Method for excavating foundation pit near lake

Abstract

The invention relates to the technical field of foundation pit excavation, in particular to a lake-near foundation pit excavation method. The foundation pit near the lake is excavated in a vertical layering and horizontal step-by-step matched grouting mode; the lake-near foundation pit comprises a first section and a second section, and the first section is arranged near the lake; the excavation method comprises the steps that S1, the first section is excavated to the vertical layered excavation depth of the second section, and horizontal grouting is conducted while excavation is conducted on the first section; s2, the second section is excavated till the vertical layered excavation depth of the second section is reached, and inclined grouting is conducted on surrounding rock on the lower side of the first section in the first section; the influence range of inclined grouting and the influence range of previous horizontal grouting are overlapped by a first length in the vertical direction, and the first length is larger than or equal to 0 m; s3, a first section is excavated within the influence range of inclined grouting; and S4, the steps S1 to S3 are repeated till the designed depth of the lake-near foundation pit is reached. By means of the arrangement, on the basis that safe excavation is guaranteed, the excavation speed of the foundation pit near the lake can be increased.

Description

Technical Field

[0001] The present application relates to the technical field of foundation pit excavation, and in particular to a method for excavating a foundation pit near a lake. Background Art

[0002] Foundation pit support engineering is one of the important and indispensable projects in geotechnical engineering, especially in lakeside areas, where the geological conditions are complex, groundwater is abundant, and the groundwater level is high and varies greatly. During the foundation pit excavation process, if the groundwater is not properly treated, it may cause water seepage or even water gushing in the foundation pit, affecting the construction progress, foundation pit stability and the safety of construction workers. The existing technology often adopts the method of layered excavation and grouting for lakeside foundation pit construction, but there are corresponding technical problems such as low construction efficiency.

[0003] Therefore, it is necessary to provide an improved technical solution to address the above-mentioned deficiencies in the prior art. Summary of the invention

[0004] The purpose of this application is to provide a method for excavating a foundation pit near a lake to solve or alleviate the problems existing in the above-mentioned prior art.

[0005] In order to achieve the above objectives, this application provides the following technical solutions: A method for excavating a foundation pit near a lake, wherein the foundation pit near the lake is excavated in a vertical layered and horizontal step-by-step manner in combination with grouting; the foundation pit near the lake comprises a first section and a second section, and the first section is arranged near the lake; The excavation method comprises: Step S1: excavating the first section to the vertical layered excavation depth of the second section, and performing horizontal grouting while excavating the first section; Step S2: excavating the second section to the vertical layered excavation depth of the second section, and performing inclined grouting on the lower surrounding rock of the first section in the first section; the influence range of the inclined grouting is vertically superimposed with the influence range of the previous horizontal grouting by a first length, and the first length is ≥0m; Step S3: excavating the first section within the influence range of the inclined grouting; Step S4: Repeat the above steps S1 to S3 until the designed depth of the lakeside foundation pit is reached.

[0006] The above-mentioned method for excavating a foundation pit near a lake, preferably, the excavation method comprises: Before step S1, a water-stop curtain is constructed on the lake-facing side of the lake-facing foundation pit, and the inner and outer sides of the water-stop curtain are backfilled.

[0007] In the above-mentioned method for excavating a foundation pit near a lake, preferably, the side of the water-stop curtain close to the foundation pit near the lake is backfilled with anti-seepage materials.

[0008] The above-mentioned method for excavating a foundation pit near a lake, preferably, the excavation method comprises: After the inner and outer sides of the water-stop curtain are backfilled, before step S1, ground grouting is performed on the side of the water-stop curtain close to the foundation pit facing the lake.

[0009] In the above-mentioned method for excavating a foundation pit near a lake, preferably, the backfill depth of the anti-seepage material is less than the vertical layered excavation depth of the second section; The excavation method comprises: After backfilling the side of the water-stop curtain close to the foundation pit facing the lake with anti-seepage material, before step S1, the first section is excavated within the backfill depth of the anti-seepage material.

[0010] In the above-mentioned method for excavating a foundation pit near a lake, preferably, in step S1, the influence range of each horizontal grouting hole is arranged in a vertically superimposed manner.

[0011] In the above-mentioned method for excavating a foundation pit near a lake, preferably, in step S1, the vertical spacing of the horizontal grouting holes is less than or equal to the influence radius of the horizontal grouting, and the first section is excavated in layers according to the vertical spacing of the horizontal grouting holes.

[0012] The above-mentioned method for excavating a foundation pit near a lake, preferably, the excavation method comprises: After step S1 and before step S2, the surrounding rock of the first section is subjected to inter-pile mesh shotcrete construction.

[0013] In the above-mentioned method for excavating a foundation pit near a lake, preferably, the construction of the mesh shotcrete between piles is specifically as follows: Pile treatment: On the basis of not damaging the reinforcement of the pile, use a pneumatic pick to break the concrete that has intruded into the clearance of the pile; Fix the steel mesh; Shotcrete: spraying operation is carried out from bottom to top, in sections and pieces.

[0014] In the method for excavating a lakeside foundation pit as described above, preferably, the earth excavated from the first section is used for emergency water stopping of the lakeside foundation pit.

[0015] Compared with the closest prior art, the technical solution of the embodiment of the present application has the following beneficial effects: On the one hand, the present application first excavates the foundation pit of the first section and cooperates with horizontal grouting. After the excavation of the first section is completed, observe whether there is any backflow of lake water. If serious water leakage occurs, immediately backfill and stop the water in the first section to effectively avoid the occurrence of safety accidents and waste of construction resources. On the other hand, based on the vertical layered excavation depth of the second section, while excavating the second section, inclined grouting is performed on the lower surrounding rock of the first section to complete the pretreatment of the lower surrounding rock of the first section, so that the next first section to be excavated can be directly excavated to the boundary of the influence range of the inclined grouting without the need for horizontal grouting, so as to effectively improve the excavation speed of the subsequent first section. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. Among them: Figure 1 A construction schematic diagram before step S1 in a lakeside foundation pit excavation method provided according to some embodiments of the present application; Figure 2 A construction schematic diagram of step S1-step S2 in a lakeside foundation pit excavation method provided according to some embodiments of the present application; Figure 3 This is a construction schematic diagram of step S3 in the lakeside foundation pit excavation method provided according to some embodiments of the present application.

[0017] Description of reference numerals: 1. First section; 2. Second section; 3. Mud pump; 4. Water-stop curtain; 5. Cast-in-place piles; 6. Ground grouting; 7. Horizontal grouting; 8. Inclined grouting. DETAILED DESCRIPTION

[0018] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. Each example is provided by way of explanation of the present application and does not limit the present application. In fact, it will be clear to those skilled in the art that modifications and variations may be made in the present application without departing from the scope or spirit of the present application. For example, a feature shown or described as a part of an embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desired that the present application includes such modifications and variations within the scope of the appended claims and their equivalents.

[0019] In the following description, the terms "first / second / third" involved are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It can be understood that "first / second / third" can be interchanged with a specific order or sequence where permitted, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present disclosure belongs. The terms used herein are only for the purpose of describing the embodiments of the present disclosure and are not intended to limit the present disclosure.

[0021] In the description of the present application, the terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present application and do not require that the present application must be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present application. The terms "connected", "connected", and "set" used in the present application should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component; it can be a wired electrical connection, a radio connection, or a wireless communication signal connection. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0022] The following will be combined with the attached Figure 1-3 A lakeside foundation pit excavation method of the present application is further described in detail.

[0023] A method for excavating a foundation pit near a lake, wherein the foundation pit near the lake is excavated in a vertical layered and horizontal step-by-step manner in combination with grouting; the foundation pit near the lake comprises a first section 1 and a second section 2, and the first section 1 is arranged near the lake; Excavation methods include: Step S1: excavating the first section 1 to the vertical layered excavation depth of the second section 2, and performing horizontal grouting 7 while excavating the first section 1; Step S2: excavating the second section 2 to the vertical layered excavation depth of the second section 2, and performing inclined grouting 8 on the lower surrounding rock of the first section 1 in the first section 1; the influence range of the inclined grouting 8 and the influence range of the previous horizontal grouting 7 are vertically superimposed by a first length, and the first length is ≥0m; Step S3: excavating the first section 1 within the influence range of the inclined grouting 8; Step S4: Repeat the above steps S1 to S3 until the designed depth of the lakeside foundation pit is reached.

[0024] In a specific embodiment of the present application, the first section 1 and the second section 2 are arranged in parallel along a horizontal direction perpendicular to the lakeside. The first section 1 is an area within a horizontal range of 2m on the lakeside of the lakeside foundation pit, and the excavation slope ratio is 1:1; the second section 2 is the remaining area outside the first section 1 in the lakeside foundation pit, and the vertical layered excavation depth of the second section 2 is 2m. The lakeside foundation pit uses a mud pump 3 with a φ48mm sleeve valve pipe for horizontal grouting 7 and inclined grouting 8. The grouting uses cement-water glass double liquid slurry, wherein the cement uses ordinary Portland cement with a strength grade of 42.5R, the designed water-cement ratio is 1:1, the water glass concentration is 35Be, the designed grouting influence radius is 0.25m, the grouting speed is 30-50L / min, the hydrostatic pressure at the grouting point is 0.5MPa, and the first length of the vertical superposition of the influence range of the inclined grouting 8 and the influence range of the previous horizontal grouting 7 is 0m, that is, the influence range of the inclined grouting 8 is seamlessly connected with the bottom boundary of the influence range of the previous horizontal grouting 7.

[0025] On the one hand, the present application first carries out foundation pit excavation of the first section 1 and cooperates with horizontal grouting 7. After the excavation of the first section 1 is completed, observe whether there is lake water backflow. If serious water leakage occurs, immediately backfill and stop the water in the first section 1, so as to effectively avoid the occurrence of safety accidents and waste of construction resources. On the other hand, based on the vertical layered excavation depth of the second section 2, while excavating the second section 2, inclined grouting 8 is performed on the lower surrounding rock of the first section 1 at the current depth of the first section 1 to complete the pretreatment of the lower surrounding rock of the first section 1, so that the next first section 1 to be excavated can be directly excavated to the bottom boundary of the influence range of the inclined grouting 8 without the need for horizontal grouting 7, so as to effectively improve the subsequent excavation speed of the first section 1.

[0026] Excavation methods include: Before step S1 , a water-stopping curtain 4 is constructed on the lake-facing side of the lake-facing foundation pit, and the inner and outer sides of the water-stopping curtain 4 are backfilled.

[0027] In a specific embodiment of the present application, the water-stop curtain 4 is specifically a steel sheet pile water-stop curtain, which is used to reduce the risk of lake water backflow in the foundation pit near the lake.

[0028] The side of the water-stop curtain 4 close to the lake foundation pit is backfilled with anti-seepage materials.

[0029] In a specific embodiment of the present application, the lake side of the water-stop curtain 4 is backfilled with clay or C15 concrete, and the lake side of the water-stop curtain 4 is backfilled with waterproof concrete to reduce the risk of water seepage in the initial excavation of the lake side foundation pit, wherein the water-stop curtain 4 is backfilled to the top elevation of the foundation pit close to the lake side, and the backfill height of the water-stop curtain 4 on the lake side is less than the backfill height of the water-stop curtain 4 on the lake side of the foundation pit, and the backfill height of the water-stop curtain 4 on the lake side exceeds the lake surface height by 500 mm and a slope belt is provided to buffer the impact of lake water.

[0030] Excavation methods include: After the inner and outer sides of the water-stop curtain are backfilled, before step S1, ground grouting 6 is performed on the side of the water-stop curtain 4 close to the foundation pit facing the lake.

[0031] In a specific embodiment of the present application, a mud pump 3 is used in conjunction with a φ48mm sleeve valve pipe for ground grouting 6 in a lakeside foundation pit. The grouting depth is 8m, and cement-water glass double liquid slurry is used for grouting. The cement is ordinary Portland cement with a strength grade of 42.5R, the designed water-cement ratio is 1:1, the water glass concentration is 35Be, the designed grouting influence radius is 0.25m, the grouting speed is 30-50L / min, and the hydrostatic pressure at the grouting point is 0.5MPa.

[0032] By performing ground grouting 6 on the side of the water-stop curtain 4 close to the lake-facing foundation pit, on the one hand, the risk of water seepage in the lake-facing foundation pit can be further reduced. On the other hand, by reducing the risk of water seepage in the lake-facing foundation pit, construction conditions can be created for the horizontal grouting 7 of the first section 1, and construction time can be gained to effectively form a combined water-stopping structure of the ground grouting 6 and the horizontal grouting 7.

[0033] The backfill depth of the anti-seepage material is less than the vertical layered excavation depth of the second section 2; Excavation methods include: After the side of the water-stop curtain close to the foundation pit facing the lake is backfilled with anti-seepage materials, before step S1, the first section 1 is excavated within the backfill depth of the anti-seepage materials.

[0034] In a specific embodiment of the present application, after backfilling the side of the water-stop curtain close to the lake foundation pit with anti-seepage material, before step S1, the first section 1 is directly excavated to the bottom boundary of the backfill depth of the anti-seepage material, and there is no need to perform horizontal grouting 7 to improve construction efficiency.

[0035] In step S1, the influence ranges of the horizontal grouting holes are arranged in a vertically superimposed manner.

[0036] In a specific embodiment of the present application, the influence ranges of the horizontal grouting holes constructed in the first section 1 are superimposed on each other and connected as a whole, forming an effective water stop for the lake-facing foundation pit on the lake side.

[0037] In step S1 , the vertical spacing of the horizontal grouting holes is less than or equal to the influence radius of the horizontal grouting 7 , and the first section 1 is excavated in layers according to the vertical spacing of the horizontal grouting holes.

[0038] In a specific embodiment of the present application, the vertical spacing of the horizontal grouting holes is 0.25m, and accordingly, the vertical layered excavation depth of the first section 1 is also 0.25m, and thus the horizontal grouting holes are set at the bottom of the first section 1 after each layered excavation, and the bottom of the first section 1 after each layered excavation is located at the boundary of the influence range of the previous horizontal grouting hole.

[0039] Excavation methods include: After step S1 and before step S2, the surrounding rock of the first section 1 is subjected to inter-pile mesh shotcrete construction.

[0040] The specific construction of inter-pile mesh shotcrete is as follows: Pile treatment: On the basis of not damaging the reinforcement of the pile, use a pneumatic pick to break the concrete that has intruded into the clearance of the pile; Fix the steel mesh; Shotcrete: spraying operation is carried out from bottom to top, in sections and pieces.

[0041] In a specific embodiment of the present application, The steel mesh is fixed on the cast-in-place pile 5 with φ6mm expansion bolts. The steel mesh is placed in the middle of the mesh shotcrete as much as possible. The size of the steel mesh is 200mm×200mm.

[0042] First, the shotcrete is mixed according to the construction mix ratio. The mixing is done by a JZC350 forced mixer and transported to the spraying site by a loader. The mixing process specifically includes: adding crushed stone, sand and cement, then adding an appropriate amount of water (sand and stone moisture content is not more than 8%) and stirring evenly to make the mixture slightly moist and free of a large amount of dust. The mixing time is two minutes, and then adding an accelerator when adding it to the sprayer.

[0043] The spraying operation specifically includes: (1) Adjustment of working wind pressure: Generally, it is between 0.15Mpa and 0.2Mpa. Adjust the working wind pressure in time according to the location of the shotcrete, the distance and the specific moisture content of the shotcrete mixture. If the wind pressure is too high, the rebound will increase and even blow off the concrete that has not been completely solidified; if the wind pressure is too low, the coarse aggregate will not be able to enter the mortar layer and will fall off, affecting the quality of the shotcrete. If the wind pressure is too low, it may even cause pipe blockage. The wind pressure should be controlled on site to ensure that the rebound of the shotcrete is small, the surface is glossy and easy to adhere.

[0044] (2) After the spray machine is installed and debugged, water should be injected first and then ventilated to clear the barrel and pipeline for feeding. Feed continuously and keep the hopper full of materials at all times. A 10mm aperture screen should be installed on the hopper to prevent oversized aggregates from entering the machine and causing pipe blockage.

[0045] (3) Adjustment of water addition amount: When spraying, first add water (note that the nozzle should be facing downward to prevent water from flowing into the feed pipe), then supply air, and then add material. Adjust the amount of water addition according to the sprayed surface and the sprayed mixture. The amount should be such that the surface is easy to adhere after spraying, has little rebound, and has a moist and shiny surface without dry spots or flow.

[0046] (4) Spraying sequence: The spraying operation should be carried out in sections and pieces from bottom to top, and the length of each section should not exceed 6m.

[0047] (5) Movement trajectory of the spray beam: Circular rotation and horizontal movement with one circle and half a circle, the diameter of the circular rotation is about 0.3m. When spraying the second row, start from the top of the starting point of the first row in sequence, with an overlap of 2 to 3cm between rows.

[0048] (6) Optimal spraying distance and angle: The distance between the nozzle and the surface should be 0.6m to 1.2m. At the top, it can be appropriately increased to 1.5m to 2.0m. The spraying beam is basically perpendicular to the sprayed surface, and it is best when it forms an angle of 5° to 15° with the vertical line of the sprayed surface.

[0049] (7) Primary spraying thickness: Determined according to the design thickness and spraying location, the initial spraying thickness should not be less than 4-6 cm. When spraying the first layer of concrete, it is important to fill and level it, and spray small pits into a round shape.

[0050] (8) Shotcrete thickness control: The thickness of shotcrete is controlled by the stake method. When installing anchor rods, the exposed length of the anchor rods is used as stakes.

[0051] (9) Shotcrete flatness control: The surface flatness should be smooth when visually inspected, otherwise additional spraying is required.

[0052] (10) When the spraying operation is finished, the mixed materials in the machine and the pipe should be used up before stopping the machine, turning off the water and cutting off the air. The spraying machine should be cleaned and repaired after each shift to ensure that the machine is in good working condition for the next shift.

[0053] (11) Spraying concrete curing: 2 hours after the final setting of the concrete, water spraying curing shall begin. The curing time shall not be less than 7 days. When the temperature is below +5℃, water spraying curing shall not be carried out.

[0054] The earth excavated from the first section 1 is used for emergency water stopping of the foundation pit near the lake.

[0055] In a specific embodiment of the present application, after the excavation of the first section 1 is completed, observe whether there is any backflow of lake water. If serious water leakage occurs, immediately backfill the first section 1 to stop the water. When the backfilling and water-stopping effect is not good, pour plain concrete and grouting construction are carried out. On the one hand, it can effectively improve the speed of risk emergency response, and on the other hand, it can also avoid the waste of construction resources.

[0056] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for excavating a foundation pit near a lake, characterized in that: The lakefront foundation pit is excavated by vertical stratification, horizontal stepping and grouting; the lakefront foundation pit includes a first section and a second section, and the first section is arranged near the lake; The excavation method comprises: Step S1: excavating the first section to the vertical layered excavation depth of the second section, and performing horizontal grouting while excavating the first section; Step S2: excavating the second section to the vertical layered excavation depth of the second section, and performing inclined grouting on the lower surrounding rock of the first section in the first section; the influence range of the inclined grouting is vertically superimposed with the influence range of the previous horizontal grouting by a first length, and the first length is ≥0m; Step S3: excavating the first section within the influence range of the inclined grouting; Step S4: Repeat the above steps S1 to S3 until the designed depth of the lakeside foundation pit is reached.

2. A lakeside foundation pit excavation method as claimed in claim 1, characterized in that: The excavation method comprises: Before step S1, a water-stop curtain is constructed on the lake-facing side of the lake-facing foundation pit, and the inner and outer sides of the water-stop curtain are backfilled.

3. A lakeside foundation pit excavation method as claimed in claim 2, characterized in that: The side of the water-stop curtain close to the foundation pit facing the lake is backfilled with anti-seepage materials.

4. A lakeside foundation pit excavation method as claimed in claim 2, characterized in that: The excavation method comprises: After the inner and outer sides of the water-stop curtain are backfilled, before step S1, ground grouting is performed on the side of the water-stop curtain close to the foundation pit facing the lake.

5. The method for excavating a lakeside foundation pit according to claim 3, characterized in that: The backfill depth of the anti-seepage material is less than the vertical layered excavation depth of the second section; The excavation method comprises: After backfilling the side of the water-stop curtain close to the foundation pit facing the lake with anti-seepage material, before step S1, the first section is excavated within the backfill depth of the anti-seepage material.

6. The method for excavating a foundation pit near a lake as claimed in claim 1, characterized in that: In step S1, the influence ranges of the horizontal grouting holes are arranged in a vertically superimposed manner.

7. A lake-side foundation pit excavation method as claimed in claim 6, characterized in that: In step S1, the vertical spacing of the horizontal grouting holes is less than or equal to the influence radius of the horizontal grouting, and the first section is excavated in layers according to the vertical spacing of the horizontal grouting holes.

8. The method for excavating a foundation pit near a lake as claimed in claim 1, characterized in that: The excavation method comprises: After step S1 and before step S2, the surrounding rock of the first section is subjected to inter-pile mesh shotcrete construction.

9. A lake-side foundation pit excavation method as claimed in claim 8, characterized in that: The concrete spraying construction between piles is specifically as follows: Pile treatment: On the basis of not damaging the reinforcement of the pile, use a pneumatic pick to break the concrete that has intruded into the clearance of the pile; Fix the steel mesh; Shotcrete: spraying operation is carried out from bottom to top, in sections and pieces.

10. A lake-side foundation pit excavation method as claimed in any one of claims 1 to 9, characterized in that: The earth excavated from the first section is used for emergency water stopping of the lakeside foundation pit.

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