Calculation method of side friction of coral reef geological bored pile

Abstract

The application discloses a method for calculating side friction of a coral reef geological bored filling pile, and comprises the following steps: S1, field filling construction, collecting slurry-containing rock core samples, and determining an effective radius; S2, determining the interface friction angle of concrete-coral reef rock of each stratum and the cementation shear strength of the slurry-containing rock core; S3, according to the effective radius, the slurry occlusion area coefficient is obtained, the interface friction and the cementation additional friction are comprehensively considered, and a side friction calculation formula is established; the method combines the field filling test, quantifies the penetration-cementation occlusion effect of the cement slurry in the coral reef rock, comprehensively considers the additional friction caused by the cementation effect, modifies the side friction calculation formula of the traditional filling pile, solves the problem that the bearing capacity of the coral reef stratum is significantly underestimated in the traditional design calculation, and reliably and accurately guides the filling pile construction design; all tests can be completed within 48 hours on site, and the cost of offshore exploration can be significantly reduced.

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 the design and construction of bored piles in coral reef geological conditions, and particularly relates to a method for calculating the side friction of a bored pile in coral reef geological conditions. BACKGROUND

[0002] As a common geological environment in marine environment, coral reef geology has characteristics such as high porosity, high internal friction and high permeability, and cannot meet the requirements of being a foundation bearing layer. In the construction of marine engineering, pile foundations need to be set. There is no existing specification that can be directly used for the calculation method of the side friction of a bored pile in reef geological conditions. In the traditional design, the coral reef is regarded as ordinary sandstone or siliceous sand, and the existing design specification of the sand soil pile foundation is directly used for calculation.

[0003] The side friction of a bored pile mainly includes the interface friction between the rock-soil and the concrete and the additional friction caused by the cement slurry penetration and cementation. In the construction process of a bored pile, the concrete will spread to the surrounding soil, produce cementation force, improve the friction between the pile foundation and the surrounding reef, and the existing patents and documents have not yet proposed a method for quantifying the "cement slurry penetration-cementation" effect as a measurable parameter and including it in the calculation, resulting in that the calculated value of the side friction of a bored pile is generally 30% to 50% lower than the measured value.

[0004] Therefore, the present application provides an accurate method for calculating the side friction of a bored pile in coral reef geological conditions, which plays a crucial role in the design of a bored pile. SUMMARY

[0005] The present application aims to overcome the defects of the prior art and provide a method for calculating the side friction of a bored pile in coral reef geological conditions to solve the problems in the background.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A method for calculating the side friction of a bored pile in coral reef geological conditions, comprising the following contents and steps:

[0008] S1, determining the effective radius: a test hole is processed to the depth of the pile end near the site pile position, cement slurry is injected into the test hole according to the grouting pressure of the bored pile construction, and after the cement slurry completes the penetration and solidification, the slurry-containing rock core is collected to determine the effective radius of the penetration zone;

[0009] S2, determining the interface friction angle between the concrete and the coral reef rock of each stratum through the test And the cementation shear strength of the slurry-containing rock core ;

[0010] S3, calculating the slurry bite area coefficient according to the effective radius :

[0011] ;

[0012] The lateral friction resistance calculation formula of each stratum is established by comprehensively considering the interface friction and the cementation additional friction resistance:

[0013] ;

[0014] Wherein, r c is the effective radius; q si is the lateral friction resistance of the i-th layer, K i is the lateral pressure coefficient of the i-th layer; is the effective vertical stress of the i-th layer; and D is the design diameter of the cast-in-place pile.

[0015] Further, the effective radius determination method comprises a tracer method, the cement slurry is a cement slurry containing a fluorescent tracer, the fluorescent sample of the slurry-containing core is continuously drilled outward from the test hole area, the fluorescent ring thickness of the fluorescent sample of the slurry-containing core is measured under ultraviolet light, and the tracer effective radius r c1 of the infiltration zone is determined accordingly.

[0016] Further, the effective radius determination method further comprises a CT-seepage coupling inversion method: the CT scanning of the slurry-containing core is performed to generate a three-dimensional scanning image, the scanning image of the infiltration zone is obtained through three-dimensional threshold segmentation processing, the total filling volume of the scanning image of the infiltration zone is counted , and the scanning effective radius r c2 is inversely calculated according to the cylindrical diffusion model.

[0017] Further, when , the effective radius takes the tracer effective radius r c1 ; when , the effective radius takes the scanning effective radius r c2 .

[0018] Further, the effective radius determination method further comprises a pore empirical determination method: the undisturbed coral reef core is collected on site, the porosity n thereof is measured, and the empirical effective radius r is calculated according to the empirical formula c3 .

[0019] Further, the undisturbed saturated coral core of each stratum is collected, the unconfined compressive strength q ui of the saturated undisturbed coral core is determined through a saturated unconfined compressive strength test, the slurry-containing core is collected, the cementation shear strength of each corresponding stratum is determined through a shear test , and a regional - relationship is established, which is used to determine the cementation shear strength .

[0020] Further, the shearing test is carried out in a saturated state, a multi-stage loading is implemented in a normal stress range of [50 KPa, 400 KPa], and the peak shearing strength is taken as the cementing shearing strength of the stratum .

[0021] Further, the undisturbed saturated coral core of each stratum is collected, the peak friction angle is determined through a triaxial shearing test , the core containing slurry is collected, the interface friction angle of the concrete-coral reef rock of each corresponding stratum is determined through an interface shearing box test , a regional - relationship is established, and is used to determine the interface friction angle .

[0022] Further, when the unconfined compressive strength q ui of the coral reef rock is greater than 5 MPa, .

[0023] Further, when there is a loose coral sand cover layer on the top of the coral reef rock, the side friction resistance of the loose coral sand cover layer is not taken into the cementing additional friction resistance.

[0024] Further, when , the calculation formula of the slurry engagement area coefficient is simplified as: .

[0025] Compared with the prior art, the method for calculating the side friction resistance of the bored pile in the coral reef geological stratum has the following beneficial effects:

[0026] The method combines the field pouring test, quantifies the penetration-cementing engagement effect of the cement slurry in the coral reef rock, comprehensively considers the additional friction resistance caused by the cementing effect, modifies the calculation formula of the side friction resistance of the traditional bored pile, solves the problem that the bearing capacity of the coral reef stratum is significantly underestimated in the traditional design calculation, reliably and accurately guides the design of the bored pile construction, and has the following beneficial effects:

[0027] All the tests can be completed within 48 hours on site, can significantly reduce the cost of offshore survey, for the region where there is construction data or test data, the field pouring test can be omitted, the simple performance test is conducted on the coral rock, and the calculation result of the side friction resistance meeting the engineering error requirement can be obtained by combining the experience formula. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The flowchart of the method for calculating the side friction resistance of the bored pile disclosed by the application is shown. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only the best embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0030] Reference to "embodiments" herein means that the specific method, step or content described in combination with the embodiments can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] The present embodiment provides a method for calculating the side friction of a coral reef geological bored pile, as shown in Figure 1 which quantifies the occlusion effect caused by the penetration of cement slurry in combination with conventional tests, and determines the pile side friction of the coral rock by comprehensively quantifying the interface friction of the coral rock-concrete and the additional friction of the penetrated cementation, as the best example embodiment, specifically including the following steps and contents:

[0032] S1, determining the effective radius r of the penetration of cement slurry into the coral rock wall c , the determination method of which includes a tracer method, a CT-seepage coupling inversion method and a porosity determination method, any one of which can be selected according to the test conditions; as the best determination method, the effective radius r is determined by comprehensive analysis of the tracer method and the CT-seepage coupling inversion method c .

[0033] First, the slurry-containing core sample is made on site: a test hole is processed on the side of the pile site, the drilling depth is the depth of the pile end, the hole diameter is φ110mm, the cement slurry containing fluorescent tracer (only the CT-seepage coupling inversion method does not need to use fluorescent tracer) is injected, the fluorescent tracer is fluorescein sodium or rhodamine B, the concentration is 3%~5%, the water-cement ratio of the cement slurry is 0.5, the grouting pressure is generally 0.2MPa~0.4MPa, the grouting amount reaches 1 / 20 of the designed slurry amount per pile, after the cement slurry is penetrated and solidified, generally for 24h, the slurry-containing core sample is drilled by coring drilling, the sample specification is φ75mm, the thickness of the fluorescent ring is measured under the ultraviolet lamp irradiation environment, the core is taken from the concrete area of the test hole outward in turn until the edge area of the penetration zone is obtained, and the tracer effective radius r of the penetration zone is obtained by fluorescent measurement and statistics c1 .

[0034] Simultaneously, CT scans were performed on the aforementioned magmatic core samples with a resolution ≤18μm to generate three-dimensional scan images. Avizo software was used to perform three-dimensional threshold segmentation on the three-dimensional scan images to separate the infiltration zones. The total filling volume of the infiltration zones was then statistically determined. The effective scanning radius r of the penetration zone is calculated by reverse calculation using the cylindrical diffusion model. c2 :

[0035] (1)

[0036] In equation (1), L y Given the length of the magmatic core sample, r c1 and r c2 Comparative analysis, when When, the effective radius r c Directly using the effective radius r of the tracer c1 ;when When, the effective radius r c Take the effective scanning radius r c2 ;

[0037] When there is insufficient time or conditions for on-site preparation of magmatic core samples, or when the testing conditions for tracer methods and CT-flow coupled inversion methods are lacking, undisturbed coral reef core samples can be collected on-site, and their porosity n can be determined using empirical formulas. Estimating the empirical effective radius r c3 For example, under the following engineering construction conditions: 0.2≤n≤0.5, water-cement ratio of 0.45~0.55, grouting pressure of 0.2~0.4MPa, and grouting construction on multiple islands and reefs, the empirical formula for obtaining the effective radius-porosity is: Therefore, this empirical formula can be directly used in the design calculations for this region and its neighboring regions.

[0038] S2. Collect magmatic rock cores for shear tests to simulate overburden pressure or structural pressure and determine the cemented shear strength of each stratum. ; Collect magmatic rock cores for interfacial shear box tests, and determine the interfacial friction angle between concrete and coral reef rock at each stratum according to the design normal stress level. ;

[0039] S3. Based on the test results from steps S1 and S2, calculate the side friction resistance q of each stratum. si :

[0040] First, the slurry interlocking area coefficient is introduced. The effective radius r c Quantifying the additional bite effect:

[0041] (2)

[0042] Understandably, when D and r c are about one order of magnitude apart, the value of r c / D can be ignored, and the formula for calculating the slurry bite area coefficient can be simplified as:

[0043] The lateral frictional resistance q si of each stratum is calculated by combining the interfacial friction and the cementation additional friction:

[0044] (3)

[0045] In formula (2), D is the design diameter of the bored pile; in formula (3), K i is the lateral pressure coefficient, which is generally taken as 0.7-1.0 for coral rock, 0.8 when the stress release of the borehole is significant, or increased otherwise, and can be uniformly assigned for each stratum; is the effective vertical stress of the ith layer;

[0046] S4, Layered summation of total single-pile lateral friction Q s ;

[0047] If the site geological conditions are single coral reef rock, then:

[0048] (4)

[0049] If the site geology includes coral reef rock and loose coral sand cover on top, the lateral friction of the loose coral sand cover is not included in the cementation additional friction, and the total single-pile lateral friction Q s is calculated using formula (5):

[0050] (5)

[0051] In formula (4), l i is the thickness of the ith layer of coral rock, and n is the number of grading levels; in formula (5), l1 is the thickness of the top layer of coral sand, K1 is the lateral pressure coefficient of the coral sand, taken as 0.5~0.7, is the effective vertical stress at the center of the coral sand layer, is the interfacial friction angle between the undisturbed coral sand and the concrete.

[0052] A regional database is established for coral reef geology, a regional empirical formula is built, and the steps of field grouting tests are reduced to facilitate rapid engineering design and calculation in the same region or adjacent regions, including:

[0053] S5, explore the common engineering conditions (grouting pressure 0.2 MPa ~ 0.4 MPa, cement slurry water-cement ratio is 0.5), the cemented shear strength of the slurry containing core and the unconfined compressive strength of the original coral rock:

[0054] Collect the original saturated coral rock core of each level of stratum, and determine the unconfined compressive strength q ui by saturated unconfined compressive strength test, which is carried out according to the standard of "GB / T 50266-2013 Engineering Rock Mass Test Method"; make and collect the slurry containing core according to step S1, and carry out shear test, the normal stress of [50 KPa, 400 KPa] is divided into at least 50 kPa, 100 kPa, 200 kPa, and 400 kPa four stress levels, respectively, load and take the peak shear strength as the cemented shear strength of the stratum , regress and establish the - relationship of the region:

[0055] (6)

[0056] In formula (6), a is the shear pressure ratio; when the unconfined compressive strength q ui of the coral reef rock is greater than 5 MPa, it is considered that the coral rock structure is dense, and the penetration bite effect can be ignored, so that , the calculation formula of side friction only considers the interface friction term;

[0057] S6, explore the empirical relationship between the interface friction angle of concrete-coral reef rock and the peak friction angle of the original coral rock under common engineering conditions (grouting pressure 0.2 MPa ~ 0.4 MPa, cement slurry water-cement ratio is 0.5):

[0058] Collect the original saturated coral rock core of each level of stratum, and determine the peak friction angle by triaxial shear test; determine the interface friction angle of concrete-coral reef rock of each corresponding stratum by referring to the interface shear box test method in step S2 , regress and establish the relationship of the region:

[0059] (7)

[0060] In formula (7), b is the viscous friction ratio, generally taking the value of 0.7 ~ 0.85.

[0061] Application example:

[0062] I. A certain island reef implements cast-in-place pile, pile diameter D = 1.0 m, total pouring depth is 12 m, the peak friction angle of a certain reef layer , , ;

[0063] According to the statistical experience formula of a certain area island reef: , , the lateral pressure coefficient K i 0.8, combined with the tracer method and CT-seepage coupling inversion method comprehensive analysis to determine the effective radius r c =0.118 m, then , the calculation of side friction:

[0064] ;

[0065] Compared with the side friction of the general sand layer cast-in-place pile in the same stratum, ), it is increased by about 77%, which is in good agreement with the average value of 82 kPa of the static load test of 6 cast-in-place piles on site.

[0066] 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 platform, and of course can also be realized by hardware function. Based on such understanding, the technical solutions of the present application or the parts that make essential contributions to the prior art can be embodied in the form of software products, which are stored in a storage medium, including a plurality of instructions for causing a computer device, such as but not limited to 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.

[0067] Although embodiments of the present application 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 therein without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for calculating the side friction of a coral reef geologic bored pile, characterized by, The method comprises the following steps and contents: S1, determining effective radius: the determination method of the effective radius includes tracer method, processing test hole near the site pile position to the depth of pile end, injecting cement slurry containing fluorescent tracer into the test hole according to the grouting pressure of pouring construction, after the cement slurry completes penetration and solidification, continuously drilling fluorescent sample containing slurry core outward from the test hole area, measuring the fluorescent ring thickness of the fluorescent sample containing slurry core under ultraviolet light environment, and determining the tracer effective radius r of the penetration zone according to the above c1 ; S2, determining the interface friction angle of concrete-coral rock of each level of stratum and cemented shear strength of slurry-filled cores ; wherein, Collecting undisturbed saturated coral core of each stratum, determining peak friction angle by triaxial shear test ; collecting said slurry-containing core, determining said interface friction angle of said concrete-coral reef rock of each corresponding stratum by interface shear box test , establishing the relationship of the region - , for quickly determining the interface friction angle ; Collecting the undisturbed saturated coral core of each stratum, determining its unconfined compressive strength q by saturated unconfined compressive strength test ui ; collecting the slurry-containing core, determining the cementation shear strength of each corresponding stratum by shear test , establishing the relationship of the region - , for quickly determining the cementation shear strength ; S3. calculating the slurry bite area coefficient according to the effective radius : ； The side friction calculation formula of each stratum is established by comprehensively considering the interface friction and the cementation additional friction. ； where r c is the effective radius; q si is the side friction of the i-th layer, K i is the side pressure coefficient of the i-th layer; is the effective vertical stress of the i-th layer; D is the design diameter of the bored pile.

2. The method of claim 1, wherein the method is characterized by: The method for determining the effective radius further comprises a CT-seepage coupling inversion method: the slurry-containing core is scanned by CT to generate a three-dimensional scanning image, a seepage zone scanning image is obtained through three-dimensional threshold segmentation processing, total filling volume of the seepage zone scanning image is counted , and the scanning effective radius r is inversely deduced according to a cylindrical diffusion model c2 . When , the effective radius takes the tracing effective radius r c1 ; when , the effective radius takes the scanning effective radius r c2 .

3. The method of claim 1, wherein the method is characterized by: The shear test is carried out in a saturated state, in a normal stress range of [50 KPa, 400 KPa], a multi-stage loading is implemented, and a peak shear strength is taken as the cementation shear strength of the stratum .

4. The method of claim 3, wherein the method is characterized by: when said unconfined compressive strength q of the coral reef rock is greater than 5 MPa, ui .​ 5. The method of claim 4, wherein the method is characterized by: When the loose coral sand cover layer exists on the top of the coral reef rock, the side friction of the loose coral sand cover layer is not included in the cementation additional friction.

6. The method for calculating the side friction of a coral reef geologic bored pile according to claim 1, characterized in that: When the calculation formula of the slurry occlusal area coefficient can be simplified as: .

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