Raft foundation existing building basement storey adding method

Abstract

The invention discloses a basement storey adding method for a raft foundation existing building. Belongs to the technical field of constructional engineering in civil engineering, and utilizes steel drum concrete piles which are inserted into floppy foundation soil after being rotated and stirred from drilling holes in the top surface of a raft foundation to support a building load, so that columns of an original building are lengthened, and the columns and a basement bottom plate form an integral new foundation. The foundation soil under the basement bottom plate and the steel drum concrete piles jointly bear the load of the upper building; according to the method, an original raft foundation is locally holed to form a soil outlet to provide conditions for excavation of a soil body below the original raft foundation, surrounding soil bodies are supported and blocked through the original raft foundation, an additionally-arranged force transmission plate belt and a foundation pit supporting and blocking structure, horizontal deformation of the excavated soil bodies is controlled, and therefore storey adding is conducted on the basement. According to the method, construction is convenient, and soil deformation and building deformation in the foundation underpinning and foundation pit excavation process can be strictly controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of building engineering in civil engineering, and relates to the technical field of building engineering in civil engineering; specifically, it relates to a method for increasing basement floors by reinforcing foundation soil of an existing building with a raft foundation and replacing the foundation with a reverse construction method. Background Art

[0002] With the continuous acceleration of urban construction and urbanization, the problems of over-saturation of urban population, traffic congestion and crowded building space have been greatly expanded, and the expansion of cities is often restricted by limited land resources; therefore, the development and utilization of urban underground space has become an inevitable way to solve the problems of urban development; orderly, reasonable, comprehensive and efficient development and utilization of urban underground space resources is one of the effective ways to expand infrastructure capacity, improve land utilization efficiency and save land resources; especially now that the number of private cars in cities has increased rapidly, the construction of underground parking lots has become one of the constraints on the healthy development of cities, especially the defects of existing buildings without facilities such as basements and underground parking lots in terms of use functions are becoming increasingly apparent. Therefore, the demand for the development of underground space in existing buildings is becoming increasingly prominent; in addition, the building density, population density and vehicle density of old urban areas in large and megacities are very large, but the buildings in old communities are built a long time ago, and most of them do not consider setting up underground parking lots, which has a serious contradiction with the increasing number of motor vehicles, resulting in parking difficulties, traffic jams, insufficient social public resources and even social contradictions in cities. Seriously affecting people's quality of life and work.

[0003] A Chinese patent (patent number: 201410690050.7) proposes a method of "supporting the underground increase of existing buildings by using a supporting structure and a supporting structure". On the outside of the independent foundation of the frame structure, that is, close to the outside of the outermost row of frame columns, a circular reinforced concrete underground continuous wall is constructed by a mud wall method. The bottom of the continuous wall is supported on a hard rock layer to reduce settlement; the wall acts as a supporting structure to retain soil and stop water during earthwork excavation; the patent proposes an underground increase method for an independent foundation of a frame structure, but does not solve the problem of underground increase of buildings with raft foundations. A Chinese patent (patent number: 201310390195.0) discloses a method of "supporting the underground increase of existing buildings by using the original pile foundation"; this method does not consider setting up a supporting structure for retaining soil and stopping water on the outside of the newly added basement, and does not use the supporting structure to support the upper structure. This method mainly considers the method of adding underground floors to existing buildings with end-bearing pile foundations; for friction piles, press piles or supplementary bored piles are used. Due to the space limitations of existing buildings, this method is difficult to construct. For soft soil foundations in East China, pile driving squeezes and disturbs the foundation soil, which easily causes deformation and affects the safety of existing buildings. This method does not solve the problem of adding underground floors to buildings with raft foundations. A Chinese patent (patent number: ZL200610045257.4) discloses a "patented plate foundation underpinning method", which uses part of the top plate and bottom plate of the proposed basement as underpinning components, plays the role of a temporary foundation, bears the upper load, and constructs the vertical components of the basement; this technology does not use pile foundations, which can reduce the underpinning cost, but only relies on the suspended soil columns around the underpinning plate to support the upper load, and is only applicable to working conditions with good foundation soil. When the soil quality is poor and the groundwater level is high, the use of this method may cause excessive structural deformation and even structural instability. Therefore, it is of great significance and application prospects to develop a technology for adding basements to existing buildings in areas with poor soil quality and high groundwater levels. A Chinese patent (patent number: 201110075492.7) discloses "a method for adding floors to the basement of an existing building with a frame structure and an independent foundation". It uses steel barrel concrete piles drilled from the top surface of the original independent foundation to support the original independent foundation and the upper load, and then extends the original frame column to form a new foundation with the basement floor. After the original independent foundation is cut off, a space is formed for the added basement. This technology can solve the problem of adding floors to the basement of a frame structure with an independent foundation, but it fails to solve the problem of adding floors to the basement of a frame structure with a pile foundation. Therefore, it is of great significance and application prospects to develop a technology for adding floors to the basement of an existing building with a raft foundation. Summary of the invention

[0004] In view of the above problems, the present invention aims to propose a method for adding a basement floor to an existing building with a raft foundation. The method is convenient to construct and can strictly control the settlement during the upper load transfer process.

[0005] The technical scheme of the present invention is: a method for adding a floor to a basement of an existing building with a raft foundation described in the present invention, the process vertically drills a hole from the top surface of the original raft foundation, uses a drill rod with a high-pressure rotary jet pile suspended in a large-diameter high-pressure rotary jet pile device to be inserted into the vertical drill hole to rotary stir the foundation soil under the original raft foundation, inserts a steel pipe into the foundation soil that is temporarily softened after rotary stirring, and then pours concrete into the steel pipe pile to form a steel barrel concrete pile foundation, and the steel barrel concrete pile supports the load of the upper building; then a hole is partially opened in the original raft foundation to provide conditions for excavating the foundation soil under the original raft foundation, and the original raft foundation and the additional force transmission plate belt and retaining structure are used to support the surrounding foundation soil; the space formed after the foundation soil under the original raft foundation is excavated is the added basement.

[0006] Further, the operation steps are as follows:

[0007] Step 1: Construct the retaining structure of the foundation pit around the existing building where the additional floors are to be added;

[0008] Step 2: Excavate the foundation soil from the indoor floor until the top surface of the original raft foundation;

[0009] Step 3: Drill vertical holes on the top surface of the original raft foundation, insert the drill rod of the large-diameter high-pressure jet-jet pile equipment into the vertical hole to the designed depth, and spray high-pressure cement slurry from the nozzle at the end of the drill rod to perform 360-degree rotation and stirring of the foundation soil under the original raft from bottom to top;

[0010] Step 4: Press the steel pipe from the vertical drilled hole of the original raft foundation into the temporarily softened foundation soil after rotation and stirring to the designed depth;

[0011] Step 5: Pour concrete into the steel pipe and pour the drilled holes at the same time to form a whole with the original raft foundation;

[0012] Step 6: Drill well point drainage pipes inside the retaining structure of the foundation pit to conduct drainage;

[0013] Step 7: Use the additional force-transmitting plate belt to connect the original raft foundation and the retaining structure of the foundation pit into a whole to jointly support the surrounding soil;

[0014] Step 8: partially open a hole on the original raft foundation to form an excavation opening;

[0015] Step 9: After 28 days of curing, when the strength of the foundation soil after rotary mixing reaches the design requirements again, excavate the soil from the excavation port downward to the elevation of the new basement floor; the load of the existing building is supported by the newly added steel barrel concrete piles and the reinforced foundation soil;

[0016] Step 10: Smooth the excavated base with concrete, drill oblique holes on the original raft foundation, extend and cast the frame columns on the original raft foundation to the bottom of the foundation pit to form extended frame columns, and cast the bottom plate to form a new raft;

[0017] Step 11: Cut off the steel barrel concrete piles on the new basement floor;

[0018] Step 12: Construction of new basement side walls;

[0019] Step 13: Pour concrete at the opening of the original raft foundation, which together with the original raft and the added force transfer belt forms the top slab of the new basement.

[0020] Furthermore, in step one, the retaining structure is composed of a steel-cement-soil mixing wall structure in which a row of high-pressure jet-jet piles are inserted with H-shaped steel.

[0021] Furthermore, in step 2, the large-diameter high-pressure jet grouting equipment is placed on both sides of two adjacent vertical boreholes, and the construction work is carried out by high-pressure jet grouting after the drill rod passes through the vertical boreholes;

[0022] The high-pressure cement slurry is sprayed from the nozzle at the end of the drill rod to form a solid high-pressure rotary jet pile, that is, the completed high-pressure rotary jet pile.

[0023] Furthermore, in step 2, the high-pressure cement slurry is sprayed through the drill rod to form a steel barrel concrete pile in the high-pressure jet jet pile.

[0024] Furthermore, in step seven, the force transfer plate belt is respectively arranged at both ends of the original raft foundation, and the other end is connected to the retaining structure; longitudinal steel bars are arranged in the force transfer plate belt, which are implanted in the original raft foundation to form a whole.

[0025] Furthermore, in step eight, the excavation opening is opened at the center of the original raft foundation.

[0026] Furthermore, in step ten, frame columns and frame beams are arranged on the original raft foundation to form a cross, and extended frame columns are formed by drilling inclined holes;

[0027] Furthermore, in step eleven, the frame column penetrates the basement floor.

[0028] Furthermore, in step twelve, the basement side walls are respectively connected to both ends of the original raft foundation and the basement floor.

[0029] The beneficial effect of the present invention is that after the construction of the present invention is completed, the load of the upper building is transferred to the basement floor and the pile foundation under the floor through the extended frame column, and is borne by the reinforced foundation soil. The deformation of the second floor caused by the construction of the basement floor can be effectively controlled, reducing the impact on the original building structure, and the normal use of the floors above the second floor of the original building will not be affected during the construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the column grid diagram of the existing building of the present invention;

[0031] Figure 2 It is a plan layout diagram of the foundation pit retaining structure around the existing building of the frame structure of the present invention;

[0032] Figure 3 It is a Ⅰ-Ⅰ cross-sectional view of an existing building before adding an underground floor of the present invention;

[0033] Figure 4 It is a sectional view of the completed foundation pit retaining structure of the present invention taken along line Ⅰ-Ⅰ;

[0034] Figure 5 It is a sectional view taken along line Ⅰ-Ⅰ after the foundation soil of the present invention is partially excavated to the top surface of the original raft foundation;

[0035] Figure 6 It is a Ⅰ-Ⅰ cross-sectional view of the original raft foundation after vertical drilling of the present invention;

[0036] Figure 7 It is a Ⅰ-Ⅰ cross-sectional view of the drill rod of the present invention inserted into the drill hole to reinforce the foundation soil under the original raft foundation;

[0037] Figure 8 It is a cross-sectional view of the original raft foundation of the present invention after the foundation soil is stirred;

[0038] Fig. 9 It is a sectional view taken along line Ⅰ-Ⅰ of the foundation soil after the steel pipe of the present invention is inserted into and stirred;

[0039] Fig.10 This is a cross-sectional view taken along line Ⅰ-Ⅰ after the foundation soil under the raft foundation at each frame column of the present invention is reinforced and a steel pipe is inserted;

[0040] Fig.11 It is a sectional view taken along line Ⅰ-Ⅰ after the soil opening of the original raft foundation of the present invention is opened;

[0041] Fig.12 This is a cross-sectional view taken along line Ⅰ-Ⅰ after the invention adds a force transmission plate belt and implants the longitudinal reinforcement in the force transmission plate belt into the raft slab to form an integral body;

[0042] Fig.13 This is a Ⅰ-Ⅰ cross-sectional view of the present invention after excavation downward from the excavation opening to the elevation of the bottom surface of the newly added basement;

[0043] Fig.14 It is a Ⅰ-Ⅰ cross-sectional view after the original frame column is extended and the newly added basement bottom slab is poured after the inclined hole is drilled on the top surface of the original raft foundation of the present invention;

[0044] Fig.15 This is a sectional view of the present invention after the steel barrel concrete piles on the original raft foundation are removed;

[0045] Fig.16 It is a Ⅰ-Ⅰ cross-sectional view after the basement side wall, part of the top plate and the original raft foundation are cast;

[0046] Fig.17 It is a cross-sectional view taken along line Ⅰ-Ⅰ after the foundation soil of the present invention is backfilled;

[0047] In the figure: 1 is a frame column, 2 is a frame beam, 3 is the original raft foundation, 4 is foundation soil, 5 is a retaining structure, 51 is an H-shaped steel, 52 is a jet grouting pile, 6 is a vertical borehole, 7 is a drill rod, 8 is a large-diameter high-pressure jet grouting pile equipment, 9 is a high-pressure jet grouting pile under construction, 10 is a completed high-pressure jet grouting pile, 11 is a steel barrel concrete pile, 12 is an excavation port, 13 is an extended frame column, 14 is a basement floor, 15 is a basement side wall, and 16 is a force transfer plate belt. DETAILED DESCRIPTION

[0048] The specific technical scheme of the present invention is further described in detail below with reference to specific examples.

[0049] As shown in the figure, a method for adding a floor to a basement of an existing building on a raft foundation according to the present invention comprises the following steps: vertically drilling a hole 6 from the top surface of an original raft foundation 3, inserting a drill rod 7 suspended in a large-diameter high-pressure jetting pile device 8 into the vertical drill hole 6 to perform rotary stirring on the foundation soil 4 under the original raft foundation 3, inserting a steel pipe into the foundation soil 4 temporarily softened after rotary stirring, and then pouring concrete into the steel pipe pile to form a steel barrel concrete pile foundation 11, which supports the load of the upper building; then, a hole is partially opened in the original raft foundation 3 to provide conditions for excavating the foundation soil 4 under the original raft foundation 3, and the original raft foundation 3 and the additional force transmission plate belt 16 and the retaining structure 5 are used to support the surrounding foundation soil 4; the space formed after the foundation soil 4 under the original raft foundation 3 is excavated is the additional basement; the specific steps are as follows:

[0050] (1) Construct a retaining structure 5 of the foundation pit around the existing building where the underground floor is to be added. The retaining structure 5 is composed of a row of high-pressure jet grouting piles 51 with H-shaped steel 52 inserted therein;

[0051] (2) Excavate the foundation soil 4 from the indoor floor to the top surface of the original raft foundation 3;

[0052] (3) Drill a hole 6 vertically on the top surface of the original raft foundation 3, and insert the drill rod 7 of the high-pressure jet grouting pile into the designed depth through the vertical hole 6. Figure 7 It is a high pressure jet grouting pile 9 under construction. Figure 8 The high pressure jet grouting pile 10 is completed; and the foundation soil 4 under the raft is jetted and mixed;

[0053] (4) Insert the steel pipe through the vertical drill hole 6 of the original raft foundation 3 into the foundation soil 4 that has been temporarily softened after rotation and stirring to the designed depth;

[0054] (5) Pour concrete into the steel pipe and pour the drilled holes at the same time to form a whole with the original raft foundation 3;

[0055] (6) The original raft foundation 3 and the retaining structure 5 of the foundation pit are connected as a whole by using an additional force transmission plate belt 16 to jointly support the surrounding soil;

[0056] (7) partially opening a hole on the original raft foundation 3 to form an excavation opening 12;

[0057] (8) After 28 days of curing, when the strength of the foundation soil 4 after rotary mixing reaches the design requirements again, the soil is excavated downward from the excavation opening 12 to the elevation of the newly added basement floor 14; the load of the existing building is supported by the newly added steel barrel concrete piles 11 and the reinforced foundation soil 4;

[0058] (9) The excavated base is smoothed with concrete, oblique holes are drilled on the original raft foundation 3, the frame column 1 on the original raft foundation 3 is extended and cast to the bottom of the foundation pit to form an extended frame column 13, and the bottom plate is cast to form a new raft foundation;

[0059] (10) Remove the steel barrel concrete piles 11 on the newly added basement floor 14;

[0060] (11) Construction of 15 new basement side walls;

[0061] (12) Concrete is poured at the excavation opening 11 at the opening of the original raft foundation 3, and together with the original raft foundation 3 and the additional force transfer plate belt 16, a new basement top plate is formed.

[0062] After the construction of this method is completed, the upper structure load is transferred to the steel barrel concrete piles 11 under the newly added basement floor 14 and the reinforced foundation soil 4 through the extended frame columns 13, and is jointly borne by the steel barrel concrete piles 11 under the basement floor 14 and the reinforced foundation soil 4. The deformation of the second floor caused by the basement floor addition construction can be effectively controlled, reducing the impact on the original building, and the normal use of the second floor and above of the original structure will not be affected during the construction.

Claims

1. A method for adding a basement floor to an existing building with a raft foundation, characterized in that: The process comprises the following steps: vertically drilling a hole (6) from the top surface of the original raft foundation (3), inserting a drill rod (7) suspended from a large-diameter high-pressure jetting pile device (8) into the vertically drilled hole (6) to perform rotary stirring on the foundation soil (4) below the original raft foundation (3), inserting a steel pipe into the foundation soil (4) temporarily softened after the rotary stirring, and then pouring concrete into the steel pipe pile to form a steel barrel concrete pile foundation (11), wherein the steel barrel concrete pile (11) supports the load of the upper building; then, a hole is partially opened in the original raft foundation (3) to provide conditions for excavating the foundation soil (4) below the original raft foundation (3), and the original raft foundation (3) and the additional force transmission plate belt (16) and the retaining structure (5) are used to support the surrounding foundation soil (4); the space formed after the foundation soil (4) below the original raft foundation (3) is excavated is the additional basement.

2. The method for adding a basement floor to an existing building with a raft foundation according to claim 1, characterized in that: The operation steps are as follows: Step 1: construct the retaining structure (5) of the foundation pit around the existing building to be added to; Step 2: excavating foundation soil (4) from the indoor floor until the top surface of the original raft foundation (3); Step 3: Drill a vertical hole (6) on the top surface of the original raft foundation (3), then insert the drill rod (7) of the large-diameter high-pressure jet-jet pile equipment (8) into the vertical hole (6) to the designed depth, and spray high-pressure cement slurry from the nozzle at the end of the drill rod (7) to perform 360-degree rotation and stirring of the foundation soil (4) under the original raft from bottom to top; Step 4: Press the steel pipe through the vertical drill hole (6) of the original raft foundation (3) into the foundation soil (4) that has been temporarily softened after rotation and stirring to the designed depth; Step 5: Pour concrete into the steel pipe and pour the drilled holes at the same time to form a whole with the original raft slab; Step 6: Drill well-point drainage pipes inside the retaining structure (5) of the foundation pit to conduct drainage; Step 7: Using the additional force transmission plate belt (16) to connect the original raft foundation (3) and the retaining structure (5) of the foundation pit into a whole, so as to jointly support the surrounding soil; Step 8: partially opening a hole on the original raft foundation (3) to form an excavation opening (12); Step 9: After 28 days of curing, when the strength of the foundation soil (4) after rotary mixing reaches the design requirements again, the soil is excavated downward from the excavation opening (12) to the elevation of the newly added basement floor (14); the load of the existing building is supported by the newly added steel barrel concrete piles (11) and the reinforced foundation soil (4); Step 10: The excavated base is smoothed with concrete, oblique holes are drilled on the original raft foundation (3), the frame columns (1) on the original raft foundation (3) are extended and poured to the bottom of the foundation pit to form extended frame columns (13), and the bottom plate is poured to form a new raft; Step 11: Cut off the steel barrel concrete piles (11) on the newly added basement floor (14); Step 12: Construction of the new basement side wall (15); Step 13: Concrete is poured at the opening of the original raft foundation (3), and the original raft foundation (3) and the added force transfer plate belt (16) together form the newly added basement top plate.

3. The method for adding a floor to a basement of an existing building with a raft foundation according to claim 2, characterized in that: In step 1, the retaining structure (5) is composed of a steel-cement-soil mixing wall structure in which a row of high-pressure jet-jet piles (52) are inserted with H-shaped steel (51).

4. The method for adding a basement floor to an existing building with a raft foundation according to claim 2, characterized in that: In step 2, the large-diameter high-pressure jet grouting pile equipment (8) is placed on both sides of two adjacent vertical boreholes (6), and after the drill rod (7) passes through the vertical boreholes (6), the high-pressure jet grouting pile is used for construction work; After the high-pressure cement slurry is sprayed from the nozzle at the end of the drill rod (7), a solid high-pressure rotary jet pile (10) is formed, which is the completed high-pressure rotary jet pile.

5. The method for adding a basement floor to an existing building with a raft foundation according to claim 2, characterized in that: In step 2, high-pressure cement slurry is sprayed through the drill rod (7) to form a steel barrel concrete pile (11) in the high-pressure jet-jet pile.

6. The method for adding a basement floor to an existing building with a raft foundation according to claim 2, characterized in that: In step seven, the force transmission plate belt (16) is respectively placed at both ends of the original raft foundation (3), and the other end is connected to the supporting structure (5); Longitudinal steel bars are arranged in the force transmission plate belt (16) and are embedded in the original raft foundation (3) to form a whole.

7. The method for adding a floor to a basement of an existing building with a raft foundation according to claim 2, characterized in that: In step eight, the excavation opening (12) is opened at the center of the original raft foundation (3).

8. The method for adding a basement floor to an existing building with a raft foundation according to claim 2, characterized in that: In step ten, frame columns (1) and frame beams (2) that cross each other are placed on the original raft foundation (3), and extended frame columns (13) are formed by drilling inclined holes.

9. The method for adding a basement floor to an existing building with a raft foundation according to claim 2, characterized in that: In step eleven, the frame column (13) penetrates the basement floor (14).

10. The method for adding a floor to a basement of an existing building with a raft foundation according to claim 2, characterized in that: In step twelve, the basement side walls (15) are respectively connected to the two ends of the original raft foundation (3) and the basement floor (14).

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