CN109214070B - Method for leveling pile foundation of main skirt connected high-rise building - Google Patents
Method for leveling pile foundation of main skirt connected high-rise building Download PDFInfo
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Abstract
The invention discloses a leveling method of a main skirt conjoined high-rise building pile foundation, which is characterized in that a variable rigidity leveling design principle and a method of the main skirt conjoined high-rise building pile foundation are established, according to a building synergistic action system of an upper structure-a foundation-pile soil, the pile foundation settlement is restricted by the interaction of the upper structure, the foundation and the pile soil, a total balance equation is established, the settlement tends to be uniform by adjusting the support rigidity distribution of the pile soil, the punching, shearing and bending internal forces of the foundation are greatly reduced, the secondary stress of the upper structure is reduced, the effect of the foundation soil for sharing load is effectively exerted, the used pile amount and the used base material amount are reduced, under the condition that the characteristic value of the total load bearing capacity of a main skirt is balanced with the total load standard value, the conventional pile foundation is combined with a composite pile foundation through strong (weak) bearing rigidity, the rigid pile composite foundation is combined with a natural foundation, the local balance and overall coordination of each zone are realized, the strong and weak combination is realized, and the difference settlement and the minimization of material consumption are realized.
Description
Technical Field
The invention relates to the technical field of building foundation foundations, in particular to a method for leveling a main skirt connected high-rise building pile foundation.
Background
With the development of economy, because of the needs of complicated and diversified building functions, auxiliary skirt buildings which correspond to main buildings are often arranged around the high-rise building, the high-rise main building, a multi-layer skirt house, an underground garage and the like are connected into a whole, the high-rise building with the skirt buildings has obvious height difference, load difference and structural rigidity difference between the main building and the skirt buildings, and the structure is complicated in size and uneven in overall rigidity, so that overlarge differential settlement is easily generated on the basis, the ground structure is adversely affected, and the problem of uneven settlement is one of difficult problems in the foundation design of the high-rise building. The high-rise building foundation designed based on the traditional concept has two outstanding characteristics: firstly, the natural foundation shallow foundation mostly adopts a thick raft or box foundation, and the reason is to increase the bending rigidity of the foundation to overcome differential settlement deformation; and secondly, for the pile foundation, adopting a pile raft and a pile box foundation which are used for arranging piles in a full space and even for arranging piles, arranging piles in an excessive way and densely arranging soil-squeezing piles. The foundation of the high-rise building is not matched with the main skirt structure and the skirt structure of the foundation, the foundation is easy to have disc-shaped settlement, the frame-cylinder structure or the main skirt differential settlement is overlarge, the bottom plate is cracked, the base reaction force is distributed in a saddle shape, and the like, and the root of the foundation is that the pile-soil supporting rigidity distribution is unreasonable, such as the distribution situation of the saddle-shaped reaction force and the disc-shaped settlement deformation under the condition that the frame-cylinder structure is uniformly distributed with the pile foundation shown in figure 1.
In the prior art, as shown in fig. 2, the conventional pile foundation relates to a method for overcoming differential settlement of a main skirt building, and under ideal conditions: Σ F = F 1 +F 2 +F 3 ＝n·R a However, in practice, the mass of the main building is large, which results in differential settlement S 1 ＞S 2 ，S 1 ＞S 3 Then Δ S = S 1 -S 3 Or Δ S = S 1 -S 2 The difference settlement is obvious, and based on the above, the following methods are commonly used for treating the connection between the main building and the undaria pinnatifida foundation:
1. the settlement joint is arranged in the early main skirt building of the high-rise building, and in order to avoid the house cracking and even damage caused by the settlement difference, the settlement joint is usually arranged at the adjacent position of the settlement joint and the main skirt building, and the structure is disconnected by measures of double columns, double walls and the like. In order to avoid excessive sinking influence on the skirt house foundation, the skirt house foundation should be separated from the main building foundation by a certain distance as far as possible. When the foundation has high compressibility and large thickness and differential settlement is large between the main building and the skirt building, the foundation should be completely disconnected by using a settlement joint.
2. The adoption of the integral foundation can generally make the foundation of the main skirt building into a whole without arranging seams when the foundation is on a rock layer or a pebble layer or adopts a pile foundation or a deep pier and the differential settlement of the main skirt building and the skirt building is small. In the main skirt building of a high-rise building, three setting modes are usually adopted, namely the three setting modes are simultaneously arranged on a box foundation or a thick raft foundation with very high rigidity so as to resist internal force caused by differential settlement; the supporting structure is supported on bedrock or a bearing layer with larger bearing capacity through a pile foundation; when the foundation is soft and the settlement is large in the later period, the skirt house can be placed on the overhanging foundation, but the overhanging foundation cannot be long.
3. The combined arrangement of the main building and the skirt building foundation means that the main building and the skirt building adopt different foundation forms, but no settlement joint is arranged in the middle, generally, the load difference between the main building and the skirt building is large, the rigidity difference between the main building and the skirt building is very different, a certain amount of settlement difference is caused, and if the main building and the skirt building are not properly treated, the structure is cracked, so that the use is influenced.
The problems of the main skirt conjoined high-rise building foundation under normal conditions are attributed to the difference deformation, and the countermeasures for the problems at home and abroad are roughly three aspects: aiming at the problems of the foundation of the high-rise building, the thickness of the foundation plate is increased, the bending rigidity of the foundation is improved, and the differential settlement is overcome, so that the material consumption is large, the differential settlement exceeds the standard, and even the foundation cracks; reducing the settlement of the natural foundation; the design value of the pile bearing capacity is taken as the ultimate bearing capacity of a single pile to play the bearing effect of the raft, but the problem of optimizing pile arrangement to eliminate differential settlement cannot be solved by doing so.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method for leveling a main skirt conjoined high-rise building pile foundation, which is based on the design principle and method for variable rigidity leveling of the main skirt conjoined high-rise building pile foundation, so that the settlement tends to be uniform, and the problems provided by the background technology can be effectively solved.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention provides a method for leveling a pile foundation of a main skirt one-piece high-rise building, which establishes a design principle and a method for leveling the pile foundation of the main skirt one-piece high-rise building in a variable rigidity mode.
Preferably, the variable stiffness leveling principle of the pile foundation is combination of strengthening and weakening, combination of increasing and reducing sinking, and local balance and overall coordination.
In the present invention, as shown in FIG. 3, Σ F 1 ＝∑Ra1，∑F 2 ＝∑Ra2，∑F 3 The = ∑ Ra3, thereby local balance can be achieved, and the settlement of the main building and the undaria meets the condition that S ≈ S through the overall coordination effect 2 ≈S 3 。
Preferably, in the main skirt conjoined building, the strengthening and weakening combination of the variable-rigidity leveling of the pile foundation is specifically used for strengthening the supporting rigidity of the main body weakening skirt house, when the bearing capacity of the skirt house foundation is higher, the weakening and sinking measures are taken for the skirt house foundation which spans adjacent to the main body, the weakening and sinking measures comprise that a soft mattress is arranged under a raft plate except a column foundation, and when the anti-floating requirement exists, a soft cushion is arranged at the bottom of an anti-pulling pile or an anti-floating anchor rod is changed.
Preferably, the adjustment of the support rigidity is controlled by a strengthening index and a weakening index, and under the condition that the total load characteristic value of the main skirt is balanced with the total load standard value, the pile soil support rigidity is adjusted by controlling the strengthening index of the core cylinder area and the weakening index of the peripheral frame area, wherein the strengthening index of the core cylinder area is 1.05-1.30, and the weakening index of the peripheral frame area is 0.70-0.95.
Preferably, the intensifying index xi of the core barrel region s Is the resistance ratio of the core region
To the ratio of the load
The ratio of:
wherein, the first and the second end of the pipe are connected with each other,
in the above-mentioned description of the invention,
R ak respectively is the bearing capacity characteristic value of the core tube area and the bearing capacity characteristic value of the whole raft foundation,
F k respectively as the standard value of the load of the core area and the load of the whole raftAnd (4) standard value.
Preferably, in the upper structure-foundation building synergistic system, the total balance equation of the synergistic system is as follows:
([K] st +[K] F +[K] s(p,s) ){u}＝{F} st +{F} F ，
in the formula [ K] st A stiffness matrix that is condensed to the substructure at the top of the foundation; [ K ]] F A base stiffness matrix condensed on the base bottom surface; [ K ]] s(p,s) Supporting a stiffness matrix for a foundation that is agglomerated to a substrate; { u } is a displacement vector of a base bottom node; { F } st 、{F} F Respectively, the superstructure, the base load vector, condensed to the substrate.
Preferably, the layout of the pile soil supporting body is carried out on the principle of vertical dislocation or horizontal pull-apart distance, and the pile soil supporting rigidity distribution is optimized by adopting long and short piles, variable pile diameters, variable pile spacing combination, combination of conventional pile foundations and composite pile foundations and combination of composite foundations and natural foundations.
Preferably, a conventional pile foundation, a composite pile foundation or a rigid pile composite foundation is selected according to construction factors and geological characteristics, and the concrete adjusting method of the pile-soil support body rigidity distribution comprises the following steps:
for a frame tube structure with extremely uneven load distribution, a conventional pile foundation is adopted in a core tube area, and a composite pile foundation is adopted in a peripheral frame area;
for medium and low compressibility soil foundations, the height of the frame tube structure is not more than 60m, the height of the shear wall structure is not more than 100m, a rigid pile composite foundation or a rigid pile composite foundation is adopted in the local core tube area, and pile soil bearing rigidity distribution is adjusted by changing pile length and pile distance.
Preferably, the foundation pile selection of pile foundation and the confirmation of pile tip bearing layer are convenient for post-grouting reinforcement for single pile bearing capacity has the adjustment space, and the foundation pile distributes concentratedly under post or wall, in order to reduce the effect that foundation internal force furthest exerts foundation soil shared load, reduces the interact of pile foundation and core barrel region pile foundation.
Preferably, the pile foundation can be laid by adopting piles with dense inside and sparse outside and long inside and short outside according to load distribution to form strong inside and weak outside supporting rigidity distribution, the disc-shaped settlement formed by the interaction effect is eliminated, the leveling effect is tested under the synergistic action of the upper structure, the foundation and the pile soil, the pile laying is further optimized, and the internal force and the reinforcing bars of the raft are determined.
Compared with the prior art, the invention has the beneficial effects that:
based on the variable-rigidity leveling design principle and method of the main skirt conjoined high-rise building pile foundation, the invention ensures that the settlement tends to be uniform, greatly reduces the punching, shearing and bending internal force of the foundation, reduces the secondary stress of the upper structure, effectively plays the role of sharing load by the foundation soil and reduces the pile consumption and the material consumption of the bearing platform. Under the condition that the characteristic value of the total bearing capacity is balanced with the standard value of the total load, the conventional pile foundation and the composite pile foundation are used together through strengthening (weakening) the bearing rigidity, and the rigid pile composite foundation and the natural foundation are used together, so that local balance and integral coordination of all areas are realized, the strength and the weakness are combined, the rigidity and the flexibility are combined, and the minimization of differential settlement and material consumption is realized.
Drawings
FIG. 1 is a schematic diagram showing the distribution of saddle-shaped reaction force and disc-shaped settlement deformation under the condition of uniformly arranging pile foundation in a frame-cylinder structure in the background art of the invention;
fig. 2 is a schematic view of the method for overcoming differential settlement of the main skirt by the conventional pile foundation design;
FIG. 3 is a schematic diagram of a method for overcoming differential settlement of a main skirt in pile foundation design according to the present invention;
FIG. 4 is a schematic design flow diagram of the present invention;
FIG. 5 is a schematic view of a frame-core tube structure variable stiffness leveling cloth pile according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of variable-stiffness pile distribution of a large-area uniformly-distributed load pile raft in the embodiment of the invention;
fig. 7 is a schematic structural diagram of an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
The invention provides a main skirt one-piece high-rise building foundation integrated design principle and a construction method according to a main skirt one-piece high-rise building pile foundation leveling method, and partial projects can directly cancel a post-pouring zone of settlement. The core idea of the invention is as follows: the method comprises the steps of establishing a pile foundation variable stiffness leveling design principle and a pile foundation variable stiffness leveling design method of a main skirt connected high-rise building, establishing a total balance equation according to a building synergistic interaction system of an upper structure, a foundation and a foundation, wherein foundation settlement is restricted by interaction of the upper structure, the foundation and pile soil, and adjusting support stiffness distribution of the foundation to enable settlement to tend to be uniform.
As shown in fig. 4, the specific design concept of the present embodiment is as follows: the method is characterized in that pile-soil bearing rigidity is adjusted according to building structure characteristics, upper load and geological conditions to serve as a basic design concept, adjustment optimization is achieved by combining conventional pile foundations and composite pile foundations and combining composite foundations and natural foundations, in specific regional design, pile length changing, pile diameter changing and pile distance changing are mainly used as technical means for adjustment, deepening design is conducted through adjustment of the pile length changing, the pile diameter changing and the pile distance changing, and adjustment effects of strong and weak combination, local balance and overall coordination are achieved.
From the above, the general equilibrium equation of the synergistic system is first established as:
([K] st +[K] F +[K] s(p,s) ){u}＝{F} st +{F} F (1)
in the formula (1) [ K ]] st A superstructure stiffness matrix condensed on the top surface of the foundation (bearing platform); [ K ]] F A foundation (bearing platform) rigidity matrix condensed on the bottom surface of the foundation (bearing platform); [ K ]] s(p,s) Supporting a stiffness matrix for foundation soil (piling soil) condensed on a substrate; { u } displacement vector of base (bearing platform) node; { F } st 、{F} F Respectively, the superstructure, the foundation (cap) load vector condensed to the substrate.
Wherein the upper structureStiffness matrix [ K ]] st And the load vector of the superstructure and foundation { F } st 、{F} F Determined for a particular project, the stiffness matrix [ K ] of the foundation (cap)] F Has small adjustment range and small contribution, thereby the pile soil supporting rigidity is adjusted by adjusting the [ K ]] s(p,s) The uniform distribution of the settlement { u } realized by the size and the distribution is an effective, feasible and reasonable optimization design approach. The method is a theoretical principle of variable stiffness leveling design, and simultaneously, coaction analysis is used as a means for leveling inspection and rechecking in the design process.
As shown in FIGS. 4 and 5, to make the settlement uniform, only the rigidity of the foundation { F } is increased for the natural foundation F Theoretical analysis and engineering examples show that the effect of this is not obvious and is not preferable for the case of non-hard foundation and large and uneven load. Therefore, to make the settlement uniform, only adjusting the pile-soil supporting rigidity [ K ]] s(p,s) To match the load distribution and interaction effects. It is also an effective, feasible and economical way to optimize the foundation design of high-rise building foundations, reducing or even eliminating differential settlement.
In the present embodiment, the main limiting factors affecting the leveling design include four parts, which are:
1. size and distribution of load
For the same geology, foundation size and buried depth conditions, the settlement increases with increasing load, and the differential settlement increases. Therefore, the differential settlement problem of the main skirt high-rise building is more prominent than that of a multi-rise building.
The uneven distribution of the load causes uneven distribution of the sedimentation and often becomes a main cause of the occurrence of differential sedimentation.
The distribution characteristics of the load are related to the structural form and building body type of the high-rise building body, and both of them are main factors determining the load distribution. The change of the body type comprises the body type of the building main body and the body type of a main skirt conjoined formed by connecting the main body and the skirt house, wherein the main skirt conjoined is the building body type with the largest load difference.
The building structure type comprises 6 types listed in table 1, the vertical load distribution of the building structure type is more uniform, the building structure type is a floor shear wall system, and the load distribution of the building structure type is most nonuniform, namely a frame-core tube structure system and a tube-in-tube structure system. The latter two are dense because of the core tube wall, except its dead weight is larger, it also bears the floor load of the peripheral frame in about 1/2 span range, so the load concentration is about 3-4 times of the periphery, and it becomes the basic factor of the building which has obvious disc-shaped settlement and even foundation crack.
2. Superstructure stiffness
The rigidity of the upper structure mainly refers to the overall rigidity of the structure, and plays a certain role in restricting differential settlement, namely the contribution to the basic rigidity. The floor shear wall system (called a shear wall structure for short) has the largest contribution to the foundation rigidity due to large rigidity and uniform and continuous distribution. Although the rigidity of the core barrel is very high, the rigidity of the peripheral frame is relatively low, so that the rigidity of the frame-core barrel (frame barrel for short) system does not greatly contribute to the rigidity for restricting the internal and external differential deformation of the foundation. The cylinder-in-cylinder structure system is mainly used for enhancing the lateral force resistance of the structure, is suitable for super high-rise buildings and slightly contributes to the rigidity of a foundation to a frame cylinder structure.
TABLE 1 Effect of different structural systems on differential Foundation Settlement
In general, the contribution of the upper structural stiffness to the differential settlement of the constrained foundation as listed in table 1 varies with the structural type, and the contribution of the rest of the structural systems to the differential settlement of the constrained foundation is the worst of the framed-tube and framed-shear structures except for the shear wall system.
3. Conditions of foundation and pile foundation
For raft foundations on natural foundations, the uniformity of the foundations is a key factor for restricting differential settlement, and the compressibility of foundation soil is a main factor for influencing the settlement and the differential settlement. Under the condition that the bearing capacity of the natural foundation meets the load requirement of the building, the settlement deformation does not meet the requirement, so the deformation control analysis is very important under the condition. The pile foundation is the main foundation form of high-rise building, however, the differential settlement problem can be satisfactorily solved without adopting the pile foundation. The optimization design of the pile foundation is the core content of the variable stiffness leveling design, because the pile is a flexible and effective vertical supporting body for adjusting the distribution of the supporting stiffness.
4. Effect of interaction
The effect of the cap-pile-soil interaction results in: uniformly distributing load, pile feeding and soil counter-force distribution in a saddle shape with a small inside and a large outside; the basic stress field deepens along with the increase of the area; pile group settlement is increased along with the reduction of pile distance and the increase of pile number; the settlement of the foundation or the bearing platform is distributed in a disc shape with a large middle part and a small periphery; adjacent foundations are inclined due to mutual influence; the core barrel is not only high in load concentration, but also large in settlement caused by mutual influence of basic stress fields of peripheral frame areas.
In the embodiment, the main skirt one-piece high-rise building pile foundation leveling mainly adopts the adjustment of pile soil supporting rigidity distribution as a main line, and adopts the combination of reinforcement and weakening, the combination of subsidence reduction and settlement enhancement, the combination of rigidity and flexibility, local balance and integral coordination according to load, geological features and upper structure layout by considering interaction effect, so as to realize the minimization of differential settlement, bearing platform (foundation) internal force and resource consumption.
The first is according to building size, structure, load and geological conditions, select pile foundation, compound pile foundation, rigid pile composite foundation, and rational overall arrangement adjusts the distribution of pile soil bearing rigidity, makes it match with the load. For the frame-tube structure with extremely uneven load distribution, the core tube area is preferably a conventional pile foundation, and the outer frame area is preferably a composite pile foundation; the shear wall structure with the height not exceeding 100m can adopt a rigid pile composite foundation or a core tube area local rigid pile composite foundation; and the rigidity distribution is adjusted by changing the pile length and the pile distance.
And secondly, in order to reduce the weakening of the effective rigidity of the core area caused by the mutual overlapping of stress fields of all areas, the arrangement of the pile soil support body is suitable for realizing vertical dislocation or horizontal pull-apart distance. The combination of long piles and short piles, the combination of pile foundations and composite pile foundations, and the combination of composite foundations and natural foundations are adopted to reduce mutual influence and optimize rigidity distribution, as shown in figure 2.
And thirdly, considering the interaction effect of the pile soil, and the adjustment of the supporting rigidity is preferably controlled by adopting a strengthening index and a weakening index. The core area strengthening index is preferably 1.05-1.30, the outer frame has two rows of columns which are larger than one row of columns, the full pile arrangement is larger than the pile arrangement under the columns and under the cylinders, and the inner and outer pile length which are the same are larger than the arrangement with different pile lengths, vertically staggered pile bottoms and larger horizontal spacing. The weakening index of the outer frame region is preferably 0.70 to 0.95, the greater the strengthening index, the smaller the corresponding weakening index. Under the condition that the total bearing capacity characteristic value of the full-pile raft is balanced with the total load standard value, the weakening index of the outer frame area is realized along with the control of the strengthening index of the core area.
Core region intensification index xi s Is the resistance ratio of the core region
Ratio of load to load
The ratio of:
wherein the content of the first and second substances,
R ak respectively obtaining a bearing capacity characteristic value and a full raft bearing capacity characteristic value of a core area (the range from a core barrel and a core barrel edge to the span of an adjacent frame column is 1/2);
F k the standard values of the load of the core area and the standard value of the load of the whole raft are respectively. When the total bearing capacity characteristic value of the pile raft is the same as the total load standard value, the core area enhancement index xi s I.e. the resistance/load ratio of the core area.
And fourthly, the main skirt conjoined building is designed according to the principle of enhancing the high-rise main body and weakening the skirt house. When the high-rise main body adopts the pile foundation, the skirt house preferably adopts a natural foundation, a composite foundation or a loose and short composite foundation. When the bearing capacity of the natural foundation of the skirt house is high, weakening and sinking increasing measures are preferably taken for the adjacent span with the main body, including arranging soft mattresses on the raft plates outside the foundation under the column, and when the anti-floating requirement is met, arranging soft pads at the bottom of the uplift pile or changing the uplift pile into an anti-floating anchor rod.
And fifthly, the selection of the type of the foundation pile of the pile foundation and the determination of the pile end bearing layer are beneficial to applying the post-grouting reinforcement technology, and a large adjustment space for the bearing capacity of a single pile is ensured. The foundation piles are preferably distributed under the columns and the walls in a concentrated mode so as to reduce the internal force of the bearing platform, exert the load sharing effect of foundation soil at the bottom of the bearing platform to the maximum extent and reduce the interaction between the pile foundation under the columns and the core tubular pile foundation, as shown in figure 2.
And the sixth is a large-volume water pool and a large-volume storage tank. Piles which are dense inside and sparse outside and long inside and short outside are adopted, and particularly as shown in figure 3, the rigidity distribution of strong inside and weak outside supports is formed, and the disc-shaped settlement formed by the interaction effect is eliminated.
Seventhly, the synergistic effect analysis of the upper structure, the foundation (bearing platform) and the pile soil is carried out on the basis of conceptual design so as to test the leveling effect, further optimize pile arrangement, determine the internal force and the reinforcement of the bearing platform and optimize and refine the design; the differential settlement is controlled to be stricter than the standard value so as to improve the durability and reliability and prolong the normal service life of the building.
In the embodiment, the main skirt conjoined high-rise building pile foundation leveling also needs to consider structures such as a frame tube structure, a shear wall structure, a pile foundation bearing platform and the like.
The foundation piles of the core barrel and the outer frame column are preferably arranged under the core barrel and the outer frame column in a group mode so as to reduce the internal force of the bearing platform and reduce the adjacent influence of all parts. The core barrel of the load high-concentration area has a plurality of piles and small pile distance, and the load sharing effect of a bearing platform is not considered. For non-soft soil foundation, the outer frame area is designed according to the composite pile foundation, so that the bearing platform sharing load effect is fully exerted, the pile consumption is reduced, and the internal and external differential settlement can be reduced. When more than 2 pile-end bearing layers exist, the length of the core barrel pile is increased, the length of the outer frame area pile is reduced, and vertical dislocation of stress fields of the inner pile foundation and the outer pile foundation is formed, so that mutual influence is reduced, and differential settlement is reduced.
On the premise that the total bearing capacity characteristic value of the pile raft is balanced with the standard combination value of the total load effect, the core area is strengthened, and the outer frame area is weakened. The core area strengthening index is 1.05-1.15 when the end planes of the piles in the core area and the outer frame area are vertically staggered or the number of piles under the columns in the outer frame area is not more than 5, the outer frame takes a low value for one row of columns and takes a high value for two rows of columns; when the planes of the pile ends are at the same elevation and the number of piles under the piles exceeds 5, the strengthening index of the core area is preferably 1.2-1.3, and the value of a row of piles is low. The weakening index of the outer frame area is determined according to the relationship that the higher the strengthening index of the core area is, the lower the weakening index is; or according to the balance between the characteristic value of the total bearing force and the standard value of the total load, the strengthening index of the core area is independently controlled, so that the outer frame area is correspondingly weakened.
For the structural types of frame shear, frame support shear wall and tube-in-tube, piles can be distributed according to the principle of variable rigidity and leveling of the frame-tube structure, the elevator shaft and the staircase with high load concentration are reinforced, and the reinforcing index is determined according to the load distribution characteristics.
The shear wall structure has good integral rigidity, and the load is transmitted to the foundation by the wall body and is distributed more uniformly. The pile arrangement should be strengthened to the higher elevartor shaft of load concentration degree and stairwell. The foundation piles are preferably arranged below the wall, and piles are arranged at the intersections and corners of the wall. When the bearing capacity of a single pile is small and the piles are arranged according to the whole hall, the internal weakened periphery is properly strengthened.
Because the pile arrangement is optimized according to the variable stiffness leveling principle, each subarea realizes resistance and load balance, and the punching force, the shearing force and the integral bending moment borne by the bearing platform are reduced to the minimum, so that the thickness of the bearing platform can be correspondingly reduced. According to the traditional design concept, the raft type bearing platform of the piled raft foundation is always determined to have the minimum plate thickness, high beam height and the like by adopting the same requirements as those of the raft foundation on the natural foundation. Determining the section and reinforcing bars of the bearing platform designed for variable stiffness leveling according to the calculation result, wherein the minimum plate thickness and the beam height of the bearing platform are corresponding to the plate type bearing platform under the column, and the high span ratio of the beam and the thickness span ratio of the plate type bearing platform plate are preferably 1/8 (the minimum thickness of the natural foundation raft is 1/6 multiplied by 3/4); the ratio of the plate thickness of the beam-plate type raft-type bearing platform to the net span of the short side of the largest bidirectional plate grid is not less than 1/16 and not less than 400mm; the thickness span ratio of the flat plate type bearing platform under the wall is not less than 1/20, and the thickness is not less than 400mm. The minimum reinforcement ratio of the raft plate is required to meet the standard requirement.
Selecting the model of the raft type bearing platform, wherein for a frame tube structure, when a core tube and pile under-column cluster type pile arrangement are adopted, the core tube is preferably a flat plate, and an outer frame area is preferably a beam plate type; for the shear wall structure, a flat plate type is preferably adopted. And (3) reinforcing steel bars of the bearing platform can be calculated and determined according to local bending moment when variable-rigidity leveling pile arrangement is implemented.
And (3) for the frame-cylinder structure, calculation and analysis of the synergistic effect of the upper structure, the bearing platform and the pile soil are carried out, and accordingly, the settlement distribution, the pile soil reaction force distribution and the bearing platform internal force are determined. And when the calculated differential settlement does not reach the optimal target, the pile arrangement is readjusted until the calculated differential settlement is satisfied.
When the synergistic effect analysis is not carried out, the settlement is calculated according to the specification, and indexes such as differential settlement and the like are analyzed and checked according to the settlement. Various conditions such as single-column single-pile, single-row pile, sparse pile composite foundation and the like are common in variable-rigidity leveling design, and settlement is calculated according to corresponding regulations of building pile foundation technical Specification JGJ 94-2008.
Based on the above, to better illustrate the beneficial effects of the embodiment, taking the beijing jiamei fashion center located in the new city of beijing as an example, the beijing jiamei fashion center is a comprehensive building of two high-rise main buildings with a height of 99.8m and skirts with 4-6 floors above the ground, and the building area is 18 ten thousand square meters, wherein the main building is a frame core tube structure, a pile raft foundation, and the skirts are frame structures, and a raft structure, and further comprises an underground garage with 3 floors, which is a frame structure, and a raft foundation, wherein all the buildings are located on the same integral large chassis foundation, and the building plane is 260 meters × 75 meters.
As shown in fig. 7, the foundation of the integral chassis is a combination of long piles and short piles, wherein the long piles are 37 meters, the pile sides and the pile ends are both subjected to compound grouting, the standard value of the ultimate bearing capacity of a single pile is 12800kN, the standard value of the ultimate bearing capacity of the short piles is 17.4 meters, the pile ends are subjected to grouting, the standard value of the ultimate bearing capacity of the single pile is 5600kN, and a natural foundation is used as a secondary bearing area on the basis of the combination of the short piles and the long piles.
The mechanism of action is divided into two parts:
firstly, reinforcing an inner cylinder area by pile arrangement, weakening the periphery of a core area with dispersed load, and carrying out settlement analysis under the synergistic action so as to optimize pile arrangement in the core cylinder area;
secondly, the natural foundation is mainly used in the peripheral skirt house and the pure underground, and the purpose is to reduce differential settlement and optimize the internal force of the raft.
The pile arrangement is optimized according to the principle of the embodiment, the maximum value of the differential settlement amount is 8 mm when the integral structure is capped for 1 month, and the technical indexes are as follows:
1) Maximum value of settlement difference Delta S of adjacent vertical bearing members max 0.5 per mill, far below 2 per mill of the standard allowed value;
2) Calculating that the settlement of the pile foundation of the main skirt conjoined high-rise building is close to an actual measurement value under the synergistic action of the superstructure, the foundation and the foundation (pile soil);
3) After the pile foundation engineering is optimized, the engineering quantity of the pile foundation is reduced by about 40%, and the investment of the pile foundation engineering is saved by about 300 ten thousand yuan by the optimized design.
According to the embodiment, based on the variable-rigidity leveling design principle and method for the main skirt conjoined high-rise building pile foundation, the settlement tends to be uniform, the punching, shearing and bending internal forces of the bearing platform (raft) are greatly reduced, the secondary stress of the upper structure is reduced, the load sharing effect of the bearing platform is effectively exerted, and the pile consumption and the material consumption of the bearing platform are reduced. Under the condition that the characteristic value of the total bearing capacity is balanced with the standard value of the total load, the conventional pile foundation and the composite pile foundation are used together through strengthening (weakening) the bearing rigidity, and the rigid pile composite foundation and the natural foundation are used together, so that local balance and integral coordination of all areas are realized, the strength and the weakness are combined, the rigidity and the flexibility are combined, and the minimization of differential settlement and material consumption is realized.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Claims (6)
1. A leveling method for a main skirt conjoined high-rise building pile foundation is characterized in that a variable stiffness leveling design principle and method for the main skirt conjoined high-rise building pile foundation are established, according to a building synergistic action system of an upper structure-a foundation-pile soil, the settlement of the pile foundation is restricted by the interaction of the upper structure, the foundation and the pile soil, a total balance equation is established, and the settlement tends to be uniform by adjusting the support stiffness distribution of the pile soil;
the pile foundation variable stiffness leveling principle is reinforcement and weakening combination, settlement increasing and settlement reducing combination, local balance and overall coordination;
in the main skirt conjoined building, the strengthening and weakening combination of the variable-rigidity leveling of the pile foundation is specifically strengthening the supporting rigidity of a main body and weakening a skirt house, when the bearing capacity of the skirt house foundation is higher, the weakening and sinking measures are taken for the skirt house foundation which spans adjacent to the main body, the weakening and sinking measures comprise that a soft mattress is arranged under a raft plate outside a column foundation, and when the foundation has an anti-floating requirement, a soft cushion is arranged at the bottom of an anti-pulling pile or an anti-floating anchor rod is changed;
the adjustment of the support rigidity is controlled through a strengthening index and a weakening index, and under the condition that the characteristic value of the total bearing force of the main skirt is balanced with the standard value of the total load, the adjustment of the support rigidity of the pile soil is realized through controlling the strengthening index of a core barrel area and the weakening index of a peripheral frame area, wherein the strengthening index of the core barrel area is 1.05-1.30, and the weakening index of the peripheral frame area is 0.70-0.95;
in the building synergistic action system of the upper structure-foundation-pile soil, the total balance equation of the synergistic action system is as follows:
([K] st +[K] F +[K] s(p,s) ){u}＝{F} st +{F} F ，
in the formula [ K] st A stiffness matrix that is condensed to the substructure at the top of the foundation; [ K ]] F A base stiffness matrix condensed on the base bottom surface; [ K ]] s(p,s) Supporting a stiffness matrix for the pile soil condensed on the substrate; { u } is a displacement vector of a base bottom node; { F } st 、{F} F Respectively, the superstructure, the base load vector, condensed to the substrate.
2. The method for leveling the pile foundation of the main skirt conjoined high-rise building according to claim 1, wherein the strengthening index xi of the core tube area s Resistance ratio of core region
Ratio of load to load
The ratio of:
wherein the content of the first and second substances,
in the above-mentioned description,
R ak respectively is the bearing capacity characteristic value of the core tube area and the bearing capacity characteristic value of the whole raft foundation,
F k the standard values of the load of the core area and the standard value of the load of the whole raft are respectively.
3. The method for leveling the pile foundation of the main skirt one-piece high-rise building according to claim 1, wherein the layout of the pile-soil supporting body is performed on the principle of vertical dislocation or horizontal pull-apart distance, and the support stiffness distribution is optimized by adopting the combination of long and short piles, variable pile diameters, variable pile spacing, the combination of conventional pile foundations and composite pile foundations, and the combination of composite foundations and natural foundations.
4. The method for leveling the pile foundation of the main skirt one-piece high-rise building according to claim 1, wherein a conventional pile foundation, a composite pile foundation or a rigid pile composite foundation is selected according to construction factors and geological characteristics, and the concrete method for adjusting the pile-soil support rigidity distribution is as follows:
for a frame tube structure with extremely uneven load distribution, a conventional pile foundation is adopted in a core tube area, and a composite pile foundation is adopted in a peripheral frame area;
for medium and low compressibility soil foundations, the height of the frame tube structure is not more than 60m, the height of the shear wall structure is not more than 100m, a rigid pile composite foundation or a rigid pile composite foundation is adopted in the local core tube area, and the rigidity distribution is adjusted by changing the pile length and the pile distance.
5. The method for leveling the pile foundation of the main skirt one-piece high-rise building according to claim 1, wherein the selection of the type of the foundation pile of the pile foundation and the determination of the pile end bearing layer facilitate post grouting reinforcement, so that the bearing capacity of the foundation pile has an adjustment space, and the foundation pile is intensively distributed under the column or the wall, thereby reducing the foundation internal force, maximally exerting the load sharing effect of foundation soil, and reducing the interaction between the pile foundation and the pile foundation in the core barrel area.
6. The method for leveling the pile foundation of the main skirt one-piece high-rise building according to claim 1, wherein pile foundation arrangement adopts pile arrangement with inner density, outer sparsity, inner length and outer short length to form inner strong and outer weak support rigidity distribution, eliminate dish-shaped settlement formed due to interaction effect, test leveling effect under the synergistic effect analysis of upper structure-foundation-pile soil, further optimize pile arrangement and determine bearing platform internal force and reinforcement.
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