Method and device for removing temporary support of deep foundation pit

Abstract

The application provides a deep foundation pit temporary support removal method and device, S1, during construction, temporary lattice columns are used as the vertical column structure of temporary support; S2, during pouring of the temporary support, pipes along the horizontal width direction are pre-buried to form pre-buried holes; S3, during cutting of the temporary support, a rope saw is inserted into the pre-buried holes to cut; S4, the cut concrete blocks are crushed and transported out of the foundation pit; S5, the temporary lattice columns are removed; the temporary support in the deep foundation pit is removed through the above steps. The cut concrete blocks are crushed by a crushing device in a resonance mode; the temporary support at the connecting position is removed by a portable crushing device mainly in a resonance mode. The scheme of removing the temporary support in one piece by the rope saw improves construction efficiency and reduces construction difficulty. The pre-buried hole structure is convenient for the rope saw to be inserted, and greatly reduces construction difficulty.

Description

Technical Field

[0001] This invention relates to the field of construction technology for large-scale underground engineering, and in particular to a method and apparatus for dismantling temporary supports in deep foundation pits. Background Technology

[0002] A single independent foundation pit in a large underground project involved over 200,000 cubic meters of earthwork. The pit was 420 meters long, approximately 14.9-17.3 meters wide, and 30-50 meters deep. During construction, a horizontal temporary support structure was installed, with lattice beams as the support columns. After the permanent support was completed, the temporary support structure needed to be dismantled. Due to the confined construction environment of large underground projects, especially those near urban commercial areas such as shopping malls and transportation hubs, large construction equipment was difficult to access, leading to high construction difficulty and significant safety hazards. The interweaving and interference between permanent and temporary supports further increased the difficulty of dismantling. Existing technology employs a support replacement method, such as the method described in CN105756067A for replacing horizontal temporary supports in deep foundation pits. However, this method is particularly cumbersome, further reducing construction efficiency. Since transport channels are usually located at the bottom of the pit, dismantling must proceed from bottom to top. When the foundation pit is very deep, the subsequent removal of the upper horizontal temporary supports becomes more difficult, increasing safety risks. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method and device for dismantling temporary supports in deep foundation pits, which can quickly and safely dismantle the temporary support structure without the need to build a full-span scaffold, thereby improving construction efficiency.

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is: a method for dismantling temporary supports in deep foundation pits includes the following steps:

[0005] S1. During construction, temporary lattice columns are used as temporary support columns.

[0006] S2. When pouring temporary supports, pre-embed pipes along the horizontal width direction to form pre-embedded holes;

[0007] S3. When cutting temporary supports, insert a wire saw through the pre-embedded hole to make the cut;

[0008] S4. After breaking up the cut concrete blocks, transport them out of the foundation pit;

[0009] S5. Remove the temporary lattice columns;

[0010] Remove the temporary supports inside the deep foundation pit by following the steps above.

[0011] In the preferred embodiment, dismantling is carried out from the top layer to the bottom layer. During the dismantling process, temporary supports are used to protect the panels and prevent them from being impacted.

[0012] In the preferred embodiment, the cut concrete blocks are crushed using a crushing device in a resonant manner;

[0013] The temporary supports at the connection points were dismantled using portable breaking devices, primarily through resonance.

[0014] In a preferred embodiment, the temporary support is set to a specific natural frequency, and the natural frequency of the temporary support differs from that of the permanent support by at least 3 Hz.

[0015] In a preferred embodiment, the step of detecting the natural frequency of the temporary support is also included.

[0016] In the preferred embodiment, the concrete composition of the temporary support is as follows (by weight): 500-600 parts cement, 160-180 parts water, 600-650 parts sand, 850-950 parts gravel, 140-160 parts fly ash, 5-10 parts silica fume, 2-5 parts polycarboxylate superplasticizer, 5-10 parts phosphogypsum, and 0.01-0.1 parts EEA plastic expansion agent.

[0017] In the preferred embodiment, the cement composition by weight is 95-98% silicate cement and the remainder is aluminate cement.

[0018] In the preferred embodiment, the stones are stones with a particle size of less than 5mm.

[0019] In a preferred embodiment, the crushing device includes an impact beam without grooves or through holes. A limiting block is provided at the bottom of the impact beam near the middle position. The impact beam is supported on a support head, and the support head is restricted in its front-to-back position by the limiting block.

[0020] The support head is fixed to the vehicle body, and a flexible pad is provided between the vehicle body and the impact beam. One end of the impact beam is equipped with a hydraulic vibration motor, and the other end is equipped with an impact hammer.

[0021] An additional weight is also provided on the impact hammer.

[0022] In the preferred embodiment, the impact beam passes through a hole in the impact hammer, and a wedge is provided in the hole to wed the impact beam and the impact hammer tightly.

[0023] A support cylinder is installed between the vehicle body and the impact beam.

[0024] This invention provides a method and apparatus for dismantling temporary supports in deep foundation pits, which has the following advantages compared with the prior art:

[0025] 1. The method of using a wire saw to completely dismantle the temporary support improves construction efficiency and reduces construction difficulty. The pre-embedded hole structure facilitates the insertion of the wire saw, significantly reducing construction difficulty.

[0026] 2. The temporary supports adopted a scheme of breaking them up on-site and then transporting them, which facilitates transportation in the narrow underground space and enables dismantling from top to bottom, saving time and cost in setting up full-span scaffolding.

[0027] 3. A resonance method was used to break up the temporary support concrete blocks, improving the breaking efficiency. Furthermore, by adjusting the concrete composition, the natural frequencies of the temporary support concrete blocks were made different from those of the permanent support concrete, thus avoiding damage to the permanent support concrete during dismantling.

[0028] 4. The concrete components of the temporary supports utilize the long hydration time of phosphogypsum to allow the components within the temporary supports to accumulate internal stress due to continuous hydration and expansion, which facilitates vibration transmission, adjusts the elastic modulus of the concrete, and further improves the crushing effect. Attached Figure Description

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0030] Figure 1 This is a schematic elevation view of the foundation pit structure of the present invention.

[0031] Figure 2 This is a flowchart of the present invention.

[0032] Figure 3 This is a schematic diagram of the crushing device in this invention.

[0033] Figure 4 This is a schematic diagram of the portable crushing device of the present invention.

[0034] In the diagram: 1. Permanent support; 2. Foundation pit; 3. Wire saw device; 4. Panel; 5. Embedded hole; 6. Temporary support; 7. Temporary lattice column; 8. Crushing device; 81. Impact hammer; 82. Wedge; 83. Impact beam; 84. Support cylinder; 85. Limiting block; 86. Support head; 87. Hydraulic pump station; 88. Vehicle body; 89. Hydraulic vibration motor; 9. Portable crushing device; 10. Additional weight; 11. Flexible pad. Detailed Implementation

[0035] like Figure 1 , 2 In this context, the removal of temporary supports for deep foundation pits includes the following steps:

[0036] S1. During construction, temporary lattice columns 7 are used as the column structure for temporary support 6;

[0037] S2. When pouring the temporary support 6, a pipe is pre-embedded along the horizontal width direction to form a pre-embedded hole 5; preferably, a PVC pipe is pre-embedded to form the pre-embedded hole 5, and the pre-embedded hole 5 is located at the top of the horizontally arranged temporary support 6.

[0038] S3. When cutting the temporary support 6, insert the wire saw through the pre-embedded hole 5 to make the cut;

[0039] Preferably, for locations where it is not suitable to install the wire saw device 3, a portable crushing device 9 is used to crush and demolish the structure in a resonant manner.

[0040] S4. After breaking up the cut concrete blocks, transport them out of the foundation pit;

[0041] S5. Remove temporary lattice columns 7;

[0042] Remove the temporary supports inside the deep foundation pit by following the steps above.

[0043] In the preferred embodiment, during dismantling, the dismantling is carried out from the upper layer to the lower layer. During the dismantling process, the temporary support 6 is supported by a temporary bracket, and some passable positions are supported by a small excavator to avoid impact on the panel 4.

[0044] Preferred solutions include Figure 3 In the process, the cut concrete blocks are crushed using a resonant crushing device 8;

[0045] The temporary support 6 at the connection point is removed primarily using a portable crushing device 9 via resonance. When the portable crushing device 9 uses a shovel-shaped or conical tool head, impact crushing is also employed. Through these steps, the temporary support 6 is removed safely and efficiently. Figure 4 In this portable crushing device 9, an adjustable-frequency vibrating rod is used as the main working mechanism. The vibrating rod is driven by hydraulic or electric power to vibrate at an adjustable frequency, transmitting the vibration to the temporary support 6. Preferably, the head tool of the vibrating rod of the portable crushing device 9 has a replaceable structure, with various head tools such as shovel type, cone type, round type and rectangular type available for switching.

[0046] In a preferred embodiment, the temporary support 6 is set to a specific natural frequency, which differs from the natural frequency of the permanent support 1 by at least 3 Hz. In this example, the preferred setting for the temporary support 6 is 35 Hz to 42 Hz. Preliminary analysis suggests that the change in natural frequency is related to the change in elastic modulus caused by component adjustment, while the natural frequency of the permanent support 1 is between 45 Hz and 52 Hz. This structure avoids resonance damage to the concrete of the permanent support 1.

[0047] In a preferred embodiment, the method further includes a step of detecting the natural frequencies of the temporary support 6. Preferably, a vibration sensor is used to detect the natural frequencies of the temporary support 6. The temporary support 6 is excited by striking it with a rubber hammer, and the vibration data is collected by a vibration sensor attached to the concrete surface. The waveforms of each order are expanded using Fourier transform to obtain the natural frequencies of the temporary support 6.

[0048] In the preferred embodiment, the concrete composition of the temporary support 6 is as follows (by weight): 500-600 parts cement, 160-180 parts water, 600-650 parts sand, 850-950 parts gravel, 140-160 parts fly ash, 5-10 parts silica fume, 2-5 parts polycarboxylate superplasticizer, 5-10 parts phosphogypsum, and 0.01-0.1 parts EEA plastic expansion agent.

[0049] Preferably, the concrete composition consists of 550 parts cement, 170 parts water, 650 parts sand, 900 parts aggregate, 150 parts fly ash, 7 parts silica fume, 4 parts polycarboxylate superplasticizer, 10 parts phosphogypsum, and 0.05 parts EEA plastic expansion agent. The concrete uses a low water-cement ratio to ensure the strength of the subsequent temporary support 6. However, because the hydration time of phosphogypsum is long, requiring 1-3 years (roughly the same time as maintaining the temporary support 6), the continuously hydrating phosphogypsum will continue to expand, making the temporary support 6 more susceptible to breakage through resonance.

[0050] In the preferred embodiment, the cement composition by weight is 95-98% silicate cement and the remainder is aluminate cement. This design allows the sulfate ions in phosphogypsum to hydrate with alumina over a period of 1-3 years, forming ettringite and causing expansion. This leads to the accumulation of internal stress within the temporary support 6, a change in the elastic modulus, making it more conducive to vibration transmission and more susceptible to resonant fracture.

[0051] In the preferred embodiment, the pebbles are smaller than 5mm in diameter. This design ensures a more uniform material for the temporary support 6 and maintains a consistent resonant frequency.

[0052] Preferred solutions include Figure 3 In the middle, the crushing device 8 includes an impact beam 83. The impact beam 83 has no grooves or through holes. A limiting block 85 is provided at the bottom of the impact beam 83 near the middle position. The impact beam 83 is supported on the support head 86. The support head 86 is restricted in its front and rear position by the limiting block 85.

[0053] The support head 86 is fixed on the top of the vehicle body 88. A flexible pad 11 is also provided between the top of the vehicle body 88 and the impact beam 83. One end of the impact beam 83 is provided with a hydraulic vibration motor 89, and the other end is provided with an impact hammer 81.

[0054] An additional weight 10 is also provided on the impact hammer 81. With this structure, the impact hammer 81 is placed on the surface of the temporary support 6 that needs to be broken. The hydraulic vibration motor 89 is started to vibrate at the natural frequency of the temporary support 6, causing the temporary support 6 to break quickly. The broken concrete blocks are then transported out of the pit 2 using a small excavator or small transport vehicle combined with vertical excavation equipment. During operation, it is necessary to ensure that the impact hammer 81 is in full contact with the temporary support 6; otherwise, the impact beam 83 can easily be damaged.

[0055] Preferred solutions include Figure 3 In the middle, the impact beam 83 passes through the hole on the impact hammer 81, and a wedge 82 is provided in the hole to wedge the impact beam 83 and the impact hammer 81 tightly; this structure makes the connection between the impact hammer 81 and the impact beam 83 reliable.

[0056] A support cylinder 84 is provided between the vehicle body 88 and the impact beam 83. This structure facilitates the adjustment of the pitch angle of the impact beam 83. In a preferred embodiment, the support cylinder 84 is loosely coupled, meaning that the gap between the support cylinder 84 and the connection point between it and the vehicle body 88 and the impact beam 83 is greater than the amplitude of the impact beam 83 at that location. This structure prevents damage to the support cylinder 84.

[0057] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The embodiments and features described in these embodiments can be arbitrarily combined without conflict. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for removing temporary supports in deep foundation pits, characterized in that: Includes the following steps: S1. During construction, temporary lattice columns (7) are used as the column structure for temporary support (6); S2. When pouring the temporary support (6), a pipe is pre-embedded along the horizontal width direction to form a pre-embedded hole (5). S3. When cutting the temporary support (6), insert the wire saw through the pre-embedded hole (5) to cut; The temporary support (6) at the connection point was dismantled using a portable crushing device (9) in a resonant manner; The temporary support (6) is set to a specific natural frequency, and the natural frequency of the temporary support (6) differs from the natural frequency of the permanent support (1) by more than 3 Hz. The concrete composition of the temporary support (6) is as follows (by weight): 500-600 parts cement, 160-180 parts water, 600-650 parts sand, 850-950 parts gravel, 140-160 parts fly ash, 5-10 parts silica fume, 2-5 parts polycarboxylate superplasticizer, 5-10 parts phosphogypsum, and 0.01-0.1 parts EEA plastic expansion agent. S4. After breaking up the cut concrete blocks, transport them out of the foundation pit; S5. Remove the temporary lattice column (7); Remove the temporary supports inside the deep foundation pit by following the steps above.

2. The method for removing temporary supports in a deep foundation pit according to claim 1, characterized in that: During dismantling, the dismantling is carried out from the top layer to the bottom layer. During the dismantling process, the temporary support (6) is supported by a temporary bracket to avoid impact on the panel (4).

3. The method for removing temporary supports in a deep foundation pit according to claim 1, characterized in that: The cut concrete blocks are crushed using a crushing device (8) in a resonant manner.

4. The method for removing temporary supports in a deep foundation pit according to claim 1, characterized in that: It also includes the step of detecting the inherent frequency of the temporary support (6).

5. The method for removing temporary supports in a deep foundation pit according to claim 1, characterized in that: The cement components of the temporary support (6) by weight are 95-98% silicate cement and the remainder is aluminate cement.

6. The method for removing temporary supports in a deep foundation pit according to claim 1, characterized in that: The pebbles are those with a particle size of less than 5mm.

7. The method for removing temporary supports in a deep foundation pit according to claim 3, characterized in that: The crushing device (8) includes an impact beam (83), which has no grooves or through holes. A limiting block (85) is provided at the bottom of the impact beam (83) near the middle position. The impact beam (83) is supported on a support head (86), and the support head (86) is restricted in its front and rear positions by the limiting block (85). The support head (86) is fixed on the vehicle body (88). A flexible pad (11) is provided between the vehicle body (88) and the impact beam (83). One end of the impact beam (83) is provided with a hydraulic vibration motor (89), and the other end is provided with an impact hammer (81). An additional weight (10) is also provided on the impact hammer (81).

8. The method for removing temporary supports in a deep foundation pit according to claim 7, characterized in that: The impact beam (83) passes through a hole in the impact hammer (81), and a wedge (82) is provided in the hole to wed the impact beam (83) and the impact hammer (81) tightly. A support cylinder (84) is provided between the vehicle body (88) and the impact beam (83).

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