Coral reef geological cast-in-situ bored pile end bearing force calculation method

Abstract

The invention discloses a coral reef geological cast-in-situ bored pile end bearing force calculation method which comprises the steps that S1, an original coral reef rock core is collected on site, and the porosity of the coral reef rock core is measured; s2, the effective radius of the coral reef rock under the conventional pouring construction condition is determined according to the relational expression; s3, testing to determine the shear strength of the coral reef rock body and the interface shear strength of the cementation interface of the coral reef rock penetrated by the cement paste; s4, the coral reef rock body bearing capacity, the cementation interface bearing capacity and the pile end effective stress are integrated, and an end bearing capacity calculation formula of the cast-in-situ bored pile is established; according to the method, the pore-cementation effect of the coral reef is quantified and is incorporated into an end bearing force calculation formula, the calculation result and the measured value error meet the engineering design requirement, the result deviation calculated according to the traditional specification is remarkably reduced, it is indicated that the parameter determination method and the end bearing force calculation formula provided by the method better meet the actual construction condition of the coral reef rock, and the construction efficiency is improved. The method is high in operability, good in economical efficiency, high in efficiency and good in compatibility with current specifications.

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 under coral reef geological conditions, and particularly relates to a method for calculating the end bearing force of a bored pile under coral reef geological conditions. BACKGROUND

[0002] As a common geological environment in marine environment, the coral reef rock has the characteristics of "weak cementation and porous", which cannot meet the requirements of being a foundation bearing layer. In the construction of marine engineering, a pile foundation needs to be set. The pile end of the ordinary pile foundation is prone to compression-shear failure within a range of 3D-5D (D is the pile diameter) below the pile end. The bored pile can enhance the bearing strength of the coral reef rock below the pile end through permeation. Therefore, the bored pile is a common foundation form under coral reef geological conditions. However, there is no existing specification that can be directly used for calculating the end bearing force of the bored pile in reef rock geological conditions. In the traditional design, the coral reef is regarded as ordinary sandstone or siliceous sand, and the existing design specification for ordinary sandstone or rock-embedded piles is directly used for calculation.

[0003] After the bored pile is grouted, a cement slurry-coral cementation reinforced ring will be formed on the hole wall. The cement slurry seeps into the pores to form an interface reinforcement body. The end bearing force of the bored pile is contributed by the strength of the rock mass and the strength of the cementation interface. Therefore, for reef rock geological conditions, if the existing specification is used for the design of the bored pile, the end bearing force will deviate by more than 30%. This not only increases the scale of the marine engineering foundation, resulting in an increase in construction cost, but also prolongs the construction period, which is not conducive to safe operation in harsh marine environments.

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

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

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

[0007] A method for calculating the end bearing force of a bored pile under coral reef geological conditions, comprising the following contents and steps:

[0008] S1, collecting undisturbed coral reef cores on site and measuring the porosity n thereof;

[0009] S2, determining the effective radius r c of the coral reef rock under conventional bored pile construction conditions according to the relationship between r c :

[0010] ;

[0011] wherein a is a penetration radius offset parameter, and b is a porosity weight parameter;

[0012] S3, determining the shear strength of the coral reef rock mass through tests and the interfacial shear strength of the cement paste penetrating into the cementation interface of the coral reef rock ;

[0013] S4, comprehensively considering the bearing capacity of the coral reef rock mass body, the bearing capacity of the cementation interface, and the effective stress at the pile end, to establish a calculation formula of the end bearing force of the cast-in-place pile:

[0014] ;

[0015] wherein, the end bearing force, the cross-sectional area of the pile end, the strength reduction coefficient of the coral reef rock mass, the strength reduction coefficient of the cementation interface, D is the design diameter of the cast-in-place pile, the effective vertical stress at the pile end.

[0016] Further, the porosity is determined by the saturated weighing method to calculate the saturated porosity n1.

[0017] Further, the porosity is determined by the mercury intrusion method to calculate the mercury intrusion porosity n2.

[0018] Further, when the relative error between the saturated porosity n1 and the mercury intrusion porosity n2 is less than 5%, the porosity n is n1.

[0019] Further, when the relative error between the saturated porosity n1 and the mercury intrusion porosity n2 is equal to or exceeds 5%, the saturated weighing method is combined with the CT scanning method to determine the porosity n:

[0020] ;

[0021] wherein n3 is the scanning porosity determined by the CT scanning method, and k is a weight coefficient.

[0022] Further, the saturated coral core directly below the pile end is collected, and the unconfined compressive strength of the coral reef rock mass is determined through the saturated unconfined compressive strength test and the shear strength , to establish a regional - empirical relationship; the slurry-containing core of the same stratum directly below the pile end is collected, and the shear strength of the slurry-containing core is determined through the shear box test, to establish a regional - Relationship for quickly determining the shear strength of cementation interface .

[0023] Further, the effective radius r of the cementation interface formed by the penetration of the cement slurry into the coral reef rock is measured on site under the conventional engineering conditions c , and the porosity n of the undisturbed coral reef rock core near the test point is measured to determine the regional r c -n relationship.

[0024] Further, when the unconfined compressive strength of the saturated coral reef rock core is 1MPa, .

[0025] Compared with the prior art, the method for calculating the end bearing force of the coral reef geological bored pile has the following beneficial effects:

[0026] The method quantifies the "pore-cementation" effect of the coral reef and incorporates it into the end bearing force calculation formula, and the calculation result can be directly used for the end bearing force design of the coral geological bored pile. The error with the measured value meets the engineering design requirements, significantly reduces the deviation of the result calculated according to the traditional specification, and indicates 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. Moreover, the method has strong operability, good economy, high efficiency, and good compatibility with the existing specification. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The flowchart of the method for calculating the end bearing force of the bored pile disclosed in the present application is shown. DETAILED DESCRIPTION

[0028] 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 scope of protection of the present application.

[0029] In this document, reference to "an embodiment" 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 various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is explicitly contemplated that embodiments described herein can be combined with other embodiments.

[0030] The embodiment provides a method for calculating end bearing force of a coral reef geological bored pile, cementation pores of coral reef rocks are formed in a rock forming process, the pores have strong pore connectivity, and a pore ratio and a permeation radius are positively correlated, according to a large amount of test data of the coral reef rocks, in a range of 0.2<=pore ratio n<=0.5, the cementation pores of the coral reef rocks after calcification cementation, the permeation radius of cement slurry and the pore ratio are linearly related under conventional engineering conditions, therefore, the permeation radius r c of the cement slurry and the pore ratio n are taken as basic characteristics, a key characteristic database of regional coral reef rocks is established, a regional r c -n relationship is constructed by statistical regression, in the process of marine engineering construction in the region or the adjacent region with small differences in geological environment, the pore ratio of the in-situ coral reef rock is determined, the permeation radius of the cement slurry is estimated according to the r c -n relationship, and the field implementation of the grouting test is not needed, therefore, the method is not affected by weather and construction period window, has strong flexibility in preparation work, can greatly shorten the engineering design cycle, and improve construction efficiency, therefore, the embodiment combines conventional tests, quantifies the effective radius of the cementation permeation zone of the cement slurry through the pore ratio, and determines the end bearing force of the bored pile of the coral reef rock by comprehensively considering the self-bearing capacity of the coral reef rock body, the cementation interface bearing capacity and the effective stress of the pile end, which is taken as the best example embodiment, as shown in Figure 1 , specifically, the following steps and contents are included:

[0031] S0, a regional r c -n relationship of the coral reef rock is established: first, the in-situ core sample containing the slurry is made on site, the cement slurry is bored and grouted under conventional engineering conditions (that is, the water-cement ratio of the cement slurry is 0.45~0.55, and the grouting pressure is 0.2 MPa~0.4 MPa), the grouting test points not only cover the vicinity of the design construction pile point, but also are evenly distributed to test multiple reefs in the region according to the equal distribution law, the drilling depth is the pile end depth, the hole diameter is φ110mm, the grouting amount reaches 1 / 20 of the design slurry amount of a single pile, the core sample containing the slurry is obtained after 24 hours, the sample specification is φ75mm, the effective radius r c of the permeation zone can be determined by using the tracer method or the CT-seepage coupling inversion method; the tracer method refers to injecting the cement slurry containing the fluorescent tracer, and measuring the fluorescent ring thickness of the core sample containing the slurry under the ultraviolet lamp irradiation environment, so as to determine the effective radius; the CT-seepage coupling inversion method determines the effective radius by inversely deducing the total volume of the permeation zone through CT scanning;

[0032] secondly, the in-situ coral rock core near the grouting test point is collected, and the corresponding pore ratio n is determined according to step S1;

[0033] finally, the test data are statistically regressed, and the r c -n relationship of the region is established:

[0034] (1)

[0035] In formula (1), a is a penetration radius offset parameter, and b is a porosity weight parameter;

[0036] Understandably, for the region where the feature database already exists, and the relationship formula of the region r c -n is established, the S0 step can be omitted;

[0037] S1, according to the construction plan, the undisturbed coral reef core near the designed pile point is collected on site, and its porosity n is determined. The porosity determination method includes the saturated weighing method, the mercury intrusion method, and the CT scanning method. Any one of the determination methods can be used under the test conditions. As the best example of the implementation, the porosity is determined by the "joint three-step method", that is, the saturated weighing method, the mercury intrusion method, and the CT scanning method are used together to determine the best porosity. Since the "in-situ" value of the porosity can better reflect the actual penetration and cementation performance, and the laboratory sample represents the "appearance" porosity value, the coral reef rock has strong pore connectivity, and the sampling disturbance can significantly underestimate the porosity. Therefore, the "joint three-step method" can effectively ensure the accuracy of the porosity determination result:

[0038] S11, the saturated porosity n1 obtained by the saturated weighing method is used as the lower limit value: the undisturbed coral reef core is dried at 100-105°C for 24 hours to obtain the dry mass m d ; the 24-hour saturated test is carried out under vacuum conditions to obtain the saturated mass m w ;

[0039] The saturated porosity n1 is calculated according to the saturated porosity formula:

[0040] (2)

[0041] In formula (2), is the water density, is the total volume of the coral reef core sample;

[0042] S12, the mercury intrusion porosity n2 obtained by the mercury intrusion method is used as the upper limit value: the undisturbed coral reef core is cut into 10mm thick slices and dried, and the mercury intrusion porosity n2 is tested and calculated according to the mercury intrusion method (MIP) test specification;

[0043] The relative error of the upper and lower limit values is analyzed When , it is considered that the saturated porosity n1 obtained by the saturated weighing method basically reflects the in-situ value on site, and n1 is directly used as the best porosity n; when , the CT scanning method is further used for judgment;

[0044] S13, the best porosity n is confirmed by the joint CT scanning method:

[0045] The original coral reef core is scanned and reconstructed in three dimensions by industrial CT with a resolution of 18 μm, and the scanning porosity n3 is obtained by local threshold segmentation;

[0046] The results of the saturated weighing method and the CT scanning method are fused by combining formula (3), and the "isolated pores" and "connected pores" of the coral reef rock are unified to the best porosity n with operability:

[0047] (3)

[0048] In formula (3), k is a weight coefficient, generally taken as 0.6-0.8, and the recommended value is 0.7;

[0049] S2, according to the r c -n relationship formula (1) of the region, the effective radius r c of the coral reef rock under the condition of conventional cast-in-place construction is calculated;

[0050] S3, the coral reef core below the pile end is collected, and the shear strength of the coral reef rock mass is determined by a shear test ;

[0051] The cement paste infiltration coral reef rock cementation interface sample below the pile end is collected, and the interface shear strength is determined by an interface shear box test , the interface shear box test is carried out in a saturated state, the normal stress is 20 KPa-400 KPa, and the peak shear strength is taken as the result ;

[0052] S4, according to the results of steps S2 and S3, the bored pile end bearing force calculation formula of the comprehensive coral reef rock mass body bearing capacity, cementation interface bearing capacity and pile end effective stress is established:

[0053] (4)

[0054] Wherein, is the end bearing force, is the pile end cross-sectional area, is the coral reef rock mass strength reduction coefficient, taken as 0.5-0.65; is the cementation interface strength reduction coefficient, taken as 0.7-0.85; is the pore-cementation coupling coefficient, D is the design diameter of the cast-in-place pile, is the pile end effective vertical stress.

[0055] S5, the regional database of coral reef geology also includes the shear strength characteristics of the original stone and the shear strength characteristics of the slurry-containing rock core after cement slurry penetration strengthening, through test data, the regional strength empirical formula is built, the on-site grouting test steps are reduced, and the engineering design calculation of the same region or adjacent region is facilitated;

[0056] Under the common engineering conditions (grouting pressure 0.2 MPa ~0.4MPa, water-cement ratio of cement slurry 0.45~0.55), the empirical relationship between the shear strength of the original coral rock and the unconfined compressive strength, and the empirical relationship between the cemented shear strength of the slurry-containing rock core and the unconfined compressive strength of the original coral rock are explored:

[0057] The original saturated coral rock core below the pile end is collected, and the unconfined compressive strength of the coral reef rock mass is determined through the saturated unconfined compressive strength test , the saturated unconfined compressive strength test is carried out according to the standard of “GB / T 50266-2013 Engineering Rock Mass Test Method”; at the same time, the shear strength is determined through the shear test , and the relationship formula - is fitted and established:

[0058] (5)

[0059] Similarly, the on-site grouting construction is carried out according to step S0, the slurry-containing rock core of the same stratum below the pile end is collected, the shear strength of the slurry-containing rock core is determined through the shear box test , and according to the above corresponding unconfined compressive strength data, the linear fitting is carried out to obtain the relationship formula - :

[0060] (6)

[0061] In formula (5), is the shear pressure ratio of the original coral rock core; in formula (6), is the shear pressure ratio of the slurry-containing rock core and the original coral rock core;

[0062] Based on the empirical formula, the island reef only needs to collect the original coral reef rock, and determine the porosity and unconfined compressive strength, so as to calculate the remaining characteristic values, the flexibility and operability of the design stage are strong, the test and calculation process of the engineering design is significantly simplified, and the calculation result of the end bearing capacity of the grouting pile is accurate and compatible with the current specification;

[0063] Understandably, when the unconfined compressive strength of the coral reef rock 1MPa, the coral reef rock is considered to be a low-cemented coral sand, so , the bearing strength of the rock mass itself is not considered.

[0064] For the island to be developed lacking test conditions, the default empirical relationship can be used to calculate the end bearing force of the bored pile, and the test pile is checked in the construction stage, wherein the default empirical relationship is respectively: ; ; ; Take 0.55, Take 0.8.

[0065] Application example: a certain island implements a bored pile, the pile diameter D = 1.0 m, the strength test of the original coral reef rock obtains , the "joint three-step method" is used to determine the porosity n = 0.35, according to the empirical formula: Calculate to obtain the effective radius , ; according to the strength empirical formula , , Take 0.6, Take 0.8, substitute into equation (4) to obtain the end bearing force ; the static load test obtains the measured value of the same pile end depth of 4.8 MN, the error between the calculation result and the measured value is about 2%, which meets the engineering design requirements.

[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 essentially or the part of the prior art which makes a contribution can be embodied in the form of software product, which is stored in a storage medium, including a plurality of instructions for making a computer device, such as but not limited to personal computer, server, or network device, etc. to execute all or part of the steps of the method described in any embodiment of the present application.

[0067] Although the embodiments of the present application have been shown and described, it can 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 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 relationship between -n determines the effective radius r of coral reefs under conventional grouting construction conditions. 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 borehole piles in coral reef geological drilling 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 - Empirical formula; collect magmatic rock cores from the same stratum directly below the pile tip, and determine the shear strength using shear cell tests. , 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 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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