A foundation pit supporting structure for deep silt stratum and a construction method thereof

Abstract

The application provides a foundation pit supporting structure of deep silt stratum and a construction method thereof. The foundation pit supporting structure comprises cast-in-situ bored piles arranged in rows and a water stop curtain. The water stop curtain comprises a plurality of rotary jet piles located in the silt layer and the upper stratum thereof and a plurality of swing jet piles located in the lower stratum of the silt layer. The cast-in-situ bored piles are constructed by using rotary drilling machines; adjacent rotary jet piles are overlapped and engaged with each other; adjacent swing jet piles are overlapped and engaged with each other; and adjacent cast-in-situ bored piles are not engaged with each other. The application combines the construction of the water stop curtain and the cast-in-situ bored piles, firstly constructs the rotary jet piles of the water stop curtain, overlaps and engages the rotary jet piles with each other, then constructs the cast-in-situ bored piles by using rotary drilling machines in the rotary jet piles, the diameter of the rotary jet piles is larger than that of the cast-in-situ bored piles, the former serves as the water stop curtain and also serves as the temporary casing during the construction of the latter, one pile has two uses, the construction process is reduced, the engineering cost is lowered, and the application has good popularization value.

Description

Technical Field

[0001] This invention belongs to the field of foundation pit engineering technology, and in particular relates to a foundation pit support structure and its construction method in deep silt strata. Background Technology

[0002] When using pile foundations combined with a cutoff wall as the foundation pit support structure, the pile foundations are generally constructed first, followed by the cutoff wall. When constructing pile foundations as the foundation pit retaining structure in silty soil, temporary steel casings are typically required to prevent borehole collapse during pile construction. When the silt layer is deep or thick, the temporary steel casings cannot be removed after pile foundation construction, significantly increasing construction costs.

[0003] To reduce the construction costs of pile foundations in deep silt strata, it is necessary to develop a new type of foundation pit support scheme. Summary of the Invention

[0004] This invention provides a foundation pit support structure and its construction method in deep silt strata, aiming to solve the problem of high engineering costs caused by the need for permanent steel casings when constructing bored piles in deep silt strata in the prior art.

[0005] This invention is implemented as follows: a foundation pit support structure for a deep silt stratum includes bored cast-in-place piles arranged in rows and a water-stop curtain; the water-stop curtain includes a number of jet grouting piles arranged in rows in the silt layer and the upper stratum of the silt layer, and a number of swing grouting piles arranged in rows in the lower stratum of the silt layer; the bored cast-in-place piles are constructed using a rotary drilling rig, and the bored cast-in-place piles, jet grouting piles, and swing grouting piles at the same location are concentric, wherein adjacent jet grouting piles overlap and interlock, adjacent swing grouting piles overlap and interlock, and adjacent bored cast-in-place piles do not interlock.

[0006] Furthermore, the pile diameter D2 of the jet grouting pile or swing grouting pile shall not be less than the larger of the following two values:

[0007] D2≥D1+300

[0008] D²≥D+150

[0009] In the formula, D2 is the diameter of the jet grouting pile or the swing grouting pile, D1 is the diameter of the bored pile, and D is the center distance between two adjacent bored piles. All units in the formula are millimeters.

[0010] Furthermore, the jet grouting pile is constructed with the centerline of the pile row as the center, and the jet grouting angle is ±arccos((D2-d) / D2).

[0011] In the formula, D2 is the diameter of the jet grouting pile, and d is the overlap depth between two adjacent jet grouting piles.

[0012] Furthermore, both the jet grouting piles and the swing grouting piles are constructed using the triple-pipe method.

[0013] To solve the above-mentioned technical problems, the present invention also provides a construction method for a foundation pit support structure, which includes the following steps:

[0014] S1. Construction layout;

[0015] S2, rotary jet spraying, and swing jet spraying construction site tests were conducted to determine construction parameters;

[0016] S3, pilot holes for jet grouting piles and swing jet grouting piles;

[0017] S4. Jet grouting piles and swing grouting piles for construction water-stop curtains;

[0018] S5. After the jet grouting piles and swing jet grouting piles have initially solidified, rotary drilling rigs are used to construct bored cast-in-place piles.

[0019] Compared with the prior art, the beneficial effects of this invention are as follows:

[0020] The foundation pit support structure and construction method provided by this invention for deep silt strata combine the construction of the foundation pit water-stop curtain with the construction of bored cast-in-place piles (i.e., support piles). First, the jet grouting piles of the water-stop curtain are constructed and interlocked with each other. Then, a rotary drilling rig is used to construct bored cast-in-place piles inside the jet grouting piles. The diameter of the jet grouting piles is larger than that of the bored cast-in-place piles. The former serves as both a water-stop curtain and a temporary casing during the construction of the latter, achieving two purposes with one pile. This reduces construction procedures and lowers project costs, making it highly valuable for widespread application. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the horizontal cross-section of a foundation pit support structure in a deep silt stratum provided in an embodiment of the present invention, at the location of the silt layer and the stratum above the silt layer.

[0022] Figure 2 This is a schematic diagram of the horizontal cross-section of a foundation pit support structure in a deep silt stratum provided in an embodiment of the present invention, located in the lower stratum of the silt layer. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] Please see Figure 1 and Figure 2 This illustration shows a preferred embodiment of the present invention, a foundation pit support structure for a deep silt stratum, comprising bored cast-in-place piles 1 (i.e., support piles) arranged in rows and a water-stop curtain. The water-stop curtain comprises a plurality of jet grouting piles 2 arranged in rows in the silt layer and the upper stratum of the silt layer, and a plurality of swing jet grouting piles 3 arranged in rows in the lower stratum of the silt layer.

[0026] The aforementioned bored pile 1 was constructed using a rotary drilling rig. The bored pile 1 at the same location is concentric with the jet grouting pile 2 and the swing jet grouting pile 3. Adjacent jet grouting piles 2 interlock, adjacent swing jet grouting piles 3 interlock, and adjacent bored piles 1 do not interlock.

[0027] Specifically, the diameter D2 of either jet grouting pile 2 or swing grouting pile 3 shall not be less than the larger of the following two values:

[0028] D2≥D1+300

[0029] D²≥D+150

[0030] In the formula, D2 is the diameter of the jet grouting pile 2 or the swing grouting pile 3, D1 is the diameter of the bored pile 1, and D is the center distance between two adjacent bored piles 1. All units in the formula are millimeters.

[0031] The grouting pile 3 is grouting constructed with the center line of the pile row as the center. The grouting angle is ±arccos((D2-d) / D2); where D2 is the pile diameter of the grouting pile 3 and d is the overlap depth between two adjacent grouting piles 3.

[0032] In this embodiment, both the jet grouting pile 2 and the swing grouting pile 3 are constructed using the triple-pipe method. The triple-pipe method is a type of high-pressure jet grouting method, and its specific construction method is as follows: a triple grouting pipe is used to transport water, air and grout respectively. A cylindrical airflow surrounds the high-pressure water flow generated by a high-pressure pump or other high-pressure generating device. The high-pressure water flow and airflow are coaxially jetted and cut the soil, forming a large void. Then, a mud pump injects cement grout into the cut and broken foundation at a lower pressure. The nozzle rotates and lifts, causing the cement grout to mix with the soil and solidify in the soil, forming a large solidified body.

[0033] This embodiment also provides a construction method for the above-mentioned foundation pit support structure, including the following steps:

[0034] S1. Construction layout;

[0035] S2, rotary jet spraying, and swing jet spraying construction site tests were conducted to determine construction parameters;

[0036] S3, jet grouting pile 2 and swing jet grouting pile 3 construction pilot holes;

[0037] S4, jet grouting piles 2 and swing jet grouting piles 3 for constructing the water-stopping curtain;

[0038] S5. After the jet grouting pile 2 and the swing jet grouting pile 3 have initially solidified, the bored pile 1 is constructed using a rotary drilling rig.

[0039] The foundation pit support structure and construction method provided in this embodiment for deep silt strata combine the construction of the foundation pit water-stop curtain with the construction of bored piles 1 (i.e., support piles). First, the jet grouting piles 2 of the water-stop curtain are constructed and interlocked with each other. Then, a rotary drilling rig is used to construct bored piles 1 inside the jet grouting piles 2. The diameter of the jet grouting piles 2 is larger than that of the bored piles 1. The former serves as both a water-stop curtain and a temporary casing during the construction of the latter, thus serving two purposes with one pile. This reduces construction procedures and lowers project costs, and has good promotional value.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A foundation pit support structure for deep silt strata, characterized in that, It includes bored cast-in-place piles arranged in rows and a water-stop curtain; the water-stop curtain includes a number of jet grouting piles arranged in rows in the silt layer and the upper stratum of the silt layer, and a number of swing jet grouting piles arranged in rows in the lower stratum of the silt layer; the bored cast-in-place piles are constructed using a rotary drilling rig, and the bored cast-in-place piles, jet grouting piles, and swing jet grouting piles at the same location are concentric, wherein adjacent jet grouting piles overlap and interlock, adjacent swing jet grouting piles overlap and interlock, and adjacent bored cast-in-place piles do not interlock.

2. The foundation pit support structure as described in claim 1, characterized in that, The diameter D2 of the jet grouting pile or swing grouting pile shall not be less than the larger of the following two values: D2≥D1+300 D²≥D+150 In the formula, D2 is the diameter of the jet grouting pile or the swing grouting pile, D1 is the diameter of the bored pile, and D is the center distance between two adjacent bored piles. All units in the formula are millimeters.

3. The foundation pit support structure as described in claim 2, characterized in that, The jetting pile is constructed with the centerline of the pile row as the center, and the jetting angle is ±arccos((D2-d) / D2). In the formula, D2 is the diameter of the jet grouting pile, and d is the overlap depth between two adjacent jet grouting piles.

4. The foundation pit support structure as described in any one of claims 1 to 3, characterized in that, Both the jet grouting piles and the swing grouting piles are constructed using the triple-tube method.

5. A construction method for a foundation pit support structure as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Construction layout; S2, rotary jet spraying, and swing jet spraying construction site tests were conducted to determine construction parameters; S3, pilot holes for jet grouting piles and swing jet grouting piles; S4. Jet grouting piles and swing grouting piles for construction water-stop curtains; S5. After the jet grouting piles and swing jet grouting piles have initially solidified, rotary drilling rigs are used to construct bored cast-in-place piles.

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