Calculation method of end bearing force of coral reef geological bored pile

Abstract

The application discloses a method for calculating end bearing force of a coral reef geological bored cast-in-place pile, which comprises the following steps: S1, collecting an original coral reef core on site and measuring its porosity; S2, determining the effective radius of the coral reef rock under conventional cast-in-place construction conditions according to a relational expression; S3, experimentally determining the shear strength of the coral reef rock mass and the interface shear strength of the cement slurry infiltrated into the cementation interface of the coral reef rock; and S4, comprehensively considering the self-bearing capacity of the coral reef rock mass, the bearing capacity of the cementation interface and the effective stress of the pile end, and establishing an end bearing force calculation formula of the bored cast-in-place pile. The method quantifies the "pore-cementation" effect of the coral reef and incorporates it into the end bearing force calculation formula, the error between the calculation result and the measured value meets the engineering design requirement, the deviation of the result calculated according to the traditional specification is significantly reduced, and it is indicated that the parameter determination method and the end bearing force calculation formula provided by the method are more in line with the actual construction conditions of the coral reef rock, the method has strong operability, good economy, high efficiency and good compatibility with the existing specification.

Description

Technical Field

[0001] This invention relates to the fields of marine geological engineering, geotechnical engineering, and port engineering, and is particularly applicable to the design and construction of cast-in-place piles under coral reef geological conditions. Specifically, it refers to a method for calculating the end bearing capacity of drilled cast-in-place piles in coral reef geological conditions. Background Technology

[0002] Coral reef geology is a common geological feature in marine environments. Coral reef rocks exhibit "weak cementation and high porosity," which cannot meet the requirements for foundation bearing layers. In marine engineering construction, pile foundations are required. Ordinary pile foundations are prone to compressive-shear failure within 3D to 5D (D is the pile diameter) below the pile tip. Drilled cast-in-place piles, through permeation, can enhance the bearing strength of the coral reef rock below the pile tip. Therefore, drilled cast-in-place piles are a commonly used foundation form in coral reef geology. However, there are no existing standards for calculating the pile tip bearing capacity of drilled cast-in-place piles in reef geology. Traditional designs treat coral reefs as ordinary sandstone or siliceous sand, directly using existing design standards for ordinary sandstone or embedded piles for calculations.

[0003] After drilling and grouting, a cement grout-coral bonded reinforcing ring will form on the borehole wall of the cast-in-place pile. The cement grout seeps into the pores to form an interface reinforcement. The end bearing capacity of the cast-in-place pile is contributed by the strength of the rock mass and the strength of the bonded interface. Therefore, for reef geological conditions, if the existing specifications are used for the design of the cast-in-place pile, the end bearing capacity deviation will be more than 30%. This will not only increase the scale of the marine engineering foundation and lead to an increase in construction costs, but also prolong the construction period, which is unfavorable for safe operation in harsh marine environments.

[0004] Therefore, this paper provides an accurate method for calculating the end bearing capacity of bored cast-in-place piles in coral reef geology, which is of vital importance for the design of cast-in-place piles. Summary of the Invention

[0005] The purpose of this invention is to overcome the deficiencies of the prior art and provide a method for calculating the end bearing capacity of drilled piles in coral reef geology, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for calculating the end bearing capacity of drilled piles in coral reef geology includes the following contents and steps:

[0008] S1. Collect undisturbed coral reef core samples on-site and determine their porosity n;

[0009] S2, according to r c The relationship between -n determines the effective radius r of coral reefs under conventional grouting construction conditions. c :

[0010] ;

[0011] Where a is the permeability radius bias parameter and b is the porosity weight parameter;

[0012] S3. Test to determine the shear strength of coral reef rock mass. and the interfacial shear strength of the cemented interface where cement grout penetrates into the coral reef rock. ;

[0013] S4. Based on the bearing capacity of the coral reef rock mass itself, the bearing capacity of the cemented interface, and the effective stress at the pile tip, a formula for calculating the end bearing capacity of bored cast-in-place piles is established:

[0014] ;

[0015] in, For end bearing, The cross-sectional area of ​​the pile tip. This is the strength reduction factor for coral reef rock mass. Where is the reduction factor for the strength of the cemented interface, and D is the design diameter of the cast-in-place pile. This represents the effective vertical stress at the pile end.

[0016] Furthermore, the porosity was determined by the saturated water weighing method, and the saturated porosity n1 was calculated.

[0017] Furthermore, the porosity was determined by mercury intrusion porosimetry, and the mercury intrusion porosimetry porosity n2 was calculated.

[0018] Furthermore, when the relative error between the water-saturated porosity n1 and the mercury porosity n2 is less than 5%, the porosity n = n1.

[0019] Furthermore, when the relative error between the saturated porosity n1 and the mercury porosity n2 is equal to or exceeds 5%, the porosity n is determined by a combination of the saturated water weighing method and CT scanning.

[0020] ;

[0021] Where n3 is the scanning porosity determined by CT scanning, and k is the weighting coefficient.

[0022] Furthermore, saturated coral core samples were collected directly below the pile tip, and the unconfined compressive strength of the coral reef rock mass was determined through saturated unconfined compressive strength tests. and shear strength , create a region - Empirical formula; collect magmatic rock cores from the same stratum directly below the pile tip and determine their shear strength through shear cell tests. , create a region - The formula is used to quickly determine the shear strength of the bonded interface. .

[0023] Furthermore, following standard engineering conditions, cement grout was injected into boreholes on-site, and the effective radius r of the cement grout penetrating into the coral reef rock mass to form a cemented interface was determined. c The porosity n of undisturbed coral reef cores near the injection test points was measured to determine the regional r. c -n relational expression.

[0024] Furthermore, when the unconfined compressive strength of saturated coral reef cores... At 1MPa, .

[0025] Compared with the prior art, the method for calculating the end bearing capacity of drilled piles in coral reef geology according to the present invention has the following beneficial effects:

[0026] This method quantifies the "pore-cementation" effect of coral reefs and incorporates it into the end bearing capacity calculation formula. The calculation results can be directly used for the end bearing capacity design of borehole piles in coral geology. The error between the calculated results and the measured values ​​meets the engineering design requirements, significantly reducing the deviation of the results calculated according to traditional specifications. This indicates that the parameter determination method and end bearing capacity calculation formula provided by this method are more in line with the actual construction conditions of coral reefs. Moreover, this method is highly operable, economical, efficient, and compatible with current specifications. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method for calculating the end bearing capacity of bored cast-in-place piles disclosed in this invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely the best embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The term "embodiment" as used herein means that a particular method, step, or content described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0030] This embodiment provides a method for calculating the end bearing capacity of drilled cast-in-place piles in coral reef geology. Coral reef rocks, during diagenesis, form cemented pores with strong connectivity. There is a positive correlation between porosity and permeability radius. Extensive test data on coral reef rocks show that, within the porosity range of 0.2 ≤ porosity n ≤ 0.5, after calcification and cementation, the permeability radius of cement slurry exhibits a linear relationship with porosity under conventional engineering conditions. Therefore, the permeability radius r of the cement slurry is... c Using porosity (n) as a fundamental characteristic, a database of key features of regional coral reef rocks was established, and statistical regression was used to construct regional r. c The -n relationship is used in marine engineering construction in this region or neighboring regions with relatively similar geological environments. Porosity is measured by collecting undisturbed coral reef rocks on-site, based on r... c The -n relational formula estimates the cement grout penetration radius without requiring on-site grouting tests. Therefore, it is unaffected by weather and construction schedule windows, offering high flexibility in preparation and significantly shortening the engineering design cycle while improving construction efficiency. Thus, this embodiment combines conventional testing, quantifying the effective radius of the cement grout-bonded penetration zone through porosity, and comprehensively considering the bearing capacity of the coral reef rock mass, the bearing capacity of the cemented interface, and the effective stress at the pile tip to determine the bearing capacity of the pile end of the coral reef borehole. This serves as the best example embodiment. Figure 1 As shown, specifically, it includes the following steps and contents:

[0031] S0, Establishing regional coral reefs c -n Relationship: First, grout-bearing core samples are prepared on-site. Cement grout is injected into boreholes under standard engineering conditions (i.e., water-cement ratio of 0.45~0.55, grouting pressure 0.2 MPa~0.4 MPa). The injection test points not only cover the vicinity of the designed construction pile points but also distribute evenly across multiple islands and reefs in the area. The drilling depth is the pile tip depth, the borehole diameter is φ110mm, and the grouting volume reaches 1 / 20 of the designed single-pile grouting volume. Core samples containing grout are obtained after 24 hours. The sample size is φ75mm. The effective radius r of the infiltration zone can be determined using the tracer method or the CT-seepage coupling inversion method. c The tracer method involves injecting cement slurry containing fluorescent tracers and measuring the thickness of the fluorescent ring in the magma-bearing rock core under ultraviolet light irradiation to determine the effective radius; the CT-seepage coupling inversion method uses the total volume of the infiltration zone determined by CT scanning to infer the effective radius.

[0032] Secondly, collect undisturbed coral cores near the injection test points and determine their corresponding porosity n according to step S1.

[0033] Finally, statistical regression was performed based on the test data to establish the r-value for this region. c -n relation:

[0034] (1)

[0035] In equation (1), a is the permeability radius bias parameter and b is the porosity weight parameter;

[0036] Understandably, for regions with existing feature databases, and having established a region r c For -n relational expressions, the S0 step can be omitted;

[0037] S1. According to the construction plan, undisturbed coral reef core samples were collected near the design pile points to determine their porosity (n). Porosity determination methods included saturated water weighing, mercury intrusion porosimetry, and CT scanning. Any one of these methods could be used depending on the test conditions. As the best example for this implementation, the porosity was determined using a "combined three-step method"; that is, the optimal porosity was determined by combining the saturated water weighing method, mercury intrusion porosimetry, and CT scanning. Since the "in-situ" porosity value better reflects the actual permeability and cementation performance, while laboratory samples only represent "apparent" porosity values, and coral reef rocks have strong pore connectivity, sampling disturbances can significantly underestimate the porosity. Therefore, the "combined three-step method" can effectively ensure the accuracy of the porosity determination results.

[0038] S11. The saturated porosity n1 is obtained as the lower limit by the saturated water weighing method: the undisturbed coral reef core is dried at 100℃-105℃ for 24 hours to obtain the dry mass m. d A 24-hour water saturation test was conducted under vacuum conditions to obtain the saturated water mass m. w ;

[0039] Calculate the saturated porosity n1 using the formula for saturated porosity:

[0040] (2)

[0041] In equation (2), For the density of water, This represents the total volume of the coral reef core sample.

[0042] S12. Obtain the upper limit value of mercury intrusion porosimetry porosimetry n2 as the upper limit value: Cut the original coral reef rock core into several 10mm thick slices and dry them. Test and calculate the mercury intrusion porosimetry porosimetry n2 according to the mercury intrusion porosimetry (MIP) test specifications.

[0043] Analyze the relative error of the upper and lower limits ,when When the saturated porosity n1 obtained by the saturated water weighing method is considered to basically reflect the in-situ value, n1 is directly used as the optimal porosity n; when At that time, CT scans were used for further identification;

[0044] S13. Confirmation of optimal porosity n using combined CT scanning:

[0045] An industrial CT scanner with a resolution of 18μm was used to perform three-dimensional scanning and reconstruction of the original coral reef core, and the scanning porosity n3 was obtained by local threshold segmentation.

[0046] By combining the results of the saturated weighing method and the CT scan results using the combined formula (3), the "isolated pores" and "connected pores" of coral reef rocks are unified to an operable optimal porosity n:

[0047] (3)

[0048] In equation (3), k is the weighting coefficient, which is generally taken as 0.6~0.8, and the recommended value is 0.7;

[0049] S2, based on the region's r c -n relation (1), calculate the effective radius r of coral reef under conventional grouting construction conditions. c ;

[0050] S3. Collect coral reef rock cores directly below the pile tip and determine the shear strength of the coral reef rock mass through shear tests. ;

[0051] Cement interface samples were collected from the cement grout infiltrating the coral reef rock directly below the pile tip, and the interfacial shear strength was determined by interfacial shear box tests. The interfacial shear box test was conducted under saturation conditions, with normal stress ranging from 20 kPa to 400 kPa. The peak shear strength was taken as the result. ;

[0052] S4. Based on the results of steps S2 and S3, establish a calculation formula for the bearing capacity of bored pile ends, which integrates the bearing capacity of the coral reef rock mass, the bearing capacity of the cemented interface, and the effective stress at the pile tip:

[0053] (4)

[0054] in, For end bearing, The cross-sectional area of ​​the pile tip. The strength reduction factor for coral reef rock mass is taken as 0.5~0.65; The strength reduction factor for the cemented interface is taken as 0.7~0.85; Where is the pore-cement coupling coefficient, and D is the design diameter of the cast-in-place pile. This represents the effective vertical stress at the pile end.

[0055] S5, the regional database of coral reef geology also includes the shear strength characteristics of raw rocks and the shear strength characteristics of grout cores after cement grout penetration and strengthening. Through test data, regional strength empirical formulas are established to reduce on-site grouting test steps and facilitate rapid engineering design calculations in the same or adjacent regions.

[0056] This study investigates the empirical relationship between the shear strength and unconfined compressive strength of undisturbed coral reefs under common engineering conditions (grouting pressure 0.2 MPa ~ 0.4 MPa, cement grout water-cement ratio 0.45 ~ 0.55), and the empirical relationship between the cemented shear strength of magma-bearing cores and the unconfined compressive strength of undisturbed coral reefs.

[0057] Unconfined compressive strength of the coral reef rock mass was determined by collecting undisturbed saturated coral core samples directly below the pile tip and conducting saturated unconfined compressive strength tests. The saturated unconfined compressive strength test was performed according to GB / T 50266-2013 Standard for Testing Methods of Engineering Rock Mass; simultaneously, the shear strength was determined through shear tests. , fitting and establishing - Relationship:

[0058] (5)

[0059] Similarly, following step S0, on-site grouting was carried out, and magmatic rock cores were collected from the same stratum directly below the pile tip. The shear strength of the magmatic rock cores was determined through shear box tests. Based on the corresponding unconfined compressive strength data mentioned above, linear fitting was used to obtain... - Relationship:

[0060] (6)

[0061] In equation (5), The shear-compression ratio of the undisturbed coral core; in equation (6), The shear-compression ratio is between the magmatic rock core and the undisturbed coral rock core.

[0062] Based on empirical formulas, for developed islands and reefs, only undisturbed coral reef rocks need to be collected and the porosity and unconfined compressive strength are measured to deduce the remaining characteristic values. This provides strong flexibility and operability in the design stage, significantly simplifies the testing and calculation process of engineering design, and the calculation results of the end bearing capacity of the cast-in-place piles are highly accurate and compatible with current specifications.

[0063] Understandably, when the unconfined compressive strength of coral reefs... At 1 MPa, the coral reef rock is considered to be low-cementation coral sand, making... The bearing capacity of the rock mass itself is not considered.

[0064] For undeveloped islands and reefs lacking testing conditions, default empirical formulas can be used to calculate the end bearing capacity of cast-in-place piles, and pile testing can be conducted during the construction phase for verification. The default empirical formulas are as follows: ; ; ; Take 0.55, Take 0.8.

[0065] Application Example: Drilled cast-in-place piles with a diameter D=1.0 m were installed on an island reef. Strength tests of the undisturbed coral reef rock yielded... The porosity n=0.35 was determined using a "combined three-step method" based on the empirical formula: Calculate and obtain the effective radius. , According to the empirical formula for strength , , Take 0.6, Taking 0.8, substituting it into equation (4) yields the end bearing capacity. The static load test on site yielded a measured value of 4.8MN for the same pile end depth. The error between the calculated result and the measured value was approximately 2%, which meets the engineering design requirements.

[0066] Through the above description of the embodiments, those skilled in the art can clearly understand that the various embodiments of this application can be implemented by means of software or software combined with necessary general-purpose hardware platforms, and of course, they can also be implemented by hardware functions. Based on this understanding, the technical solution of this application, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. The software product is stored in a storage medium and includes several instructions to cause a computer device, such as including but not limited to a personal computer, server, or network device, to execute all or part of the steps of the method described in any embodiment of this application.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for calculating the end bearing capacity of drilled cast-in-place piles in coral reef geological formations, characterized in that, Includes the following steps and content: S1. Collect undisturbed coral reef core samples on-site and determine their porosity n; S2, according to r c The effective radius r of the coral reef under grouting conditions is determined by the relationship -n. c : ； Where a is the permeability radius bias parameter and b is the porosity weight parameter; S3. Test to determine the shear strength of coral reef rock mass. and the interfacial shear strength of the cemented interface where cement grout penetrates into the coral reef rock. ; S4. Based on the bearing capacity of the coral reef rock mass itself, the bearing capacity of the cemented interface, and the effective stress at the pile tip, establish the calculation formula for the bearing capacity at the end of the bored pile: ； in, For end bearing, The cross-sectional area of ​​the pile tip. This is the strength reduction factor for the coral reef rock mass. The strength reduction factor of the cemented interface is given, and D is the design diameter of the cast-in-place pile. This represents the effective vertical stress at the pile end.

2. The method for calculating the end bearing capacity of borehole piles in coral reef geological drilling as described in claim 1, characterized in that: The porosity was determined by the saturated water weighing method, and the saturated porosity n1 was calculated.

3. The method for calculating the end bearing capacity of borehole piles in coral reef geological drilling according to claim 2, characterized in that: The porosity was determined by mercury intrusion porosimetry, and the mercury intrusion porosimetry porosity n2 was calculated.

4. The method for calculating the end bearing capacity of borehole piles in coral reef geological drilling according to claim 3, characterized in that: When the relative error between the water-saturated porosity n1 and the mercury porosity n2 is less than 5%, the porosity n = n1.

5. The method for calculating the end bearing capacity of drilled piles in coral reef geological formations according to claim 4, characterized in that: When the relative error between the saturated porosity n1 and the mercury porosity n2 is equal to or exceeds 5%, the porosity n is determined by the saturated weighing method combined with CT scanning. ； Where n3 is the scanning porosity determined by CT scanning, and k is the weighting coefficient.

6. The method for calculating the end bearing capacity of borehole piles in coral reef geological drilling according to claim 1, characterized in that: A saturated coral rock core was collected directly below the pile tip, and the unconfined compressive strength of the coral reef rock mass was determined by a saturated unconfined compressive strength test. and the shear strength , create a region - The relationship is as follows: Collect magmatic rock cores from the same stratum directly below the pile tip, and determine the shear strength using a shear cell test. , create a region - The relationship is used to quickly determine the shear strength of the cemented interface. .

7. The method for calculating the end bearing capacity of borehole piles in coral reef geological drilling according to claim 5, characterized in that: Cement grout was injected into the site using conventional engineering conditions through drilling, and the effective radius r of the cement grout penetrating the coral reef rock mass to form the cemented interface was measured. c The porosity n of the undisturbed coral reef core near the injection test point was measured to determine the regional r. c -n relational expression.

8. The method for calculating the end bearing capacity of borehole piles in coral reef geological drilling according to claim 6, characterized in that: When the unconfined compressive strength of the saturated coral core At 1MPa, .

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