Construction method for pit-in-pit shallow area joint

Abstract

The application discloses a construction method for a pit-in-pit deep-shallow area joint, wherein the pit-in-pit comprises a shallow foundation pit and a deep foundation pit located at the bottom of the shallow foundation pit, and the construction method comprises the following steps: constructing a first supporting pile along the outer periphery of the shallow foundation pit and constructing a second supporting pile along the outer periphery of the deep foundation pit; excavating to the bottom elevation of the shallow foundation pit, and breaking the overfilling part of the second supporting pile; pouring the bottom plate of the shallow foundation pit, so that the bottom plate extends to the top of the second supporting pile and is connected with the second supporting pile to replace the corbel; excavating the deep foundation pit and constructing the basement structure; and constructing a trough cross-connection plate at the top of the trough, so that the trough cross-connection plate is connected with the basement structure inside and with the bottom plate outside. The method replaces the corbel at the top of the deep foundation pit with the bottom plate of the shallow foundation pit, saves the corbel material and the dismantling process, realizes the cooperative stress of the deep-shallow area structure, shortens the construction period and improves the structural integrity.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and in particular to a construction method for joints in shallow and deep areas of pits. Background Technology

[0002] During the construction of foundation pit projects, it is usually necessary to set up retaining piles along the perimeter of the foundation pit and set up capping beams on top of the retaining piles to improve the integrity of the retaining structure and to bear and transfer the loads during the foundation pit support process.

[0003] For pit-within-a-pit structures, since the deep foundation pit is located at the bottom of the shallow foundation pit, in addition to setting retaining piles along the perimeter of the shallow foundation pit, retaining piles are also required along the perimeter of the deep foundation pit. In traditional construction, a capping beam is typically installed on top of the retaining piles in the deep foundation pit. During the construction of the shallow foundation pit floor slab, the floor slab is connected to the capping beam to support the retaining piles. Subsequently, the deep foundation pit is excavated and the basement structure is constructed. After the basement structure is completed, the capping beam at the top of the deep foundation pit is removed, and the area created by the removal of the capping beam is re-poured with concrete.

[0004] When using the above construction method, the capping beam at the top of the deep foundation pit requires separate reinforcement binding, formwork erection, and concrete pouring. Subsequent removal of the capping beam and subsequent concrete pouring are also necessary, increasing the construction procedures, material, and labor inputs. Furthermore, the construction and removal of the capping beam will occupy construction space at the boundary between the deep and shallow foundation pits, hindering continuous construction at this junction. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a construction method for shallow and deep pit nodes. By replacing the top cap beam of the deep pit with a shallow pit bottom plate, the cap beam material is eliminated, the construction period is saved, and the construction efficiency is improved.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is a construction method for shallow and deep sections of a pit within a pit, wherein the pit within a pit includes a shallow foundation pit and a deep foundation pit located at the bottom of the shallow foundation pit, and the construction method includes the following steps: Step 1: Construct a ring of first support piles around the outer perimeter of the shallow foundation pit design location, and construct a ring of second support piles around the outer perimeter of the deep foundation pit design location. Step 2: Excavate the shallow foundation pit until the bottom design elevation of the shallow foundation pit is reached, and remove the portion of the second support pile located above the bottom design elevation of the shallow foundation pit; Step 3: Pour the bottom slab of the shallow foundation pit, so that the bottom slab extends to the top of the second support pile and connects with the second support pile, so that the bottom slab replaces the concrete cap beam at the top of the second support pile; Step 4: Excavate the deep foundation pit until the bottom of the deep foundation pit reaches the design elevation, and construct the basement structure within the deep foundation pit; Step 5: Construct a ring of trench bridging plates at the top of the deep foundation pit, so that the trench bridging plates are connected to the basement structure inside and the base slab outside.

[0007] A further improvement of the construction method of the present invention for the shallow-deep zone node of the pit is that, when performing step 2 above, the steel bars at the top of the second support pile are exposed, and when performing step 3 above, the steel bars of the bottom plate are tied first, and the steel bars of the bottom plate are connected with the steel bars at the top of the second support pile to form an integral whole, and then the bottom plate is poured.

[0008] A further improvement of the construction method of the present invention for the shallow and deep zone nodes of the pit is that, when performing step 3 above, a steel bar connector is pre-embedded on the end face of the bottom plate that is relatively close to the deep foundation pit, and when performing step 5 above, the steel bars of the trench bridging plate are first tied, and the steel bars of the trench bridging plate are connected to the steel bar connector.

[0009] A further improvement of the construction method for shallow and deep pit nodes of the present invention is that, when performing step 5 above, when the basement structure is constructed to the elevation of the bottom slab, the reinforcing bars of the basement structure are tied so that the reinforcing bars of the basement structure overlap with the reinforcing bars of the trench bridging plate, and finally the basement structure and the trench bridging plate are cast together.

[0010] A further improvement of the construction method of the present invention for the shallow and deep zone nodes of the pit is that, when performing step 3 above, a water-swellable sealing strip is pre-embedded along the entire length of the end face of the bottom plate that is relatively close to the deep foundation pit, and when performing step 5 above, the water-swellable sealing strip is sandwiched between the cross-connecting plate of the trench and the bottom plate.

[0011] A further improvement of the construction method of the present invention for the shallow and deep zone nodes of the pit is that, when performing step 4 above, as the deep foundation pit is excavated, multiple internal supports are constructed from top to bottom. When constructing the basement structure from bottom to top, whenever the basement structure approaches the internal support, a force transmission band is first set between the basement structure and the second support pile, and then the corresponding internal support is removed to achieve support replacement, until all the internal supports are removed.

[0012] Compared with the prior art, the advantages of the present invention are: 1. By replacing the top capping beam of the deep foundation pit with the bottom slab of the shallow foundation pit, the bottom slab can also serve as the capping beam during the construction phase to bear the horizontal force transmitted from the second support piles. After completion, it can be retained as a permanent structure, saving the cost of steel bars and concrete materials of the traditional capping beam, as well as the labor and machinery costs generated by the later demolition. It also avoids the interruption of the construction period and the generation of a large amount of construction waste caused by the demolition of the capping beam. 2. By connecting the basement structure internally to the foundation slab and the bottom slab externally through the cross-connection plate and casting them together, the shallow foundation pit bottom slab, the cross-connection plate and the deep foundation pit basement structure form an integrated load-bearing system, realizing the coordinated work of the shallow and deep areas of the structure. This avoids the problem of the shallow foundation pit bottom slab and the deep foundation pit support piles bearing the load independently in the traditional method, and improves the overall structure integrity. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram showing the connection between the deep foundation pit internal support and the shallow foundation pit bottom plate of the present invention.

[0015] Figure 2 This is a schematic diagram showing the connection between the deep foundation pit basement structure and the shallow foundation pit bottom slab of the present invention.

[0016] In the diagram: 1. Second support pile; 2. Base plate; 3. Internal support; 4. Rebar connector; 5. Water-swellable sealing strip; 6. Basement structure; 7. Trench cross-connector plate; 8. Trench; 9. Force transmission belt. Detailed Implementation

[0017] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0018] The construction method of the present invention for shallow-depth nodes in pits will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Please see Figures 1-2 As shown, a construction method for shallow and deep sections of a pit-within-a-pit joint is described, wherein the pit-within-a-pit includes a shallow foundation pit and a deep foundation pit located at the bottom of the shallow foundation pit. The construction method includes the following steps: Step 1: Construct a ring of first retaining piles around the outer perimeter of the shallow foundation pit at the designed location, and construct a ring of second retaining piles around the outer perimeter of the deep foundation pit at the designed location. Step 2: Excavate the shallow foundation pit until the bottom design elevation of the shallow foundation pit is reached, and remove the portion of the second support pile 1 located above the bottom design elevation of the shallow foundation pit; Step 3: Pour the bottom slab 2 of the shallow foundation pit, so that the bottom slab 2 extends to the top of the second support pile 1 and connects with the second support pile 1, so that the bottom slab 2 replaces the concrete cap beam at the top of the second support pile 1. Step 4: Excavate the deep foundation pit until the bottom of the deep foundation pit reaches the design elevation, and construct the basement structure 6 within the deep foundation pit; Step 5: Construct a ring of trench bridging plates 7 on the top of the trench 8 in the deep foundation pit, so that the trench bridging plates 7 are connected to the basement structure 6 inside and the bottom slab 2 outside.

[0020] Through the above steps, the bottom slab 2 of the shallow foundation pit is used to replace the capping beam at the top of the deep foundation pit and is directly connected to the top of the second support pile 1. During the construction phase, it also serves as the capping beam to bear the horizontal force transmitted from the second support pile 1. After completion, it is retained as a permanent structure, saving the steel reinforcement, concrete materials and subsequent demolition costs of the traditional capping beam. At the same time, the trench bridging plate 7 connects the basement structure 6 internally and the bottom slab 2 externally, so that the bottom slab 2 of the shallow foundation pit, the trench bridging plate 7 and the basement structure 6 of the deep foundation pit form an integrated force-bearing system, realizing the coordinated work of the deep and shallow areas of the structure and ensuring the safety of the foundation pit and the integrity of the structure.

[0021] Preferably, when performing step 2 above, the steel bars at the top of the second support pile 1 are exposed. When performing step 3 above, the steel bars of the base plate 2 are tied first, and the steel bars of the base plate 2 are connected with the steel bars at the top of the second support pile 1 to form an integral whole, and then the base plate 2 is poured.

[0022] By directly connecting the reinforcing bars of the base plate 2 with the top reinforcing bars of the second support pile 1 to form an integral whole, the base plate and the second support pile 1 are rigidly anchored, enabling the base plate 2 to directly bear and transmit the horizontal force on the second support pile 1, thereby improving the structural connection reliability and the stress performance of the reinforcing bars.

[0023] Specifically, when breaking the portion of the second support pile 1 located above the bottom design elevation of the shallow foundation pit, some of the reinforcing bars inside the second support pile 1 are retained for connection with the reinforcing bars of the bottom slab 2.

[0024] Preferably, when performing step 3 above, a steel bar connector 4 is pre-embedded on the end face of the base plate 2 that is relatively close to the deep foundation pit. When performing step 5 above, the steel bars of the trench bridging plate 7 are first tied, and the steel bars of the trench bridging plate 7 are connected to the steel bar connector 4.

[0025] By connecting the cross-connecting plate 7 and the bottom plate 2 with the pre-embedded steel bar connector 4, the steel bars of the two can be quickly connected without chiseling or planting steel bars. This avoids the structural damage caused by chiseling the side wall of the bottom plate 2 in the later stage in the traditional method, reduces wet work and construction procedures, and improves construction efficiency.

[0026] Specifically, the rebar connector 4 is connected to the end of a portion of the rebar in the base plate 2.

[0027] Specifically, when tying the reinforcing bars of the base slab 2, the reinforcing bars are densified in the area near the deep foundation pit.

[0028] By increasing the reinforcement density of the bottom plate 2 near the deep foundation pit area, the local stiffness and shear bearing capacity of the connection between the bottom plate 2 and the second support pile 1 are enhanced, effectively dispersing the concentrated force at the pile top, avoiding cracks in the connection area due to stress concentration, and improving the reliability of force transmission at the node.

[0029] Preferably, when performing step 5 above, when the basement structure 6 is constructed to the elevation of the base slab 2, the reinforcing bars of the basement structure 6 are tied so that the reinforcing bars of the basement structure 6 overlap with the reinforcing bars of the cross-connecting plate 7, and finally the basement structure 6 and the cross-connecting plate 7 are poured together.

[0030] By lapping the steel bars of the basement structure 6 with the steel bars of the cross-connecting plate 7 and casting them together, the cross-connecting plate 7 and the basement structure 6 form a rigid whole. There is no need to set construction joints or post-pouring strips, which avoids the cold joints and water seepage risks caused by staged pouring. At the same time, it ensures that the horizontal force is smoothly transferred to the basement structure 6 through the cross-connecting plate 7, which improves the structural integrity and waterproof reliability.

[0031] Specifically, before binding the reinforcing bars of the cross-connecting plate 7, the bottom plate 2 of the shallow foundation pit is roughened on several end faces that are relatively close to the deep foundation pit.

[0032] By roughening the end face of the base plate 2, the mechanical interlocking force and bonding area between the cross-connecting plate 7 and the base plate 2 are increased, so that the interface between the new and old concrete forms a strong chemical bond and physical lock, avoiding interface cracks caused by shrinkage differences, and improving the shear resistance and waterproof reliability of the joint.

[0033] Preferably, when performing step 3 above, a water-swellable sealing strip 5 is pre-embedded along the end face of the base plate 2 that is relatively close to the deep foundation pit. When performing step 5 above, the water-swellable sealing strip 5 is sandwiched between the trough cross-connecting plate 7 and the base plate 2.

[0034] By pre-embedding a water-swellable sealing strip 5 along the end face of the base plate 2, the strip expands in volume after contact with water to fill the joint between the cross-connecting plate 7 and the base plate 2, forming a reliable seal using the principle of water-stopping, effectively preventing groundwater from seeping in along the interface between the new and old concrete. At the same time, the strip maintains an elastic and compacted state after installation, which can compensate for the micro-cracks at the interface caused by temperature shrinkage, thus improving the long-term waterproof reliability of the joint.

[0035] Preferably, when performing step 4 above, as the deep foundation pit is excavated, multiple internal supports 3 are constructed from top to bottom. When constructing the basement structure 6 from bottom to top, whenever the basement structure 6 approaches an internal support 3, a force transmission band 9 is first set between the basement structure 6 and the second support pile 1, and then the corresponding internal support 3 is removed to achieve a replacement support, until all the internal supports 3 are removed.

[0036] By installing a force transmission belt 9 before removing the inner support 3, the horizontal force on the second support pile 1 is transmitted to the completed basement structure 6 via the force transmission belt 9. This ensures that the force path during the support replacement process is clear and the force transmission is reliable. It avoids the risk of support pile displacement or foundation pit instability caused by sudden changes in horizontal force during support removal, and ensures the safety of the foundation pit and the continuous construction of the basement structure 6 during the support removal stage.

[0037] Specifically, such as Figure 1 As shown: The uppermost inner support 3 is located at the elevation of the base plate 2. Step 5 above can only be performed after the uppermost inner support 3 is removed, and the construction of the trough cross-connector plate 7 can be carried out.

[0038] It should be noted that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A construction method for a shallow-deep section node in a pit-within-a-pit system, the pit-within-a-pit comprising a shallow foundation pit and a deep foundation pit located at the bottom of the shallow foundation pit, characterized in that, The construction method includes the following steps: Step 1: Construct a ring of first support piles around the outer perimeter of the shallow foundation pit design location, and construct a ring of second support piles around the outer perimeter of the deep foundation pit design location. Step 2: Excavate the shallow foundation pit until the bottom design elevation of the shallow foundation pit is reached, and remove the portion of the second support pile located above the bottom design elevation of the shallow foundation pit; Step 3: Pour the bottom slab of the shallow foundation pit, so that the bottom slab extends to the top of the second support pile and connects with the second support pile, so that the bottom slab replaces the concrete cap beam at the top of the second support pile; Step 4: Excavate the deep foundation pit until the bottom of the deep foundation pit reaches the design elevation, and construct the basement structure within the deep foundation pit; Step 5: Construct a ring of trench bridging plates at the top of the deep foundation pit, so that the trench bridging plates are connected to the basement structure inside and the base slab outside.

2. The construction method for shallow-depth nodes in a pit as described in claim 1, characterized in that, When performing step 2 above, the steel bars at the top of the second support pile are exposed. When performing step 3 above, the steel bars of the base plate are first tied, and the steel bars of the base plate are connected with the steel bars at the top of the second support pile to form a whole, and then the base plate is poured.

3. The construction method for shallow-depth nodes in a pit as described in claim 1, characterized in that, When performing step 3 above, a steel bar connector is pre-embedded on the end face of the bottom plate that is relatively close to the deep foundation pit. When performing step 5 above, the steel bars of the trench bridging plate are first tied, and the steel bars of the trench bridging plate are connected to the steel bar connector.

4. The construction method for shallow-depth nodes in a pit as described in claim 3, characterized in that, When performing step 5 above, when the basement structure is constructed to the elevation of the base slab, the reinforcing bars of the basement structure are tied so that the reinforcing bars of the basement structure overlap with the reinforcing bars of the cross-connecting plate. Finally, the basement structure and the cross-connecting plate are cast together.

5. The construction method for shallow-depth nodes in a pit as described in claim 1, characterized in that, When performing step 3 above, a water-swellable sealing strip is pre-embedded along the entire length of the end face of the base plate that is relatively close to the deep foundation pit. When performing step 5 above, the water-swellable sealing strip is sandwiched between the trough cross-connecting plate and the base plate.

6. The construction method for shallow-depth nodes in a pit as described in claim 1, characterized in that, When performing step 4 above, as the deep foundation pit is excavated, multiple internal supports are constructed from top to bottom. When constructing the basement structure from bottom to top, whenever the basement structure approaches an internal support, a force transmission band is first set between the basement structure and the second support pile, and then the corresponding internal support is removed to achieve a replacement support, until all the internal supports are removed.

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