Method for detecting single-pile bearing capacity of deep foundation pit precast pile foundation on natural ground

Abstract

The invention discloses a method for detecting the single-pile bearing capacity of a deep foundation pit precast pile foundation on a natural ground. The method comprises the steps that a single-pile vertical bearing capacity characteristic value Ra2 is obtained on the natural ground through a load test; according to geological exploration report parameters and related specifications, a theoretical single-pile vertical bearing capacity characteristic value Ra2a starting from the natural ground is obtained; lateral resistance Ra4 of inner-layer soil in the foundation pit range and friction force Ra3 generated by the lateral resistance Ra4 to the effective pile length are obtained; and the expression of the characteristic value Ra1 of the vertical bearing capacity of the single pile of the effective pile length of the bottom surface of the foundation pit is Ra1 = Ra2-Ra4 * Ra2 / Ra2a-Ra3 / 2. According to the method, the characteristic value of the vertical bearing capacity of the single pile with the effective pile length can be determined. The method is convenient to implement, the construction period is shortened, and the good economic effect is achieved.

Description

Technical Field

[0001] The invention belongs to the field of pile bearing capacity detection, and in particular relates to a method for detecting the bearing capacity of a single pile of a deep foundation pit prefabricated pile foundation on natural ground. Background Art

[0002] In the field of pile vertical compressive bearing capacity testing, there are many situations where the conditions for conducting tests in accordance with actual conditions are not available. For example, for deep foundation pit pile foundations, load tests must be conducted at the bottom of the pit according to specifications to determine the characteristic value of the vertical bearing capacity of a single pile. However, piles are generally easier to construct on natural ground and are less expensive. Before construction, a load test must be conducted to determine the characteristic value of the vertical bearing capacity of a single pile. This requires excavating the foundation pit first, which is troublesome and expensive to construct. The two are contradictory. In addition, since the test conducted on natural ground does not match the actual state of the pile, the characteristic value of the vertical bearing capacity of a single pile is also inaccurate.

[0003] Therefore, the art needs a new method for detecting the bearing capacity of a single pile to solve the above problems. Summary of the invention

[0004] The purpose of the present invention is to provide a method for detecting the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground, aiming to solve the problem of how to accurately determine the characteristic value of the vertical bearing capacity of a single pile with an effective pile length.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for testing the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground, the method comprising:

[0007] Obtain the characteristic value R of the vertical bearing capacity of a single pile through load tests on natural ground a2 ;

[0008] According to the geological survey report parameters and relevant specifications, the theoretical single pile vertical bearing capacity characteristic value R starting from the natural ground is obtained. a2a ;

[0009] Get the lateral resistance R of the soil layer within the foundation pit range a4 and the friction force R generated by the effective pile length a3 ;

[0010] Then, the characteristic value of the vertical bearing capacity of a single pile with an effective pile length at the bottom of the foundation pit is R a1 The expression is: R a1 =R a2 -R a4 ×R a2 / R a2a -R a3 / 2.

[0011] There are three layers of soil from the natural ground to the bottom elevation of the foundation pit, namely the first layer of soil, the second layer of soil and the third layer of soil. The characteristic values ​​of the pile side resistance corresponding to the first layer of soil, the second layer of soil and the third layer of soil are q sia1 ,q sia2 ,q sia3 ;

[0012] The lateral resistance R of the soil layer within the foundation pit is obtained as shown in the following formula a4 :

[0013] R a4 =μ p (q sia1 h1+q sia2 h2+q sia3 h3)

[0014] Among them, μ p is the circumference of the pile, h1 is the length of the pile corresponding to the first layer of soil, h2 is the length of the pile corresponding to the second layer of soil, and h3 is the length of the pile corresponding to the third layer of soil above the bottom elevation of the foundation pit.

[0015] Preferably, the pile has a third layer of soil, a fourth layer of soil, and a fifth layer of soil corresponding to the portion below the bottom elevation of the foundation pit;

[0016] The friction force R generated by the effective pile length is as shown in the following formula a3 :

[0017] R a3 =(h1γ1+h2γ2+h3γ3)kμ s μ p (h4+h5+h6)

[0018] Among them, γ1 is the bulk density of the first layer of soil, γ2 is the bulk density of the second layer of soil, γ3 is the bulk density of the third layer of soil, k is the lateral pressure coefficient of the layer of soil, μ s is the average friction coefficient between the fourth, fifth and sixth soil layers and the pile, h4 is the length of the pile corresponding to the third soil layer below the bottom elevation of the foundation pit, h5 is the length of the pile corresponding to the fourth soil layer, and h6 is the length of the pile corresponding to the fifth soil layer.

[0019] The “relevant standards” mentioned include: “Code for Design of Building Foundations GB50007-2011” 8.5.6-1.

[0020] The advantages of the present invention are:

[0021] The present invention provides a method for testing the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground, obtains a characteristic value of the vertical bearing capacity of a single pile through a load test on natural ground, and corrects and determines the characteristic value of the vertical bearing capacity of a single pile of an effective pile length through calculation. The method is easy to implement, saves construction time, and has a good economic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the main process of a method for testing the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground according to the present invention;

[0023] Figure 2 It is a schematic diagram of the construction structure of a test pile of the present invention. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0025] See attached Figure 1 , which is the main process of the method for testing the bearing capacity of a single pile of a deep foundation pit prefabricated pile foundation on natural ground of the present invention. The method comprises:

[0026] Step S1: Obtain the vertical bearing capacity characteristic value R of a single pile through a load test on natural ground a2 Specifically, a test pile is constructed to the natural ground, and the pile static load test is carried out on the natural ground. The test method can be in accordance with the requirements of the specification.

[0027] See attached Figure 2 The test pile has three layers of soil from the natural ground to the bottom elevation of the foundation pit, namely the first layer of soil, the second layer of soil and part of the third layer of soil. The characteristic values ​​of the pile side resistance corresponding to the first layer of soil, the second layer of soil and the third layer of soil are q sia1 ,q sia2 ,q sia3 , unit is kPa; the part of the test pile below the bottom elevation of the foundation pit is the effective pile length, which corresponds to part of the third soil layer, the fourth soil layer, and the fifth soil layer respectively.

[0028] Step S2: Obtain the theoretical single pile vertical bearing capacity characteristic value R starting from the natural ground according to the geological survey report parameters and relevant specifications a2a The “relevant specifications” may be 8.5.6-1 of “Code for Design of Building Foundations GB50007-2011”.

[0029] Step S3: Obtain the lateral resistance R of the soil layer within the foundation pit range a4 and the friction force R generated by the effective pile length a3 .

[0030] Specifically, the lateral resistance R of the soil layer within the foundation pit is obtained according to the method shown in formula (1): a4 :

[0031] R a4 =μp (q sia1 h1+q sia2 h2+q sia3 h3) (1)

[0032] Among them, μ p is the circumference of the pile, h1 is the length of the pile corresponding to the first layer of soil, h2 is the length of the pile corresponding to the second layer of soil, and h3 is the length of the pile corresponding to the third layer of soil above the bottom elevation of the foundation pit.

[0033] According to the method shown in formula (2), the friction force R generated by the effective pile length a3 :

[0034] R a3 =(h1γ1+h2γ2+h3γ3)kμ s μ p (h4+h5+h6) (2)

[0035] Among them, γ1 is the bulk density of the first layer of soil, γ2 is the bulk density of the second layer of soil, γ3 is the bulk density of the third layer of soil, the layer below the groundwater level can use the floating bulk density, k is the lateral pressure coefficient of the layer of soil, generally taken as 0.5, μ s is the average friction coefficient between the fourth, fifth and sixth soil layers and the pile, in m; h4 is the length of the pile corresponding to the third soil layer below the bottom elevation of the foundation pit; h5 is the length of the pile corresponding to the fourth soil layer; and h6 is the length of the pile corresponding to the fifth soil layer.

[0036] Step S4: The vertical bearing capacity characteristic value R of the single pile of the effective pile length at the bottom of the foundation pit a1 The expression is: R a1 =R a2 -R a4 ×R a2 / R a2a -R a3 / 2.

[0037] In summary, the present invention provides a method for testing the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground. The characteristic value of the vertical bearing capacity of the single pile obtained from the ground test includes the lateral resistance of the soil layer within the foundation pit to be excavated, and also includes the friction force generated by the lateral pressure of the excavated layer of soil on the pile due to its gravity. The present invention is to deduct the lateral resistance of the excavated layer of soil and the friction force generated on the effective pile length from the characteristic value of the vertical bearing capacity of the single pile obtained from the ground test, and use the ratio of the characteristic value of the vertical bearing capacity of the single pile to the characteristic value of the vertical bearing capacity of the single pile calculated theoretically as the lateral resistance R calculated according to the parameters. a4 The correction coefficient is used to correct the vertical bearing capacity characteristic value of the effective pile length, and then the method is easy to implement, saves construction time, and has a good economic effect.

[0038] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for testing the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground, characterized in that: The method comprises: Obtain the characteristic value R of the vertical bearing capacity of a single pile through load tests on natural ground a2 ; According to the geological survey report parameters and relevant specifications, the theoretical single pile vertical bearing capacity characteristic value R starting from the natural ground is obtained. a2a ; Get the lateral resistance R of the soil layer within the foundation pit range a4 and the friction force R generated by the effective pile length a3 ; Then, the characteristic value of the vertical bearing capacity of a single pile with an effective pile length at the bottom of the foundation pit is R a1 The expression is: R a1 =R a2 -R a4 ×R a2 / R a2a -R a3 / 2.

2. The method for testing the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground according to claim 1, characterized in that: There are three layers of soil from the natural ground to the bottom elevation of the foundation pit, namely the first layer of soil, the second layer of soil and the third layer of soil. The characteristic values ​​of the pile side resistance corresponding to the first layer of soil, the second layer of soil and the third layer of soil are q sia1 ,q sia2 ,q sia3 ; The lateral resistance R of the soil layer within the foundation pit is obtained as shown in the following formula a4 : R a4 =μ p (q sia1 h1+q sia2 h2+q sia3 h3) Among them, μ p is the circumference of the pile, h1 is the length of the pile corresponding to the first layer of soil, h2 is the length of the pile corresponding to the second layer of soil, and h3 is the length of the pile corresponding to the third layer of soil above the bottom elevation of the foundation pit.

3. The method for testing the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground as claimed in claim 2, characterized in that: The part below the bottom elevation of the foundation pit corresponds to the third, fourth and fifth layers of soil; The friction force R generated by the effective pile length is as shown in the following formula a3 : R a3 =(h1γ1+h2γ2+h3γ3)km s m p (h4+h5+h6) Among them, γ1 is the bulk density of the first layer of soil, γ2 is the bulk density of the second layer of soil, γ3 is the bulk density of the third layer of soil, k is the lateral pressure coefficient of the layer, μ s is the average friction coefficient between the fourth, fifth and sixth soil layers and the pile, h4 is the length of the pile corresponding to the third soil layer below the bottom elevation of the foundation pit, h5 is the length of the pile corresponding to the fourth soil layer, and h6 is the length of the pile corresponding to the fifth soil layer.

4. The method for testing the bearing capacity of a single pile of a deep foundation pit precast pile foundation on natural ground according to claim 1, characterized in that: The "relevant specifications" include: "Code for Design of Building Foundations GB50007-2011" 8.5.6-1。

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