A method for excavating a shallow foundation pit by grouting and reinforcing a surrounding support in a pebble stratum

Abstract

This invention provides a method for grouting reinforcement and support of shallow foundation pits in pebble strata, comprising the following steps: determining the excavation area to form a shallow foundation pit excavation zone; sequentially inserting multiple steel pipes arranged in a quincunx pattern along the outer edge of the shallow foundation pit excavation zone; sequentially grouting the spaced steel pipes; cyclically grouting each steel pipe; excavating the foundation pit according to the shallow foundation pit excavation zone; repeatedly excavating the pebble strata within the shallow foundation pit excavation zone, and repeatedly installing anchor bolts on the sidewalls within the shallow foundation pit excavation zone; finally excavating the pebble strata within the shallow foundation pit excavation zone to a predetermined position. This invention solves the technical problem that the support of shallow foundation pits in pebble strata still requires large-area reinforcement and support measures, leading to increased costs and long construction periods.

Description

Technical Field

[0001] This invention relates to the field of shallow foundation pit excavation construction technology in gravel strata, and in particular to a method for shallow foundation pit excavation with grouting reinforcement and support in gravel strata. Background Technology

[0002] Excavation of foundation pits in pebble strata is frequently encountered in engineering construction. However, due to the large gaps between pebbles, the susceptibility of pebble strata to disturbance and damage, and the risk of borehole collapse during excavation, reinforced retaining support measures are often required in pebble strata excavation. This is especially true in areas with site constraints and / or where slope excavation is not permitted, where strong retaining support measures are necessary, such as sheet piles, retaining piles, interlocking piles, walers, and internal bracing. However, due to site limitations, such as the presence of existing buildings or roads nearby, and in cases where the excavation depth is not deep, implementing large-scale reinforced retaining support measures increases investment, affects efficiency, and extends the construction period. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for excavating shallow foundation pits in gravel strata with grouting reinforcement and support. This method solves the technical problems of existing technologies that still require large-area reinforcement and support measures for shallow foundation pits in gravel strata, leading to increased costs and long construction periods.

[0004] According to an embodiment of the present invention, a method and apparatus for grouting reinforcement and support of shallow foundation pits in gravel strata includes the following steps:

[0005] Determine the excavation area to form a shallow foundation pit excavation zone;

[0006] Multiple steel pipes arranged in a quincunx pattern are inserted sequentially along the outer edge of the shallow foundation pit excavation area;

[0007] Grouting was performed sequentially on the steel perforated pipes arranged at intervals.

[0008] Grouting is circulated into each of the aforementioned steel pipes;

[0009] Excavate the foundation pit according to the shallow foundation pit excavation area;

[0010] The gravel strata within the shallow foundation pit excavation area were excavated multiple times, and anchor bolts were installed on the sidewalls within the shallow foundation pit excavation area multiple times.

[0011] Finally, the gravel strata within the shallow foundation pit excavation area are excavated to the preset position.

[0012] Preferably, the grouting holes of the steel perforated pipe are arranged in a spiral pattern; and / or

[0013] The diameter of the grouting hole is D, and D = 5 mm.

[0014] Preferably, the bottom of the steel pipe is welded with a cap, which is a steel plate with a thickness of 5 mm.

[0015] Preferably, the distance between two adjacent steel pipes is L1, and L1 = 1000 mm; and / or

[0016] The spacing between two adjacent groups of steel pipes is L2, and L2 = 1000 mm.

[0017] Preferably, the number of times the "grouting is performed sequentially on the steel perforated pipes arranged at intervals" is defined as N1, and N1≥2; and / or

[0018] The time for "successfully grouting the steel pipes arranged at intervals" is defined as T, and T = 1 min.

[0019] Preferably, the grouting pressure for "sequentially grouting the steel pipes arranged at intervals" is P1, and P1 = 0.

[0020] Preferably, the number of times the "circulating grouting is performed on each of the steel pipes" is defined as N2, and N2≥1; and / or

[0021] The grouting pressure for "circulating grout into each of the steel pipes" is defined as P2, and P2 > 0.

[0022] Preferably, the depth of the preset position is H, and 0m < H ≤ 3m.

[0023] Preferably, the step of "multiple excavations of the gravel strata within the shallow foundation pit excavation area, and multiple installations of anchor bolts on the sidewalls within the shallow foundation pit excavation area" includes:

[0024] The anchor rods are inserted at H≤1m and / or H≤2m.

[0025] Preferably, the plurality of anchor rods are arranged in a quincunx pattern along the transverse direction, and the distance between two adjacent anchor rods is L3, where L3 = 0.5m.

[0026] Compared with existing technologies, this invention has the following advantages: By inserting multiple steel pipes arranged in a quincunx pattern in the shallow foundation pit excavation area, and sequentially grouting the spaced steel pipes, the gaps formed between the pebble strata are filled, and the pebble strata are solidified, so that the grout, pebbles, and steel pipes form a whole, providing support and enclosure for the shallow foundation pit in the pebble strata; simultaneously, by sequentially grouting each steel pipe in an intermittent pouring manner, the grout flows through the steel pipes to various parts of the pebble strata, and the grout has a certain diffusion area, so that the grout and the pebble strata can better contact to form a stable support system, thereby utilizing the existing pebble strata and turning its original disadvantages into advantages; furthermore, by circulating grout into each steel pipe until the grouting pressure is reached... The grout is used to fill the diffused and lost slurry within the pebble stratum until the required strength is met. During this process, the grout and pebble stratum form a dynamic equilibrium, and the degree of solidification and area are continuously adjusted and compensated, ultimately enabling the grout and pebble stratum to form a stable support system. In addition, anchor bolts are used for support during the excavation of shallow foundation pits, so that the above support system and anchor bolts work together to provide stable support for the shallow foundation pit. This method is suitable for the excavation of shallow foundation pits. By injecting grout into the pebble stratum multiple times, the pebble stratum and grout form a stable structure, solving the problem that large-area reinforced support measures cannot be taken due to site constraints. Furthermore, the existing characteristics of the pebble stratum can better combine with the grout, resulting in lower costs and shorter construction periods. Attached Figure Description

[0027] Figure 1 This is a schematic flowchart of a shallow foundation pit excavation method for grouting reinforcement and support in pebble strata according to an embodiment of the present invention.

[0028] Figure 2 This is a structural diagram illustrating the determination of the excavation area in an embodiment of the present invention to form a shallow foundation pit excavation zone;

[0029] Figure 3 This is a schematic diagram of the structure of a plurality of steel pipes arranged in a quincunx pattern inserted sequentially along the outer edge of the shallow foundation pit excavation area according to an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of the structure when grouting is performed sequentially on steel perforated pipes arranged at intervals in one embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of the structure during circulatory grouting of each of the steel pipes in one embodiment of the present invention;

[0032] Figure 6 This is a schematic diagram of the structure when excavating a foundation pit according to the shallow foundation pit excavation area in one embodiment of the present invention;

[0033] Figure 7This is a schematic diagram of the structure in one embodiment of the present invention, showing the repeated excavation of the gravel strata in the shallow foundation pit excavation area and the repeated installation of anchor bolts on the sidewalls in the shallow foundation pit excavation area.

[0034] In the above attached figures:

[0035] 1. Gravel strata; 2. Shallow foundation pit excavation area; 3. Steel pipe; 4. Anchor bolt. Detailed Implementation

[0036] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] In embodiments of the present invention, such as Figure 1 As shown, the method for grouting reinforcement and support of shallow foundation pits in gravel strata includes the following steps:

[0038] Step S100: Determine the excavation area to form shallow foundation pit excavation area 2;

[0039] Step S200: Insert multiple steel pipes 3 arranged in a quincunx pattern along the outer edge of the shallow foundation pit excavation area 2.

[0040] Step S300: Grouting is performed sequentially on the steel perforated pipes 3 arranged at intervals;

[0041] Step S400: Circulate grout into each of the steel perforated pipes 3;

[0042] Step S500: Excavate the foundation pit according to the shallow foundation pit excavation area 2;

[0043] Step S600: Excavate the gravel stratum in the shallow foundation pit excavation area 2 multiple times, and install anchor bolts 4 on the inner sidewall of the shallow foundation pit excavation area 2 multiple times.

[0044] Step S700: Finally excavate the pebble stratum in the shallow foundation pit excavation area 2 to the preset position.

[0045] Specifically, in this embodiment of the invention, the pebble stratum is characterized by large gaps between pebbles, easy disturbance and damage to the pebble layer, easy collapse of the hole during excavation, low compressibility, and high shear strength. Specifically, when excavating a pebble stratum, large-area reinforced support measures are often required around it; however, the existing site is often insufficient to install these support measures, and implementing large-area reinforced support measures when the excavation depth is shallow increases investment, affects efficiency, and prolongs the construction period. Therefore, an economical, fast, and convenient support method is needed for shallow foundation pit excavation with limited perimeter around pebble strata.

[0046] In embodiments of the present invention, such as Figure 2As shown, the excavation area needs to be determined first according to the construction requirements, and it is defined as shallow foundation pit excavation area 2; as Figure 3 As shown, steel pipes 3 are laid out around the shallow foundation pit excavation area 2. The steel pipes 3 are arranged in a quincunx pattern to inject grout into the pebble stratum, thereby filling the gaps between the pebbles; as shown... Figure 4 As shown, the grout used is P.C42.5 silicate pure cement grout with a water-cement ratio of 0.4-0.5; the grouting adopts an intermittent grouting method, allowing the injected grout to diffuse and form strength; in this way, not only can the grout fully bond with the gravel stratum, but the grout can also repeatedly and cyclically diffuse into the gaps between each gravel, forming a stable support structure with the gravel stratum, and solidifying the easily disturbed and damaged gravel stratum through grout solidification, thereby preventing the gravel stratum from collapsing during excavation; as shown Figure 5 As shown, grouting is performed in a cyclic manner until the grouting pressure meets the requirements; this is used to fill the grout that has diffused and lost within the pebble stratum. During this process, the grout and the pebble stratum form a dynamic equilibrium, and the degree of solidification and area are continuously adjusted and compensated to ultimately enable the grout and the pebble stratum to form a stable support system; as shown. Figure 6 , Figure 7 As shown, the shallow foundation pit excavation area 2 is repeatedly excavated, and anchor bolts 4 are inserted during the excavation process to make the cement grout, pebbles, steel pipes 3 and anchor bolts 4 form a whole, which plays a supporting and protective role for the shallow foundation pit in the pebble stratum.

[0047] This invention addresses shallow foundation pit excavation in pebble strata. Firstly, the support system for shallow foundation pits does not require a large-area support system, and large-area support systems are not suitable for such scenarios due to site constraints. Secondly, pebble strata are inherently low in compressibility; therefore, by gradually diffusing cement grout into their voids, the inherent disadvantages of pebble strata are transformed into advantages, resulting in a stronger support system. Furthermore, the sequential, intermittent grouting method provides sufficient time for the grout flowing through each steel pipe 3 to solidify, preventing interference between adjacent grout flows and allowing the grout to diffuse and solidify within the corresponding pebble stratum. This also reduces the amount of grout used. Finally, combined with circulating grouting, the lost grout from the pebble stratum is replenished. When the injected grout reaches a certain strength, the surrounding pebble gaps are solidified through grout penetration, thereby improving the overall stability of the pebble stratum.

[0048] Of course, in other embodiments, in order to further prevent the grout injected into the pebble stratum from spreading and being lost, or to reduce the amount of grout used, protective casings and protective arms are installed at two locations in the shallow foundation pit excavation area; or clay or dry cement is dumped and filled, and / or the viscosity of the grout is increased and some expansive soil or yellow mud or an appropriate amount of anti-seepage agent is added to prevent the grout from seeping into the gaps between the pebbles to prevent the hole from collapsing.

[0049] Reference Figure 3 In one embodiment, the grouting holes of the steel perforated pipe 3 are arranged in a spiral pattern; the diameter of the grouting hole is D, and D = 5 mm. Specifically, in order to allow the grout to diffuse into every void of the pebble stratum, the grouting holes of the steel perforated pipe 3 are arranged in a spiral pattern, that is, there is only one grouting hole at the same cross section, so that the grout can be injected into various parts of the pebble stratum in a layered manner from top to bottom; and the combination of multiple steel perforated pipes 3 arranged in a quincunx pattern can fill the pebble stratum in the current shallow foundation pit excavation area with grout, which is also conducive to the diffusion of the grout; and to avoid the grout spreading to different degrees in the top and bottom directions, the diameter of the grouting hole is defined as 5 mm, and the steel perforated pipe 3 is made of φ110mm×4mm steel pipe. Further, in one embodiment, the bottom of the steel perforated pipe 3 is welded with a cap, and the cap is a steel plate with a thickness of 5 mm. Specifically, in order to prevent excessive grout leakage from the pebble formation at the bottom of the hole, a cap is welded to the bottom of the steel pipe 3. This cap is used to seal the bottom end of the steel pipe 3, so that the grout can be evenly distributed to different locations in the pebble formation under the guidance of each grouting hole.

[0050] Reference Figure 3 As shown, in one embodiment, the spacing between two adjacent steel pipes 3 is L1, and L1 = 1000 mm; the spacing between two adjacent groups of steel pipes 3 is L2, and L2 = 1000 mm. Specifically, in order to improve the diffusion rate of the slurry and to ensure that the slurry is evenly diffused to all parts of the pebble stratum, the spacing between two adjacent steel pipes 3 and two adjacent groups of steel pipes 3 is 1000 mm, so that the slurry and the steel pipes 3 form a stable support structure.

[0051] In one embodiment, the number of times the "grouting is performed sequentially on the spaced steel perforated pipes 3" is defined as N1, and N1 ≥ 2; the time for the "grouting is performed sequentially on the spaced steel perforated pipes 3" is defined as T, and T = 1 min. Specifically, in order to ensure that the grout can fully diffuse to all parts of the pebble stratum, this embodiment takes two interval grouting sessions as an example. Figure 4 As shown, the steel pipes 3 arranged at intervals are grouted sequentially in the first stage, and the remaining ungrouted steel pipes 3 are grouted in the second stage to complete the gradual grouting of the steel pipes 3. The grouting time is 1 minute to control the grouting speed and amount, reduce the amount of grout used, and also enable the grout to spread quickly.

[0052] In one embodiment, the grouting pressure for "sequentially grouting the steel perforated pipes 3 arranged at intervals" is P1, and P1 = 0. Specifically, since the first and second grouting are for initially filling the voids in the pebble stratum, there is no need to limit the grouting pressure, making construction simpler; at the same time, it also facilitates grout diffusion.

[0053] In one embodiment, the number of times the "grout is circulated into each of the steel pipes 3" is defined as N2, and N2≥1; the grouting pressure for the "grouting is circulated into each of the steel pipes 3" is defined as P2, and P2>0. Specifically, in order to further fill the pebble stratum with grout, this embodiment takes one circumferential grouting as an example. One circumferential grouting can compensate for the grout lost from the pebble stratum, so as to form a final stable support structure. Of course, since the circumferential grouting is the final grouting, its grouting pressure should be guaranteed to completely fill the gaps in the pebble stratum.

[0054] Reference Figure 7 As shown, in one embodiment, the depth of the preset position is H, and 0m < H ≤ 3m. Specifically, a foundation pit with a height not exceeding 3m is considered a shallow foundation pit. This method can be used when excavating shallow foundation pits in pebble strata within this range, without the need for large-area installation of retaining support measures, and is not limited by the construction site. At the same time, when using this method to excavate shallow foundation pits within the above-mentioned range, the grouted pebble strata can provide good support and prevent hole collapse.

[0055] Reference Figure 7 As shown, in one embodiment, the step of "multiple excavations of the gravel stratum within the shallow foundation pit excavation area 2, and multiple installations of anchor bolts 4 on the inner sidewall of the shallow foundation pit excavation area 2" includes: inserting the anchor bolts 4 at locations H≤1m and / or H≤2m. Specifically, to further improve the stability of the aforementioned support structure, anchor bolts 4 are inserted during the excavation of the shallow foundation pit. It can be understood that, in this embodiment, the height H of the shallow foundation pit is defined as 3m, so anchor bolts 4 need to be installed at H=1m and H=2m respectively, to integrate the gravel in the grouting area, the steel pipe 3 reinforcement, and the anchor bolts 4 reinforcement into a whole, thereby forming an overall support system for the gravel stratum shallow foundation pit and preventing hole collapse. Further, in one embodiment, multiple anchor bolts 4 are arranged in a quincunx pattern along the transverse direction, with a spacing of L3 between adjacent anchor bolts 4, and L3=0.5m.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for excavating shallow foundation pits with grouting reinforcement and support in pebble strata, characterized in that, Includes the following steps: Determine the excavation area to form a shallow foundation pit excavation zone; Multiple steel pipes arranged in a quincunx pattern are inserted sequentially along the outer edge of the shallow foundation pit excavation area; Grouting was performed sequentially on the steel perforated pipes arranged at intervals. Grouting is circulated into each of the aforementioned steel pipes; Excavate the foundation pit according to the shallow foundation pit excavation area; The gravel strata within the shallow foundation pit excavation area were excavated multiple times, and anchor bolts were installed on the sidewalls within the shallow foundation pit excavation area multiple times. Finally, the gravel strata within the shallow foundation pit excavation area are excavated to the preset position; The number of times grouting is performed sequentially on the spaced steel perforated pipes is N1, and N1≥2; and / or The time for grouting the steel perforated pipes arranged at intervals is T, and T = 1 min; The grouting pressure for sequentially grouting the steel perforated pipes arranged at intervals is P1, and P1=0; The depth of the preset position is H, and 0m < H ≤ 3m; The steps of repeatedly excavating the gravel strata within the shallow foundation pit excavation area and repeatedly installing anchor bolts on the sidewalls within the shallow foundation pit excavation area include: The anchor rod is inserted at a position H≤2m; The multiple anchor bolts are arranged in a quincunx pattern along the transverse direction, and the distance between two adjacent anchor bolts is L3, where L3 = 0.5m; The number of times grout is injected into each of the steel pipes is N2, and N2≥1; The grouting pressure for circulating grouting into each of the steel pipes is P2, and P2 > 0.

2. The method for excavating shallow foundation pits with grouting reinforcement and support in pebble strata as described in claim 1, characterized in that, The grouting holes of the steel pipe are arranged in a spiral pattern; and / or The diameter of the grouting hole is D, and D=5mm.

3. The method for excavating shallow foundation pits with grouting reinforcement and support in pebble strata as described in claim 1, characterized in that, The bottom of the steel pipe is welded with a cap, which is a steel plate with a thickness of 5 mm.

4. A method for excavating shallow foundation pits with grouting reinforcement and support in pebble strata as described in any one of claims 1-3, characterized in that, The distance between two adjacent steel pipes is L1, and L1 = 1000 mm; and / or The spacing between two adjacent groups of steel pipes is L2, and L2 = 1000 mm.

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