A method for predicting the pile-forming strength of the high-pressure jet grouting pile based on the backflow slurry test at the construction site

Abstract

The present invention discloses a method for predicting the strength of the formed pile body of a high-pressure jet grouting pile based on the return slurry test at the construction site, including: configuring and testing strength specimens with different cement dosages, and drawing the relationship curve between the age strength and the cement dosage; obtaining the standard curve of the return slurry EDTA titration under different cement dosages through experiments; taking samples of the cement-soil return slurry at the return slurry outlet of the high-pressure jet grouting pile to determine the corresponding cement mass m1 in the quantitative cement-soil return slurry sample; monitoring the construction spraying flow rate Q and the return slurry flow rate V2 on site; obtaining the density of the cement-soil return slurry sample; obtaining the mass m2 of the dried cement-soil return slurry sample; calculating the cement mass M6 in the pile body; calculating the cement dosage in the pile body, predicting the unconfined compressive strength of the pile body at the age, and determining whether it meets the design requirements; realizing the accurate prediction of the age strength of the pile body through the age standard curve of the specimen strength under different cement dosages, which has important practical significance for predicting the construction quality of high-pressure jet grouting piles.

Description

Technical Field

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

[0002] Since it was first successfully developed in Japan in the 1970s and applied to deep foundation reinforcement, due to its advantages such as a wide range of applications, excellent construction quality, and little disturbance to the surrounding environment, the high-pressure jet grouting method has been widely used in underground projects such as subways, tunnels, and basements of high-rise buildings. Although there are a large number of successful cases, the detection of the pile-forming quality is still a pain point in the industry. After the construction of high-pressure jet grouting piles, for the range and strength of the solidified body formed underground, the commonly used method at home and abroad is core drilling test, but coring needs to wait until 28d or a certain age when the pile body reaches a certain strength. If the pile body quality is found not to meet the requirements at this time and rework is carried out, it will inevitably cause greater construction costs. Summary of the Invention

[0003] To solve the deficiencies of the existing technology, the problem to be solved by the present invention is that the detection time of the pile-forming strength of the high-pressure jet grouting pile in the existing technology is lagged, and rework will bring greater construction costs when the pile body quality does not meet the requirements. A rapid test method is provided, which can, during the construction process of high-pressure jet grouting piles, through testing and monitoring various data of the cement-soil backflow slurry, achieve accurate measurement of the cement content in the pile body, and then deduce the pile body strength of the high-pressure jet grouting pile at 28d or 90d age, and determine whether the construction quality meets the design requirements.

[0004] To achieve the above object, the present invention relates to a method for predicting the pile-forming strength of a high-pressure jet grouting pile based on the backflow slurry test at the construction site, which is characterized by including the following steps:

[0005] Step 1: Configure strength test blocks with different cement dosages and conduct strength tests, and draw a relationship curve between the age strength and the cement dosage;

[0006] Step 2: Take undisturbed soil samples and obtain the backflow slurry EDTA titration standard curve under different cement dosages through tests;

[0007] Step 3: Take samples of the cement-soil backflow slurry at the backflow port of the high-pressure jet grouting pile, and conduct on-site EDTA titration of the cement content in the backflow slurry to determine the corresponding cement mass m in the quantitative cement-soil backflow slurry sample 1 ;

[0008] Step 4: Monitor the on-site construction grouting flow rate Q and the backflow flow rate V 2 ;

[0009] Step 5: Conduct on-site backflow slurry specific gravity test to obtain the density ρ of the cement-soil backflow slurry sample 混合物;

[0010] Step 6: Dry the quantitatively measured cement soil backflow sample to obtain the mass m of the dried cement soil backflow sample 2 ;

[0011] Step 7: Based on the relevant curves and parameters obtained in Steps 2 - 6, calculate the cement mass M in the pile body 6 ;

[0012] Step 8: Calculate the cement content in the pile body based on the cement mass in the pile body obtained in Step 7, refer to the strength test block configuration and strength test curve with different cement contents obtained in Step 1, predict the unconfined compressive strength of the pile body at the age, and determine whether it meets the design requirements

[0013] Furthermore, the method of Step 1 is specifically as follows: Before the on-site high-pressure jet grouting pile construction, drill to obtain undisturbed soil samples, take representative strata within the reinforcement range, configure cement soil mixtures according to the design cement content ± 20% with a variation value of 5%, and according to the water-cement ratio in the construction parameters

[0014] After each cement content of the cement soil mixture is stirred evenly, pour it into at least 2 triple plastic mortar molds (size: 70.7mm × 70.7mm × 70.7mm), use a vibrating rod to vibrate evenly, and then place it in a standard curing room for curing to obtain multiple test blocks

[0015] After reaching the age (such as 28 days), use a pressure testing machine to test the strength of multiple test blocks. After averaging the strength data, draw the relationship curve between the age strength and the cement content

[0016] Furthermore, the method of Step 2 specifically includes the following steps: Take 300g of undisturbed soil for titration test, and the consumption of EDTA disodium is within 3mL. For 300g of pure cement, the EDTA consumption is above 250mL. Therefore, the calcium ions involved in the chemical reaction during titration mainly exist in the cement. When the mass of pure cement powder is within 40g, the standard curve is linear. As long as the EDTA consumption is known, the corresponding cement mass can be calculated inversely. Therefore, when configuring the on-site standard curve, determine the mass of the cement soil mixture to be 100g, and calculate inversely according to the on-site construction parameters. At this time, the mass of the cement powder is within 40g

[0017] (1) Preparation of test instruments and equipment

[0018] 1) Burette (acid type): 50mL, 1 piece

[0019] 2) Burette stand: 1 piece

[0020] 3) Burette clamp: 1 piece

[0021] 4) Bulb pipette: 10 mL, 50 mL, 10 pieces.

[0022] 5) Conical flask (i.e., Erlenmeyer flask): 200 mL, 20 pieces.

[0023] 6) Beaker: 2000 mL (or 1000 mL), 1 piece; 300 mL, 10 pieces.

[0024] 7) Volumetric flask: 1000 mL, 1 piece.

[0025] 8) Enamel cup: with a capacity greater than 1200 mL, 10 pieces.

[0026] 9) Stainless steel rod (or thick glass rod): 10 pieces.

[0027] 10) Measuring cylinder: 100 mL and 5 mL, 1 piece each; 50 mL, 2 pieces.

[0028] 11) Brown wide-mouth bottle: 60 mL, 1 piece (containing calcon indicator).

[0029] 12) Electronic balance: with a measuring range of not less than 1500 g and a sensitivity of 0.01 g.

[0030] 13) Stopwatch: 1 piece.

[0031] 14) Watch glass: Φ9 cm, 10 pieces.

[0032] 15) Mortar: Φ12 - 13 cm, 1 piece.

[0033] 16) Rubber bulb: 1 piece.

[0034] 17) Precision test paper: pH 12 - 14.

[0035] 18) Polyethylene bucket: 20 L (filled with distilled water, ammonium chloride, and EDTA disodium standard solution), 3 pieces; 5 L (filled with sodium hydroxide), 1 piece; 5 L (large-mouth bucket), 10 pieces.

[0036] 19) Brush, scouring powder, suction tube, plastic spoon, special pencil, centimeter paper.

[0037] 20) Wash bottle (plastic): 500 mL, 1 piece.

[0038] (2) Test reagents

[0039] 1) 0.1 mol / m 3Sodium ethylenediaminetetraacetate (EDTA disodium) standard solution (hereinafter referred to as EDTA disodium standard solution); accurately weigh 37.23 g of EDTA disodium (analytical pure), dissolve it with carbon dioxide-free distilled water at 40 - 50 °C, and after complete dissolution and cooling to room temperature, make up the volume to 1000 mL. If there are many test samples, it can be weighed in multiples and made up to multiples of 1000 mL. When not in use, it needs to be stored in a sealed environment at room temperature and avoid direct sunlight.

[0040] 2) 10% ammonium chloride (NH 4 Cl) solution: Put 500 g of ammonium chloride (analytical pure or chemical pure) in a 10 L polyethylene bucket, add 4500 mL of distilled water, and shake well to completely dissolve the ammonium chloride. It can also be prepared in batches in a 1000 mL beaker and then poured into a plastic bucket and shaken well. To avoid a decrease in the concentration of the ammonium chloride solution, try to use the ammonium chloride solution prepared on the same day for the test.

[0041] 3) 1.8% sodium hydroxide (containing triethanolamine) solution: Weigh 18 g of sodium hydroxide (NaOH) (analytical pure) with an electronic balance, put it into a clean and dry 1000 mL beaker, add 1000 mL of distilled water to completely dissolve it. After the solution cools to room temperature, add 2 mL of triethanolamine (analytical pure), stir well and store it in a plastic bucket.

[0042] 4) Calconcarboxylic acid indicator: Mix 0.2 g of sodium carboxymethylcongo red (molecular formula C 21 H 13 N 2 NaO 7 S, molecular weight 460.39) with 20 g of potassium sulfate that has been pre-dried in an oven at 105 °C for 1 h. Put them together in a mortar and grind them into a very fine powder, and store it in a brown wide-mouth bottle to prevent moisture absorption.

[0043] (3) Preparation of standard curve

[0044] 1) Sampling and testing of undisturbed soil: Before construction, drill cores in the construction site, divide the soil samples within the pile body range according to the strata during construction, and test the natural moisture content of each soil layer of the undisturbed soil. Classify and put them into sampling buckets (soils from different strata are put into different sampling buckets), seal them and store them in a cool place;

[0045] 2) Assume that the designed cement content is A%, and the water-cement ratio is the water-cement ratio B in the designed construction parameters. Prepare mixtures of cement + water + undisturbed soil according to the cement content of A ± 20% with a variation value of 5%. After stirring evenly, take 100 g of each mixture and put them into enamel cups marked with the designed cement content respectively;

[0046] (3) Add 600 mL of 10% ammonium chloride solution to an enamel cup, stir with a glass rod for 3 min (stir 110 - 120 times per minute). After stirring, let it stand for sedimentation for 10 min, then transfer the upper clear liquid to a 300 mL beaker, stir well, cover with a watch glass for later measurement;

[0047] (4) Use a pipette to suck 10.0 mL of the upper suspension (1 - 2 cm below the liquid surface) into a 200 mL conical flask. Use a measuring cylinder to measure 50 mL of 1.8% sodium hydroxide (containing triethanolamine) solution and pour it into the conical flask. At this time, the pH value of the solution is 12.5 - 13.0 (which can be tested with a precision pH test paper of pH 12 - 14). Then add calconcarboxylic acid indicator (about 0.2 g in mass), shake well, and the solution turns rose red. Record the volume V of the EDTA disodium standard solution in the burette 1 , then titrate with the EDTA disodium standard solution, shake well while titrating, and carefully observe the color of the solution; when the color of the solution changes to purple, slow down the titration speed and shake well; until the end point is pure blue, record the volume V of the EDTA disodium standard solution in the burette 2 (in mL, read to 0.1 mL). Calculate V 1 - V 2 , which is the consumption of the EDTA disodium standard solution;

[0048] (5) For the samples in other sampling buckets, conduct tests in the same way and record the consumption of the EDTA disodium standard solution for each;

[0049] (6) Use the average value of the consumption (mL) of the EDTA disodium standard solution for the same cement material as the ordinate and the cement dosage as the abscissa to draw a graph. If the cement batch changes during construction, the standard curve must be redone.

[0050] 4. The method for predicting the pile-forming strength of the high-pressure jet grouting pile based on the return slurry test at the construction site according to claim 1, wherein the specific method of step (3) is as follows:

[0051] (3) Cement return slurry sampling: Take cement-soil return slurry at the return slurry outlet of the high-pressure jet grouting pile every meter. Pay attention to the representativeness of the sampling and select fresh and undiluted cement-soil return slurry samples;

[0052] (4) After the backflow slurry is stirred evenly, weigh 100 g and put it into an enamel cup. Then, perform the EDTA titration operation (that is, repeat steps (3) to (5) in the standard curve configuration in step two). According to the standard curve drawn in step two 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 consumed by the cement, therefore, the consumption of the EDTA disodium standard solution can be considered to be all consumed by the cement. After checking the standard curve, the cement mass can be determined.

[0053] Further, the method in step 4 is specifically as follows:

[0054] (1) Install a flow meter 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.

[0055] (2) During large-area construction, excavate a trench near the backflow port of the high-pressure jet grouting pile and install a flow meter to monitor the backflow flow rate. After time accumulation, determine the total backflow volume.

[0056] Further, the method in step 5 is specifically as follows: Use a mud hydrometer to test the specific gravity of the backflow per meter on site to obtain the density ρ of the cement soil backflow sample 混合物 .

[0057] Further, the specific method in step 6 is as follows: Take 100 g of cement backflow, pour it into an enamel cup, and put it into an oven at 105 °C for 8 hours to test the mass m of the dried sample 2 . Since during the drying process, hydration reactions will occur among the cement, soil, and water and cause condensation, the sample should be taken out and mashed during the drying process to facilitate thorough drying.

[0058] Further, the specific method in step 7 includes the following steps:

[0059] (1) Combining the EDTA titration test on the cement content in the on-site backflow, determine that the mass of cement dry powder in every 100 g of the cement soil slurry mixture is m 1 , and the product after cement hydration is (1 + Y%)m 1 (A large number of indoor tests have proved that during the cement hydration reaction, the mass will increase. Assuming that the increase percentage is Y%, therefore, after drying, there will be moisture with a mass of Y% of the cement mass absorbed by the cement and unable to be dried. From the existing technical data, this increase percentage can be taken as 25%). After drying, the mass is m 2 , then the mass of the soil particles is m 3 = m 2 - (1 + Y%)m 1; If the water content w of the undisturbed soil is known, the mass of the undisturbed soil in 100 g of the cement soil slurry is (1 + w)m 3 , and the mass of the added water is m 4 = 100 - m 1 - (1 + w)m 3 , and the cement content is m 1 / (1 + w)m 3 ;

[0060] (2) Assume that the undisturbed soil is saturated soil and the voids are filled with water;

[0061] (3) According to the lifting rate v (cm / min) of the grouting rod, calculate the time t = 100 / v (min) required for the grouting rod to lift 1 m;

[0062] (4) Assume that the pile body is uniform within each meter. According to the grout injection flow rate Q (L / min) of the cement slurry measured in step four, calculate the cumulative amount of cement slurry ejected per meter V 1 = Q / 10 × v (m 3 );

[0063] (5) According to step 4, the backflow volume of the cement slurry mixture per meter is V 2 . When considering the overall backflow volume, the volume of the cement slurry in the backflow channel needs to be considered. Assume the diameter of the backflow hole is d 1 and the depth of the backflow hole is h, and calculate the volume of the cement slurry mixture in the backflow hole V 3 = 0.25 × 3.14 × d 1 × d 1 × h, and the total backflow volume is V 返浆 = V 2 + V 3 ;

[0064] (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, calculate the volume of each meter of the pile V 2 = 0.25 × 3.14 × d 4 × d 2 × d 2 ;

[0065] (7) According to the water - cement ratio B of the cement slurry, calculate the density ρ 水泥浆 of the cement slurry, then the mass of the cement dry powder in each meter of grouting is m 5 = ρ 水泥浆 × V 1 × 1 / (B + 1);

[0066] (8) In each meter of backflow, according to the measured backflow density ρ 混合物 , and the backflow volume V 2, the total mass of the return slurry per meter, \(m\), is calculated 6 = ρ 混合物 ×V 2 ;

[0067] (9) According to the proportion of the undisturbed soil mass in every 100 g of the return slurry in the titration test, the mass of the undisturbed soil, \(M\), in the return slurry per meter is calculated 3 = m 6 ×(1 + w)m 3 / 100, and the mass of the undisturbed soil remaining in the pile body is \(M\) 4 = ρ 原状土 ×V 4 - M 3 ;

[0068] (10) According to the proportion of the cement mass in every 100 g of the return slurry in the titration test, the mass of the cement, \(M\), in the return slurry per meter is calculated 5 = m 6 ×m 1 / 100, and the mass of the cement remaining in the pile body is calculated as \(M\) 6 = m 5 - M 5 ;

[0069] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0070] (1) The method for predicting the forming strength of the high-pressure jet grouting pile based on the return slurry test at the construction site of the present invention overcomes the deficiency of the traditional EDTA test method for the cement content in the subgrade mixed soil for testing high cement content methods. By adjusting the EDTA titration sampling mass, the EDTA titration standard curve is controlled within the linear range, and the cement mass can be accurately obtained according to the EDTA titration consumption of the return slurry. Combining the on-site grouting construction parameters, return slurry volume monitoring, return slurry specific gravity, return slurry moisture content, and return slurry EDTA titration test data, the cement mass (or cement content) of the pile body can be accurately measured. Combining with the strength curves of the test blocks with different cement contents, the age strength of the pile body is predicted, realizing the rapid prediction of the forming quality of the pile body.

[0071] (2) The method for predicting the forming strength of the high-pressure jet grouting pile based on the return slurry test at the construction site of the present invention overcomes the deficiency that the traditional core drilling method can only carry out the post-detection of the forming quality of the high-pressure jet grouting pile after reaching the age. Prediction can be carried out during the construction of the high-pressure jet grouting pile. When problems are found, the construction parameters are adjusted in time to ensure the construction quality, which is of great significance for the application and popularization of the high-pressure jet technology. Description of the Drawings

[0072] Figure 1 is the overall flow schematic diagram of the preferred embodiment of the present invention; Specific Embodiments

[0073] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0074] Embodiment 1:

[0075] Please refer to Figure 1 , the present invention relates to: a method for predicting the pile-forming strength of the pile body of a high-pressure jet grouting pile based on the backflow slurry test at the construction site, which is carried out according to the steps of configuring and testing strength specimens with different cement dosages, configuring the EDTA titration standard curve for the backflow slurry, titrating the cement content in the on-site backflow slurry by EDTA, monitoring the on-site construction grouting flow rate and backflow slurry flow rate, testing the specific gravity of the on-site backflow slurry, testing the moisture content of the on-site backflow slurry, predicting the cement content in the pile body, and predicting the pile body strength. The specific prediction method is as follows:

[0076] Step 1: Configuration and strength testing of strength specimens with different cement dosages

[0077] Before the construction of the on-site high-pressure jet grouting pile, undisturbed soil samples are taken by drilling, and representative strata within the reinforcement range are taken. Cement-soil mixtures are configured according to the designed cement dosage ± 20% and a variation value of 5%, and according to the water-cement ratio in the construction parameters.

[0078] After each type of cement-soil mixture is stirred evenly, it is filled into at least 2 triple plastic mortar molds (preferably with dimensions of 70.7 mm × 70.7 mm × 70.7 mm). After being vibrated evenly with a vibrating rod, it is placed in a standard curing room for curing to obtain multiple specimens;

[0079] After reaching the age (for example, 28 days), the strength of multiple specimens is tested using a compression testing machine. After the strength data is averaged, a relationship curve between the age strength and the cement dosage of this type is plotted.

[0080] Step 2: Configuration of the EDTA titration standard curve for the backflow slurry

[0081] (4) According to the method recommended in the "Test Regulations for Inorganic Binding Material Stabilized Materials for Highway Engineering" (JTG E51-2009), 300 g of undisturbed soil was taken for titration test, and the consumption of disodium EDTA was within 3 mL. For 300 g of pure cement, the EDTA consumption was above 250 mL. Therefore, the calcium ions that underwent chemical reactions during titration mainly existed in the cement. When the mass of pure cement powder was within 40 g, the standard curve was linear. As long as the EDTA consumption was known, the corresponding cement mass could be calculated inversely. Therefore, when configuring the on-site standard curve, the mass of the cement-soil mixture was determined to be 100 g, and according to the on-site construction parameters for inverse calculation, the mass of the cement powder was within 40 g at this time.

[0082] (5) Preparation of test instruments and equipment

[0083] 21) Burette (acid type): 50 mL, 1 piece.

[0084] 22) Burette stand: 1 piece.

[0085] 23) Burette clamp: 1 piece.

[0086] 24) Volumetric pipette: 10 mL, 50 mL, 10 pieces.

[0087] 25) Conical flask (i.e., Erlenmeyer flask): 200 mL, 20 pieces.

[0088] 26) Beaker: 2000 mL (or 1000 mL), 1 piece; 300 mL, 10 pieces.

[0089] 27) Volumetric flask: 1000 mL, 1 piece.

[0090] 28) Enamel cup: with a capacity greater than 1200 mL, 10 pieces.

[0091] 29) Stainless steel rod (or thick glass rod): 10 pieces.

[0092] 30) Measuring cylinder: 100 mL and 5 mL, 1 piece each; 50 mL, 2 pieces.

[0093] 31) Brown wide-mouth bottle: 60 mL, 1 piece (containing calcon indicator).

[0094] 32) Electronic balance: with a measuring range of not less than 1500 g and a sensitivity of 0.01 g.

[0095] 33) Stopwatch: 1 piece.

[0096] 34) Watch glass: Φ9 cm, 10 pieces.

[0097] 35) Mortar: Φ12 - 13 cm, 1 piece.

[0098] 36) Rubber suction bulb: 1 piece.

[0099] 37) Precision test paper: pH 12 - 14.

[0100] 38) Polyethylene barrels: 20L (filled with distilled water, ammonium chloride, and disodium EDTA standard solution), 3 pieces; 5L (filled with sodium hydroxide), 1 piece; 5L (large - mouth barrel), 10 pieces.

[0101] 39) Brush, scouring powder, water suction pipe, plastic spoon, special pencil, centimeter paper.

[0102] 40) Plastic wash bottle: 500 mL, 1 piece.

[0103] (6) Test reagents

[0104] 1) 0.1 mol / m 3 Disodium ethylenediaminetetraacetate (disodium EDTA) standard solution (abbreviation: disodium EDTA standard solution); accurately weigh 37.23 g of disodium EDTA (analytical pure), dissolve it with carbon - dioxide - free distilled water at 40 - 50 °C. After complete dissolution and cooling to room temperature, make up the volume to 1000 mL. If there are many test samples, it can be weighed in multiples and made up to multiples of 1000 mL. When not in use, it needs to be stored in a sealed environment at room temperature and avoid direct sunlight.

[0105] 2) 10% ammonium chloride (NH 4 Cl) solution: Put 500 g of ammonium chloride (analytical pure or chemically pure) into a 10 - L polyethylene barrel, add 4500 mL of distilled water, and shake well to completely dissolve the ammonium chloride. It can also be prepared in batches in a 1000 - mL beaker and then poured into the plastic barrel and shaken well. To avoid a decrease in the concentration of the ammonium chloride solution, try to use the ammonium chloride solution prepared on the same day for the test.

[0106] 3) 1.8% sodium hydroxide (containing triethanolamine) solution: Weigh 18 g of sodium hydroxide (NaOH) (analytical pure) with an electronic balance, put it into a clean and dry 1000 - mL beaker, add 1000 mL of distilled water to completely dissolve it. After the solution cools to room temperature, add 2 mL of triethanolamine (analytical pure), stir well and store it in a plastic barrel.

[0107] 4) Calconcarboxylic acid indicator: Mix 0.2 g of sodium 1 - (2 - hydroxy - 1 - naphthylazo) - 6 - nitro - 2 - naphthol - 4 - sulfonate (molecular formula C 21 H 13 N 2 NaO 7 S, molecular weight 460.39) with 20 g of potassium sulfate that has been pre - dried in an oven at 105 °C for 1 h. Put them together into a mortar and grind into a very fine powder, and store it in a brown wide - mouth bottle to prevent moisture absorption.

[0108] (7) Preparation of standard curve

[0109] 1) Undisturbed soil sampling and testing: Before construction, drill cores in the construction site. Divide the soil samples within the pile body according to the strata, and test the natural moisture content of each soil layer of the undisturbed soil. Classify and put them into the sampling buckets, seal them and store them in a cool place.

[0110] 2) Assume that the designed cement content is A%, and the water-cement ratio is B, which is the water-cement ratio in the designed construction parameters. Prepare mixtures of cement + water + undisturbed soil according to the cement content of A±20% with a variation value of 5%. After stirring evenly, take 100g of each mixture and put them into enamel cups marked with the designed cement content respectively.

[0111] 3) Add 600 mL of 10% ammonium chloride solution to the enamel cup, stir with a glass rod for 3 min (stir 110 - 120 times per minute). After stirring, let it stand for precipitation for 10 min, then transfer the upper clear liquid to a 300 mL beaker, stir well, cover it with a watch glass and wait for testing.

[0112] 4) Use a pipette to suck 10.0 mL of the upper suspension (1 - 2 cm below the liquid surface) into a 200 mL conical flask, measure 50 mL of 1.8% sodium hydroxide (containing triethanolamine) solution with a measuring cylinder and pour it into the conical flask. At this time, the pH value of the solution is 12.5 - 13.0 (which can be tested with a precision pH test paper of pH 12 - 14). Then add calconcarboxylic acid indicator (about 0.2 g in mass), shake well, and the solution turns rose red. Record the volume V of the EDTA disodium standard solution in the burette 1 , then titrate with the EDTA disodium standard solution, shake well while titrating, and carefully observe the color of the solution; when the color of the solution changes to purple, slow down the titration speed and shake well; until the end point is pure blue, record the volume V of the EDTA disodium standard solution in the burette 2 (in mL, read to 0.1 mL). Calculate V 1 - V 2 , which is the consumption of the EDTA disodium standard solution.

[0113] 5) Conduct tests on the samples in other sampling buckets in the same way, and record the consumption of the EDTA disodium standard solution for each of them.

[0114] 6) Plot a graph with the average value of the consumption (mL) of the EDTA disodium standard solution for the same cement material as the ordinate and the cement content as the abscissa. If the cement batch changes during construction, the standard curve must be redone.

[0115] Step 3: EDTA titration of the cement content in the on-site backflow slurry

[0116] (5) Cement backflow slurry sampling: Take the cement-soil backflow slurry at the backflow port of the high-pressure jet grouting pile every meter. Pay attention to the representativeness of the sampling, and select the fresh and undiluted cement-soil backflow slurry.

[0117] (6) After the backflow slurry is stirred evenly, weigh 100 g and put it into an enamel cup. Then repeat steps 3) - 5) in the preparation of the standard curve in step (4) of step two. According to the standard curve drawn in step two and the consumption of the EDTA disodium standard solution, determine the mass of cement in 100 g of the mixture. Since in 100 g of the mixture, the consumption of the EDTA disodium standard solution brought by the pure soil can be ignored compared with that consumed by 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 mass of the cement can be determined.

[0118] Step Four: Monitoring of the Injection Flow Rate and the Backflow Flow Rate during On-site Construction

[0119] (1) Install a flow meter on the injection equipment to determine the consumption of cement dry powder and water during the construction process, determine the injection flow rate, and after time accumulation, determine the total flow rate.

[0120] (2) During large-area construction, excavate a trench near the backflow outlet of the high-pressure jet grouting pile and install a flow meter to monitor the backflow flow rate. After time accumulation, determine the total backflow volume.

[0121] Step Five: On-site Backflow Specific Gravity Test

[0122] Use a mud specific gravity meter to test the specific gravity of the backflow per meter on-site to obtain the density ρ of the cement-soil mixture 混合物 .

[0123] Step Six: On-site Backflow Moisture Content Test

[0124] Take 100 g of the cement backflow, pour it into an enamel cup, and put it into an oven at 105 °C for 8 hours to test the mass m of the dried sample 2 . Since during the drying process, hydration reactions will occur among the cement, soil, and water, causing condensation. During the drying process, the sample should be taken out and mashed to facilitate thorough drying.

[0125] A large number of indoor tests have shown that during the cement hydration reaction, the mass will increase by 25%. Therefore, after drying, 25% of the moisture in the cement mass will be absorbed by the cement and cannot be dried.

[0126] Step Seven: Prediction of the Cement Content in the Pile Body

[0127] (4) Combining the EDTA titration test on the cement content in the on-site backflow, determine that the mass of the cement dry powder in every 100 g of the cement-soil slurry mixture is m 1 , and the product after the hydration of the cement is 1.25m 1 , the mass after drying is m 2 , then the mass of the soil particles is m 3 = m 2 - 1.25m 1; If the water content w of the undisturbed soil is known, the mass of the undisturbed soil in 100 g of the cement soil slurry is (1 + w)m 3 , and the mass of the added water is m 4＝ 100 - m 1 -(1 + w)m 3 , and the cement content is m 1 / (1 + w)m 3 .

[0128] (5) Assume that the undisturbed soil is saturated soil and the voids are filled with water.

[0129] (6) According to the lifting rate V (cm / min) of the grouting rod, calculate the time t = 100 / V (min) required for the grouting rod to lift 1 m.

[0130] (7) Assume that the pile body is uniform within each meter. According to the measured grout injection flow rate Q (L / min) of the cement slurry in step four, calculate the cumulative amount of cement slurry ejected per meter V 1 = Q / 10×v (m 3 );

[0131] (8) According to step four, the backflow volume of the cement slurry mixture per meter is V 2 . When considering the overall backflow volume, the volume of the cement slurry in the backflow channel needs to be considered. Assume the diameter of the backflow hole is d 1 and the depth of the backflow hole is h, and calculate the volume of the cement slurry mixture in the backflow hole V 3 = 0.25×3.14×d 1 ×d 1 ×h. The total backflow volume is V 返浆 = V 2 + V 3 .

[0132] (9) 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, calculate the volume of each meter of the pile V 2 , and calculate the volume of each meter of the pile V 4 = 0.25×3.14×d 2 ×d 2 ;

[0133] (10) According to the water-cement ratio B of the cement slurry, calculate the density ρ 水泥浆 of the cement slurry. Then, the mass of the cement dry powder in each meter of grouting is m 5 = ρ 水泥浆 ×V 1 ×1 / (B + 1).

[0134] (11) In each meter of backflow, according to the measured backflow density ρ 混合物 , and the backflow volume V 2, the total mass of the returned slurry per meter, \(m\), is calculated 6 =\(\rho\) 混合物 \(\times V\) 2 .

[0135] (12) According to the proportion of the original soil mass in every 100 g of the returned slurry in the titration test, the mass of the original soil, \(M\), in the returned slurry per meter is calculated 3 =\(m\) 6 \(\times(1 + w)m\) 3 / 100. The mass of the original soil remaining in the pile body is \(M\) 4 =\(\rho\) 原状土 \(\times V\) 4 -\(M\) 3 .

[0136] (13) According to the proportion of the cement mass in every 100 g of the returned slurry in the titration test, the mass of the cement, \(M\), in the returned slurry per meter is calculated 5 =\(m\) 6 \(\times m\) 1 / 100. The mass of the cement remaining in the pile body is calculated as \(M\) 6 =\(m\) 5 -\(M\) 5 .

[0137] Step Eight: Prediction of the pile body strength

[0138] Calculate the cement content in the pile body as \(M\) 6 / \(M\) 4 . Refer to the strength test block configuration and strength test curve with different cement contents obtained in Step One to predict the unconfined compressive strength of the pile body at a certain age, and determine whether it meets the design requirements.

[0139] The present invention provides a method that can accurately test the cement content in the returned slurry in segments based on test results such as the grouting flow rate / quantity, the returned slurry flow rate / quantity, the cement content in the returned slurry titration, the specific gravity of the returned slurry, the moisture content of the returned slurry, and the EDTA standard curve during the high-pressure jet grouting construction process, and then deduce the cement content remaining in the pile body. Through the age-standard curve of the test block strength under different cement contents, the accurate prediction of the pile body strength at a certain age is realized, which has important practical significance for predicting the construction quality of high-pressure jet grouting piles.

[0140] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for predicting the forming strength of the pile body of a high-pressure jet grouting pile based on the backflow slurry test on 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 backflow EDTA titration standard curves under different cement dosages through tests; Step 3: Take samples of the cement-soil backflow at the backflow port 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: Conduct on-site construction grouting flow Q and return grouting flow monitoring V 2 ; Step 5: Conduct an on-site backflow specific gravity test to obtain the density of the cement soil backflow sample ; Step 6: Dry the quantitative cement-soil backflow sample to obtain the mass of the dried cement-soil backflow sample m 2 ; Step 7: Combine the relevant curves and parameters obtained in Steps 2 to 6 to calculate the mass of cement in the pile shaft M 6 ; The specific method of Step 7 includes the following steps: (1)Combined with the on-site backflow cement content EDTA titration test, it is determined that the mass of cement dry powder in every 100 g 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 ; The water content of the undisturbed soil w is known, then the mass of undisturbed soil in 100 g 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 of the shotcrete rod v , calculate the time required for the shotcrete rod to lift 1 meter t= 100 / v ; (4)Assume that the pile body is uniform within each meter, and calculate the cumulative amount of cement slurry ejected per meter according to the cement slurry injection flow rate measured in Step 4 Q , calculate the cumulative amount of cement slurry ejected per meter V 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) Based on the pile diameter obtained after designing and validating the pile diameter according to the design construction parameters in the process test before large-area construction, d 2 , calculate the volume of each meter of the pile V 4 = 0.25 × 3.14 × d 2 × d 2 ; (7) Calculate the density of the cement slurry based on the water-cement ratio B of the cement slurry , then the mass of the dry cement in the grout per meter is m 5 = × V 1 × 1 / (B + 1); (8) In the slurry return per meter, based on the measured slurry return density , the slurry return volume V 2 , calculate the total mass of the slurry return per meter m 6 = × V 2 ; (9) Calculate the mass of undisturbed soil in the slurry per meter based on the proportion of undisturbed soil mass in every 100 g of slurry returned during the titration test. M 3 = m 6 × (1 + w ) m 3 / 100. The mass of undisturbed soil remaining in the pile is M 4 = × V 4 - M 3 ; Calculate the mass of cement in the slurry per meter based on the proportion of the mass of cement in every 100 g of the returned slurry in the titration test M 5 = m 6 × m 1 / 100. The calculated mass of cement remaining in the pile body is M 6 = m 5 - M 5 ; Step 8: Calculate the cement dosage in the pile body obtained in Step 7, look up the relationship curve of the strength test of the 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 a high-pressure jet grouting pile based on the backflow slurry test on the construction site according to Claim 1, characterized in that, the method of Step 1 is specifically as follows: Before the construction of the on-site high-pressure jet grouting pile, 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 variation 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, vibrate evenly with a vibrating rod, 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 averaging the strength data, 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 a high-pressure jet grouting pile based on the backflow slurry test on 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 on the construction site. Divide the soil samples within the pile body range to be constructed 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 the water-cement ratio B in the design construction parameters. Configure mixtures of cement + water + undisturbed soil according to the design cement dosage A ± 20% and a variation value of 5%. After stirring evenly, take 100g of each mixture and put them into enamel cups marked with the corresponding design cement dosage respectively; 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 and wait for testing; 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 Then titrate with the disodium EDTA standard solution, shaking well during titration and observing the color of the solution carefully. When the color of the solution changes to purple, slow down the titration speed and shake well. Titrate 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 of them; 6) Draw 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 a high-pressure jet grouting pile based on the backflow slurry test on the construction site according to Claim 1, characterized in that, the specific method of Step 3 is: Cement backflow sampling: At the backflow outlet 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; After the backflow is stirred evenly, weigh 100 g and put it into an enamel cup, and 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 quality 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 consumption, therefore, the consumption of the EDTA disodium standard solution can be considered to be all due to the cement consumption. After checking the standard curve, the cement quality can be determined.

5. The method for predicting the forming strength of the high-pressure jet grouting pile based on the backflow test at the construction site according to claim 1, characterized in that, the method of Step 4 is specifically as follows: (1) Install a flow meter 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 outlet of the high-pressure jet grouting pile and install a flow meter to monitor the backflow flow rate, and after time accumulation, determine the total backflow volume.

6. The method for predicting the forming strength of the high-pressure jet grouting pile based on the backflow test at 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 return slurry per meter on site to obtain the density of the cement-soil return slurry sample per meter .

7. The method for predicting the forming strength of the high-pressure jet grouting pile based on the backflow test at 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 of the dried sample. m 2 During the drying process, hydration reactions will occur among the cement, soil, and water, causing condensation. Therefore, the sample should be taken out and mashed during the drying process.

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