Test method for reducing errors in shear strength test of root-soil composite

Abstract

A test method for reducing errors in a shear strength test of a root-soil composite, relating to the field of agricultural engineering test methods, and comprising: using a ring cutter perpendicular to an actual shear plane to perform sampling to ensure that the direction of the actual shear plane of a root-soil composite is consistent with that of a direct shear test shear plane; performing layered measurement on the shear strength of soil layers within an actual shear depth range at a minimal ring cutter thickness; and planning an annular sampling area and performing sampling in different directions of the annular area. In this way, test errors in the determination of shear characteristics of the root-soil composite are reduced from three aspects.

Description

A test method for reducing test error of root-soil composite shear strength TECHNICAL FIELD

[0001] The present application belongs to the field of agricultural engineering technology and test, in particular relates to a kind of test method for reducing test error of root-soil composite shear strength. BACKGROUND

[0002] In the design process of tillage machinery, the shear strength of the soil to be worked is determined as basic test data and the design basis of tillage parts. The commonly used method for determining the shear strength of field soil is to take samples vertically to the surface with a cutting ring and then determine it with a direct shear instrument. However, the soil and plant roots in the farmland actually exist in the form of a root-soil composite, which is anisotropic. Moreover, the root content and water content of the soil in different depth ranges are different. TECHNICAL PROBLEM

[0003] The test method for determining the shear strength of the root-soil composite in the farmland has the following three problems: first, the actual shear surface of the tillage part during operation and the test shear surface of the direct shear test are not consistent. If the test shear surface of the sample is not consistent with the actual shear surface during tillage, the anisotropy of the root-soil composite will cause test error; second, the root content and water content of the soil in different depths are different, and the shear characteristics of each layer are different. Taking samples without stratification will cause test error due to the difference in physical properties; third, there are a large number of roots in the farmland soil. Under the influence of the roots in the soil, the root structure and distribution in each direction of the same layer of soil are also different. Single-direction sampling will cause test error due to the distribution of roots. TECHNICAL SOLUTION

[0004] To solve the above technical problems, the present application provides a test method for reducing test error of root-soil composite shear strength to accurately determine the shear strength of the root-soil composite in the field. It mainly includes taking samples vertically to the actual shear surface to ensure that the actual shear surface direction of the root-soil composite is consistent with the shear surface direction of the direct shear test, stratifying the soil in the actual shear depth range with the minimum cutting ring thickness to determine the shear strength of each layer, and planning a ring-shaped sampling area and sampling in each direction along the ring-shaped area to reduce the test error of the shear characteristics of the root-soil composite from three aspects.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] A test method for reducing the test error of the shear strength of root-soil complex, comprising the following steps:

[0007] Step one: determine the actual shear occurrence surface of the shear process between the tillage component and the soil during tillage, measure the dihedral angle between the actual shear occurrence surface and the soil level surface at the tillage depth, and measure the actual shear depth H of the tillage component to the soil during tillage;

[0008] Step two: according to the actual shear depth H generated by the actual tillage to the soil, plan sampling along the actual shear occurrence surface according to the ring cutter diameter within the range from the horizontal ground surface to the tillage depth, and obtain the layered measurement depth;

[0009] Step three: according to the planned layered measurement depth, plan a ring-shaped sampling area for each layer;

[0010] Step four: within the same depth range, make a sampling plane according to the dihedral angle α of the actual shear occurrence surface, vertically sample the ring cutter to the sampling plane, and sample in all directions along the planned ring-shaped area;

[0011] Step five: obtain root-soil complex samples in each layer, and carry out root direct shear test layer by layer to obtain test results;

[0012] Step six: according to the test results, describe the shear strength of each layer of soil layer by layer.

[0013] Further, in step two, the sampling is planned along the actual shear occurrence surface according to the ring cutter diameter within the range from the horizontal ground surface to the tillage depth, and the layered measurement depth is obtained, including: the length of the shear occurrence surface is L, then L=H / cosα; the diameter of the ring cutter is D, then the number of layers n=(H / cosα) / D, the depth of the first layer H1=D×sinα, the depth of the second layer H2=2D×sinα, the depth of the third layer H3=2D×sinα,..., the depth of the nth layer Hn=nD×sinα (n=1, 2, 3,...).

[0014] Further, in step three, according to the planned layered measurement depth, a ring-shaped sampling area is planned for each layer, including: when the depth of the nth layer is Hn=nD×sinα (n=1, 2, 3,...), a convex ring-shaped sampling area is made; wherein the radius of the convex top surface circle (i.e. the inner circle) of the ring-shaped sampling area is R1=k×D (k=3, 4, 5,..., 10), and the radius of the convex bottom surface circle (i.e. the outer circle) of the ring-shaped sampling area is R2=k×D+Hcosα.

[0015] Further, in step four, when making the sampling plane, from the outer circle of the annular sampling area R1, an annular cutter sampling plane is made on the outer circle of R2, which is the outer surface of the boss, and the sampling plane is the tangent plane of the outer surface of the boss. The annular cutter is sampled vertically to the sampling plane, so that the dihedral angle between the annular cutter sampling plane and the soil horizontal plane is α, and R2-R1=Hcosα exists, and the number of samples taken in the annular sampling area N=π(R1+R2) / D.

[0016] Further, in step four, in the actual annular cutter sampling operation, the second annular cutter center axis is perpendicular to the sampling plane, and the sampling is carried out in each direction along the outer surface of the boss at the corresponding sampling depth.

[0017] Further, in step five, the root-soil complex samples in the annular area of each layer are obtained, and the root direct shear test is carried out layer by layer to obtain the test results, including: taking the average value of the direct shear test of the root-soil complex samples in each annular area as the test result. Advantages

[0018] 1. The present application determines the dihedral angle between the actual shear plane and the soil horizontal plane, and then makes the sampling plane. The annular cutter is sampled vertically to the actual shear plane, which ensures that the direction of the actual shear plane of the root-soil complex is consistent with the direction of the shear plane of the direct shear test, and avoids errors caused by the anisotropy of the root-soil complex.

[0019] 2. The present application samples layer by layer along the actual shear plane with the diameter of the annular cutter as the layering distance, determines the shear strength of the soil in each layer within the actual shear depth range, and expresses the test results layer by layer, so as to avoid test errors caused by differences in root content and water content at different depths.

[0020] 3. The present application plans an annular sampling area within the same depth range, and samples in each direction along the planned annular area, which offsets the deviation caused by the different distribution directions of the roots of each sample, and avoids test errors caused by the root structure and distribution in each direction of the soil in the same layer. BRIEF DESCRIPTION OF DRAWINGS

[0021] Fig. 1 is a flow chart of the test method for reducing the test error of the root-soil complex shear strength provided by the embodiment of the present application;

[0022] Fig. 2 is a schematic diagram of the test method provided by the embodiment of the present application;

[0023] Fig. 3 is a schematic diagram of the sampling plane design and annular cutter sampling method provided by the embodiment of the present application;

[0024] Fig. 4 is a top view of the annular cutter sampling plane of Fig. 3.

[0025] Wherein, 1 is horizontal ground surface, 2 is root, 3 is ring knife, 4 is the first ring knife center axis, 5 is the first straight shear test shear plane, 6 is the second straight shear test shear plane, 7 is the second ring knife center axis, 8 is tillage component, 9 is the first movement direction, 10 is the tillage component rotation center, 11 is the second movement direction, 12 is the actual shear plane, 13 is soil, 14 is ring knife sampling plane, 15 is soil horizontal plane, 16 is planned ring knife sampling position. Best mode of the present application

[0026] The present application is described in detail below with reference to the accompanying drawings and examples.

[0027] Example: the present application embodiment proposes a test method for reducing the shear strength test error of root-soil complex, as shown in Figure 1, by determining the dihedral angle of the actual shear plane 12, making a sampling plane, layering the soil 13 according to the height of the ring knife 3, designing a ring-shaped sampling area and sampling along each direction of the ring-shaped sampling area, measuring the strength of root-soil complex at different depths and layering the test results, which can avoid the test error caused by the inconsistency of the actual shear plane and the shear plane of the straight shear test, the test error caused by the difference of physical properties of soil at different depths, and the test error caused by the difference of root distribution in soil. Specifically, the following steps are included:

[0028] Step one: determine the actual shear plane 12 of the shear process between the tillage component 8 and the soil during tillage, measure the dihedral angle between the actual shear plane 12 and the soil horizontal plane 15 when the tillage depth is reached, and measure the actual shear depth H of the tillage component 8 to the soil during tillage.

[0029] As shown in Figures 2-4, determining the actual shear plane 12 of the shear process between the tillage component 8 and the soil during tillage means determining the angle α formed by the tillage component 8 during tillage and the soil horizontal plane 15, measuring the dihedral angle between the actual shear plane 12 and the soil horizontal plane 15 when the tillage depth is reached, i.e. measuring the angle α between the actual shear plane formed by tillage and the soil horizontal plane 15, and measuring the actual shear depth H of the tillage component to the soil during tillage, which refers to the vertical distance H from the ground surface to the maximum tillage depth when the tillage component is working.

[0030] Step two: according to the actual shear depth H generated by the actual shear process of tillage to the soil, layering the sampling according to the diameter of the ring knife 3 along the actual shear plane 12 from the horizontal ground surface 1 to the tillage depth range, and obtaining the layering measurement depth.

[0031] The actual shear depth H measured in step one is the actual tillage depth range. Specifically, as shown in FIGS. 2-4, the sampling is planned in layers along the shear occurrence surface from the horizontal ground surface 1 to the tillage depth range according to the diameter of the ring knife 3, the depth of each layer is measured, including: the length of the shear occurrence surface is L, then L = H / cos a; the diameter of the ring knife 3 is D, then the number of layers n = (H / cos a) / D, the depth of the first layer H1 = D x sin a, the depth of the second layer H2 = 2D x sin a, the depth of the third layer H3 = 2D x sin a,..., the depth of the nth layer Hn = nD x sin a (n = 1, 2, 3,...). The ring knife sampling position 16 of the layered planning is shown in FIG. 3.

[0032] Step three: According to the planned layered measurement depth, a ring sampling area is planned for each layer.

[0033] Specifically, when the depth of the nth layer is Hn = nD x sin a (n = 1, 2, 3,...), a convex ring sampling area is made. Considering the actual needs, the ring sampling area cannot be too large or too small. In this embodiment, as shown in FIGS. 3-4, the radius of the convex top surface circle (i.e. the inner circle) of the ring sampling area is R1 = k x D (k = 3, 4, 5,..., 10), and the radius of the convex bottom surface circle (i.e. the outer circle) of the ring sampling area is R2 = k x D + Hcos a.

[0034] Step four: In the same depth range, a sampling plane is made according to the dihedral angle a of the actual shear occurrence surface 12, and the ring knife 3 is vertically sampled to ensure that the dihedral angle between the sampling plane and the soil horizontal plane 15 in any sampling direction is consistent with the dihedral angle between the actual shear occurrence surface 12 and the soil horizontal plane 15. At the same time, multiple samples are taken in various directions along the planned ring area, and the average value of the sample shear strength is calculated to offset the positive and negative deviation effects caused by the root distribution direction and reduce the test error.

[0035] Specifically, as shown in FIG. 3, when the sampling plane is made, the ring knife sampling plane 14 is made from the outer circle of the ring sampling area R1 to the outer circle of R2, which is the outer surface of the convex, and the sampling plane is the tangent plane of the outer surface of the convex. The ring knife 3 is vertically sampled to make the dihedral angle between the ring knife sampling plane 14 and the soil horizontal plane a, and R2-R1 = Hcos a, the number of samples N = π(R1+R2) / D in the ring sampling area.

[0036] In the actual cutting ring sampling operation, the samples are taken in each direction along the outer surface of the boss at the corresponding sampling depth in the state that the second cutting ring central axis 7 is perpendicular to the sampling plane, so as to offset the deviation of each sample caused by the different distribution directions of the roots, and avoid the test error caused by the root structure and distribution in each direction of the same layer soil. Meanwhile, the sampling mode ensures that the actual shear occurrence surface direction of the root-soil complex is consistent with the shear occurrence surface direction of the direct shear test, and avoids the error caused by the anisotropy of the root-soil complex.

[0037] Step five: respectively obtain the root-soil complex samples in the ring area of each layer, and carry out the root direct shear test layer by layer to obtain the test results.

[0038] It should be noted that the direct shear test is carried out on the obtained samples by layer, and since the same layer and the same sampling surface have the same probability of overestimation or underestimation caused by the different distribution directions of the roots, the average value of the shear strength of the direct shear test of the root-soil complex samples in each layer of the ring area can be taken as the test result, so that the test error of the same layer and the same direction soil caused by the different distribution directions of the roots can be offset.

[0039] Step six: according to the test results, the shear strength of each layer of soil is expressed layer by layer.

[0040] It can be understood that the samples are taken layer by layer along the actual shear occurrence surface with the cutting ring diameter as the layering distance, the shear strength of each layer of soil in the actual shear depth range is determined, and the test results are expressed layer by layer, so as to avoid the test error caused by the differences in root content, water content and the like at different depths.

[0041] In order to more clearly understand the present application, the design principle of the present application will be specifically described as follows:

[0042] I. The overall design principle of the test method: as shown in Figure 2, taking a rotary active penetration type extremely narrow cutting knife as an example, the cutting knife (i.e. the tillage component 8) rotates along the rotation center 10, the cutting knife at the upper end of the rotation surface moves outward along the first movement direction 9, the cutting knife at the lower end of the rotation surface moves inward along the second movement direction 11, under the rotation cutting movement of the cutting knife, the actual shear occurrence surface 12 with an angle α with the horizontal direction is formed. However, the method commonly used for measuring the soil shear resistance of farmland does not consider the shear surface formed by the tillage component and the soil in the actual operation process, and the method for sampling the root-soil complex is: through the first ring knife center axis 4 of the ring knife with the horizontal surface at an angle θ = 90°, and the first direct shear test shear occurrence surface 5 formed by the soil directly sheared when developing a direct shear test with the horizontal surface at an angle α = 0°. However, as can be seen from the principle diagram 2, when the tillage component 8 operates at an angle α with the horizontal surface, the dihedral angle between the actual shear occurrence surface 12 and the horizontal surface 1 is α, and when α is not 0, the actual shear occurrence surface 12 is inconsistent with the first direct shear test shear occurrence surface 5 formed by the direct shear test, since the root-soil complex has anisotropic characteristics, the test results and the actual values are different, and the test error caused by the selection error of the sampling surface is caused. Therefore, the method proposed by the present application is to make the dihedral angle between the sampling plane and the soil horizontal surface 15 be α, and the second ring knife center axis 7 is perpendicular to the sampling plane when sampling (the dihedral angle between the second ring knife center axis 7 and the horizontal surface 1 is θ = 90°-α), in this case, the second direct shear test shear occurrence surface 6 formed by the sample obtained in the direct shear test is consistent with the actual shear occurrence surface 12, so that the test error caused by the selection error of the sampling surface can be overcome.

[0043] II. Sampling surface design and sampling method: as shown in Figure 3, in order to avoid the test error caused by the difference in physical properties of soil at different depths, the annular sampling area is planned according to the tillage depth H, the dihedral angle α between the actual shear occurrence surface 12 and the soil horizontal surface, the main view of the whole sampling area is a convex table, and the dihedral angle between the annular sampling surface 14 and the soil horizontal surface 15 is α. The length of the shear surface is L, then L = H / cosα; the diameter of the ring knife is D, then the number of layers n = (H / cosα) / D, the depth of the first layer H1 = D×sinα, the depth of the second layer H2 = 2D×sinα, the depth of the third layer H3 = 2D×sinα,..., the depth of the nth layer H n =nD×sinα (n = 1, 2, 3,...). The depth of the nth layer H nWhen nDxsinα (n=1, 2, 3...) is used to make the ring-shaped sampling area in the form of a convex platform, considering the actual needs, the sampling area cannot be too large or too small, and a positive integer k (k=3, 4, 5,..., 10) is introduced to establish a correlation between the radius of the ring-shaped area and the diameter D of the ring cutter 3, wherein the top surface circle of the convex platform is R1=kxD (k=3, 4, 5,..., 10), and the bottom surface circle R2=kxD+Hcosα. When making, the ring cutter sampling surface 14 is made from the outer circle of the ring-shaped sampling area R1 to the outer circle of R2, and the sampling surface is the outer surface of the convex platform, the dihedral angle between the sampling surface and the soil horizontal plane is α, and R1-R2=Hcosα exists.

[0044] A ring-shaped sampling area is planned in each layer within the same depth range, and sampling is carried out along the planned ring-shaped area, and the second ring cutter center axis is perpendicular to the ring cutter sampling surface in the state of sampling along the outer surface of the convex platform, and the number of samples taken in the ring-shaped sampling area is N=π(R1+R2) / D. The obtained samples are subjected to direct shear test according to the layer, and since the distribution direction of the roots in the same layer and the same sampling surface is different, the probability of overestimation or underestimation is consistent, so the average value of the measured values of the samples in each ring-shaped area can offset the test error caused by the different distribution directions of the roots in the same layer and the same direction. Finally, the measured results are obtained, and the shear strength test results of the root-soil complex are expressed in layers.

[0045] It can be understood that the above specific description of the present application is only used to illustrate the technical solutions described in the embodiments of the present application, and the ordinary skilled in the art should understand that the present application can still be modified or replaced equivalently to achieve the same technical effect; as long as the use needs are met, it is within the protection scope of the present application. Industrial applicability

[0046] The present application determines the dihedral angle between the actual shear plane and the soil horizontal plane, makes a sampling plane, and samples vertically to the actual shear plane with a ring cutter, so as to ensure that the direction of the actual shear plane of the root-soil complex is consistent with the direction of the shear plane in the direct shear test, and avoid errors caused by the anisotropy of the root-soil complex. A ring-shaped sampling area is planned within the same depth range, and sampling is carried out in all directions along the planned ring-shaped area, so as to offset the deviation of each sample caused by the different distribution directions of the roots, and avoid test errors caused by the root structure and distribution in the same layer. The determination of the shear strength of the field soil is improved.

Claims

1. A test method for reducing errors in root-soil complex shear strength tests, characterized by, The method comprises the following steps: Step 1: determining the actual shear occurrence surface of the shear process between the tillage component and the soil in the tillage process, measuring the dihedral angle between the actual shear occurrence surface and the soil level surface at the tillage depth, and measuring the actual shear depth H of the tillage component to the soil in the tillage process; Step 2: according to the actual shear depth H generated by the actual tillage to the soil shear process, layering planning sampling along the actual shear occurrence surface according to the ring knife diameter from the horizontal ground surface to the tillage depth range to obtain the layering measurement depth; Step 3: according to the layering measurement depth, planning a ring sampling area for each layer; Step 4: in the same depth range, according to the dihedral angle α of the actual shear occurrence surface, manufacturing a sampling plane, vertically sampling the ring knife to the sampling plane, and sampling in all directions along the planned ring area; Step 5: obtaining root-soil complex samples in the ring area of each layer, respectively, and layering to carry out root direct shear tests to obtain test results; Step 6: according to the test results, layering to express the shear strength of each layer of soil.

2. The test method of claim 1, wherein, In step 2, layering planning sampling along the actual shear occurrence surface according to the ring knife diameter from the horizontal ground surface to the tillage depth range to obtain the layering measurement depth, including: the length of the shear occurrence surface is L, then L=H / cosα; the diameter of the ring knife is D, then the number of layers n=(H / cosα) / D, the first layer depth H1=D×sinα, the second layer depth H2=2D×sinα, the third layer depth H3=2D×sinα,..., and the n-th layer depth Hn=nD×sinα (n=1, 2, 3,...).

3. The test method of claim 1, wherein, In step 3, according to the layering measurement depth, planning a ring sampling area for each layer, including: manufacturing a convex ring sampling area at the depth of the n-th layer Hn=nD×sinα (n=1, 2, 3,...); wherein the convex top surface circle (i.e. inner circle) radius of the ring sampling area is R1=k×D (k=3, 4, 5,..., 10), and the convex bottom surface circle (i.e. outer circle) radius of the ring sampling area is R2=k×D+Hcosα.

4. The test method of claim 3, wherein, In step 4, when manufacturing the sampling plane, the ring knife sampling surface is the outer surface of the convex, and the sampling plane is the tangent plane of the outer surface of the convex, the ring knife is vertically sampled to the sampling plane, the dihedral angle between the ring knife sampling surface and the soil level surface is α, and R2-R1=Hcosα exists, and the number of samples N taken in the ring sampling area is π(R1+R2) / D.

5. The test method of claim 3, wherein In step 4, in the actual ring knife sampling operation process, the second ring knife center axis is perpendicular to the sampling plane, and sampling is performed in all directions along the outer surface of the convex at the corresponding sampling depth.

6. The test method of claim 1, wherein, In step 5, obtaining root-soil complex samples in the ring area of each layer, respectively, and layering to carry out root direct shear tests to obtain test results, including: taking the average value of the shear strength of the direct shear test of the root-soil complex samples in each ring area as the test result.

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