Static penetration testing and evaluation method for cement-soil mixing piles within 3D age

Abstract

The present invention proposes a static penetration test and evaluation method for cement-soil mixing piles within a 3D age period. The test method comprises the following steps: step 1, within 0.5-1h after the construction of the cement mixing pile is completed, a reserved mark is made at the center of the pile body, and then a PVC pipe with a closed bottom is vertically inserted into the cement mixing pile at a radius of 1 / 3 of the pile core to form a reserved detection hole and mark it; wherein the length of the PVC pipe is less than the depth of the cement mixing pile; step 2, when the cement mixing pile reaches a certain age, the static penetration test method is used to continuously detect the pile body strength of the cement mixing pile, and the age range of the cement mixing pile is 1 day to 3 days; wherein: within the age range, different detection times are selected according to different construction conditions. The present invention has the advantages of short detection age and high detection accuracy, while avoiding the problem of probe damage.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, and in particular to a static penetration testing and evaluation method for cement-soil mixing piles within a 3D age period. Background Art

[0002] Cement mixing piles are a commonly used reinforcement solution for soft soil foundation treatment projects, and pile testing is an important quality link. Current regulations stipulate that cement mixing pile testing is mainly based on compressive strength testing of drilled core samples, with a sampling rate of 3%-5%. The core sampling testing method has a long cycle, low efficiency, and high cost, and cannot achieve the purpose of quickly testing the quality of mixing piles. Static penetration testing can obtain continuous strength characteristic information of the test object, and has the advantages of being easy to implement, fast, and low-cost. Conventional static penetration testing is used to test cement mixing piles, and the probe is easily deflected from the pile and cannot fully test the pile body.

[0003] The existing 7D-age static penetration testing method and the full-length PVC pipe static penetration testing method both have the following defects: (1) Due to the long age, the probe is easily damaged, resulting in high economic costs; (2) The full-length PVC pipe is set, resulting in high economic costs. (3) The center of the cement mixing pile is vertically inserted into the bottom-sealed PVC pipe to form a reserved testing hole. During construction, because the mixing rod is approximately at the pile center position, the pile quality at the center position of the mixing pile will be reduced during the drilling and lifting process. Therefore, the detection position is not representative, resulting in low detection accuracy. Summary of the Invention

[0004] The present invention proposes a static penetration testing and evaluation method for cement-soil mixing piles within the 3D age period to solve the above technical problems, which adopts the following technical solutions:

[0005] A static penetration testing method for cement-soil mixing piles within a 3D age period includes the following steps:

[0006] Step 1: Within 0.5-1h after the construction of the cement mixing pile is completed, a reserved mark is made at the center of the pile body. Then, a PVC pipe with a closed bottom is vertically inserted into the cement mixing pile at a position 1 / 3 of the radius away from the pile center to form a reserved detection hole and mark it;

[0007] Among them, the length of the PVC pipe is less than the depth of the cement mixing pile;

[0008] Step 2: When the cement mixing pile reaches a certain age, the pile strength of the cement mixing pile is continuously tested using a static penetration test method, wherein the age of the cement mixing pile ranges from 1 day to 3 days; wherein:

[0009] Within the age range, different inspection times are selected according to different construction conditions;

[0010] The construction conditions include mixing pile construction data and construction temperature;

[0011] The mixing pile construction data refers to the real-time monitoring data of the intelligent terminal during the mixing pile construction, including the shotcrete volume, water-cement ratio, and sinking speed; the construction temperature refers to the surface temperature during the mixing pile construction;

[0012] The specific steps of continuously testing the pile strength of the cement mixing pile using the static penetration test method are as follows:

[0013] A probe is aligned with the center of the reserved detection hole, the probe is fixed on the sounding rod, and the sounding rod is uniformly pressed into the cement mixing pile along the PVC pipe using a static pressure device. The in-situ data is detected using the probe, and the in-situ data includes the cone tip resistance and the side wall resistance.

[0014] Preferably, the length of the PVC pipe is 0.3m~0.8m.

[0015] Preferably, the diameter of the PVC tube is 38±1 mm.

[0016] Preferably, the probe has a diameter of 43.7 mm.

[0017] Preferably, the probe is a double-bridge static penetration probe, and the probe adopts a resistance strain gauge sensor.

[0018] Preferably, it further comprises a static detection data collector, and a wire connects the static detection data collector and the probe.

[0019] Preferably, the cone tip resistance of the PVC pipe is less than 0.5 MPa, and the side wall resistance is less than 5 kPa.

[0020] Preferably, the error of the inclination angle of the probe rod penetrating the cement mixing pile is within 2°; and the speed at which the PVC pipe is uniformly pressed into the cement mixing pile is 0.4-1.0 m / min.

[0021] A quality evaluation method for cement mixing piles comprises the following steps:

[0022] (1) During the trial stage of cement mixing piles, within 3 days after the construction of cement mixing piles, the quality of 5% of the cement mixing piles within the inspection range shall be inspected by the static penetration test method of cement-soil mixing piles within the 3D age period, and the corresponding in-situ data of each cement mixing pile shall be obtained;

[0023] (2) The obtained in-situ data were correlated with the 7-day and 28-day core sample compressive strength to evaluate the pile quality of the cement mixing pile.

[0024] A method for evaluating the foundation treatment effect of cement mixing piles comprises the following steps:

[0025] (1) During the trial stage of cement mixing piles, within 3 days after the construction of cement mixing piles, the quality of 5% of the cement mixing piles within the inspection range shall be inspected by the static penetration test method of cement-soil mixing piles within the 3D age period, and the corresponding in-situ data of each cement mixing pile shall be obtained;

[0026] (2) Compare and analyze the in-situ data with the static penetration data of the disturbed soil after the construction of the mixing piles to evaluate the effect of the mixing piles in reinforcing the soft foundation.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] (1) The detection age is 1 to 3 days. Compared with the current detection age, the detection age is shortened. During the detection age of 1 to 3 days, the cement soil is completely solidified and the pile strength is moderate, thus avoiding the problem of probe damage.

[0029] (2) A closed-bottom PVC pipe is inserted vertically into the cement mixing pile at a point 1 / 3 of the radius from the pile center. This means that a representative position on the pile body is selected for testing, which improves the testing accuracy. Specifically, the cement mixing pile at a point 1 / 3 of the radius from the pile center mixes the cement most evenly, resulting in the best and most representative pile quality.

[0030] (3) The length of the PVC pipe is less than the depth of the cement mixing pile, that is, the PVC pipe is not set at the full length. Compared with the full-length PVC prefabricated pipe, it is more cost-effective and solves the problem of easy deflection of the probe, ensuring the accuracy of the test data. A large number of piles can be tested in a short time, which reduces the economic cost and shortens the penetration time. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The figure is a flow chart of the static penetration testing method for cement-soil mixing piles within the 3D age period.

[0032] Figure 2 This is a structural diagram of a cement mixing pile. Implementation Method

[0033] The present invention will be described in more detail below with reference to schematic diagrams, which illustrate preferred embodiments of the present invention. It should be understood that those skilled in the art may modify the present invention as described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as a general guide for those skilled in the art and not as a limitation of the present invention.

[0034] like Figures 1 and 2 A static penetration testing method for cement-soil mixing piles within a 3D age period includes the following steps:

[0035] After the construction of cement soil mixing pile a is completed, promptly remove construction residues and slurry to keep the construction surface flat.

[0036] Step 1: Within 0.5-1h after the construction of the cement mixing pile is completed, make a reserved mark at the center of the pile body. Then, vertically insert a PVC pipe b with a closed bottom into the cement mixing pile at a radius of 1 / 3 of the pile center to form a reserved detection hole c and mark it.

[0037] Among them, the length of the PVC pipe is less than the depth of the cement mixing pile.

[0038] Specifically, the length of the PVC pipe is 0.3m~0.8m, depending on the pile head, season, and construction conditions, which provides a preset channel for the penetration of the sounding rod e, preventing the deviation of the probe d during the penetration of the static sounding rod e, shortening the PVC pipe and saving costs.

[0039] The diameter of the PVC pipe is 38 ± 1 mm, slightly smaller than the diameter of the static penetration probe d. The cone resistance of the PVC pipe is less than 0.5 MPa, and the side wall resistance is less than 5 kPa. The PVC pipe is uniformly pressed into the cement mixing pile at a speed of 0.4-1.0 m / min.

[0040] Step 2: When the cement mixing pile reaches a certain age, the static penetration test method is used to continuously test the pile strength of the cement mixing pile. The age range of the cement mixing pile is 1 day to 3 days.

[0041] Within the age range, different inspection times are selected based on different construction conditions. Specifically, if the construction is carried out during low water content and high temperatures in summer, the inspection time should be one day after the age. If the construction is carried out during high water content and low temperatures, the inspection time should be within 2 to 3 days.

[0042] Construction conditions include mixing pile construction data and construction temperature;

[0043] The mixing pile construction data refers to the real-time monitoring data of the intelligent terminal during the mixing pile construction, including the shotcrete volume, water-cement ratio, and sinking speed; the construction temperature refers to the surface temperature during the mixing pile construction.

[0044] The specific steps for continuously testing the strength of cement mixing piles using the static penetration test method are as follows:

[0045] Align the probe d with the center of the reserved detection hole c, fix the probe on the sounding rod, use the static pressure device f to uniformly press the sounding rod e along the PVC pipe b into the cement mixing pile, and use the probe to detect in-situ data, which includes the cone tip resistance and side wall resistance.

[0046] The static penetration data acquisition instrument g is used to read and store the in-situ data of static penetration (cone tip resistance and cone side resistance). The wire connects the static penetration data acquisition instrument g and the probe d.

[0047] The probe has a diameter of 43.7 mm. It is a double-bridge static penetration probe using a resistance strain gauge sensor. The inclination angle error of the probe rod penetrating the cement mixing pile is within 2°.

[0048] Within the test section, 15 bored piles were randomly selected for pile body quality testing. The test results of this method were completely consistent with the results of the core drilling test, and the test success rate reached 100%, proving that this method is successful.

[0049] A quality evaluation method for cement mixing piles:

[0050] (1) During the trial stage of cement mixing piles, within 3 days after the construction of cement mixing piles, the quality of 5% of the cement mixing piles within the inspection range is inspected by using the static penetration test method of cement soil mixing piles within the 3D age period to obtain the corresponding in-situ data of each cement mixing pile.

[0051] (2) The obtained in-situ data were correlated with the 7-day and 28-day core sample compressive strength to evaluate the pile quality of the cement mixing pile.

[0052] Specifically, the process of establishing the corresponding relationship between the in-situ data and the 28-day core sample compressive strength is as follows:

[0053] By conducting static penetration testing and unconfined compressive strength tests on cement-mixed piles (a), and combining the cone tip resistance of the static penetration test with the 28-day unconfined compressive strength, a corresponding relationship between the cone tip resistance and the unconfined compressive strength of different soil layers under a specific process was established, and a standard curve was developed. After successful pile trials, large-scale construction can be carried out using the cone tip resistance obtained from static penetration testing and the 28-day unconfined compressive strength determined using the standard curve to evaluate pile quality.

[0054] Evaluation method for foundation treatment effect of cement mixing piles:

[0055] (1) During the trial stage of cement mixing piles, within 3 days after the construction of cement mixing piles, the quality of 5% of the cement mixing piles within the inspection range is inspected by using the static penetration test method of cement soil mixing piles within the 3D age period to obtain the corresponding in-situ data of each cement mixing pile.

[0056] (2) Compare and analyze the in-situ data with the static penetration data of the soil disturbed by the mixing pile construction to evaluate the effectiveness of the mixing pile in reinforcing the weak foundation. The static penetration data of the soil disturbed by the mixing pile construction can be obtained by directly conducting CPT penetration tests in the soil around the pile.

[0057] Specifically, the effectiveness of cement-soil mixing piles in reinforcing soft soil is evaluated based on the variation in soil penetration resistance before and after construction.

[0058] The method of the present invention has been tried out in the treatment of a domestic highway subgrade with good application effect. It can evaluate the pile quality and the reinforcement effect of soft soil foundation with low cost, high efficiency and low error, and has good application prospects.

[0059] The above description is merely a preferred embodiment of the present invention and does not limit the present invention in any way. Any person skilled in the art who, without departing from the scope of the present invention, makes any equivalent substitution, modification, or other changes to the technical solution and technical content disclosed in the present invention shall be deemed to be within the scope of the present invention and still fall within the scope of protection of the present invention.

Claims

1. A static penetration testing method for cement-soil mixing piles within the 3D age period, characterized in that: The following steps are involved: Step 1: Within 0.5-1h after the construction of the cement mixing pile is completed, a reserved mark is made at the center of the pile body. Then, a PVC pipe with a closed bottom is vertically inserted into the cement mixing pile at a position 1 / 3 of the radius away from the pile center to form a reserved detection hole and mark it; Among them, the length of the PVC pipe is less than the depth of the cement mixing pile; Step 2: When the cement mixing pile reaches a certain age, the pile strength of the cement mixing pile is continuously tested using a static penetration test method, wherein the age of the cement mixing pile ranges from 1 day to 3 days; wherein: Within the age range, different inspection times are selected according to different construction conditions; The construction conditions include mixing pile construction data and construction temperature; The mixing pile construction data refers to the real-time monitoring data of the intelligent terminal during the mixing pile construction, including the shotcrete volume, water-cement ratio, and sinking speed; the construction temperature refers to the surface temperature during the mixing pile construction; The specific steps of continuously testing the pile strength of the cement mixing pile using the static penetration test method are as follows: A probe is aligned with the center of the reserved detection hole, the probe is fixed on the sounding rod, and the sounding rod is uniformly pressed into the cement mixing pile along the PVC pipe using a static pressure device. The in-situ data is detected using the probe, and the in-situ data includes the cone tip resistance and the side wall resistance.

2. The static penetration testing method for cement-soil mixing piles within the 3D age period according to claim 1 is characterized in that: The length of the PVC pipe is 0.3m~0.8m.

3. The static penetration testing method for cement-soil mixing piles within the 3D age period according to claim 1 is characterized in that: The diameter of the PVC tube is 38±1 mm.

4. The static penetration testing method for cement-soil mixing piles within the 3D age period according to claim 1 is characterized in that: The probe has a diameter of 43.7 mm.

5. The static penetration testing method for cement-soil mixing piles within the 3D age period according to claim 1 is characterized in that: The probe is a double-bridge static penetration probe, and the probe adopts a resistance strain gauge sensor.

6. The static penetration testing method for cement-soil mixing piles within the 3D age period according to claim 1 is characterized in that: It also includes a static detection data collector, and a wire connects the static detection data collector and the probe.

7. The static penetration testing method for cement-soil mixing piles within the 3D age period according to claim 1 is characterized in that: The cone tip resistance of the PVC pipe is less than 0.5 MPa, and the side wall resistance is less than 5 kPa.

8. The static penetration testing method for cement-soil mixing piles within the 3D age period according to claim 1 is characterized in that: The error of the inclination angle of the probe rod penetrating the cement mixing pile is within 2°; the PVC pipe is uniformly pressed into the cement mixing pile at a speed of 0.4-1.0 m / min.

9. A quality evaluation method for cement mixing piles, characterized in that: The following steps are involved: (1) During the trial pile stage of cement mixing piles, within 3 days after the construction of cement mixing piles, 5% of the cement mixing piles within the inspection range shall be inspected for quality by the static penetration test method for cement-soil mixing piles within the 3D age period as described in any one of claims 1 to 8, and in-situ data corresponding to each cement mixing pile shall be obtained; (2) The obtained in-situ data were correlated with the 7-day and 28-day core sample compressive strength to evaluate the pile quality of the cement mixing pile.

10. A method for evaluating the foundation treatment effect of cement mixing piles, characterized in that: The following steps are involved: (1) During the trial pile stage of cement mixing piles, within 3 days after the construction of cement mixing piles, 5% of the cement mixing piles within the inspection range shall be inspected for quality by the static penetration test method for cement-soil mixing piles within the 3D age period as described in any one of claims 1 to 8, and in-situ data corresponding to each cement mixing pile shall be obtained; (2) Compare and analyze the in-situ data with the static penetration data of the disturbed soil after the construction of the mixing piles to evaluate the effect of the mixing piles in reinforcing the soft foundation.

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