Method for measuring saturated hydraulic conductivity of soil

Abstract

The invention relates to the technical field of soil characteristic testing, in particular to a soil saturated hydraulic conductivity measuring method which comprises the following steps: preparing a cylindrical soil sample; preparing a wax-sealed cylindrical soil sample; preparing a soil sample piece for measuring the saturated hydraulic conductivity; and executing a water penetration test. Due to the large forming thickness of the wax sealing body, the phenomenon that the wax sealing body cracks in the ring cutting process can be avoided, it is guaranteed that the wax sealing body in the ring cutting state has good forming regularity and tissue continuity, and the phenomenon that the wax sealing body is overcut can be avoided; furthermore, in the girdling process, the sampling cutting ring in the temperature rising state can heat the wax sealing body in the pre-removal area to soften the wax sealing body, so that the sampling cutting ring can smoothly go deep into the wax sealing body, and the original solidification forming defect can be repaired in an accompanied manner; besides, in the water penetration testing process, testing water can only penetrate through the cylindrical soil sample, and even if the wax sealing body and the sampling cutting ring are not in tight contact, the accuracy of the saturated hydraulic conductivity of the soil can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of soil property testing, in particular to a method for measuring soil saturated hydraulic conductivity. Background Art

[0002] Soil saturated hydraulic conductivity is one of the important physical properties of soil and has a significant impact on the quality of earthwork construction. Soil saturated hydraulic conductivity is defined as the amount of water passing through a unit area per unit time under a unit water potential gradient when the soil is saturated with water. It is a function of soil texture, bulk density, and pore distribution characteristics.

[0003] The commonly used methods for testing soil saturated hydraulic conductivity in indoor experiments include the constant head test method and the variable head test method. In the past few years, a sampling ring knife was used to directly cut the cylindrical soil sample in a ring, that is, to form a soil sample for saturated hydraulic conductivity measurement. However, in actual tests, the soil is very likely to collapse after long-term immersion, and under the long-term influence of the test water, a large number of grooves are easily eroded on the circumferential side walls of the soil sample, which is bound to affect the amount of water flowing through the soil sample per unit time interval. In recent years, in order to cope with the above problems, a sampling ring knife is used to cut the wax-sealed cylindrical soil sample in a ring to form a soil sample for saturated hydraulic conductivity measurement, as described in Chinese invention patent CN107192650B. However, after many tests and verifications, the soil saturated hydraulic conductivity calculated by the measurement method disclosed in CN107192650B still deviates greatly from the actual value. The reasons are: 1) According to the current consensus in the industry, the thickness of the wax seal formed on the circumferential side wall of the cylindrical soil sample is extremely thin, generally controlled within 3 mm. Therefore, in the process of the sampling ring knife penetrating into the wax seal, due to improper control of the applied pressure value, the wax seal is very likely to generate cracks and extend along the height direction; or, due to deviations in the control of the direction of the applied pressure, the wax seal is very likely to be "overcut" locally, and part of the circumferential side wall of the cylindrical soil sample is exposed. Both of the above factors will directly lead to the wax seal application effect not meeting expectations, which will affect the accuracy of the test results; 2) Affected by various uncontrollable factors, after the wax seal is cut, it is extremely difficult to achieve tight contact between the outer wall of the wax seal and the inner wall of the sampling ring knife. The test water is very easy to flow out through the gap, which will inevitably affect the amount of water flowing through the soil sample per unit time interval, and then the soil saturated hydraulic conductivity calculated by Darcy's law will be greatly different from the actual one. Therefore, it is urgent for technicians to solve the above problems. Summary of the invention

[0004] Therefore, in view of the above-mentioned existing problems and defects, the designers of the present invention collected relevant information, conducted multiple evaluations and considerations, and continued to experiment and modify the method after many years of research and development experience in this industry, which ultimately led to the emergence of the soil saturated hydraulic conductivity measurement method.

[0005] In order to solve the above technical problems, the present invention relates to a method for measuring soil saturated hydraulic conductivity, which comprises the following steps:

[0006] S1. Prepare cylindrical soil samples;

[0007] The soil is sampled and cut and shaped by a knife cutting method to form a cylindrical soil sample; the diameter of the cylindrical soil sample is smaller than the inner diameter of the sampling ring knife, and the height of the cylindrical soil sample is greater than the sampling ring knife;

[0008] S2, preparing wax-sealed cylindrical soil samples;

[0009] Forming a wax seal body on the circumferential side wall of the cylindrical soil sample to prepare a wax-sealed cylindrical soil sample;

[0010] The diameter of the wax-sealed cylindrical soil sample is larger than the inner diameter of the sampling ring cutter;

[0011] The diameter of the wax-sealed cylindrical soil sample is a, the wall thickness of the wax-sealed body is b, and the inner diameter of the sampling ring knife is c, then 3mm≤ac≤5mm, b≥6mm;

[0012] S3, preparing soil samples for saturated hydraulic conductivity measurement, including the following sub-steps:

[0013] S31, placing the sampling ring knife on the top wall of the wax-sealed cylindrical soil sample, and applying pressure to make it penetrate into the wax seal body until the top surface of the sampling ring knife is flush with the top wall of the wax-sealed cylindrical soil sample;

[0014] Before the formal ring cutting operation is performed on the wax-sealed cylindrical soil sample, the sampling ring knife is preheated and heated; assuming that the melting point of the wax seal is T, and the sampling ring knife is heated to t1, then T-3℃≤t1<T, and its instantaneous temperature value after the ring cutting is completed is not lower than T-8℃.

[0015] S32, using a soil trimming knife to remove excess soil and wax seals at both ends of the sampling ring knife from the edge to the middle;

[0016] S33, shaping the top of the wax-sealed cylindrical soil sample by means of a first grooving tool to partially remove the wax seal between the sampling ring cutter and the cylindrical soil sample until an upper annular groove is formed;

[0017] S34, filling waterproof glue into the upper annular groove to form an upper waterproof sealing ring;

[0018] S35, turning the sampling ring knife 180 degrees, and then trimming the bottom of the wax-sealed cylindrical soil sample with the aid of a second grooving tool to partially remove the wax seal between the sampling ring knife and the cylindrical soil sample until a lower annular groove is formed;

[0019] S36, filling waterproof glue into the lower annular groove to form a lower waterproof sealing ring;

[0020] S37, the shortened wax seal body is sealed in an annular cavity surrounded by the cylindrical soil sample, the sampling ring knife, the upper waterproof sealing ring and the lower waterproof sealing ring. At this point, the saturated hydraulic conductivity test soil sample is prepared;

[0021] S4. Place the soil sample for saturated hydraulic conductivity measurement into the infiltometer for testing.

[0022] As a further improvement of the technical solution disclosed in the present invention, in step S33, the first slotting tool is heated and heated until its temperature reaches t2. Before the top of the wax-sealed cylindrical soil sample is formally reshaped, T-3°C ≤ t2 < T, and its instantaneous temperature value after the reshaping is completed is not lower than T-8°C.

[0023] As a further improvement of the technical solution disclosed in the present invention, in step S35, the second slotting tool is heated and heated until its temperature reaches t3. Before the bottom of the wax-sealed cylindrical soil sample is formally reshaped, T-3°C ≤ t3 < T, and its instantaneous temperature value after the reshaping is completed is not lower than T-8°C.

[0024] As a further improvement of the technical solution disclosed in the present invention, in step S3, the waterproof glue filling the upper annular groove and the lower annular groove is thermosetting waterproof glue, and after the waterproof glue is filled, it is heated to accelerate the curing process.

[0025] As a further improvement of the technical solution disclosed in the present invention, in step S3, the depths of the upper annular groove and the lower annular groove are both controlled to be 2 to 3 mm.

[0026] In practical applications, the soil saturated hydraulic conductivity determination method disclosed in the present invention can achieve at least the following beneficial technical effects, specifically:

[0027] 1) The wax seal formed on the circumferential side wall of the cylindrical soil sample has a large thickness, and the diameter of the prepared wax-sealed cylindrical soil sample is significantly larger than the inner diameter of the sampling ring. In this way, on the one hand, thanks to the large molding thickness of the wax seal, it can not only effectively avoid the occurrence of cracks in the wax seal during the ring cutting process, ensuring that the ring cut wax seal has good molding regularity and structural continuity, but also avoid the occurrence of "overcutting" of the wax seal due to improper control of the ring cutting force direction;

[0028] 2) Before the formal ring cutting operation is carried out, the sampling ring knife needs to be preheated and heated to a temperature not lower than the melting point of the wax seal. During the ring cutting operation of the wax-sealed cylindrical soil sample, the sampling ring knife can heat the wax seal in the pre-removal area to soften it, which is conducive to the sampling ring knife to penetrate the wax seal more smoothly, laying a good foundation for shortening the ring cutting time. In the hot cutting process, the original solidification defects of the wax seal (such as cracks, holes, etc.) can also be repaired;

[0029] 3) The wax seal formed on the circumferential side wall of the cylindrical soil sample and shortened by shaping is enclosed in the annular cavity. In this way, in the process of performing water penetration test on the soil sample for saturated hydraulic conductivity measurement, under the synergistic effect of the upper waterproof sealing ring and the lower waterproof sealing ring, the test water can only penetrate through the cylindrical soil sample, even if there is a gap between the outer wall of the wax seal and the inner wall of the sampling ring knife, which is conducive to improving the accuracy of the obtained soil saturated hydraulic conductivity, thereby providing data support for subsequent earthwork construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 The present invention is a schematic diagram of the structure of a sampling ring cutter in the soil saturated hydraulic conductivity determination method disclosed in the present invention.

[0032] Figure 2 It is a structural schematic diagram of a cylindrical soil sample in the soil saturated hydraulic conductivity determination method disclosed in the present invention.

[0033] Figure 3 The invention discloses a schematic diagram of the structure of a wax-sealed cylindrical soil sample in the soil saturated hydraulic conductivity determination method disclosed in the present invention.

[0034] Figure 4 It is a structural schematic diagram of a soil sample for measuring saturated hydraulic conductivity in the soil saturated hydraulic conductivity measuring method disclosed in the present invention.

[0035] Figure 5 It is a schematic diagram of the forming process of a soil sample for measuring saturated hydraulic conductivity in the soil saturated hydraulic conductivity measuring method disclosed in the present invention. DETAILED DESCRIPTION

[0036] In order to facilitate those skilled in the art to fully understand the technical solutions disclosed in the present invention, the contents of the present invention are further described in detail below in conjunction with specific embodiments.

[0037] The method for measuring soil saturated hydraulic conductivity disclosed in the present invention comprises the following steps:

[0038] S1. Prepare cylindrical soil samples;

[0039] The soil is sampled and cut and shaped by a knife cutting method to form a cylindrical soil sample; the diameter of the cylindrical soil sample is smaller than the inner diameter of the sampling ring knife, and the height of the cylindrical soil sample is greater than the sampling ring knife;

[0040] S2, preparing wax-sealed cylindrical soil samples;

[0041] Forming a wax seal body on the circumferential side wall of the cylindrical soil sample to prepare a wax-sealed cylindrical soil sample;

[0042] The diameter of the wax-sealed cylindrical soil sample is larger than the inner diameter of the sampling ring cutter;

[0043] Assuming that the diameter of the wax-sealed cylindrical soil sample is a, the wall thickness of the wax seal is b, and the inner diameter of the sampling ring knife is c, then 3mm≤ac≤5mm, b≥6mm;

[0044] S3. Prepare soil samples for saturated hydraulic conductivity measurement, such as Figure 5 As shown in , it includes the following sub-steps:

[0045] S31, placing the sampling ring knife on the top wall of the wax-sealed cylindrical soil sample, and applying pressure to make it penetrate into the wax seal body until the top surface of the sampling ring knife is flush with the top wall of the wax-sealed cylindrical soil sample;

[0046] Before the formal ring cutting operation is performed on the wax-sealed cylindrical soil sample, the sampling ring knife is preheated and heated; assuming that the melting point of the wax seal is T, and the sampling ring knife is heated to t1, then T-3℃≤t1<T, and its instantaneous temperature value after the ring cutting is completed is not lower than T-8℃.

[0047] S32, using a soil trimming knife to remove excess soil and wax seals at both ends of the sampling ring knife from the edge to the middle;

[0048] S33, shaping the top of the wax-sealed cylindrical soil sample with the aid of a first grooving tool to partially remove the wax seal between the sampling ring cutter and the cylindrical soil sample until an upper annular groove is formed, and the groove depth is controlled to be 2 to 3 mm;

[0049] S34, filling the upper annular groove with waterproof glue, and waiting for the waterproof glue to solidify to form an upper waterproof sealing ring;

[0050] S35, turning the sampling ring knife 180 degrees, and then trimming the bottom of the wax-sealed cylindrical soil sample with the aid of a second grooving tool to partially remove the wax seal between the sampling ring knife and the cylindrical soil sample until a lower annular groove is formed, and the groove depth is controlled to be 2 to 3 mm;

[0051] S36, filling the lower annular groove with waterproof glue, and waiting for the waterproof glue to solidify to form a lower waterproof sealing ring;

[0052] S37, the shortened wax seal body is sealed in an annular cavity surrounded by the cylindrical soil sample, the sampling ring knife, the upper waterproof sealing ring and the lower waterproof sealing ring. At this point, the saturated hydraulic conductivity test soil sample is prepared;

[0053] S4. Place the soil sample for saturated hydraulic conductivity measurement into the permeameter for testing. Saturated hydraulic conductivity is mainly used to reflect the infiltration and water permeability of soil, and is also used to indirectly reflect the unsaturated hydraulic conductivity of soil. The testing principle of the permeameter is: saturated hydraulic conductivity is used to measure the amount of water passing through a unit area per unit time under a unit water potential gradient when the soil sample is saturated with water, and is calculated based on the Darcy quantitative value of the porous medium under saturated state.

[0054] In order to facilitate understanding by those skilled in the art, Figure 1 , Figure 2 , Figure 3 , Figure 4 The schematic diagrams of the structures of the sampling ring cutter, cylindrical soil sample, wax-sealed cylindrical soil sample and saturated hydraulic conductivity measurement soil sample involved in the above-mentioned soil saturated hydraulic conductivity measurement method are respectively shown.

[0055] In practical applications, the soil saturated hydraulic conductivity determination method disclosed in the present invention has achieved the following beneficial technical effects, specifically:

[0056] 1) The wax seal formed on the circumferential side wall of the cylindrical soil sample has a large thickness, and the diameter of the prepared wax-sealed cylindrical soil sample is significantly larger than the inner diameter of the sampling ring. In this way, on the one hand, thanks to the large molding thickness of the wax seal, it not only effectively avoids the occurrence of cracks in the wax seal during the ring cutting process, ensuring that the ring cut wax seal has good molding regularity and structural continuity, but also avoids the occurrence of "overcutting" of the wax seal due to improper control of the ring cutting force direction;

[0057] 2) Before the formal ring cutting operation is carried out, the sampling ring knife needs to be preheated and heated to a temperature not lower than the melting point of the wax seal. During the ring cutting operation of the wax-sealed cylindrical soil sample, the sampling ring knife can heat the wax seal in the pre-removal area to soften it, which is conducive to the sampling ring knife to penetrate the wax seal more smoothly, laying a good foundation for shortening the ring cutting time. In the hot cutting process, the original solidification defects of the wax seal (such as cracks, holes, etc.) are also repaired.

[0058] Here, it is particularly important to emphasize that the wax seal formed on the circumferential side wall of the cylindrical soil sample and shortened by shaping is enclosed in the annular cavity. In this way, in the process of performing water penetration test on the soil sample for saturated hydraulic conductivity measurement, under the synergistic effect of the upper waterproof sealing ring and the lower waterproof sealing ring, the test water can only penetrate through the cylindrical soil sample. Even if the wax seal cannot fit tightly against the inner wall of the sampling ring knife and there is a gap, it is beneficial to improve the accuracy of the obtained soil saturated hydraulic conductivity, thereby providing data support for subsequent earthwork construction.

[0059] In order to speed up the forming speed of the upper annular groove and the lower annular groove and ensure good shape regularity after forming, as a further optimization of the above technical solution, in step S33, the first slotting tool is heated and heated until its temperature reaches t2. Before the top of the wax-sealed cylindrical soil sample is formally trimmed, T-3℃≤t2<T, and its instantaneous temperature value after the trimming is not lower than T-8℃. In step S35, the second slotting tool is heated and heated until its temperature reaches t3. Before the bottom of the wax-sealed cylindrical soil sample is formally trimmed, T-3℃≤t3<T, and its instantaneous temperature value after the trimming is not lower than T-8℃. In this way, during the forming of the upper annular groove and the lower annular groove, the heated first grooving tool and the second grooving tool can effectively heat the wax seal body, and the wax seal body softens due to the heat, which is conducive to the first grooving tool and the second grooving tool to smoothly penetrate into the wax seal body, and effectively avoids the occurrence of the phenomenon that part of the wax seal body is broken due to improper force or the integrity of the peripheral wall of the cylindrical soil sample is destroyed due to accidental rigid contact.

[0060] Furthermore, as a further optimization of the above technical solution, in step S3, the waterproof glue used to fill the upper annular groove and the lower annular groove is a thermosetting waterproof glue, and after the waterproof glue is filled, it is heated to accelerate the curing process. The thermosetting waterproof glue can preferably be SBS modified asphalt waterproof glue, polyurethane waterproof glue, acrylic waterproof glue, etc.

[0061] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest range of convergences with the principles and novel features disclosed herein.

Claims

1. A method for measuring soil saturated hydraulic conductivity, characterized in that: The following steps are involved: S1. Prepare cylindrical soil samples; Sampling the soil, and cutting and shaping it by knife cutting to form the cylindrical soil sample; the diameter of the cylindrical soil sample is smaller than the inner diameter of the sampling ring knife, and the height of the cylindrical soil sample is greater than the sampling ring knife; S2, preparing wax-sealed cylindrical soil samples; Forming a wax seal on the circumferential side wall of the cylindrical soil sample to prepare a wax-sealed cylindrical soil sample; The diameter of the wax-sealed cylindrical soil sample is larger than the inner diameter of the sampling ring cutter; The diameter of the wax-sealed cylindrical soil sample is a, the wall thickness of the wax-sealed body is b, and the inner diameter of the sampling ring knife is c, then 3mm≤ac≤5mm, b≥6mm; S3, preparing soil samples for saturated hydraulic conductivity measurement, including the following sub-steps: S31, placing the sampling ring knife on the top wall of the wax-sealed cylindrical soil sample, and applying pressure to make it penetrate into the wax seal body until the top surface of the sampling ring knife is flush with the top wall of the wax-sealed cylindrical soil sample; Before the formal ring cutting operation is performed on the wax-sealed cylindrical soil sample, the sampling ring knife is preheated and heated; assuming that the melting point of the wax seal is T, and the sampling ring knife is heated to t1, then T-3°C ≤ t1 < T, and its instantaneous temperature value after the ring cutting is completed is not less than T-8°C; S32, using a soil trimming knife to remove excess soil at both ends of the sampling ring knife and the wax seal from the edge to the middle; S33, trimming the top of the wax-sealed cylindrical soil sample by means of a first grooving tool to partially remove the wax seal between the sampling ring cutter and the cylindrical soil sample until an upper annular groove is formed; S34, filling the upper annular groove with waterproof glue to form an upper waterproof sealing ring; S35, turning the sampling ring knife 180 degrees, and then trimming the bottom of the wax-sealed cylindrical soil sample with the aid of a second grooving tool to partially remove the wax seal between the sampling ring knife and the cylindrical soil sample until a lower annular groove is formed; S36, filling the lower annular groove with waterproof glue to form a lower waterproof sealing ring; S37, the shortened wax seal body is sealed in an annular cavity surrounded by the cylindrical soil sample, the sampling ring knife, the upper waterproof sealing ring and the lower waterproof sealing ring, and the saturated hydraulic conductivity test soil sample is now prepared; S4. placing the soil sample for saturated hydraulic conductivity measurement into a permeameter for testing.

2. The method for measuring soil saturated hydraulic conductivity according to claim 1, characterized in that: In step S33, the first slotting tool is heated until its temperature reaches t2; before the top of the wax-sealed cylindrical soil sample is formally reshaped, T-3°C ≤ t2 < T, and its instantaneous temperature value after the shaping is completed is not lower than T-8°C.

3. The method for measuring soil saturated hydraulic conductivity according to claim 1, characterized in that: In step S35, the second slotting tool is heated until its temperature reaches t3; before the bottom of the wax-sealed cylindrical soil sample is formally reshaped, T-3°C ≤ t3 < T, and its instantaneous temperature value after the shaping is completed is not lower than T-8°C.

4. The method for measuring soil saturated hydraulic conductivity according to claim 1, characterized in that: In step S3, the waterproof glue used to fill the upper annular groove and the lower annular groove is thermosetting waterproof glue, and after the waterproof glue is filled, it is heated to accelerate the curing process.

5. The method for measuring soil saturated hydraulic conductivity according to claim 1, characterized in that: In step S3, the depths of the upper annular groove and the lower annular groove are both controlled to be 2-3 mm.

Images