Evaluation method of unconfined compressive strength of cement mixing pile core sample

Abstract

The present invention discloses a method for evaluating the unconfined compressive strength of a cement mixing pile core sample, comprising segmenting a cement mixing pile to be evaluated, and selecting cement mixing pile core samples of each segment in the cement mixing pile based on a core drilling method; measuring the compressive strength of the cement mixing pile core samples of each segment to obtain first compressive strength data; determining RQD data of the cement mixing pile core samples of each segment according to the first compressive strength data; determining second compressive strength data of the cement mixing pile core samples of each segment according to the first compressive strength data and the RQD data; determining a representative value calculation method for unconfined compressive strength according to the number of segments of the cement mixing pile; and determining the representative value of unconfined compressive strength of the cement mixing pile core sample according to the second compressive strength data based on the representative value calculation method for unconfined compressive strength. The present invention can reasonably calculate the unconfined compressive strength of the cement mixing pile core sample, which is conducive to improving the authenticity and accuracy of the evaluation method.

Description

Technical Field

[0001] The invention relates to the technical field of construction engineering, and in particular to a method for evaluating the unconfined compressive strength of a cement mixing pile core sample. Background Art

[0002] Soft soil has the characteristics of high water content, low strength, high compressibility and poor permeability. Due to the low bearing capacity, large settlement and significant rheological characteristics of soft soil foundation, cement mixing piles are often used to reinforce soft soil foundation in soft soil areas to improve the bearing capacity of soft soil foundation and reduce settlement deformation. Cement mixing piles have low construction cost, high environmental protection, short construction period and little disturbance to the original soil. Cement mixing pile technology has been widely used in the reinforcement of soft soil foundation.

[0003] At present, the core drilling method is widely used at home and abroad to test the unconfined compressive strength of the core sample of the mixing pile. The core sample is loaded with a hydraulic testing machine, and the compressive strength of the cement mixing pile is directly calculated based on the relationship between the compressive strength and the failure load, the core sample size, and the compressive strength conversion coefficient. The calculation method specified in the specification JGJ106-2003 "Technical Specifications for Building Foundation Pile Testing" is mainly for concrete piles. The pile body material of the concrete pile is concrete, which has the characteristics of isotropy and small discreteness; the cement mixing pile is a composite of cement base and soft soil, which has the characteristics of anisotropy and large discreteness. It can be seen that there is an essential difference between cement soil mixing piles and concrete piles. It is not reasonable to use the concrete pile compressive strength evaluation method to evaluate the compressive strength of cement mixing piles. Therefore, it is necessary to invent a set of methods specifically for evaluating the unconfined compressive strength of cement mixing pile core samples. The evaluation method of the unconfined compressive strength of cement soil mixing pile core samples should consider factors such as pile integrity. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for evaluating the unconfined compressive strength of a cement mixing pile core sample, which can reasonably calculate the unconfined compressive strength of the cement mixing pile core sample and improve the authenticity and accuracy of the evaluation method.

[0005] The method for evaluating the unconfined compressive strength of a cement mixing pile core sample according to an embodiment of the present invention comprises the following steps:

[0006] Divide the cement mixing pile to be evaluated into sections, and select cement mixing pile core samples of each section of the cement mixing pile based on the core drilling method;

[0007] Determine the compressive strength and rock basic quality index of the cement mixing pile core sample of each segment to obtain first compressive strength data and RQD data;

[0008] Determine the second compressive strength data of the cement mixing pile core sample of each segment according to the first compressive strength data and the RQD data;

[0009] Determine a method for calculating a representative value of the unconfined compressive strength of the core sample of the cement mixing pile according to the number of segments of the cement mixing pile;

[0010] Based on the method for calculating the representative value of the unconfined compressive strength of the cement mixing pile core sample, the representative value of the unconfined compressive strength of the cement mixing pile core sample is determined according to the second compressive strength data.

[0011] The method for evaluating the unconfined compressive strength of a cement mixing pile core sample according to an embodiment of the present invention has at least the following beneficial effects:

[0012] Determining the second strength data of each segmented cement mixing pile core sample based on the first compressive strength data and RQD data can well consider the influence of pile body integrity on strength. At the same time, determining the calculation method of the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the number of segments of the cement mixing pile can reduce the influence of the number of samples, thereby reasonably calculating the unconfined compressive strength of the cement mixing pile core sample, which is conducive to improving the authenticity and accuracy of the evaluation method.

[0013] According to some embodiments of the present invention, the second compressive strength data is equal to the product of the first compressive strength data and the RQD data.

[0014] According to some embodiments of the present invention, the method for calculating the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the second compressive strength data determines the representative value of the unconfined compressive strength of the cement mixing pile core sample, including:

[0015] When the number of segments of the cement mixing pile core sample is less than or equal to a first threshold, determining a range value and an average value of the second compressive strength data;

[0016] Determine a ratio between a range value and an average value of the second compressive strength data to obtain a first ratio;

[0017] When the first ratio is less than or equal to the second threshold, the average value of the second compressive strength data is determined as the representative value of the unconfined compressive strength of the cement mixing pile core sample.

[0018] According to some embodiments of the present invention, the method for calculating the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the second compressive strength data determines the representative value of the unconfined compressive strength of the cement mixing pile core sample, and further includes:

[0019] When the first ratio is greater than the second threshold, removing the maximum values ​​in the second compressive strength data one by one until the first ratio is less than or equal to the second threshold;

[0020] The average value of the remaining data in the second compressive strength data is determined as the representative value of the unconfined compressive strength of the cement mixing pile core sample.

[0021] According to some embodiments of the present invention, the method for calculating the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the second compressive strength data determines the representative value of the unconfined compressive strength of the cement mixing pile core sample, including:

[0022] When the number of segments of the cement mixing pile core sample is greater than a first threshold, determining the average value and standard deviation of the second compressive strength data;

[0023] Acquire depth data corresponding to the second compressive strength data;

[0024] determining a correlation coefficient according to the second compressive strength data and the depth data;

[0025] determining, according to the correlation coefficient, an analysis type between the second compressive strength data and the depth data;

[0026] Based on the analysis type, a representative value of the unconfined compressive strength of the cement mixing pile core sample is determined according to the average value and standard deviation of the second compressive strength data.

[0027] According to some embodiments of the present invention, determining the analysis type between the second compressive strength data and the depth data according to the correlation coefficient comprises the steps of:

[0028] When the correlation coefficient is zero, the analysis type is determined as non-correlation type;

[0029] When the correlation coefficient is not zero, the analysis type is determined to be a correlation type.

[0030] According to some embodiments of the present invention, the method of determining the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the analysis type and the average value and standard deviation of the second compressive strength data comprises the steps of:

[0031] In the case where the analysis type is non-correlation type, determining a first coefficient of variation according to the mean value and standard deviation of the second compressive strength data;

[0032] Determining a first statistical correction coefficient according to the first coefficient of variation;

[0033] A representative value of the unconfined compressive strength of the cement mixing pile core sample is determined according to the average value of the second compressive strength data and the first statistical correction coefficient.

[0034] According to some embodiments of the present invention, the representative value of the unconfined compressive strength of the cement mixing pile core sample is equal to the product of the first statistical correction coefficient and the average value of the second compressive strength data.

[0035] According to some embodiments of the present invention, the method of determining the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the analysis type and the average value and standard deviation of the second compressive strength data comprises the steps of:

[0036] In the case where the analysis type is a correlation type, determining a residual standard deviation according to the standard deviation of the second compressive strength data and the correlation coefficient;

[0037] determining a second coefficient of variation according to the residual standard deviation and an average value of the second compressive strength data;

[0038] determining a second statistical correction coefficient according to the second coefficient of variation;

[0039] A representative value of the unconfined compressive strength of the cement mixing pile core sample is determined according to the average value of the second compressive strength data and the second statistical correction coefficient.

[0040] According to some embodiments of the present invention, the representative value of the unconfined compressive strength of the cement mixing pile core sample is equal to the product of the second statistical correction coefficient and the average value of the second compressive strength data.

[0041] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0043] Figure 1 This is one of the flow charts of the steps of the method for evaluating the unconfined compressive strength of a cement mixing pile core sample according to an embodiment of the present invention;

[0044] Figure 2 A schematic diagram of a first cement mixing pile in a segmented manner of a method for evaluating the unconfined compressive strength of a cement mixing pile core sample according to an embodiment of the present invention;

[0045] Figure 3 A schematic diagram of sections of a second cement mixing pile of the method for evaluating the unconfined compressive strength of a cement mixing pile core sample according to an embodiment of the present invention;

[0046] Figure 4 This is a second flow chart of the steps of the method for evaluating the unconfined compressive strength of a cement mixing pile core sample according to an embodiment of the present invention;

[0047] Figure 5 It is a scatter plot of compressive strength and depth of the method for evaluating the unconfined compressive strength of a cement mixing pile core sample according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0049] In the description of the present invention, "several" means one or more, "multiple" means more than two, greater than, less than, and exceeding are understood as not including the number itself, and "above", "below", and "within" are understood as including the number itself. If there is a description of "first", "second", etc., it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0050] Please refer to Figure 1 This embodiment discloses a method for evaluating the unconfined compressive strength of a cement mixing pile core sample, including steps S100 to S500, and each step is described in detail below. It is worth understanding that in the description of the embodiment of the present invention, the continuous numbering of each step is for the convenience of review and understanding. In combination with the overall technical solution of the embodiment of the present invention and the logical relationship between each step, adjusting the implementation order between the steps does not necessarily affect the technical effect achieved by the technical solution of the present invention.

[0051] S100, dividing the cement mixing pile to be evaluated into sections, and selecting cement mixing pile core samples of each section of the cement mixing pile based on the core drilling method.

[0052] After the cement mixing piles on site reach the age (e.g. 28 days, 60 days or 90 days), the cement mixing piles are evaluated. Since the drilling length of the cement mixing piles will affect the integrity of the pile body, it is necessary to discuss two cement mixing pile lengths. Please refer to Figure 2 and Figure 3, the following discussion takes the shorter first cement mixing pile 100 and the longer second cement mixing pile 200 as examples. In this embodiment, the cement mixing piles are divided into shorter cement mixing piles and longer cement mixing piles with a length of 15m (meter) as the boundary. The length of the first cement mixing pile 100 is 15m, which is evenly divided into 5 sections. The sections are numbered 101, 102, 103, 104 and 105, and the length of each section is 3m; the length of the second cement mixing pile 200 is 18m, which is divided into 6 sections. The sections are numbered 201, 202, 203, 204, 205 and 206, and the length of each section is 3m. Based on the core drilling method, the core samples of the cement mixing piles in each section are drilled and sampled to obtain the core samples of the cement mixing piles in each section. It is worth understanding that the core drilling method is a method well known to those skilled in the art. In order to avoid redundancy, it will not be discussed here.

[0053] S200, determining the compressive strength and basic rock quality index of the cement mixing pile core sample of each segment, and obtaining first compressive strength data and RQD (Rock Quality Designation) data.

[0054] After obtaining the cement mixing pile core samples of each segment based on the core drilling method, the compressive strength of the cement mixing pile core samples of each segment is measured, for example, the unconfined compressive strength is measured by the existing compressive strength testing equipment to obtain the first compressive strength data, for example, q 1 ,q 2 ,...,q n , n is an integer greater than 1. The RQD data is equal to the percentage of the quotient of the cumulative length of the cement mixing pile core samples greater than or equal to 10 cm (centimeter) in each segment of the cement mixing pile and the length of the corresponding segment of the cement mixing pile, that is,

[0055]

[0056] Among them, the RQD data is denoted as RQD 1 , RQD 2 , ..., RQD n , n is an integer greater than 1.

[0057] S300, determining the second compressive strength data of the cement mixing pile core sample of each segment according to the first compressive strength data and the RQD data.

[0058] According to the first compressive strength data and RQD data, the compressive strength of each segment of the cement mixing pile after RQD reduction is calculated, so as to obtain the second compressive strength data, which is recorded as: q′ 1 ,q′ 2 , ..., q′ n, n is an integer greater than 1. Wherein, q′=RQD×q. This embodiment can well consider the influence of pile body integrity on strength by calculating the unconfined compressive strength of the cement mixing pile core sample after RQD reduction.

[0059] S400. Determine a method for calculating a representative value of the unconfined compressive strength of a cement mixing pile core sample based on the number of segments of the cement mixing pile.

[0060] Since the drilling length of cement mixing piles will affect the integrity of the pile body, it is necessary to discuss it in different situations. In practice, the general segment length of cement mixing piles is 3m. Therefore, with five segments as the boundary, when n≤5, it represents the case where the length of the cement mixing pile is shorter, and when n≥6, it represents the case where the length of the cement mixing pile is longer, where n is the number of segments of the cement mixing pile. This embodiment determines the calculation method of the representative value of the unconfined compressive strength of the cement mixing pile core sample according to the number of segments of the cement mixing pile, which can reduce the impact of the number of samples.

[0061] S500. Based on a method for calculating a representative value of unconfined compressive strength of a cement mixing pile core sample, determine a representative value of unconfined compressive strength of the cement mixing pile core sample according to second compressive strength data.

[0062] This embodiment determines the second strength data of each segmented cement mixing pile core sample based on the first compressive strength data and the RQD data, which can well consider the influence of the pile body integrity on the strength. At the same time, according to the number of segments of the cement mixing pile, the calculation method of the representative value of the unconfined compressive strength of the cement mixing pile core sample is determined, which can reduce the influence of the number of samples, thereby reasonably calculating the unconfined compressive strength of the cement mixing pile core sample, which is conducive to improving the authenticity and accuracy of the evaluation method.

[0063] Specifically, step S500 includes steps S511 to S513:

[0064] S511. When the number of segments of the cement mixing pile core sample is less than or equal to the first threshold, determine the range and average value of the second compressive strength data.

[0065] For example, in this embodiment, the first threshold value is 5, and the number of segments of the first cement mixing pile 100 is n=5, which is a shorter cement mixing pile. When n≤5, the range method is used to screen the representative value of the unconfined compressive strength of the cement mixing pile core sample. For the first cement mixing pile 100, the second compressive strength data is q′ 1 ,q′ 2 , ..., q′ 5 , the range of the second compressive strength data R = max{q′ 1 ,q′ 2 , ..., q′ 5}-min{q′ 1 ,q′ 2 , ..., q′ 5}, where max is the maximum value operation, min is the minimum value operation, and the average value of the second compressive strength data is q m .

[0066] S512: Determine the ratio between the extreme value and the average value of the second compressive strength data to obtain a first ratio.

[0067] Among them, the first ratio is denoted as β,

[0068]

[0069] The first ratio can be used to reflect the sample uniformity effect of the cement mixing pile core sample. When the sample quantity is small and the sample uniformity effect is good, it means that the difference between the compressive strengths of the cement mixing pile core samples of each segment is within a reasonable range.

[0070] S513. When the first ratio is less than or equal to the second threshold, the average value of the second compressive strength data is determined as the representative value of the unconfined compressive strength of the cement mixing pile core sample.

[0071] For example, in this embodiment, the second threshold value is 30%. When β≤30%, it means that the sample uniformity effect is better at this time. m Determined as the representative value of the unconfined compressive strength of the cement mixing pile core sample.

[0072] When β>30%, it means that the sample uniformity effect is poor, and samples with large differences need to be eliminated. Therefore, step S500 also includes steps S514 to S515:

[0073] S514: When the first ratio is greater than the second threshold, remove the maximum values ​​in the second compressive strength data one by one until the first ratio is less than or equal to the second threshold.

[0074] For example, for the first cement mixing pile 100, when β>30%, the maximum value in the second compressive strength data is found and removed, for example, q′ 1 , and then recalculate the first ratio β. If the first ratio β is still greater than 30%, then in the remaining second compressive strength data, such as q′ 2 ,q′ 3 , ..., q′ 5 , find and remove the maximum value, such as q′ 2 , until β≤30%.

[0075] S515. Determine the average value of the remaining data in the second compressive strength data as the representative value of the unconfined compressive strength of the cement mixing pile core sample.

[0076] For example, after removing the maximum value from the second compressive strength data, the remaining data includes q′ 2 ,q′ 3 , ..., q′ 5 , then q′ 2 ,q′ 3 , ..., q′ 5 The average value of is determined as the representative value of the unconfined compressive strength of the cement mixing pile core sample; for example, when the second compressive strength data removes the maximum value, the remaining data includes q′ 3 ,q′ 4 ,q′ 5 , then q′ 3 ,q′ 4 ,q′ 5 The average value is determined as the representative value of the unconfined compressive strength of the cement mixing pile core sample.

[0077] For the case of a large number of samples, the error in selecting representative strength values ​​can be reduced by analyzing the variation of strength along depth, calculating multiple statistically related parameters, and comprehensively selecting representative values ​​of unconfined compressive strength.

[0078] Therefore, step 500 includes the steps of:

[0079] S521. When the number of segments of the cement mixing pile core sample is greater than a first threshold, determine the average value and standard deviation of the second compressive strength data.

[0080] For example, in this embodiment, the first threshold value is 5. The number of segments of the second cement mixing pile 200 is n=6, which is a relatively long cement mixing pile. When n>5, the average value q of the second compressive strength data is determined according to the following formula: m and standard deviation σ f ,

[0081]

[0082]

[0083] In the formula, q i 'The compressive strength of each segment of the cement mixing pile after RQD reduction, that is, the i-th data in the second compressive strength data.

[0084] S522: Obtain depth data corresponding to the second compressive strength data.

[0085] When core sampling is performed based on the core drilling method, the core drilling depth corresponding to each segment of the cement mixing pile can be obtained, thereby obtaining depth data corresponding to the second compressive strength data.

[0086] S523: Determine a correlation coefficient according to the second compressive strength data and the depth data.

[0087] According to the second compressive strength data and depth data, a scatter plot of unconfined compressive strength and depth can be drawn for analysis and the correlation coefficient r can be calculated, so as to use the correlation coefficient r to analyze the variation characteristics of the unconfined compressive strength of cement mixing piles along the depth.

[0088]

[0089] Where n is the number of segments of cement mixing pile, Zj is the depth corresponding to the jth segment of cement mixing pile, that is, the jth data in the depth data, Z m It is the mean of the depth of each segment of the cement mixing pile, that is, the average value of the depth data.

[0090] S524: Determine the analysis type between the second compressive strength data and the depth data according to the correlation coefficient.

[0091] According to the different variation characteristics of the unconfined compressive strength of cement mixing pile core samples along the depth, the variation law of compressive strength in the depth direction can be analyzed by dividing it into two types: correlation type and non-correlation type. Among them, when the correlation coefficient is zero, the analysis type is determined as non-correlation type; when the correlation coefficient is not zero, the analysis type is determined as correlation type.

[0092] S525. Based on the analysis type, determine the representative value of the unconfined compressive strength of the cement mixing pile core sample according to the average value and standard deviation of the second compressive strength data.

[0093] a1. When the analysis type is non-correlated, determine the first coefficient of variation based on the mean and standard deviation of the second compressive strength data, denoted as δ 1 :

[0094]

[0095] In the formula, σ f is the standard deviation of the second compressive strength data, q m is the average value of the second compressive strength data q m .

[0096] a2. According to the first coefficient of variation, determine the first statistical correction coefficient, denoted as γ s1 :

[0097]

[0098] Where n is the number of segments of the cement mixing pile.

[0099] a3. According to the average value of the second compressive strength data and the first statistical correction coefficient, determine the representative value of the unconfined compressive strength of the cement mixing pile core sample, denoted as q k The representative value of the unconfined compressive strength of the cement mixing pile core sample is equal to the product of the first statistical correction coefficient and the average value of the second compressive strength data, that is, q k =γ s1 q m .

[0100] b1. When the analysis type is correlation type, determine the residual standard deviation based on the standard deviation and correlation coefficient of the second compressive strength data, denoted as σ r :

[0101]

[0102] b2. Determine the second coefficient of variation based on the residual standard deviation and the average value of the second compressive strength data, denoted as δ 2 :

[0103]

[0104] b3. According to the second coefficient of variation, determine the second statistical correction coefficient, denoted as γ s2 :

[0105]

[0106] Where n is the number of segments of the cement mixing pile.

[0107] b4. According to the average value of the second compressive strength data and the second statistical correction coefficient, determine the representative value of the unconfined compressive strength of the cement mixing pile core sample, denoted as q k The representative value of the unconfined compressive strength of the cement mixing pile core sample is equal to the product of the second statistical correction coefficient and the average value of the second compressive strength data, that is, q k =γ s2 q m .

[0108] It should be noted that the first statistical correction coefficient and the second statistical correction coefficient may also take empirical values ​​according to the project type, importance, parameter variability and number of statistical data.

[0109] Please refer to Figure 2 , Figure 3 and Figure 4 The following is a detailed description of the unconfined compressive strength assessment method for cement mixing piles according to an embodiment of the present invention using a specific example. It is worth noting that the following description is merely an exemplary description and is not a specific limitation of the present invention.

[0110] When cement mixing piles are used to reinforce soft soil foundations, there are two types of cement mixing piles with different numbers of sections, such as Figure 2 The first cement mixing pile 100 and Figure 3 The second cement mixing pile 200 shown is that the pile length h1 of the first cement mixing pile 100 is 15m, the number of sections is 5, the sections are numbered 101, 102, 103, 104 and 105 in sequence, and the length L1 of each section is 3m; the pile length h2 of the second cement mixing pile 200 is 18m, the number of sections is 6, the sections are numbered 201, 202, 203, 204, 205 and 206 in sequence, and the length L2 of each section is 3m.

[0111] In the on-site pile test, core sampling is performed on each segment of the first cement mixing pile 100 and the second cement mixing pile 200 based on the core drilling method, and a 90-day unconfined compressive strength test is performed. A double-tube single-action sampler is used on-site for core sampling.

[0112] After sampling from the on-site core drilling, the cement mixing pile core sample (hereinafter referred to as the specimen) was obtained, and the size and shape of the specimen were checked, the length of each segmented specimen was counted, the rock quality index of each segmented specimen was determined, and the RQD data was obtained.

[0113] After taking out the specimen, immediately conduct an unconfined compressive strength test to obtain the first compressive strength data. It should be noted that before placing the specimen on the testing machine, wipe the outer surface of the specimen and the upper and lower pressure plates of the testing machine clean. Place the specimen upright on the lower pressure plate or steel pad of the testing machine, and align the axis of the specimen with the center of the lower pressure plate. Turn on the testing machine, and the surface of the specimen is in uniform contact with the upper and lower pressure plates or steel pads. Apply load continuously and evenly during the test.

[0114] The unconfined compression test results of the segmented core samples of the first cement mixing pile 100 are shown in Table 1, and the unconfined compression test results of the segmented core samples of the second cement mixing pile 200 are shown in Table 2.

[0115] Table 1

[0116]

[0117] Table 2

[0118]

[0119] Calculate the unconfined compressive strength qˊ of each segmented specimen after RQD reduction, that is, determine the second compressive strength data.

[0120] Among them, the second compressive strength data corresponding to each segmented specimen of the first cement mixing pile 100 are 2.09MPa, 1.64MPa, 1.68MPa, 1.58MPa, and 1.3MPa, respectively. Since the number of segments of the first cement mixing pile 100 is less than or equal to the first threshold, that is, 5 segments, the range and average value of the second compressive strength data are taken, the range value R = 2.09-1.3MPa = 0.79MPa, and the average value q m =(2.09+1.64+1.68+1.58+1.3) / 5=1.66MPa, then the first ratio β=0.79 / 1.66×100%=47.6%>30%. After removing the maximum value of 2.09MPa, the average value q m =(1.64+1.68+1.58+1.3) / 4=1.55MPa, range R=1.68-1.3=0.38MPa, first ratio β=0.38 / 1.55×100%=24.5%<30%. The requirement is met, and 1.55MPa can be taken as the representative value of the compressive strength of the mixing pile.

[0121] The second compressive strength data corresponding to each segmented specimen of the second cement mixing pile 200 are 2.37MPa, 2.54MPa, 1.85MPa, 1.36MPa, 1.73MPa, and 1.47MPa, respectively. The average value q m =(2.37+2.54+1.85+1.36+1.73+1.47) / 6=1.89MPa,

[0122] Standard Deviation

[0123] The depth of each segment of the cement mixing pile is taken as the midpoint of the segment depth, and the depths are 1.5m, 4.5m, 7.5m, 10.5m, 13.5m, and 16.5m. Draw a scatter plot of unconfined compressive strength and depth as shown in the figure below: Figure 5 shown.

[0124] The average value of the depth

[0125] Correlation coefficient

[0126] Correlation coefficient r≠0, analysis type is correlation type, residual standard deviation The second coefficient of variation δ is calculated 2 =0.14, the second statistical correction coefficient γ s =0.94, representative value of compressive strength of cement mixing pile q k =1.78MPa.

[0127] This example can well consider the influence of pile integrity on strength by calculating the unconfined compressive strength of cement mixing pile core samples after RQD reduction. At the same time, according to the number of segments of cement mixing piles, the corresponding representative value selection method can reduce the influence of sample quantity. For the case of a large number of samples, the variation law of strength along the depth is analyzed, multiple statistically related parameters are calculated, and representative values ​​are comprehensively selected to reduce the error of selecting strength representative values.

[0128] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A method for evaluating the unconfined compressive strength of cement mixing pile core samples. It is characterized in that Includes steps: Divide the cement mixing pile to be evaluated into sections, and select cement mixing pile core samples of each section of the cement mixing pile based on the core drilling method; Determine the compressive strength and rock basic quality index of the cement mixing pile core sample of each segment to obtain first compressive strength data and RQD data; Determine the second compressive strength data of the cement mixing pile core sample of each segment according to the first compressive strength data and the RQD data; Determine a method for calculating a representative value of the unconfined compressive strength of the core sample of the cement mixing pile according to the number of segments of the cement mixing pile; Based on the representative value calculation method of the unconfined compressive strength of the cement mixing pile core sample, and according to the second compressive strength data, determining the representative value of the unconfined compressive strength of the cement mixing pile core sample; The method for calculating the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the second compressive strength data determines the representative value of the unconfined compressive strength of the cement mixing pile core sample, including: When the number of segments of the cement mixing pile core sample is less than or equal to a first threshold, determining a range value and an average value of the second compressive strength data; Determine a ratio between a range value and an average value of the second compressive strength data to obtain a first ratio; When the first ratio is less than or equal to the second threshold, the average value of the second compressive strength data is determined as the representative value of the unconfined compressive strength of the cement mixing pile core sample.

2. The method for evaluating the unconfined compressive strength of cement mixing pile core samples according to claim 1, It is characterized in that The second compressive strength data is equal to the product of the first compressive strength data and the RQD data.

3. The method for evaluating the unconfined compressive strength of cement mixing pile core samples according to claim 1, It is characterized in that The method for calculating the representative value of the unconfined compressive strength based on the cement mixing pile core sample, determining the representative value of the unconfined compressive strength of the cement mixing pile core sample according to the second compressive strength data, further includes: When the first ratio is greater than the second threshold, removing the maximum values ​​in the second compressive strength data one by one until the first ratio is less than or equal to the second threshold; The average value of the remaining data in the second compressive strength data is determined as the representative value of the unconfined compressive strength of the cement mixing pile core sample.

4. The method for evaluating the unconfined compressive strength of cement mixing pile core samples according to claim 1 or 3, It is characterized in that The method for calculating the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the second compressive strength data determines the representative value of the unconfined compressive strength of the cement mixing pile core sample, including: When the number of segments of the cement mixing pile core sample is greater than a first threshold, determining the average value and standard deviation of the second compressive strength data; Acquire depth data corresponding to the second compressive strength data; determining a correlation coefficient according to the second compressive strength data and the depth data; determining, according to the correlation coefficient, an analysis type between the second compressive strength data and the depth data; Based on the analysis type, a representative value of the unconfined compressive strength of the cement mixing pile core sample is determined according to the average value and standard deviation of the second compressive strength data.

5. The method for evaluating the unconfined compressive strength of cement mixing pile core samples according to claim 4, It is characterized in that Determining the analysis type between the second compressive strength data and the depth data according to the correlation coefficient comprises the steps of: When the correlation coefficient is zero, the analysis type is determined as non-correlation type; When the correlation coefficient is not zero, the analysis type is determined to be a correlation type.

6. The method for evaluating the unconfined compressive strength of cement mixing pile core samples according to claim 4, It is characterized in that The method of determining the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the analysis type and the average value and standard deviation of the second compressive strength data comprises the following steps: In the case where the analysis type is non-correlation type, determining a first coefficient of variation according to the mean value and standard deviation of the second compressive strength data; Determining a first statistical correction coefficient according to the first coefficient of variation; A representative value of the unconfined compressive strength of the cement mixing pile core sample is determined according to the average value of the second compressive strength data and the first statistical correction coefficient.

7. The method for evaluating the unconfined compressive strength of a cement mixing pile core sample according to claim 6, It is characterized in that The representative value of the unconfined compressive strength of the cement mixing pile core sample is equal to the product of the first statistical correction coefficient and the average value of the second compressive strength data.

8. The method for evaluating the unconfined compressive strength of cement mixing pile core samples according to claim 4, It is characterized in that The method of determining the representative value of the unconfined compressive strength of the cement mixing pile core sample based on the analysis type and the average value and standard deviation of the second compressive strength data comprises the following steps: In the case where the analysis type is a correlation type, determining a residual standard deviation according to the standard deviation of the second compressive strength data and the correlation coefficient; determining a second coefficient of variation according to the residual standard deviation and an average value of the second compressive strength data; determining a second statistical correction coefficient according to the second coefficient of variation; A representative value of the unconfined compressive strength of the cement mixing pile core sample is determined according to the average value of the second compressive strength data and the second statistical correction coefficient.

9. The method for evaluating the unconfined compressive strength of cement mixing pile core samples according to claim 8, It is characterized in that The representative value of the unconfined compressive strength of the cement mixing pile core sample is equal to the product of the second statistical correction coefficient and the average value of the second compressive strength data.

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