Method for detecting subgrade compactness

Abstract

The application discloses a kind of detection methods of subgrade compactness, comprising: extracting soil sample from the construction site to be measured, it is divided into multiple indoor soil sample samples according to moisture content size;Detect the moisture content and dry density of each indoor soil sample sample, draw relationship curve I;According to the method that steel ball free fall impacts the top surface of soil sample sample, obtain the depth value of each indoor soil sample sample hemispherical pit, establish fitting relationship;Randomly select a point in the subgrade to be detected area as the test point of outdoor subgrade soil moisture content and dry density, obtain the moisture content and dry density of measured subgrade soil sample;According to the steel ball impact method, obtain the depth value of each detection point hemispherical pit in the subgrade to be detected area;Finally, the subgrade compactness of each detection point is fitted to obtain.The application can quickly and directly obtain the subgrade compactness, the detection period is short, the detection efficiency is high, the detection result has high reliability and accuracy, can meet the large-scale large-area continuous filling construction requirement of subgrade.

Description

Technical Field

[0001] This invention relates to the field of roadbed compaction testing technology, and in particular, to a method for testing roadbed compaction. Background Technology

[0002] With the rapid development of urban rail transit, town roads, highways, railways, airports, train stations, and large industrial plants, the roadbed, as a crucial component of the entire project, directly bears the long-term effects of the superstructure load and the static and dynamic loads of vehicles or equipment. Therefore, the quality of roadbed filling construction is of paramount importance. Compaction degree is one of the key indicators for testing the quality of roadbed filling construction, characterizing the density after on-site compaction. Higher compaction degree means greater density and better overall material performance.

[0003] Currently, my country's existing compaction testing methods typically include the ring cutter method, sand cone method, water cone method, and nuclear moisture density meter method. The ring cutter method is a destructive testing method, only suitable for fine-grained soils without stone particles, and unsuitable for loose materials. Furthermore, its measurement error is greatly affected by the location of the measuring point, and obtaining a single data point takes more than half an hour. The sand cone method is also a destructive testing method, with cumbersome procedures, requiring more than half an hour to obtain a single data point. It is slow, time-consuming, and has a long testing cycle, making compaction testing time-consuming, labor-intensive, and inefficient. Moreover, the sand cone method is highly susceptible to weather and human factors. The water cone method is also a destructive testing method, similar to the sand cone method, but with even more stringent environmental and equipment requirements. The testing process is significantly affected by the plastic film bag, resulting in substantial errors, and the testing process is extremely slow. The nuclear moisture density meter method uses expensive equipment, has extremely high environmental requirements, produces results with poor stability and large dispersion, and its radioactive materials can cause irreversible harm to the human body, severely limiting its large-scale use.

[0004] The existing compaction testing methods described above are insufficient to meet the requirements of large-scale, continuous filling construction of roadbeds. Rapidly testing the compaction degree of roadbeds at construction sites to facilitate large-scale, continuous filling construction is an urgent problem that needs to be solved. Summary of the Invention

[0005] This invention provides a method for detecting the compaction degree of roadbed, addressing the technical problems inherent in existing compaction degree detection methods: expensive testing equipment, stringent environmental and equipment requirements; slow testing speed, long testing time and cycle; time-consuming, labor-intensive, and inefficient compaction degree testing; and susceptibility to weather and human factors, leading to poor stability, large dispersion, and low accuracy of compaction degree test results, making it difficult to meet the requirements of large-scale, large-area continuous filling construction of roadbeds.

[0006] According to one aspect of the present invention, a method for detecting the compaction degree of a roadbed is provided, comprising the following steps:

[0007] (1) Preparation of indoor soil samples:

[0008] Soil samples were taken from the construction site to be tested, and the soil samples were air-dried and sieved.

[0009] The soil sample was divided into multiple samples, and different amounts of water were added to each sample. After stirring and soaking, multiple indoor soil sample samples were obtained.

[0010] (2) Detection of indoor soil samples and establishment of fitting formula:

[0011] According to the compaction test method in standard JTG 3430-2020, the indoor moisture content and indoor dry density of each indoor soil sample were tested. The relationship curve between indoor soil moisture content and indoor soil dry density was plotted with indoor soil moisture content on the x-axis and indoor soil dry density on the y-axis to obtain the optimum moisture content and maximum dry density of indoor soil samples.

[0012] Using the same compaction hammer and drop height as in the standard JTG 3430-2020 compaction test method, a steel ball of the same mass and drop height was dropped freely onto the top surface of the indoor soil sample. The depth of the hemispherical indentation on the top surface of each indoor soil sample was obtained. A fitting relationship was established between the indoor soil sample dry density and the hemispherical indentation depth, with the hemispherical indentation depth as the x-axis and the indoor soil sample dry density as the y-axis. The fitting relationship is: y = ax 2 +bx+c, where a>0, b<0, c>0;

[0013] (3) Detection and fitting of various test points on the outdoor subgrade and calculation of subgrade compaction degree:

[0014] A point is randomly selected in the subgrade inspection area as the test point for the moisture content and dry density of the outdoor subgrade soil sample, and the measured moisture content and dry density of the subgrade soil sample are obtained.

[0015] The depth of the hemispherical pit on the top surface of the roadbed at each test point in the roadbed inspection area is obtained by using the method of the steel ball falling freely and impacting the top surface of the roadbed.

[0016] From the relationship curve I between the dry density and moisture content of the indoor soil sample, the dry density D1 of the indoor soil sample at the measured moisture content of the subgrade soil sample is obtained.

[0017] Divide the measured dry density of the subgrade soil sample by D1 to obtain the correction factor for the dry density of the subgrade soil sample. , where 0 < <1;

[0018] Substitute the depth of the hemispherical pit on the top surface of the roadbed at each test point into the fitting formula to calculate the dry density D2 of the indoor soil sample at each test point.

[0019] Multiply D2 by the roadbed soil sample dry density correction factor in turn. The dry density D3 of the subgrade soil sample at each test point was obtained;

[0020] Divide D3 by the maximum dry density of the indoor soil sample in turn to obtain the subgrade compaction degree at each test point.

[0021] Furthermore, different amounts of water were added to each sample so that the moisture content of each sample increased by 2% by mass.

[0022] Furthermore, in relation curve I, the highest point of the curve corresponds to the optimum moisture content of the indoor soil sample; the highest point corresponds to the maximum dry density of the indoor soil sample; to the left of the optimum moisture content of the indoor soil sample, the dry density of the indoor soil sample increases with the increase of the indoor soil sample moisture content; to the right of the optimum moisture content of the indoor soil sample, the dry density of the indoor soil sample decreases with the increase of the indoor soil sample moisture content.

[0023] Furthermore, using the indoor soil sample moisture content as the abscissa and the hemispherical pit depth on the top surface of the indoor soil sample as the ordinate, a relationship curve II was plotted between the indoor soil sample hemispherical pit depth and the indoor soil sample moisture content. In curve II, the indoor soil sample moisture content corresponding to the lowest point of the curve is the optimum moisture content of the indoor soil sample; the indoor soil sample hemispherical pit depth corresponding to the lowest point is the minimum indoor soil sample hemispherical pit depth; to the left of the optimum moisture content of the indoor soil sample, the indoor soil sample hemispherical pit depth decreases as the indoor soil sample moisture content increases; to the right of the optimum moisture content of the indoor soil sample, the indoor soil sample hemispherical pit depth increases as the indoor soil sample moisture content increases.

[0024] Furthermore, when the soil sample is low liquid limit clay, the fitting equation is: y = 0.0027x 2 -0.037x + 1.711; When the soil sample is clayey sand, the fitting equation is: y = 0.0033x 2 -0.0375x + 1.9827; When the soil sample is clayey gravel, the fitting equation is y = 0.0026x 2 -0.0416x+2.034.

[0025] Furthermore, the goodness of fit in the fitting equation is R. 2 , of which 0.9 <R 2 <1.

[0026] Furthermore, in the fitted relationship, when the dry density of the indoor soil sample is at its maximum, the depth of the hemispherical pit on the top surface of the indoor soil sample is at its minimum, and the dry density of the indoor soil sample decreases as the depth of the hemispherical pit on the top surface of the indoor soil sample increases.

[0027] Furthermore, the dry density correction factor of the subgrade soil sample , of which 0.99 < <1.

[0028] Furthermore, the absolute value of the difference between the fitted subgrade compaction degree obtained by the subgrade compaction degree detection method and the measured subgrade compaction degree outdoors is no greater than 0.6%.

[0029] Furthermore, the goodness of fit in the fitted roadbed compaction degree is R. 2 , of which 0.8 <R 2 <0.9.

[0030] The present invention has the following beneficial effects:

[0031] This invention provides a method for detecting the compaction degree of roadbed, which can quickly and accurately obtain the compaction degree of roadbed, specifically including:

[0032] (1) Simulation of indoor standard test equipment and test conditions: First, simulate the test equipment and test conditions of the same 4.5kg compaction hammer and the same 450mm drop height in the heavy compaction II-2 of the compaction test of the "Highway Geotechnical Test Specification" (JTG 3430-2020) standard T0131-2019, so as to obtain the impact mark of a steel ball of equal mass 4.5kg and equal drop height 450mm falling freely and impacting the top surface of the soil sample specimen or the top surface of the subgrade, leaving a hemispherical pit on the top surface of the soil sample specimen or the top surface of the subgrade. Measure the depth of the hemispherical pit on the top surface of the soil sample specimen or the top surface of the subgrade, so that the fitting relationship between the dry density of the soil sample and the depth of the hemispherical pit on the top surface of the soil sample established indoors and the fitting relationship between the hemispherical pit depth on the top surface of the subgrade obtained by fitting the hemispherical pit depth value on the top surface of the subgrade measured outdoors have authenticity, thereby improving the reliability and accuracy of the fitted subgrade compaction degree; Second If the steel ball's mass is less than 4.5 kg and its free fall height is less than 450 mm, the impact force of the falling steel ball will be insufficient due to its light weight and low free fall height. This will result in no hemispherical impact mark being left on the top surface of the soil sample or roadbed at its maximum dry density, making it impossible to measure the depth of the hemispherical indentation. If the steel ball's mass is greater than 4.5 kg and its free fall height is greater than 450 mm, the excessive weight, large diameter, and high free fall height will inevitably make carrying and testing the steel ball inconvenient, and may even cause the steel ball to bounce off the top surface of the soil sample or roadbed, injuring the operators. Thirdly, the "Highway Geotechnical Testing Procedures" (JTG) also applies. Standard T 0131-2019 (3430-2020) stipulates that the compaction cylinder in the heavy compaction II-2 test has an inner diameter of 152 mm, and the top surface of the compaction cylinder is not affected by the impact of the steel ball, thus limiting the impact test results. The diameter of the steel ball must not exceed 104 mm. If the steel ball is heavier, its diameter increases accordingly, exceeding or covering the inner diameter cavity of the compaction cylinder. This causes the steel ball to impact and damage the inner edge of the top surface of the compaction cylinder each time it falls freely, increasing the volume of the compaction cylinder cavity and altering the original fixed volume of the compaction cylinder (2177 cm³). 3 This increases the dry density of the soil sample, and consequently, the maximum dry density of the soil sample. This not only affects the compaction test results of the soil sample, but also the test results of the depth of the hemispherical indentation on the top surface of the soil sample and the compaction degree of the roadbed.

[0033] (2) Establish the fitting relationship between the dry density of indoor soil samples and the depth of the hemispherical pit on the top surface of the soil sample: Taking advantage of the characteristics of preparing soil samples with different dry densities by heavy compaction of soil samples with different moisture contents in the compaction test, the indoor standard soil sample compaction test and the hemispherical pit depth test on the top surface of the soil sample were conducted to obtain the indoor soil sample optimum moisture content, indoor soil sample maximum dry density and indoor soil sample hemispherical pit depth. The indoor soil sample dry density and soil sample moisture content relationship curve I and the indoor soil sample hemispherical pit depth and soil sample moisture content relationship curve II were plotted to establish the fitting relationship between the indoor soil sample dry density and the hemispherical pit depth on the top surface of the soil sample. Among them, the main functions of relationship curve I are: first, to obtain the indoor soil sample dry density corresponding to the measured subgrade soil sample moisture content through the indoor soil sample dry density and soil sample moisture content relationship curve I; and second, to verify whether the soil sample filling material used outdoors is consistent with the indoor soil sample. Otherwise, relevant tests must be conducted on the soil samples used outdoors in a timely manner. The main function of the relationship curve II is as a comparison standard: firstly, to verify whether the measured soil moisture content and the depth of the hemispherical pit on the top surface of the subgrade are accurate and reliable; secondly, to verify whether the soil samples used outdoors are consistent with the indoor soil samples. Otherwise, relevant tests must be conducted on the soil samples used outdoors in a timely manner. The main function of the fitted relationship is to correctly guide the subgrade compaction test and subgrade filling construction at the outdoor construction site, so that the subgrade compaction test can be fast, direct, accurate, time-saving, and short-cycle, meeting the requirements of large-scale, large-area continuous filling construction of the subgrade.

[0034] (3) Single-point verification method for dry density and moisture content of subgrade soil samples at each outdoor layer: When conducting the hemispherical pit depth test on the top surface of each subgrade layer at the outdoor construction site, the single-point verification of dry density and moisture content of subgrade soil samples at each outdoor layer must be carried out simultaneously: First, the actual situation of dry density and moisture content of subgrade soil samples at each layer is known as the comparison standard; Second, the dry density, moisture content and hemispherical pit depth of subgrade soil samples at each subgrade layer are obtained by actual measurement at the top surface of each subgrade layer at the outdoor construction site, and the corresponding indoor soil sample dry density and subgrade soil sample dry density correction coefficient are calculated accordingly. The process involves three steps: first, fitting the soil samples to obtain the dry density and compaction degree of the subgrade soil samples; second, verifying whether the soil properties of each subgrade soil sample at the outdoor construction site are the same as those used in the indoor compaction test, and then determining whether the compaction degree test results of each subgrade layer obtained by fitting the hemispherical pit depth values ​​measured on the top surface of each subgrade layer at the outdoor construction site are true, reliable, and accurate.

[0035] (4) A fast, direct, and accurate method for fitting subgrade compaction: The following values ​​are obtained by measuring the top surface of each subgrade layer at the outdoor construction site: dry density of subgrade soil sample, moisture content of subgrade soil sample, and depth of hemispherical pit on the top surface of the subgrade. Based on the relationship curve between indoor soil sample dry density and soil sample moisture content, the corresponding indoor soil sample dry density is obtained when the outdoor measured subgrade soil sample moisture content is obtained. The outdoor measured subgrade soil sample dry density is divided by the indoor soil sample dry density to calculate the subgrade soil sample dry density correction coefficient. Then, based on the fitting relationship between the dry density of the indoor soil sample and the depth of the hemispherical pit on the top surface of the soil sample, the values ​​of the depth of the hemispherical pit at each measuring point on the top surface of the outdoor subgrade layer are directly substituted into the fitting relationship to calculate the dry density of the indoor soil sample at each measuring point, and then multiplied by the subgrade soil sample dry density correction coefficient. The dry density of the subgrade soil samples at each measuring point was obtained by fitting the data, and then divided by the maximum dry density of the indoor soil samples to obtain the subgrade compaction degree at each measuring point. This result is close to the measured subgrade compaction degree outdoors, and the difference between the two meets the specified requirements. Furthermore, the goodness of fit R0 is also satisfactory. 2 Values ​​greater than 0.8 fall within the 0.7–0.9 range, indicating a good fit and high reliability. The roadbed compaction degree fitted using this method is fast, direct, easy to understand and operate, produces a large number of data points efficiently, and the results are truthful, reliable, and accurate.

[0036] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0037] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 This is a flowchart of a preferred embodiment of the present invention for rapid on-site testing of roadbed compaction.

[0039] Figure 2 This is a schematic diagram of the test of the depth of the hemispherical pit on the top surface of the soil sample according to a preferred embodiment of the present invention;

[0040] Figure 3 This is curve I showing the relationship between the dry density and moisture content of the indoor soil sample in Example 1;

[0041] Figure 4 This is curve I showing the relationship between the dry density and moisture content of the indoor soil sample in Example 2;

[0042] Figure 5 This is curve I showing the relationship between the dry density and moisture content of the indoor soil sample in Example 3;

[0043] Figure 6This is curve II showing the relationship between the depth of the hemispherical pit on the top surface of the indoor soil sample and the soil moisture content in Example 1.

[0044] Figure 7 This is curve II showing the relationship between the depth of the hemispherical pit on the top surface of the indoor soil sample and the soil moisture content in Example 2.

[0045] Figure 8 This is curve II showing the relationship between the depth of the hemispherical pit on the top surface of the indoor soil sample and the soil moisture content in Example 3.

[0046] Figure 9 This is the fitting formula for the dry density of indoor soil samples and the depth of the hemispherical indentation on the top surface of the soil sample in Example 1;

[0047] Figure 10 This is the fitting formula for the dry density of indoor soil samples and the depth of the hemispherical indentation on the top surface of the soil sample in Example 2;

[0048] Figure 11 This is the fitting formula for the dry density of the indoor soil sample and the depth of the hemispherical pit on the top surface of the soil sample in Example 3;

[0049] Figure 12 Example 1 shows the polynomial fitting curve of the subgrade compaction degree and the depth of the hemispherical pit on the top surface of the subgrade.

[0050] Figure 13 Example 2 shows the polynomial fitting curve of the subgrade compaction degree and the depth of the hemispherical pit on the top surface of the subgrade.

[0051] Figure 14 This is a polynomial fitting curve of the subgrade compaction degree and the depth of the hemispherical pit on the top surface of the subgrade in Example 3.

[0052] Legend: 1-Steel ball; 2-Dent. Detailed Implementation

[0053] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described in this specification are merely illustrative of the invention and are not intended to limit the invention.

[0054] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an unspecified range.

[0055] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, "multiple" in "one or more" means two or more, and "more than" in "one or more" means two or more.

[0056] An embodiment of the present invention provides a method for detecting the compaction degree of a roadbed, comprising the following steps:

[0057] (1) Preparation of indoor soil samples:

[0058] Soil samples were taken from the construction site to be tested, and the soil samples were air-dried and sieved.

[0059] The soil sample was divided into multiple samples, and different amounts of water were added to each sample. After stirring and soaking, multiple indoor soil sample samples were obtained.

[0060] (2) Detection of indoor soil samples and establishment of fitting formula:

[0061] According to the compaction test method in standard JTG 3430-2020, the indoor moisture content and indoor dry density of each indoor soil sample were tested. The relationship curve between indoor soil moisture content and indoor soil dry density was plotted with indoor soil moisture content on the x-axis and indoor soil dry density on the y-axis to obtain the optimum moisture content and maximum dry density of indoor soil samples.

[0062] Using the same compaction hammer and drop height as in the standard JTG 3430-2020 compaction test method, a steel ball of the same mass and drop height was dropped freely onto the top surface of the indoor soil sample. The depth of the hemispherical indentation on the top surface of each indoor soil sample was obtained. A fitting relationship was established between the indoor soil sample dry density and the hemispherical indentation depth, with the hemispherical indentation depth as the abscissa and the indoor soil sample dry density as the ordinate. The fitting relationship is: y = ax 2 +bx+c, where a>0, b<0, c>0;

[0063] (3) Detection and fitting of various test points on the outdoor subgrade and calculation of subgrade compaction degree:

[0064] A point is randomly selected in the subgrade inspection area as the test point for the moisture content and dry density of the outdoor subgrade soil sample, and the measured moisture content and dry density of the subgrade soil sample are obtained.

[0065] The depth of the hemispherical pit on the top surface of the roadbed at each test point in the roadbed inspection area is obtained by the method of the steel ball 1 falling freely and impacting the top surface of the roadbed.

[0066] From the relationship curve I between the dry density and moisture content of the indoor soil sample, the dry density D1 of the indoor soil sample at the measured moisture content of the subgrade soil sample is obtained.

[0067] Divide the measured dry density of the subgrade soil sample by D1 to obtain the correction factor for the dry density of the subgrade soil sample. , where 0 < <1;

[0068] Substitute the depth of the hemispherical pit on the top surface of the roadbed at each test point into the fitting formula to calculate the dry density D2 of the indoor soil sample at each test point.

[0069] Multiply D2 by the roadbed soil sample dry density correction factor in turn. The dry density D3 of the subgrade soil sample at each test point was obtained;

[0070] Divide D3 by the maximum dry density of the indoor soil sample in turn to obtain the subgrade compaction degree at each test point.

[0071] This invention provides a method for detecting the compaction degree of roadbed. The method includes establishing a fitting relationship between the dry density of indoor soil samples and the depth of the hemispherical pit on the top surface of the soil sample, verifying the dry density and moisture content of outdoor roadbed soil samples, and conducting outdoor hemispherical pit depth tests on the top surface of the roadbed, and analyzing the fitted roadbed compaction degree indoors.

[0072] The method establishes a fitting relationship between the dry density of indoor soil samples and the depth of the hemispherical indentation on the top surface of the soil sample. Using the depth of the hemispherical indentation on the top surface of the soil sample as the X-axis (horizontal axis) and the dry density of the soil sample as the Y-axis (vertical axis), a polynomial fitting curve and a fitting relationship are established. The fitting relationship is: y = ax 2 +bx+c (where a>0, b<0, and c>0). For example... Figures 9-11 As shown, the polynomial fitting curves all open upwards, so the coefficient 'a' in the fitting equation is positive. The axis of symmetry of the polynomial fitting curves is to the right of the soil sample dry density (Y-axis (ordinate)). The sign of the coefficient 'b' is opposite to that of the coefficient 'a', so the coefficient 'b' in the fitting equation is negative. The constant 'c' in the fitting equation is the ordinate of the intersection point of the polynomial fitting curve and the soil sample dry density (Y-axis (ordinate)). It intersects the positive half-axis of the soil sample dry density (Y-axis (ordinate)) and is related to the particle size and the content of particles smaller than 0.075 mm in the soil sample. The value of constant 'c' increases with the increase of soil sample particle size and also increases with the decrease of the content of particles smaller than 0.075 mm in the soil sample, so the coefficient 'c' is positive.

[0073] The verification of the dry density and moisture content of the outdoor subgrade soil samples and the test of the depth of the hemispherical pit on the top surface of the outdoor subgrade. Includes: (1) Verification of the dry density and moisture content of the outdoor subgrade soil samples: According to the requirements of large-scale continuous filling construction of the subgrade at the outdoor construction site, a subgrade area to be tested for compaction must be selected on the top surface of each layer of subgrade that has been compacted by the road roller. A measuring point is randomly selected on the top surface of the subgrade in the area to be tested as the verification measuring point for the dry density and moisture content of the outdoor subgrade soil samples. The compaction degree of the subgrade is tested by the sand cone method, and the dry density and moisture content of the subgrade soil samples are measured. (2) Outdoor roadbed top surface hemispherical pit depth test: steel ball 1 is dropped freely to hit the top surface of the roadbed and leaves an impact mark of hemispherical pit 2 on the top surface of the roadbed; in the two perpendicular directions of the impact mark circular plane, the maximum value of the hemispherical pit depth is measured by depth calipers to obtain the hemispherical pit depth value of the roadbed top surface at each outdoor measuring point.

[0074] The indoor analysis of the roadbed compaction degree was obtained by measuring the dry density, moisture content, and hemispherical indentation depth of each roadbed layer at the outdoor construction site. The indoor dry density was calculated based on the relationship curve between the indoor dry density and moisture content of the roadbed samples. The correction coefficient for the roadbed dry density was then calculated by dividing the outdoor dry density by the indoor dry density. Then, based on the fitting relationship between the dry density of the indoor soil sample and the depth of the hemispherical pit on the top surface of the soil sample, the values ​​of the depth of the hemispherical pit at each measuring point on the top surface of the outdoor subgrade layer are directly substituted into the fitting relationship to calculate the dry density of the indoor soil sample at each measuring point, and then multiplied by the subgrade soil sample dry density correction coefficient. The dry density of the subgrade soil sample at each measuring point is obtained by fitting the data, and then divided by the maximum dry density of the indoor soil sample to obtain the subgrade compaction degree at each measuring point. This method of fitting subgrade compaction degree is fast, direct, easy to understand and operate, produces a large number of data points with high efficiency, and the test results are true, reliable and accurate.

[0075] This application provides a method for detecting the compaction degree of roadbed. It utilizes the characteristic of preparing soil samples with different dry densities through heavy compaction of soil samples with different moisture contents in compaction tests. Through indoor standard soil sample compaction tests and hemispherical pit depth tests on the top surface of the soil sample, the optimal moisture content, maximum dry density, and hemispherical pit depth of the indoor soil sample are obtained. Curve I showing the relationship between indoor soil sample dry density and soil sample moisture content, and curve II showing the relationship between indoor soil sample hemispherical pit depth and soil sample moisture content, are plotted. A fitting formula for the indoor soil sample dry density and hemispherical pit depth is established. Furthermore, the dry density, moisture content, and hemispherical pit depth of the roadbed are obtained through on-site measurements at the top surface of each layer of roadbed in outdoor engineering construction sites. Based on the relationship curve between indoor soil sample dry density and soil sample moisture content, the corresponding indoor soil sample dry density at the measured outdoor subgrade soil sample moisture content is obtained. The subgrade soil sample dry density correction factor is calculated by dividing the measured outdoor subgrade soil sample dry density by the indoor soil sample dry density. Then, based on the fitting relationship between the dry density of the indoor soil sample and the depth of the hemispherical pit on the top surface of the soil sample, the values ​​of the depth of the hemispherical pit at each measuring point on the top surface of the outdoor subgrade layer are directly substituted into the fitting relationship to calculate the dry density of the indoor soil sample at each measuring point, and then multiplied by the subgrade soil sample dry density correction coefficient. The dry density of the subgrade soil sample at each measuring point is obtained by fitting the data, and then divided by the maximum dry density of the indoor soil sample to obtain the subgrade compaction degree at each measuring point. The subgrade compaction degree fitted by this invention is fast, direct, easy to understand and operate, has a fast testing speed, short testing cycle, and a large number of test results with high efficiency; the testing equipment is simple to process and manufacture, inexpensive, has low environmental and equipment requirements, and is less affected by weather and human factors; the compaction degree test results are true, reliable and accurate, and can meet the requirements of large-scale continuous filling construction of subgrade.

[0076] like Figure 1 As shown, a preferred embodiment of the present invention provides a method for detecting the compaction degree of a roadbed, the method comprising the following steps:

[0077] S1: Preparation of indoor soil samples.

[0078] The indoor soil samples were low liquid limit clay (CL) (Example 1), clay sand (SC) (Example 2), and clay gravel (GC) (Example 3) from the construction site of the road restoration and filling project on the top of an underground station of a city rail transit project in Guangxi.

[0079] Example 1: A 500kg sample of low liquid limit clay (CL) was taken from the construction site. It is a fine-grained soil. The measured values ​​are as follows: natural moisture content 24.8%, maximum particle size 5mm, particle content greater than 60mm (giant group) 0%, particle content of 60mm to 2mm (gravel group) 1.2%, particle content of 2mm to 0.075mm (sand group) 9.5%, particle content of less than 0.075mm (fine group) 89.3%, liquid limit 46.3%, plasticity index 24.5. The soil sample was air-dried and crushed with a wooden roller and passed through a 5mm sieve for later use.

[0080] Example 2: A 500kg sample of clayey sand (SC) was taken from the construction site. This sandy soil is a coarse-grained soil. Actual measurements showed the following: natural moisture content 18.6%; maximum particle size 20mm; 0% content of particles larger than 60mm (giant group); 34.1% content of particles between 60mm and 2mm (gravel group); 39.3% content of particles between 2mm and 0.075mm (sand group); 26.6% content of particles smaller than 0.075mm (fine group); liquid limit 33.6%; and plasticity index 16.8. The soil sample was air-dried for later use.

[0081] Example 3: A 500kg sample of clayey gravel (GC) soil was extracted from the construction site. This sample is classified as gravelly soil within the coarse-grained soil category. Actual measurements showed the following: natural moisture content 15.2%; maximum particle size 40mm; 0% content of particles larger than 60mm (giant group); 55.8% content of particles between 60mm and 2mm (gravel group); 24.4% content of particles between 2mm and 0.075mm (sand group); 19.8% content of particles smaller than 0.075mm (fine group); liquid limit 30.6%; and plasticity index 16.3. The soil sample was air-dried for later use.

[0082] S2. Establish a fitting relationship between the dry density of indoor soil samples and the depth of the hemispherical indentation on the top surface of the soil sample.

[0083] Utilizing the characteristics of preparing soil specimens with different dry densities through heavy compaction of soil samples with different moisture contents in the compaction test, and through indoor standard soil sample compaction tests and hemispherical pit depth tests on the top surface of soil specimens, the optimum moisture content, maximum dry density, and hemispherical pit depth of indoor soil samples were obtained. Curve I, showing the relationship between indoor soil sample dry density and soil sample moisture content, and curve II, showing the relationship between indoor soil sample hemispherical pit depth and soil sample moisture content, were plotted. A fitting formula for the relationship between indoor soil sample dry density and hemispherical pit depth was established. The main functions of curve I are: first, to calculate the indoor soil sample dry density corresponding to the measured moisture content of the subgrade soil sample; and second, to verify whether the soil filler used outdoors is consistent with the indoor soil sample. Otherwise, relevant tests must be conducted on the soil samples used outdoors in a timely manner. The main function of the relationship curve II is as a comparison standard: firstly, to verify whether the measured soil moisture content and the depth of the hemispherical pit on the top surface of the subgrade are accurate and reliable; secondly, to verify whether the soil samples used outdoors are consistent with the indoor soil samples. Otherwise, relevant tests must be conducted on the soil samples used outdoors in a timely manner. The main function of the fitted relationship is to correctly guide the subgrade compaction test and subgrade filling construction at the outdoor construction site, so that the subgrade compaction test can be fast, direct, accurate, time-saving, and short-cycle, meeting the requirements of large-scale, large-area continuous filling construction of the subgrade.

[0084] S201: Preparation of indoor soil samples.

[0085] After passing the air-dried soil sample through a 40mm sieve, measure its air-dried moisture content. Prepare at least 5 samples using the quartering method, adding different amounts of water to each sample (increasing by 2% each time). Mix the soil samples thoroughly and let them sit overnight. The amount of water to be added when preparing samples at the predetermined moisture content is calculated using the following formula: Required water for soil sample (g) = [Mass of soil sample at air-dried moisture content (g) / (1 + 0.01 × air-dried moisture content (%))] × 0.01 × (Required moisture content of soil sample (%) - air-dried moisture content (%)) (Based on the formula in Clause 2.2 of Standard T0102-2007, Soil Sample and Test Specimen Preparation, of the "Highway Geotechnical Testing Procedures" (JTG 3430-2020) (T0102-2)).

[0086] S202: Indoor standard soil sample compaction test and soil sample specimen top surface hemispherical indentation depth test.

[0087] 1. Using the sample with the lowest predetermined moisture content, perform heavy compaction of the first soil sample specimen according to the compaction test method in Standard T0131-2019 of the "Specifications for Geotechnical Testing of Highways" (JTG 3430-2020) (II-2 compaction hammer mass 4.5kg, hammer base diameter 50mm, free fall height 450mm). After compaction, the soil sample specimen should not protrude more than 6mm above the top surface of the compaction cylinder. Remove the sleeve, carefully level the soil sample specimen with the top of the cylinder, remove the pad and compaction base plate, wipe the outer wall of the compaction cylinder clean, weigh the total mass of the compaction cylinder and the soil sample specimen, and record the data.

[0088] 2. Place the compaction plate on a hard surface, then place a pad and install the compaction test cylinder on the compaction plate. When installing the compaction test cylinder, ensure the top surface of the soil sample specimen at the inner sleeve end of the compaction test cylinder is facing upwards.

[0089] 3. Place a 4.5 kg steel ball 1 directly above the top surface of the soil sample in the compaction test cylinder, ensuring that the steel ball 1 is centered inside the cylinder and the vertical distance between the bottom surface of the steel ball 1 and the top surface of the soil sample is 450 mm. Let the steel ball 1 fall freely, impacting the top surface of the soil sample and leaving a hemispherical indentation 2. Measure and record the depth of the hemispherical indentation.

[0090] The test equipment and conditions were simulated using standard indoor testing equipment: Firstly, the test equipment and conditions were simulated using the same 4.5kg compaction hammer and the same 450mm drop height as in the heavy compaction II-2 test of the "Highway Geotechnical Test Procedure" (JTG3430-2020) standard T 0131-2019, to obtain the impact mark (e.g., a 4.5kg steel ball with a drop height of 450mm) falling freely onto the top surface of the soil sample or subgrade, leaving a hemispherical indentation on the top surface of the soil sample or subgrade. Figure 2As shown), the measured depth of the hemispherical pit on the top surface of the soil sample or the top surface of the roadbed ensures the authenticity of the roadbed compaction test results obtained by fitting the indoor relationship between the dry density of the soil sample and the depth of the hemispherical pit on the top surface of the soil sample and the outdoor measured depth of the hemispherical pit on the top surface of the roadbed, thereby improving the reliability and accuracy of the fitted roadbed compaction results; secondly, if the mass of steel ball 1 is less than 4.5 kg and the free fall height is less than 450 mm, the impact force of steel ball 1 falling freely is insufficient due to its light weight and low free fall height. This results in the inability to leave hemispherical impact marks on the top surface of the soil sample or the top surface of the subgrade at the maximum dry density state, thus making it impossible to measure the depth of the hemispherical impact. If the mass of steel ball 1 is greater than 4.5 kg and the free fall height is greater than 450 mm, the excessive weight, diameter, and free fall height of steel ball 1 will inevitably cause inconvenience in carrying steel ball 1 and testing operations, and may even cause the steel ball 1 to bounce back and injure the operators after impacting the top surface of the soil sample or the top surface of the subgrade. Thirdly, due to the limitation of the 152 mm inner diameter cavity of the compaction cylinder in the heavy compaction II-2 of the compaction test of the "Highway Geotechnical Test Procedure" (JTG 3430-2020) standard T 0131-2019, and the limitation that the top surface of the compaction cylinder is not affected by the impact of steel ball 1, the diameter of steel ball 1 shall not exceed 104 mm. If the steel ball 1 is heavier, its diameter will increase accordingly, exceeding or covering the inner cavity of the compaction cylinder. This will cause the steel ball 1 to impact and damage the inner edge of the top surface of the compaction cylinder each time it falls freely, increasing the volume of the compaction cylinder cavity and changing the original fixed volume of the compaction cylinder (2177 cm³). 3 This increases the dry density of the soil sample, and consequently, the maximum dry density of the soil sample. This not only affects the compaction test results of the soil sample, but also the test results of the depth of the hemispherical indentation on the top surface of the soil sample and the compaction degree of the roadbed.

[0091] 4. Use a bulldozer to push the soil sample specimen out of the compacted test tube, take a representative soil sample from the center of the soil sample specimen to measure its moisture content, and record the data.

[0092] 5. Following steps 1 to 4 in S202 above, complete the soil compaction test and the depth test of the hemispherical pit 2 on the top surface of the soil sample specimen for the remaining 4 samples with predetermined moisture content, and record the test data.

[0093] 6. The results of the soil compaction test and the test of the depth of the hemispherical pit 2 on the top surface of the soil sample are shown in Tables 1, 2 and 3.

[0094] Table 1 Results of soil compaction test and hemispherical pit depth test on top surface of soil sample (Example 1)

[0095]

[0096] Table 2 Results of soil compaction test and hemispherical pit depth test on top surface of soil sample (Example 2)

[0097]

[0098] Table 3 Results of soil compaction test and hemispherical indentation depth test on top surface of soil sample (Example 3)

[0099]

[0100] S203: Draw relation curve I and relation curve II.

[0101] 1. Plot the curve showing the relationship between the dry density and moisture content of the soil sample (I): [Example] Figures 3-5 As shown, a curve (Example 1, Example 2, Example 3) is plotted with soil dry density as the ordinate and soil moisture content as the abscissa to represent the relationship between soil dry density and soil moisture content. The ordinate and abscissa of the peak points on the curve represent the maximum dry density and the optimum moisture content of the soil sample, respectively. If the curve does not show a clear peak point, additional points must be added or the curve must be redone. To the left of the optimum moisture content, the soil dry density increases with increasing soil moisture content; to the right of the optimum moisture content, the soil dry density decreases with increasing soil moisture content. At the optimum moisture content, the soil dry density is the maximum dry density. The curve showing the relationship between soil dry density and soil moisture content is a smooth upward curve.

[0102] 2. Plot the curve showing the relationship between the depth of the hemispherical depression on the top surface of the soil sample and the soil moisture content (II): [Example] Figures 6-8 As shown, curve II (Examples 1, 2, and 3) is plotted with the depth of the hemispherical depression on the top surface of the soil sample as the ordinate and the soil moisture content as the abscissa. The ordinate and abscissa of the peak point under the curve represent the minimum depth of the hemispherical depression on the top surface of the soil sample and the optimum moisture content of the soil sample, respectively. If the curve cannot show a clear peak point, points must be added or the curve must be redone. To the left of the optimum moisture content, the depth of the hemispherical depression on the top surface of the soil sample decreases as the soil moisture content increases. To the right of the optimum moisture content, the depth of the hemispherical depression on the top surface of the soil sample increases as the soil moisture content increases. At the optimum moisture content, the depth of the hemispherical depression on the top surface of the soil sample is at its minimum. The curve showing the relationship between the depth of the hemispherical depression on the top surface of the soil sample and the soil moisture content is a downward-smooth curve.

[0103] S204: Establish a fitting relationship between the dry density of indoor soil samples and the depth of the hemispherical indentation on the top surface of the soil sample.

[0104] 1. Based on the soil compaction test and hemispherical pit depth test results in Tables 1, 2, and 3 above, the data points formed by the soil dry density and the hemispherical pit depth are scattered, making it impossible to plot a smooth curve to describe the data trend and pattern. Since polynomial curve fitting is a common data analysis method that uses a series of data points to fit a smooth curve, it better describes the data trend and pattern. Therefore, using soil dry density as the Y-axis (ordinate) and the hemispherical pit depth as the X-axis (horizontal axis), a polynomial fitting curve, fitting formula, and goodness-of-fit R are established for the relationship between soil dry density and hemispherical pit depth. 2 Value. Where: the fitted relation is y=ax 2 +bx+c.

[0105] The specific fitting formulas for Examples 1 to 3 are as follows: Figures 9-11 As shown, the specific fitting relationship and goodness of fit R are... 2 The values ​​are as follows:

[0106] (1) Fitting equation for low liquid limit clay (CL) in Example 1: y = 0.0027x 2 -0.037x+1.711, goodness of fit R 2 =0.9932;

[0107] (2) Fitting equation for clay sand (SC) in Example 2: y = 0.0033x 2 -0.0375x + 1.9827, goodness of fit R 2 =0.9978;

[0108] (3) Fitting equation for clay gravel (GC) in Example 3: y = 0.0026x 2 -0.0416x+2.034, goodness of fit R 2 =0.9936.

[0109] The goodness of fit R in the above three fitting relationships 2 The closer the value is to 1, the better the fit, and the higher the degree of fit and reliability of the polynomial fitting curve. When the goodness of fit R... 2 The fitting formula can only be used when the value is greater than 0.9.

[0110] 2. The maximum particle size and the content of particles smaller than 0.075 mm in the soil samples of Examples 1 to 3 were measured by particle size analysis: In Example 1, the maximum particle size of the low liquid limit clay sample was 5 mm, and the content of particles smaller than 0.075 mm was 89.3%; in Example 2, the maximum particle size of the clayey sand sample was 20 mm, and the content of particles smaller than 0.075 mm was 26.6%; in Example 3, the maximum particle size of the clayey gravelly soil sample was 40 mm, and the content of particles smaller than 0.075 mm was 19.8%.

[0111] 3. In summary, the soil samples from Examples 1 to 3, through comprehensive analysis of measured particle size and the content of particles smaller than 0.075mm, show that: the polynomial fitting curves all open upwards, therefore the coefficient 'a' in the fitting equation is always positive; the axis of symmetry of the polynomial fitting curves is to the right of the soil sample dry density (Y-axis (ordinate)), and the sign of coefficient 'b' is opposite to that of coefficient 'a', therefore the coefficient 'b' in the fitting equation is always negative; the constant 'c' in the fitting equation is the ordinate of the intersection point of the polynomial fitting curve and the soil sample dry density (Y-axis (ordinate)), intersecting at the positive half-axis of the soil sample dry density (Y-axis (ordinate)), and is related to the particle size and the content of particles smaller than 0.075mm in the soil sample. The value of constant 'c' increases with increasing particle size and also increases with decreasing content of particles smaller than 0.075mm, therefore the coefficient 'c' is always positive. Figures 9-11 As shown.

[0112] S3: Verification of dry density and moisture content of outdoor subgrade soil samples, and test of depth of hemispherical pit on top surface of outdoor subgrade.

[0113] S301: Verification of dry density and moisture content of outdoor subgrade soil samples.

[0114] Example 1: Based on the requirements of large-scale continuous filling construction of roadbeds at outdoor engineering construction sites, a section of roadbed with compaction to be tested needs to be selected from the top surface of each layer of roadbed already compacted by a road roller. A measuring point is randomly selected on the top surface of the roadbed within the testing area as a verification measuring point for the dry density and moisture content of the roadbed soil sample. The roadbed compaction degree is tested using the sand cone method, and the measured dry density of the roadbed soil sample is 1.621 g / cm³. 3 The moisture content of the roadbed soil sample was 22.3%.

[0115] Example 2: Based on the requirements of large-scale continuous filling construction of roadbeds at outdoor engineering construction sites, a section of roadbed with compaction to be tested must be selected from the top surface of each layer of roadbed already compacted by a road roller. A measuring point is randomly selected on the top surface of the roadbed within the testing area as a verification measuring point for the dry density and moisture content of the roadbed soil sample. The roadbed compaction degree is tested using the sand cone method, and the measured dry density of the roadbed soil sample is 1.944 g / cm³. 3 The moisture content of the roadbed soil sample was 16.5%.

[0116] Example 3: Based on the requirements of large-scale continuous filling construction of roadbeds at outdoor engineering construction sites, a section of roadbed with compaction to be tested must be selected from the top surface of each layer of roadbed already compacted by a road roller. A measuring point is randomly selected on the top surface of the roadbed within this testing area as a verification measuring point for the dry density and moisture content of the roadbed soil sample. The roadbed compaction degree is tested using the sand cone method, and the measured dry density of the roadbed soil sample is 2.004 g / cm³. 3 The moisture content of the roadbed soil sample was 13.7%.

[0117] Single-point verification method for the dry density and moisture content of subgrade soil samples at each outdoor layer: When conducting the hemispherical pit depth test on the top surface of each subgrade layer at the outdoor construction site, the dry density and moisture content of the subgrade soil samples at each outdoor layer must be verified simultaneously through single-point measurements. This serves two purposes: first, to use the actual dry density and moisture content of the subgrade soil samples at each layer as a comparison standard; and second, to obtain the dry density, moisture content, and hemispherical pit depth values ​​of the subgrade soil samples at the top surface of each subgrade layer through on-site measurements at the outdoor construction site, and to calculate the corresponding indoor soil sample dry density and the subgrade soil sample dry density correction coefficient for the outdoor measured moisture content. The process involves three steps: first, fitting the soil samples to obtain the dry density and compaction degree of the subgrade soil samples; second, verifying whether the soil properties of each subgrade soil sample at the outdoor construction site are the same as those used in the indoor compaction test, and then determining whether the compaction degree test results of each subgrade layer obtained by fitting the hemispherical pit depth values ​​measured on the top surface of each subgrade layer at the outdoor construction site are true, reliable, and accurate.

[0118] S302: Test on the depth of hemispherical pits on the top surface of outdoor roadbed.

[0119] To ensure the accuracy of the hemispherical pit depth test results, an outdoor hemispherical pit depth test was conducted on the top surface of the roadbed at a test point within a 500mm radius of the aforementioned verification test point. The test procedure is as follows:

[0120] (1) At the selected measuring point location, use a scraper to level the top surface of the roadbed with an area of ​​450mm×450mm, and use a spirit level to check whether the top surface of the roadbed is level after leveling.

[0121] (2) On the top surface of the roadbed, the depth of the hemispherical pit on the top surface of the roadbed is measured according to the test method of the hemispherical pit depth on the top surface of the indoor soil sample specimen, and the data is recorded.

[0122] (3) Following steps (1) to (2) in S302 above, complete the test of the depth of the hemispherical pit on the top surface of the roadbed at the remaining measuring points, and record the depth data of the hemispherical pit 2.

[0123] (4) After the test, the same soil as the roadbed fill material was used to backfill and compact the hemispherical depression 2 on the top surface of the roadbed, and level the surface. This was to prevent the hemispherical depression 2 from being filled loosely and from accumulating water.

[0124] S4: Indoor analysis of the fitted roadbed compaction degree.

[0125] The following values ​​were obtained by measuring the top surface of each subgrade layer at the outdoor construction site: dry density, moisture content, and depth of the hemispherical indentation on the top surface of the subgrade. Based on the relationship curve between indoor soil dry density and moisture content, the corresponding indoor soil dry density was obtained for the outdoor measured subgrade soil density. The outdoor measured subgrade soil dry density was divided by the indoor soil dry density to calculate the subgrade soil dry density correction factor. Then, based on the fitting relationship between the dry density of the indoor soil sample and the depth of the hemispherical pit on the top surface of the soil sample, the values ​​of the depth of the hemispherical pit at each measuring point on the top surface of the outdoor subgrade layer are directly substituted into the fitting relationship to calculate the dry density of the indoor soil sample at each measuring point, and then multiplied by the subgrade soil sample dry density correction coefficient. The dry density of the subgrade soil samples at each measuring point was obtained by fitting the data, and then divided by the maximum dry density of the indoor soil samples to obtain the subgrade compaction degree at each measuring point. This result is close to the measured subgrade compaction degree outdoors, and the difference between the two meets the specified requirements. Furthermore, the goodness of fit R0 is also satisfactory. 2 Values ​​greater than 0.8 fall within the 0.7–0.9 range, indicating a good fit and high reliability. The roadbed compaction degree fitted using this method is fast, direct, easy to understand and operate, produces a large number of data points efficiently, and the results are truthful, reliable, and accurate.

[0126] S401: Correction factor for calculating the dry density of subgrade soil samples .

[0127] 1. Example 1: Low Liquid Limit Clay (CL) Subgrade. Through verification of the dry density and moisture content of outdoor subgrade soil samples, and by conducting an outdoor test to measure the depth of a hemispherical indentation on the top surface of the subgrade, the following results were obtained: The dry density of this layer of subgrade soil sample at the outdoor construction site was 1.621 g / cm³. 3 The subgrade soil samples had a moisture content of 22.3%, a compaction degree of 96.5%, and hemispherical pit depths at various measuring points on the top surface of the subgrade: 2.98 mm, 3.06 mm, 2.96 mm, 2.93 mm, 3.03 mm, 3.07 mm, 3.00 mm, 2.91 mm, 2.93 mm, 3.03 mm, 3.05 mm, 3.12 mm, 2.97 mm, 2.88 mm, and 2.97 mm. These measurements were taken from outdoor subgrade soil samples. Figure 3 Analysis revealed that the dry density of the indoor soil sample corresponding to the measured moisture content of the outdoor subgrade soil sample was 1.632 g / cm³. 3 The correction factor for the dry density of the subgrade soil sample is... =Outdoor measured dry density of roadbed soil sample / Indoor dry density of soil sample = (1.621 g / cm³) 3 ) / (1.632g / cm 3 =0.993.

[0128] 2. Example 2: Clay-sand (SC) subgrade. Through verification of the dry density and moisture content of outdoor subgrade soil samples, and by conducting an outdoor test to measure the depth of a hemispherical indentation on the top surface of the subgrade, the following results were obtained: The dry density of this layer of subgrade soil samples at the outdoor construction site was 1.944 g / cm³. 3 The subgrade soil samples had a moisture content of 16.5%, a compaction degree of 99.2%, and hemispherical pit depths at various measuring points on the top surface of the subgrade: 0.89 mm, 0.88 mm, 0.91 mm, 0.98 mm, 0.94 mm, 0.97 mm, 0.91 mm, 0.91 mm, 0.95 mm, 0.89 mm, 0.88 mm, 0.88 mm, 0.88 mm, and 0.89 mm. These measurements were taken from outdoor subgrade soil samples. Figure 4 Analysis revealed that the dry density of the indoor soil sample corresponding to the measured moisture content of the outdoor subgrade soil sample was 1.952 g / cm³. 3 The correction factor for the dry density of the subgrade soil sample is... =Outdoor measured dry density of subgrade soil sample / Indoor dry density of soil sample = (1.944 g / cm³) 3 ) / (1.952g / cm 3 =0.996.

[0129] 3. Example 3: Clay-gravel (GC) subgrade. Through verification of outdoor subgrade soil dry density and moisture content, and by experimental measurement of the depth of a hemispherical indentation on the top surface of the outdoor subgrade, the following results were obtained: The dry density of this subgrade soil layer at the outdoor construction site was 2.004 g / cm³. 3 The subgrade soil samples had a moisture content of 13.7%, a compaction degree of 99.2%, and hemispherical pit depths at various measuring points on the top surface of the subgrade: 0.49 mm, 0.52 mm, 0.56 mm, 0.51 mm, 0.53 mm, 0.52 mm, 0.50 mm, 0.56 mm, 0.52 mm, 0.55 mm, 0.50 mm, 0.52 mm, 0.54 mm, 0.57 mm, and 0.56 mm. These measurements were taken from outdoor subgrade soil samples. Figure 5 Analysis revealed that the dry density of the indoor soil sample corresponding to the measured moisture content of the outdoor subgrade soil sample was 2.015 g / cm³. 3 The correction factor for the dry density of the subgrade soil sample is... =Outdoor measured dry density of subgrade soil sample / Indoor dry density of soil sample = (2.004 g / cm³) 3 ) / (2.015g / cm 3 =0.995.

[0130] S402: Fitting the dry density and compaction degree of the subgrade soil sample.

[0131] 1. Example 1: Low Liquid Limit Clay (CL) Subgrade. In Example 1, the measured values ​​of the hemispherical pit depths on the top surface of this outdoor subgrade layer were: 2.98mm, 3.06mm, 2.96mm, 2.93mm, 3.03mm, 3.07mm, 3.00mm, 2.91mm, 2.93mm, 3.03mm, 3.05mm, 3.12mm, 2.97mm, 2.88mm, and 2.97mm, respectively. These values ​​were directly substituted into the fitted relation y=0.0027x. 2 In -0.037x+1.711, the dry density of the indoor soil sample at each measuring point is calculated, and then multiplied by the correction factor for the dry density of the subgrade soil sample. The dry density and compaction degree of the subgrade soil samples at each measuring point were obtained by fitting, as shown in Table 4.

[0132] Table 4. Test results of dry density and compaction of subgrade soil samples at various measuring points in Example 1.

[0133]

[0134] 2. Example 2: Clay-sand (SC) subgrade. In Example 2, the measured values ​​of the hemispherical pit depths on the top surface of this outdoor subgrade layer at various points were: 0.89mm, 0.88mm, 0.91mm, 0.98mm, 0.94mm, 0.97mm, 0.91mm, 0.91mm, 0.95mm, 0.89mm, 0.88mm, 0.89mm, 0.88mm, 0.88mm, and 0.89mm. These values ​​were directly substituted into the fitted relation y=0.0033x. 2 In -0.0375x+1.9827, the dry density of the indoor soil samples at each measuring point is calculated, and then multiplied by the correction factor for the dry density of the subgrade soil samples. The dry density and compaction degree of the subgrade soil samples at each measuring point were obtained by fitting, as shown in Table 5.

[0135] Table 5. Results of the test on dry density and compaction of subgrade soil samples at various measuring points in Example 2.

[0136]

[0137] 3. Example 3: Clay-gravel (GC) subgrade. In Example 3, the measured values ​​of the hemispherical pit depths on the top surface of this outdoor subgrade layer at various points were: 0.49mm, 0.52mm, 0.56mm, 0.51mm, 0.53mm, 0.52mm, 0.50mm, 0.56mm, 0.52mm, 0.55mm, 0.50mm, 0.52mm, 0.54mm, 0.57mm, and 0.56mm. These values ​​were directly substituted into the fitted equation y=0.0026x. 2 In -0.0416x+2.034, the dry density of the indoor soil samples at each measuring point is calculated, and then multiplied by the correction factor for the dry density of the subgrade soil samples. The dry density and compaction degree of the subgrade soil samples at each measuring point were obtained by fitting, as shown in Table 6.

[0138] Table 6 shows the test results of dry density and compaction of subgrade soil samples at various measuring points in Example 3.

[0139]

[0140] S403: Plot the polynomial fitting curve of the roadbed compaction degree and the depth of the hemispherical pit on the top surface of the roadbed.

[0141] Based on the test results of the dry density and compaction degree of the subgrade soil samples at each measuring point in Tables 4, 5, and 6 above, with the fitted subgrade compaction degree as the ordinate and the depth of the hemispherical pit on the top surface of the subgrade as the abscissa, polynomial fitting curves of the fitted subgrade compaction degree versus the depth of the hemispherical pit on the top surface of the subgrade were plotted for Examples 1 to 3, respectively, and the goodness of fit R was obtained. 2 Value, such as Figures 12-14 As shown.

[0142] S404: Determination of the reliability and accuracy of test results.

[0143] 1. Dry density comparison method

[0144] (1) In Example 1, the depth of the hemispherical pit on the top surface of the roadbed was measured at 15 points, and the minimum dry density of the fitted roadbed soil sample was 1.611 g / cm³. 3 The dry density of the roadbed soil sample measured outdoors was 1.621 g / cm³. 3 The absolute value of the difference is 0.010 g / cm³. 3 The maximum dry density of the fitted subgrade soil sample was 1.616 g / cm³. 3 The dry density of the roadbed soil sample measured outdoors was 1.621 g / cm³. 3 The absolute value of the difference is 0.005 g / cm³. 3 ;

[0145] (2) In Example 2, the depth of the hemispherical pit on the top surface of the roadbed was measured at 15 points, and the minimum dry density of the fitted roadbed soil sample was 1.941 g / cm³. 3 The dry density of the roadbed soil sample measured outdoors was 1.944 g / cm³. 3 The absolute value of the difference is 0.003 g / cm³. 3 The maximum dry density of the fitted subgrade soil sample was 1.944 g / cm³. 3 The dry density of the roadbed soil sample measured outdoors was 1.944 g / cm³. 3 The absolute value of the difference is 0 g / cm³ 3 ;

[0146] (3) In Example 3, the depth of the hemispherical pit on the top surface of the roadbed was measured at 15 points, and the minimum dry density of the fitted roadbed soil sample was 2.001 g / cm³. 3 The dry density of the roadbed soil sample measured outdoors was 2.004 g / cm³. 3 The absolute value of the difference is 0.003 g / cm³. 3 The maximum dry density of the fitted subgrade soil sample was 2.004 g / cm³. 3 The dry density of the roadbed soil sample measured outdoors was 2.004 g / cm³. 3 The absolute value of the difference is 0 g / cm³ 3 ;

[0147] In Examples 1 to 3 above, the absolute value of the difference between the minimum or maximum dry density of the fitted subgrade soil sample and the measured dry density of the outdoor subgrade soil sample is less than 0.03 g / cm³, which is specified in the standard density test of the "Highway Geotechnical Testing Procedures" (JTG 3430-2020). 3 The allowable difference is specified.

[0148] 2. Compaction degree comparison method.

[0149] (1) In Example 1, the depth of the hemispherical pit on the top surface of the roadbed was measured at 15 points. The absolute value of the difference between the minimum compaction degree of the fitted roadbed (95.9%) and the measured compaction degree of the roadbed (96.5%) was 0.6%. The absolute value of the difference between the maximum compaction degree of the fitted roadbed (96.2%) and the measured compaction degree of the roadbed (96.5%) was 0.3%.

[0150] (2) In Example 2, the depth of the hemispherical pit on the top surface of the roadbed was measured at 15 points. The absolute value of the difference between the minimum compaction degree of the fitted roadbed (99.0%) and the measured compaction degree of the roadbed (99.2%) was 0.2%. The absolute value of the difference between the maximum compaction degree of the fitted roadbed (99.2%) and the measured compaction degree of the roadbed (99.2%) was 0%.

[0151] (3) In Example 3, the depth of the hemispherical pit on the top surface of the roadbed was measured at 15 points. The absolute value of the difference between the minimum compaction degree of the fitted roadbed (99.1%) and the measured compaction degree of the roadbed (99.2%) was 0.1%, and the absolute value of the difference between the maximum compaction degree of the fitted roadbed (99.2%) and the measured compaction degree of the roadbed (99.2%) was 0%.

[0152] In Examples 1 to 3 above, the absolute value of the difference between the minimum or maximum value of the fitted subgrade compaction degree and the measured subgrade compaction degree in the outdoors is less than 0.03 g / cm³, which is stipulated in the standard density test of the "Highway Geotechnical Testing Procedures" (JTG 3430-2020). 3 Therefore, the difference between two parallel measurements of compaction degree should not exceed 1.79%, 1.53%, and 1.49% (i.e., the difference between two parallel measurements of density should not exceed 0.03 g / cm³). 3 Divide by the maximum dry density of the indoor soil sample (g / cm³) 3 The allowable difference is specified as 100%.

[0153] 3. Goodness of fit R 2 Value determination method.

[0154] (1) In Example 1, the depth values ​​of each measuring point of the hemispherical pit on the top surface of the outdoor roadbed were directly substituted into the fitting relationship y=0.0027x 2 In -0.037x+1.711, the dry density of the indoor soil sample at each measuring point is calculated, and then multiplied by the correction factor for the dry density of the subgrade soil sample. The roadbed compaction degree at each measuring point was obtained by fitting the data. A polynomial fitting curve was plotted, with the fitted roadbed compaction degree as the ordinate and the depth of the hemispherical indentation on the top surface of the roadbed as the abscissa, to compare the fitted roadbed compaction degree with the depth of the hemispherical indentation. Figure 12 As shown, the goodness of fit R can be obtained. 2 =0.8784 falls within the range of 0.7 to 0.9, indicating a good fit and high reliability of the polynomial fitting curve.

[0155] (2) In Example 2, the depth values ​​of the hemispherical pits on the top surface of the outdoor roadbed were directly substituted into the fitting equation y=0.0033x. 2 In -0.0375x+1.9827, the dry density of the indoor soil samples at each measuring point is calculated, and then multiplied by the correction factor for the dry density of the subgrade soil samples. The roadbed compaction degree at each measuring point was obtained by fitting the data. A polynomial fitting curve was plotted, with the fitted roadbed compaction degree as the ordinate and the depth of the hemispherical indentation on the top surface of the roadbed as the abscissa, to compare the fitted roadbed compaction degree with the depth of the hemispherical indentation. Figure 13 As shown, the goodness of fit R can be obtained. 2=0.8891 falls within the range of 0.7 to 0.9, indicating a good fit and high reliability of the polynomial fitting curve.

[0156] (3) In Example 3, the depth values ​​of each measuring point on the hemispherical pit on the top surface of the outdoor roadbed were directly substituted into the fitting relationship y=0.0026x 2 In -0.0416x+2.034, the dry density of the indoor soil samples at each measuring point is calculated, and then multiplied by the correction factor for the dry density of the subgrade soil samples. The roadbed compaction degree at each measuring point was obtained by fitting the data. A polynomial fitting curve was plotted, with the fitted roadbed compaction degree as the ordinate and the depth of the hemispherical indentation on the top surface of the roadbed as the abscissa, to compare the fitted roadbed compaction degree with the depth of the hemispherical indentation. Figure 14 As shown, the goodness of fit R can be obtained. 2 =0.8309 falls within the range of 0.7 to 0.9, indicating a good fit and high reliability of the polynomial fitting curve.

[0157] In summary, based on the dry density comparison method, compaction degree comparison method, and goodness-of-fit R-squared, 2 Comprehensive judgment by the value judgment method: The reliability and accuracy of the fitted roadbed compaction test results are both high.

[0158] S5: The above describes the rapid on-site testing method for the compaction of roadbed filling materials using soil samples from Example 1 (low liquid limit clay, CL), Example 2 (clay sand, SC), and Example 3 (clay gravel, GC). For each layer of roadbed filling, the top surface must undergo outdoor testing for dry density, moisture content, and hemispherical pit depth. For different soil types, a fitting relationship between the indoor dry density and the hemispherical pit depth must be established using the above method. The outdoor dry density, moisture content, and hemispherical pit depth of the top surface of each layer of roadbed filling must be verified, and the compaction degree of the top surface of each layer of roadbed filling must be obtained by fitting the data using the above method.

[0159] S6: This test method is applicable to fine-grained soil and coarse-grained soil with a maximum particle size of 40 mm or less.

[0160] This invention provides a method for detecting the compaction degree of roadbed. This method utilizes the characteristic of preparing soil samples with different dry densities through heavy compaction of soil samples with different moisture contents in compaction tests. Through indoor standard soil sample compaction tests and hemispherical pit depth tests on the top surface of the soil sample, the optimal moisture content, maximum dry density, and hemispherical pit depth of the indoor soil sample are obtained. Curve I showing the relationship between indoor soil sample dry density and soil sample moisture content, and curve II showing the relationship between indoor soil sample hemispherical pit depth and soil sample moisture content, are then established. Finally, the dry density, moisture content, and hemispherical pit depth of the roadbed are obtained through on-site measurements at the top surface of each layer of the roadbed in outdoor engineering construction sites. Based on the relationship curve between indoor soil sample dry density and soil sample moisture content, the corresponding indoor soil sample dry density at the measured outdoor subgrade soil sample moisture content is obtained. The subgrade soil sample dry density correction factor is calculated by dividing the measured outdoor subgrade soil sample dry density by the indoor soil sample dry density. Then, based on the fitting relationship between the dry density of the indoor soil sample and the depth of the hemispherical pit on the top surface of the soil sample, the values ​​of the depth of the hemispherical pit at each measuring point on the top surface of the outdoor subgrade layer are directly substituted into the fitting relationship to calculate the dry density of the indoor soil sample at each measuring point, and then multiplied by the subgrade soil sample dry density correction coefficient. The dry density of the subgrade soil sample at each measuring point is obtained by fitting the data, and then divided by the maximum dry density of the indoor soil sample to obtain the subgrade compaction degree at each measuring point. The subgrade compaction degree fitted by this invention is fast, direct, easy to understand and operate, has a fast testing speed, short testing cycle, and a large number of test results with high efficiency; the testing equipment is simple to process and manufacture, inexpensive, has low environmental and equipment requirements, and is less affected by weather and human factors; the compaction degree test results are true, reliable and accurate, and can meet the requirements of large-scale continuous filling construction of subgrade.

[0161] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for detecting the compaction degree of roadbed, characterized in that, Includes the following steps: Preparation of indoor soil samples: Soil samples were taken from the construction site to be tested, and the soil samples were air-dried and sieved. The soil sample was divided into multiple samples, and different amounts of water were added to each sample. After stirring and soaking, multiple indoor soil sample samples were obtained. Testing of indoor soil samples and establishment of fitting equations: According to the compaction test method in standard JTG 3430-2020, the indoor moisture content and indoor dry density of each indoor soil sample were tested. The relationship curve between indoor soil moisture content and indoor soil dry density was plotted with indoor soil moisture content on the x-axis and indoor soil dry density on the y-axis to obtain the optimum moisture content and maximum dry density of indoor soil samples. Using the same compaction hammer and drop height as in the standard JTG 3430-2020, a steel ball (1) of the same mass and drop height was dropped freely to impact the top surface of the indoor soil sample. The depth of the hemispherical indentation on the top surface of each indoor soil sample was obtained. Then, with the depth of the hemispherical indentation on the top surface of the indoor soil sample as the abscissa and the dry density of the indoor soil sample as the ordinate, a fitting relationship between the dry density of the indoor soil sample and the depth of the hemispherical indentation on the top surface of the indoor soil sample was established. The fitting relationship is: y = ax 2 +bx+c, where a>0, b<0, c>0; Detection and fitting of various test points on outdoor roadbed for calculation of roadbed compaction degree: A point is randomly selected in the subgrade inspection area as the test point for the moisture content and dry density of the outdoor subgrade soil sample, and the measured moisture content and dry density of the subgrade soil sample are obtained. According to the method of the steel ball (1) falling freely and hitting the top surface of the roadbed, the depth value of the hemispherical pit on the top surface of the roadbed at each test point in the roadbed to be inspected area is obtained; From the relationship curve I between the dry density and moisture content of the indoor soil sample, the dry density D1 of the indoor soil sample at the measured moisture content of the subgrade soil sample is obtained. Divide the measured dry density of the subgrade soil sample by D1 to obtain the correction coefficient δ for the dry density of the subgrade soil sample, where 0 < δ < 1; Substitute the depth of the hemispherical pit on the top surface of the roadbed at each test point into the fitting formula to calculate the dry density D2 of the indoor soil sample at each test point. Multiply D2 by the roadbed soil sample dry density correction coefficient δ in sequence to obtain the roadbed soil sample dry density D3 at each test point; Divide D3 by the maximum dry density of the indoor soil sample in turn to obtain the subgrade compaction degree at each test point.

2. The method for detecting the compaction degree of roadbed according to claim 1, characterized in that, Different amounts of water were added to each sample so that the moisture content of each sample increased by 2% by mass.

3. The method for detecting the compaction degree of roadbed according to claim 1, characterized in that, In relationship curve I, the highest point of the curve corresponds to the optimum moisture content of the indoor soil sample; the highest point corresponds to the maximum dry density of the indoor soil sample; to the left of the optimum moisture content of the indoor soil sample, the dry density of the indoor soil sample increases with the increase of the indoor soil sample moisture content; to the right of the optimum moisture content of the indoor soil sample, the dry density of the indoor soil sample decreases with the increase of the indoor soil sample moisture content.

4. The method for detecting the compaction degree of roadbed according to claim 1, characterized in that, Plot curve II showing the relationship between the depth of the hemispherical indentation on the top surface of the indoor soil sample and the moisture content of the indoor soil sample, with the moisture content of the indoor soil sample as the x-axis and the depth of the hemispherical indentation on the top surface of the indoor soil sample as the y-axis. In curve II, the moisture content of the indoor soil sample corresponding to the lowest point of the curve is the optimum moisture content of the indoor soil sample; the depth of the hemispherical indentation on the top surface of the indoor soil sample corresponding to the lowest point is the minimum depth of the hemispherical indentation on the top surface of the indoor soil sample; to the left of the optimum moisture content of the indoor soil sample, the depth of the hemispherical indentation on the top surface of the indoor soil sample decreases as the moisture content of the indoor soil sample increases; to the right of the optimum moisture content of the indoor soil sample, the depth of the hemispherical indentation on the top surface of the indoor soil sample increases as the moisture content of the indoor soil sample increases.

5. The method for detecting the compaction degree of roadbed according to claim 1, characterized in that, When the soil sample is low liquid limit clay, the fitting equation is: y = 0.0027x 2 -0.037x + 1.711; When the soil sample is clayey sand, the fitting equation is: y = 0.0033x 2 -0.0375x + 1.9827; When the soil sample is clayey gravel, the fitting equation is y = 0.0026x 2 -0.0416x+2.

034.

6. The method for detecting the compaction degree of roadbed according to claim 5, characterized in that, The goodness-of-fit in the fitting equation is R. 2 , of which 0.9 <R 2 <1.

7. The method for detecting the compaction degree of roadbed according to claim 1, characterized in that, In the fitted relationship, when the dry density of the indoor soil sample is at its maximum, the depth of the hemispherical pit on the top surface of the indoor soil sample is at its minimum, and the dry density of the indoor soil sample decreases as the depth of the hemispherical pit on the top surface of the indoor soil sample increases.

8. The method for detecting the compaction degree of roadbed according to claim 1, characterized in that, The correction factor for the dry density of the subgrade soil sample is δ, where 0.99 < δ < 1.

9. The method for detecting the compaction degree of roadbed according to claim 1, characterized in that, The absolute value of the difference between the fitted subgrade compaction degree obtained by the aforementioned subgrade compaction degree detection method and the measured subgrade compaction degree outdoors is no greater than 0.6%.

10. The method for detecting the compaction degree of roadbed according to claim 9, characterized in that, The goodness of fit of the fitted roadbed compaction degree is R. 2 , of which 0.8 <R 2 <0.9.

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