A calculation method for the bearing capacity of bored cast-in-place piles

Abstract

The present invention discloses a method for calculating the bearing capacity of bored cast-in-place piles, which relates to the field of construction technology; it includes obtaining soil samples at different depths of the engineering site; determining the slurry seepage pressure of indoor tests; preparing pile-soil transition zone specimens at different depths; curing the pile-soil transition zone specimens according to the on-site construction conditions; obtaining the widths of the pile-soil transition zones at different depths through an image processing software; plotting the variation relationship of the widths of the pile-soil transition zones with the increase of the depth of the site soil and performing fitting to obtain a functional relationship; obtaining the equivalent diameter of the cast-in-place pile considering the width of the pile-soil transition zone based on this functional relationship; and obtaining the calculation formula for the vertical bearing capacity of the cast-in-place pile considering the width of the pile-soil transition zone. This method fully considers the process of concrete slurry infiltrating into the soil during the actual construction of bored cast-in-place piles, can calculate the vertical bearing capacity of bored cast-in-place piles more accurately, and effectively avoids the problem that the vertical bearing capacity obtained by traditional calculation methods is too small due to the failure to consider the pile-soil transition zone.

Description

Technical Field

[0001] The present invention relates to the field of construction technology, and particularly relates to a method for calculating the bearing capacity of bored cast-in-place piles. Background Art

[0002] Pile foundations are widely used in the construction of bridges, high-rise buildings, etc. because of their many advantages such as high bearing capacity, good stability, small and uniform settlement. A pile foundation is a deep foundation that connects the tops of several piles into a whole through a cap to jointly bear static and dynamic loads. A pile is a vertical or inclined foundation member set in the soil, and its function is to penetrate soft, highly compressible soil layers or water and transfer the load borne by the pile to a harder, denser or less compressible foundation bearing stratum. A bored cast-in-place pile is a type of pile, which refers to a pile formed by means of mechanical drilling, steel pipe soil extrusion or manual excavation at the construction site in the foundation soil, and a steel reinforcement cage is placed therein and concrete is poured.

[0003] The bearing capacity of bored cast-in-place piles mainly depends on the physical and mechanical properties of the soil on the pile side and at the pile end and the interaction between the pile and the surrounding soil. During the construction process of bored cast-in-place piles, the concrete will diffuse into the surrounding soil, increasing the cohesion and internal friction angle of the soil around the pile, and thus increasing the bearing capacity of the pile foundation. The traditional design calculation method does not consider the increase in the soil parameters of this part, resulting in a smaller calculated result of the actual bearing capacity. How to provide an accurate method for calculating the bearing capacity of bored cast-in-place piles is crucial for pile foundation design. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] In view of the deficiencies of the prior art, the present invention provides a method for calculating the bearing capacity of bored cast-in-place piles, which solves at least one technical problem raised in the background art.

[0006] (2) Technical Solutions

[0007] The technical solution adopted by the present invention is: a method for calculating the bearing capacity of bored cast-in-place piles, the method comprising:

[0008] Obtaining soil samples at different depths within the project site;

[0009] Determining the concrete slurry penetration pressure for indoor tests according to the soil sampling depth;

[0010] Preparing pile-soil transition zone specimens at different depths by using a penetration device;

[0011] Curing the prepared pile-soil transition zone specimens at different depths;

[0012] Obtaining the concrete slurry penetration images of the pile-soil transition zone specimens at different depths by using a high-definition digital camera;

[0013] Process the image of the pile-soil transition zone to obtain the widths of the pile-soil transition zone at different depths;

[0014] Fit to obtain the functional relationship w(l) between the width of the pile-soil transition zone and the depth of the site soil;

[0015] Based on the functional relationship w(l), obtain the equivalent diffusion width d of the bored cast-in-place pile within the pile body burial depth range;

[0016] Based on the functional relationship w(l) and the equivalent diffusion width d, obtain the equivalent diameter D′ of the bored cast-in-place pile;

[0017] Obtain the calculation formula for the vertical ultimate bearing capacity of the bored cast-in-place pile, and calculate the bearing capacity of the bored cast-in-place pile based on the bearing capacity calculation formula.

[0018] Preferably, the penetration pressure of the concrete slurry is equal to the product of the specific gravity of the concrete slurry and the depth of soil sampling.

[0019] Preferably, the penetration device includes:

[0020] A model box filled with soil inside, and the soil is a soil sample obtained from different depths within the engineering site;

[0021] A cylindrical hole is vertically arranged in the soil of the model box perpendicular to the bottom of the model box, and the height of the cylindrical cover is the same as the depth of the model box;

[0022] A pressurizing device that can pressurize the concrete slurry inside the cylindrical hole.

[0023] Preferably, the curing of the pile-soil transition zone specimen is to let it stand still after controlling the temperature and humidity on site.

[0024] Preferably, the width w of the pile-soil transition zone at different depths is calculated after binarizing the image of the pile-soil transition zone: w = S / h;

[0025] Where S is the diffusion area of the slurry around the pile; h is the height of the specimen.

[0026] Preferably, the equivalent diffusion width is:

[0027] Where w(l) is the functional relationship between the width w of the pile-soil transition zone and the burial depth l around the pile; l1 is the burial depth of the pile top; l2 is the burial depth of the pile end.

[0028] Preferably, the equivalent diameter of the cast-in-place pile is obtained by adding the average width of the slurry around the pile body to the original pile diameter, that is:

[0029] Among them, D′ is the equivalent diameter of the cast-in-place pile; D is the original diameter of the cast-in-place pile.

[0030] Preferably, the calculation formula for the vertical ultimate bearing capacity of the bored cast-in-place pile is:

[0031]

[0032] Among them, q sik is the standard value of the ultimate side friction resistance of the pile; q pk is the standard value of the ultimate end resistance of the pile.

[0033] (III) Beneficial effects

[0034] The present invention provides a method for calculating the bearing capacity of a bored cast-in-place pile. Compared with the prior art, it has the following beneficial effects:

[0035] 1. A method for calculating the bearing capacity of a bored cast-in-place pile provided by an embodiment of the present invention includes obtaining soil samples at different depths of the engineering site; determining the slurry penetration pressure of the indoor test; preparing pile-soil transition zone specimens at different depths; curing the pile-soil transition zone specimens according to the on-site construction conditions; obtaining the width of the pile-soil transition zone at different depths through image processing software; plotting the variation relationship of the width of the pile-soil transition zone with the increase of the depth of the site soil and fitting to obtain a functional relationship; obtaining the equivalent diameter of the cast-in-place pile considering the width of the pile-soil transition zone based on this functional relationship; and obtaining the calculation formula for the vertical bearing capacity of the cast-in-place pile considering the width of the pile-soil transition zone. This method fully considers the process of concrete slurry infiltrating into the soil during the actual construction of the bored cast-in-place pile, can calculate the vertical bearing capacity of the bored cast-in-place pile more accurately, and effectively avoids the problem that the vertical bearing capacity obtained by the traditional calculation method is too small due to the failure to consider the pile-soil transition zone. Description of the drawings

[0036] The present invention will be further described below with reference to the drawings and embodiments:

[0037] Figure 1 is the penetration device of the embodiment of the present invention;

[0038] Figure 2 is a schematic diagram of the penetration device of the embodiment of the present invention after pressurization;

[0039] Figure 3 is a schematic diagram of the slurry diffusion around the pile of the embodiment of the present invention;

[0040] Figure 4 is a schematic diagram of the soil sample profile at the 4m position of the embodiment of the present invention before binarization;

[0041] Figure 5 is a schematic diagram of the soil sample profile at the 4m position of the embodiment of the present invention after binarization;

[0042] Figure 6 It is the fitting function of the slurry diffusion width and the soil depth in the embodiment of the present invention;

[0043] Among them are model box 1, soil 2, cylindrical hole 3, pressurizing device 4, and sealed piston 5. Specific implementation method

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0045] To better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific implementation manners:

[0046] The bearing capacity of a pile foundation mainly depends on the physical and mechanical properties of the soil on the pile side and at the pile tip, and the interaction between the pile and the surrounding soil. The soil around the pile is a porous medium and is compressible and deformable. During the grouting process, part of the concrete will diffuse along the pores in the soil into the surrounding soil, forming a pile-soil transition zone. Moreover, the distribution of the pile-soil transition zone on the side and at the tip of the cast-in-place pile varies due to differences in soil layer pores, compressibility, and the stress on the slurry. The diffusion of the concrete into the soil around the pile will increase the cohesion and internal friction angle of the soil around the pile, thereby increasing the bearing capacity of the pile foundation. Considering the diffusion of the slurry in the pile-soil transition zone when designing a pile foundation will make the calculation of the pile foundation bearing capacity more accurate. At the same time, it can save certain materials and is more environmentally friendly and economical. Based on this, the embodiments of the present invention provide a method for calculating the bearing capacity of a bored cast-in-place pile, which is specifically described as follows.

[0047] Specific implementation cases are as Figures 1-6 shown:

[0048] The first step: Obtain soil samples at different depths around the pile. Undisturbed soil samples are obtained from 4m, 8m, 12m, and 16m below the ground surface of the engineering site respectively, and are wrapped with plastic film and transported back to the laboratory; the soil sampling depth at the site should cover the range from the pile top to the pile bottom embedment depth of the bored cast-in-place pile;

[0049] The second step: Determine the slurry penetration pressure for the indoor test according to the sampling depth; the self-weight of the concrete slurry is generally 25kN / cm 3 , from which the penetration pressures of the concrete around the pile at 4m, 8m, 12m, and 16m below the ground surface are 100kPa, 200kPa, 300kPa, and 400kPa respectively;

[0050] Step 3: Prepare the pile-soil transition zone specimens at different depths using a penetration device; layer the soil samples taken in Step 1 into the model box 1 of the penetration and pressurization device. During the soil filling process, place the cylindrical cover (the cylindrical cover is made of plexiglass, and the outside of the plexiglass is roughened) in the model box 1, and fill the soil 2 between the glass cover and the model box. After the entire soil filling process is completed, remove the cylindrical cover, and a cylindrical hole 3 will be formed in the middle. Pour the concrete slurry into the cylindrical hole 3, and use the pressurization device 4 to perform pressure penetration on it. The penetration pressure is applied according to that determined in Step 2. A sealing piston 5 is provided at the connection between the pressurization device 4 and the cylindrical hole 3.

[0051] Step 4: Cure the prepared pile-soil transition zone specimens according to the on-site construction conditions; the temperature and humidity for curing the pile-soil transition zone specimens are determined according to the on-site construction environment. For example, if the on-site temperature is 20 °C, the humidity is 95%, and the curing days are 28 days, then place the prepared pile-soil transition zone specimens in the curing box and cure them under the same conditions.

[0052] Step 5: Plot the relationship between the width of the pile-soil transition zone and the increase in pile depth and perform fitting to obtain the functional relationship; take the image of the pile-soil transition zone at 4 m as an example. As shown in Figure 4, w1 and w3 are the maximum diffusion width and the minimum diffusion width respectively. After binarization using computer software, Figure 5 specifically, the width w of the pile-soil transition zone at different depths is calculated by performing binarization processing on the pile-soil transition zone image using the image pro plus software, where w = S / h; S is the diffusion area of the slurry around the pile; h is the height of the specimen. For example, Figure 3 .

[0053] Use computer software to identify the area S (the area of the concrete diffusion part) of the black region within the maximum diffusion width w1. Then, the average diffusion width of the concrete slurry in the black region is w = S / L h , and finally, the width of the concrete pile-soil transition zone at 4 m below the ground surface of the site is obtained as 8.22 mm; similarly, the width of the pile-soil transition zone at 8 m below the ground surface of the site is obtained as 16.04 mm; the width of the pile-soil transition zone at 12 m below the ground surface of the site is obtained as 17.7 mm; the width of the pile-soil transition zone at 16 m below the ground surface of the site is obtained as 29.56 mm. Fitting the data can obtain the functional relationship between the pile-soil transition zone w and the pile circumference burial depth l within 16 m below the ground surface as shown in Figure 5 Figure, and the functional relationship is w = 1.7637l.

[0054] Step 6: The concrete slurry diffusion function obtained from the test is a linear function. Based on the calculation formula of the equivalent diffusion width the average width of the pile-soil transition zone within the pile length is obtained as Furthermore, based on the equivalent diameter formula of the bored cast-in-place pile The equivalent pile diameter of the cast-in-place pile considering the width of the concrete slurry is the original pile length plus twice the equivalent pile length. Among them, D′ is the equivalent diameter of the cast-in-place pile, considering the width of the pile-soil transition zone; D is the original diameter of the cast-in-place pile, without considering the width of the pile-soil transition zone. Taking a cast-in-place pile with a pile length of 12 m and a pile diameter of 600 mm as an example, the average diffusion width of the slurry around the pile is 10.58 mm, then the equivalent pile diameter of the cast-in-place pile considering the width of the concrete slurry is 621.16 mm; if the cast-in-place pile has a pile length of 15 m and a pile diameter of 300 mm, then the average diffusion width of the slurry around the pile is 13.23 mm, and the equivalent pile diameter of the cast-in-place pile considering the width of the concrete slurry is 626.46 mm.

[0055] Step 7: The conventional calculation formula for the bearing capacity of a cast-in-place pile is:

[0056] In the formula, D is the original diameter of the cast-in-place pile, without considering the width of the pile-soil transition zone. After replacing D in the formula with the equivalent pile diameter obtained by this method, the calculation formula for the bearing capacity of the cast-in-place pile considering the width of the pile-soil transition zone is:

[0057] Using this formula, the vertical bearing capacity of the cast-in-place piles in this area can be predicted and calculated. In the formula, l1 and l2 are the embedment depths of the pile top and the pile end respectively.

[0058] It should be noted that in this article, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A calculation method for the bearing capacity of bored cast-in-place piles, characterized in that, The method includes: Obtaining soil samples at different depths within the engineering site; Determining the concrete slurry penetration pressure for the indoor test according to the soil sampling depth; Preparing pile-soil transition zone specimens at different depths by using a penetration device; Curing the prepared pile-soil transition zone specimens at different depths; Obtaining the concrete slurry penetration images of the pile-soil transition zone specimens at different depths by using a high-definition digital camera; Processing the pile-soil transition zone images to obtain the widths of the pile-soil transition zones at different depths; Fitting to obtain the functional relationship w(l) between the width of the pile-soil transition zone and the depth of the site soil; Obtaining the equivalent diffusion width d of the bored cast-in-place pile within the pile body burial depth range based on the functional relationship w(l); The equivalent diameter of the bored cast-in-place pile is obtained based on the functional relationship w(l) and the equivalent diffusion width d ; Obtaining the calculation formula for the vertical ultimate bearing capacity of the bored cast-in-place pile, and calculating the bearing capacity of the bored cast-in-place pile based on the bearing capacity calculation formula; The equivalent diffusion width is: ; Where w(l) is the functional relationship between the width w of the pile-soil transition zone and the burial depth l around the pile; l1 is the pile top burial depth; l2 is the pile tip burial depth; The equivalent diameter of the cast-in-place pile is obtained by adding the average width of the slurry around the pile body to the original pile diameter, that is: ; where is the equivalent diameter of the cast-in-place pile; is the original diameter of the cast-in-place pile; The calculation formula for the vertical ultimate bearing capacity of the bored cast-in-place pile: ； Among them, is the standard value of the ultimate lateral frictional resistance around the pile; is the standard value of the ultimate end resistance of the pile.

2. The calculation method for the bearing capacity of bored cast-in-place piles according to claim 1, wherein: The concrete slurry penetration pressure is equal to the product of the concrete slurry specific weight and the soil sampling depth.

3. The calculation method of the bearing capacity of a bored cast-in-place pile according to claim 1, characterized in that: The penetration device includes: A model box (1), with soil (2) filled inside the model box (1), and the soil (2) being soil samples obtained from different depths within the engineering site; A cylindrical hole (3), which is vertically arranged inside the soil (2) of the model box (1) perpendicular to the bottom of the model box (1), and the height of the cylindrical hole (3) is the same as the depth of the model box (1); A pressurizing device (4), which can pressurize the concrete slurry inside the cylindrical hole (3).

4. The calculation method for the bearing capacity of a bored cast-in-place pile according to claim 1, characterized in that: Curing the pile-soil transition zone specimens means statically placing them after controlling the temperature and humidity on-site.

5. The calculation method of the bearing capacity of a bored cast-in-place pile according to claim 1, wherein: The widths w of the pile-soil transition zones at different depths are calculated after binarizing the pile-soil transition zone images: w = S / h; Where S is the diffusion area of the slurry around the pile; h is the specimen height.

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