Rapid detection method for cement mixing amount of cement-soil mixing pile

Abstract

The invention relates to the technical field of geotechnical engineering, in particular to a rapid detection method for the cement mixing amount of a cement-soil mixing pile, which comprises the following steps: preparing a series of standard samples with different cement mixing amounts: curing the series of standard samples to prepare a series of cured standard samples; measuring calcium element concentration values in the series of maintenance standard samples, and drawing a calcium element concentration increasing curve; drawing a calcium element concentration standard curve according to the calcium element concentration growth curve; and measuring the cement mixing amount of the cement-soil mixing pile according to the calcium element concentration standard curve. The rapid detection method for the cement mixing amount of the cement-soil mixing pile has the advantages of being easy to operate, high in detection speed, high in field applicability, low in cost and the like.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and in particular to a rapid detection method for cement content in cement-soil mixing piles. Background Technology

[0002] Soft soil foundations are widely distributed in coastal areas and inland river and lake basins. To meet the requirements for foundation strength and stability in engineering construction, cement-soil mixing is commonly used to reinforce the foundation. The quality of cement-soil mixing piles is crucial to the success of foundation treatment. Extensive research and engineering practice have shown that uneven mixing leading to cement enrichment or discontinuous piles, as well as insufficient cement content compared to design standards, are the main causes of insufficient pile strength and even engineering accidents.

[0003] Studies have shown that cement content is a key factor affecting the unconfined compressive strength of cement-soil. Wang Baotian et al. proposed to quantitatively estimate the cement content in cement-soil by using EDTA consumption. Fan Jiangtao et al. studied the effects of different factors such as sampling method, ambient temperature, and moisture content on EDTA titration results to determine the cement dosage in cement-improved loess subgrade. Luo Yilian et al. conducted a principal-subjective analysis of the interaction between multiple factors, including cement dosage, moisture content, and hydration time, and established a regression equation for the consumption of EDTA standard reagents under the combined influence of these three factors.

[0004] Currently, EDTA titration is commonly used to detect the cement content in cement-soil mixing piles. However, this method requires core sampling and delivery to a laboratory for testing, which results in a long testing cycle and complex operation, making it difficult to meet the needs of rapid on-site testing.

[0005] Therefore, finding a method to quickly detect the cement content in cement-soil mixing piles has become a research hotspot. Summary of the Invention

[0006] To address at least one of the aforementioned technical problems, this invention provides a rapid detection method for cement content in cement-soil mixing piles, enabling on-site, rapid, low-cost, and accurate detection of cement content in cement-soil mixing piles in geotechnical engineering.

[0007] In one aspect, the present invention provides a rapid detection method for cement content in cement-soil mixing piles, comprising: preparing a series of standard samples with different cement contents; curing the series of standard samples to prepare a series of cured standard samples; determining the calcium element concentration value in the series of cured standard samples and plotting a calcium element concentration growth curve; plotting a calcium element concentration standard curve based on the calcium element concentration growth curve; and determining the cement content in the cement-soil mixing pile based on the calcium element concentration standard curve.

[0008] In some embodiments of the present invention, the step of preparing a series of standard samples with different cement content includes: mixing the in-situ soil sample and the cement slurry with the same water-cement ratio as the on-site construction to obtain a series of standard samples with different cement content.

[0009] In some embodiments of the present invention, the criterion for determining uniform mixing is: if the spatial variation coefficient of calcium element... δ ≤5% and uniformity coefficient UC If the concentration is ≥0.95, then mix thoroughly.

[0010] In some embodiments of the present invention, the spatial variation coefficient of calcium element is... δ The calculation formula is: (1) In the formula, δ The spatial variation coefficient of calcium element. σ The standard deviation of the test sample. R This represents the average value of the test sample data.

[0011] In some embodiments of the present invention, the uniformity coefficient is... UC The calculation formula is: (2) (3) In the formula, To measure the average calcium concentration in the test samples, n For the sample size, c i For the first i The calcium concentration in this test. UC This is the uniformity coefficient.

[0012] In some embodiments of the present invention, the number of times the cement-soil mixing pile is stirred when the criteria for achieving uniform mixing are met. N The calculation formula is as follows: (4) In the formula, h Width of the stirring blades, in meters (m); β Σ is the perpendicular angle between the stirring blades and the stirring shaft; Z This represents the total number of stirring blades; n This refers to the rotational speed of the stirring head; V The lifting speed of the mixing head is expressed in m / min; the number of mixing cycles of the cement-soil mixing pile is the number of cycles required to achieve uniform mixing. N ≥5.

[0013] In some embodiments of the present invention, the cement content in the series of standard samples is 10%, 15%, 20% and 25%, respectively.

[0014] In some embodiments of the present invention, the step of preparing a series of curing standard samples includes: curing the series of standard samples in a standard curing chamber to obtain a series of curing standard samples; wherein the curing temperature is 18~22℃ and the relative humidity is ≥95%.

[0015] In some embodiments of the present invention, the step of plotting the calcium element concentration growth curve includes: during the preparation of a series of standard curing samples, the calcium element concentration on the sample surface is detected by an XRF spectrometer between curing and the designed age; the calcium element concentration growth curve with curing age under the same cement admixture condition is plotted to obtain the corresponding calcium element concentration growth curve.

[0016] In some embodiments of the present invention, the step of plotting a standard curve of calcium element concentration includes: plotting a curve of calcium element concentration changing with cement admixture under the same age conditions based on the calcium element concentration growth curve, thereby obtaining the corresponding standard curve of calcium element concentration.

[0017] The technical solution provided by this invention has the following advantages: The rapid detection method for cement content in cement-soil mixing piles according to this invention has the characteristic of "fast detection speed". The time required for a single measurement is only 1 to 2 minutes, which can meet the needs of "instant feedback and instant adjustment" in on-site construction and reduce construction delays.

[0018] The rapid detection method for cement content in cement-soil mixing piles according to the present invention has the characteristics of "minimally destructive and pollution-free". The detection process causes minimal damage to the core sample, and the sample can be preserved for retesting or strength testing. In addition, the detection process does not require chemical reagents, which can avoid waste liquid pollution.

[0019] The rapid detection method for cement content in cement-soil mixing piles according to the present invention has the feature of "wide age range", which can cover the entire age period from 0h to 90d. It is especially suitable for the engineering practice of core sampling and testing of cement mixing piles at 7d, 14d and 28d, and solves the age limitation problem of traditional methods.

[0020] The rapid detection method for cement content in cement-soil mixing piles according to this invention is characterized by "simple operation" and high field applicability. It uses a portable XRF spectrometer, requires no laboratory conditions, is suitable for field construction environments, and can be operated by only one person.

[0021] Furthermore, the rapid detection method for cement content in cement-soil mixing piles according to the present invention is applicable to the detection of cement-soil mixing piles in various foundations such as silty soil, clay, and silt. It is compatible with common cements of various grades, and the water-cement ratio is applicable in the range of 0.5 to 2.0, meeting the needs of most engineering scenarios.

[0022] Therefore, the rapid detection method for cement content in cement-soil mixing piles according to the present invention has the advantages of fast detection speed, low destructiveness and no pollution, wide age range, simple operation, high on-site applicability and low cost. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0025] Figure 1 In the rapid detection method for cement content in cement-soil mixing piles according to an embodiment of the present invention, the growth curve of calcium element concentration (PPM) in standard samples with different cement content (10%, 15%, 20% and 25%) as a function of age (d) is shown (i.e., the growth curve of calcium element concentration). Figure 2 The graphs show the calcium element concentration (PPM) at different ages (7d, 28d, 49d and 90d) of this invention as a function of cement admixture (%) (i.e., the calcium element concentration standard curve). Figure 3 The standard curves for EDTA titration of cement-soil with different initial soil moisture contents (20%, 30%, and 40%) and different cement admixtures (0%, 10%, 15%, 20%, and 25%) in Example 2 of this invention are shown. Figure 4 The standard curves of calcium element concentration by XRF for cement soil with different initial soil moisture contents (20%, 30%, and 40%) and different cement admixtures (0%, 10%, 15%, 20%, and 25%) in Example 2 of the present invention are shown. Figure 5 This is a comparison chart of the changes in cement content with the depth of the mixing pile as tested by XRF detection and EDTA titration in Embodiment 2 of the present invention. Detailed Implementation

[0026] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0028] According to an embodiment of the present invention, a rapid detection method for cement content in cement-soil mixing piles is provided, specifically including the following steps: (1) Preparation of standard test samples: Select in-situ soil samples and cement used in the on-site mixing pile construction, mix them evenly, and prepare standard samples of cement-soil unconfined compressive strength with different cement admixtures.

[0029] (2) Curing of standard specimens: The series of standard samples obtained in step (1) were placed in a standard curing chamber for curing at a temperature of 20±2℃ and a relative humidity of ≥95%.

[0030] (3) Construction of the calcium concentration growth curve with the age of maintenance: When the samples have been cured to the designed age, the samples with different cement content obtained in step (2) are taken out from the standard curing box and placed on the test bench. Wipe off the moisture on the surface of the sample and lightly touch the surface with qualitative filter paper to ensure there are no wet marks.

[0031] A portable XRF spectrometer was used, with the intersection of the sample axis and the upper surface as the center, and detection was performed within a circular area with a diameter of 5 mm. Each detection should avoid cracks or depressions on the sample surface to ensure consistency of the detection location and reduce data deviation. At least three detection locations were used for each sample, and the average value was taken as the final detection result for that sample.

[0032] After testing, the samples are returned to the curing chamber for continued curing until the designed age is reached, and then the above steps are repeated.

[0033] The test results were used to plot the relationship between calcium concentration and curing age under different cement admixture conditions. The experimental data were then fitted to obtain the calcium concentration growth curve over time. Each cement admixture corresponds to a separate calcium concentration growth curve; that is, several different cement admixtures correspond to several different calcium concentration growth curves.

[0034] (4) Construction of standard curves for XRF detection at different ages: The calcium concentration growth curves of different cement admixtures with age obtained in step (3) are used to calculate the calcium concentration of each cement admixture at each age, and standard curves for XRF detection at each age (i.e., calcium concentration standard curves) are prepared. There is a calcium concentration standard curve corresponding to each age.

[0035] (5) Determination of cement content in core samples from cement-soil mixing piles: Core samples were taken from each of the cement-soil mixing piles to be tested. The core samples were cleaned to remove surface impurities and dried.

[0036] The calcium concentration of the samples was detected using a portable XRF spectrometer. At least three detection sites were used for each sample, and the average value of the results was taken.

[0037] (6) Calculation results: Substitute the average calcium concentration of the sample obtained in step (5) into the standard curve established by the XRF detection method at different ages obtained in step (4) to calculate the cement content of core samples taken from cement mixing piles at different depths at the same age.

[0038] In some embodiments of the present invention, in step (1), "uniform mixing" is defined as follows: Calcium is the most active key element in the cement-soil solidification mechanism, and its relative content has a close influence on both the early and later strength of the cement-soil. To evaluate the characteristics of the uniformity of cement-soil mixing piles, after each mixing, 15 samples are taken radially along different directions of the pile body, and the concentration of calcium in the samples is rapidly determined using a handheld XRF. The spatial variation coefficient of calcium is introduced using formula (1). δ The concept of uniformity. To eliminate the influence of extreme data, formulas (2) and (3) are introduced to calculate the uniformity of calcium in cement-soil after each mixing. The calculation result is defined as the uniformity coefficient of cement-soil ( UC ).like UC A value of 1 indicates that the cement and soil are completely and evenly mixed. UC The smaller the value, the more uneven the distribution of calcium, that is, the greater the degree of unevenness of cement soil.

[0039] (1) (2) (3) In the formula, σ The standard deviation of the test sample. R This represents the average value of the test sample data. n For the sample size, c i For the first i The calcium concentration in this test. This represents the average calcium concentration of the test samples.

[0040] In some embodiments of the present invention, in step (1), the criterion for determining whether the cement-soil mixing pile is "uniformly mixed" is as follows: according to the statistical analysis results of the XRF detection method on the uniformity of cement-soil mixing piles, when the number of mixing times of the cement-soil mixing pile reaches 5, the cement-soil mixing effect tends to be uniform, and the corresponding coefficient of variation of calcium element concentration is [value missing]. δ The analysis results are generally no greater than 5%, and the uniformity coefficient is [missing information]. UC The value reaches approximately 0.95. Therefore, the coefficient of variation of the cement content at different locations in the cement-soil mixing pile, which characterizes the factors, is... δ ≤5%, uniformity coefficient UC ≥0.95 is used as an indicator to determine the uniformity of cement-soil mixing piles.

[0041] According to Clause 6.3.4 of the "Technical Specification for Composite Foundations" (GB / T 50783-2012), the strength of the soil at any point within the reinforcement range of cement-soil mixing piles can reach a relatively high value after 20 mixing cycles. The number of mixing cycles for cement-soil mixing piles is [not specified]. N Calculate using the following formula: (4) In the formula, h Width of the stirring blades, in meters (m); β Σ is the angle between the stirring blades and the stirring shaft; Z This represents the total number of stirring blades; n This refers to the rotational speed of the stirring head; V The lifting speed of the stirring head is expressed in m / min.

[0042] Based on equation (4) and the mixing blade parameters in the indoor model test, the number of times the cement-soil is mixed at any point when the mixing head mixes once from top to bottom is determined. N The total number of mixing times is 2.74. After 5 mixing cycles, the cement-soil mixture tends to be homogeneous. At any point on this point, the total number of mixing cycles is 2.74 × 5 × 2 = 27.4, slightly higher than the standard requirement of 20 mixing cycles at any point. Therefore, to improve the mixing uniformity of cement-soil mixing piles, the number of mixing cycles at any point should be appropriately increased compared to the standard, with an increase of no less than 30% of the standard value.

[0043] Example 1 The following example uses the testing of a core sample taken from a 7-day-old cement mixing pile to illustrate the technical solution of the present invention.

[0044] 1. Sample preparation Cement and undisturbed soil used at the construction site were sealed in airtight plastic bags to maintain stable moisture content.

[0045] (1) Prepare standard samples of unconfined compressive strength of cement-soil with cement content of 10%, 15%, 20% and 25% respectively. The cement is 42.5 ordinary Portland cement with a water-cement ratio of 1:2. The mix proportions are shown in Table 1.

[0046] Table 1 Sample Proportioning Parameters (2) Put the weighed soil sample, cement and water into the mixing bucket and mix for 15 minutes to make the cement-soil sample evenly mixed.

[0047] (3) The mold is a 40×70mm cylindrical unconfined compressive strength test mold. After applying Vaseline to the inner wall, the well-mixed cement soil is put into the mold and then placed on the vibrating table and vibrated for 2 minutes to make the sample fully compacted.

[0048] 2. Sample curing (1) Place the sample obtained in the above steps into a standard curing chamber and cure it for 1 day, and then demold it after it is formed.

[0049] (2) Continue to cure the demolded sample in the curing chamber. The curing chamber temperature is set to 20℃ and the relative humidity is ≥95%.

[0050] 3. XRF spectroscopy detection The samples were removed from the curing chamber at curing ages of 7 days, 28 days, 49 days, and 90 days, and the calcium concentration of the samples was detected using a portable XRF spectrometer.

[0051] 4. Determination of the standard curve Using the data obtained from the above experimental steps, a coordinate graph was plotted with calcium concentration on the vertical axis and age on the horizontal axis, resulting in a curve showing the increase of calcium concentration (PPM) with age (d). Figure 1 .

[0052] right Figure 1 The data was further processed, and the relationship between cement admixture and calcium concentration at different ages was plotted on a coordinate graph. The experimental data were then fitted to obtain a curve showing the relationship between cement admixture and calcium concentration (i.e., a standard curve for calcium concentration), as shown in the figure below. Figure 2 As shown.

[0053] 5. Determination of cement admixture in cement mixing piles Core samples were taken from the cement mixing piles to be tested. Following the steps described above, the core samples were analyzed using an XRF spectrometer to obtain the calcium concentration of the core samples.

[0054] The cement content of the core sample can be found on the standard curve.

[0055] This embodiment employs a standard sample comparison method. First, it simulates the preparation and curing conditions of the pile body on-site to complete the sample preparation and curing process. Then, for samples with different cement contents, it detects the growth pattern of calcium concentration with age, thereby obtaining standard curves at different ages. Subsequently, it uses the standard curves at different ages to calculate the cement content of the core samples from the cement-soil mixing pile. When calculating the cement content of core samples at different ages, a standard curve corresponding to that age should be selected. Figure 2 It can be seen that the curing age has a significant impact on the determination results of cement content in core samples. Taking the standard curve for a curing age of 28 days as an example, the cement content corresponding to a sample with a calcium concentration of 159064 PPM is 20%. If the standard curve for a curing age of 7 days is used, the corresponding cement content for the same calcium concentration is 24.8%. Therefore, when calculating the content of core samples at different curing ages, the corresponding standard curve must be used.

[0056] Example 2 On-site sampling test results The construction project is a flood control project in a flood storage and detention area in Bazhou, Hebei Province, using cement-soil mixing piles for foundation treatment. The designed cement content for the cement-soil mixing piles is 20%, and the water-cement ratio is 0.5. Cement content is a key factor affecting the quality of the mixing piles. In this embodiment, a self-made sampling device was used to immediately sample the cement-soil mixing piles after construction. XRF was used to rapidly detect the cement content of samples at different depths, and the reliability of the XRF test results was verified by EDTA titration. Soil samples and cement were taken from the construction site, and cement-soil EDTA titration standard curves were established for different initial soil moisture contents (20%, 30%, and 40%) and different cement contents (0%, 10%, 15%, 20%, and 25%) (e.g., ...). Figure 3 (as shown) and the XRF calcium elemental concentration standard curve (as shown) Figure 4 (As shown). Tests were performed on samples taken from different depths by the sampling device, and the corresponding cement content could be obtained by referring to the standard curve.

[0057] Figure 5 The variation of cement content with the depth of the mixing pile is presented using XRF detection and EDTA titration methods. Figure 5As shown, the average cement content measured in this study was slightly higher than the design value at the construction site, which is consistent with the actual engineering practice of cement-soil mixing piles to achieve construction quality control and avoid strength deficiencies caused by process fluctuations. Within the 0-1.5m test range, the actual cement content of the mixing piles was higher, and during construction, cement slurry overflowed from the top of the pile, resulting in a significant increase in the measured data at the top. The average cement content obtained by EDTA titration was 21.44%, and the average cement content obtained by XRF detection was 21.35%, with the two test results being basically consistent. At a depth of 3.7m, the lower XRF detection value may be related to the quality of local sampling, but the deviation between the XRF and EDTA detection results at this point was only 1.6%, which is within an acceptable range. The EDTA titration method further verified that the XRF detection method can be used for rapid detection of cement content in cement-soil mixing piles in actual engineering projects.

[0058] In summary, the rapid detection method for cement content in cement-soil mixing piles according to this invention first prepares samples with different cement contents using in-situ soil samples and cement slurry, and then cures them under standard conditions. After curing to the designed age, a portable X-ray fluorescence (XRF) spectrometer is used to detect the calcium concentration on the sample surface. Multiple measurements are taken and averaged to establish a growth curve of calcium concentration with age. The calcium concentration values ​​corresponding to different cement contents at specific ages are extracted from the growth curve, and a standard curve between cement content and calcium concentration is plotted. By comparing the calcium concentration of core samples from actual engineering projects at the same age with the standard curve, the cement content can be quickly and accurately determined, and whether the cement-soil mixing pile meets the design requirements can be judged. This invention has the advantages of simple operation, fast detection speed, high field applicability, and low cost.

[0059] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rapid detection method for cement content in cement-soil mixing piles, characterized in that, include: Prepare a series of standard samples with different cement admixtures: The series of standard samples were cured to prepare a series of cured standard samples; The calcium concentration in the series of maintenance standard samples was determined, and the calcium concentration growth curve was plotted. Based on the calcium concentration growth curve, draw a standard curve for calcium concentration. The cement content of cement-soil mixing piles was determined based on the calcium element concentration standard curve.

2. The rapid detection method according to claim 1, characterized in that, The steps for preparing a series of standard samples with different cement admixtures include: The in-situ soil sample and the cement slurry with the same water-cement ratio as the on-site construction were mixed evenly to obtain a series of standard samples with different cement admixtures.

3. The rapid detection method according to claim 2, characterized in that, The criteria for determining whether the mixture is uniform are: If the spatial variation coefficient of calcium δ ≤5% and uniformity coefficient UC If the concentration is ≥0.95, then mix thoroughly.

4. The rapid detection method according to claim 3, characterized in that, Spatial variation coefficient of calcium δ The calculation formula is: （1） In the formula, δ The spatial variation coefficient of calcium element. σ The standard deviation of the test sample. R This represents the average value of the test sample data.

5. The rapid detection method according to claim 3 or 4, characterized in that, Uniformity coefficient UC The calculation formula is: （2） （3） In the formula, To measure the average calcium concentration in the test samples, n For the sample size, c i For the first i The calcium concentration in this test. UC This is the uniformity coefficient.

6. The rapid detection method according to any one of claims 2 to 5, characterized in that, The number of mixing cycles for cement-soil mixing piles is required to achieve the criteria for uniform mixing. N The calculation formula is as follows: （4） In the formula, h Width of the stirring blades, in meters (m); β The angle between the stirring blades and the stirring shaft is perpendicular to each other. Σ Z This represents the total number of stirring blades; n This refers to the rotational speed of the stirring head; V The lifting speed of the stirring head is expressed in m / min. Among them, the number of mixing cycles for cement-soil mixing piles is required to reach the standard for uniform mixing. N ≥5.

7. The rapid detection method according to any one of claims 1 to 6, characterized in that, The cement content in the series of standard samples was 10%, 15%, 20%, and 25%, respectively.

8. The rapid detection method according to any one of claims 1 to 7, characterized in that, The steps for preparing a series of maintenance standard test specimens include: A series of standard samples were cured in a standard curing chamber to obtain a series of cured standard samples. The maintenance temperature is 18~22℃, and the relative humidity is ≥95%.

9. The rapid detection method according to any one of claims 1 to 8, characterized in that, The steps for plotting a calcium concentration growth curve include: During the preparation of a series of standard curing samples, the calcium concentration on the sample surface was detected by XRF spectrometer between curing and the designed age. Plot the growth curve of calcium concentration with curing age under the same cement admixture conditions to obtain the corresponding calcium concentration growth curves.

10. The rapid detection method according to any one of claims 1 to 9, characterized in that, The steps for plotting a calcium concentration standard curve include: Based on the calcium concentration growth curve, a curve showing the change of calcium concentration with cement admixture under the same age conditions was plotted, thus obtaining the corresponding standard curve for calcium concentration.

Images