Method for predicting pile-forming strength of body of high-pressure jet-grouted pile on basis of testing of return grout at construction site

Abstract

Provided is a method for predicting the pile-forming strength of the body of a high-pressure jet-grouted pile on the basis of the testing of return grout at a construction site. The method comprises: configuring strength test blocks having different cement dosages, testing the strengths thereof, and drawing an age strength-cement dosage relationship curve; obtaining an EDTA titration standard curve of return grout in the case of different cement dosages by means of trails; sampling cement-soil return grout at a grout return port for a high-pressure jet-grouted pile, and determining the corresponding mass m1 of cement in a quantified cement-soil return grout sample; monitoring a jet grout flow rate Q and a return grout flow rate V2 during on-site construction; obtaining the density of the cement-soil return grout sample; obtaining the mass m2 of the dried cement-soil return grout sample; calculating the mass M6 of cement in a pile body; and calculating the dosage of the cement in the pile body, predicting the unconfined compression strength of the pile body at different ages, and determining whether design requirements are met. The accurate prediction of the age strength of a pile body is realized by means of an age-strength standard curve of test blocks having different cement dosages, which is of significant practical importance for predicting the construction quality of a high-pressure jet-grouted pile.

Description

A method for predicting the pile strength of high-pressure jet grouting piles based on on-site grouting tests Technical Field

[0001] The present invention relates to the field of geotechnical engineering technology, and in particular to a method for predicting the pile strength of a high-pressure jet grouting pile based on a grouting test at a construction site. Background Art

[0002] Since it was first successfully developed and applied to deep foundation reinforcement in Japan in the 1970s, the high-pressure rotary grouting method has been widely used in underground projects such as subways, tunnels, and high-rise building basements due to its wide range of applications, excellent construction quality, and little disturbance to the surrounding environment. Although there have been a large number of successful cases, the inspection of pile quality is still a pain point in the industry. After the construction of high-pressure rotary grouting piles, the scope and strength of the reinforcement body formed underground are tested by core drilling at home and abroad. However, the core sampling needs to wait until 28 days or a certain age, and the pile body reaches a certain strength. If it is found at this time that the quality of the pile body does not meet the requirements, rework is bound to result in greater construction costs.

[0003] Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention addresses the problem of delayed testing of pile strength in conventional high-pressure jet grouting piles, which results in increased construction costs due to rework when pile quality does not meet requirements. This invention provides a rapid testing method that can accurately measure the cement content in the pile body by testing and monitoring various cement-soil slurry data during the construction of high-pressure jet grouting piles. This method can then derive the pile strength at 28 or 90 days of age, thereby determining whether the construction quality meets design requirements.

[0005] In order to achieve the above object, the present invention relates to a method for predicting the pile strength of a high-pressure jet grouting pile body based on a construction site grouting test, which is characterized in that it comprises the following steps:

[0006] Step 1: Prepare and test strength test blocks with different cement content, and draw a curve showing the relationship between age strength and cement content.

[0007] Step 2: Take samples of undisturbed soil and obtain the EDTA titration standard curve of the slurry at different cement dosages through experiments;

[0008] Step 3: Take cement soil slurry sampling at the slurry outlet of the high-pressure jet grouting pile, and perform on-site EDTA titration of the slurry cement content to determine the corresponding cement mass m1 in the quantitative cement soil slurry sample;

[0009] Step 4: Conduct on-site construction shotcrete flow rate Q and return grout flow rate monitoring V2;

[0010] Step 5: Conduct on-site slurry specific gravity test to obtain the cement soil slurry sample density ρ 混合物 ;

[0011] Step 6: Dry the quantitative cement-soil slurry sample to obtain the mass m2 of the dried cement-soil slurry sample;

[0012] Step 7: Combine the relevant curves and parameters obtained in steps 2 to 6 to calculate the cement mass M6 in the pile body;

[0013] Step 8: Calculate the cement content in the pile body based on the cement mass in the pile body obtained in step 7. Consult the strength test block configuration and strength test curves of different cement content obtained in step 1 to predict the unconfined compressive strength of the pile body at the age of aging to determine whether the design requirements are met.

[0014] Furthermore, the method of step 1 is specifically as follows: before the on-site high-pressure jet grouting pile construction, undisturbed soil samples are drilled and taken, representative strata within the reinforcement range are taken, and a cement-soil mixture is prepared according to the designed cement content ±20%, with a variation of 5%, and the water-cement ratio in the construction parameters;

[0015] After each cement-soil mixture is stirred evenly, it is placed into at least two triple plastic mortar test molds (size 70.7mm×70.7mm×70.7mm), vibrated evenly with a vibrating rod, and then placed in a standard curing room for curing to obtain multiple test blocks;

[0016] After reaching the age (for example, 28 days), the strength of multiple test blocks is tested using a pressure testing machine. After the strength data are averaged, a relationship curve between the age strength and the cement content is plotted.

[0017] Furthermore, the method of step 2 specifically includes the following steps: 300g of undisturbed soil is titrated, and the disodium EDTA consumed is less than 3mL. However, for 300g of pure cement, the EDTA consumption is greater than 250mL. Therefore, the calcium ions that undergo chemical reactions during titration are primarily present in the cement. When the mass of pure cement dry powder is less than 40g, the standard curve is linear. As long as the EDTA consumption is known, the corresponding cement mass can be calculated. To this end, when configuring the on-site standard curve, the mass of the cement-soil mixture is determined to be 100g. Based on the on-site construction parameters, the cement dry powder mass is then calculated to be less than 40g.

[0018] (1) Preparation of test instruments and equipment

[0019] 1) Burette (acid type): 50mL, 1 piece.

[0020] 2) Titration stand: 1.

[0021] 3) Burette clamp: 1 pc.

[0022] 4) Large-bellied pipettes: 10mL, 50mL, 10 pieces.

[0023] 5) Erlenmeyer flasks (i.e., triangular flasks): 200 mL, 20 pcs.

[0024] 6) Beakers: 2000mL (or 1000mL), 1; 300mL, 10.

[0025] 7) Volumetric flask: 1000mL, 1 piece.

[0026] 8) Enamel cups: capacity greater than 1200mL, 10 pieces.

[0027] 9) Stainless steel rods (or thick glass rods): 10 pieces.

[0028] 10) Graduated cylinders: 100mL and 5mL, 1 each; 50mL, 2.

[0029] 11) Brown wide-mouth bottle: 60 mL, 1 (for calcium red indicator).

[0030] 12) Electronic balance: measuring range not less than 1500g, sensitivity 0.01g.

[0031] 13) Stopwatch: 1.

[0032] 14) Watch glasses: Φ9cm, 10 pieces.

[0033] 15) Mortar: Φ12-13cm, 1 piece.

[0034] 16) Ear cleaning bulb: 1 piece.

[0035] 17) Precision test paper: pH 12-14.

[0036] 18) Polyethylene barrels: 20L (for distilled water, ammonium chloride, and disodium EDTA standard solution), 3 pieces; 5L (for sodium hydroxide), 1 piece; 5L (wide-mouth barrels), 10 pieces.

[0037] 19) Brush, scouring powder, suction tube, plastic spoon, special pencil, centimeter paper.

[0038] 20) Wash bottle (plastic): 500mL, 1 piece.

[0039] (2) Test drug

[0040] 1) 0.1 mol / m 3Disodium EDTA (Disodium EDTA) Standard Solution (referred to as Disodium EDTA Standard Solution): Accurately weigh 37.23g of disodium EDTA (analytical grade) and dissolve it in carbon dioxide-free distilled water at 40-50°C. Once completely dissolved and cooled to room temperature, dilute to 1000mL. If testing a large amount of sample, weigh multiples and dilute to a multiple of 1000mL. When not in use, store in a sealed environment at room temperature and avoid direct sunlight.

[0041] 2) 10% Ammonium Chloride (NH4Cl) Solution: Place 500g of ammonium chloride (analytical or chemical grade) in a 10L polyethylene bucket, add 4500mL of distilled water, and shake thoroughly to completely dissolve the ammonium chloride. Alternatively, prepare the solution in batches in 1000mL beakers, then pour into the plastic bucket and shake thoroughly. To avoid reducing the concentration of the ammonium chloride solution, try to use the ammonium chloride solution prepared on the same day.

[0042] 3) 1.8% Sodium Hydroxide (Containing Triethanolamine) Solution: Weigh 18g of sodium hydroxide (NaOH) (analytical grade) using an electronic balance and place it in a clean, dry 1000mL beaker. Add 1000mL of distilled water to dissolve it completely. After the solution cools to room temperature, add 2mL of triethanolamine (analytical grade), stir well, and store in a plastic bucket.

[0043] 4) Calcium red indicator: 0.2g of calcium reagent sodium carboxylate (molecular formula C 21 H 13 Mix N2NaO7S (molecular weight 460.39) with 20g of potassium sulfate, previously oven-dried at 105°C for 1 hour. Place both ingredients in a mortar and pestle, grind into a very fine powder, and store in a brown wide-mouth bottle to prevent moisture absorption.

[0044] (3) Standard curve configuration

[0045] 1) Sampling and testing of undisturbed soil: Before construction, drill holes and take cores at the construction site. Soil samples within the area of ​​the pile to be constructed are divided according to strata, and the natural moisture content of each undisturbed soil layer is tested. The soil is then placed into sampling buckets (different strata of soil are placed in different sampling buckets), sealed, and stored in a cool, dry place.

[0046] 2) Assuming the designed cement content is A%, and the water-cement ratio is the water-cement ratio B in the design construction parameters, prepare a mixture of cement, water, and undisturbed soil according to the designed cement content A ± 20%, with a variation of 5%. After stirring evenly, take 100g of each mixture and place it into the enamel cup corresponding to the designed cement content;

[0047] 3) Add 600 mL of 10% ammonium chloride solution to an enamel cup and stir with a glass rod for 3 minutes (110-120 times per minute). After stirring, let the solution settle for 10 minutes. Then transfer the supernatant to a 300 mL beaker, stir well, and cover with a watch glass for testing.

[0048] 4) Use a pipette to draw 10.0mL of the upper layer (1-2cm below the liquid surface) of the suspension into a 200mL Erlenmeyer flask. Use a measuring tube to measure 50mL of 1.8% sodium hydroxide (containing triethanolamine) solution and pour it into the Erlenmeyer flask. At this time, the pH value of the solution is 12.5-13.0 (can be tested with pH12-14 precision test paper). Then add calcium red indicator (mass of about 0.2g), shake well, and the solution will turn rose red. Record the volume V1 of the disodium EDTA standard solution in the burette, and then titrate with the disodium EDTA standard solution, shaking well while titrating, and carefully observe the color of the solution; when the color of the solution turns purple, slow down the titration speed and shake well; until the pure blue color is the end point, record the volume V2 of the disodium EDTA standard solution in the burette (in mL, read to 0.1mL). Calculate V1-V2, which is the consumption of the disodium EDTA standard solution;

[0049] 5) Test the samples in the other sampling barrels in the same way and record the consumption of the respective disodium EDTA standard solutions;

[0050] 6) Graph the average consumption (mL) of disodium EDTA standard solution for the same cement material as the y-axis and the cement content as the abscissa. If the cement batch is changed during construction, the standard curve must be re-created.

[0051] 4. The method for predicting the pile strength of a high-pressure jet grouting pile based on a construction site grouting test according to claim 1, wherein the specific method of step 3 is as follows:

[0052] (3) Cement slurry sampling: Take cement soil slurry per meter at the slurry outlet of the high-pressure rotary jet grouting pile. Pay attention to the representativeness of the sampling and select fresh undiluted cement soil slurry samples;

[0053] (4) After the slurry is stirred evenly, 100 g is weighed and placed in an enamel cup, and then the EDTA titration operation is performed (i.e., repeating 3) to 5) in the standard curve configuration of step 2 (4)). According to the standard curve drawn in step 2, the corresponding cement mass in the 100 g cement soil slurry sample is determined according to the consumption of disodium EDTA standard solution. Since the consumption of disodium EDTA standard solution brought by pure soil in the 100 g cement soil slurry sample is negligible relative to the cement consumption, the consumption of disodium EDTA standard solution can be considered to be all consumed by cement. After checking the standard curve, the cement mass can be determined.

[0054] Furthermore, the method of step 4 is specifically as follows:

[0055] (1) Install a flow meter on the spraying equipment to determine the consumption of cement powder and water during the construction process, determine the spraying flow rate, and determine the total flow rate after accumulating time.

[0056] (2) During large-scale construction, trenches are excavated near the return grouting outlets of high-pressure jet grouting piles and flow meters are installed to monitor the return grouting flow rate. After accumulating the time, the total return grouting volume is determined.

[0057] Furthermore, the method of step 5 is specifically as follows: using a slurry density meter to test the specific gravity of the slurry per meter on site, and obtaining the density of the cement soil slurry sample ρ 混合物 .

[0058] Furthermore, the specific method of step 6 is: take 100g of cement slurry, pour it into an enamel cup, put it into a 105℃ oven and dry it for 8 hours to test the mass m2 of the dried sample. Since cement, soil and water will undergo hydration reaction and condensation during the drying process, the sample must be taken out and crushed during the drying process to facilitate thorough drying.

[0059] Furthermore, the specific method of step 7 includes the following steps:

[0060] (1) Combined with the EDTA titration test of the cement content of the on-site slurry, the mass of the cement powder in every 100g of cement-soil slurry mixture is determined to be m1, and the product after cement hydration is (1+Y%) m1 (a large number of indoor tests have shown that the mass of cement will increase during the hydration reaction. Assuming that the percentage of increase is Y%, after drying, there will be Y% of the cement mass of water, which will be absorbed by the cement and cannot be dried. According to existing technical data, the percentage of increase can be taken as 25%). The mass after drying is m2, and the mass of the soil particles is m 3＝ m2-(1+Y%)m1; if the moisture content w of the original soil is known, the mass of the original soil in 100g of cement soil slurry is (1+w)m3, and the mass of the added water is m 4＝ 100-m1-(1+w)m3, cement content is m1 / (1+w)m3;

[0061] (2) Assume that the original soil is saturated soil and the voids are filled with water;

[0062] (3) Based on the lifting rate v (cm / min) of the shotcrete rod, calculate the time t = 100 / V (min) required for the shotcrete rod to be lifted 1 meter;

[0063] (4) Assuming that the pile body is uniform within the range of one meter, according to the cement slurry spraying flow rate Q (L / min) measured in step 4, the cumulative amount of cement slurry sprayed per meter is calculated as V1 = Q / 10 × v (m 3 );

[0064] (5) According to step 4, the return slurry volume per meter is V2. When the return slurry volume is considered as a whole, the volume of cement slurry in the return slurry channel needs to be considered. Assuming the return slurry hole diameter d1 and the return slurry hole depth h, the volume of cement slurry mixture in the return slurry hole is calculated as V3 = 0.25 × 3.14 × d1 × d1 × h. The total return slurry volume is V 返浆 =V2+V3;

[0065] (6) According to the process test before large-scale construction, the pile diameter is designed and verified according to the design construction parameters, and the pile diameter is obtained as d2. The volume of the pile per meter is calculated as V4 = 0.25 × 3.14 × d2 × d2;

[0066] (7) According to the water-cement ratio B of the cement slurry, the density of the cement slurry ρ is calculated 水泥浆 , then the mass of cement powder per meter of shotcrete is m5 = ρ 水泥浆 ×V1×1 / (B+1);

[0067] (8) In each meter of back slurry, according to the measured back slurry density ρ 混合物 , the return slurry volume V2, the total mass of return slurry per meter m6 = ρ 混合物 ×V2;

[0068] (9) According to the proportion of the original soil mass in every 100g of return slurry in the titration test, the original soil mass in each meter of return slurry is calculated as M3 = m6 × (1 + w) m3 / 100, and the original soil mass remaining in the pile body is M4 = ρ 原状土 ×V4-M3;

[0069] (10) According to the mass ratio of cement in every 100g of return slurry in the titration test, the mass of cement in each meter of return slurry is calculated to be M5 = m6 × m1 / 100, and the mass of cement remaining in the pile is calculated to be M6 = m5 - M5;

[0070] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0071] (1) The method for predicting the pile strength of high-pressure rotary jet piles based on the on-site back-slurry test of the present invention overcomes the shortcomings of the traditional EDTA test method for cement content in roadbed mixed soil in testing high cement content. By adjusting the EDTA titration sampling quality and controlling the EDTA titration standard curve within the linear range, the cement quality can be accurately obtained according to the back-slurry EDTA titration consumption. Combined with the on-site spraying construction parameters, back-slurry amount monitoring, back-slurry specific gravity, back-slurry moisture content, and back-slurry EDTA titration test data, the cement quality (or cement content) of the pile body can be accurately measured. Combined with the configured test block strength curves of different cement contents, the pile body age strength is predicted, and a rapid prediction of the pile quality is achieved.

[0072] (2) The method for predicting the pile strength of high-pressure rotary jet piles based on the on-site slurry return test of the present invention overcomes the deficiency of the traditional coring method that the pile quality of high-pressure rotary jet piles must be tested after the pile reaches the age. The method can be used to predict the pile strength during the construction of high-pressure rotary jet piles. When problems are found, the construction parameters can be adjusted in time to ensure the construction quality. This method is of great significance to the application and promotion of high-pressure rotary jet technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] FIG1 is a schematic diagram of the overall process of a preferred embodiment of the present invention; DETAILED DESCRIPTION

[0074] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0075] Example 1:

[0076] Please refer to Figure 1. The present invention relates to a method for predicting the strength of a high-pressure jet grouting pile based on a construction site grouting test. The method comprises the following steps: configuring strength test blocks with different cement content and performing strength tests; configuring a grouting EDTA titration standard curve; titrating EDTA content of grouting cement on site; monitoring grouting flow rate and grouting flow rate on site; testing grouting specific gravity; testing grouting moisture content on site; predicting the cement content of the pile body; and predicting the pile body strength. The specific prediction method is as follows:

[0077] Step 1: Configuration and strength test of strength test blocks with different cement content

[0078] Before the construction of high-pressure rotary jet grouting piles on site, drill to obtain original soil samples and take representative strata within the reinforcement range. Cement-soil mixture is prepared according to the designed cement content ±20%, with a variation value of 5%, and the water-cement ratio in the construction parameters.

[0079] After the cement-soil mixture of each dosage is stirred evenly, it is placed into at least two triple plastic mortar test molds (preferably with a size of 70.7 mm × 70.7 mm × 70.7 mm), vibrated evenly with a vibrating rod, and then placed in a standard curing room for curing to obtain multiple test blocks;

[0080] After reaching the age (for example, 28 days), the strength of multiple test blocks is tested using a pressure testing machine. After the strength data are averaged, a relationship curve between the age strength and the cement content is plotted.

[0081] Step 2: Configuring the standard curve for EDTA titration

[0082] (4) According to the method recommended in the "Testing Procedures for Stabilized Materials of Inorganic Binders for Highway Engineering" (JTG E51-2009), 300g of undisturbed soil was titrated. The amount of disodium EDTA consumed was less than 3mL. However, for 300g of pure cement, the EDTA consumption was more than 250mL. Therefore, the calcium ions that reacted during titration were mainly present in the cement. When the mass of pure cement powder was less than 40g, the standard curve was linear. As long as the EDTA consumption was known, the corresponding cement mass could be calculated. Therefore, when configuring the on-site standard curve, the mass of the cement-soil mixture was determined to be 100g. Based on the on-site construction parameters, the mass of the cement powder was less than 40g.

[0083] (5) Preparation of test instruments and equipment

[0084] 21) Burette (acid type): 50mL, 1 piece.

[0085] 22) Titration stand: 1.

[0086] 23) Burette clamp: 1 pc.

[0087] 24) Large-bellied pipettes: 10mL, 50mL, 10 pieces.

[0088] 25) Erlenmeyer flasks (i.e., triangular flasks): 200 mL, 20 pcs.

[0089] 26) Beakers: 2000mL (or 1000mL), 1; 300mL, 10.

[0090] 27) Volumetric flask: 1000mL, 1 piece.

[0091] 28) Enamel cups: capacity greater than 1200mL, 10 pieces.

[0092] 29) Stainless steel rods (or thick glass rods): 10 pieces.

[0093] 30) Graduated cylinders: 100mL and 5mL, 1 each; 50mL, 2.

[0094] 31) Brown wide-mouth bottle: 60 mL, 1 (for calcium red indicator).

[0095] 32) Electronic balance: measuring range not less than 1500g, sensitivity 0.01g.

[0096] 33) Stopwatch: 1.

[0097] 34) Watch glasses: Φ9cm, 10 pieces.

[0098] 35) Mortar: Φ12~13cm, 1 piece.

[0099] 36) Ear cleaning ball: 1 piece.

[0100] 37) Precision test paper: pH 12-14.

[0101] 38) Polyethylene barrels: 20L (for distilled water, ammonium chloride, and disodium EDTA standard solution), 3 pieces; 5L (for sodium hydroxide), 1 piece; 5L (wide-mouth barrels), 10 pieces.

[0102] 39) Brush, scouring powder, suction tube, plastic spoon, special pencil, centimeter paper.

[0103] 40) Wash bottle (plastic): 500mL, 1 piece.

[0104] (6) Test drugs

[0105] 1) 0.1 mol / m 3 Disodium EDTA (Disodium EDTA) Standard Solution (referred to as Disodium EDTA Standard Solution): Accurately weigh 37.23g of disodium EDTA (analytical grade) and dissolve it in carbon dioxide-free distilled water at 40-50°C. Once completely dissolved and cooled to room temperature, dilute to 1000mL. If testing a large amount of sample, weigh multiples and dilute to a multiple of 1000mL. When not in use, store in a sealed environment at room temperature and avoid direct sunlight.

[0106] 2) 10% Ammonium Chloride (NH4Cl) Solution: Place 500g of ammonium chloride (analytical or chemical grade) in a 10L polyethylene bucket, add 4500mL of distilled water, and shake thoroughly to completely dissolve the ammonium chloride. Alternatively, prepare the solution in batches in 1000mL beakers, then pour into the plastic bucket and shake thoroughly. To avoid reducing the concentration of the ammonium chloride solution, try to use the ammonium chloride solution prepared on the same day.

[0107] 3) 1.8% Sodium Hydroxide (Containing Triethanolamine) Solution: Weigh 18g of sodium hydroxide (NaOH) (analytical grade) using an electronic balance and place it in a clean, dry 1000mL beaker. Add 1000mL of distilled water to dissolve it completely. After the solution cools to room temperature, add 2mL of triethanolamine (analytical grade), stir well, and store in a plastic bucket.

[0108] 4) Calcium red indicator: 0.2g of calcium reagent sodium carboxylate (molecular formula C 21 H 13 Mix N2NaO7S (molecular weight 460.39) with 20g of potassium sulfate, previously oven-dried at 105°C for 1 hour. Place both ingredients in a mortar and pestle, grind into a very fine powder, and store in a brown wide-mouth bottle to prevent moisture absorption.

[0109] (7) Standard curve configuration

[0110] 1) In-situ soil sampling and testing: Before construction, drill holes and collect cores at the construction site. Soil samples within the area of ​​the pile to be constructed are divided according to strata, and the natural moisture content of each layer of the in-situ soil is tested. The soil is then sorted and placed into sampling barrels, sealed, and stored in a cool, dry place.

[0111] 2) Assuming the designed cement content is A%, and the water-cement ratio is the water-cement ratio B in the design construction parameters, prepare a mixture of cement + water + undisturbed soil according to the designed cement content A±20%, with a variation of 5%. After stirring evenly, take 100g of the mixture and put it into the corresponding enamel cup marked with the designed cement content.

[0112] 3) Add 600 mL of 10% ammonium chloride solution to an enamel cup and stir with a glass rod for 3 minutes (110-120 times per minute). After stirring, allow to settle for 10 minutes. Transfer the supernatant to a 300 mL beaker, stir thoroughly, and cover with a watch glass for testing.

[0113] 4) Use a pipette to draw 10.0 mL of the upper layer (1-2 cm below the liquid surface) of the suspension into a 200 mL Erlenmeyer flask. Using a measuring tube, measure 50 mL of 1.8% sodium hydroxide solution (containing triethanolamine) and pour it into the flask. The pH of the solution should now be between 12.5 and 13.0 (this can be checked with pH 12-14 precision test paper). Add calcium red indicator (approximately 0.2 g) and shake well. The solution should turn rose red. Record the volume V1 of the disodium EDTA standard solution in the burette. Then titrate with the disodium EDTA standard solution, shaking well while titrating and carefully observing the color of the solution. When the solution turns purple, slow the titration and shake well. As the solution turns pure blue, record the volume V2 of the disodium EDTA standard solution in the burette (in mL, read to the nearest 0.1 mL). Calculate V1 - V2 to obtain the amount of disodium EDTA standard solution consumed.

[0114] 5) Conduct the same test on the samples in the other sampling barrels and record the consumption of the respective disodium EDTA standard solutions.

[0115] 6) Graph the average consumption (mL) of disodium EDTA standard solution for the same cement material as the y-axis and the cement content as the abscissa. If the cement batch is changed during construction, the standard curve must be re-created.

[0116] Step 3: EDTA titration of cement content in on-site slurry

[0117] (5) Cement slurry sampling: Take cement soil slurry per meter at the slurry outlet of the high-pressure rotary jet pile. Pay attention to the representativeness of the sampling and select fresh undiluted cement soil slurry.

[0118] (6) After the slurry is stirred evenly, weigh 100g and place it in an enamel cup. Then repeat steps 3) to 5) of the standard curve configuration in step 2 (4). Based on the standard curve drawn in step 2 and the consumption of disodium EDTA standard solution, determine the mass of cement in 100g of the mixture. Since the consumption of disodium EDTA standard solution brought by pure soil in 100g of the mixture is negligible compared to the consumption of cement, the consumption of disodium EDTA standard solution can be considered to be entirely consumed by cement. After checking the standard curve, the mass of cement can be determined.

[0119] Step 4: On-site construction shotcrete flow and return flow monitoring

[0120] (1) Install a flow meter on the spraying equipment to determine the consumption of cement powder and water during the construction process, determine the spraying flow rate, and determine the total flow rate after accumulating time.

[0121] (2) During large-scale construction, trenches are excavated near the return grouting outlets of high-pressure jet grouting piles and flow meters are installed to monitor the return grouting flow rate. After accumulating the time, the total return grouting volume is determined.

[0122] Step 5: On-site slurry density test

[0123] Use a slurry density meter to test the density of the slurry per meter on site to obtain the density of the cement-soil mixture ρ 混合物 .

[0124] Step 6: On-site slurry moisture content test

[0125] Take 100g of cement slurry, pour it into an enamel cup, put it into a 105℃ oven and dry it for 8 hours. Test the mass m2 of the dried sample. Since cement, soil and water will undergo hydration reaction and condensation during the drying process, the sample must be taken out and crushed during the drying process to facilitate thorough drying.

[0126] A large number of indoor tests have shown that cement hydration reaction will increase its mass by 25%. Therefore, after drying, 25% of the cement's mass will be absorbed by the cement and cannot be dried.

[0127] Step 7: Prediction of cement content in pile body

[0128] (4) Combined with the EDTA titration test of the cement content in the field, it is determined that the mass of cement powder in every 100g of cement-soil slurry mixture is m1, the product after cement hydration is 1.25m1, and the mass after drying is m2. The mass of the soil particles is m 3＝ m2-1.25m1; the water content w of the original soil is known, then the mass of the original soil in 100g of cement soil slurry is (1+w)m3, and the mass of the added water is m 4＝ 100-m1-(1+w)m3, the cement content is m1 / (1+w)m3.

[0129] (5) Assume that the original soil is saturated soil and the voids are filled with water.

[0130] (6) Based on the lifting rate V (cm / min) of the shotcrete rod, calculate the time t = 100 / V (min) required to lift the shotcrete rod 1m.

[0131] (7) Assuming that the pile body is uniform within the range of one meter, according to the cement slurry spraying flow rate Q (L / min) measured in step 4, the cumulative amount of cement slurry sprayed per meter is calculated as V1 = Q / 10 × v (m 3 );

[0132] (8) According to step 4, the return slurry volume per meter is V2. When the return slurry volume is considered as a whole, the volume of cement slurry in the return slurry channel needs to be considered. Assuming the return slurry hole diameter d1 and the return slurry hole depth h, the volume of cement slurry mixture in the return slurry hole is calculated as V3 = 0.25 × 3.14 × d1 × d1 × h. The total return slurry volume is V 返浆 =V2+V3.

[0133] (9) According to the process test before large-scale construction, the pile diameter is designed and verified according to the design construction parameters, and the pile diameter is d2. The volume of the pile per meter is calculated to be V4 = 0.25 × 3.14 × d2 × d2;

[0134] (10) According to the water-cement ratio B of the cement slurry, the density of the cement slurry ρ is calculated 水泥浆 , then the mass of cement powder per meter of shotcrete is m5 = ρ 水泥浆 ×V1×1 / (B+1).

[0135] (11) In each meter of back slurry, according to the measured back slurry density ρ 混合物 , the return slurry volume V2, the total mass of return slurry per meter m6 = ρ混合物 ×V2.

[0136] (12) According to the proportion of the original soil mass in every 100g of return slurry in the titration test, the original soil mass in each meter of return slurry is calculated as M3 = m6 × (1 + w) m3 / 100, and the original soil mass remaining in the pile body is M4 = ρ 原状土 ×V4-M3.

[0137] (13) According to the mass ratio of cement in every 100g of return slurry in the titration test, the mass of cement in each meter of return slurry is calculated to be M5 = m6 × m1 / 100, and the mass of cement remaining in the pile is calculated to be M6 = m5 - M5.

[0138] Step 8: Pile strength prediction

[0139] Calculate the cement content in the pile as M6 / M4. Refer to the strength test block configuration and strength test curves for different cement content obtained in step 1 to predict the unconfined compressive strength of the pile body at the age of aging to determine whether it meets the design requirements.

[0140] The present invention provides a method for accurately measuring the cement content in the return slurry during high-pressure jet grouting construction based on test results such as the grouting flow rate / volume, return slurry flow rate / volume, return slurry titrated cement content, return slurry specific gravity, return slurry moisture content, and an EDTA standard curve, thereby deriving the cement content remaining in the pile body. Using the age-based standard curve of the test block strength at different cement content, accurate prediction of the pile body's age-based strength is achieved, which has important practical significance for predicting the construction quality of high-pressure jet grouting piles.

[0141] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for predicting the forming strength of the pile body of high-pressure jet grouting piles based on the return slurry test at the construction site, characterized in that, it includes the following steps: Step 1: Configure and test strength specimens with different cement dosages, and draw the relationship curve between the age strength and the cement dosage; Step 2: Take undisturbed soil samples and obtain the return slurry EDTA titration standard curves under different cement dosages through tests; Step 3: Take samples of the cement-soil backflow at the backflow outlet of the high-pressure jet grouting pile, and conduct EDTA titration on the cement content in the on-site backflow to determine the corresponding cement mass m in the quantitative cement-soil backflow sample 1 ; Step 4: Monitor the shotcrete flow rate Q and the return slurry flow rate V during on-site construction 2 ; Step 5: Conduct on-site backflow specific gravity test to obtain the density ρ of the cement soil backflow sample 混合物 ; Step 6: Dry the quantitative cement soil backflow sample to obtain the mass m of the dried cement soil backflow sample 2 ; Step 7: Combine the relevant curves and parameters obtained in Steps 2 to 6 to calculate the mass M of cement in the pile body 6 ; Step 8: Calculate the cement dosage in the pile body based on the cement mass in the pile body obtained in Step 7, consult the relationship curve of the configuration and strength test of strength specimens with different cement dosages obtained in Step 1, predict the unconfined compressive strength of the pile body at the age, and determine whether it meets the design requirements.

2. The method for predicting the forming strength of the pile body of high-pressure jet grouting piles based on the return slurry test at the construction site according to Claim 1, characterized in that, the method of Step 1 is specifically as follows: Before the construction of on-site high-pressure jet grouting piles, drill to take undisturbed soil samples, take representative strata within the reinforcement range, and configure multiple groups of cement-soil mixtures with different cement dosages according to the design cement dosage ±20% and a change value of 5%, and according to the water-cement ratio in the construction parameters; After each cement-soil mixture with a certain dosage is stirred evenly, pour it into at least 2 triple plastic mortar molds, use a vibrating rod to vibrate it evenly, and then place it in a standard curing room for curing to obtain multiple specimens; After reaching the age, use a pressure testing machine to test the strength of multiple specimens. After the strength data is averaged, draw the relationship curve between the age strength and the cement dosage of this kind.

3. The method for predicting the forming strength of the pile body of high-pressure jet grouting piles based on the return slurry test at the construction site according to Claim 2, characterized in that: the method of Step 2 specifically includes the following steps: 1) Undisturbed soil sampling and testing: Before construction, drill and take core samples at the construction site. Divide the soil samples within the pile body range according to the strata, and test the natural moisture content of each soil layer of the undisturbed soil; Classify and put them into sampling buckets, seal and store them in a cool place; 2) Assume that the design cement dosage is A%, and the water-cement ratio is B in the design construction parameters. Configure the mixture of cement + water + undisturbed soil according to the design cement dosage A ± 20% and a change value of 5%. After stirring evenly, take 100g of the mixture for each and put them into enamel cups marked with the corresponding design cement dosage; 3) Add 600 mL of 10% ammonium chloride solution to the enamel cup, stir with a glass rod for 3 minutes, let it stand for precipitation for 10 minutes after stirring, and then transfer the upper clear liquid to a 300 mL beaker, stir well, cover with a watch glass for later measurement; 4) Pipette 10.0 mL of the upper suspension into a 200 mL Erlenmeyer flask. Measure 50 mL of 1.8% sodium hydroxide solution with a graduated cylinder and pour it into the Erlenmeyer flask. At this time, the pH value of the solution is 12.5 - 13.

0. Then add calcon indicator and shake well. The solution turns rose red; record the volume V of the disodium EDTA standard solution in the burette. 1 , and then titrate with the disodium EDTA standard solution. Shake well while titrating and carefully observe the color of the solution; when the color of the solution turns purple, slow down the titration speed and shake well; until the end point is pure blue, record the volume V of the disodium EDTA standard solution in the burette. 2 ; Calculate V 1 - V 2 , which is the consumption of the disodium EDTA standard solution; 5) Conduct tests on the specimens in other sampling buckets in the same way, and record the consumption of the EDTA disodium standard solution for each; 6) Plot a graph with the average value of the consumption of the EDTA disodium standard solution of the same cement material as the vertical coordinate and the cement dosage as the horizontal coordinate; If the cement batch changes during construction, the standard curve must be redone.

4. The method for predicting the forming strength of the pile body of high-pressure jet grouting piles based on the return slurry test at the construction site according to Claim 1, characterized in that, the specific method of Step 3 is: (1) Cement backflow sampling: At the backflow port of the high-pressure jet grouting pile, take the cement-soil backflow every meter. Pay attention to the representativeness of the sampling and select fresh and undiluted cement-soil backflow samples. (2) After the backflow is stirred evenly, weigh 100 g and put it into an enamel cup. Then carry out the EDTA titration operation. According to the standard curve drawn in Step 2 and the consumption of the EDTA disodium standard solution, determine the corresponding cement mass in the 100 g cement-soil backflow sample. Since in the 100 g cement-soil backflow sample, the consumption of the EDTA disodium standard solution brought by the pure soil can be ignored compared with that of the cement, therefore, the consumption of the EDTA disodium standard solution can be considered to be all due to the consumption of the cement. After checking the standard curve, the cement mass can be determined.

5. The method for predicting the formed pile strength of the high-pressure jet grouting pile based on the backflow test on the construction site according to claim 1, characterized in that, the method of Step 4 is specifically as follows: (1) Install a flowmeter on the grouting equipment to determine the consumption of cement dry powder and water during the construction process, determine the grouting flow rate, and after time accumulation, determine the total flow rate; (2) During large-area construction, excavate a trench near the backflow port of the high-pressure jet grouting pile and install a flowmeter to monitor the backflow flow rate. After time accumulation, determine the total backflow volume.

6. The method for predicting the formed pile strength of the high-pressure jet grouting pile based on the backflow test on the construction site according to claim 1, characterized in that, The method of step 5 is specifically as follows: Use a mud hydrometer to test the specific gravity of the returned slurry per meter on site, and obtain the density ρ of the cement-soil returned slurry sample per meter 混合物 .

7. The method for predicting the formed pile strength of the high-pressure jet grouting pile based on the backflow test on the construction site according to claim 1, characterized in that, The specific method for step 6 is as follows: Take 100 g of cement return slurry, pour it into an enamel cup, and place it in an oven at 105 °C for 8 hours to test the mass m of the dried sample. 2 Since hydration reactions and condensation occur among cement, soil, and water during the drying process, the sample should be taken out and mashed during drying.

8. The method for predicting the formed pile strength of the high-pressure jet grouting pile based on the backflow test on the construction site according to claim 1, characterized in that, the specific method of Step 7 includes the following steps: (1) Combine the on-site backflow cement content EDTA titration test to determine that the mass of cement dry powder in every 100g of cement-soil slurry mixture is m 1 , and the product after cement hydration is (1 + Y%)m 1 , and the mass after drying is m 2 , then the mass of soil particles is m 3 = m 2 - (1 + Y%)m 1 ; Given the water content w of the undisturbed soil, the mass of undisturbed soil in 100g of cement-soil slurry is (1 + w)m 3 , and the mass of the added water m 4 = 100 - m 1 - (1 + w)m 3 , and the cement content is m 1 / (1 + w)m 3 ; (2) Assume that the undisturbed soil is saturated soil and the voids are filled with water; (3) According to the lifting rate v of the grouting rod, calculate the time t required for the grouting rod to lift 1 m, t = 100 / v; (4) Assume that the pile body is uniform within each meter. According to the measured grout injection flow rate Q in Step 4, calculate the cumulative grout volume V ejected per meter 1 = Q / 10 × v; (5) According to step 4, the slurry return volume per meter of the cement slurry mixture is V 2 , when considering the overall slurry return volume, the volume of the cement slurry in the slurry return channel needs to be considered. Assume the diameter of the slurry return hole is d 1 and the depth of the slurry return hole is h, calculate the volume of the cement slurry mixture in the slurry return hole V 3 = 0.25 × 3.14 × d 1 × d 1 × h, the total slurry return volume is V 返浆 = V 2 + V 3 ; (6) According to the pile diameter d obtained after designing and verifying the pile diameter according to the design construction parameters in the process test before large-area construction 2 , the volume V of each meter of pile is calculated 4 = 0.25 × 3.14 × d 2 × d 2 ; (7) Calculate the density ρ of the cement slurry according to the water-cement ratio B of the cement slurry 水泥浆 , then the mass of the dry cement in the grout per meter is m 5 = ρ 水泥浆 × V 1 × 1 / (B + 1); (8) In the slurry return per meter, based on the measured slurry return density ρ 混合物 , the slurry return volume V 2 , calculate the total mass m 6 of the slurry return per meter = ρ 混合物 × V 2 ; (9) Calculate the mass M of the undisturbed soil in the slurry per meter based on the proportion of the undisturbed soil mass in every 100 g of the returned slurry in the titration test. 3 = m 6 ×(1 + w)m 3 / 100. The mass of the undisturbed soil remaining in the pile body is M 4 = ρ 原状土 ×V 4 - M 3 ; (10) Calculate the mass of cement M per meter of the returned slurry based on the proportion of the mass of cement in every 100 g of the returned slurry in the titration test. 5 = m 6 × m 1 / 100, and calculate the mass of cement remaining in the pile body The quantity is M 6 = m 5 - M 5 .

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