A loading device for pile group foundation scale model and calculation method thereof

Abstract

The present invention relates to the technical field of pile group foundations, and in particular to a loading device for a scaled model of a pile group foundation and a calculation method thereof. The loading device comprises a model box, wherein a test component is arranged in the model box, and the bottom of the test component is fixed to the inner bottom of the model box via a circular tube; pads are fixed on all four sides of the top of the test component, and steel beams are fixed on two pads on the front side and two pads on the rear side. High-strength screws are arranged on both left and right sides of the top of the steel beam, and the high-strength screws penetrate the steel beam and are connected to the inner bottom of the model box via a threaded sleeve; a pressure sensor is installed on the upper end of the high-strength screw, and the bottom of the pressure sensor is in contact with the top of the steel beam. The present invention can solve the problem of equivalent application of negative friction resistance during model testing, improve the accuracy of the test and the accuracy of the conclusion, and can be used in the fields of power transmission line engineering, bridge engineering, wind power generation engineering, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of pile group foundations, in particular to a loading device for a scaled model of a pile group foundation and a calculation method thereof. Background Art

[0002] In recent years, my country's nuclear power technology has developed rapidly. Due to the special nature of nuclear power plants, most of them are built in coastal island areas. Due to the shortage of land in coastal areas, many nuclear power plant lands are formed by reclaimed land, so most of the nuclear power transmission lines pass through reclaimed areas.

[0003] Soft soil foundations are composed of weak soils such as silt and silty soil. They are characterized by high water content, high compressibility, high porosity, low shear strength and bearing capacity, low permeability, and high fluidity. Some projects treat soft soil foundations by removing the soft soil and then replacing it with backfill. In soft soil foundations with rock backfill, the settlement of the backfill is greater than the settlement of the cast-in-place pile foundation itself, generating negative friction, which adversely affects the bearing capacity of the piles. This negative friction imposes additional downward loads on the piles, which not only causes additional settlement but also increases the axial force in the piles. For pile groups subject to significant negative friction, its effects must be considered during testing. Negative friction is distributed along the pile shaft and cannot be fully simulated in tests. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a loading device and a calculation method for a scaled model of a pile group foundation, which can achieve equivalent loading of negative friction resistance during model testing, thereby improving the accuracy of the test and the conclusion.

[0005] The present invention is implemented by the following technical solution: a loading device for a scaled model of a pile group foundation, comprising a model box, wherein a test component is arranged in the model box, and the bottom of the test component is fixed to the inner bottom of the model box via a circular tube; pads are fixed on all four sides of the top of the test component, and steel beams are fixed on the two pads on the front side and the two pads on the rear side, and high-strength screws are arranged on the left and right sides of the top of the steel beam, and the high-strength screws penetrate the steel beam and are connected to the inner bottom of the model box via a threaded sleeve; a pressure sensor is installed on the upper end of the high-strength screw, and the bottom of the pressure sensor is in contact with the top of the steel beam; a nut is connected to the high-strength screw above the pressure sensor via a gasket.

[0006] Preferably, the model box is fixed to the foundation via high-strength bolts.

[0007] Preferably, the threaded sleeve is connected to the inner bottom of the model box via stiffening ribs.

[0008] Preferably, the pressure sensor comprises a sleeve sleeved on a high-strength screw, and a strain gauge is fixed on the outer side of the sleeve.

[0009] A calculation method for a loading device of a scaled model of a pile group foundation, the method comprising the following steps:

[0010] Step S1, calculating the downward pull load of the prototype structure of the pile group foundation caused by the friction resistance of the pile body;

[0011] Step S2: converting the downward pull load caused by the friction resistance of the prototype pile into the load required for the scaled test through the structural similarity ratio;

[0012] Step S3: applying the converted load to the test component of the scaled model.

[0013] Preferably, the step S1 is further specifically as follows:

[0014] Step S11: Calculate the average vertical effective stress of the i-th layer of soil around the pile caused by the soil's own weight. The calculation formula is:

[0015] ;

[0016] in, is the average vertical effective stress of the i-th layer of soil around the pile caused by the soil’s own weight,

[0017] 、 are the thickness of the i-th soil layer and the density of the e-th soil layer,

[0018] 、 are the thicknesses of the i-th soil layer and the e-th soil layer respectively;

[0019] Step S12: Calculate the standard value of negative friction resistance of the i-th layer of soil around a single pile above the neutral point. The calculation formula is:

[0020] ;

[0021] is the standard value of the negative friction resistance of the pile side in the i-th layer of soil, is the negative friction coefficient of the i-th layer of soil around the pile,

[0022] is the average vertical effective stress of the i-th layer of soil around the pile;

[0023] Step S13: Calculate the pull-down load of the piles considering the pile group effect. The calculation formula is:

[0024] ;

[0025] ;

[0026] is the pile pull-down load,

[0027] is the pile circumference length,

[0028] is the number of soil layers above the neutral point,

[0029] is the thickness of the i-th soil layer above the neutral point,

[0030] is the negative friction pile group effect coefficient,

[0031] It is the standard value of the weighted average negative friction resistance of the soil layer around the pile above the neutral point.

[0032] is the weighted average density of the soil layer around the pile above the neutral point.

[0033] s ax 、 s ay are the center distances of the longitudinal and transverse piles,

[0034] d is the pile diameter.

[0035] Preferably, the step S2 is further specifically as follows:

[0036] Step S21, determining a similarity ratio 1:n of a scaled model test structure of a pile group foundation;

[0037] Step S22: The negative frictional resistance calculation formula of the pile group foundation scale model is:

[0038] ;

[0039] Step S23: Calculate the negative friction required for the test based on the pull-down load caused by the negative friction of the prototype structure calculated in step S13 and the structural similarity ratio.

[0040] Preferably, the step S3 is further specifically as follows:

[0041] Step S31: Calibrate the pressure sensor using a press, apply a negative friction force required for the test to the pressure sensor through the press, and record the strain value on the pressure sensor at this time;

[0042] Step S32: Tighten the nut to squeeze the pressure sensor, so that the pressure sensor squeezes the steel beam, and so that the steel beam squeezes the test component. Stop tightening the nut when the value on the pressure sensor is the same as the strain value in step S31.

[0043] Step S33: Loading of forces of different magnitudes can be achieved by tightening the nut to different degrees.

[0044] Beneficial effects of the present invention:

[0045] The present invention can solve the problem of equivalent application of negative friction during model testing, improve the accuracy of the test and the conclusion, and can be used in fields such as power transmission line engineering, bridge engineering, and wind power generation engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a structural diagram of the model box.

[0047] Figure 2 This is the internal structure diagram of the model box. DETAILED DESCRIPTION

[0048] The present invention will be further described below with reference to the accompanying drawings.

[0049] See also Figures 1 to 2 The present invention provides a loading device for a scale model of a pile group foundation, comprising a model box 1, wherein a test component 2 is arranged in the model box 1 for simulating a pile group foundation, and the bottom of the test component 2 is fixed to the inner bottom of the model box 1 via a circular tube 3; pads 4 are fixed on all four sides of the top of the test component 2 for connecting to a steel beam 11, and the steel beam 11 is fixed on the two pads 4 on the front side and the two pads 4 on the rear side; high-strength screws 5 are arranged on the left and right sides of the top of the steel beam 11, and the high-strength screws 5 penetrate the steel beam 11 and are connected to the inner bottom of the model box 1 via a threaded sleeve 6; a pressure sensor is installed on the upper end of the high-strength screw 5 for detecting the force applied to the test component 2, and the bottom of the pressure sensor is in contact with the top of the steel beam 11; a nut 8 is connected to the high-strength screw 5 above the pressure sensor via a gasket.

[0050] The model box 1 is fixed to the foundation via high-strength bolts 9 , so that the model box 1 can be fixed.

[0051] The threaded sleeve 6 is connected to the inner bottom of the model box 1 via the reinforcing ribs 10 , which can strengthen the fixation of the threaded sleeve 6 .

[0052] The pressure sensor includes a sleeve 7 sleeved on a high-strength screw, and a strain gauge (not shown) is fixed to the outer side of the sleeve 7. When the sleeve 7 is squeezed by the nut 8, it is deformed in the vertical direction, and the value can be sensed and detected by the sensor sheet.

[0053] Fill the model box 1 with test soil so that the test soil buries the test component 2. Tighten the nut 8 to squeeze the sleeve 7, so that the induction plate squeezes the steel beam 11, and so that the steel beam 11 squeezes the test component 2. When the induction plate detects the corresponding value, stop tightening the nut 8. At this time, the squeezing force of the steel beam 11 on the test component 2 is the simulated negative friction resistance.

[0054] The present invention also provides a calculation method for a loading device of a scaled model of a pile group foundation, the method comprising the following steps:

[0055] Step S1, calculating the downward pull load of the prototype structure of the pile group foundation caused by the friction resistance of the pile body;

[0056] Step S2: converting the downward pull load caused by the friction resistance of the prototype pile into the load required for the scaled test through the structural similarity ratio;

[0057] Step S3: applying the converted load to the test component of the scaled model.

[0058] The step S1 is further specifically as follows:

[0059] Step S11: Calculate the average vertical effective stress of the i-th layer of soil around the pile caused by the soil's own weight. The calculation formula is:

[0060] ;

[0061] in, is the average vertical effective stress of the i-th layer of soil around the pile caused by the soil’s own weight,

[0062] 、 are the thickness of the i-th soil layer and the density of the e-th soil layer,

[0063] 、 are the thicknesses of the i-th soil layer and the e-th soil layer respectively;

[0064] Step S12: Calculate the standard value of negative friction resistance of the i-th layer of soil around a single pile above the neutral point. The calculation formula is:

[0065] ;

[0066] is the standard value of the negative friction resistance of the pile side in the i-th layer of soil, is the negative friction coefficient of the i-th layer of soil around the pile,

[0067] is the average vertical effective stress of the i-th layer of soil around the pile;

[0068] Step S13: Calculate the pull-down load of the piles considering the pile group effect. The calculation formula is:

[0069] ;

[0070] ;

[0071] is the pile pull-down load,

[0072] is the pile circumference length,

[0073] is the number of soil layers above the neutral point,

[0074] is the thickness of the i-th soil layer above the neutral point,

[0075] is the negative friction pile group effect coefficient,

[0076] It is the standard value of the weighted average negative friction resistance of the soil layer around the pile above the neutral point.

[0077] is the weighted average density of the soil layer around the pile above the neutral point.

[0078] s ax 、 s ay are the center distances of the longitudinal and transverse piles,

[0079] d is the pile diameter.

[0080] The step S2 is further specifically as follows:

[0081] Step S21, determining a similarity ratio 1:n of a scaled model test structure of a pile group foundation;

[0082] Step S22: The negative frictional resistance calculation formula of the pile group foundation scale model is:

[0083] ;

[0084] Step S23: Calculate the negative friction required for the test based on the pull-down load caused by the negative friction of the prototype structure calculated in step S13 and the structural similarity ratio.

[0085] The step S3 is further specifically as follows:

[0086] Step S31: Calibrate the pressure sensor using a press, apply a negative friction force required for the test to the pressure sensor through the press, and record the strain value on the pressure sensor at this time;

[0087] Step S32: Tighten the nut to squeeze the pressure sensor, so that the pressure sensor squeezes the steel beam, and so that the steel beam squeezes the test component. Stop tightening the nut when the value on the pressure sensor is the same as the strain value in step S31.

[0088] Step S33: Loading of forces of different magnitudes can be achieved by tightening the nut to different degrees.

[0089] Based on an actual engineering pile group foundation, different soil layer conditions were considered. First, the downward pull load caused by negative friction on the prototype structure was calculated according to steps S11 to S13. Based on the similarity criteria that the test model design must meet, the required load size for each case was determined.

[0090] The soft soil layer is below the hard soil layer, and the stratification is as follows:

[0091] (1) When the thickness of the hard soil layer is less than 1 / 2 of the thickness of the soft soil layer, the lower limit depth of the soft soil layer around the pile is Calculate the soft soil layer ground;

[0092] (2) The hard soil layer and the soft soil layer below it are both thick. When the hard soil layer is buried at a relatively small depth, Calculate to the bottom of the soft soil layer, when the hard soil layer is buried deep, Count to the top of the hard soil layer;

[0093] (3) When the hard soil layer is thicker and the soft soil layer is thinner, Calculate to the top of the hard soil layer.

[0094] The test was conducted by considering the three soil layers mentioned above separately, calculating the magnitude of the negative friction resistance in each case, and calculating the load loaded on the scaled model of the pile group foundation according to the similarity ratio, and then conducting the test loading.

[0095] The above description is only a preferred embodiment of the present invention and should not be understood as limiting the present application. All equivalent changes and modifications made within the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A calculation method for a loading device of a scaled model of a pile group foundation, characterized by: The invention comprises a model box, wherein a test member is provided in the model box, and the bottom of the test member is fixed to the inner bottom of the model box via a round tube; pads are fixed on all four sides of the top of the test member, and steel beams are fixed on the two pads on the front side and the two pads on the rear side, and high-strength screws are provided on the left and right sides of the top of the steel beam, and the high-strength screws penetrate the steel beam and are connected to the inner bottom of the model box via a threaded sleeve; a pressure sensor is installed on the upper end of the high-strength screw, and the bottom of the pressure sensor is in contact with the top of the steel beam; a nut is connected to the high-strength screw above the pressure sensor via a gasket; The method comprises the following steps: Step S1, calculating the downward pull load of the prototype structure of the pile group foundation caused by the friction resistance of the pile body; Step S2: converting the downward pull load caused by the friction resistance of the prototype pile into the load required for the scaled test through the structural similarity ratio; Step S3: applying the converted load to the test component of the scaled model.

2. The calculation method for a loading device for a scaled model of a pile group foundation according to claim 1, characterized in that: The model box is fixed on the foundation via high-strength bolts.

3. The calculation method for a loading device for a scaled model of a pile group foundation according to claim 1, characterized in that: The threaded sleeve is connected to the inner bottom of the model box via stiffening ribs.

4. The calculation method for a loading device for a scaled model of a pile group foundation according to claim 1, characterized in that: The pressure sensor comprises a sleeve sleeved on a high-strength screw, and a strain gauge is fixed on the outer side of the sleeve.

5. The calculation method for a loading device for a scaled model of a pile group foundation according to claim 1, characterized in that: The step S1 is further specifically as follows: Step S11: Calculate the average vertical effective stress of the i-th layer of soil around the pile caused by the soil's own weight. The calculation formula is: ； in, is the average vertical effective stress of the i-th layer of soil around the pile caused by the soil’s own weight, 、 are the thickness of the i-th soil layer and the density of the e-th soil layer, 、 are the thicknesses of the i-th soil layer and the e-th soil layer respectively; Step S12: Calculate the standard value of negative friction resistance of the i-th layer of soil around a single pile above the neutral point. The calculation formula is: ； is the standard value of the negative friction resistance of the pile side in the i-th layer of soil, is the negative friction coefficient of the i-th layer of soil around the pile, is the average vertical effective stress of the i-th layer of soil around the pile; Step S13: Calculate the pull-down load of the piles considering the pile group effect. The calculation formula is: ； ； is the pile pull-down load, is the pile circumference length, is the number of soil layers above the neutral point, is the thickness of the i-th soil layer above the neutral point, is the negative friction pile group effect coefficient, It is the standard value of the weighted average negative friction resistance of the soil layer around the pile above the neutral point. is the weighted average density of the soil layer around the pile above the neutral point. s ax 、 s ay are the center distances of the longitudinal and transverse piles, d is the pile diameter.

6. The calculation method for a loading device for a scaled model of a pile group foundation according to claim 5, characterized in that: The step S2 is further specifically as follows: Step S21, determining a similarity ratio 1:n of a scaled model test structure of a pile group foundation; Step S22: The negative frictional resistance calculation formula of the pile group foundation scale model is: ； Step S23: Calculate the negative friction required for the test based on the pull-down load caused by the negative friction of the prototype structure calculated in step S13 and the structural similarity ratio.

7. The calculation method for a loading device for a scaled model of a pile group foundation according to claim 1, characterized in that: The step S3 is further specifically as follows: Step S31: Calibrate the pressure sensor using a press, apply a negative friction force required for the test to the pressure sensor through the press, and record the strain value on the pressure sensor at this time; Step S32: Tighten the nut to generate a pre-tightening force, so that the pressure sensor squeezes the steel beam, and the steel beam squeezes the test component. When the value on the pressure sensor is the same as the strain value in step S31, stop tightening the nut. Step S33: Loading of forces of different magnitudes can be achieved by tightening the nut to different degrees.

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