A method for evaluating the collapsibility of sand using dry density
By using a dry density evaluation method, the inaccuracy of sand collapsibility evaluation is solved, a method for accurately calculating the collapsibility coefficient is provided, the correctness of the test results is verified, and the accuracy of sand collapsibility evaluation is improved.
Patent Information
- Application Number
- CN202211627857.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-12-17
- Publication Date
- 2025-03-11
- Estimated Expiration
- 2042-12-17
AI Technical Summary
The existing technology lacks a clear evaluation standard for the collapsibility of sandy soil. The results of indoor tests and field immersion load tests are inconsistent, and sampling and sample preparation are difficult, resulting in inaccurate evaluation of collapsibility.
The dry density evaluation method was adopted. The collapsibility coefficient was calculated by measuring the natural density and moisture content of sand, including the ring cutter method, sand cone method and water cone method. The collapsibility coefficient was calculated by combining the compressed dry density and the water-immersed compressed dry density and compared with the maximum collapsibility coefficient to verify the test results.
This paper provides an accurate method for calculating the collapsibility coefficient of sandy soil, which can verify the correctness of test results, make up for the deficiencies of existing standards, and improve the accuracy of sandy soil collapsibility evaluation.
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Figure CN115825395B_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of geotechnical testing, and in particular relates to a method for evaluating the collapsibility of sand soil by using dry density. Background Art
[0002] At present, for the test method of collapsibility of water-sensitive soil, the "Building Standard for Collapsible Loess Areas" (GB50025-2018) stipulates detailed indoor test methods and on-site load test methods for determining the collapsibility coefficient. These two methods are only applicable to clayey silts with high clay content such as aeolian loess and alluvial loess, but there are currently no clear regulations or evaluation standards for sandy soils; in the "Geotechnical Engineering Investigation Code" (GB 50021-2001) (2009 edition), for collapsible sandy soil, it is stipulated that the collapsibility coefficient of sandy soil should be measured by immersion load test, but there is no corresponding indoor test method.
[0003] The above two methods often show inconsistency when evaluating the collapsibility of sand, combined with relevant tests at home and abroad. The main manifestation is that the results of indoor tests and on-site immersion load tests are very different, resulting in opposite conclusions when evaluating the collapsibility of sand. The main reasons for the above gap may be two aspects: First, during the immersion horizontal plate load test, the strength of the sand decreases after saturation. Under the pressure of 200kPa, the sand under the load plate not only has deformation caused by the reduction of the porosity ratio, but also has deformation caused by lateral extrusion; second, the stress state of the sand under the load plate is completely different from the stress state of the sand in the ring cutter, and the thickness of the compressed soil layer is unclear. The Code for Geotechnical Engineering Investigation (GB50021-2001) (2009 Edition) assumes the thickness of the compressed soil layer as 1.5 times the width of the load plate. The corresponding limit value for determining whether it is collapsible is 0.015×1.5=0.023 (rounded off after the third decimal point), but this assumption may not be in line with objective reality in actual tests.
[0004] In addition, since the particle composition and sedimentary environment of sand are quite different from those of loess, there are some difficulties in on-site sampling, indoor sample preparation and on-site immersion load testing of sand in actual geotechnical engineering investigations. The main difficulties are: 1) When the water content of sand is low (generally less than 5%), it is difficult to obtain undisturbed soil samples; 2) The success rate of indoor sample preparation (making ring knife samples) is low, and the samples are easy to break and easily fall out of the ring knife; 3) After the sand ring knife sample is immersed in water, a small amount of fine-grained soil occasionally flows out from the gap between the permeable stone and the ring knife, which may be one of the reasons why the collapsibility coefficient measured in indoor tests is not accurate enough.
[0005] Due to the problems existing in the above indoor tests and on-site immersion loads, in order to overcome the difficulties in evaluating the collapsibility of sandy soil, the present invention provides a method for evaluating the collapsibility of sandy soil using dry density. On the one hand, the collapsibility coefficient or maximum collapsibility coefficient of sandy soil can be measured by the present invention; on the other hand, when the collapsibility coefficient measured by the test is greater than or close to the above maximum collapsibility coefficient, it can be checked whether the test result is correct. The method provided by the present invention can make up for the shortcomings of the current specifications, which is of great significance for evaluating the collapsibility of sandy soil. Summary of the invention
[0006] The purpose of the present invention is to provide a method for evaluating the collapsibility of sandy soil by using dry density, so as to calculate the collapsibility coefficient of sandy soil.
[0007] To solve the above problems, the present invention provides a method for evaluating the collapsibility of sand by using dry density, comprising the following steps: measuring the natural density of sand; measuring the natural moisture content of sand; calculating the natural dry density of sand by the natural density of sand and the natural moisture content of sand; if the original soil sample can be obtained, then calculating the compressed dry density under a certain pressure and the water-immersed compressed dry density under the pressure, and calculating the collapsibility coefficient of sand; if the original soil sample cannot be obtained, then calculating the water-immersed compressed dry density under a certain pressure, and calculating the collapsibility coefficient; comparing the calculated collapsibility coefficient of sand with the collapsibility coefficient of sand measured by experiment to check whether the test result is correct.
[0008] Furthermore, the calculation formula for the natural dry density of sand in the above method for evaluating the collapsibility of sand using dry density is as follows:
[0009]
[0010] Among them, ρ is the natural density and ω is the natural moisture content of sand.
[0011] Furthermore, in the above method of evaluating the collapsibility of sandy soil by dry density, if the original soil sample can be obtained, the natural density of the sandy soil is measured by the knife ring method; the calculation formula of the natural density of the sandy soil in the knife ring method is as follows:
[0012]
[0013] Among them, m 0 is the sample mass, and V is the sample volume.
[0014] Furthermore, the calculation formula for the compressed dry density under a certain pressure in the above method for evaluating the collapsibility of sand soil by using dry density is as follows:
[0015]
[0016] Among them, ρ d is the natural dry density of soil, ρdp is the compressed dry density of the soil, h is the height of the ring cutter, h 1 is the compression deformation of the soil sample under a certain pressure; the calculation formula for the water-immersed compressed dry density under the pressure is as follows:
[0017]
[0018] Among them, ρ dwp is the water-immersed compressed dry density, h 2 It is the total deformation of the soil sample after being immersed in water and stabilized under a certain pressure.
[0019] Furthermore, the calculation formula of the collapsibility coefficient in the above method of evaluating the collapsibility of sand soil by dry density is:
[0020] Furthermore, if the original soil sample cannot be obtained in the above method of evaluating the collapsibility of sandy soil by dry density, the natural density of sandy soil is measured by the sand filling method; the calculation formula of the natural density of sandy soil in the sand filling method is as follows:
[0021]
[0022] Among them, m y1 The mass of the sand container plus the original sand, m y2 The mass of the remaining sand in the sand container after adding the original sand, m y3 is the mass of sand removed from the ring, m y4 is the mass of the sample container plus the sample, m y5 The mass of the remaining sand in the sand container after the second addition, m y6 is the mass of the sample container; ρ 1s is the average density of the sand in the test pit, ρ′ 1s To measure the average density of sand when pouring sand into the collar before digging a test pit.
[0023] Furthermore, if the original soil sample cannot be obtained in the above method of evaluating the collapsibility of sandy soil by dry density, the natural density of sandy soil is measured by water filling method; the calculation formula of the natural density of sandy soil in the water filling method is as follows:
[0024]
[0025] Among them, m 0 is the sample mass, V sk is the test pit volume.
[0026] Furthermore, the calculation formula of the maximum collapsibility coefficient in the above method of evaluating the collapsibility of sand soil by dry density is:
[0027] The above technical solution of the present invention has the following beneficial technical effects: on the one hand, the collapsibility coefficient or the maximum collapsibility coefficient of sandy soil can be measured; on the other hand, when the collapsibility coefficient measured in the test is greater than or close to the above maximum collapsibility coefficient, it can be checked whether the test result is correct. The method provided by the present invention can make up for the shortcomings of the current specifications and is of great significance for evaluating the collapsibility of sandy soil areas. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 It is a flow chart of an embodiment shown in the present invention;
[0029] Figure 2 It is a schematic diagram of a ring sand filling method in the embodiment shown in the present invention;
[0030] Figure 3 It is a schematic diagram of the watering method in the embodiment shown in the present invention;
[0031] Figure 4 Schematic diagram of wax sealing method in the embodiment shown in the present invention.
[0032] Reference numerals:
[0033] 11: Funnel; 12: Funnel stand; 13: Wind shield; 14: Ring; 21: Plastic film; 22: Reference horizontal plane; 23: Steel ring; 31: Water cup; 32: Wax seal sample; 33: Thin wire; 34: Weight. DETAILED DESCRIPTION
[0034] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.
[0035] The embodiments of the present invention will be described below in conjunction with the accompanying drawings.
[0036] refer to Figure 1 The present embodiment specifically includes the following steps: firstly, measuring the natural density of sand and soil, and then measuring the natural moisture content of sand and soil. The natural density of sand and soil can be measured by the ring knife method, the on-site water filling method or the sand filling method.
[0037] refer to Figure 2 The specific steps of the sand filling method are as follows: select a representative site with an area of 40cm×40cm, flatten the site, weigh the sand container, add the sand mass, and press Figure 2As shown, place the instrument on a leveled surface and fix the collar with a fixture. Open the funnel valve and pour the sand into the collar through the funnel. When the collar is full, remove the funnel, funnel stand and wind shield. If there is no wind, do not use the wind shield. Use a ruler to scrape the sand surface on the collar to make it flush with the edge of the collar. Carefully pour the scraped sand back into the sand container and do not lose it. Weigh the sand container and the remaining sand from the first time. Take out the sand in the collar, weigh it, and pour it back into the sand container. A small amount of sand in the ring is allowed to remain in the ring. Dig a test pit in the collar. Be especially careful when digging the pit and take out all the loose samples. Put it into the container containing the sample, cover it, weigh the container and the sample, and take a representative sample to determine the moisture content. Reinstall the wind shield, funnel stand and funnel on the collar. Pour the sand into the test pit through the funnel. The falling speed of the sand should be roughly equal until the collar is full. ⑥ Remove the funnel, funnel stand and wind shield, and use a ruler to scrape the sand surface on the collar to make it flush with the edge of the collar. Pour all the scraped sand back into the sand container without losing it. Weigh the sand container and add the remaining sand from the second weighing.
[0038] The natural density calculation formula is as follows:
[0039]
[0040] The dry density calculation formula is as follows:
[0041]
[0042] Where ρ is the natural density (g / cm 3 ), m y1 is the mass of the sand container plus the original sand mass (g), m y2 is the mass of the remaining sand in the sand container after the first measurement (g), m y3 is the mass of sand removed from the ring (g), m y4 is the mass of the sample container plus the sample (including a small amount of residual sand) (g), m y5 is the mass of the remaining sand in the sand measuring container after the second addition (g), m y6 is the mass of the sample container (g), ρ 1s is the average density of the sand in the test pit when it is filled (g / cm 3 ), ρ′ 1s The average density of the sand when filling the ring before digging the test pit (g / cm 3 ), ω is the natural moisture content of sand.
[0043] In addition to the sand filling method, the water filling method can also be used for measurement. Figure 3, level the ground at the measuring point and check it with a level ruler; select a representative site with an area of about 40cm×40cm and flatten the ground, draw the outline of the pit mouth according to the determined test pit diameter, and dig down to the required depth within the outline. Put the sample in the pit into the soil container, weigh the sample mass, and take a representative sample to determine the natural moisture content of the sand; after the test pit is dug, put a ring of corresponding size, and level it with a level ruler, and stick the plastic film larger than the volume of the test pit tightly along the bottom and wall of the pit; record the initial water level in the water storage cylinder, turn on the water injection switch in the water storage cylinder, and slowly inject water into the plastic film. When the water surface approaches the upper edge of the ring, reduce the water flow until the water surface is flush with the upper edge of the ring, pay attention to the water switch, and the water in the ring should not overflow; continue for 3min~5min, and record the water level in the water storage cylinder.
[0044] The calculation formula for the test pit volume is:
[0045] V sk =(H t2 -H t1 )A w -V th (3)
[0046] Among them, V sk is the test pit volume (cm 3 ),H t1 is the initial water level in the water storage cylinder (cm), H t2 V is the water level height of the water storage tank when the water ends (cm), th is the ring volume (cm 3 ), A w is the ring volume and the cross-sectional area of the water storage cylinder (cm 2 ).
[0047] The natural density calculation formula is as follows:
[0048]
[0049] Among them, m 0 is the sample mass (g), V sk is the test pit volume (cm 3 ).
[0050] The wax seal method can also be used to determine the density of irregular original samples. Figure 4 , cut about 30cm 3After removing the loose surface soil and sharp edges, tie it to a thin wire and weigh it to an accuracy of 0.01g. Take a representative sample to determine the natural moisture content of the sand; hold the wire and slowly immerse the sample in the wax just above the melting point. When it is completely immersed, immediately take out the sample. Check whether there are bubbles in the wax applied around the sample. If there are bubbles, pierce them with a hot needle and smooth the hole. After cooling, weigh the wax-sealed sample to an accuracy of 0.1g; hang the sample on one end of the balance with a wire, and immerse the sample in pure water and weigh it to an accuracy of 0.1g. Measure and record the temperature of the pure water; take out the sample, wipe off the moisture on the surface of the wax, and weigh the wax-sealed sample with a balance to an accuracy of 0.1g. When the mass of the sample increases, another sample should be taken and the test should be repeated.
[0051] The formula for calculating the natural density of the wax seal method is as follows:
[0052]
[0053] Among them, m 0 is the sample mass (g), m n is the wax mass of the sample (g), m nw is the mass of wax added to the sample in water (g), ρ wT is the density of pure water at T℃ (g / cm 3 ), ρ n is the density of the wax (g / cm 3 ).
[0054] You can also use the ring knife method. Take the original soil sample or prepare the disturbed soil sample in the required state according to the project needs, level the two ends, apply a thin layer of vaseline on the inner wall of the ring knife, and place the cutting edge down on the sample; use a soil cutter (or wire saw) to cut the soil sample into a soil column slightly larger than the diameter of the ring knife. Then press the ring knife vertically downward, while pressing and cutting, until the soil sample extends out of the ring knife. Cut off the excess soil at both ends and level them, take the remaining representative soil sample to determine the natural moisture content of the sand and soil; wipe the outer wall of the ring knife and weigh it to an accuracy of 0.1g.
[0055] The formula for calculating the natural density of the ring knife method is as follows:
[0056]
[0057] Among them, m 0 is the sample mass (g), V is the sample volume (cm 3 ).
[0058] After completing the steps of measuring the natural density of sand and the natural moisture content of sand, the natural dry density of sand can be calculated. The calculation formula is as follows:
[0059]
[0060] Where ω is the natural moisture content of sand.
[0061] Next, if the original soil sample can be obtained, a conventional compression test is performed. dw200 ) The dry density that sand can reach after the deformation is stable. In addition to being related to pressure, the compressed dry density is also closely related to the water content of the sand.
[0062] If the knife ring method is used, since the dry soil mass of the soil sample in the knife ring is unchanged before and after compression, we have:
[0063] ρ d Ah=ρ dp A(hh 1 )
[0064] After sorting, we can get:
[0065]
[0066] Among them, ρ d is the natural dry density of soil, ρ dp is the compressed dry density of the soil, A is the area of the cutter ring, h is the height of the cutter ring, and h 1 It is the compression deformation of the soil sample under a certain pressure.
[0067] You can also use the water-immersion compression dry density, that is, the dry density that sand can reach after the deformation stabilizes under a certain pressure. The calculation formula for the water-immersion compression dry density is:
[0068]
[0069] Among them, ρ dwp is the water-immersed compressed dry density, h 2 It is the total deformation of the soil sample after it is stabilized by water under a certain pressure, that is, the sum of the compression deformation and the collapsible deformation.
[0070] Next, calculate the collapsibility coefficient, assuming that the area of the ring is A, the height is h, and the natural density is ρ d , the compression deformation of the soil sample under a certain pressure is h 1 , the corresponding dry density is ρ dp The total deformation after immersion is h 2 , the deformation includes the compression deformation h 1 and the collapsible deformation Δh, that is, h 2 =h 1 +Δh, the corresponding dry density is ρ dwp Before and after compression deformation in the natural state (not immersed in water), the mass of dry soil in the ring cutter is unchanged, so:
[0071] ρ d Ah=ρ dpA(hh 1 ) (11)
[0072] After sorting, we can get:
[0073]
[0074] Similarly, compared with the natural state, after the compression and immersion deformation are stabilized, the mass of dry soil in the ring cutter remains unchanged, so:
[0075]
[0076] The shrinkage deformation is:
[0077]
[0078] So the collapsibility coefficient is:
[0079]
[0080] The collapsibility coefficient is related to three dry densities, namely the natural dry density ρ d , compressed dry density ρ under a certain pressure (usually 200 kPa) dp And the water-immersed compressed dry density ρ under this pressure dwp .
[0081] In general, the collapsibility coefficient of foundation soil is the collapsibility coefficient under 200kPa, that is, the dry density that sand can reach under 200kPa pressure. When the water content of sand is small, its compression deformation is small and the collapsibility deformation is large, that is, the compression dry density is relatively small, and the collapsibility coefficient δ s The value is relatively large; on the contrary, when the water content of sand is large, the collapsibility coefficient δ s The value is relatively small.
[0082] If the original soil sample can be obtained, it is usually necessary to estimate the maximum collapsibility coefficient that the sand can reach, that is, when the compressed dry density of the sand is equal to the dry density, its collapsibility coefficient reaches the maximum value. In extreme cases, when the water content of the sand is very small, its strength is very high. Assuming there is no compression deformation, that is, the compressed dry density is the same as the natural dry density (ρ dp =ρ d ), at this time, the collapsibility coefficient will reach the theoretical maximum value, that is:
[0083]
[0084] Finally, the calculated collapsibility coefficient or maximum collapsibility coefficient of sand can be compared with the experimentally measured collapsibility coefficient to check whether the test results are correct.
[0085] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.
Claims
1. A method for evaluating the collapsibility of sand using dry density, characterized in that: The steps include: Measuring the natural density of sand; Measure the natural moisture content of sand; Calculate the natural dry density of the sand soil by the natural density of the sand soil and the natural moisture content of the sand soil; If the original soil sample can be obtained, the compressed dry density under a certain pressure and the water-immersed compressed dry density under the pressure are calculated, and the collapsibility coefficient of the sand is calculated; If the original soil sample cannot be obtained, the water-immersed compressed dry density under a certain pressure is calculated, and the wetting coefficient is calculated; The calculation formula of the collapsibility coefficient is: Among them, ρ d is the natural dry density of soil, ρ dp is the compressed dry density of soil, ρ dwp It is the water-immersed compressed dry density; In extreme cases, when the water content of sand is very low, the compressed dry density is the same as the natural dry density, and the collapsibility coefficient will reach the theoretical maximum value, that is, the maximum collapsibility coefficient, and the calculation formula is: The calculated collapsibility coefficient of the sand is compared with the collapsibility coefficient of the sand measured in the test to check whether the test result is correct.
2. The method for evaluating the collapsibility of sandy soil by using dry density according to claim 1, characterized in that: The calculation formula of the natural dry density of sand is as follows: Among them, ρ is the natural density and ω is the natural moisture content of sand.
3. The method for evaluating the collapsibility of sandy soil by using dry density according to claim 2, characterized in that: If the original soil sample can be obtained, the ring knife method is used to measure the natural density of sand; The calculation formula of the natural density of sand in the ring knife method is as follows: Where m0 is the sample mass and V is the sample volume.
4. The method for evaluating the collapsibility of sand by using dry density according to claim 3, characterized in that: The calculation formula of the compressed dry density under a certain pressure is as follows: Among them, ρ d is the natural dry density of soil, ρ dp is the compressed dry density of soil, h is the height of the ring cutter, and h1 is the compression deformation of the soil sample under a certain pressure; The calculation formula of water-immersed compressed dry density under the pressure is as follows: Among them, ρ dwp is the water-immersed compressed dry density, and h2 is the total deformation of the soil sample after stabilization under water immersion under a certain pressure.
5. The method for evaluating the collapsibility of sand by using dry density according to claim 2, characterized in that: If the original soil sample cannot be obtained, the natural density of sandy soil is measured by the sand filling method; The calculation formula of the natural density of sand in the sand filling method is as follows: Among them, m y1 The mass of the sand container plus the original sand, m y2 The mass of the remaining sand in the sand container after adding the original sand, m y3 is the mass of sand removed from the ring, m y4 is the mass of the sample container plus the sample, m y5 The mass of the remaining sand in the sand container after the second addition, m y6 is the mass of the sample container; ρ ls is the average density of the sand in the test pit, ρ′ ls To measure the average density of sand when pouring sand into the collar before digging a test pit.
6. The method for evaluating the collapsibility of sandy soil by using dry density according to claim 2, characterized in that: If the original soil sample cannot be obtained, the water filling method is used to measure the natural density of sandy soil; The calculation formula of the natural density of sand in the irrigation method is as follows: Where m0 is the mass of the sample, V sk is the test pit volume.