CN111749054A

CN111749054A - Pile length variable rigid pile composite foundation for improving stability of embankment with inclined embedded layer

Info

Publication number: CN111749054A
Application number: CN202010772999.7A
Authority: CN
Inventors: 周海祚; 于晓旋; 郑刚; 赵佳鹏; 夏博洋; 杨新煜
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2020-08-04
Filing date: 2020-08-04
Publication date: 2020-10-09

Abstract

The invention discloses a pile length variable rigid pile composite foundation for improving the stability of an embankment with an inclined embedded layer, which comprises an embankment arranged on a reinforced soil body, wherein the upper part of the reinforced soil body is a soft soil layer, the lower part of the reinforced soil body is an embedded layer, the thickness of the soft soil layer is gradually reduced from one side to the other side of the cross section of the embankment, a plurality of rigid piles are arranged in the reinforced soil body, and the arrangement area of all the rigid piles is an area covered by the embankment; all the rigid piles comprise long piles and conventional piles, the arrangement area of the long piles is an area corresponding to the slope surface on one side with the large thickness of the soft soil layer, and the rest area is the arrangement area of the conventional piles; the pile length of the conventional pile is 2 times of the pile diameter of the embedded layer, the pile length of the long pile is 5-7 times of the pile diameter of the embedded layer, and the construction cost is greatly reduced on the basis of ensuring that the stability of the embankment is greatly improved by only lengthening the pile length under the embankment on one side. The construction is simple, the total settlement control effect is good, the safety is high, the applicability is strong, and the economical efficiency is good.

Description

Pile length variable rigid pile composite foundation for improving stability of embankment with inclined embedded layer

Technical Field

The invention relates to a civil engineering foundation, in particular to a variable pile length rigid pile composite foundation with an inclined embedded layer.

Background

At present, with the rapid development of construction of high-speed railways and the like in China, higher requirements are put forward on the construction speed, settlement control and the like of embankments. The soft soil is widely distributed in coastal areas of China, has large natural water content, high compressibility, low bearing capacity and low shear strength, and provides great challenges for engineering construction. In the southeast coastal areas of China, the upper soil layer is mostly saturated soft clay, and the lower soil layer is sandy soil and silty clay with relatively good engineering properties. The shear strength of the upper soil body is low, and the drainage capacity is poor, so that the embankment is easy to be damaged by instability. In order to meet the requirements of bearing capacity, stability and settlement control in engineering, the rigid pile foundation is widely applied. The rigid pile comprises a plurality of pile types such as a CFG pile, a plain concrete pile, a reinforced concrete pile, prestressed cement, a PCC pile and the like, has the advantages of high bonding strength, strong bearing capacity, good sedimentation control effect, high construction speed and the like, and is very wide in engineering application. Usually, the embedded layer is a horizontal embedded layer, and the depth of the rigid pile embedded into the lower hard soil layer is 0-2 times of the pile diameter. However, because of the existence of complex mountain land topography in partial areas, the inclined embedded and fixed layers are distributed, namely the inclination angle of the hard soil embedded and fixed layer is 5-20 degrees. The inclined embedded layer weakens the constraint action of the inclined embedded layer on the pile due to the inclined surface. If the pile embedding depth is 0-2 times of the pile diameter under the condition, the pile embedding effect is insufficient, and the pile body is easy to be wholly overturned and damaged, so that the embankment is unstable, and huge personnel and property losses are caused. The soft soil foundation containing the inclined embedded layer has the advantages that how to reasonably utilize the rigid piles to reinforce the embankment in engineering due to the fact that the engineering accidents of embankment instability caused by the overturning damage of the rigid piles occur in the engineering, the stability of the embankment is improved, meanwhile, the cost is effectively controlled, and the problem to be solved is solved urgently.

In embankment filling and use, along with the constantly increasing of embankment and the load on embankment upper portion constantly increase, the atress of each stake is also showing and is increasing, however there is great difference in the atress of different positions pile body, in embankment center department, the stake is with bearing vertical axial force as the main, it is less to bear the horizontal load of the soil body, and because soft soil thickness is less on one side that the soft soil layer thickness of embankment is less, the horizontal load of the soil body is less relatively, therefore embankment center department and the less one side soil body horizontal load of embankment soft soil layer thickness is little, the horizontal load that the pile body bore is less. The pile bearing on the side with the larger thickness of the soft soil layer is relatively smaller in axial force, but larger in horizontal load of the soil body, but the embedding effect of the hard soil layer is weakened due to the inclined plane, under the action of larger horizontal thrust, the pile body does not bend and deform, the pile topples towards the side with the larger thickness of the soft soil layer of the embankment, the bearing capacity of the pile on the side is not fully utilized, the pile is toppled integrally to be damaged, and finally the embankment is unstable, so that huge personnel and property losses are caused. Meanwhile, the pile length has obvious influence on the pile embedding effect, however, the conventional pile length is adopted in most of the existing composite foundation designs, the embedding depth is 0-2 times of the pile diameter, and even if a few long piles are distributed in the pile distribution project, the long piles are uniformly distributed; from the aspect of pile body bending resistance, a composite foundation form that long piles are distributed on one side with a larger soft soil layer thickness and conventional pile bodies are distributed on the other side is adopted, and a non-equal-length embankment design method for improving the stability of the embankment does not exist.

In summary, how to make the outer pile body and the inner pile body play respective roles when building the composite foundation and improve the stability of the embankment on the basis of controlling the cost becomes a problem to be solved urgently.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a variable-pile-length rigid pile composite foundation for improving the stability of an embankment with an inclined embedded layer, which solves the engineering problems that the pile body of the traditional isometric traditional rigid pile composite foundation is easy to topple at the inclined left side (the side with larger thickness of a soft soil layer) of the embedded layer under the horizontal load of a larger soil body, so that the pile body is prone to topple and damage integrally, and further the embankment is unstable, the bearing capacity is greatly reduced, and simultaneously solves the problems that the construction period is long, the construction cost is remarkably increased and resources are wasted because large embedded depth piles are adopted completely.

In order to solve the technical problem, the invention provides a pile length variable rigid pile composite foundation for improving the stability of an embankment with an inclined embedded layer, which comprises an embankment arranged on a reinforced soil body; the embankment comprises an embankment top surface and embankment side slopes on two sides of the embankment top surface, and the distance from the slope toe of the embankment side slope to the slope shoulders of the embankment side slope on the cross section of the embankment is L; the upper part of the reinforced soil body is a soft soil layer, the lower part of the reinforced soil body is an embedded layer, the thickness of the soft soil layer in the reinforced soil body is gradually reduced from one side of the cross section of the embankment to the other side, and the side with the large thickness of the soft soil layer is marked as an A side; a plurality of rigid piles are arranged in the reinforced soil body according to a row-column matrix, and the arrangement area of all the rigid piles is the area covered by the embankment; all the rigid piles comprise long piles and conventional piles, the arrangement area of the long piles is the area occupied by the long piles extending from the slope toe of the side A of the embankment to the center line of the width of the cross section of the embankment to the position L, and the rest area is the arrangement area of the conventional piles; the pile diameter of the long pile and the pile diameter of the conventional pile are both D & lt 0.7-0.9m, the pile spacing is 2-2.5m, the pile length of the long pile is from the top of the reinforced soil body to 5D-7D deep into the embedded layer, and the pile length of the conventional pile is from the top of the reinforced soil body to 2D deep into the embedded layer.

Further, the specific numerical values of the pile diameter, the pile distance and the pile length of the long pile and the conventional pile are determined by checking and calculating according to the bearing capacity and the deformation requirement of the composite foundation in the technical specification of building foundation treatment with the standard number of JGJ 79-2012.

The long pile with the stake type of conventional stake is the same, the long pile with one of CFG stake, plain concrete pile, reinforced concrete pile and tubular pile is selected to conventional stake.

When the filling height H of the embankment is larger than or equal to 5m and the side slope angle beta is larger than or equal to 27 degrees, selecting the pile type with higher tensile strength, and otherwise, selecting the pile type with lower tensile strength.

The long pile is flush with the top surface of the conventional pile, and a mattress layer with the thickness of 15-30 cm is laid on the reinforced soil body.

Compared with the prior art, the invention has the beneficial effects that:

the composite foundation solves the engineering problems that the conventional long rigid pile composite foundation with equal piles cannot fully exert the function of the pile body due to insufficient embedment when the inclined embedment layer is contained, so that the pile body is overturned and damaged, thereby causing the instability of the embankment and the great reduction of the bearing capacity, and simultaneously solves the problems of high construction cost and uneconomic performance when the long rigid pile composite foundation is adopted for treating the embankment. In addition, the displacement of the soil body behind the pile on the side (B side in figure 1) with smaller thickness of the soft soil layer is smaller, the horizontal load born by the soil body is smaller, so that the pile body bears smaller bending moment and larger axial force, and the requirement of bearing the axial force can be met by adopting the conventional pile. The pile body of the side B adopts a conventional pile, so that the cost can be controlled on the basis of ensuring the stability of the embankment, and meanwhile, the pile body of the side A is lengthened to play a role in bending resistance, so that the engineering cost is effectively controlled while the bearing capacity of the embankment is ensured. The pile body of the invention can adopt a unified pile type, unify materials and sizes, ensure that the pile body at the side A can fully exert the advantage of large rigidity of the rigid pile, and further save the cost on the basis of improving the stability.

The composite foundation has the advantages of simple construction, high safety, strong applicability and good economical efficiency.

Drawings

FIG. 1 is a vertical cross-sectional view of the composite foundation of the present invention;

FIG. 2 is a plan view of the composite foundation of the present invention;

in the figure: the method comprises the following steps of 1-embankment, 2-reinforced soil body, 3-embedded layer, 4-long pile and 5-conventional pile, wherein A represents the side with large thickness of soft soil layer in the reinforced soil body, and B represents the side with small thickness of soft soil layer in the reinforced soil body.

Detailed Description

The technical solutions of the present invention are further described in detail with reference to the accompanying drawings and specific embodiments, which are only illustrative of the present invention and are not intended to limit the present invention.

As shown in fig. 1 and fig. 2, the pile length variable rigid pile composite foundation for improving the stability of an embankment with an inclined embedded layer, which is provided by the invention, comprises an embankment 1 arranged on a reinforced soil body 2; the embankment 1 comprises an embankment top surface and embankment side slopes on two sides of the embankment top surface, and the distance from a slope foot of the embankment side slope to a slope shoulder of the embankment side slope on the cross section of the embankment 1 is L; the upper part of the reinforced soil body 2 is a soft soil layer, the lower part of the reinforced soil body 2 is an embedded layer 3, the thickness of the soft soil layer in the reinforced soil body 2 is gradually reduced from one side to the other side of the cross section of the embankment 1, one side with the large thickness of the soft soil layer is marked as an A side, and the other side is marked as a B side; a plurality of rigid piles 3 are arranged in the reinforced soil body 2 according to a row-column matrix, and the arrangement area of all the rigid piles 3 is the area covered by the embankment 1.

All the rigid piles 3 comprise long piles 4 and conventional piles 5, the arrangement area of the long piles 4 is the area occupied by the slope toe of the embankment side A extending to the center line of the cross section width of the embankment to the position L, and the rest area is the arrangement area of the conventional piles 5.

The long pile 4 is a rigid pile with a large pile embedding depth and the embedding depth is 5-7 times of the pile diameter, namely the pile length of the long pile 4 is from the top of the reinforced soil body 2 to the pile diameter 5-7 times deeper than the embedding layer 3, the embedding depth of the conventional pile is 2 times of the pile diameter, namely the pile length of the conventional pile 5 is from the top of the reinforced soil body 2 to the pile diameter 2 times deeper than the embedding layer 3; the pile diameter of the long pile 4 is equal to that of the conventional pile 5 and is 0.7-0.9m, and the pile spacing is equal to that of the conventional pile 5 and is 2-2.5 m.

The long pile 4 with conventional stake 5's stake type is the same, long stake 4 with conventional stake 5 can select arbitrary type rigidity stake such as CFG stake, plain concrete pile, reinforced concrete stake and tubular pile, and specific selection can be according to site conditions etc. and confirms, long stake 4 with the concrete numerical value of the stake footpath of conventional stake, stake interval and pile height requires the checking calculation according to composite foundation bearing capacity and deformation in "building foundation treatment technical specification" (JGJ 79-2012) and confirms. The long piles 4 are arranged only in the area of one side (namely the side A shown in figure 1) with larger thickness of the soft soil layer of the embankment, and the conventional piles 5 are used in most areas, so that the bending resistance bearing capacity is fully exerted, the stability of the embankment is maintained, and meanwhile, the pile length is reduced on the basis of meeting the safety and normal use of the composite foundation, thereby greatly saving the cost.

In the specific implementation process of the invention, when the embankment filling height is higher, such as embankment filling H is more than or equal to 5m, and the side slope is steeper, such as the side slope angle beta is more than or equal to 27 degrees, the pile type with higher tensile strength is selected from the pile types which can be selected by the long pile 4 and the conventional pile 5, and the pile type with lower tensile strength is selected on the contrary.

The variable-spacing composite foundation is obviously different from a common conventional equal-length pile composite foundation, and is essentially different from the existing composite foundation which completely adopts long piles, the existing composite foundation does not consider that the embedding effect is weakened by the inclination of an embedding layer, the stability of the composite foundation is overestimated, in the scheme of completely adopting the long piles, the horizontal displacement of the soil body on the side with smaller thickness of a soft soil layer is small, the axial force is large, the requirement on the embedding effect of the pile bottom is not large, the conventional piles can meet the requirement, the variable-spacing composite foundation considers different performance effects of pile bodies at different positions by adjusting the pile length, and further improves the stability of the embankment, and the method only changes the pile embedding depth to have less requirement on the type of the pile body, reduces the construction difficulty and improves the operability in the engineering.

The long piles 4 are flush with the top surfaces of the conventional piles 5 and the upper surfaces of the reinforced soil bodies 2; a mattress layer with the thickness of 15-30 cm is paved on the reinforced soil body 2. If the lower surface of the reinforced soil body 2 is an inclined embedded layer, the mattress layer on the reinforced soil body 2 can improve the integrity of the composite foundation, so that pile bodies with different pile lengths can coordinate, the embedded depth of the pile body on the side with larger thickness of the soft soil layer can improve the bending resistance and the anti-sliding bearing capacity of the pile body, and the pile body is prevented from overturning and damaging to further cause the instability of the embankment.

The pile length variable rigid pile composite foundation provided by the invention solves the engineering problems that when the rigid pile composite foundation contains an inclined embedded layer, piles are overturned and damaged due to insufficient embedding, so that embankment is unstable, and the bearing capacity is greatly reduced, and meanwhile, the construction cost is greatly reduced on the basis of ensuring the stability of the embankment by only lengthening the piles under the embankment at the side with the larger thickness of a soft soil layer. The method has the advantages of simple construction, good total settlement control effect, high safety, strong applicability and good economical efficiency, and can greatly improve the stability of the embankment.

Although the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above embodiments, which are only illustrative and not restrictive, and those skilled in the art can make many modifications without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A variable pile length rigid pile composite foundation for improving the stability of an embankment with an inclined embedded layer comprises an embankment (1) arranged on a reinforced soil body (2); the embankment (1) comprises an embankment top surface and embankment side slopes on two sides of the embankment top surface, and the distance from the slope foot of the embankment side slope to the embankment side slope shoulder on the cross section of the embankment (1) is L; the upper part of the reinforced soil body (2) is a soft soil layer, the lower part of the reinforced soil body (2) is an embedded layer (3), the thickness of the soft soil layer in the reinforced soil body (2) is gradually reduced from one side of the cross section of the embankment (1) to the other side, and the side with the large thickness of the soft soil layer is marked as side A; a plurality of rigid piles (3) are arranged in the reinforced soil body (2) according to a row-column matrix, and the arrangement area of all the rigid piles (3) is the area covered by the embankment (1);

the method is characterized in that:

all the rigid piles (3) comprise long piles (4) and conventional piles (5), the arrangement area of the long piles (4) is the area occupied by the long piles extending from the slope toe of the side A of the embankment to the center line of the width of the cross section of the embankment to the position L, and the rest area is the arrangement area of the conventional piles (5);

the pile diameter of the long pile (4) and the pile diameter of the conventional pile (5) are equal to each other and are D-0.7-0.9 m, the pile spacing is equal to each other and are 2-2.5m, the pile length of the long pile (4) is from the top of the reinforced soil body (2) to 5D-7D deep into the embedded layer (3), and the pile length of the conventional pile (5) is from the top of the reinforced soil body (2) to 2D deep into the embedded layer (3).

2. The variable-pile-length rigid-pile composite foundation according to claim 1, characterized in that: the specific numerical values of the pile diameter, the pile distance and the pile length of the long piles (4) and the conventional piles are determined by checking calculation according to the bearing capacity and the deformation requirement of the composite foundation in the technical Specification for treating the building foundation with the standard number of JGJ 79-2012.

3. The variable-pile-length rigid-pile composite foundation according to claim 1, characterized in that: the long pile (4) with the stake type of conventional stake (5) is the same, long stake (4) with one of CFG stake, plain concrete pile, reinforced concrete pile and tubular pile is selected in conventional stake (5).

4. The variable-pile-length rigid-pile composite foundation according to claim 3, characterized in that: when the filling height H of the embankment is larger than or equal to 5m and the side slope angle beta is larger than or equal to 27 degrees, selecting the pile type with higher tensile strength, and otherwise, selecting the pile type with lower tensile strength.

5. The variable-pile-length rigid-pile composite foundation according to claim 1, characterized in that: the long piles (4) are flush with the top surfaces of the conventional piles (5) and are flush with the upper surfaces of the reinforced soil bodies (2); a mattress layer with the thickness of 15-30 cm is paved on the reinforced soil body (2).