Method for calculating side friction of pile driven into coral reef geological foundation

Abstract

The application discloses a method for calculating the pile side friction of a coral reef geological driven pile foundation, comprising the following steps: S1, collecting undisturbed coral sand in the field, breaking the undisturbed coral sand by using an indoor pressure crushing test, and quantifying the particle crushing degree of the undisturbed coral sand into a relative crushing rate; S2, measuring the wet density of the coral sand in the design pile foundation point area range of a construction site, and calculating the relative compactness of the coral sand according to the indoor extreme value density test result of the coral sand; S3, establishing a particle crushing correction formula coupled with the relative crushing rate and a loose filling correction formula coupled with the relative compactness; and S4, correcting the pile side friction calculation model and calculating based on the two correction coefficients. According to the method, the coral sand crushing effect and the compacting effect are quantified into the relative crushing rate and the relative compactness by combining tests, the pile side friction calculation model coupled with the particle crushing correction coefficient and the loose filling correction coefficient is constructed, the method is more in line with the data of the construction site, and the pile foundation construction design can be effectively, reliably and accurately guided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of marine geology engineering, geotechnical engineering and port engineering, and is especially suitable for pile foundation design and construction under coral reef geological conditions, and particularly relates to a method for calculating the pile side friction of a driven pile foundation in a coral reef geological condition. BACKGROUND

[0002] As a common stratum in island reef construction engineering, the coral reef stratum has three characteristics of high porosity, high internal friction and easy particle breakage. For medium and large structures with large loads, uneven settlement and other problems are prone to occur due to insufficient bearing strength of the coral reef stratum, which cannot meet the requirements of the foundation bearing stratum, and it is necessary to set a pile foundation for pile end bearing.

[0003] The structural properties and stress changes of the coral reef stratum are different from those of the sand and clay stratum. In the process of pile driving, the particles of the coral reef stratum are broken, and the broken particles have a loose filling effect. According to the existing standard "Port Engineering Pile Foundation Specification" (JTS 167-2018), the calculated pile side friction is often higher than the actual measured value. For example, in the construction design of a certain artificial island, the calculated value of the pile side friction is 50% higher than the actual measured value during construction. It has been proven that the breakage effect and compaction effect of the coral reef stratum cannot be ignored. The existing pile side friction design in the standard is not suitable for the coral reef stratum, which is very unfavorable for the design and construction of island reef engineering.

[0004] The existing technology can be seen as a special design method for the characteristics of the coral reef stratum, such as 202410975986.8 Method for calculating the side resistance of driven piles in coral reef strata and anti-sinking construction device. This technical solution considers the elastic-plastic behavior of coral reef debris and analyzes the side friction of the coral reef shallow layer and deep layer respectively, solving the "pile sliding" and sudden sinking problems in the process of pile driving. For example, CN202311361965.9 Method for calculating the bearing capacity of super-long inclined angle CFG pile in coral reef stratum under heavy load. This technical solution mainly solves the calculation method of the bearing capacity and interface friction of the super-long CFG pile under different degrees of pile body deflection, and considers the influence of different water pressures. Therefore, the material properties of coral reef strata in different regions are different, and the breakage effect and compaction effect in the process of pile driving are also different. The existing technology only determines the stress of the pile foundation based on the basic interface friction characteristics of the coral reef stratum, and does not consider the fundamental influence of the breakage effect and compaction effect on the stress of the pile foundation.

[0005] Therefore, there is an urgent need for a method for calculating the pile side friction of a driven pile foundation in a coral reef geological condition to solve the above problems. SUMMARY

[0006] The present application aims to overcome the defects of the prior art, and provides a pile side friction resistance calculation method for a coral reef geological driven pile foundation, so as to solve the problems in the background art.

[0007] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0008] A pile side friction resistance calculation method for a coral reef geological driven pile foundation, comprising the following contents and steps:

[0009] S1, collecting undisturbed coral sand at the construction site, simulating a multi-level buried depth pressure to implement an undisturbed coral sand indoor pressure crushing test, and quantifying the particle crushing degree as a relative crushing rate ;

[0010] S2, measuring the wet density of the coral sand at the construction site, combining the indoor extreme density test results of the coral sand, and calculating the relative density of the coral sand ;

[0011] S3, establishing a particle crushing correction formula about the relative crushing rate and a loose filling correction formula about the relative density :

[0012] ;

[0013] ;

[0014] wherein, is the particle crushing correction coefficient, is the loose filling correction coefficient, is the peak friction angle of the undisturbed coral sand, is the peak friction angle of the crushed coral sand, k is the crushing influence index, a is the density influence rate, and b is the correction value of the loose state of the coral sand;

[0015] S4, coupling the particle crushing correction coefficient and the loose filling correction coefficient to the pile side friction resistance calculation model to calculate the pile side friction resistance of the i-th layer :

[0016] ;

[0017] wherein, is the effective overburden pressure of the i-th layer, is the interface friction angle between the pile foundation and the coral sand.

[0018] Further, the inversion step S5 of the correction term is further included: first, the actual pile side friction resistance of each layer is measured by the field construction test pile Secondly, based on the actual pile side friction of the same stratum , a particle breakage correction coefficient , and a loose filling correction coefficient As the coefficient to be inverted, the least square method is used to invert the pile side friction calculation model, and the gradient descent method is used to repeatedly solve the iteration to obtain the inversion result that meets the convergence condition. Finally, the particle breakage correction coefficient and the loose filling correction coefficient are corrected, and the pile side friction calculation model is updated.

[0019] Further, the actual pile side friction is collected in the field by using the high-strain dynamic pile test method or the two-way self-balancing method A test pile is constructed in the same stratum at the design pile foundation point or its adjacent range, the test pile is a small-diameter open steel pipe test pile, and at least two test piles are used, and the average value of the test results of all test piles is taken as the result.

[0020] Further, the indoor pressure breakage test uses triaxial shear test, and at least four groups of confining pressures are set for consolidation drainage shear failure test, and the confining pressure ∈ Each group of confining pressure is tested at least three times, and the particle breakage degree under different confining pressures is quantified as the relative breakage rate :

[0021] ;

[0022] Wherein, is the particle content of 0.075 below in the original gradation of the original coral sand, is the particle content of 0.075 below in the original coral sand after the indoor pressure breakage test;

[0023] The relative breakage rate under the same confining pressure The average value of the results is taken to obtain a plurality of relative breakage rates corresponding to different strata .

[0024] Further, the relative density Based on the wet density determination within the range of 0-2D of the design pile foundation point, D is the design pile diameter of the pile foundation; the maximum dry density and the minimum dry density of the coral sand are obtained by implementing the extreme density test after pretreatment of the coral sand, and the relative density is calculated: Wherein, is the wet density;

[0025] The pretreatment includes drying, grading saturation and re-drying of the coral sand in sequence, which is used to eliminate the influence of the easily soluble salt adsorbed on the coral sand.

[0026] Further, the diameter d of the test pile satisfies the condition: 0.25D≤d≤0.4D, and D is the design pile diameter of the pile foundation.

[0027] Further, the interface friction angle The interface friction angle is obtained by a pile foundation-coral sand interface shear box test; when the test condition is not available, the interface friction angle is assigned .

[0028] Further, when the relevant experiments or measurements of steps S1 and S2 cannot be performed, the step 3 is assigned by default, wherein the particle crushing correction coefficient is assigned , the loose filling correction coefficient is assigned , and the pile side friction calculation result is checked by a test pile.

[0029] Compared with the prior art, the pile side friction calculation method of the pile foundation driven into the coral reef geological structure has the following beneficial effects:

[0030] 1. The crushing effect and the compaction effect of the coral sand are quantified as the relative crushing rate and the relative density to construct the calculation formula of the particle crushing correction coefficient coupled with the relative crushing rate and the loose filling correction coefficient coupled with the relative density, the original specification formula of the pile side friction is corrected by introducing the correction coefficient, the calculation value of the pile side friction is more consistent with the data on the construction site, and the pile foundation construction design can be effectively, reliably and accurately guided;

[0031] 2. For the construction of the conventional island reef or the conventional coral sand region, the triaxial shear test, the wet density and the indoor extreme density test can be performed to design the pile construction parameters, the test workload is small, the efficiency is high, the economy is good, and the flexibility is high, and the operation demand of the window period of the far sea island can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The flowchart of the pile side friction calculation method disclosed in the present application is shown. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only the best embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0034] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all referring to a particular embodiment logically divided into parts. It is explicitly contemplated that embodiments described herein can be combined with each other in various combinations.

[0035] Embodiment One: This embodiment provides a method for calculating the pile side friction of a coral reef geologic driven pile foundation, as shown in Figure 1 , including the following contents and steps:

[0036] S1, quantifying the particle crushing degree of coral sand according to the indoor pressure crushing test; collecting at least 50 kg of undisturbed coral sand at the construction site, and the collection points should cover at least the test pile point and its pile circumference, keeping the natural moisture content and natural gradation of the undisturbed coral sand, determining the initial gradation, and using a high-pressure triaxial apparatus to perform triaxial shear test in a consolidated drained shear mode; divide the undisturbed coral sand into at least 12 equal crushing test samples with the same gradation, design the surrounding pressure ∈ in sections according to the buried depth, test the crushing rate of coral sand under surrounding pressures of at least 50 MPa, 100 MPa, 200 MPa, and 400 MPa, respectively, and repeat the test at least three times for each surrounding pressure to obtain the average particle crushing degree of the coral sand under the same surrounding pressure, quantified by the relative crushing rate :

[0037] (1)

[0038] In formula (1), is the particle content of the undisturbed coral sand below 0.075 mm in the original gradation, is the particle content of the undisturbed coral sand below 0.075 mm after triaxial shear test;

[0039] obtain the relative crushing rates , , and ...... under different surrounding pressures;

[0040] S2, use a nuclear density meter to determine the wet density within the range of 0-2D of the design pile foundation point at the construction site, D is the design pile diameter of the pile foundation, and at least three different points are determined, and the wet density is the average value of the determination results; collect undisturbed coral sand for indoor extreme density test, and according to the ASTM D4253 standard and ASTM D4254 standard test formulated by the American Society for Testing and Materials, respectively obtain the minimum dry density and the maximum dry density , the relative density Quantitative expression of the compacting effect of coral sand pile loose filling:

[0041] (2)

[0042] In order to eliminate the influence of easily soluble salt adsorbed by coral sand on the indoor extreme density test, the coral sand sample needs to be pretreated before the test. First, the coral sand is dried to remove its own moisture; Set up multiple different concentrations of dissolved solution, and then saturate the dried coral sand with easily soluble salt and fully dissolve the easily soluble salt; After separating the easily soluble salt from the coral sand, re-dry it to completely eliminate the influence of easily soluble salt;

[0043] S3, the particle breakage correction formula about the relative breakage rate and the loose filling correction formula about the relative density :

[0044] (3)

[0045] Combined with the results of triaxial shear test, the relative breakage rate and the corresponding breakage peak friction angle of coral sand when breaking are fitted, that is, according to , , and ......, the peak friction angle of coral sand with different breakage degrees is obtained in turn , , , and ......, and the relationship model between the two is obtained after fitting:

[0046] (4)

[0047] In formula (3) and formula (4), is the particle breakage correction coefficient, is the peak friction angle of the original coral sand, generally 50°~58°;

[0048] The relationship formula of - is established, the relative density has a linear change on the influence of pile side friction, according to the result data of step S2, the relationship formula of coupling relative density can be obtained by combining the model pile test results and statistical regression:

[0049] (5)

[0050] In formula (5), is the loose filling correction coefficient, a is the density influence rate, and b is the correction value of the loose state of the coral sand;

[0051] S4, according to the above relationship formula, the relative crushing rate under the corresponding confining pressure is obtained by combining the test and the relative density , the particle crushing correction coefficient and the loose filling correction coefficient are coupled to the pile side friction calculation model to calculate the pile side friction of the corresponding stratum :

[0052] (6)

[0053] In formula (6), is the calculated value of the pile side friction at the i-th layer, is the effective overburden pressure of the i-th layer, is the interface friction angle between the pile foundation and the coral sand, which is obtained by the interface shear box test of the pile foundation-coral sand. In the case where the test conditions are not met, the interface friction angle can be assigned by default, that is, =0.75 ;

[0054] According to the construction experience of some islands and reefs in the sea, the particle crushing correction coefficient is: , Generally between 50° and 58°; the loose filling correction coefficient is: ; for the to-be-developed islands and reefs with small distance span and developed experience, the particle crushing correction coefficient and the loose filling correction coefficient can be obtained by using the developed island and reef correction coefficient calculation according to the test results of the relative crushing rate and the relative density , and substituted into the calculation model of the pile side friction to calculate the calculated pile side friction of each stratum, and then according to the design pile diameter and pile length of the pile foundation, the total pile side friction of the single pile is calculated;

[0055] Application example: according to the above method and steps, the pile foundation construction design of an island is carried out:

[0056] The pile foundation adopts 800mm PHC pipe pile, the test pile diameter is 250mm, the coral sand of the island in the region is collected, the relative crushing rate under one confining pressure is calculated according to step S1 is 0.22, the relative density is calculated according to step S2 is 0.34, the average value of the peak friction angle of the unbroken coral sand is 55°, and under the confining pressure is calculated;

[0057] At the same time, ;

[0058] The pile side friction of the stratum is calculated to be 43.53 KPa;

[0059] Therefore, the crushing rate under the remaining confining pressure is tested, and the pile side friction of each segmented stratum is solved, and the total pile side friction is obtained by integral summation.

[0060] Example Two: For islands with a large development area or significant differences in coral sand properties, the relative crushing rate and the relative density of the coral sand in the area are combined with the actual pile side friction measured by the field construction test pile and as the coefficients to be inverted, and the calculation model of the pile side friction of the same stratum is iteratively inverted based on the actual pile side friction to correct the particle crushing modification and loose filling modification, and update the pile side friction calculation model; specifically, as shown in Figure 1 , the pile side friction calculation model in the pile driving design of the different areas also needs to be confirmed through the S5 step:

[0061] S51, the actual pile side friction of the ith layer is measured by the field construction test pile ; the actual pile side friction is collected on site using high-strain dynamic pile testing or two-way self-balancing method, and any of the collection methods or a combination of both is flexibly used for testing according to the actual conditions on site, the test pile uses a small-diameter open steel pipe test pile, and at least two, and the diameter d of the small-diameter open steel pipe test pile should meet: 0.25D ≤ d ≤ 0.4D, two test piles are implemented at the same test point, the test pile depth is consistent, and the average value of the two test pile results is taken as the actual pile side friction ;

[0062] S52, based on the actual pile side friction , the calculation model of the pile side friction of the same stratum is iteratively inverted with and as the coefficients to be inverted; first, according to the tests of steps S1 and S2 and the construction empirical formula, the two correction coefficients are initially valued as and , and the pile side friction is calculated according to the calculation model;

[0063] According to the least squares method, the best function matching of the data is found by minimizing the sum of squares of errors, an error function is constructed, a partial derivative equation of the error and the coefficients to be inverted is established, and a convergence condition is set: The optimal particle breakage correction coefficient is obtained by repeatedly iterating and updating the coefficients to be inverted using the gradient descent method until the convergence condition is met. and optimal loose fill correction factor ;

[0064] S53, Based on the optimal particle breakage correction coefficient and optimal loose fill correction factor Combined with relative breakage rate and relative density Based on the experimental results, two correction terms were fitted to determine the k value in the particle fragmentation correction term and the a and b values ​​in the loose filling correction term for the coral sand of the island reef. A calculation model for pile side friction coupling the coral sand fragmentation effect and the loose filling effect was then determined.

[0065] (7)

[0066] Using the design pile diameter and pile length of the pile foundation, calculate the total side friction of a single pile.

[0067] Application example: Using the islands and reefs from Example 1 for inversion correction:

[0068] Similarly, the relative fragmentation rate of a certain stratum under confining pressure The value is 0.22. The relative density is calculated according to step S2. The average peak friction angle of unbroken coral sand is 0.34. The angle is 55°, based on the empirical formula for particle crushing and trimming. Assign initial values, ;

[0069] Based on the empirical formula for loose filling repair... Assign initial values, ;

[0070] According to step S4, test piles were tested to obtain the average actual pile side friction of two test piles in multiple strata. And inversion to obtain a certain stratum , The values ​​of k, a, and b were corrected; the pile side friction calculation model was updated, and the pile diameter and length were substituted and integrated to obtain a total side friction of 1.97MN for a single pile, which is 38% lower than the calculation result of the original standard formula. According to the static load test error analysis, the error of the total side friction of a single pile calculated by the corrected pile side friction calculation model is 4.7%, which meets the engineering requirements.

[0071] Embodiment three: for construction site with insufficient test conditions or test time, the initial correction value of the characteristics of coral sand cannot be assigned according to step S1 and step S2, then step S6 is implemented, and step S3 is assigned by default: according to experience, the default particle crushing correction coefficient is assigned as 0.55, the default loose filling correction coefficient is assigned as 0.65, and a test pile is supplemented for checking, the pile side friction calculation model is corrected, and it is ensured that the error of the calculation result of the side friction is within 10%.

[0072] Application example: according to the above method and steps, a pile foundation construction design is performed on a certain island abroad: because there is no triaxial equipment on site, the default values = 0.65 are used; two test piles are supplemented for checking during the construction stage, the corrected pile side friction calculation value is analyzed through subsequent static load tests, the error is controlled within 6.1%, and the engineering requirements are met.

[0073] Through the description of the above embodiments, those skilled in the art can clearly understand that the embodiments of the present application can be realized by means of software or software combined with necessary general hardware platforms, and of course, they can also be realized by hardware functions. Based on this understanding, the technical solutions of the present application can be embodied in the form of a software product, which is stored in a storage medium and includes a plurality of instructions for causing a computer device, such as a personal computer, a server, or a network device, to execute all or part of the steps of the method described in any embodiment of the present application.

[0074] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.​​​

Claims

1. A method for calculating the pile side friction of driven pile foundations in coral reef geology, characterized in that, Includes the following steps and content: S1. Collect undisturbed coral sand from the construction site and conduct an indoor pressure crushing test on the undisturbed coral sand, simulating multi-level burial depth pressure, to quantify the degree of particle crushing as a relative crushing rate. ; S2. Determine the wet density of the coral sand at the construction site, and calculate the relative density of the coral sand based on the results of the indoor extreme density test. ; S3. Establish information regarding relative breakage rate Particle crushing repair and relative density Loose filling repair: ； ； in, This is the correction factor for particle breakage. For loose filling correction factor, The peak friction angle of the undisturbed coral sand is ( ) represents the peak friction angle of the broken coral sand, k represents the breakage influence index, a represents the density influence rate, and b represents the correction value of the coral sand in the loose state. S4. Adjust the particle breakage correction coefficient. and the loose filling correction factor Coupled to the pile side skin friction calculation model, calculate the pile side skin friction of the i-th layer. : ； in, The effective overburden pressure of the i-th layer is... The angle of friction between the pile foundation and the coral sand is denoted as .

2. The method for calculating the pile side friction of a driven pile foundation in coral reef geology according to claim 1, characterized in that: It also includes the inversion step S5 for the correction term: First, the actual pile side friction of each stratum is measured in the field during test pile construction. Secondly, the actual pile side friction based on the same stratum. With the particle breakage correction coefficient and the loose filling correction factor As the coefficients to be inverted, the pile side friction calculation model is inverted using the least squares method, and the gradient descent method is used to iteratively solve the problem to obtain the inversion results that meet the convergence conditions. Finally, the particle breakage modification form and the loose filling modification form are corrected to update the pile side friction calculation model.

3. The method for calculating the pile side friction of a driven pile foundation in coral reef geology according to claim 2, characterized in that: The actual pile side friction was collected on-site using either the high-strain dynamic pile test method or the two-way self-balancing method. Test piles are constructed in the same stratum at or around the designed pile foundation point. The test piles are small-diameter open steel pipe test piles, and there are at least two of them. The result is the average of the test results of all the test piles.

4. The method for calculating the pile side friction of a driven pile foundation in coral reef geology according to claim 1, characterized in that: The indoor pressure failure test employs a triaxial shear test, and at least four sets of confining pressures are used for consolidated drained shear failure testing. The confining pressures ∈ The test was repeated at least three times under each confining pressure, and the degree of particle breakage under different confining pressures was quantified as the relative breakage rate. : ； in, The content of particles smaller than 0.075 in the original gradation of the undisturbed coral sand. The particle content of the undisturbed coral sand below 0.075 after the indoor pressure crushing test; The relative breakage rate under the same confining pressure The average of the results is taken to obtain the relative fragmentation rates corresponding to different strata. .

5. The method for calculating the pile side friction of a driven pile foundation in coral reef geology according to claim 1, characterized in that: The relative density Based on the wet density measurement within the 0-2D range of the designed pile foundation points, where D is the designed pile diameter; the coral sand, after pretreatment, underwent the indoor extreme density test to obtain its maximum dry density. and minimum dry density Calculate the relative density: ,in, The wet density; The pretreatment process includes drying, grading and saturation of the coral sand, and re-drying, in order to eliminate the influence of easily soluble salts adsorbed on the coral sand.

6. The method for calculating the pile side friction of a driven pile foundation in coral reef geology according to claim 3, characterized in that: The diameter d of the test pile satisfies the condition: 0.25D≤d≤0.4D, where D is the design pile diameter of the pile foundation.

7. The method for calculating the pile side friction of a driven pile foundation in coral reef geology according to any one of claims 1 to 6, characterized in that: Under test conditions, the interface friction angle The interface friction angle was obtained through a shear box test of the pile foundation-coral sand interface; when the test conditions were not available, the interface friction angle was assigned. .

8. The method for calculating the pile side friction of a driven pile foundation in coral reef geology according to any one of claims 2 to 6, characterized in that: When the relevant experiments or measurements in steps S1 and S2 cannot be performed, a default value is assigned to step 3, wherein the particle breakage correction coefficient is assigned a value. The loose filling correction coefficient is assigned a value. The calculation results of the pile side friction were verified by test piles.

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