Underwater ultra-soft clay gravel pile composite foundation construction pretreatment method

Abstract

The invention discloses a pretreatment method for construction of an underwater ultra-soft clay gravel pile composite foundation. The pretreatment method comprises the steps that S1, the undrained strength of soft clay needed for pile forming is calculated; s2, calculating the thickness and the treatment time of the sand cushion layer; s3, a self-propelled belt ship is matched with a flat barge to position and construct an underwater sand cushion, and a special overwater plastic row ship is adopted to construct a drainage plate; s4, the reinforcing effect is detected through the cross plate drainage plate, and whether the gravel pile construction condition is met or not is judged; and S5, if yes, gravel pile overwater construction is carried out. The bearing capacity and stability of the foundation can be effectively improved, and the method is suitable for foundation reinforcement in underwater ultra-soft clay areas.

Description

Technical Field

[0001] The invention relates to a pretreatment method for underwater super-soft clay gravel pile composite foundation construction Background Art

[0002] The surface layer of my country's offshore waters is covered with thick soft clay with high water content, high compressibility and low strength. When carrying out engineering construction on this soft clay seabed foundation, it is often necessary to use composite foundation for reinforcement. Gravel piles are one of the commonly used reinforcement methods.

[0003] Due to its low strength and high compressibility, ultra-soft clay foundation often requires pretreatment to improve its bearing capacity and stability.

[0004] In the prior art, the treatment methods for underwater ultra-soft clay foundations often have problems such as great construction difficulty and poor treatment effect.

[0005] Therefore, a pretreatment method for underwater super-soft clay gravel pile composite foundation construction is provided. Summary of the invention

[0006] The purpose of the present invention is to overcome the existing defects and provide an underwater super-soft clay gravel pile composite foundation construction pretreatment method, which can effectively improve the bearing capacity and stability of the foundation and is suitable for foundation reinforcement in underwater super-soft clay areas.

[0007] The technical solution to achieve the above purpose is:

[0008] A method for pretreatment of underwater super-soft clay gravel pile composite foundation construction, comprising:

[0009] Step S1, calculating the undrained strength of soft clay required for pile formation;

[0010] Step S2, calculating the thickness of the sand cushion layer and the processing time according to the required undrained strength growth value;

[0011] Step S3, using a self-propelled belt boat in conjunction with a flat barge to position and construct an underwater sand cushion layer, and using a special water plastic rowing boat to construct a drainage board;

[0012] Step S4, testing the reinforcement effect by using the cross-plate drainage board to determine whether the conditions for constructing gravel piles are met;

[0013] Step S5: If the conditions are met, then perform the above-water construction of gravel piles.

[0014] Preferably, in step S1, the formula for calculating the undrained strength of soft clay required for pile formation is as follows:

[0015]

[0016] Where q is the upper load of the gravel pile, qu is the ultimate bearing capacity of super-soft clay gravel pile composite foundation, c u is the undrained shear strength of the surrounding soft clay, N s is the number of gravel piles, A s is the area replacement ratio, and L / D is the ratio of pile length to pile diameter.

[0017] Preferably, in step S2, the calculation formula is as follows:

[0018]

[0019] Where c is the undrained shear strength of the soil after considering the strength growth, η is the strength reduction factor, which is taken as 0.9, c s is the C value of the original soil cross plate, U z is the consolidation degree of soil at a certain moment, σ z is the additional stress in the soil, is the internal friction angle of the original soil during consolidation.

[0020] Preferably, in step S2, the thickness H of the sand cushion layer needs to satisfy the following formula:

[0021] H*γ s ≥1.2σ z ;

[0022] Where H is the thickness of the sand cushion layer; γ s is the weight of the sand cushion layer, the buoyant density taken underwater, σ z Add stress to the soil;

[0023] The processing time t is calculated according to the following formula, satisfying U z Not less than 0.85, then:

[0024]

[0025] In the formula, C h is the horizontal consolidation coefficient of the underwater foundation, F(n) is the well diameter ratio factor, d e It is the equivalent diameter of the radial drainage range of the plastic drain board.

[0026] Preferably, in step S4, whether the conditions for constructing gravel piles are met is:

[0027] If the cross-plate drainage board test result is greater than or equal to the undrained strength of the soft clay required for pile construction calculated in step S1, the conditions for constructing gravel piles are met;

[0028] If the cross-plate drainage board test result is less than the undrained strength of the soft clay required for pile construction calculated in step S1, the conditions for constructing gravel piles are not met.

[0029] The beneficial effects of the present invention are as follows: the present invention effectively improves the bearing capacity and stability of the ultra-soft clay foundation through precise calculation and construction; at the same time, the method is simple to construct and has a significant treatment effect, and is suitable for the treatment of various underwater ultra-soft clay foundations. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of a method for pre-treating underwater super-soft clay gravel pile composite foundation construction according to the present invention;

[0031] Figure 2 It is a structural diagram of a method for pretreatment of underwater super-soft clay gravel pile composite foundation construction according to the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0033] The present invention will be further described below in conjunction with the accompanying drawings.

[0034] like Figure 1 As shown, a method for pretreatment of underwater super-soft clay gravel pile composite foundation construction comprises:

[0035] Step S1, calculating the undrained strength of soft clay required for pile formation.

[0036] In the embodiment, the formula for calculating the undrained strength of soft clay required for pile formation is as follows:

[0037]

[0038] Where q is the upper load of the gravel pile, q u is the ultimate bearing capacity of super-soft clay gravel pile composite foundation, c u is the undrained shear strength of the surrounding soft clay, N s is the number of gravel piles, A s is the area replacement ratio, and L / D is the ratio of pile length to pile diameter.

[0039] Step S2, calculating the thickness of the sand cushion layer and the processing time according to the required undrained strength growth value.

[0040] In the embodiment, the required undrained strength growth value is used, that is, the soil cohesion after considering the strength growth is calculated, and the calculation formula is as follows:

[0041]

[0042] Where c is the undrained shear strength of the soil after considering the strength growth, η is the strength reduction factor, which is taken as 0.9, c s is the C value of the original soil cross plate, U z is the consolidation degree of soil at a certain moment, σ z is the additional stress in the soil, is the internal friction angle of the original soil during consolidation.

[0043] In the embodiment, the thickness H of the sand cushion layer needs to satisfy the following formula:

[0044] H*γ s ≥1.2σ z ;

[0045] Where H is the thickness of the sand cushion layer; γ s is the weight of the sand cushion layer, the buoyant density taken underwater, σ z Add stress to the soil;

[0046] The processing time t is calculated according to the following formula, satisfying U z Not less than 0.85, then:

[0047]

[0048] In the formula, C h is the horizontal consolidation coefficient of the underwater foundation, F(n) is the well diameter ratio factor, d e It is the equivalent diameter of the radial drainage range of the plastic drain board.

[0049] Step S3, using a self-propelled belt boat in conjunction with a flat barge to position and construct the underwater sand cushion layer, and using a special water plastic rowing boat to construct the drainage board.

[0050] Step S4, testing the reinforcement effect through the cross-plate drainage board to determine whether the conditions for constructing gravel piles are met.

[0051] In the embodiment, the conditions for determining whether the gravel pile construction is met are:

[0052] If the cross-plate drainage board test result is greater than or equal to the undrained strength of the soft clay required for pile construction calculated in step S1, the conditions for constructing gravel piles are met;

[0053] If the cross-plate drainage board test result is less than the undrained strength of the soft clay required for pile construction calculated in step S1, the conditions for constructing gravel piles are not met.

[0054] Step S5: If the conditions are met, then perform the above-water construction of gravel piles.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for pretreatment of underwater super-soft clay gravel pile composite foundation construction, characterized in that: include: Step S1, calculating the undrained strength of soft clay required for pile formation; Step S2, calculating the thickness of the sand cushion layer and the processing time according to the required undrained strength growth value; Step S3, using a self-propelled belt boat in conjunction with a flat barge to position and construct an underwater sand cushion layer, and using a special water plastic rowing boat to construct a drainage board; Step S4, testing the reinforcement effect by using the cross-plate drainage board to determine whether the conditions for constructing gravel piles are met; Step S5: If the conditions are met, then perform the above-water construction of gravel piles.

2. The method for pretreatment of underwater super-soft clay gravel pile composite foundation construction according to claim 1, characterized in that: In step S1, the formula for calculating the undrained strength of soft clay required for pile formation is as follows: Where q is the upper load of the gravel pile, q u is the ultimate bearing capacity of super-soft clay gravel pile composite foundation, c u is the undrained shear strength of the surrounding soft clay, N s is the number of gravel piles, A s is the area replacement ratio, and L / D is the ratio of pile length to pile diameter.

3. The method for pretreatment of underwater super-soft clay gravel pile composite foundation construction according to claim 1, characterized in that: In step S2, the calculation formula is as follows: Where c is the undrained shear strength of the soil after considering the strength growth, η is the strength reduction factor, which is taken as 0.9, c s is the C value of the original soil cross plate, U z is the consolidation degree of soil at a certain moment, σ z is the additional stress in the soil, is the internal friction angle of the original soil during consolidation.

4. The method for pretreatment of underwater super-soft clay gravel pile composite foundation construction according to claim 1, characterized in that: In step S2, the thickness H of the sand cushion layer needs to satisfy the following formula: H*c s ≥1.2σ z ; Where H is the thickness of the sand cushion layer; γ s is the weight of the sand cushion layer, the buoyant density taken underwater, σ z Add stress to the soil; The processing time t is calculated according to the following formula, satisfying U z Not less than 0.85, then: In the formula, C h is the horizontal consolidation coefficient of the underwater foundation, F(n) is the well diameter ratio factor, d e It is the equivalent diameter of the radial drainage range of the plastic drain board.

5. The method for pretreatment of underwater super-soft clay gravel pile composite foundation construction according to claim 1, characterized in that: In step S4, whether the conditions for constructing gravel piles are met is determined as follows: If the cross-plate drainage board test result is greater than or equal to the undrained strength of the soft clay required for pile construction calculated in step S1, the conditions for constructing gravel piles are met; If the cross-plate drainage board test result is less than the undrained strength of the soft clay required for pile construction calculated in step S1, the conditions for constructing gravel piles are not met.

Images