Pile foundation reinforcement soft soil foundation treatment method based on foundation settlement feedback

Abstract

The invention provides a pile foundation reinforcement soft soil foundation treatment method based on foundation settlement feedback, and belongs to the technical field of pile foundation reinforcement. Sequentially obtaining a composite foundation bearing capacity characteristic value fspk, calculating a single-pile vertical bearing capacity characteristic value # imgabs0 #, calculating a pile body area replacement rate # imgabs1 #, determining a pile number N and a pile arrangement form, determining an area replacement rate m1 after actual pile arrangement and a composite foundation bearing capacity fsp after actual pile arrangement; and the settlement S of the composite foundation is calculated by combining the settlement S1 of the reinforced area and the settlement S2 of the underlying layer, and the overall stability of the composite foundation is analyzed. The pile foundation structure is fed back and reinforced through composite foundation deformation control, the pile foundation is effectively optimized to reduce the construction cost, and the economic benefits of construction are improved; by controlling the deformation of the whole soft foundation, the problems of pavement unevenness and cracks caused by uneven settlement of the whole road pavement are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of pile foundation reinforcement, and in particular relates to a pile foundation reinforcement soft soil foundation treatment method based on foundation settlement feedback. Background Art

[0002] In the road construction in coastal areas, there will be a large number of soft soil foundations, which have the characteristics of high water content, large porosity, not easy to compress, poor bearing capacity, etc., and over time, under the action of external loads, the pore water pressure decreases, the soil is compressed and compacted, causing differential settlement, which can easily lead to the generation of road cracks, reduce the comfort of vehicles driving on the road, and gradually cause the road structure to become less stable and even further cause road collapse. There are two main means of controlling the settlement and deformation of soft soil foundations in the prior art. One is to improve the consolidation degree of the soil, usually using drainage preloading or vacuum preloading, and the other is to reduce the additional stress of the soft soil layer, that is, by using a pile-type composite foundation to transfer most of the overlying load to the pile body, reducing the additional stress of the soft soil foundation.

[0003] Pile foundation reinforcement for soft soil foundation usually adopts foundation treatment structures such as cement soil mixing piles, lime piles, cement fly ash gravel (CFG) piles, high pressure rotary jet piles, prestressed pipe piles, reinforced concrete pile net structure and reinforced concrete pile board structure. For shallow soft soil foundation, foundation treatment structures such as cement soil mixing piles, cement fly ash gravel piles and high pressure rotary jet piles can be used; for deep soft soil foundation, foundation treatment structures such as reinforced concrete pile net structure and reinforced concrete pile board structure can be used. For soft soil foundation, some existing methods use outward extending connecting ribs to increase the contact area with soft soil, and auxiliary pipes extending up and down to pour reinforcement slurry to improve the bearing capacity of pile foundation, and some methods use a combination of steel pipe piles and grouting reinforcement to treat weak sandwich foundation. However, the existing technology for reinforcing soft soil foundation still causes tensile stress at the bottom of the upper roadbed, which in turn causes cracks and unevenness in the road surface. At the same time, for the soft soil transition section between the shallow soft soil foundation and the deep soft soil foundation, the thickness of the soft soil foundation will change along the driving direction, and there is no reasonable and economical method to ensure the overall stability of the foundation of the soft soil transition section. Summary of the invention

[0004] An embodiment of the present invention provides a method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback, aiming to solve the problem that the technology of controlling settlement deformation in the prior art cannot avoid the tensile stress of the roadbed subgrade caused by the settlement difference between the roadbed and the reinforced foundation, thereby causing cracks and unevenness in the road surface.

[0005] To achieve the above object, the technical solution adopted by the present invention is: A method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback is provided, comprising the following steps: S10, divide the strata and determine the characteristic value of the soil bearing capacity of each stratum; S20, dividing the soft soil foundation transition section between soft soil foundations of different depths into regions, and determining the characteristic value of the composite foundation bearing capacity of each region; S30. Preliminary setting of pile length and pile diameter, calculation of characteristic value of vertical bearing capacity of single pile ; S40, based on the determined characteristic value of the composite foundation bearing capacity of the corresponding area f spk , according to the characteristic value of composite foundation bearing capacity f spk Calculate the pile area replacement rate ; S50, determine the number of piles N and cloth pile forms; S60, according to the number of piles N and pile layout form to determine the area replacement rate after actual pile layout m 1. Determine the bearing capacity of the composite foundation after actual pile arrangement f sp,k1 ; S70. Calculate the composite foundation settlement S, where S is the sum of the settlement of the reinforcement area S1 and the settlement of the underlying layer S2. The calculation formula (7) for S1 is:

[0006] The calculation formula (8) of S2 is:

[0007] in, E spi For the i The pile-soil composite compression modulus of the soil layer, For the i The additional stress increment at the midpoint of the soil layer is For the i The thickness of the soil layer, s’ is the foundation deformation obtained based on the layer-by-layer summation method, ψ Calculate the empirical coefficient for settlement, n is the number of soil layers divided within the depth range of foundation deformation calculation, E si The bottom of the reinforcement area i Compression modulus of the layer soil; S80. Conduct overall stability analysis on composite foundation; S90, looping steps S30 to S80, designing pile foundations in each area one by one, and controlling the composite foundation settlement difference of the overall soft soil foundation.

[0008] In a possible implementation, in step S30, The calculation formula (1) is:

[0009] in, is the perimeter of the pile section, For the week i The lateral friction of the soil layer, l i The first i The thickness of the soil layer, q p is the bearing capacity of the soil at the pile end, is the bearing capacity reduction factor of the pile end soil, A p is the cross-sectional area of ​​the pile.

[0010] In some embodiments, the vertical bearing capacity characteristic value of a single pile is The following calculation formula (2) must also be satisfied:

[0011] in, is the pile strength reduction factor, f cu It is the average value of the cubic compressive strength of indoor standard test blocks with the same proportion as the pile body under standard curing conditions for 90 days. A p is the cross-sectional area of ​​the pile.

[0012] In some embodiments, in step S40, the pile area replacement rate The calculation formula (3) is:

[0013] in, is the reduction factor of the bearing capacity of the soil between piles, f sp is the characteristic value of soil bearing capacity between piles, λ is the bearing capacity factor of a single pile.

[0014] In some embodiments, in step S50, the number of piles N The calculation formula (4) is:

[0015] in, A 1 is the area of ​​the calculation region.

[0016] In one possible implementation, the compression modulus of the overall composite foundation is calculated E sp , the calculation formula is: Calculation formula (5):

[0017] Calculation formula (6):

[0018] in, E s is the compression modulus of the soil between piles, E p is the compression modulus of the pile foundation, n is the pile-soil stress ratio; The compression modulus of the composite foundation reinforcement area under the embankment is calculated. The compression modulus of the composite foundation reinforcement area under the embankment is the average value of the compression modulus of the soil between piles obtained by calculation formula (5) and calculation formula (6).

[0019] In a possible implementation, in step S80, the calculation formula (9) for the overall stability analysis of the composite foundation is:

[0020] in, F s Estimate the overall safety factor of the composite foundation for the pile foundation, For the i Composite shear strength of the bottom of the soil strip foundation, l i For the i The length of the bottom of the soil strip foundation soil, c spi For the i Composite cohesion at the bottom of the soil strip foundation, For the i The composite internal friction angle at the bottom of the strip foundation soil, W i For the i Vertical load at the bottom of the strip foundation soil, For the i The angle between the bottom of the soil strip foundation and the horizontal line. c i For the i The cohesion of the fill at the bottom of the soil strip, For the i Soil strip bottom i The internal friction angle at the bottom of the soil strip.

[0021] In some embodiments, if the overall safety factor of the pile foundation or composite foundation is lower than a preset factor value, reinforcement measures are adopted.

[0022] In a possible implementation, in step S90, controlling the composite foundation settlement difference of the entire soft soil foundation specifically includes: Ensure that the maximum longitudinal slope of the highway is within the range, and take the slope change of the preset settlement value as the allowable value, and the preset settlement value is 0.15%~0.25%.

[0023] In some embodiments, controlling the composite foundation settlement difference of the entire soft soil foundation further includes: A cushion layer is set on the composite foundation to ensure uniform stress distribution of the upper roadbed load on the composite foundation.

[0024] Compared with the prior art, the solution shown in the embodiment of the present application proposes a pile foundation optimization design for the soft soil foundation transition section between different soft soil foundation thicknesses to achieve soft soil foundation reinforcement and effectively control the settlement of the reinforced soft foundation. The composite foundation deformation control is used to feedback the reinforced pile foundation structure, effectively optimize the pile foundation to reduce construction costs and improve the economic benefits of construction; by controlling the deformation of the overall soft foundation, the uneven settlement of the overall road surface causing bumps and cracks in the road surface is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A design flow chart of a method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback provided by an embodiment of the present invention; Figure 2 A longitudinal cross-sectional view of a pile foundation reinforcement road project according to the present invention; Figure 3 It is a transverse cross-sectional view and a schematic diagram of a potential damage surface of a pile foundation reinforcement road project of the present invention; Description of reference numerals: 1. Soft soil foundation transition section; 2. Pile foundation; 3. Cushion layer; 4. Roadbed; 5. Pavement; 6. Potential damage surface. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] In the claims, description and the above-mentioned drawings of the present invention, unless otherwise clearly defined, the use of terms such as "first", "second" or "third" etc. are for distinguishing different objects rather than for describing a specific order.

[0028] In the claims, specification and the above-mentioned drawings of the present invention, unless otherwise explicitly defined, directional words, such as the terms "center", "lateral", "longitudinal", "horizontal", "vertical", "top", "bottom", "inside", "outside", "up", "down", "front", "back", "left", "right", "clockwise", "counterclockwise", "high", "low", etc., indicating directions or positional relationships are based on the directions and positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, and therefore cannot be understood as limiting the specific protection scope of the present invention.

[0029] In the claims, specification and the above drawings of the present invention, unless otherwise clearly defined, if the term "fixed connection" or "fixed connection" is used, it should be understood in a broad sense, that is, any connection method without a displacement relationship and relative rotation relationship between the two, that is to say, including non-detachable fixed connection, detachable fixed connection, integrated connection and fixed connection through other devices or elements.

[0030] In the claims, description and drawings of the present invention, if the terms "include", "have" and their variations are used, they are intended to mean "including but not limited to".

[0031] Please also read Figure 1 and Figure 2 The pile foundation reinforcement soft soil foundation treatment method based on foundation settlement feedback provided by the present invention is now described. The pile foundation reinforcement soft soil foundation treatment method based on foundation settlement feedback comprises the following steps: S10, divide the strata and determine the characteristic value of the soil bearing capacity of each stratum; S20, dividing the soft soil foundation transition section between soft soil foundations of different depths into regions, and determining the characteristic value of the composite foundation bearing capacity of each region; S30. Preliminary setting of pile length and pile diameter, calculation of characteristic value of vertical bearing capacity of single pile ; S40, based on the determined characteristic value of the composite foundation bearing capacity of the corresponding area f spk , according to the characteristic value of composite foundation bearing capacity f spk Calculate the pile area replacement rate ; S50, determine the number of piles N and cloth pile forms; S60, according to the number of piles N and pile layout form to determine the area replacement rate after actual pile layout m 1. Determine the bearing capacity of the composite foundation after actual pile arrangement fsp,k1 ; S70. Calculate the composite foundation settlement S, where S is the sum of the settlement of the reinforcement area S1 and the settlement of the underlying layer S2. The calculation formula (7) for S1 is:

[0032] The calculation formula (8) of S2 is:

[0033] in, E spi For the i The pile-soil composite compression modulus of the soil layer, For the i The additional stress increment at the midpoint of the soil layer is For the i The thickness of the soil layer, s’ is the foundation deformation obtained based on the layer-by-layer summation method, ψ Calculate the empirical coefficient for settlement, n is the number of soil layers divided within the depth range of foundation deformation calculation, E si The bottom of the reinforcement area i Compression modulus of the layer soil; S80. Conduct overall stability analysis on composite foundation; S90, looping steps S30 to S80, designing pile foundations in each area one by one, and controlling the composite foundation settlement difference of the overall soft soil foundation.

[0034] In this embodiment, the empirical coefficient of settlement calculation is ψ The value can be taken according to the requirements of "Highway Roadbed Design Specifications".

[0035] Figure 2 , a longitudinal section of a pile foundation reinforced road project is shown, which includes the distribution of a soft soil foundation transition section 1, a pile foundation 2, a cushion layer 3, a roadbed 4 and a road surface 5. Figure 3 The cross section and potential damage surface of the pile foundation reinforcement road project are shown in Figure 6 ( Figure 3 The most dangerous failure surface is determined by continuously searching for sliding surfaces, and the safety factor of the sliding soil is determined by the limit equilibrium method. In engineering design, a certain stability must be met to ensure the safety of engineering use; when the stability is not met, the pile structure needs to be re-optimized or reinforcement measures need to be taken.

[0036] The pile foundation reinforcement soft soil foundation treatment method based on foundation settlement feedback in this embodiment is based on the premise of regional division, and designs are carried out separately for different regions. By obtaining the characteristic value of the bearing capacity of the composite foundation f spk→ Calculate the characteristic value of the vertical bearing capacity of a single pile → Calculate the pile area replacement rate →Determine the number of piles N and pile layout → determine the area replacement rate after actual pile layout m 1. Bearing capacity of composite foundation after actual pile arrangement f sp,k1 → The settlement S of the composite foundation is calculated by combining the settlement S1 of the reinforcement area with the settlement S2 of the underlying layer, and then the settlement of the foundation in this area is measured. In addition, the anti-slip calculation of the roadbed 4 is realized by performing an overall stability analysis on the composite foundation, and the pile foundation design of a single area is realized. Finally, the settlement difference of the composite foundation of the overall soft soil foundation is controlled by performing pile foundation design on each area.

[0037] The pile foundation reinforcement soft soil foundation treatment method based on foundation settlement feedback provided in this embodiment, compared with the prior art, proposes a pile foundation optimization design for the soft soil foundation transition section 1 between different soft soil foundation thicknesses to achieve soft soil foundation reinforcement and effectively control the settlement of the reinforced soft foundation. The composite foundation deformation control is used to feedback the reinforced pile foundation 2 structure, and the pile foundation 2 is effectively optimized to reduce construction costs and improve the economic benefits of construction; by controlling the deformation of the overall soft foundation, the uneven settlement of the overall road surface 5 causing the road surface 5 to be uneven and cracked is solved.

[0038] In some embodiments, step S10 specifically includes: S11. Use digging, probing, penetration or other in-situ measurement methods to determine the type, distribution range and physical and mechanical properties of soft soil and the location of groundwater level; When encountering a soft soil foundation transition section 1 between soft soil foundations of different depths, the drilling position needs to be encrypted; S12. Divide the strata.

[0039] In specific implementation, when drilling for exploration, the drilling position is less than 35m (e.g. 33m, 30m, 28m, 26m, 23m, 20m, 15m, 10m) along the center line of the roadbed 4, and less than 18m (e.g. 17m, 15m, 13m, 10m, 8m, 5m) along the vertical center line. More specifically, the exploration process follows the Highway Geotechnical Test Code JTG3430-2020.

[0040] In some embodiments, step S20 specifically includes: Divide the soft soil foundation transition section 1 between soft soil foundations of different depths into regions and determine the characteristic value of the composite foundation bearing capacity in each region f sp,k ; Divide the area to control external loads separately; The principle for dividing the area range is as follows: the preset calculated length is used along the direction of the lane, the lane is used as the dividing area along the cross-section direction of the road, and the boundary is the bottom of the slope of the roadbed.

[0041] On the highway, along the direction of the lane, the depth of the soft soil foundation will gradually change, and the bearing capacity of the foundation soil will also change; at the same time, along the cross-section direction of the road, because the cross-section of the roadbed has a slope, and the isolation belt in the middle of the road and the protective facilities in the shoulder area are fixed loads, while the middle lane is a live load and needs to bear traffic loads of different axle weights. Therefore, it is necessary to divide the area to regulate the external load separately.

[0042] This embodiment divides the soft soil foundation into regions along the longitudinal and transverse directions of the road, controls the settlement difference between the divided regions and the settlement difference of the overall pile foundation reinforced soft soil foundation transition section 1, and enables the overall embankment to have advantages such as good overall stability and uniform settlement.

[0043] Optionally, a vertical difference in height of 1m to 3m of the soft soil foundation along the direction of the driving lane is used as a preset calculation length, and examples of the values ​​of the preset calculation length are as follows: 1m, 1.5m, 2m, 2.5m, 3m.

[0044] Optionally, the bearing capacity characteristic value of the composite foundation in each area can be determined based on the thickness of the overlying roadbed fill, live load and other fixed loads specified in the Highway Roadbed Design Code JTG D30-2015 f sp,k .

[0045] In some embodiments, in step S30, The calculation formula (1) is:

[0046] in, is the circumference of the pile section (m), For the week i The lateral friction of the soil layer (kPa), l i The first i Thickness of soil layer (mm), q p is the bearing capacity of the soil at the pile end (kPa), is the bearing capacity reduction factor of the pile end soil, A p is the cross-sectional area of ​​the pile.

[0047] Optionally, the pile length and pile diameter of the pile foundation 2 are predetermined according to the "Highway Roadbed Design Code" JTG D30-2015 and the design experience of the actual geological conditions. The pile diameter is 300 mm to 700 mm (for example, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, 650 mm), and the pile end bearing layer should be selected from a stratum with relatively high bearing capacity.

[0048] Optional, bearing capacity of soil at pile tip q p According to the requirements of the Highway Roadbed Design Code, the bearing capacity reduction factor of the pile end soil is The value of is 0.3~0.7 (for example, 0.4, 0.5, 0.6).

[0049] Based on the above embodiment, the characteristic value of the vertical bearing capacity of a single pile is The following calculation formula (2) must also be satisfied:

[0050] in, is the pile strength reduction factor, f cu is the average cubic compressive strength of indoor standard test blocks with the same mix ratio as the pile body under standard curing conditions for 90 days (kPa), A p is the cross-sectional area of ​​the pile (m 2 ).

[0051] This embodiment actually makes the vertical bearing capacity characteristic value of the single pile The single pile bearing capacity determined by the material strength of the pile foundation 2 according to calculation formula (2) should be greater than the single pile bearing capacity provided by the resistance of the soil at the side of the pile and the soil at the end of the pile. The value of is 0.1~0.4 (for example, 0.2, 0.3), as f cu The cube from which the values ​​come is a cube with a side length of 70mm~71mm (for example, 70.3mm, 70.5mm, 70.7mm).

[0052] Based on the above embodiment, in step S40, the pile area replacement rate The calculation formula (3) is:

[0053] in, is the reduction factor of the bearing capacity of the soil between piles, f sp is the characteristic value of soil bearing capacity between piles, is the bearing capacity factor of a single pile.

[0054] Optional, reduction factor for bearing capacity of soil between piles The value of is 0~0.15 (for example, 0.05, 0.1).

[0055] Optional, single pile bearing capacity factor λ The value of is 1.0 when penetrating soft soil. If it is a suspended pile, it is 0.8 to 1.05 (for example, 0.85, 0.9, 0.95, 1.0).

[0056] Based on the above embodiment, in step S50, the number of piles N The calculation formula (4) is:

[0057] in, A 1 is the area of ​​the calculation region.

[0058] Optionally, the distance between piles is 2 to 6 times the pile diameter, for example, 3 times the pile diameter, 4 times the pile diameter, or 5 times the pile diameter.

[0059] In some embodiments, the compression modulus of the overall composite foundation is calculated E sp , the calculation formula is: Calculation formula (5):

[0060] Calculation formula (6):

[0061] in, E s is the compression modulus of the soil between piles (kPa), E p is the compression modulus of pile foundation 2 (kPa), n is the pile-soil stress ratio; Calculate the compression modulus of the composite foundation reinforcement area under the embankment. The compression modulus of the composite foundation reinforcement area under the embankment is the average value of the compression modulus of the soil between piles obtained by calculation formula (5) and calculation formula (6), that is: .

[0062] In this embodiment, since the properties of each layer of foundation soil are different, the compression modulus of the soil between the piles is different. Therefore, when summing the layers, it is necessary to first divide each layer of soil according to different geological soils and thicknesses, and calculate the average value of formula (5) and formula (6) for each layer of soil to obtain the compression modulus of each layer of composite foundation: E spi Come bring in.

[0063] Optional, pile-soil stress ratio nThe value of is 9~16 (for example, 10, 12, 14, 15). When the pile-soil compression modulus ratio is small and the soft soil depth is large, the smaller value is taken; the compression modulus of pile foundation 2 E p Determined by compression test.

[0064] In some embodiments, in step S60, according to the number of piles N and pile layout form to determine the area replacement rate after actual pile layout m 1 Specifically include: ,in d is the actual average diameter of the pile body, d e is the equivalent circle diameter of the ground area treated by a single pile related to the pile arrangement form. For equilateral triangle pile arrangement, d e =1.05 s ; Square cloth pile d e =1.13 s ; Rectangular cloth pile ; s , s 1. s 2 are the pile spacing, longitudinal pile spacing along the lane direction, and transverse pile spacing.

[0065] In some embodiments, in step S80, the calculation formula (9) for the overall stability analysis of the composite foundation is:

[0066] in, F s Estimate the overall safety factor of the composite foundation for the pile foundation, For the i Composite shear strength of the bottom of the soil strip foundation, l i For the i The length of the bottom of the soil strip foundation soil, c spi For the i Composite cohesion at the bottom of the soil strip foundation, For the i The composite internal friction angle at the bottom of the strip foundation soil, W i For the i Vertical load at the bottom of the strip foundation soil, For the i The angle between the bottom of the soil strip foundation and the horizontal line. c i For the i The cohesion of the fill at the bottom of the soil strip, For the iSoil strip bottom i The internal friction angle at the bottom of the soil strip.

[0067] In this embodiment, the circular arc sliding method is used to analyze the overall stability of the composite foundation, and the calculation method thereof can adopt the effective consolidation stress method.

[0068] The basic principle of the circular sliding method for overall stability analysis is static balance. This method divides the sliding soil into several strips, calculates the sliding moment and anti-sliding moment of each strip about the sliding circle center, and then takes the ratio of the two moments as the stability coefficient K to determine whether the slope is stable. The circular sliding method is mainly applicable to the following situations: homogeneous simple soil slopes (slopes with uniform soil), non-homogeneous soil slopes (slopes with circular sliding surfaces despite uneven soil), and complex-shaped soil slopes (slopes with complex shapes but still circular sliding surfaces). It can be seen that the circular sliding method is applicable to the reinforcement of soft soil foundation piles.

[0069] The effective consolidation stress method is a method used to calculate the strength change of soil during the consolidation process under load. It is mainly used to calculate the situation where the construction loading rate is slow or there is a vertical drainage channel in the foundation. At this time, the foundation can produce drainage consolidation. The effective consolidation stress method combines the advantages of the total stress method and the effective stress method. It not only considers the favorable effect of soil strength growth caused by consolidation under load, but also does not ignore the adverse effect of increased pore water pressure caused by undrained damage. By considering the consolidation process of the soil, the safety factor of the soil can be more reasonably evaluated. The effective consolidation stress method is applicable to the following situations: 1) The construction loading rate is slow. In this case, the foundation has enough time for drainage consolidation, and the strength of the soil will increase with the consolidation process; 2) There is a vertical drainage channel in the foundation, which can promote the drainage consolidation of the foundation, thereby affecting the strength of the soil. Therefore, this calculation method is also applicable to the scenario of pile foundation reinforcement in soft soil foundation.

[0070] The stability calculation of composite foundation is an important part of ensuring the safety of engineering construction. The stability calculation can ensure that the engineering quality meets the shear strength requirements, guide the design and construction of composite foundation, avoid delays and re-construction caused by foundation problems, and thus save time and engineering costs. At the same time, reasonable stability calculation can evaluate the bearing capacity and deformation characteristics of the foundation under various working conditions, ensure that the foundation will not be damaged, and thus ensure the safety of the overall engineering structure. The pile foundation of this embodiment estimates the overall safety factor of the composite foundation. F s , which is calculated as the ratio of the anti-sliding force to the sliding force on the potential damage surface, and the safety factor F s The value is not less than 1.4.

[0071] On the basis of the above embodiment, if the overall safety factor of the pile foundation composite foundation is lower than the preset coefficient value, reinforcement measures are adopted. Optionally, if the anti-slip stability cannot be met, the implementation of reinforcement measures includes but is not limited to the use of counter-pressure berms, geotextiles, geogrids, etc. for reinforcement. During the specific construction, the geogrid is laid directly on the cushion layer 3 in the longitudinal and transverse sections. The laying should be flat and even, and tightened; at the overlap of the geogrid, the overlap width is not less than 25cm, and it is fixed with "U"-shaped nails; sandbags are stacked on both sides of the cross section of the roadbed, and the geogrid is folded back to form a wrapped end, and the folded length is not less than 30cm.

[0072] In some embodiments, in step S90, controlling the composite foundation settlement difference of the overall soft soil foundation specifically includes: ensuring that the maximum longitudinal slope of the highway is within the range, with the slope change of the preset settlement value as the allowable value, wherein the preset settlement value is 0.15%~0.25% (for example, 0.18%, 0.2%, 0.2.3%).

[0073] During the specific implementation, according to the requirements of Highway Engineering Technical Standards (JTG B01-2014), the maximum longitudinal slope of the highway should be ensured. Due to the influence of soft soil geological conditions, a slope change of 0.2% is preferably used as the allowable preset settlement value, that is, the allowable settlement value for a route longitudinal slope of 50m~100m is 10cm~20cm.

[0074] On the basis of the above embodiment, controlling the composite foundation settlement difference of the overall soft soil foundation also includes: the slope difference of the uneven settlement of the transverse slope of the road surface 5 is 0.4%~0.6% (for example, 0.5%), which is beneficial to the drainage of the road surface 5.

[0075] On the basis of the above embodiment, in addition to the longitudinal and transverse slope restrictions, the flatness of the road also needs to be paid attention to. The vehicle speed is high on high-grade roads. If the road is not flat, it will cause serious bumps on the vehicle. If the vehicle comfort is not reduced, the vehicle speed will also be reduced. Therefore, the standard deviation of the flatness measurement is used. As an evaluation index, after the completion of the highway and first-class highway pavement ≤1.5, after the completion of other grades of highway pavement ≤2.5.

[0076] On the basis of the above embodiment, the composite foundation settlement difference of the overall soft soil foundation is controlled, and further includes: in order to coordinate the deformation between the pile and the soil, a cushion layer 3 needs to be set on the composite foundation to make the stress distribution of the upper roadbed load on the composite foundation uniform and avoid stress concentration. For the cushion layer 3, medium sand, coarse sand, crushed stone or graded sand and gravel can be used for laying, and the maximum particle size is less than 30 mm, and the thickness is 150 mm to 300 mm (for example, 150 mm, 200 mm, 250 mm).

[0077] The pile foundation reinforcement soft soil foundation treatment method based on foundation settlement feedback of the present application is mainly aimed at the soft soil foundation transition section 1 between the shallow soft soil foundation and the deep soft soil foundation, and the area is divided to arrange the pile foundation and reduce the cost of the pile foundation, which has good economic benefits and can effectively solve the uneven settlement caused by different soft foundation depths. At the same time, the pile foundation structure is reinforced based on the composite foundation deformation control to feedback, and then the pile foundation structure is optimized, and the settlement of the overall composite soft soil foundation is effectively controlled. By controlling the settlement of each divided area, the uneven settlement and crack phenomenon of the road surface 5 can be effectively guaranteed. In addition, by performing anti-slip calculation on the roadbed 4 and using a cushion layer 3 to weaken the uneven stress borne by the composite foundation, the overall stability of the overall embankment is good, the settlement is uniform, and the overall deformation control effect is good.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback, characterized in that: The following steps are involved: S10, divide the strata and determine the characteristic value of the soil bearing capacity of each stratum; S20, dividing the soft soil foundation transition section between soft soil foundations of different depths into regions, and determining the characteristic value of the composite foundation bearing capacity of each region; S30. Preliminary setting of pile length and pile diameter, calculation of characteristic value of vertical bearing capacity of single pile ; S40, based on the determined characteristic value of the composite foundation bearing capacity of the corresponding area f spk , according to the characteristic value of composite foundation bearing capacity f spk Calculate the pile area replacement rate ; S50: Determine the number of piles N and cloth pile forms; S60, according to the number of piles N and pile layout form to determine the area replacement rate after actual pile layout m 1. Determine the bearing capacity of the composite foundation after actual pile arrangement f sp,k1 ; S70. Calculate the composite foundation settlement S, where S is the sum of the settlement of the reinforcement area S1 and the settlement of the underlying layer S2. The calculation formula (7) for S1 is: The calculation formula (8) of S2 is: in, E spi For the i The pile-soil composite compression modulus of the soil layer, For the i The additional stress increment at the midpoint of the soil layer is For the i The thickness of the soil layer, s’ is the foundation deformation obtained based on the layer-by-layer summation method, ψ Calculate the empirical coefficient for settlement, n is the number of soil layers divided within the depth range of foundation deformation calculation, E si The bottom of the reinforcement area i Compression modulus of the layer soil; S80. Conduct overall stability analysis on composite foundation; S90, looping steps S30 to S80, designing pile foundations in each area one by one, and controlling the composite foundation settlement difference of the overall soft soil foundation.

2. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 1, characterized in that: In step S30, The calculation formula (1) is: in, is the perimeter of the pile section, For the week i The lateral friction of the soil layer, l i The first i The thickness of the soil layer, q p is the bearing capacity of the soil at the pile end, is the bearing capacity reduction factor of the pile end soil, A p is the cross-sectional area of ​​the pile.

3. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 2, characterized in that: Characteristic value of vertical bearing capacity of single pile The following calculation formula (2) must also be satisfied: in, is the pile strength reduction factor, f cu It is the average value of the cubic compressive strength of indoor standard test blocks with the same proportion as the pile body under standard curing conditions for 90 days. A p is the cross-sectional area of ​​the pile.

4. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 2, characterized in that: In step S40, the pile area replacement rate The calculation formula (3) is: in, is the reduction factor of the bearing capacity of the soil between piles, f sp is the characteristic value of soil bearing capacity between piles, is the bearing capacity factor of a single pile.

5. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 2 or 4, characterized in that: In step S50, the number of piles N The calculation formula (4) is: in, A 1 is the area of ​​the calculation region.

6. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 1, characterized in that: Calculating the compression modulus of a monolithic composite foundation E sp , the calculation formula is: Calculation formula (5): Calculation formula (6): in, E s is the compression modulus of the soil between piles, E p is the compression modulus of the pile foundation, n is the pile-soil stress ratio; The compression modulus of the composite foundation reinforcement area under the embankment is calculated. The compression modulus of the composite foundation reinforcement area under the embankment is the average value of the compression modulus of the soil between piles obtained by calculation formula (5) and calculation formula (6).

7. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 1, characterized in that: In step S80, the calculation formula (9) for the overall stability analysis of the composite foundation is: in, F s Estimate the overall safety factor of the composite foundation for the pile foundation, For the i Composite shear strength of the bottom of the soil strip foundation, l i For the i The length of the bottom of the soil strip foundation soil, c spi For the i Composite cohesion at the bottom of the soil strip foundation, For the i The composite internal friction angle at the bottom of the strip foundation soil, W i For the i The vertical load at the bottom of the strip foundation soil, For the i The angle between the bottom of the soil strip foundation and the horizontal line. c i For the i The cohesion of the fill at the bottom of the soil strip, For the i Soil strip bottom i The internal friction angle at the bottom of the soil strip.

8. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 7, characterized in that: If the overall safety factor of the pile-based composite foundation is lower than the preset factor value, reinforcement measures are adopted.

9. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 1, characterized in that: In step S90, controlling the composite foundation settlement difference of the entire soft soil foundation specifically includes: Ensure that the maximum longitudinal slope of the highway is within the range, and take the slope change of the preset settlement value as the allowable value, and the preset settlement value is 0.15%~0.25%.

10. The method for treating soft soil foundation by pile reinforcement based on foundation settlement feedback according to claim 9, characterized in that: Controlling the composite foundation settlement difference of the overall soft soil foundation also includes: A cushion layer is set on the composite foundation to ensure uniform stress distribution of the upper roadbed load on the composite foundation.

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