A method for determining the composite modulus of waste solid tire reinforced soil

Abstract

This invention belongs to the field of geotechnical engineering testing technology, specifically relating to a method for determining the composite modulus of waste tire reinforced soil, aiming to solve the problem of data distortion in traditional testing. The method includes conducting uniaxial tensile tests on waste tires to obtain the tire tensile modulus for circumferential stress analysis. Waste tire-fill soil composite samples are prepared and subjected to unconfined compression tests. A linear variable differential displacement gauge is placed along the tire diameter direction to monitor the overall diameter change. Resistance strain gauges are attached to the inner wall of the tire to measure local circumferential strain. The readings of the resistance strain gauges are calibrated using the monitoring results of the linear variable differential displacement gauge to obtain calibrated circumferential strain data. Based on circumferential tension theory, the equivalent confining pressure increment provided by the tire to the filler soil is calculated from the obtained calibrated circumferential strain data. The obtained equivalent confining pressure increment is substituted into the relationship between the modulus of the filler soil and the confining pressure to calculate and determine the composite modulus of waste tire reinforced soil.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering testing technology, and in particular to a method for determining the composite modulus of waste reinforced soil. Background Technology

[0002] With the continuous increase in the amount of waste tires generated, their indiscriminate dumping or landfilling not only occupies a large amount of land resources, but also easily causes environmental problems such as soil pollution, groundwater pollution and fire hazards. At the same time, it causes the waste of resources such as rubber and fiber. The resource utilization of waste tires has become an important need in the field of environmental protection and sustainable development.

[0003] In the field of geotechnical engineering, waste tires, with their excellent elasticity, toughness, and durability, are widely recognized as a highly promising environmentally friendly material for improving soil properties. Existing research has clearly demonstrated that they can effectively enhance the shear strength and bearing capacity of soil, and optimize soil deformation characteristics, showing significant application value in slope stabilization and foundation reinforcement projects. However, current research has significant limitations: most studies focus on macroscopic properties such as bearing capacity, strength indicators, and slope stability, while research on the modulus characteristics of waste tire-soil composites remains relatively weak. Regarding computational methods, there is currently a lack of mechanical models that can accurately quantify the circumferential constraint effect of tires on the surrounding soil. The modulus calculation of waste tire-soil composites typically relies on the precise measurement of circumferential strain, but traditional methods often involve directly attaching strain gauges to the inner wall of the tire for monitoring. This method inevitably introduces the reinforcing effect of the strain gauges themselves, thereby altering the local stress state of the tire and causing deviations between the measured data and the actual strain. The resulting errors in modulus calculation not only fail to accurately reflect the mechanical response of the composite, but also fall short of the requirements for refined design and high-precision numerical simulation. In summary, due to the lack of suitable monitoring result verification techniques and composite model calculation methods, the core mechanical properties of the waste-reinforced solid soil composite system have not been systematically evaluated. This critical bottleneck has become a significant factor restricting the large-scale promotion and engineering application of this environmentally friendly material in the field of geotechnical engineering. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining the composite modulus of waste tire reinforced soil, which aims to solve the technical problems in traditional testing, such as data distortion due to lack of strain verification, difficulty in accurately reflecting the circumferential constraint effect of tires, and inability to accurately calculate the composite modulus of waste tire reinforced soil.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for determining the composite modulus of waste tire reinforced soil, comprising: S1: conducting a uniaxial tensile test on the waste tire to obtain the tire tensile modulus for circumferential stress analysis; the tire tensile modulus is the ratio of stress to strain of the tire under uniaxial tension; S2: preparing a waste tire-fill soil composite sample and conducting an unconfined compression test, arranging a linear variable differential displacement gauge in the tire diameter direction to monitor the overall diameter change, and simultaneously attaching a resistance strain gauge to the inner wall of the tire to measure the local circumferential strain, calibrating the resistance strain gauge readings using the monitoring results of the linear variable differential displacement gauge to obtain calibrated circumferential strain data; S3: based on the circumferential tension theory, combined with the calibrated circumferential strain data obtained in step S2, calculating the equivalent confining pressure increment provided by the tire to the fill soil; the equivalent confining pressure increment is the additional confining pressure generated by the tire on the fill soil due to circumferential tension; S4: substituting the tire equivalent confining pressure increment obtained in step S3 into the relationship between the modulus and confining pressure of the fill soil to calculate and determine the composite modulus of waste tire reinforced soil.

[0007] In step S1, a uniaxial tensile test is conducted by cutting strip samples from waste tires, and the stress-strain curve obtained from the test is linearly fitted to determine the tire tensile modulus based on the fitted slope.

[0008] The strip specimen was subjected to three or more repeated uniaxial tensile tests, and the average value of the fitted slopes obtained from the multiple tests was taken as the final tire tensile modulus.

[0009] In step S2, at least two linear variable differential displacement gauges are installed in the same diameter direction, or on two mutually perpendicular diameters respectively.

[0010] In step S2, three or more resistance strain gauges are arranged at equal intervals along the inner circumference of the tire, and the resistance strain gauges are successively bonded to the inner wall of the tire through surface grinding, degreasing, base coating, and curing processes.

[0011] In step S2, the unconfined compression test adopts a strain control method to control the change of moisture content of the sample within a preset range, and monitors and records the axial strain of the fill soil; the axial strain is the ratio of the deformation of the fill soil under axial pressure to the initial length.

[0012] The equivalent confining pressure increment provided by the tires to the fill soil is calculated using the following formula:

[0013]

[0014]

[0015] in: This refers to the tensile stiffness of the tire. The overall circumferential strain of the tire; The tire circumferential strain is The radius at that time; The axial strain of the fill soil; For local circumferential strain measured by strain gauges; This is the calibration coefficient.

[0016] In step S4, the modulus-confining pressure relationship of the fill soil is determined by conventional drained consolidation triaxial test.

[0017] In step S4, the dimensionless base and dimensionless exponent in the modulus-confining pressure relationship of the fill soil are determined by plotting the logarithmic relationship curve between the initial modulus and the confining pressure and performing linear fitting.

[0018] The composite modulus of waste reinforced soil in whole-timber installation is calculated using the following formula:

[0019]

[0020] in: is atmospheric pressure (standard atmosphere); K is the dimensionless cardinality, and n is the dimensionless exponent; This represents the increase in confining pressure.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. The method for determining the composite modulus of waste reinforced soil provided in this application addresses the problems of local data distortion and lack of verification methods caused by the self-reinforcing effect of strain gauges in traditional strain measurement. By simultaneously arranging linear variable differential displacement gauges and resistance strain gauges in unconfined compression tests, the overall circumferential strain is calculated by converting the overall diameter change monitored by the displacement gauges, and the readings of the resistance strain gauges are calibrated, effectively eliminating local strain distortion and providing accurate strain data for subsequent modulus calculation. This solves the core problem that traditional methods cannot accurately reflect the circumferential constraint effect.

[0023] 2. Unlike traditional modulus calculations that only focus on the stress-strain relationship of the soil itself and ignore the circumferential tensile constraint of the tire, the method provided in this application is based on the circumferential tension theory. It transforms the circumferential constraint effect of the tire on the fill soil into a quantifiable equivalent confining pressure increment. Then, it combines the relationship between the fill soil modulus and the confining pressure to calculate the composite modulus. For the first time, it realizes the quantitative characterization of the tire constraint effect, making the calculation results more consistent with the actual mechanical behavior of the "waste tire-fill soil" composite system. This significantly improves the accuracy of composite modulus calculation and meets the needs of refined design and numerical simulation in geotechnical engineering. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating a method for determining the composite modulus of waste tire reinforced soil provided in an embodiment of this application;

[0025] Figure 2 This is a schematic diagram of an unconfined compression test of a waste solid tire reinforced soil composite provided in an embodiment of this application;

[0026] Figure 3 This is a schematic diagram of circumferential strain measurement of a waste tire provided in an embodiment of this application;

[0027] Figure 4 This application provides an embodiment of a fill soil log( under different confining pressures). / Pa) and log( / Pa) relationship curve and its linear fitting result quantization graph;

[0028] Figure 5 This application provides a calibration diagram for measuring tire circumferential strain.

[0029] Figure 6 This is a quantitative diagram of the deformation modulus of a tire-filler composite provided in an embodiment of this application.

[0030] In the figure, 1 is the reaction frame, 2 is the electro-hydraulic servo actuator, 3 is the loading plate, 4 is the tire, 5 is the fill soil, 6 is the linear variable differential displacement gauge, 7 is the strain gauge, 8 is the test platform, 9 is the initial tire position, and 10 is the tire position during the loading process. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] This application provides a method for determining the composite modulus of waste reinforced soil, for example, such as... Figure 1 As shown. The method includes:

[0033] S1: Conduct a uniaxial tensile test on waste tires to obtain the tire tensile modulus for circumferential stress analysis.

[0034] Among them, the tire tensile modulus is the ratio of stress to strain of the tire under uniaxial tension.

[0035] In step S1, a uniaxial tensile test is performed on a strip sample cut from a waste tire. The stress-strain curve obtained from the test is linearly fitted, and the tensile modulus of the tire is determined by the fitted slope. For example, in the waste tire tensile test, the rate of change of tensile displacement of the tire strip sample by the equipment used to apply the tensile force, such as a universal testing machine, needs to be controlled within the range of no more than 5 mm per minute. This slow and stable displacement change avoids distortion of the material's mechanical response due to excessively rapid stretching.

[0036] The strip specimen was subjected to three or more repeated uniaxial tensile tests, and the average value of the fitted slopes obtained from the multiple tests was taken as the final tire tensile modulus.

[0037] It is important to note that after each uniaxial tensile test on the strip specimen, the load must be reduced to zero before reloading. Reloading to zero after each loading cycle allows the specimen to return to its initial stress state, ensuring that the stress-strain curves from each loading cycle are compared under the same benchmark, and preventing residual stress from the previous loading cycle from interfering with subsequent loading. Repeated loading ensures that the material deformation during subsequent loading cycles is a purely elastic response, guaranteeing that the final measured mechanical parameters closely match the stress characteristics of a tire in actual engineering applications. Furthermore, multiple experiments reduce the impact of random factors, effectively offsetting random errors and making the results more statistically representative.

[0038] For example, waste tires are cleaned and dried, and dumbbell-shaped or strip-shaped specimens are cut in the same circumferential direction as the tire. The effective measurement length is 10cm ± 2cm; the width is 5cm ± 1cm; and the thickness is maintained at the original tire thickness, ensuring that the direction of force is consistent with the actual circumferential force. Tensile tests are performed using an electro-hydraulic servo universal testing machine, with uniaxial tension and a loading rate controlled below 5mm / min. To eliminate the initial viscoelastic effect of the rubber, the same specimen is subjected to at least three repeated tensile tests, each time unloaded to zero load and then reloaded, and the average value is taken as the final result. The slope of the linear segment of the stress-strain curve is calculated using the least squares method as the tensile modulus of the tire.

[0039] S2: Prepare waste tire-fill soil composite samples and conduct unconfined compression tests. Linear variable differential displacement gauges (LVDTs) are placed in the tire diameter direction to monitor the overall diameter change. At the same time, resistance strain gauges (hereinafter referred to as strain gauges) are attached to the inner wall of the tire to measure the local circumferential strain. The readings of the resistance strain gauges are calibrated using the monitoring results of the linear variable differential displacement gauges to obtain the calibrated circumferential strain data.

[0040] For example, in combination Figure 2 After drying and sieving with a 0.5mm-2mm sieve, the moisture content of the fill soil is controlled within the range of the optimum moisture content ±0.5% to ensure compaction density. Figure 2 The experimental setup shown includes a reaction frame 1, an electro-hydraulic servo actuator 2, a loading plate 3, a tire 4, filler soil 5, a linear variable differential displacement gauge 6, a resistance strain gauge 7, and an experimental platform 8. The tire 4 is placed on the experimental platform 8, and the electro-hydraulic servo actuator 2 applies a vertical load to the loading plate 3, causing the tire 4 to deform.

[0041] As one possible implementation method, combined Figure 3 In step S2, resistance strain gauges 7 are attached to the inner wall of the tire 4 to measure the local circumferential strain. At least two linear variable differential displacement gauges 6 are installed in the same diameter direction, or on two mutually perpendicular diameters, to monitor changes in tire position. The radius increment of tire 4 is calculated from the initial tire position 9 and the tire position 10 during loading. And based on the initial radius of tire 4 The tire radius during the loading process was calculated. . Figure 3 Taking the setting of two linear variable differential displacement gauges 6 as an example, the exemplary resolution is 0.001mm.

[0042] For example, in combination Figure 4 A calibration relationship is established between the radius increment strain measured by LVDT and the local circumferential strain measured by resistance strain gauges to ensure the reliability of circumferential strain measurement. For example... Figure 4 As shown, the calibration coefficient K is obtained by linearly fitting the two types of data obtained from three sets of unconfined compression tests: the overall tire strain measured by LVDT and the local strain measured by strain gauges. g .

[0043] For example, the calculation formula is as follows:

[0044]

[0045] In the formula: The overall circumferential strain of the tire; For local circumferential strain measured by strain gauges; This is the calibration coefficient.

[0046] At least two linear variable differential displacement gauges are arranged along the same diameter of the tire, for example, symmetrically distributed on both sides of the tire, or arranged on two mutually perpendicular diameters. Figure 6The linear variable differential displacement gauges 6 shown are positioned on both sides of the tire along the same diameter direction. This symmetrical distribution can counteract the effects of eccentric loading that may occur during the loading process. For example, a slight misalignment between the press loading center and the sample center could lead to excessive deformation on one side of the tire. Arranging the linear variable differential displacement gauges on two mutually perpendicular diameters further allows for the assessment of the uniformity of the tire's circumferential deformation. For instance, excessive differences in diameter changes between the two diameter directions indicate uneven circumferential deformation, requiring investigation into potential problems in sample preparation. Finally, the overall tire diameter change is calculated by averaging the data from multiple linear variable differential displacement gauges, improving the reliability of the baseline data.

[0047] A linear variable differential displacement gauge (LVDT) is a high-precision displacement measurement device that achieves accurate measurement by converting "displacement changes" into "electrical signal changes." Its measurement range is adapted to tire diameter changes (typically at the millimeter level), and it boasts high resolution (up to the micrometer level), enabling real-time capture of minute changes in tire diameter throughout the loading process. Because the LVDT is positioned along the tire's diameter, it measures the overall tire diameter change, reflecting the macroscopic deformation state of the tire under stress. It is unaffected by localized minor defects (such as localized bulges on the tire's inner wall), and the data is representative overall, serving as a benchmark for strain calibration.

[0048] In step S2, three or more resistance strain gauges are arranged at equal intervals along the inner circumference of the tire, and the resistance strain gauges are successively bonded to the inner wall of the tire through surface grinding, degreasing, base coating, and curing processes.

[0049] Resistance strain gauges work based on the principle that the resistance of a metal wire changes with strain. They can be directly attached to the inner wall of a tire to measure the local circumferential strain of the tire's inner wall, that is, the minute deformation rate in the tire's circumferential direction.

[0050] In step S2, the unconfined compression test adopts a strain control method to control the change of moisture content of the sample within a preset range, and monitors and records the axial strain of the fill soil; the axial strain is the ratio of the deformation of the fill soil under axial pressure to the initial length.

[0051] For example, in the entire step S2, strain control is selected for the unconfined compression test. Strain control pushes the specimen to deform at a preset axial strain rate, which can stably capture the entire process from elastic deformation to plastic deformation. In particular, it can accurately obtain the correspondence between axial displacement, load and circumferential strain in the small strain range, providing continuous and complete basic data for subsequent calculation of small strain tangential modulus (the core index of composite modulus), and avoiding the loss of key data due to sudden failure.

[0052] As one possible implementation, the axial strain rate (the increment of axial strain of the specimen per unit time) is limited to 0.5% / min–2% / min.

[0053] As one possible implementation, the data sampling frequency (the number of times data is collected per unit time) is greater than or equal to 10Hz, that is, at least 10 sets of data are collected per second.

[0054] As one possible approach, the moisture content of the sample should not vary by more than ±0.5%.

[0055] S3: Based on the circumferential tension theory and combined with the calibrated circumferential strain data obtained in step S2, calculate the equivalent confining pressure increment provided by the tire to the fill soil.

[0056] The equivalent confining pressure increment is the additional confining pressure generated by the tires on the fill soil due to circumferential stretching.

[0057] For example, the calculation formula is as follows:

[0058]

[0059] In the formula: This refers to the tensile stiffness of the tire. The overall circumferential strain of the tire; The tire circumferential strain is The radius at that time; This represents the axial strain of the fill soil.

[0060] S4: Substitute the tire equivalent confining pressure increment obtained in step S3 into the relationship between the modulus of the fill soil and the confining pressure, and calculate and determine the composite modulus of the waste tire reinforced soil.

[0061] For example, the modulus-confining pressure relationship is as follows:

[0062] In the formula: is atmospheric pressure (standard atmosphere); K is the dimensionless cardinality, and n is the dimensionless exponent; This represents the increase in confining pressure.

[0063] Reference Figure 5 In step S4, the modulus-confining pressure relationship of the fill soil is determined by conducting conventional triaxial tests on the fill soil. Specifically, determining the parameters K and n involves conducting conventional triaxial tests on the fill soil.

[0064] In step S4, the initial modulus log( / Pa) and confining pressure log( The relationship curve between modulus and confining pressure (Pa) was used to perform linear fitting, and the dimensionless base K and dimensionless exponent n in the modulus-confining pressure relationship of the fill soil were determined. For example... Figure 5 As shown, the modulus of the fill soil under confining pressure was obtained from four sets of conventional triaxial tests, and the initial modulus log( / Pa) and confining pressure log( The relationship curve (Pa) is obtained by linearly fitting the curve to obtain its slope and intercept. The dimensionless cardinality K is calculated from the intercept of the fitted curve, and the dimensionless exponent n is the slope of the fitted curve. (The calculation at this stage only considers the conventional triaxial test modulus of the fill soil and does not take into account the constraint of the tire.)

[0065] like Figure 6 As shown, using Figure 4 The obtained calibration coefficient K g The accurate circumferential strain of the tire can be calculated; this circumferential strain is then substituted into the calculation formula to obtain different equivalent confining pressure increments; further substituting each level of equivalent confining pressure increment into the corresponding calculation formula, the modulus of the tire-reinforced soil composite under different equivalent confining pressure increments is solved, finally obtaining the confining pressure-composite modulus relationship curve. This curve shows that the confining pressure and composite modulus have an exponential relationship. The equivalent confining pressure and composite modulus obtained by the method provided in this application embodiment are both quantified, systematically reflecting the restraining effect of waste tires in the reinforced soil composite.

[0066] It should be understood that in actual roadbed engineering, waste tires are directly buried in the fill layer as reinforcement material. Due to site limitations, it is often impossible to deploy LVDT (Low-Low Temperature Detection and Testing) devices for radius change monitoring. In this case, resistance strain gauges that have been calibrated indoors can be attached to the circumference of the tire's inner wall. By collecting the local circumferential strain data output by the strain gauges in real time, and combining it with the LVDT-resistance strain gauge calibration relationship established indoors, the strain can be converted into equivalent overall circumferential strain. Since the strain gauges have been calibrated through indoor comparative tests, they can be directly used for modulus inversion calculation of waste tires in the field, without the need to conduct separate indoor tensile tests to determine the tire modulus. This method ensures the operability of field testing and the engineering applicability of the data, enabling the constraint effect of the waste tire-soil composite to be quantified and fed back in real time during construction, thus providing a reliable basis for roadbed filling quality control and the correction of numerical simulation input parameters.

[0067] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0068] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for determining the composite modulus of reinforced soil with used whole tires, characterized by, Comprise: S1: One-way tensile test is carried out on the waste whole tire to obtain the tire tensile modulus for the analysis of the ring force; the tire tensile modulus is the ratio of stress to strain of the tire under one-way tensile state; S2: Prepare the waste whole tire-filler soil composite sample and carry out the unconfined compression test, arrange the linear variable differential transducer in the tire diameter direction to monitor the overall diameter change, paste the resistance strain gauge on the inner wall of the tire to measure the local ring strain, calibrate the resistance strain gauge reading by using the linear variable differential transducer monitoring result, and obtain the calibrated ring strain data; S3: Based on the hoop tension theory, the equivalent confining pressure increment provided by the tire to the filled soil is calculated based on the calibrated hoop strain data obtained in step S2; the equivalent confining pressure increment is the additional confining pressure generated by the tire on the filled soil due to the hoop tension; wherein the equivalent confining pressure increment provided by the tire to the filled soil The formula is as follows: the tensile stiffness of the tire; the overall circumferential strain of the tire; the tire circumferential strain is the radius at which the tire circumferential strain is the axial strain of the embankment; the local circumferential strain measured by the strain gauges; the calibration factor; S4: The tire equivalent confining pressure increment obtained in step S3 is substituted into the modulus-confining pressure relationship of the filler soil to calculate and determine the waste whole tire reinforced soil composite modulus; wherein the waste whole tire reinforced soil composite modulus is calculated according to the following formula: P is the standard atmospheric pressure; K is a dimensionless base number and n is a dimensionless exponent.

2. The method of claim 1, wherein, In step S1, the one-way tensile test is carried out on the strip sample cut from the waste whole tire, the stress-strain curve obtained by the test is linearly fitted, and the fitting slope is used to determine the tire tensile modulus.

3. The method for determining the composite modulus of waste tire reinforced soil according to claim 2, characterized in that, The strip sample is subjected to more than or equal to three repeated one-way tensile tests, and the average value of the fitting slope obtained by multiple tests is taken as the final tire tensile modulus.

4. The method of claim 1, wherein the method is characterized by: In step S2, the linear variable differential transducer is arranged on at least two diameters in the same diameter direction, or on two diameters perpendicular to each other.

5. The method of claim 1, wherein the method is characterized by: In step S2, the resistance strain gauges are arranged at more than or equal to three equidistant positions along the circumferential direction of the inner side of the tire, and the resistance strain gauges are sequentially pasted on the inner wall of the tire through the processes of surface polishing, degreasing, primer coating and curing.

6. The method of claim 1, wherein the method is characterized by: In step S2, the unconfined compression test adopts strain control mode, controls the water content change of the sample within the preset range, monitors and records the axial strain of the filler soil; the axial strain is the ratio of the deformation amount of the filler soil under the action of axial pressure to the initial length.

7. The method of claim 1, wherein the method is characterized by: In step S4, the modulus-confining pressure relationship of the filler soil is determined by the conventional drained consolidation triaxial test.

8. The method of claim 7, wherein the method is characterized by: In step S4, the non-dimensional base and non-dimensional index in the modulus-confining pressure relationship of the filler soil are determined by drawing the logarithmic relationship curve of the initial modulus and confining pressure and linear fitting.

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