Accurate geotechnical dry-wet cycle test method

Abstract

The invention discloses an accurate geotechnical dry-wet cycle test method which comprises the following steps: preparing a sample, humidifying, braising, drying, humidifying again, braising again, completing at least five cycles according to the method, and then performing a mechanical test on the sample. In the sample preparation process, the initial water content of the sample needs to be measured, and the water content of the sample is humidified to the initial water content in the humidifying stage. According to the method, the change of the moisture content amplitude in the dry-wet cycle is determined according to the change of the actual moisture content under the field climate condition, meanwhile, a re-humidifying and re-braising stage is added after each dry-wet cycle, the moisture content of the sample is adjusted to the initial moisture content, then the sample is subjected to a mechanical property test, and the test result is more accurate. At the moment, the change of the mechanical property of the test sample after multiple cycles is caused by the change of the soil sample structure, and the obtained mechanical property test result can well guide engineering design.

Description

Technical Field

[0001] The invention relates to an accurate geotechnical dry-wet cycle test method and belongs to the technical field of civil engineering. Background Art

[0002] The purpose of conducting dry-wet cycles on soil samples is to study the changing rules of the mechanical properties of the samples after dry-wet cycles, to provide more realistic indicators for engineering design, and to ensure the quality and safety of the project. However, the current methods are very rough in describing the dry-wet cycle test. For example, the amplitude of the moisture content of the dry-wet cycle is not based on the actual moisture content changes of the on-site climatic conditions, resulting in the dry-wet cycle not being consistent with the actual situation; furthermore, the moisture content of the soil sample is not tested after the dry-wet cycle, and the mechanical properties test is directly carried out, which makes it impossible to determine whether the change in mechanical properties is caused by the change in the soil sample structure or the change in moisture content. Due to the certain differences between the test method and the actual working conditions, the results obtained cannot guide the engineering design well.

[0003] In view of the above problems, it is necessary to determine the range of dry-wet cycle test according to the actual moisture content variation range of on-site climatic conditions, and an accurate geotechnical dry-wet cycle test method was invented. Summary of the invention

[0004] The purpose of the present invention is to provide an accurate geotechnical dry-wet cycle test method to ensure that the moisture content of the mechanical test specimen after each dry-wet cycle is consistent with the initial moisture content, so as to verify that the dry-wet cycle process changes the soil structure and causes the mechanical properties of the soil to decay.

[0005] The technical solution of the present invention is: a precise geotechnical dry-wet cycle test method, comprising sample preparation → humidification stage → stewing stage → drying stage → re-humidification stage → re-stewing stage → completing at least 5 cycles according to this method, and then conducting a mechanical test on the sample; during the sample preparation process, it is necessary to determine the initial moisture content of the sample, and in the re-humidification stage the moisture content of the sample is increased to the initial moisture content.

[0006] In the aforementioned precise geotechnical dry-wet cycle test method, the specific steps of the method are as follows: (1) Prepare initial moisture content and dry density samples; (2) Humidification stage: Calculate the amount of water required to humidify the sample until the moisture content reaches 50%, and humidify the sample by injecting water in batches; (3) Stewing stage: After the water injection is completed, the material is stewed in a natural state for 24 hours, and the moisture content of the upper, middle and lower layers of the sample is measured to ensure that the moisture content of the upper, middle and lower layers of the sample is within the range of 50% ± 2%; (4) Drying stage: Place the above sample in an oven at 25-30°C for drying, and measure the moisture content of the sample every hour until the moisture content of the sample drops to 10%; (5) Rehumidification stage: Calculate the amount of water required to humidify the sample until the moisture content reaches the initial moisture content, and add water in batches to humidify the sample; (6) Re-stewing stage: After the water injection is completed, the material is stewed in a natural state for 24 hours, and the moisture content of the upper, middle and lower layers of the sample is measured to ensure that the moisture content of the upper, middle and lower layers of the sample is within the range of ±2% of the initial moisture content; Repeat steps (2) to (6) for at least 5 cycles until the mechanical properties of the sample become stable, and then perform mechanical tests on the sample.

[0007] In the aforementioned precise geotechnical dry-wet cycle test method, in the steps (3) and (6), the moisture content of the upper, middle and lower layers of the sample is determined by the alcohol combustion method.

[0008] In the aforementioned precise geotechnical dry-wet cycle test method, in the steps (2) and (5), the sample is humidified by injecting water with a syringe in batches.

[0009] The beneficial effects of the present invention are as follows: compared with the prior art, in the method of the present invention, the change in the moisture content amplitude of the dry-wet cycle is determined according to the change in the actual moisture content under the on-site climatic conditions; at least 5 dry-wet cycles are performed simultaneously, so that the mechanical properties of the sample tend to be stable; and after each dry-wet cycle, a rehumidification and re-stewing stage is added to adjust the moisture content of the sample to the initial moisture content, and then the sample is subjected to a mechanical property test, so that it can be ensured that the change in the mechanical properties of the sample after multiple cycles is due to the change in the soil sample structure, and the obtained mechanical property test results can well guide engineering design. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a flow chart of the present invention; Figure 2 is the depth-water content relationship curve of a slope profile; Figure 3 This is the test map of the humidity field of the slope K17+720 by Yu Kai; Figure 4 This is the test diagram of the slope humidity field of Yu Kai K18+060. DETAILED DESCRIPTION

[0011] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0012] An embodiment of the present invention: A precise geotechnical dry-wet cycle test method, comprising sample preparation → humidification stage → stewing stage → drying stage → re-humidification stage → re-stewing stage → completing at least 5 cycles according to this method, and then performing a mechanical test on the sample; during the sample preparation process, it is necessary to measure the initial moisture content of the sample, and in the re-humidification stage the moisture content of the sample is increased to the initial moisture content.

[0013] The specific steps are as follows: (1) Prepare initial moisture content and dry density samples; (2) Humidification stage: Calculate the amount of water required to humidify the sample from the initial moisture content to a moisture content of 50%, and humidify the sample by injecting water with a syringe in batches; (3) Stewing stage: After the water injection is completed, the material is stewed in a natural state for 24 hours, and the moisture content of the upper, middle and lower layers of the sample is measured by the alcohol combustion method to ensure that the moisture content of the upper, middle and lower layers of the sample is within the range of 50% ± 2% to ensure uniform moisture distribution; (4) Drying stage: Place the above sample in an oven at 25-30°C for drying, and measure the moisture content of the sample every hour until the moisture content of the sample drops to 10%; (5) Rehumidification stage: Calculate the amount of water required to humidify the sample from a moisture content of 10% to the initial moisture content, and humidify the sample by injecting water with a syringe in batches; (6) Re-stewing stage: After the water injection is completed, the material is stewed in a natural state for 24 hours, and the moisture content of the upper, middle and lower layers of the sample is measured by the alcohol combustion method to ensure that the moisture content of the upper, middle and lower layers of the sample is within the range of ±2% of the initial moisture content, (6) to ensure uniform distribution of moisture; This is a dry-wet cycle. This method should be used to complete at least 5 or even several cycles, and then the sample should be subjected to a mechanical test. After each dry-wet cycle, the moisture content of the sample used for the mechanical test should be consistent with the initial moisture content, so as to verify that the dry-wet cycle process changes the structure of the soil and causes the mechanical properties of the soil to decay.

[0014] In the method of the present invention, the determination of the range of moisture content variation in the dry-wet cycle is based on the long-term research results of the inventor of the present application. The inventor has conducted a one-year monitoring of the moisture content of a slope on site. The monitoring results are as follows: Figure 2 .in accordance with Figure 2 It can be seen that the slope moisture content varies from 25% to 50%. In addition, the slope moisture content of 33 locations in 6 sections of Guizhou Yukai Expressway and Kaiyang Expressway was tested (such as Figure 3 and Figure 4 As shown in Figure 1), the test results show that the moisture content of the slope is 16% to 45%. Therefore, based on the actual data of on-site monitoring and related research results of the inventor, and taking into account the extreme climate environment, the dry-wet cycle amplitude of the moisture content is determined to be between 10% and 50%.

[0015] The mechanical properties of soil are usually affected more by the dry-wet cycles in the first three dry-wet cycles, and then the mechanical properties tend to be stable as the number of dry-wet cycles increases. Therefore, in the method of the present invention, the number of dry-wet cycles and the synergistic effect of loads is determined for at least 5 times. If the mechanical properties of red clay are unstable under the synergistic effect of 5 dry-wet cycles and loads, the number is increased until it tends to be stable.

Claims

1. An accurate geotechnical dry-wet cycle test method, characterized by: It includes sample preparation → humidification stage → stewing stage → drying stage → re-humidification stage → re-stewing stage → completing at least 5 cycles in this way, and then conducting a mechanical test on the sample; during the sample preparation process, it is necessary to determine the initial moisture content of the sample, and in the re-humidification stage, the moisture content of the sample is increased to the initial moisture content.

2. A precise geotechnical dry-wet cycle test method according to claim 1, characterized in that: The specific steps of the method are as follows: (1) Prepare initial moisture content and dry density samples; (2) Humidification stage: Calculate the amount of water required to humidify the sample until the moisture content reaches 50%, and humidify the sample by injecting water in batches; (3) Stewing stage: After the water injection is completed, the material is stewed in a natural state for 24 hours, and the moisture content of the upper, middle and lower layers of the sample is measured to ensure that the moisture content of the upper, middle and lower layers of the sample is within the range of 50% ± 2%; (4) Drying stage: Place the above sample in an oven at 25-30°C for drying, and measure the moisture content of the sample every hour until the moisture content of the sample drops to 10%; (5) Rehumidification stage: Calculate the amount of water required to humidify the sample until the moisture content reaches the initial moisture content, and add water in batches to humidify the sample; (6) Re-stewing stage: After the water injection is completed, the material is stewed in a natural state for 24 hours, and the moisture content of the upper, middle and lower layers of the sample is measured to ensure that the moisture content of the upper, middle and lower layers of the sample is within the range of ±2% of the initial moisture content; Repeat steps (2) to (6) for at least 5 cycles until the mechanical properties of the sample become stable, and then perform mechanical tests on the sample.

3. A precise geotechnical dry-wet cycle test method according to claim 2, characterized in that: In the steps (3) and (6), the moisture contents of the upper, middle and lower layers of the sample are determined by the alcohol combustion method.

4. The precise geotechnical dry-wet cycle test method according to claim 2, characterized in that: In the steps (2) and (5), the sample is humidified by injecting water with a syringe in batches.

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