CN111321732A - Composite foundation bearing structure for placing precast pile in high-pressure jet grouting pile - Google Patents

Composite foundation bearing structure for placing precast pile in high-pressure jet grouting pile Download PDF

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CN111321732A
CN111321732A CN202010122484.2A CN202010122484A CN111321732A CN 111321732 A CN111321732 A CN 111321732A CN 202010122484 A CN202010122484 A CN 202010122484A CN 111321732 A CN111321732 A CN 111321732A
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pile
jet grouting
pressure jet
precast
foundation
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代国忠
李书进
施维成
史贵才
李雄威
李鹏波
宋杨
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Changzhou Institute of Technology
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    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
    • E02D5/22—Piles
    • E02D5/50—Piles comprising both precast concrete portions and concrete portions cast in situ
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/04—Portland cements
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
    • E02D3/02—Improving by compacting
    • E02D3/08—Improving by compacting by inserting stones or lost bodies, e.g. compaction piles
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D33/00—Testing foundations or foundation structures

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  • Consolidation Of Soil By Introduction Of Solidifying Substances Into Soil (AREA)
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Abstract

The invention discloses a composite foundation bearing structure for placing a precast pile in a high-pressure jet grouting pile, which comprises a high-pressure jet grouting pile cement soil consolidation body formed by forcibly mixing cement soil curing agent slurry and a foundation soil body, the precast pile placed in the high-pressure jet grouting pile cement soil consolidation body, and a reinforced concrete bearing platform or a raft foundation and a box foundation form arranged at the top of the precast pile; the water-cement ratio of the slurry prepared by the cement soil curing agent is generally 0.7-1.1, and auxiliary materials and/or external additives are added into the slurry. The composite foundation bearing structure can obviously reduce the soil squeezing effect on the site foundation, increase the standard values of the lateral resistance and the end resistance of the pile, and enhance the characteristic value of the bearing capacity of the foundation soil treated by the high-pressure jet grouting pile, thereby improving the bearing capacity of the composite foundation.

Description

Composite foundation bearing structure for placing precast pile in high-pressure jet grouting pile
Technical Field
The invention relates to the technical field of building foundation engineering, in particular to a composite foundation bearing structure with a precast pile arranged in a high-pressure rotary jet grouting pile.
Background
In recent years, with the development of urban construction, prefabricated reinforced concrete piles have been widely used as foundation foundations for buildings, and cement-soil mixing piles have been mainly used for reinforcing soft soil foundations and forming composite foundations with natural foundations. At present, the precast reinforced concrete pile is usually sunk to the foundation by static pressure, hammering, vibration and other methods to a designed depth, pile sinking equipment is heavy and bulky, the transportation of a construction site is not very convenient, the soil squeezing effect in the pile sinking process is large no matter the precast pile is hollow or solid, especially the pile sinking is carried out in silt and silty sand layers below the underground water level, the pore water pressure of the soil layer is sharply increased due to the high pile sinking speed, the larger soil squeezing effect is caused, the disturbance to natural foundation soil is also large, the foundation of a building at the periphery of the construction site is greatly bulged, the cracking of a house foundation and a wall body is caused in serious conditions, and the normal use of the building is influenced. In addition, the excessive pile pressing force, hammering force and vibration force during pile sinking can cause local damage of the concrete on the pile top, and influence the normal use of the precast pile.
The high-pressure jet grouting pile is independently used for reinforcing the soft soil foundation, and the high-pressure jet grouting pile has relatively low compressive strength, shear strength and tensile strength, cannot bear overlarge vertical load, has more limited horizontal bearing capacity, and has larger sedimentation deformation, so that the application of the high-pressure jet grouting pile composite foundation is limited to a certain extent.
Disclosure of Invention
The invention aims to provide a composite foundation bearing structure for placing a precast pile in a high-pressure jet grouting pile, which fundamentally solves the soil squeezing effect in the process of sinking the precast pile by adopting the traditional methods of static pressure, hammering, vibration and the like, and avoids the problem of local damage of pile top concrete caused by overlarge pile pressing force, hammering force and vibration force during pile sinking; the problem of use high pressure jet grouting pile stake reinforcement soft soil foundation bearing capacity is low alone, the settlement of compound foundation is out of shape than great is solved.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
the high-pressure jet grouting pile and the reinforced concrete precast pile are organically combined, the reinforced concrete precast pile is placed in the high-pressure jet grouting pile constructed in advance, a bearing structure of a composite foundation is formed by a reinforced concrete bearing platform (or a raft foundation, a box foundation and other foundation forms) arranged on the pile top, and the estimation method of the characteristic value of the vertical bearing capacity of the single pile, the characteristic value of the vertical bearing capacity of the single pile of the high-pressure jet grouting pile and the characteristic value of the bearing capacity of the composite foundation is given.
A composite foundation bearing structure with a precast pile placed in a high-pressure jet grouting pile comprises the high-pressure jet grouting pile formed by stirring and mixing cement soil curing agent slurry and a foundation soil body, the precast pile placed in the high-pressure jet grouting pile, and a reinforced concrete bearing platform (or in the form of a raft foundation, a box foundation and the like) arranged at the top of the precast pile. The water cement ratio of the slurry prepared by the cement soil curing agent of the high-pressure jet grouting pile is generally 0.7-1.1, auxiliary materials and/or additives are/is added into the slurry, and the performance of the cement soil of the high-pressure jet grouting pile is adjusted to improve the physical and mechanical properties of foundation soil.
Furthermore, the construction site of the composite foundation bearing structure is arranged in a bearing platform (or raft foundation, box foundation and other foundation forms) area of the building foundation, the distribution range of the precast piles and the central position of the precast piles.
Furthermore, the high-pressure jet grouting pile mainly adopts 42.5-grade ordinary portland cement as a cement soil curing agent.
Preferably, the auxiliary materials added into the slurry comprise 20-30 wt% of fly ash and the like, and the external additive comprises 2-3 wt% of gypsum, 0.05-0.1 wt% of polycarboxylic acid high-performance water reducing agent (PCA-300P type or TOJ800-10A type), 2-3 wt% of calcium chloride, 0.03-0.08 wt% of triethanolamine, 1.0-2.0 wt% of sodium sulfate, 3-5 wt% of water glass and the like. The types and the proportion of the added auxiliary materials and the added agents can be determined through indoor tests and field tests, so that the purpose of adjusting the performance of the cement soil consolidation body of the high-pressure jet grouting pile is achieved.
Furthermore, a high-pressure jet flow (cement slurry or water flow) with the pressure of 20-50 MPa jetted by a high-pressure rotary jet machine is used for impacting and cutting a natural foundation soil body, so that cement curing agent slurry and the foundation soil body are forcibly mixed to form a cement-soil consolidated body, namely a high-pressure rotary jet pile body, the diameter size and the strength index of the cement-soil consolidated body are controlled by adjusting the lifting speed, the rotating speed and the jetting technical parameters of a rotary jet grouting pipe, and the common cement mixing ratio (the percentage of the mixed cement amount to the natural wet weight of the reinforced soft soil foundation) can reach 15-35%. The high-pressure rotary spraying machine is a single pipe, a double pipe or a triple pipe. The high-pressure rotary jet grouting pile can be in a columnar, grid-shaped or block-shaped equal-plane arrangement form, the diameter of a cement-soil consolidation body of the single-pipe high-pressure rotary jet grouting pile is 500-900 mm, the diameter of a cement-soil consolidation body of the double-pipe high-pressure rotary jet grouting pile is 600-1300 mm, the diameter of a cement-soil consolidation body of the triple-pipe high-pressure rotary jet grouting pile is 700-1800 mm, and the unconfined compressive strength, the unconfined shear strength, the unconfined tensile strength and the compressive modulus of the cement-soil consolidation body at 28d age are 1.5-12 MPa, 0.5-2.5 MPa, 0.2-2.0 MPa and 100-800 MPa.
Furthermore, after the construction of the high-pressure jet grouting pile is completed in a unit area of a foundation, a precast pile is timely placed in the corresponding high-pressure jet grouting pile, the precast pile is hoisted by a crane to vertically and downwards sink to the corresponding pile position, the placing of the precast pile can be realized, the connection of upper and lower pile sections can be realized by methods such as flange plates, welding, dowel bar sulfur cement gluing and the like for multi-section piles, the section shape of the precast pile is circular, square and the like (can be hollow or solid), and the pile diameter, the pile length, the pile interval, the pile number and the plane arrangement are determined according to the composite foundation bearing capacity calculation and the settlement deformation control requirement. The bearing structure of the composite foundation is formed by reinforced concrete bearing platforms (or basic forms such as raft foundation, box foundation and the like) arranged on the pile tops.
Furthermore, the characteristic value of the vertical bearing capacity of the single pile of the precast pile is determined through a field load test and can be estimated according to the following formula: ra1＝ατkul+βσk(Ap0+λpAp1) (ii) a In the formula, Ra1The vertical bearing capacity characteristic value (kN) of a single pile of the reinforced concrete precast pile, the reduction coefficient of the unconfined shear strength of a high-pressure jet grouting pile cement soil pile consolidation body of α, α is 0.1-0.2, and taukIs the unconfined shear strength characteristic value tau of the high-pressure jet grouting pile cement soil consolidation body 28d agek500-2500 kPa, u is the perimeter (m) of the body of the precast pile, l is the length (m) of the precast pile, β is the reduction coefficient of unconfined compressive strength of the cement-soil consolidation body of the high-pressure jet grouting pile, β is 0.4-0.6, and sigma iskIs the unconfined compression strength characteristic value, sigma, of the cement-soil consolidation body 28d age of the high-pressure jet grouting pilek＝1500～12000kPa；Ap0For the net area (m) of the pile end of the precast pile2) When the precast pile is a round pile,
Figure BDA0002393395260000031
when the precast pile is a square pile,
Figure BDA0002393395260000032
d、b、d1respectively the outer diameter, side length and inner diameter (m) of the precast pile, when the precast pile is a solid pile, d1＝0；λpIs the end soil blocking effect coefficient of the precast pile, lambdap＝0.7～0.8；Ap1For pre-forming the open area (m) of the pile2)，
Figure BDA0002393395260000033
When the precast pile is a solid pile, d1＝0。
Furthermore, the characteristic value of the vertical bearing capacity of the single high-pressure jet grouting pile is determined by a field load test. During preliminary design, the estimation can be carried out according to the following two formulas, and the smaller of the calculated values in the two formulas is taken: ra2＝ξσkAP2And
Figure BDA0002393395260000034
in the formula, Ra2The characteristic value (kN) of the vertical bearing capacity of the single high-pressure jet grouting pile, ξ is the pile body strength reduction coefficient of the high-pressure jet grouting pile, when sigma iskWhen the pressure is 1500-5000 kPa, ξ is 0.5-0.4, when sigma iskWhen the pressure is 5000-8000 kPa, ξ is 0.4-0.3, when sigma isk8000-12000 kPa, ξ is 0.3-0.2, sigmakIs the unconfined compression strength characteristic value, sigma, of the cement-soil consolidation body 28d age of the high-pressure jet grouting pilek＝1500～12000kPa；Ap2Is the effective cross-sectional area (m) of the pile body of the single high-pressure jet grouting pile2) For high-pressure rotary jet grouting pile with embedded precast pile
Figure BDA0002393395260000035
For high-pressure jet grouting pile without precast pile embedded
Figure BDA0002393395260000036
d2The effective pile diameter (m) of the high-pressure jet grouting pile is obtained; u. ofpIs the circumference (m) of the pile; n is the number of divided soil layers in the pile length range of the high-pressure jet grouting pile; q. q.ssiThe lateral resistance characteristic value (kPa) of the i-th layer soil around the high-pressure jet grouting pile is determined by combining with regional experience; lpiThe thickness (m) of the i-th layer soil in the length range of the high-pressure rotary jet grouting pile, αpCoefficient of pile tip resistance exertion for high-pressure jet grouting pile, αp＝0.45～0.65；qpThe bearing capacity characteristic value (kPa) of the foundation soil of the high-pressure jet grouting pile end soil which is not corrected is determined by combining with regional experience; a. thep0、Ap1The symbols in (a) have the same meanings as those in the preceding description.
Furthermore, the composite foundation bearing structure with the precast pile placed in the high-pressure jet grouting pile is a composite foundation bearing structure consisting of the high-pressure jet grouting pile, the precast pile and a pile top bearing platform (or a raft foundation, a box foundation and other foundation forms), wherein the composite foundation bearing capacity characteristic value is determined through an on-site composite foundation load test, and can be estimated according to the following formula during primary design:
Figure BDA0002393395260000037
in the formula (f)spkThe characteristic value of the bearing capacity (kPa) of the composite foundation is obtained; m is1、m2The area replacement rates of the reinforced concrete precast pile and the high-pressure jet grouting pile are respectively,
Figure BDA0002393395260000041
Figure BDA0002393395260000042
n1、n2the number of the reinforced concrete precast piles and the high-pressure jet grouting piles under a single bearing platform (or the area of a calculation unit in the form of a foundation such as a raft foundation, a box foundation and the like), A is the area of the bottom surface (m) of the single bearing platform (or the area of a calculation unit in the form of a foundation such as a raft foundation, a box foundation and the like)2)；λ1、λ2、λ3The exertion coefficients of the bearing capacity of the soil among the reinforced concrete precast pile, the high-pressure jet grouting pile and the pile are determined by a static load test of a multi-pile composite foundation or according to regional experience, and the lambda can be taken1＝λ2＝0.8～0.9，λ3＝0.85～0.95；fskThe characteristic value (kPa) of the bearing capacity of the soil between the treated composite foundation piles is obtained; a. thep0、Ap1、Ap2The symbols in (a) have the same meanings as those in the preceding description.
Compared with the prior art, the technical scheme provided by the invention has the following remarkable effects:
the high-pressure jet grouting pile construction method has the advantages that the physical and mechanical properties of foundation soil are improved, the pile sinking construction of the reinforced concrete precast pile is facilitated, the soil squeezing effect on a site foundation can be obviously reduced, the standard values of lateral resistance and end resistance of the pile are increased, the characteristic value of the bearing capacity of the foundation soil treated by the high-pressure jet grouting pile is enhanced, the bearing capacity of a composite foundation is improved, the settlement deformation of the foundation can be effectively controlled through the optimized arrangement of the high-pressure jet grouting pile and the reinforced concrete precast pile, and the cost of construction engineering is reduced.
(1) The high-pressure jet grouting pile mainly adopts 42.5-grade ordinary portland cement as a curing agent of cement soil, the water-cement ratio of prepared slurry is generally 0.7-1.1, and the slurry performance and the cement soil performance are adjusted by adding auxiliary materials such as fly ash, gypsum, a polycarboxylic acid high-performance water reducing agent, calcium chloride, triethanolamine, sodium sulfate, water glass and the like and an external additive into the cement slurry. The fly ash auxiliary material is selected, which mainly improves the activity of the cement soil and increases the later strength (which can be improved by more than 10%) of the cement soil consolidation period of the high-pressure jet grouting pile; the polycarboxylic acid high-performance water reducing agent is selected, and is mainly used for preventing a network structure formed by cement particles due to coalescence, improving the hydration condition of the contact of the cement particles and water and increasing the fluidity of slurry (the fluidity and the pumpability of the slurry meet the construction operation requirement of a high-pressure jet grouting pile); the additive such as gypsum, calcium chloride, triethanolamine, sodium sulfate and water glass is selected to improve the performance of the cement soil, accelerate the setting speed of the cement soil, improve the early strength of a cement soil solidification body and enhance the anticorrosion effect of the cement soil solidification body.
(2) The construction of high-pressure jet grouting pile is carried out by utilizing conventional high-pressure jet grouting pile machines (single pipes, double pipes and triple pipes), no new construction equipment is required to be input, and the method is suitable for wide variety of foundation soil, and can treat soil layers such as silt, mucky soil, cohesive soil (flow plastic, soft plastic or plastic), silt, sandy soil, loess, plain filling soil, gravel soil and the like. The diameter size and strength index of the cement-soil consolidation body can be controlled by adjusting the lifting speed, the rotating speed and the injection technical parameters of the rotary injection grouting pipe, and the cement mixing ratio (the percentage of the mixed cement amount to the natural wet weight of the reinforced soft soil foundation) can reach 15-35%. The high-pressure rotary jet grouting pile can be in a columnar, grid-shaped or block-shaped equal-plane arrangement form, the diameter of a cement soil consolidation body of the single-pipe high-pressure rotary jet grouting pile is 500-900 mm, the diameter of a cement soil consolidation body of the double-pipe high-pressure rotary jet grouting pile is 600-1300 mm, the diameter of a cement soil consolidation body of the triple-pipe high-pressure rotary jet grouting pile is 700-1800 mm, and the cement soil consolidation body has the unconfined compressive strength of 1.5-12 MPa, the unconfined shear strength of 0.5-2.5 MPa, the unconfined tensile strength of 0.2-2.0 MPa and the compression modulus of 100-800 MPa at the age of 28d, so that the design requirements of various composite foundations can be met.
(3) After the construction of the high-pressure jet grouting pile is finished, the reinforced concrete precast pile can be placed in the corresponding high-pressure jet grouting pile, the precast pile is lifted by a crane to vertically and downwards sink to the corresponding pile position, the placing of the precast pile can be realized, the section shape and the connection form of the precast pile are not limited, and a reinforced concrete bearing platform (or basic forms such as a raft foundation, a box foundation and the like) arranged on the pile top forms a bearing structure of the composite foundation.
(4) The physical and mechanical properties of foundation soil are improved through the high-pressure jet grouting pile construction, the pile sinking construction of the reinforced concrete precast pile is facilitated, the soil squeezing effect on a site foundation can be obviously reduced, the side resistance and end resistance standard values of the pile are increased, the characteristic value of the bearing capacity of the foundation soil treated by the high-pressure jet grouting pile is enhanced, the bearing capacity of the composite foundation is improved, and the settlement deformation of the foundation can be effectively controlled through the optimized arrangement of the high-pressure jet grouting pile and the reinforced concrete precast pile. Aiming at the composite foundation bearing structure with the precast pile arranged in the high-pressure jet grouting pile, the estimation formulas of the single-pile vertical bearing capacity characteristic value, the single-pile vertical bearing capacity characteristic value and the composite foundation bearing capacity characteristic value of the reinforced concrete precast pile are practical, and the error is smaller compared with a field static load test value. The high-pressure jet grouting pile and the reinforced concrete precast pile are organically combined, the application range of the high-pressure jet grouting pile and the reinforced concrete precast pile as a building foundation is expanded, the pollution to the site environment is reduced, the economic benefit and the social benefit are obvious, and the popularization and application values are realized.
Drawings
Fig. 1 is a schematic view of a composite foundation with a precast pile placed in a single-pipe high-pressure jet grouting pile according to an embodiment of the present invention.
Fig. 2 is a cross-sectional view of a composite foundation with a precast pile placed in a single-pipe high-pressure jet grouting pile according to an embodiment of the present invention.
Fig. 3 is a schematic view of the composite foundation with a precast pile placed in a double-pipe high-pressure jet grouting pile according to an embodiment of the invention.
Fig. 4 is a sectional view of the composite foundation with a precast pile placed in a double-pipe high-pressure jet grouting pile according to an embodiment of the present invention.
Fig. 5 is a schematic view of a composite foundation with a precast pile placed in a triple-pipe high-pressure jet grouting pile according to an embodiment of the present invention.
Fig. 6 is a cross-sectional view of a composite foundation with a precast pile placed in a triple-pipe high-pressure jet grouting pile according to an embodiment of the present invention.
The reference numerals in the schematic drawings illustrate:
1. a bearing platform foundation; 2. a circular hollow reinforced concrete precast pile; 3. high-pressure jet grouting piles constructed by a single-pipe method; 4. a column; 5. a raft foundation; 6. a square solid reinforced concrete precast pile; 7. high-pressure jet grouting piles constructed by a double-pipe method; 8. a foundation beam; 9. a box-shaped foundation; 10. a round solid reinforced concrete precast pile; 11. high-pressure jet grouting piles constructed by a triple pipe method; 12. an inner partition wall.
Detailed Description
The invention is further described below with reference to specific examples, but without limiting the scope of the invention.
The foundation bearing structure of the embodiment of the invention organically combines the high-pressure jet grouting pile and the reinforced concrete precast pile, the reinforced concrete precast pile is arranged in the high-pressure jet grouting pile constructed in advance, and the reinforced concrete bearing platform (or the foundation forms such as a raft foundation, a box foundation and the like) arranged on the pile top forms the bearing structure of the composite foundation. Therefore, the physical and mechanical properties of foundation soil can be improved through the high-pressure jet grouting pile construction, the pile sinking construction of the reinforced concrete precast pile is facilitated, the precast pile can be embedded by lifting the precast pile to a corresponding pile position by a crane and vertically sinking downwards, the soil squeezing effect on a site foundation in the pile sinking process of the precast pile can be obviously reduced, the noise influence during the construction is reduced, the side resistance and end resistance standard values of the pile can be increased, the characteristic value of the bearing capacity of the foundation soil treated by the high-pressure jet grouting pile is enhanced, the bearing capacity of a composite foundation is improved, the sedimentation deformation of the foundation can be effectively controlled through the optimized arrangement of the high-pressure jet grouting pile and the reinforced concrete precast pile, and the cost of construction engineering is reduced. The invention belongs to the research result funded by a national science fund project (project number: 51678083).
Example 1:
the embodiment is a high-rise building project of a certain 28-storey building, and adopts a frame structure, the center distance of 4 column bases of adjacent upright columns is 10m, the size of a single column base bearing platform foundation 1 is 4.6 × 5.2.2 m, the burial depth of the bearing platform is-2.5 m, the vertical load transmitted from an upper structure to the bearing platform at the lower end of the column is 2455 kN, and the engineering geological data of a site foundation is shown in the following table 1:
TABLE 1
Figure BDA0002393395260000061
The design adopts a composite foundation bearing structure with a precast pile placed in a high-pressure jet grouting pile, and the characteristic value of the bearing capacity of the composite foundation is required to reach 1025 kPa. The high-pressure jet grouting pile 3 constructed by the single-pipe method is constructed by adopting a single-pipe method high-pressure jet grouting pile machine, 8 high-pressure jet grouting piles 3 with effective pile diameters phi of 800mm are constructed, the pile length is 20m, the high-pressure jet grouting piles 3 constructed by the single-pipe method are arranged in a columnar mode, then a phi 500mm circular hollow reinforced concrete precast pile 2 is placed in each stirring pile, the diameter of a pile center hole is phi 250mm, the pile length of each precast pile is 18m (2 sections, each section is 9m long, and flanges are connected), and the longitudinal and plane arrangement of a pile foundation is schematically shown in the figure 1 and the figure 2.
According to the design requirement, 42.5-grade ordinary portland cement is adopted as a curing agent of cement soil for the high-pressure jet grouting pile 3 constructed by the single-pipe method, the water cement ratio of prepared slurry is selected to be 0.9, 25% of fly ash, 0.08% of polycarboxylic acid high-performance water reducing agent (PCA-300P type), 2.5% of calcium chloride, 0.05% of triethanolamine, 1.5% of sodium sulfate, 4% of water glass and other auxiliary materials and external doping agents are doped into the cement slurry for improving the performance of the cement soil of the high-pressure jet grouting pile, and the doping proportion refers to the weight percentage of the cement. The addition of the fly ash is beneficial to improving the activity of the cement soil and increasing the later strength of the cement soil consolidation body of the high-pressure jet grouting pile; the PCA-300P type polycarboxylic acid high-performance water reducing agent is doped to prevent a network structure formed by cement particles due to coalescence, improve the hydration condition of the cement particles in contact with water and increase the fluidity of slurry (so that the fluidity and pumpability of the slurry meet the construction operation requirement of a stirring pile); the calcium chloride, the triethanolamine, the sodium sulfate, the water glass and the like are added, so that the setting speed of the cement soil of the high-pressure jet grouting pile 3 constructed by the single-pipe method can be increased, the early strength of a cement soil solidification body is improved, and the corrosion prevention effect of the cement soil is enhanced.
The construction process of the high-pressure jet grouting pile 3 constructed by the single-pipe method comprises the following steps: a nozzle arranged on the side surface of the bottom of a single-gravity grouting pipe is placed into a soil layer from the bottom of a bearing platform to a depth of 20m by a drilling machine, a high-pressure slurry pump is started to spray prepared cement slurry out of the nozzle to impact and damage a soil body, the slurry and soil falling from the soil body are stirred and mixed, the lifting speed of the single-gravity rotary-spraying grouting pipe is 40-60 cm/min, the rotating speed is 18-30 r/min, the grouting flow is 90-120 l/min, the cement doping ratio (the percentage of the doped cement amount to the natural wet weight of a reinforced soft soil foundation) reaches 25%, and a cement soil consolidation body with the diameter of 800mm is formed in foundation cylindrical soil. The high-pressure jet grouting pile 3 constructed by the single-pipe method has the pile length of 20m, and the bottom of the pile is located 7.5m below the clay layer.
After 8 high-pressure jet grouting piles in a single column foundation bearing platform area are constructed, a crane is adopted to lift a first section (with the length of 9m) of hollow reinforced concrete precast pile to vertically and downwards sink to a corresponding pile position, the sinking speed is controlled, when the pile top of the first section of precast pile is 1m above the ground, the sinking is suspended, then a 2 nd section of precast pile is lifted to align to a flange plate at the top end of the first section of precast pile, the upper pile section and the lower pile section are connected through the flange plate, the sinking of the precast pile is continuously started to a pile bottom elevation (a position 2m away from the pile end of the high-pressure jet grouting pile) until the placement of the 8 reinforced concrete precast piles in the high-pressure jet grouting pile is completed, and a reinforced concrete bearing platform (the plane size is 4.6 × 5.2.2 m) arranged through the pile top forms a bearing structure of the composite foundation.
A28 d-age high-pressure jet grouting pile cement soil solidification body sample is adopted on site, an electronic universal experiment compressor is adopted to test the strength index of the cement soil solidification body sample, and the tested high-pressure jet grouting pile cement soil solidification body 28 d-age manufactured has the unconfined compressive strength of 5MPa, the unconfined shear strength of 0.75MPa, the unconfined tensile strength of 0.6MPa and the compression modulus of 350 MPa.
The characteristic value of the vertical bearing capacity of a single pile of the reinforced concrete precast pile is determined to be 3580kN through a field load test; the characteristic value of the vertical bearing capacity of the single reinforced concrete precast pile is estimated according to the formula as follows:
take α ═ 0.15，τk＝750kPa，u＝πd＝3.14×0.5＝1.57m，l＝18m，β＝0.5，σk＝5000kPa，
Figure BDA0002393395260000071
λp＝0.75，Ap1Is the open area (m) of the hollow pile2)，
Figure BDA0002393395260000081
Ra1＝ατkul+βσk(Ap0+λpAp1) 0.15 × 750 × 1.57.57 1.57 × 18+0.5 × 5000 × (0.147+0.75 × 0.0491) ═ 3638kN, R is takena1＝3580kN。
The total vertical load that 8 precast piles can bear below the bearing platform is 8 × 3580-28640 kN > 2450 kN, and the stress requirement that the upper structure transmits the vertical load of the bearing platform at the lower end of the column is met.
The characteristic value of the vertical bearing capacity of a single high-pressure jet grouting pile with a built-in precast pile is determined to be 790kN through a field load test; the characteristic value of the vertical bearing capacity of the single pile of the high-pressure jet grouting pile is estimated according to a formula as follows:
let ξ be 0.40, σk＝5000kPa，up＝πd＝3.14×0.8＝2.512m，
Figure BDA0002393395260000082
n＝3，lp1＝3.5m，qs1＝24kPa，lp2＝9m，qs2＝17kPa，lp3＝7.5m，qs3＝38kPa，αp＝0.55，qp＝230kPa。
Ra2＝ξσkAP2＝0.4×5000×0.306＝612kN
Figure BDA0002393395260000083
Get Ra2＝612kN。
Measuring the characteristic value of the bearing capacity of a composite foundation consisting of the high-pressure jet grouting pile, the precast pile and the soil among the piles under the column foundation bearing platform to be 1180kPa through a field load test; the characteristic value of the bearing capacity of the composite foundation is estimated according to the formula as follows:
Figure BDA0002393395260000084
take lambda1＝λ2＝0.85，λ3＝0.90，fsk＝110kPa，Ap0＝0.147m2，Ap1＝0.0491m2，Ap2＝0.306m2。
Figure BDA0002393395260000085
The actual bearing capacity characteristic value of the composite foundation is 1180kPa, and the design requirement of the bearing capacity characteristic value 1025kPa of the composite foundation is met.
The construction monitoring shows that the composite foundation bearing structure with the precast pile embedded in the high-pressure jet grouting pile is adopted in the engineering, so that no soil squeezing effect occurs in the construction process of the high-pressure jet grouting pile and the precast pile, and no adverse influence is caused on the foundation of a surrounding building. After the construction of 28 stories of the upper structure is finished, through long-term observation of settlement deformation of the foundation (the monitoring time is more than 365 d), the total settlement deformation of the building foundation is only 16mm, uneven settlement does not occur, and the total settlement deformation is far lower than the actual final average settlement deformation allowable value of the high-rise building foundation specified in the design Specification of building foundation (GB50007-2011) by 200 mm. Therefore, the composite foundation bearing structure for placing the precast pile in the high-pressure jet grouting pile adopted by the project meets the design requirements of foundation bearing capacity and settlement deformation.
Example 2:
the embodiment is a certain 35 storied building high-rise building engineering (1-layer basement), and the shear wall structure adopts beam slab raft foundation 5, and raft foundation 5 top is equipped with foundation beam 8. raft foundation 5 board buried depth is-5.0 m, and take raft foundation 5 plane size to be 4.5 × 8.0.0 m, and the vertical load standard value that superstructure passed to unit raft foundation 5 is 198000kN, and the engineering geological data of place ground is shown in following table 2:
TABLE 2
Figure BDA0002393395260000091
The design adopts a composite foundation bearing structure with a precast pile placed in a high-pressure jet grouting pile, and the characteristic value of the bearing capacity of the composite foundation is required to be 550 kPa. The high-pressure rotary jet grouting pile 7 constructed by the double-pipe method with the pile diameter phi of 1100mm is constructed by adopting a high-pressure rotary jet grouting pile machine, the pile length is 21m, the high-pressure rotary jet grouting pile 7 constructed by the double-pipe method is arranged in a grid shape (the effective pile diameter of the high-pressure rotary jet grouting pile is phi 900mm after circle crossing), 33 high-pressure rotary jet grouting piles 7 constructed by the double-pipe method are arranged below each raft foundation 5, then square solid reinforced concrete precast piles 6 with the side length of 600mm are placed in 9 high-pressure rotary jet grouting piles, the high-pressure rotary jet grouting piles are uniformly and symmetrically arranged, the length of the precast pile is 18m (2 sections, each section is 9m, the precast piles are connected by adopting a welding method or a rib-inserting sulfur cement method), and the longitudinal and plane arrangement of a pile foundation is schematically.
According to the design requirement, 42.5-grade ordinary portland cement is adopted as a curing agent of cement soil for the high-pressure jet grouting pile 7 constructed by the double-pipe method, the water-cement ratio of prepared slurry is selected to be 1.1, and in order to improve the performance of the cement soil of the high-pressure jet grouting pile, 30% of fly ash, 2.5% of gypsum, 0.05% of polycarboxylic acid high-performance water reducing agent (TOJ800-10A type), 5% of water glass and other auxiliary materials and external doping agents are added into the cement slurry, wherein the doping proportion refers to the weight percentage of the cement. The addition of the fly ash is beneficial to improving the activity of the cement soil and increasing the later strength of the cement soil consolidation body of the jet grouting pile; TOJ800-10A type polycarboxylic acid high-performance water reducing agent is added to prevent cement particles from forming a net structure due to coalescence, improve the hydration condition of the cement particles in contact with water and increase the fluidity of slurry (so that the fluidity and pumpability of the slurry meet the construction operation requirements of a stirring pile); the gypsum and the water glass are doped, so that the setting speed of the cement soil of the high-pressure jet grouting pile can be accelerated, the early strength of a cement soil solidification body is improved, and the corrosion prevention effect of the cement soil is enhanced.
The construction process of the high-pressure rotary jet grouting pile 7 constructed by the double-pipe method comprises the steps of jetting slurry with about 30MPa of pressure from a high-pressure slurry pump and a high-pressure generating device to jet slurry with about 0.7MPa of pressure from an inner nozzle at high speed, jetting compressed air from an outer nozzle with about 0.7MPa of pressure, and under the combined action of the high-pressure slurry and surrounding airflow of the outer ring, the energy for destroying the soil body is much larger than that of a single-pipe method, the lifting speed of the double-pipe rotary jet grouting pipe is 30-50 cm/min, the rotating speed is 12-25 r/min, the grouting flow is 90-130 l/min, the cement mixing ratio (the percentage of the cement added to the natural wet weight of a reinforced foundation) reaches 15%, and the 1100mm of high-pressure rotary jet grouting pile is formed in foundation soil, and the rotary jet grouting pile is located at the bottom of the high-pressure rotary jet grouting pile with the diameter of ④ mm, and the rotary jet grouting pile is located at the bottom of a rotary jet grouting pile with the height of 357 mm and the bottom of the high-pressure cement.
After 33 double-pipe-method-constructed high-pressure jet grouting piles 7 in the bottom area of a raft foundation 5 are constructed, a crane is adopted to lift a first section (length 9m) of square solid reinforced concrete precast pile 6 with the side length of 600mm to vertically and downwards sink to the center of the high-pressure jet grouting pile, the sinking speed is controlled, when the pile top of the first section of precast pile is 1m above the ground, the sinking is suspended, then a second section of precast pile is lifted to be aligned to the top end of the first section of precast pile, the upper pile section and the lower pile section are connected through a welding method (or an inserted bar sulfur cement mortar cementing method), the sinking of the precast pile is continuously started to reach the pile bottom elevation (the position 3m away from the pile end of the high-pressure jet grouting pile) until the placement of 9 steel reinforced concrete precast piles in the high-pressure jet grouting pile is completed, and the raft foundation 5 (unit plane size is 4.5 × 8.0.8.0 m) arranged on the pile top forms a bearing structure of the composite foundation.
A28 d-age high-pressure jet grouting pile cement soil solidification body sample is adopted on site, an electronic universal experiment compressor is adopted to test the strength index of the cement soil solidification body sample, and the tested high-pressure jet grouting pile cement soil solidification body has the unconfined compressive strength of 1.5MPa, the unconfined shear strength of 0.5MPa, the unconfined tensile strength of 0.2MPa and the compression modulus of 100MPa in the 28 d-age period.
The characteristic value of the vertical bearing capacity of a single pile of the reinforced concrete precast pile is 2376kN through a field load test; the characteristic value of the vertical bearing capacity of the single reinforced concrete precast pile is estimated according to the formula as follows:
take α ═ 0.2,. tauk＝500kPa，u＝4b＝4×0.6＝2.4m，l＝18m，β＝0.4，σk＝1500kPa，Ap0＝b2＝0.62＝0.36m2，λp＝0.7，Ap1＝0。
Ra1＝ατkul+βσk(Ap0+λpAp1)
＝0.2×500×2.4×18+0.4×1500×0.36＝4536kN
Get Ra1＝2376kN。
The total vertical load borne by the 9 precast piles under the unit raft foundation 5 is 9 × 2376 (21384 kN > 19800 kN), and the stress requirement of the vertical load transmitted from the upper structure to the unit raft foundation is met.
Determining that the characteristic value of the vertical bearing capacity of the high-pressure jet grouting pile with the embedded precast pile is 570kN through a field load test; the characteristic value of the vertical bearing capacity of the single pile of the high-pressure jet grouting pile is estimated according to a formula as follows:
let ξ be 0.50, σk＝1500kPa，
Figure BDA0002393395260000111
up＝πd＝3.14×0.9＝2.826m；n＝3，lp1＝6m，qs1＝17kPa，lp2＝8m，qs2＝21kPa，lp3＝7m，qs3＝36kPa，αp＝0.45，qp＝280kPa。
Ra21＝ξσkAP21＝0.5×1500×0.2759＝207kN
Figure BDA0002393395260000112
Get Ra21＝207kN。
Determining that the characteristic value of the vertical bearing capacity of the high-pressure jet grouting pile without the precast pile is 498kN through a field load test; the characteristic value of the vertical bearing capacity of the single pile of the high-pressure jet grouting pile is estimated according to a formula as follows:
Figure BDA0002393395260000113
Ra22＝ξσkAP22＝0.5×1500×0.6359＝477kN
Figure BDA0002393395260000114
get Ra21＝477kN。
The bearing capacity characteristic value of a composite foundation consisting of a high-pressure jet grouting pile, a precast pile and soil among piles under the raft foundation of the unit is determined to be 780kPa through an on-site load test; the characteristic value of the bearing capacity of the composite foundation is estimated according to the formula as follows:
Figure BDA0002393395260000115
Figure BDA0002393395260000116
take lambda1＝λ2＝0.8，λ3＝0.85，fsk＝118kPa，Ap0＝0.36m2，Ap1＝0，Ap21＝0.2759m2，Ap22＝0.6359m2
Figure BDA0002393395260000121
The practical composite foundation bearing capacity characteristic value is 754kPa, and the design requirement of 550kPa on the bearing capacity characteristic value of the raft foundation composite foundation is met.
The high-rise building foundation engineering adopts the composite foundation bearing structure in which the precast pile is placed in the high-pressure jet grouting pile, and through construction monitoring, no soil squeezing effect occurs in the construction process of the high-pressure jet grouting pile and the precast pile, and no adverse influence is generated on the foundation of the surrounding building. After the 35-storey construction of the superstructure is finished, through long-term observation of settlement deformation of the foundation (the monitoring time is more than 365 d), the total settlement deformation of the building foundation is only 19.5mm, no uneven settlement occurs, and the total settlement deformation is far lower than the actual final settlement deformation allowable value of the high-rise building foundation 200mm specified in the design Specification of building foundation (GB 50007-2011). Therefore, the composite foundation bearing structure for placing the precast pile in the high-pressure jet grouting pile adopted by the project meets the design requirements of foundation bearing capacity and settlement deformation.
Example 3:
the embodiment is a high-rise building engineering (2-layer basement) of a certain 38-layer building, and adopts a box foundation 9, wherein the top of the box foundation 9 is provided with an inner partition wall 12, the buried depth of a box foundation plate is-8.0 m, the plane size of the unit box foundation 9 is 7.6 × 13.6.6 m, the standard value of a vertical load transmitted to the unit box foundation by an upper structure is 41000kN, and the engineering geological data of a site foundation are shown in the following table 3:
TABLE 3
Figure BDA0002393395260000122
The design adopts a composite foundation bearing structure with a precast pile embedded in a high-pressure jet grouting pile, and the characteristic value of the bearing capacity of the composite foundation is required to reach 435 kPa. The high-pressure jet grouting pile 11 constructed by a triple pipe method with the pile diameter phi 1800mm by adopting a high-pressure jet grouting pile machine is 14m in pile length, the high-pressure jet grouting pile 11 constructed by the triple pipe method is arranged in a block shape (the effective pile diameter of the high-pressure jet grouting pile is phi 1500mm after circle crossing), 5 transverse rows are arranged below each unit box-shaped foundation, 9 high-pressure jet grouting piles are arranged in each row, then 9 round solid reinforced concrete precast piles 10 with the phi 600mm are symmetrically arranged in the high-pressure jet grouting pile below the unit box-shaped foundation 9 at intervals, the pile length of the precast pile is 12m (single-section pile), and the longitudinal and plane arrangement of a pile foundation is schematically shown in figures 4 and 5.
According to the design requirement, 42.5-grade ordinary portland cement is adopted as a curing agent of cement soil for the high-pressure jet grouting pile 11 constructed by the triple-pipe method, the water cement ratio of prepared slurry is selected to be 0.70, in order to improve the performance of the cement soil of the jet grouting pile, 20% of fly ash, 2% of gypsum, 0.1% of polycarboxylic acid high-performance water reducing agent (PCA-300P type), 0.08% of triethanolamine, 2.0% of sodium sulfate, 3% of water glass and other auxiliary materials and external doping agents are added into the cement slurry, and the doping proportion refers to the weight percentage of the cement. The addition of the fly ash is beneficial to improving the activity of the cement soil and increasing the later strength of the cement soil consolidation body of the high-pressure jet grouting pile; the PCA-300P type polycarboxylic acid high-performance water reducing agent is doped to prevent a network structure formed by cement particles due to coalescence, improve the hydration condition of the cement particles in contact with water and increase the fluidity of slurry (the fluidity and pumpability of the slurry meet the construction operation requirement of a high-pressure jet grouting pile); the additive such as gypsum, triethanolamine, sodium sulfate and water glass is selected to improve the performance of cement soil, accelerate the setting speed of cement soil, improve the early strength of cement soil concretion and enhance the anticorrosion effect of cement soil.
The construction process of the high-pressure rotary jet grouting pile 11 constructed by the triple pipe method comprises the steps of surrounding a 0.5-0.7 MPa cylindrical air flow around a high-pressure generating device such as a high-pressure pump and the like to generate 30-50 MPa high-pressure water jet flow after the triple grouting pipe is drilled to a preset depth of a soil layer (the triple grouting pipe is placed into the soil layer from a box-shaped foundation to a depth of 14 m), carrying out coaxial injection and punching of the high-pressure water jet flow and the air flow to form a larger gap, injecting normal-pressure cement slurry into the gap for filling, rotating and lifting the nozzle, and finally solidifying the gap into a larger solidified body in soil, wherein the lifting speed of the triple pipe method rotary jet grouting pipe is 30-50 cm/min, the rotating speed is 12-25 r/min, the grouting flow is 110-160 l/min, the cement mixing ratio (the percentage of the mixed cement amount to the natural wet weight of a reinforced foundation) reaches 35%, and the cement slurry pump is enabled to form 1800mm cylindrical cement-shaped solidified body in foundation soil, the end length of the high-pressure rotary jet grouting pile is 14m, the bottom of the high-pressure rotary jet grouting pile is located below ④ m, and the diameter of the high-pressure jet grouting pile is 1500.
After the construction of 45 high-pressure jet grouting piles 11 constructed by a triple tube method in the bottom area of a unit box foundation 9, a crane is adopted to lift a 12m long phi 600mm round solid reinforced concrete precast pile 10 to vertically sink downwards to the central pile position of a corresponding mixing pile, the sinking speed is controlled to sink to the pile bottom elevation (the position 2m away from the pile end of the high-pressure jet grouting pile), namely, the placement of the 9 reinforced concrete precast piles in the high-pressure jet grouting pile 11 constructed by the triple tube method is completed, and the box foundation 9 (the unit plane size is 7.6 × 13.6.6 m) arranged through the pile top forms a bearing structure of a composite foundation.
A28 d-age high-pressure jet grouting pile cement soil solidification body sample is adopted on site, an electronic universal experiment compressor is adopted to test the strength index of the cement soil solidification body sample, and the tested high-pressure jet grouting pile cement soil solidification body 28 d-age manufactured has unconfined compressive strength of 12MPa, unconfined shear strength of 2.5MPa, unconfined tensile strength of 2.0MPa and compression modulus of 800 MPa.
The characteristic value of the vertical bearing capacity of a single pile of the reinforced concrete precast pile is determined to be 6850kN through a field load test; the characteristic value of the vertical bearing capacity of the single reinforced concrete precast pile is estimated according to the formula as follows:
take α ═ 0.1,. tauk＝2500kPa，u＝πd＝3.14×0.6＝1.884m，l＝12m，β＝0.6，σk＝12000kPa，
Figure BDA0002393395260000141
λp＝0.8，Ap1＝0。
Ra1＝ατkul+βσk(Ap0+λpAp1)
＝0.1×2500×1.884×12+0.6×12000×0.2826＝7686kN
Get Ra1＝6850kN。
Deducting the side piles of 3 unit foundations, and actually taking the total vertical load born by 6 precast piles below the unit box foundation 9 as 6 × 6800 ═ 41100kN > 41000kN, so that the stress requirement of the vertical load transmitted from the upper structure to the unit box foundation 9 is met.
Determining that the characteristic value of the vertical bearing capacity of the high-pressure jet grouting pile with the embedded precast pile is 1100kN through a field load test; the characteristic value of the vertical bearing capacity of the single pile of the high-pressure jet grouting pile is estimated according to a formula as follows:
let ξ be 0.20, σk＝12000kPa，
Figure BDA0002393395260000142
up＝πd＝3.14×1.5＝4.71m；n＝3，lp1＝5m，qs1＝11kPa，lp2＝6m，qs2＝27kPa，lp3＝3m，qs3＝45kPa，αp＝0.65，qp＝328kPa。
Ra21＝ξσkAP21＝0.2×12000×1.484＝3561kN
Figure BDA0002393395260000143
Get Ra21＝1100kN。
Determining that the characteristic value of the vertical bearing capacity of the high-pressure jet grouting pile without the precast pile is 1350kN through a field load test; the characteristic value of the vertical bearing capacity of the single pile of the high-pressure jet grouting pile is estimated according to a formula as follows:
Figure BDA0002393395260000144
Ra22＝ξσkAP22＝0.2×12000×1.766＝4238kN
Figure BDA0002393395260000145
get Ra21＝1350kN。
The bearing capacity characteristic value of the composite foundation consisting of the high-pressure jet grouting pile 11 constructed by the triple-pipe method and the round solid reinforced concrete precast pile 10 under the unit box-shaped foundation 9 is determined to be 980kPa through a field load test. Because the high-pressure jet grouting piles are arranged in the full space below the box-shaped foundation 9, no inter-pile soil exists, the estimation formula for calculating the bearing capacity characteristic value of the composite foundation can be simplified to a certain extent, and the process is as follows:
Figure BDA0002393395260000151
take lambda1＝0.9，λ2＝0.8，fsk＝ξσk＝0.2×12000＝2400kPa，Ap0＝0.2826m2，Ap1＝0，
Figure BDA0002393395260000152
The practical composite foundation bearing capacity characteristic value is 980kPa, and the design requirement of 435kPa on the composite foundation bearing capacity characteristic value of the box-shaped foundation 9 is met.
The high-rise building foundation engineering adopts the composite foundation bearing structure in which the precast pile is placed in the high-pressure jet grouting pile, and through construction monitoring, no soil squeezing effect occurs in the construction process of the high-pressure jet grouting pile and the precast pile, and no adverse influence is generated on the foundation of the surrounding building. After the construction of 38 stories of the upper structure is finished, through long-term observation of settlement deformation of the foundation (the monitoring time is more than 365 d), the total settlement deformation of the building foundation is only 22mm, no uneven settlement occurs, and the total settlement deformation is far lower than the actual final settlement deformation allowable value of the high-rise building foundation, which is specified in building foundation design code (GB50007-2011), of 200 mm. Therefore, the composite foundation bearing structure for placing the precast pile in the high-pressure jet grouting pile adopted by the project meets the design requirements of foundation bearing capacity and settlement deformation.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical solution according to the technical idea of the present invention falls within the protection scope of the present invention.

Claims (7)

1. The utility model provides a put into composite foundation bearing structure of precast pile in high pressure jet grouting pile which characterized in that: the high-pressure jet grouting pile comprises a high-pressure jet grouting pile cement soil consolidation body formed by forcibly mixing cement soil curing agent slurry and a foundation soil body, a precast pile placed in the high-pressure jet grouting pile cement soil consolidation body, and a reinforced concrete bearing platform or a raft foundation or a box foundation form arranged at the top of the precast pile; the water cement ratio of the slurry prepared by the cement soil curing agent is 0.7-1.1, and auxiliary materials and/or external additives are added into the slurry.
2. The composite foundation bearing structure for placing the precast pile in the high-pressure jet grouting pile according to claim 1, wherein: the auxiliary material comprises 20 to 30 weight percent of fly ash; the external admixture comprises 2 to 3 weight percent of gypsum, 0.05 to 0.1 weight percent of polycarboxylic acid high-performance water reducing agent, 2 to 3 weight percent of calcium chloride, 0.03 to 0.08 weight percent of triethanolamine, 1.0 to 2.0 weight percent of sodium sulfate and 3 to 5 weight percent of water glass.
3. The composite foundation bearing structure for placing the precast pile in the high-pressure jet grouting pile according to claim 1, wherein: the high-pressure rotary spraying pile can be in a columnar, grid-shaped or block-shaped plane arrangement form, the diameter of the high-pressure rotary spraying pile adopting the single-pipe method is phi 500-900 mm, the diameter of the high-pressure rotary spraying pile adopting the double-pipe method is phi 600-1300 mm, and the diameter of the high-pressure rotary spraying pile adopting the triple-pipe method is phi 700-1800 mm.
4. The composite foundation bearing structure for placing the precast pile in the high-pressure jet grouting pile according to claim 1, wherein: the multi-section precast piles are connected by flanges, welding or joint bar sulfur plaster in a cementing way.
5. The composite foundation bearing structure for placing the precast pile in the high-pressure jet grouting pile according to claim 1, wherein the estimation method of the characteristic value of the vertical bearing capacity of the single pile of the precast pile is as follows:
Ra1＝ατkul+βσk(Ap0+λpAp1)； (1)
in the formula, Ra1The characteristic value of the vertical bearing capacity of a single pile of the reinforced concrete precast pile, α the reduction coefficient of the unconfined shear strength of the high-pressure jet grouting pile cement soil consolidation body, α is 0.1-0.2, and taukIs the unconfined shear strength characteristic value tau of the high-pressure jet grouting pile cement soil consolidation body 28d agek500-2500 kPa; u is the perimeter of the pile body of the precast pile; l is a preformed pileThe length of the pile is β, the breaking coefficient of unconfined compressive strength of the cement-soil consolidation body of the high-pressure jet grouting pile is β, 0.4-0.6, and the sigma iskIs the unconfined compression strength characteristic value, sigma, of the cement-soil consolidation body 28d age of the high-pressure jet grouting pilek＝1500～12000kPa；Ap0Is the net area of the pile end of the precast pile, when the precast pile is a round pile,
Figure FDA0002393395250000011
when the precast pile is a square pile,
Figure FDA0002393395250000012
d、b、d1respectively the external diameter, side length and internal diameter of the precast pile, when the precast pile is a solid pile, d1＝0；λpIs the end soil blocking effect coefficient of the precast pile, lambdap＝0.7～0.8；Ap1In order to form the open area of the precast pile,
Figure FDA0002393395250000013
when the precast pile is a solid pile, d1＝0。
6. The composite foundation bearing structure of the high-pressure jet grouting pile with the precast pile built therein according to claim 1, wherein the estimation method of the characteristic value of the vertical bearing capacity of the single high-pressure jet grouting pile is to calculate the formula (2) and the formula (3), and to take the smaller of the two calculated values:
Ra2＝ξσkAP2； (2)
Figure FDA0002393395250000021
in the formula, Ra2The characteristic value of the vertical bearing capacity of a single high-pressure jet grouting pile, ξ the coefficient of the strength reduction of the high-pressure jet grouting pile body, when sigma iskWhen the pressure is 1500-5000 kPa, ξ is 0.5-0.4, when sigma iskWhen the pressure is 5000-8000 kPa, ξ is 0.4-0.3, when sigma isk8000-12000 kPa, ξ is 0.3-0.2, sigmakIs an unconfined cement soil consolidation body 28d age of the high-pressure jet grouting pileCharacteristic value of compressive strength, σk＝1500～12000kPa；Ap2For the effective cross-sectional area of the pile body of a single high-pressure jet grouting pile, for the high-pressure jet grouting pile with a built-in precast pile
Figure FDA0002393395250000022
For high-pressure jet grouting pile without precast pile embedded
Figure FDA0002393395250000023
d2The effective pile diameter of the high-pressure jet grouting pile is obtained; u. ofpIs the perimeter of the pile; n is the number of divided soil layers in the pile length range of the high-pressure jet grouting pile; q. q.ssiThe characteristic value of the lateral resistance of the i-th layer soil around the high-pressure jet grouting pile is obtained; lpiThe thickness of the i-th layer soil within the length range of the high-pressure rotary jet pile αpCoefficient of pile tip resistance exertion for high-pressure jet grouting pile, αp＝0.45～0.65；qpThe characteristic value of the bearing capacity of the foundation soil is obtained when the pile end soil of the high-pressure jet grouting pile is not corrected; a. thep0Is the net area of the pile end of the precast pile, when the precast pile is a round pile,
Figure FDA0002393395250000024
when the precast pile is a square pile,
Figure FDA0002393395250000025
d、b、d1respectively the external diameter, side length and internal diameter of the precast pile, when the precast pile is a solid pile, d1＝0；λpIs the end soil blocking effect coefficient of the precast pile, lambdap＝0.7～0.8；Ap1In order to form the open area of the precast pile,
Figure FDA0002393395250000026
when the precast pile is a solid pile, d1＝0。
7. The composite foundation bearing structure for placing the precast pile in the high-pressure jet grouting pile according to claim 1, wherein the composite foundation bearing capacity characteristic value estimation method comprises the following steps:
Figure FDA0002393395250000027
in the formula (f)spkThe characteristic value of the bearing capacity of the composite foundation is obtained; m is1、m2The area replacement rates of the reinforced concrete precast pile and the high-pressure jet grouting pile are respectively,
Figure FDA0002393395250000028
n1、n2the number of the reinforced concrete precast piles and the number of the high-pressure jet grouting piles under the calculation unit areas in the form of a single bearing platform, a raft foundation or a box foundation are respectively, and A is the calculation unit bottom area in the form of a single bearing platform, a raft foundation or a box foundation; lambda [ alpha ]1、λ2、λ3Respectively the bearing capacity of the reinforced concrete precast pile, the high-pressure jet grouting pile and the soil between the piles, namely lambda1＝λ2＝0.8～0.9，λ3＝0.85～0.95；fskThe characteristic value of the bearing capacity of the soil between the treated composite foundation piles is obtained; a. thep0Is the net area of the pile end of the precast pile, when the precast pile is a round pile,
Figure FDA0002393395250000031
when the precast pile is a square pile,
Figure FDA0002393395250000032
d、b、d1respectively the external diameter, side length and internal diameter of the precast pile, when the precast pile is a solid pile, d1＝0；λpIs the end soil blocking effect coefficient of the precast pile, lambdap＝0.7～0.8；Ap1In order to form the open area of the precast pile,
Figure FDA0002393395250000033
when the precast pile is a solid pile, d1＝0；Ap2For the effective cross-sectional area of the pile body of a single high-pressure jet grouting pile, for the high-pressure jet grouting pile with a built-in precast pile
Figure FDA0002393395250000034
For high-pressure jet grouting pile without precast pile embedded
Figure FDA0002393395250000035
d2The effective diameter of the high-pressure jet grouting pile.
CN202010122484.2A 2020-02-27 2020-02-27 Composite foundation bearing structure for placing precast pile in high-pressure jet grouting pile Withdrawn CN111321732A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112279618A (en) * 2020-11-12 2021-01-29 中冶成都勘察研究总院有限公司 Additive for high-pressure rotary spraying construction
CN112341135A (en) * 2020-11-12 2021-02-09 中冶成都勘察研究总院有限公司 Curing agent for high-pressure rotary spraying construction

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112279618A (en) * 2020-11-12 2021-01-29 中冶成都勘察研究总院有限公司 Additive for high-pressure rotary spraying construction
CN112341135A (en) * 2020-11-12 2021-02-09 中冶成都勘察研究总院有限公司 Curing agent for high-pressure rotary spraying construction

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Application publication date: 20200623