arranged;
the test sensor 5 is a full-bridge test sensor and comprises two groups of strain gauges which are horizontally and symmetrically distributed, wherein each group comprises an axially arranged strain gauge and a circumferentially arranged strain gauge;
when the number of the test units is multiple, the same deformation coordination anchor plate assembly is shared between two adjacent test units, and the shared deformation coordination anchor plate assembly is respectively hinged with the frost heaving force test rods 6 in the two adjacent test units;
the arrangement area of the test sensor 5 on the connecting rod 4 is provided with a temperature correction probe 11.
The invention has the following beneficial effects and advantages:
according to the invention, one or more test units can be arranged according to the need, each test unit is relatively independent, and can be coordinated with the deformation of the surrounding soil to the greatest extent, so that the time course change condition of the frost heaving force field of the soil in each test unit can be relatively finely described, the acquisition frequency is set according to the need by adopting an automatic data acquisition mode, and the manual workload is reduced; the invention improves the test precision and has deeper understanding on the frost heaving force field of the deep soil body; the invention can provide an effective and reliable method for the research of actual engineering and frozen soil frost heaving mechanism.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a longitudinal cross-sectional view of the structure of the present invention;
FIG. 3 is a cross-sectional view A-A of FIG. 2 in accordance with the present invention;
FIG. 4 is a cross-sectional view B-B of FIG. 2 in accordance with the present invention;
FIG. 5 is a schematic diagram of a full bridge group approach of the test sensor of the present invention;
wherein: 1 is an anchor plate, 2 is a gasket, 3 is a fixing nut, 4 is a connecting rod, 5 is a test sensor, 6 is a frost heaving force test rod, 7 is an external protection cylinder, 8 is an assembly pipe, 9 is a data line reserved hole, 10 is a temporary fixing bolt, 11 is a temperature correction probe, 12 is a hinge, 13 is a tested backfilled soil body, and 14 is an opening.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit or scope of the invention, which is therefore not limited to the specific embodiments disclosed below.
It will be understood that when an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The words "front", "back", "left", "right" and the like are used herein for descriptive purposes only and not to indicate a unique embodiment.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
A flow chart of the method of the present invention is shown in fig. 1.
A soil frost heaving force testing method comprises the following steps: calibrating the frost heaving force test bars of each test unit, and establishing a functional relation between the strain value of the frost heaving force test bars and the load; assembling each test unit in a target test scene; connecting the assembled test unit to a static resistance strain gauge; and after the balance of the data acquisition channels is adjusted, strain data of each test unit are acquired, the axial force of the frost heaving force test rod is obtained according to the calibration relation, and the corresponding frost heaving force value is obtained through conversion.
As shown in fig. 2 to 5, the invention comprises a fitting pipe 8 and at least one test unit arranged in the fitting pipe 8, wherein the test unit comprises a deformation coordination anchor plate assembly and a test rod assembly, and both ends of the test rod assembly are provided with the deformation coordination anchor plate assemblies arranged on the fitting pipe 8; the deformation coordination anchor plate assembly comprises an anchor plate 1, a gasket 2, a fixing nut 3 and a connecting rod 4, wherein the end face of the anchor plate 1 is circular and is arranged in a fitting pipe 8, the inner diameter of the fitting pipe 8 is equal to the outer diameter of the anchor plate 1, and a through hole for the connecting rod 4 to pass through is formed in the circle center of the anchor plate 1; the both sides symmetry of anchor plate 1 is equipped with fixation nut 3, and the equal threaded connection of fixation nut 3 of every side makes anchor plate 1 and connecting rod 4 synchronous motion in one end of connecting rod 4, all is equipped with gasket 2 of cover on connecting rod 4 between fixation nut 3 and the anchor plate 1 of every side. One end of the connecting rod 4 is fixed on the anchor plate 1 through the gasket 2 and the fixing nut 3, the other end is provided with a hole, and the connecting rod is hinged with the frost heaving force testing rod 6 through a hinge 12, so that the testing rod assembly is stressed coaxially with the anchor plate 1. The two sides of the anchor plate 1 are respectively provided with a temporary fixing bolt 10, the temporary fixing bolts 10 are inserted on the assembly pipe 8 and are abutted with the anchor plate 1, and the two adjacent anchor plates 1 are positioned according to the set target distance through the temporary fixing bolts 10. The horizontal two sides of the through hole on the anchor plate 1 are symmetrically provided with data wire preformed holes 9 for the wires of the test sensor 5 to pass through. The anchoring plate 1 is made of aluminum alloy or stainless steel plate, and has high rigidity (the elastic modulus is more than 40 GPa); the outer diameter D1 of the anchor plate 1 is five to ten times the diameter D2 of the frost heaving force test rod 6, the length of the connecting rod 4 is not smaller than the diameter D1 of the connecting rod 4, and the diameter D1 of the connecting rod 4 can be one to three times the diameter D2 of the frost heaving force test rod 6.
The test rod assembly comprises a test sensor 5, an external protection cylinder 7 and a frost heaving force test rod 6 with a set length, wherein the frost heaving force test rod 6 is made of aluminum alloy, has small elastic modulus (in the range of 40-250 GPa) and strong deformability (the elastic strain energy reaches 2% -5%), and two ends of the frost heaving force test rod 6 are hinged with connecting rods 4 in deformation coordination anchor plate assemblies positioned at two ends of the test rod assembly respectively. The test sensor 5 is arranged in the middle (stress distribution uniform area) of the frost heaving force test rod 6, and the test sensor 5 is a full-bridge test sensor and comprises two groups of strain gauges which are horizontally and symmetrically distributed, wherein each group comprises one strain gauge which is axially arranged, one strain gauge which is circumferentially arranged and four strain gauges in total. When the test rod assembly is installed, the position of the test sensor 5 is placed on the surfaces of two horizontal sides instead of the upper surface and the lower surface of the frost heaving force test rod 6, and the influence of the environment on the test is reduced to the greatest extent through the arrangement of a full-bridge circuit and the geometric position; the diameter d2 of the frost heaving force test rod 6 is preferably 5 mm-30 mm, and the section should be made into a variable diameter section (the diameter of the range of 2 times d2 at the two ends of the frost heaving force test rod 6 should be 1.5-3 times d2, and the diameter is transited to the normal test diameter d2 through the gradual change region of the range of 1 times d 2) under the condition that the condition allows, mainly depends on the estimated frost heaving force of the test target. The minimum length of the frost heaving force test bar 6 should not be less than 6 times the diameter D2 of the frost heaving force test bar 6 and should not be less than 2 times the diameter D1 of the anchor sheet 1. The arrangement area of the test sensor 5 is 3 times larger than the diameters of the holes at the other ends of the fixing nut 3 and the connecting rod 4 (the stress distribution is uniform), namely, the distance between the arrangement area of the test sensor 5 on the frost heaving force test rod 6 and the holes at the other ends of the connecting rod 4 is larger than or equal to three times the diameters of the frost heaving force test rod 6. Before the strain gauge of each strain gauge is arranged, whether the strain gauge meets the standard or not (the resistance error is in the allowable range) is detected, acetone or absolute ethyl alcohol is adopted for continuous repeated unidirectional cleaning to ensure the cleanness of a sensor pasting area, high-strength quick-drying glue with stable performance is used for pasting, the axial and circumferential positioning is strictly controlled during pasting, the direction cannot be deviated, meanwhile, a waterproof and dustproof film is adopted for covering, air and redundant glue under the strain gauge are extruded in a thumb belly rolling and pressing mode, and the strain gauge is loosened after the glue is hardened; and (5) pasting one side of the adhesive on the symmetrical position of the other side in the same way. And after the four strain gauges are pasted, the four strain gauges are checked well by a universal meter, wiring terminals are arranged at proper positions, a full-bridge circuit is formed by matching the wiring terminals, and data acquisition wires are welded at corresponding positions. And removing redundant wire heads after the welding is finished, and packaging the test sensor 5 and the welding terminals by adopting silica gel. The wires pass through the data wire preformed holes 9 on the anchor plate 1.
An external protection cylinder 7 is sleeved outside the frost heaving force test rod 6, and the main function of the external protection cylinder 7 is to prevent the external soil body from affecting the performance of the frost heaving force test rod 6. The test sensor 5 is stuck to the middle position of the inner part of the external protection cylinder 7, where the frost heaving force test rod 6 is positioned. During assembly, the deformation spring 6 and the inside of the external protection cylinder 7 should be oiled to play a role in corrosion prevention and friction resistance reduction of the spring and the protection cylinder. The outer layer of the lead of each test unit can be coated with lubricating substances such as vaseline, and the like, and deformation is reserved when each test unit is arranged in a wiring way, so that the lead is prevented from being pulled tightly along with the deformation of a soil body. The corrosion-resistant treatment is carried out on related metal components such as the test rod assembly, the deformation test assembly and the like so as to prevent the performance of the test rod assembly from being changed due to corrosion in the test process and influence the test precision. The assembly pipe 8 is provided with an opening 14 along the length direction, the soil body 13 to be tested is backfilled into the assembly pipe 8 through the opening 14, and the length of the opening 14 is smaller than or equal to the length of the assembly pipe 8.
When the number of the test units is multiple, the same deformation coordination anchor plate assembly is shared between two adjacent test units, and the shared deformation coordination anchor plate assembly is hinged with the frost heaving force test rods 6 in the two adjacent test units respectively.
The connecting rod 4, the frost heaving force testing rod 6, the external protection cylinder 7, the anchoring plate 1 and the assembly pipe 8 are coaxially arranged. The invention installs a temperature correction probe 11 in the arrangement area of the test sensor 5 on the frost heaving force test rod 6.
The measuring range of the invention comprises two parts of the measuring range of the frost heaving force testing rod 6 and the measuring range of the hinge 12 at the hinge position, and finally the measuring range of each testing unit is smaller. Wherein the range of the frost heaving force test rod 6 is (0.5-0.8) A.sigma b The axial deformation strain epsilon of the frost heaving force test rod 6 should be controlled within the elastic and 2% range (except for the large strain gauge). Where A is the cross-sectional area of the frost heaving force test rod 6 and σb is the yield strength of the material.
The calculated length L1 of the frost heaving force test rod 6 (namely, the distance between the two ends of the frost heaving force test rod 6 hinged by the hinge 12) is not smaller than six times of the diameter d2 of the frost heaving force test rod 6 and not smaller than twice of the diameter of the anchor plate 1 (or not smaller than twice of the inner diameter of the assembly pipe 8). The reserved distance between the end of the external protection cylinder 7 and the nearest fixing nut 3 is 20-50 mm in tensile test.
The invention provides a simple and reliable testing device for automatically monitoring a soil frost-heaving force field (horizontal and vertical) after supporting structures such as ditches, retaining walls, foundation pits and the like in a frozen soil area, and the testing method comprises the following steps:
step 1: calibrating the frost heaving force test rod 6 of each test unit, and establishing a functional relation between the strain value of the frost heaving force test rod 6 and the load; the method comprises the following steps: after the test sensor 5 is attached, the frost heaving force test rod 6 of each unit needs to be calibrated for assembly. And (5) connecting each test unit with the length of the wire required by the target test, and carrying the wire to carry out comprehensive calibration. A test unit anchor plate 1 is fixed through a temporary fixing bolt 10, and a bridge circuit composed of strain gauges of a test sensor 5 is connected to a static resistance strain acquisition instrument, channel balance is carried out under the condition that a frost heaving force test rod 6 is not loaded, and a load is applied step by step along the axial direction of the frost heaving force test rod 6 at the other end, and response values and load values of the frost heaving force test rod 6 are recorded, wherein the load values are 0-20N-40N-80N- … … - (0.5Asigma) b ). Wherein sigma b For the yield strength of the material, i.e. the maximum load applied should be in the elastic phase of the material, the range of the frost heave force test lever 6 is (0.5Aσ b ) The maximum working condition load can be estimated according to the test conditions, and the working load can be reduced as long as the maximum working condition load is calibrated to exceed the range of the using load. The reading of each stage of loading should be read after stabilizing, and the consistent data of five continuous readings is used as the load response value of the stage, the test result is followed, and the functional relation (linear relation in the elastic range of the frost heaving force test rod 6) between the response value of the frost heaving force test rod 6 and the load is established.
Meanwhile, after the calibration of the frost heaving force test rod 6 of the test unit is finished, the temperature influence calibration under the set load should be performed. Calibrating and recording the reading change rule of the frost heaving force test rod 6 under different temperature environments (relative to the temperature at the time of balance); numbering each frost heaving force test rod 6, and recording calibration data according to the number one by one.
The inner diameter D1 of the mounting tube 8 should be the same as the outer diameter of the anchor sheet 1, and the wall thickness of the mounting tube 8 should be as small as possible and have sufficient hardness and rigidity, preferably about 1 to 3mm, so as to reduce disturbance of the filling soil sample after the mounting tube 8 is drawn out.
Step 2: assembling each test unit in a target test scene; the assembling comprises the step of performing horizontal test assembling when the target test scene is a free surface; and when the target test scene is a non-free surface, performing non-horizontal test assembly.
Horizontal test assembly: the horizontal test is mainly used for monitoring engineering implementation processes or health monitoring after project operation in trenches, slopes, foundation pits or other engineering projects with empty surfaces in frozen soil areas. Coating a thin layer of vaseline or oil on the inside and outside of the assembly pipe 8 so as to be conveniently drawn out after the assembly at the target test position is finished; using a temporary fixing bolt 10 to temporarily fix two adjacent anchor plates 1 of each test unit in a mounting pipe 8 according to a target distance, distributing posted strain gauges on two horizontal sides of a frost heaving force test rod 6 instead of upper and lower parts, assembling an external protection cylinder 7 on the frost heaving force test rod 6 (vaseline or oil is smeared inside and outside the external protection cylinder 7 to reduce friction resistance), and wrapping two ends of the external protection cylinder 7 by films to prevent soil particles from falling into the external protection cylinder 7 to influence the test; filling the prepared soil sample (1-2% higher than the soil layer water content of the target position to be measured) between two adjacent anchor plates 1 according to the target density (0.1-0.3 g/cm < 3 > higher than the soil mass density of the target position), taking care of protecting the test rod assembly in the filling process, and placing a temperature correction probe 11 on one side of a test sensor 5 on a frost heaving force test rod 6 of each test unit; extracting the temporary fixing bolt 10 after the soil sample is filled; digging holes with the same outer diameter as the assembly pipe 8 at the target test positions of the empty face of the foundation pit and other projects, wherein the depth is 10-50 cm longer than the total length of all the test units, putting the assembled test suite (the test device, the backfilled soil body 13 to be tested and the auxiliary suite) into the dug holes, and filling the part of the outside lacking the opening 14 with soil; connecting the data acquisition wires of all the test units to an acquisition instrument, and standing for 5-48 hours to start the test.
Non-horizontal test setup: the non-horizontal test assembly is divided into vertical and oblique directions and is mainly used for testing displacement fields of backfill soil such as ditches, foundations, roadbeds, retaining walls and the like in frozen soil areas. In the backfilling process, fixing a test unit at a test position at a target test position, and backfilling according to the target compactness; when backfilling the upper anchor plate 1 of the test unit, wrapping the two ends of the external protection cylinder 7 with films to prevent soil particles from falling into the external protection cylinder 7 to influence the test; and then sequentially arranging corresponding test units upwards in the backfilling process. A temperature correction probe 11 is placed on one side of the test sensor 5 on the frost heaving force test rod 6 of each test unit, and test data are corrected according to the calibrated values. Or excavating the embedded testing device after adopting the mode which is the same as the horizontal testing assembly direction.
Test lever full-bridge paster and connected mode: the frost heaving force testing rod 6 is respectively pasted on each side of the symmetrical position of the strain gauge pasting area along the axial direction and the annular direction (or the transverse direction), as shown in figure 3, four strain gauges are all connected to form a full-bridge testing circuit according to figure 4 and are connected to corresponding collecting channels of the static strain collecting instrument; a point in the bridge circuit is used as a positive end of a power supply, a point B is used as a positive end of a signal, a point C is used as a negative end of the power supply, and a point D is used as a negative end of the signal.
Connection and collection of the testing device and the collection instrument: each group of test devices (several test units are connected in series to work together to form a group) can comprise a plurality of test units, each test unit is a full-bridge test circuit, the data wire of each test unit passes through the data wire reserved hole 9 on the anchor plate 1 and then is connected to the acquisition channel of the acquisition instrument, and the channel is set to be a full-bridge circuit. After the testing device is arranged at the target position, all data are connected to the acquisition instrument, 10-20 groups of data are acquired before testing, after the data are stable, the state of a used channel is zeroed (channel balance), then the acquisition interval (1 s-1 d) is set according to the requirement, and the data (the testing unit and the temperature probe) are simultaneously acquired.
The frost heaving force calculation method comprises the following steps: collecting data epsilon 'of each unit of each group (displacement field) of testing device by a collector' ti (ti represents the value acquired at time ti), the temperature should be corrected first:
ε ti ＝ε′ ti +(T 0 -T ti )×Δε
wherein ε' ti For the strain value, epsilon, collected by the collector ti Is the true value after temperature correction, T 0 To collect the temperature at the corresponding measuring point in the channel balance of the instrument, T ti Delta epsilon is the bridge strain change per degree of change in the environment for a temperature at a certain time.
By calibrating the data relation epsilon ti ～N ti The axial force N at the corresponding moment is converted ti Then converting the frost heaving force value sigma of the test unit ti ＝N ti /A i (wherein A i Anchor plate 1 for the corresponding test unit); and after the data processing is finished, a time-course relation graph of the displacement fields can be drawn so as to analyze the change rule of the displacement fields of all soil layers.
Claims (7)
1. The soil frost heaving force testing method is characterized by comprising the following steps of:
step 1: calibrating the frost heaving force test bars of each test unit, and establishing a functional relation between the strain value of the frost heaving force test bars and the load;
step 2: assembling each test unit in a target test scene;
step 3: connecting the assembled test unit to a static resistance strain gauge;
step 4: after the balance of the data acquisition channel is adjusted, strain data of each test unit are acquired, the axial force of the frost heaving force test rod is obtained according to the calibration relation, and the corresponding frost heaving force value is obtained through conversion;
the soil body frost heaving force testing device applying the testing method comprises an assembling pipe (8) and at least one testing unit arranged in the assembling pipe (8), wherein the testing unit comprises a deformation coordination anchor plate assembly and a testing rod assembly, the two ends of the testing rod assembly are respectively provided with the deformation coordination anchor plate assembly arranged on the assembling pipe (8), the testing rod assembly comprises a testing sensor (5), a frost heaving force testing rod (6) and an external protection cylinder (7), the two ends of the frost heaving force testing rod (6) are respectively hinged with the deformation coordination anchor plate assemblies arranged at the two ends of the testing rod assembly, the external protection cylinder (7) is sleeved outside the frost heaving force testing rod (6), and the part of the frost heaving force testing rod (6) positioned in the external protection cylinder (7) is provided with the testing sensor (5) for monitoring the strain of the frost heaving force testing rod (6); an opening (14) is arranged on the assembly pipe (8), and a backfilled soil body (13) to be tested is backfilled into the assembly pipe (8) through the opening (14);
the deformation coordination anchor plate assembly comprises an anchor plate (1), a gasket (2), a fixing nut (3) and a connecting rod (4), wherein the anchor plate (1) is installed in the assembly pipe (8), a through hole for the connecting rod (4) to pass through is formed in the anchor plate (1), one end of the connecting rod (4) is connected with the anchor plate (1), and the other end of the connecting rod is hinged with the frost heaving force testing rod (6); fixing nuts (3) are symmetrically arranged on two sides of the anchor plate (1), the fixing nuts (3) on each side are connected with one end of the connecting rod (4) in a threaded mode, and gaskets (2) sleeved on the connecting rod (4) are arranged between the fixing nuts (3) on each side and the anchor plate (1);
temporary fixing bolts (10) are arranged on two sides of each anchor plate (1), the temporary fixing bolts (10) are inserted into the assembly pipe (8) and are abutted to the anchor plates (1), and two adjacent anchor plates (1) are positioned according to a set target distance through the temporary fixing bolts (10);
the horizontal two sides of the through hole on the anchoring plate (1) are symmetrically provided with data wire reserved holes (9) for the wires of the test sensor (5) to pass through;
the inner diameter of the assembly pipe (8) is equal to the outer diameter of the anchor plate (1), and the outer diameter of the anchor plate (1) is five to ten times the diameter of the frost heaving force test rod (6);
the other end of the connecting rod (4) is provided with a hole and hinged with the frost heaving force testing rod (6) through a hinge (12); the distance between the arrangement area of the test sensor (5) on the frost heaving force test rod (6) and the opening at the other end of the connecting rod (4) is more than or equal to three times of the diameter of the frost heaving force test rod (6);
the connecting rod (4), the frost heaving force testing rod (6), the external protection cylinder (7), the anchoring plate (1) and the assembly pipe (8) are coaxially arranged;
the test sensor (5) is a full-bridge test sensor and comprises two groups of strain gauges which are horizontally and symmetrically distributed, wherein each group comprises an axially arranged strain gauge and a circumferentially arranged strain gauge;
when the number of the test units is multiple, the same deformation coordination anchor plate assembly is shared between two adjacent test units, and the shared deformation coordination anchor plate assembly is respectively hinged with frost heaving force test rods (6) in the two adjacent test units;
a temperature correction probe (11) is arranged in an arrangement area where the test sensor (5) is arranged on the connecting rod (4);
calibrating the frost heaving force test rod of each test unit comprises the following steps:
and fixing an anchor plate of the test unit, connecting a bridge circuit formed by the strain gauges to a static resistance strain acquisition instrument, carrying out channel balance under the condition that the frost heaving force test rod is not loaded, applying load step by step along the axial direction of the frost heaving force test rod at the other end of the frost heaving force test rod relative to the anchor plate, and calibrating the response value and the load value of the frost heaving force test rod.
2. The soil frost heaving force test method according to claim 1, wherein: after calibrating the frost heaving force test bars of each test unit, calibrating the reading change of the frost heaving force test bars of the test units under different temperature environments.
3. The soil frost heaving force test method according to claim 1, wherein: the step of assembling each test unit in the target test scene comprises the step of performing horizontal test assembly when the target test scene is a free face; and when the target test scene is a non-free surface, performing non-horizontal test assembly.
4. A soil body frost heaving force test method as claimed in claim 3, wherein: the horizontal test assembly comprises:
1) Filling gaps between adjacent anchor plates with the prepared soil samples according to the target density;
2) And (3) opening a hole at a target test position on the free surface, wherein the hole has the same outer diameter as the horizontal test auxiliary assembly kit, placing the assembled test kit into the hole, and filling the outside with soil to complete horizontal test assembly.
5. A soil body frost heaving force test method as claimed in claim 3, wherein: the non-horizontal test assembly comprises:
1) Fixing the test unit at a target test position, and backfilling according to target density until the backfill height reaches the position of an anchor plate at the upper part of the test unit;
2) Arranging the test units according to the process of 1) upwards in sequence, and enabling the upper anchor plate of the uppermost test unit to be positioned below the ground surface structural layer to finish non-horizontal test assembly.
6. The soil frost heaving force test method according to claim 4 or 5, wherein: and setting a temperature correction probe at the position of the frost heaving force test rod of the test unit, which is close to the strain gauge, collecting the ambient temperature of the strain gauge, and correcting the test data according to the calibrated temperature value.
7. The soil frost heaving force test method of claim 6, wherein: the test data is corrected according to the calibrated temperature value:
ε ti ＝ε′ ti +(T 0 -T ti )*Δε
wherein ε' ti The strain value is acquired by a static resistance strain acquisition instrument; epsilon ti The temperature is a true value after temperature correction; t (T) 0 The temperature is the temperature when the static resistance strain acquisition instrument channel is balanced; t (T) ti Is the temperature at a certain moment; delta epsilon is the bridge strain change per unit change in ambient temperature.
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