Non-inner support support system and construction method for super-large foundation pit in soft soil area

Abstract

The present invention relates to a non-inner support support system for an ultra-large-sized foundation pit in a soft soil area and a construction method thereof, wherein the non-inner support support system comprises: a plurality of groups of oblique and straight pile groups arranged side by side at intervals along the direction of the foundation pit boundary line on the inner side of the foundation pit; a plurality of cast-in-place piles arranged side by side at intervals along the direction of the foundation pit boundary line on the inner side of the oblique and straight pile group, wherein the top of the cast-in-place pile is lower than the top of the oblique and straight pile group and higher than the bottom of the oblique and straight pile group; a plurality of rotary jet piles connected one-to-one with the plurality of cast-in-place piles, wherein the top of the rotary jet pile is connected to the top of the cast-in-place pile, and the bottom of the rotary jet pile is inclined toward the bottom of the relative oblique and straight pile group. The non-inner support support system of the present invention can make full use of the strength advantage combination of multi-level support, reduce the construction period and cost of the internal support structure on the premise of ensuring the safety of the foundation pit, and avoid material waste at the same time, which is green and environmentally friendly.

Description

Technical Field

[0001] The invention relates to the field of foundation pit construction, and in particular to an internal support-free support system for an ultra-large foundation pit in a soft soil area and a construction method thereof. Background Art

[0002] In the construction environment of soft soil foundation, the soil around the foundation pit is unstable, and the lateral soil pressure on the foundation pit support structure is large, which has an obvious "time and space effect". The safety risk of ultra-large deep foundation pits is high, and a combined support system combining connected walls or cast-in-place support piles with internal support structures is usually adopted.

[0003] When adopting the above-mentioned combined support system, a large number of internal support structures (such as supports and guard beams, etc.) need to be installed on the inner side of the foundation pit to ensure the safety of the foundation pit. However, the installation of the internal support structure requires a lot of manpower and material resources. In addition, the internal support structure and the main structure intersect, so that during the construction of the main structure, the main structure must pass through the internal support structure for construction, causing inconvenience in construction. The next step of construction must wait until the internal support structure is dismantled and temporary support is added before it can be carried out, which prolongs the construction period. In addition, in some engineering construction projects with strict requirements, due to the special requirements of the process for structural integrity, it is impossible to realize the vertical components passing through the internal support support, which does not meet the actual construction requirements.

[0004] Therefore, there is an urgent need for a non-inner support support system that can avoid the construction inconvenience caused by the main structure passing through the internal support structure, ensure the safety of the foundation pit, and is suitable for the soft soil foundation construction environment. Summary of the invention

[0005] The purpose of the present invention is to provide a non-inner support support system and its construction method under the condition of an ultra-large foundation pit in a soft soil area, which can fully utilize the strength advantage combination of multi-level supports, reduce the construction period and cost of the internal support structure while ensuring the safety of the foundation pit, and at the same time avoid material waste and be green and environmentally friendly.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions: a non-inner support support system for ultra-large foundation pits in soft soil areas, comprising:

[0007] A plurality of groups of inclined and vertical piles are arranged side by side at intervals on the inner side of the foundation pit along the direction of the foundation pit edge line;

[0008] A plurality of cast-in-place piles are arranged side by side at intervals along the direction of the foundation pit edge on the inner side of the inclined and straight pile group, wherein the top of the cast-in-place pile is lower than the top of the inclined and straight pile group and higher than the bottom of the inclined and straight pile group;

[0009] A plurality of rotary jet piles are connected one-to-one with the plurality of cast-in-place piles, the tops of the rotary jet piles are connected with the tops of the cast-in-place piles, and the bottoms of the rotary jet piles are inclined toward the bottoms of the opposite oblique and straight pile groups.

[0010] The present invention adopts an inclined straight pile group as the primary support to replace the traditional internal support structure. At the same time, taking into account the needs of ultra-large and ultra-deep foundation pits, the insufficient strength of the primary support is compensated, and cast-in-place piles and rotary jet piles are used as secondary supports to cooperate with the primary support to jointly form a support system without internal support; at the same time, through the inclined spray anchors of the rotary jet piles, the effective combination of the primary support and the secondary support is realized, the resistance of the support system without internal support to the lateral pressure of the soil is increased, and the support without internal support for ultra-large foundation pits is met; in addition, under the premise of ensuring the stability and safety of the entire support system, the continuity of the main structure construction is not affected, the construction period and cost of the traditional internal support structure are reduced, material waste is avoided, and green and environmental protection is achieved.

[0011] A further improvement of the non-inner support system for super-large foundation pits in soft soil areas of the present invention is that the inclined vertical pile group includes a first precast pile and a second precast pile, the first precast pile is arranged in a vertical direction, the top of the second precast pile is closed and fixed to the top of the first precast pile, and the bottom of the second precast pile is inclined toward the direction of the cast-in-place pile.

[0012] A further improvement of the non-inner support system for super-large foundation pits in soft soil areas of the present invention is that the bottom of the second prefabricated pile is inclined 18° to 22° toward the direction of the cast-in-place pile.

[0013] The further improvement of the non-inner support system for ultra-large foundation pits in soft soil areas of the present invention is:

[0014] The plurality of rotary jet piles include a plurality of short rotary jet piles and a plurality of long rotary jet piles arranged at intervals;

[0015] The bottom of the short rotary jet pile is located below and inside the second precast pile;

[0016] The bottom of the long jet grouting pile is located between the lower sides of the second precast pile and the first precast pile.

[0017] A further improvement of the non-inner support system for super-large foundation pits in soft soil areas of the present invention is that multiple rows of engineering piles are arranged on the inner side of the cast-in-place piles, the tops of the engineering piles are located at the bottom of the foundation pit and are lower than the tops of the cast-in-place piles, and a counter-pressure cushion layer is laid on the bottom of the foundation pit, and the counter-pressure cushion layer is combined with the cast-in-place piles and at least one row of the engineering piles.

[0018] The present invention also provides a construction method for an ultra-large foundation pit in a soft soil area without an internal support support system, comprising the following steps:

[0019] Before excavating the foundation pit, multiple groups of inclined and vertical piles are arranged side by side at intervals along the direction of the foundation pit edge line on the inner side of the foundation pit, and multiple cast-in-place piles are arranged side by side at intervals along the direction of the foundation pit edge line on the inner side of the multiple groups of inclined and vertical piles, so that the top of the cast-in-place pile is lower than the top of the inclined and vertical pile group and higher than the bottom of the inclined and vertical pile group;

[0020] Excavating earth to the top of the inclined vertical pile group;

[0021] Excavating earth to the top of the cast-in-place pile;

[0022] At each of the cast-in-place piles, the bottom of the jet-jet pile is inclined relative to the bottom of the inclined vertical pile group.

[0023] The further improvement of the construction method of the super-large foundation pit without internal support system in soft soil area of ​​the present invention is:

[0024] The inclined straight pile group includes a first precast pile and a second precast pile, the first precast pile is arranged in a vertical direction, the top of the second precast pile is closed and fixed with the top of the first precast pile, and the bottom of the second precast pile is inclined toward the cast-in-place pile;

[0025] When the earthwork is excavated to the top of the cast-in-place pile, excavation is performed along the inclined direction of the second precast pile.

[0026] A further improvement of the construction method of the extra-large foundation pit without internal support support system in soft soil area of ​​the present invention is that a plurality of short rotary jet piles and a plurality of long rotary jet piles are arranged for each of the piles, and the bottom of the short rotary jet pile is located on the inner side below the second precast pile, and the bottom of the long rotary jet pile is located between the second precast pile and the first precast pile.

[0027] The further improvement of the construction method of the super-large foundation pit without internal support system in soft soil area of ​​the present invention is:

[0028] After excavating the earthwork to the top of the inclined and vertical pile groups, constructing a first-level cap beam on the top of the plurality of inclined and vertical pile groups;

[0029] After the strength of the first-level cap beam reaches the construction requirement, excavating the earth to the top of the cast-in-place pile;

[0030] After the strength of the jet grouting piles reaches the construction requirements, a secondary cap beam is constructed on the top of a plurality of cast-in-place piles connected to the jet grouting piles.

[0031] The further improvement of the construction method of the super-large foundation pit without internal support system in soft soil area of ​​the present invention is:

[0032] Before excavating the foundation pit, multiple rows of engineering piles are arranged inside the inclined and vertical pile groups, so that the tops of the engineering piles are located at the bottom of the foundation pit and lower than the tops of the cast-in-place piles;

[0033] After the strength of the cap beam reaches the construction requirement, excavating earth to the top of the engineering pile;

[0034] A counter-pressure cushion layer is laid on the bottom surface of the foundation pit, so that the counter-pressure cushion layer is combined with the cast-in-place piles and at least one row of the engineering piles. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a plan view of the pile body before excavating the foundation pit in the construction method of the present invention.

[0036] Figure 2 yes Figure 1 The front cross-sectional view of the pile at position AA before excavation of the foundation pit.

[0037] Figure 3 yes Figure 1 The front cross-sectional view at AA in the middle when excavation reaches the top of the inclined vertical pile group.

[0038] Figure 4 yes Figure 1 The front cross-sectional view at AA in the middle is when the excavation reaches the top of the cast-in-place pile.

[0039] Figure 5 It is a plan view of the overall structure of the support system of the present invention.

[0040] Figure 6 yes Figure 5 The front section view at position BB during the construction of short rotary jet piles.

[0041] Figure 7 yes Figure 5 The front section view of the CC position during the construction of long rotary jet grouting piles.

[0042] Figure 8 yes Figure 5 The front cross-sectional view of the CC in the middle during the construction of the counter-pressure cushion. DETAILED DESCRIPTION

[0043] In order to solve the problems that the traditional internal support combined support system causes inconvenience in the construction of the main structure due to the intersection with the main structure, prolongs the construction period, cannot meet the special requirements for structural integrity, and requires a lot of manpower and material resources, the present invention provides a non-internal support support system and its construction method under the conditions of super-large foundation pits in soft soil areas, which can make full use of the strength advantage combination of multi-level supports, reduce the construction period and cost of the internal support structure while ensuring the safety of the foundation pit, and at the same time avoid material waste, which is green and environmentally friendly.

[0044] The following is a further description of the non-inner support support system for ultra-large foundation pits in soft soil areas and the construction method thereof in conjunction with the accompanying drawings.

[0045] See also Figures 5 to 8 As shown, a non-inner support system for a large foundation pit in a soft soil area includes:

[0046] A plurality of groups of inclined and vertical pile groups 20 are arranged side by side at intervals on the inner side of the foundation pit along the direction of the foundation pit edge line 10;

[0047] A plurality of cast-in-place piles 31 are arranged side by side at intervals on the inner side of the inclined and straight pile group 20 along the direction of the foundation pit edge line 10, and the top of the cast-in-place pile 31 is lower than the top of the inclined and straight pile group 20 and higher than the bottom of the inclined and straight pile group 20;

[0048] A plurality of rotary jet piles 32 are connected one-to-one with the plurality of cast-in-place piles 31 , the top of each rotary jet pile 32 is connected with the top of each cast-in-place pile 31 , and the bottom of each rotary jet pile 32 is inclined toward the bottom of the opposite oblique straight pile group 20 .

[0049] Specifically, for deep foundation pit construction, in order to prevent or reduce the inflow of groundwater from the side walls and bottom of the foundation pit, a circle of three-axis mixing piles 12 (i.e., a water-stop curtain) is usually set at the position of the foundation pit edge 10, and two circles of dewatering wells are successively set from the water-stop curtain to the inside of the foundation pit, i.e., a first dewatering well 13 and a second dewatering well 14; in order to facilitate the observation of the dewatering conditions in the foundation pit, a circle of observation wells 11 is usually set outside the foundation pit edge 10; in this embodiment, the inclined straight pile group 20 and the cast-in-place pile 31 are set at a position between the first dewatering well 13 and the second dewatering well 14, and two construction platforms, i.e., a first platform H1 and a second platform H2, are formed by the height difference between the tops of the inclined straight pile group 20 and the cast-in-place pile 31.

[0050] The inclined straight pile group 20 in this embodiment serves as a primary support, and includes a first precast pile 21 and a second precast pile 22, both of which are precast rectangular piles. The first precast pile 21 is arranged in the vertical direction, the top of the second precast pile 22 is closed and fixed with the top of the first precast pile 21, and the bottom of the second precast pile 22 is inclined toward the cast-in-place pile 31; the inclined straight pile group 20 effectively utilizes the advantages of the good compressive strength of the first precast pile 21 and the good lateral stiffness of the second precast pile 22, and because the first precast pile 21 in the vertical direction is perpendicular to the foundation pit edge line 10, the lateral stiffness is further increased, so as to minimize the risk of poor lateral stiffness of the precast pile as a foundation pit support system;

[0051] Since the maximum length of a prefabricated rectangular pile is usually only 12m, for ultra-large-scale and ultra-deep foundation pits, the primary support alone cannot meet the requirements. In order to make up for the insufficient strength of the primary support, the present embodiment adopts cast-in-place piles 31 as secondary supports to cooperate with the primary support; at the same time, through the inclined spraying anchors of the rotary jet piles 32, the primary support and the secondary support are effectively combined, the resistance of the non-inner support support system to the lateral pressure of the soil is increased, and the non-inner support support for ultra-large-scale foundation pits is met; in addition, under the premise of ensuring the stability and safety of the entire support system, the continuity of the main structure construction is not affected, the construction period and cost of the traditional internal support structure are reduced, material waste is avoided, and it is green and environmentally friendly.

[0052] As a preferred embodiment: the bottom of the second precast pile 22 is inclined at an angle O of 18° to 22° toward the cast-in-place pile 31. The angle O is determined comprehensively based on the actual size of the foundation pit and the softness of the soil, so that when excavating the second platform H2, excavation can be carried out along the second precast pile 22 to ensure the strength of the slope.

[0053] As a preferred embodiment: the plurality of rotary jet piles 32 include a plurality of short rotary jet piles 321 and a plurality of long rotary jet piles 322 arranged at intervals, and the short rotary jet piles 321 and the long rotary jet piles 322 can be alternately connected to the corresponding cast-in-place piles 31 at intervals; the bottom of the short rotary jet pile 321 is located on the inner side below the second precast pile 22; the bottom of the long rotary jet pile 322 is located between the second precast pile 22 and the bottom of the first precast pile 21.

[0054] The long and short jet grouting piles 32 can effectively avoid the combined weakening effect of the primary support and the secondary support at the connecting position, and also avoid the risk of continuous collapse of multiple jet grouting piles 32 to the greatest extent.

[0055] As a preferred embodiment: a plurality of rows of engineering piles 40 are arranged on the inner side of the cast-in-place piles 31, the tops of the engineering piles 40 are located at the bottom of the foundation pit (i.e., the third platform H3) and are lower than the tops of the cast-in-place piles 31, and the bottom of the foundation pit is paved with a back-pressure cushion layer 50, which is combined with the cast-in-place piles 31 and at least one row of the engineering piles 40.

[0056] Specifically: in order to prevent or reduce the groundwater in the main structure construction area from flowing into the foundation pit, the engineering piles 40 in this embodiment are arranged inside the second dewatering well 14;

[0057] By combining the back pressure pad layer 50 with the cast-in-place piles 31 and at least one row of the engineering piles 40, a back pressure plate belt with strong lateral stiffness is formed, which reduces the unsupported exposure time of the foundation pit, reduces the "time and space effect" in soft soil areas, and ensures the safety of the foundation pit. Further, in order to ensure the lateral stiffness of the back pressure plate belt, the back pressure pad layer 50 is preferably 8m to 10m wide and not less than 250mm thick in this embodiment.

[0058] The present invention also provides a construction method for an ultra-large foundation pit in a soft soil area without an internal support support system, comprising the following steps:

[0059] Step 1: Read Figure 1 and Figure 2 As shown, pile construction is carried out before excavating the foundation pit, and multiple groups of inclined and straight pile groups 20 are arranged side by side at intervals along the direction of the foundation pit boundary line 10 on the inner side of the foundation pit; multiple cast-in-place piles 31 are arranged side by side at intervals along the direction of the foundation pit boundary line 10 on the inner side of the multiple groups of inclined and straight pile groups 20, so that the top of the cast-in-place pile 31 is lower than the top of the inclined and straight pile group 20 and higher than the bottom of the inclined and straight pile group 20.

[0060] Specifically, the pile construction starts at the original ground 10, and the inclined straight pile group 20 and the cast-in-place pile 31 are driven into the original ground 10 according to the designated position; the constructed pile body includes, in addition to the inclined straight pile group 20 and the cast-in-place pile 31, an observation well 11 located outside the foundation pit, a three-axis mixing pile 12 arranged along the foundation pit deformation 10, a first dewatering well 13 located between the three-axis mixing pile 12 and the inclined straight pile group 20, and a second dewatering well 14 located inside the cast-in-place pile 31.

[0061] Step 2: See Figure 3 and Figure 4 As shown, the earth is excavated to the top of the inclined vertical pile group 20.

[0062] Specifically, the earth is excavated to the top of the inclined vertical pile group 20 to form a first platform H1, and a first-level cap beam 23 is constructed at the first platform H1 to connect the tops of multiple groups of inclined vertical pile groups 20 into a whole along the direction of the foundation pit edge 10 to form a first-level support.

[0063] Step 3: Read Figure 4 As shown, after the strength of the primary cap beam 23 reaches the construction requirement, earth is excavated to the top of the cast-in-place pile 31 to form a second platform H2.

[0064] Step 4: Read Figures 5 to 8 As shown, a jet grouting pile 32 is provided at each of the cast-in-place piles 31, and the top of the jet grouting pile 32 is connected to the top of the cast-in-place pile 31, so that the bottom of the jet grouting pile 32 is inclined relative to the bottom of the inclined straight pile group 20. A secondary cap beam 33 is constructed at the top of the plurality of cast-in-place piles 31 connected with the jet grouting piles 32.

[0065] Specifically, the jet grouting piles 32 are installed by jet grouting anchor cables, and concrete is sprayed from the top of each cast-in-place pile 31 toward the bottom of the relative oblique and straight pile group 20 to form a plurality of jet grouting piles 32 connected one-to-one with the plurality of cast-in-place piles 31, and the bottom of the jet grouting piles 32 is close to the bottom position of the support, so that the oblique and straight pile group 20 is effectively combined with the cast-in-place piles 31; after the jet grouting anchor cable construction is completed and tested to be qualified, a secondary cap beam 33 is constructed at the second platform H2 to connect the tops of the plurality of cast-in-place piles 31 with the jet grouting piles 32 into a whole along the direction of the foundation pit edge 10 to form a secondary support; through the combination of the primary support and the secondary support, the internal support system is formed together.

[0066] As a preferred embodiment: the inclined straight pile group 20 includes a first precast pile 21 and a second precast pile 22, the first precast pile 21 is arranged in the vertical direction, the top of the second precast pile 22 is closed and fixed with the top of the first precast pile 21, and the bottom of the second precast pile 22 is inclined toward the cast-in-place pile 31, and the inclination angle O is preferably 18° to 22°;

[0067] When performing step 3, earth is excavated along the inclined direction of the second precast pile 22 to the top of the cast-in-place pile 31 to ensure the slope strength of the second platform H2.

[0068] As a preferred embodiment: Figures 5 to 7 As shown, when the jet grouting pile 32 is installed at each cast-in-place pile 31, a plurality of short jet grouting piles 321 and a plurality of long jet grouting piles 322 are arranged at intervals, and the bottom of the short jet grouting pile 321 is located at the lower inner side relative to the second precast pile 22, and the bottom of the long jet grouting pile 322 is located between the lower side of the second precast pile 22 and the first precast pile 21.

[0069] Specifically, the short rotary jet grouting pile 321 and the long rotary jet grouting pile 322 have the same inclination direction and only have different injection lengths. The two can be alternately arranged at a one-to-one ratio, or at a one-to-many or many-to-one ratio. The specific ratio is determined comprehensively according to the actual foundation pit size and the softness of the soil.

[0070] The long and short jet grouting piles 32 can effectively avoid the combined weakening effect of the primary support and the secondary support at the connecting position, and also avoid the risk of continuous collapse of multiple jet grouting piles 32 of the secondary support to the greatest extent.

[0071] As a preferred embodiment:

[0072] When performing step 1, multiple rows of engineering piles 40 are arranged inside the inclined and vertical pile group 20, so that the tops of the engineering piles 40 are located at the bottom of the foundation pit and lower than the tops of the cast-in-place piles 31;

[0073] After the strength of the secondary cap beam 33 reaches the construction requirements, refer to Figure 8 As shown, continue to excavate the earth until the top of the engineering pile 40 to form a third platform H3 (i.e., flush with the bottom of the foundation pit);

[0074] A back pressure cushion layer 50 is laid on the bottom surface of the foundation pit, so that the back pressure cushion layer 50 is combined with the cast-in-place piles 31 and at least one row of the engineering piles 40.

[0075] Specifically, in order to prevent or reduce the groundwater in the main structure construction area from flowing into the foundation pit, the engineering piles 40 in this embodiment are arranged inside the second dewatering well 14;

[0076] After excavating the earth to the top of the engineering pile 40 (i.e., the bottom elevation of the foundation pit), a single-layer bidirectional steel bar with a thickness of not less than 250 mm is set in the ring width area 8m to 10m away from the secondary support (covering at least one row of engineering piles 40) to form a thickened reinforced cushion layer (the top elevation of the cushion layer meets the original requirements), wherein the diameter of the steel bar is preferably 14mm. When setting the thickened reinforced cushion layer, it is combined with the steel bars of the existing engineering piles 40 to form a back-pressure plate belt with strong lateral stiffness, and then concrete is poured to form a back-pressure cushion layer 50 combined with the secondary support and at least one row of the engineering piles 40.

[0077] By providing the counter-pressure cushion layer 50, the unsupported exposure time of the foundation pit is reduced, the "time-space effect" in soft soil areas is reduced, and the safety of the foundation pit is ensured.

[0078] The present invention is described in detail above in conjunction with the embodiments of the accompanying drawings. A person skilled in the art can make various variations of the present invention according to the above description. Therefore, certain details in the embodiments should not constitute a limitation of the present invention, and the scope of protection of the present invention shall be defined by the scope of the attached claims.

Claims

1. A non-inner support system for ultra-large foundation pits in soft soil areas, characterized in that: include: A plurality of groups of inclined and vertical piles are arranged side by side at intervals on the inner side of the foundation pit along the direction of the foundation pit edge line; A plurality of cast-in-place piles are arranged side by side at intervals along the direction of the foundation pit edge on the inner side of the inclined and straight pile group, wherein the top of the cast-in-place pile is lower than the top of the inclined and straight pile group and higher than the bottom of the inclined and straight pile group; A plurality of rotary jet piles connected one-to-one with a plurality of cast-in-place piles, the top of each rotary jet pile is connected with the top of each cast-in-place pile, and the bottom of each rotary jet pile is inclined toward the bottom of the opposite oblique vertical pile group; wherein, The inclined straight pile group includes a first precast pile and a second precast pile, the first precast pile is arranged in a vertical direction, the top of the second precast pile is closed and fixed with the top of the first precast pile, and the bottom of the second precast pile is inclined 18° to 22° toward the direction of the cast-in-place pile; The plurality of rotary jet piles include a plurality of short rotary jet piles and a plurality of long rotary jet piles arranged at intervals; the bottom of the short rotary jet pile is located on the inner side below the second precast pile; the bottom of the long rotary jet pile is located between the second precast pile and the first precast pile.

2. The non-inner support system for ultra-large foundation pits in soft soil areas according to claim 1, characterized in that: A plurality of rows of engineering piles are arranged inside the cast-in-place piles, the tops of the engineering piles are located at the bottom of the foundation pit and are lower than the tops of the cast-in-place piles, a back-pressure cushion is laid on the bottom of the foundation pit, and the back-pressure cushion is combined with the cast-in-place piles and at least one row of the engineering piles.

3. A construction method for a super-large foundation pit in a soft soil area without an internal support system, characterized in that: The steps include: Before excavating the foundation pit, multiple groups of inclined and vertical piles are arranged side by side at intervals along the direction of the foundation pit edge line on the inner side of the foundation pit, and multiple cast-in-place piles are arranged side by side at intervals along the direction of the foundation pit edge line on the inner side of the multiple groups of inclined and vertical piles, so that the top of the cast-in-place pile is lower than the top of the inclined and vertical pile group and higher than the bottom of the inclined and vertical pile group; Excavating earth to the top of the inclined vertical pile group; Excavating earth to the top of the cast-in-place pile; A jet grouting pile is arranged at each of the cast-in-place piles, and the top of the jet grouting pile is connected to the top of the cast-in-place pile, and the bottom of the jet grouting pile is inclined relative to the bottom of the inclined vertical pile group; wherein, The inclined straight pile group includes a first precast pile and a second precast pile, the first precast pile is arranged in a vertical direction, the top of the second precast pile is closed and fixed with the top of the first precast pile, and the bottom of the second precast pile is inclined toward the cast-in-place pile; When the earthwork is excavated to the top of the cast-in-place pile, excavation is performed along the inclined direction of the second precast pile; When arranging the jet grouting piles at each of the cast-in-place piles, a plurality of short jet grouting piles and a plurality of long jet grouting piles are arranged at intervals, and the bottom of the short jet grouting pile is located on the inner side below the second precast pile, and the bottom of the long jet grouting pile is located between the second precast pile and the first precast pile.

4. The construction method of the super-large foundation pit without internal support system in soft soil area as claimed in claim 3, characterized in that: After excavating the earthwork to the top of the inclined and vertical pile groups, constructing a first-level cap beam on the top of the plurality of inclined and vertical pile groups; After the strength of the first-level cap beam reaches the construction requirement, excavating the earth to the top of the cast-in-place pile; After the strength of the jet grouting piles reaches the construction requirements, a secondary cap beam is constructed on the top of a plurality of cast-in-place piles connected to the jet grouting piles.

5. The construction method of the super-large foundation pit without internal support system in soft soil area as claimed in claim 4, characterized in that: Before excavating the foundation pit, multiple rows of engineering piles are arranged inside the inclined and vertical pile groups, so that the tops of the engineering piles are located at the bottom of the foundation pit and lower than the tops of the cast-in-place piles; After the strength of the secondary cap beam reaches the construction requirement, excavating earth to the top of the engineering pile; A counter-pressure cushion layer is laid on the bottom surface of the foundation pit, so that the counter-pressure cushion layer is combined with the cast-in-place piles and at least one row of the engineering piles.

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