Overlapping structure and construction method of two support systems in deep foundation pit in soft soil

Abstract

The present invention relates to an overlapping structure and construction method of two support systems in a soft soil deep foundation pit, wherein the two support systems are respectively an SMW method pile support system and a Larsen steel sheet pile support system, wherein the SMW method pile support system is composed of SMW method piles to form a method pile support wall, and the Larsen steel sheet pile support system is composed of Larsen steel sheet piles to form a steel sheet pile support wall, and at the junction of the method pile support wall and the steel sheet pile support wall, a pair of plain piles with a plurality of Larsen steel sheet piles is provided, and the Larsen steel sheet piles in the plain piles are used as overlapping steel sheet piles, wherein the overlapping steel sheet piles at the edge are engaged with the Larsen steel sheet piles at the edge of the steel sheet pile support wall. The overlapping structure and construction method can integrate the two support systems into a whole, effectively solve the leakage and support stability problems when different support structures are connected in a narrow and long deep foundation pit, prevent groundwater from seeping out from the gaps between adjacent retaining piles, and ensure the safety and stability of the foundation pit.

Description

Technical Field

[0001] The invention belongs to the field of foundation pit retaining structures of construction projects, and specifically relates to an overlapping structure of two supporting systems, SMW method piles and Larsen steel sheet piles, in a soft soil deep foundation pit and an overlapping construction method. Background Art

[0002] With the rapid development of urban pipe network systems, the excavation depth of underground space is getting deeper and deeper. The Larsen steel sheet pile support system and the SMW method pile support system are increasingly widely used due to their advantages of fast construction speed, convenient construction machinery, and obvious economic benefits. They are suitable for deep foundation pit support in soft soil areas such as coastal areas. When two support systems are used at the same time in the support of narrow and deep foundation pits, how to solve the leakage and support stability problems of the joints of the Larsen steel sheet pile support system and the SMW method pile support system during the construction process, ensure the construction safety of the narrow and deep foundation pit, and effectively avoid the collapse of the foundation pit due to leakage during the construction process. Therefore, how to deal with the joint problem caused by the cross-lap of the two support systems has become a major problem in the project. Summary of the invention

[0003] The purpose of the present invention is to provide a lap joint structure and a construction method for two support systems in a soft soil deep foundation pit, which can effectively solve the problems of leakage at the joint position of the two support systems and support stability.

[0004] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: a lap joint structure of two support systems in a soft soil deep foundation pit, wherein the two support systems are respectively an SMW method pile support system and a Larsen steel sheet pile support system, wherein the SMW method pile support system is composed of SMW method piles to form a method pile support wall, and the Larsen steel sheet pile support system is composed of Larsen steel sheet piles to form a steel sheet pile support wall, and at the junction of the method pile support wall and the steel sheet pile support wall, a pair of Larsen steel plates is provided. The Larsen steel sheet piles are plain piles, and the number of Larsen steel sheet piles is less than the number of plain piles; the Larsen steel sheet piles in the plain piles are used as lap steel sheet piles, wherein the lap steel sheet piles at the edge are engaged with the Larsen steel sheet piles at the edge of the steel sheet pile support wall; the excavation side of the steel sheet pile support wall is also provided with a surrounding purlin located on the upper part of the Larsen steel sheet pile, and the upper part of the SMW method piles in the method pile support wall is provided with a cap beam, and in the two support systems, a plurality of steel supports are respectively provided between the cap beams located on the opposite sides of the foundation pit and between the surrounding purlins.

[0005] The plain piles described include five concrete piles, and the overlapping steel sheet piles are provided in three pieces.

[0006] A construction method for overlapping two support systems in a soft soil deep foundation pit comprises the following steps:

[0007] Step 1: construct the SMW method pile support wall in the SMW method pile support system and the steel sheet pile support wall in the Larsen steel sheet pile support system of the foundation pit, and reserve a space for driving two SMW method piles at the position where the SMW method pile support wall and the steel sheet pile support wall meet;

[0008] Step 2: completing the driving of a SMW method pile near the already driven method pile supporting wall in the space, and then continuing to drive a plain pile in the direction of the steel sheet pile supporting wall;

[0009] Step 3: Continue to drive Larsen steel sheet piles one by one in the direction of the construction pile support wall at the already driven steel sheet pile support wall until reaching the plain pile driven in step 2;

[0010] Step 4: Apply friction reducer on the surface of Larsen steel sheet pile to be driven into the plain pile;

[0011] Step 5, drive the Larsen steel sheet piles brushed with friction reducer into the plain piles followed by the Larsen steel sheet piles that have been driven before the plain piles in step 3, and control the depth and verticality of the Larsen steel sheet piles according to the design requirements, wherein the Larsen steel sheet piles inside the plain piles at the edge and the Larsen steel sheet piles outside the plain piles support the edge of the wall and interlock with each other, thereby completing the overlap of the two support systems.

[0012] During the construction of the steel sheet pile supporting wall, a guide frame is arranged before the Larsen steel sheet piles are driven to ensure the verticality of the Larsen steel sheet piles. The guide frame is mainly composed of a guide beam and surrounding purlin piles.

[0013] When a construction cold joint is formed at the joint of the construction method pile support wall and the steel sheet pile support wall, supplementary piles are driven outside the construction method pile support wall at the construction cold joint position, and the overlap thickness of the supplementary piles and the construction method pile support wall is 10 cm.

[0014] When constructing the pile support wall, H-shaped steel is driven into the piles in the method of inserting two and jumping one. The "insert two and jump one method" means that among three consecutive piles, after H-shaped steel is driven into two adjacent piles, the other pile is used as an empty pile and no H-shaped steel is driven. Instead, H-shaped steel is driven into the fourth pile after the three consecutive piles, and so on.

[0015] The friction reducer is cold primer oil.

[0016] The beneficial effects of the present invention are as follows: first, after a plain pile at the joint of the two systems is driven into the Larsen steel sheet pile, the driven Larsen steel sheet pile can form an overlapping steel sheet pile, which is connected to the SMW method pile as a whole on the one hand, and is snap-fitted with other Larsen steel sheet piles to form a whole on the other hand. In this way, the Larsen steel sheet pile support system and the SMW method pile support system are formed into a whole, which can effectively solve the leakage and support stability problems when different support structures are connected in a narrow and deep foundation pit, prevent groundwater from seeping out from the gaps between adjacent retaining piles, and ensure the safety and stability of the foundation pit.

[0017] Second, the construction steps described in the present invention are simple and clear, and the construction method can improve work efficiency, shorten construction period, reduce foundation pit risks, avoid rework, and improve support construction quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A top view of the overlap structure of the present invention;

[0019] Figure 2 It is a partial schematic diagram of the top view of the overlapping position of two support systems of the present invention;

[0020] Figure 3 It is the process flow chart of SMW pile construction in the present invention;

[0021] Figure 4 It is a schematic diagram of the treatment of cold joints in SMW pile construction in the present invention;

[0022] Markings in the figure: 1. SMW method piles, 2. Larsen steel sheet piles, 3. Crown beams, 4. Peripheral purlins, 5. Steel supports, 6. H-shaped steel, 7. Plain piles, 8. Overlap steel sheet piles, 9. Supplementary plain piles, 10. Construction cold joints. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the invention in any way.

[0024] like Figure 1 , 2 As shown, the two support systems described in the overlapping structure of the two support systems in the soft soil deep foundation pit are the SMW method pile support system and the Larsen steel sheet pile support system. The SMW method pile support system is composed of SMW method piles 1 to form a method pile support wall, and the Larsen steel sheet pile support system is composed of Larsen steel sheet piles 2 to form a steel sheet pile support wall. The overlapping of the two support systems mainly refers to the overlapping between the two support walls. The overlapping structure is mainly: at the junction of the method pile support wall and the steel sheet pile support wall, a pair of plain piles 7 with multiple Larsen steel sheet piles 2 is provided, and the Larsen steel sheet piles 2 in the plain piles 7 are used as overlapping steel sheet piles 8, wherein the overlapping steel sheet piles 8 located at the edge are engaged with the Larsen steel sheet piles 2 at the edge of the steel sheet pile support wall.

[0025] In addition, a purlin 4 located on the top of the Larsen steel sheet pile 2 is provided on the excavation side of the steel sheet pile support wall, and a crown beam 3 is provided on the top of the SMW method pile 1 in the method pile support wall. In the two support systems, multiple steel supports 5 are respectively provided between the crown beams 3 and between the purlins 4 located on opposite sides of the foundation pit.

[0026] In the SMW pile construction, a five-axis pile mixer is used to drive the piles 7, so a pile consists of five concrete piles. To save costs, three Larsen steel sheet piles are driven in a pile at the overlap position.

[0027] See attached Figure 3 , 4 As shown, a method for constructing a lap joint structure of two support systems in a deep foundation pit of soft soil, wherein the two support systems are an SMW method pile support system and a Larsen steel sheet pile support system, and the specific steps are as follows:

[0028] (1) When constructing the SMW pile support system, follow Figure 3 The construction process shown in the figure uses a five-axis pile mixing machine to drive the pile 7. The first unit I is constructed first by a single-side extrusion method, and then the second unit II is constructed. The A axis of the second unit II is inserted into the E axis of the first unit I, and the side holes are overlapped. The following units (such as Figure 3 The size of the piles 7 constructed in the third unit III, fourth unit IV and fifth unit V is φ650;

[0029] (2) Within 30 minutes after the completion of the pile construction, insert the H-shaped steel 6 with the size of HM500×300×11×18mm. Before the H-shaped steel 6 is inserted, the anti-friction agent should be evenly applied. Before the H-shaped steel 6 is used, a central circular hole with a diameter of about 40mm is opened at a distance of 0.07m from its top, and two reinforcing plates with a thickness of 2cm are welded on both sides of the H-shaped steel 6. The specifications are 400mm×400mm, and the central opening of the reinforcing plate is aligned with the central circular hole of the H-shaped steel 6. According to the elevation control point, the design elevation is measured to the positioning steel with a level. According to the height difference between the positioning steel and the top elevation of the H-shaped steel 6, the hanger bars are welded on the outside of the two webs of the H-shaped steel 6, and the error is controlled within ±5cm;

[0030] (3) The surveying personnel determine the axis of the steel sheet pile supporting wall, and set guide piles at a certain interval. Then, ropes are hung between the guide piles as guide wires. The guide wires are used to control the axis of the steel sheet pile supporting wall during pile driving, and the verticality deviation of the Larsen steel sheet piles 2 on both sides is controlled within 0.5%, so that the Larsen steel sheet piles 2 can be well engaged with each other. When the Larsen steel sheet piles 2 are too deflected to be adjusted by the alignment method, they are pulled up and re-driven to ensure the verticality of the wall surface of the steel sheet pile supporting wall.

[0031] (4) A space with the length of two SMW method piles 1 is reserved at the joint between the steel sheet pile support wall formed by Larsen steel sheet piles 2 and the method pile support wall formed by SMW method piles 1, and then the first pile 7 is constructed following the already-installed SMW method piles 1 according to the construction process of step (1), and then H-shaped steels 6 are inserted into the first piles 7 in a two-insert-one-jump manner, and then the second piles 7 are constructed in the reserved space, and then the Larsen steel sheet piles 2 brushed with friction reducer are driven into the second piles 7, and the driving depth and verticality are controlled, and the Larsen steel sheet piles 2 driven into the piles 7 are used as overlapping steel sheet piles 8, and the overlapping steel sheet piles 8 at the edge of the second piles 7 are interlocked with the Larsen steel sheet piles 2 at the edge of the steel sheet pile support wall;

[0032] (5) After completing step (4), a double HW350 steel perimeter purlin 4 is constructed at the excavation side wall of the steel sheet pile support wall formed by the Larsen steel sheet piles 2. The perimeter purlin 4 can be supported by a steel calf, and the strength should meet the design requirements. The perimeter purlin 4 is reinforced and connected to the support wall formed by the Larsen steel sheet piles 2 by tie bars;

[0033] (6) After completing step (4), the crown beam 3 is constructed on the construction pile support wall formed by the SMW construction pile 1. After measurement and layout, the concrete above the bottom elevation of the crown beam 3 is chiseled off to expose the top surface of the H-shaped steel 6 and the lap steel sheet pile 8, with an exposed length of 1 m. Then, the inter-column layer is leveled and rolled, and then the cushion concrete of the crown beam 3 is poured, the steel bars of the crown beam 3 are tied, and then the side formwork is erected and the concrete is poured;

[0034] (7) Complete the construction of the two support systems on one side of the foundation pit according to the above steps (1) to (6), then repeat steps (1) to (6) to complete the construction of the support system on the opposite side of the foundation pit. Finally, when the foundation pit is excavated, install the steel support 5 between the support systems on both sides.

[0035] In the construction of the above step (4), if the pouring time interval of concrete exceeds the initial setting time, a construction cold joint 10 will be formed in the construction pile supporting wall, resulting in a weak joint surface at the connection between the front and rear concrete. In this case, the method adopts the method of constructing the outer side of the construction pile supporting wall at the construction cold joint 10. The scheme is as follows: Figure 4 The reinforcement pile 9 needs to be added after the SMW method pile 1 reaches a certain strength to prevent eccentric drilling and ensure the reinforcement effect. The overlap thickness of the reinforcement pile 9 and the method pile supporting wall is 10cm.

[0036] The following points should be noted during construction:

[0037] 1. The sinking and drilling speed of the five-axis mixer used in the construction of plain piles shall be controlled within 0.5-1m / min, and the lifting speed shall be controlled within 1-2m / min, and the sinking or lifting speed shall be maintained at a uniform speed, and the mixing and grouting shall be continued for 30s at the bottom of the pile. The verticality of the plain pile 7 shall not exceed 1 / 200, and the pile position layout error shall not exceed 20mm.

[0038] 2. Before construction, dirt and rust on the surface of H-shaped steel 6 and Larsen steel sheet pile 2 must be removed. Use an electric heating rod to heat the anti-friction agent until it is completely melted, and stir it with a mixer until the thickness is even before applying it to the surface of H-shaped steel 6 and Larsen steel sheet pile 2. If it rains and the surface is wet, first wipe off the surface water with a rag, then heat and dehumidify, and when it is dry, apply the anti-friction agent. The anti-friction agent can be cold primer oil.

[0039] 3. When inserting H-shaped steel 6, the left and right error shall not be greater than 30mm, and it should be inserted close to the side of the foundation pit. The verticality deviation shall not be greater than 1 / 150, and the bottom elevation error shall not be greater than 200mm.

[0040] 4. In order to facilitate the extraction of the H-shaped steel 6, the H-shaped steel 6 anchored in the crown beam 3 must be wrapped with a 10 mm thick foam plastic sheet to ensure that the H-shaped steel 6 is well isolated from the concrete.

[0041] 5. Lubrication and anti-seepage measures for the lock of Larsen steel sheet pile 2: For the Larsen steel sheet pile 2 that has passed the inspection, in order to ensure that the Larsen steel sheet pile 2 can be smoothly inserted and removed during the construction process and to increase the anti-seepage performance of the Larsen steel sheet pile 2 when in use, the lock of each Larsen steel sheet pile 2 must be evenly coated with mixed oil.

[0042] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Those skilled in the art should understand that the specific implementation modes of the present invention may be modified or replaced by equivalents with reference to the above embodiments. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the pending claims.

Claims

1. An overlapping structure of two support systems in a soft soil deep foundation pit, wherein the two support systems are an SMW method pile support system and a Larsen steel sheet pile support system, wherein the SMW method pile support system comprises an SMW method pile support wall, and the Larsen steel sheet pile support system comprises a Larsen steel sheet pile support wall, wherein: At the junction of the construction method pile support wall and the steel sheet pile support wall, there is a plain pile with multiple Larsen steel sheet piles, and the number of Larsen steel sheet piles is less than the number of plain piles; the Larsen steel sheet piles in the plain piles are used as overlapping steel sheet piles, wherein the overlapping steel sheet piles at the edge are engaged with the Larsen steel sheet piles at the edge of the steel sheet pile support wall; the excavation side of the steel sheet pile support wall is also provided with a surrounding purlin located on the upper part of the Larsen steel sheet pile, and the upper part of the SMW construction method pile in the construction method pile support wall is provided with a crown beam, and in the two support systems, a plurality of steel supports are respectively provided between the crown beams and between the surrounding purlins located on opposite sides of the foundation pit; Filling piles are driven into the cold joints at the joints of the construction method pile support wall and the steel sheet pile support wall, and the filling piles are located outside the construction method pile support wall.

2. The overlapping structure of two support systems in a soft soil deep foundation pit according to claim 1 is characterized in that: The plain piles described include five concrete piles, and the overlapping steel sheet piles are arranged in three pieces.

3. A construction method for overlapping two support systems in a soft soil deep foundation pit to obtain the overlapping structure according to claim 1, characterized in that: The steps include: Step 1: construct the SMW method pile support wall in the SMW method pile support system and the steel sheet pile support wall in the Larsen steel sheet pile support system of the foundation pit, and reserve a space for driving two SMW method piles at the position where the SMW method pile support wall and the steel sheet pile support wall meet; Step 2: completing the driving of a SMW method pile near the already driven method pile supporting wall in the space, and then continuing to drive a plain pile in the direction of the steel sheet pile supporting wall; Step 3: Continue to drive Larsen steel sheet piles one by one in the direction of the construction pile support wall at the already driven steel sheet pile support wall until reaching the plain pile driven in step 2; Step 4: Apply friction reducer on the surface of Larsen steel sheet pile to be driven into the plain pile; Step 5, drive the Larsen steel sheet piles brushed with friction reducer into the plain piles followed by the Larsen steel sheet piles that have been driven before the plain piles in step 3, and control the depth and verticality of the Larsen steel sheet piles according to the design requirements, wherein the Larsen steel sheet piles inside the plain piles at the edge and the Larsen steel sheet piles outside the plain piles support the edge of the wall and interlock with each other, thereby completing the overlap of the two support systems.

4. The construction method for overlapping two support systems in a soft soil deep foundation pit according to claim 3 is characterized in that: During the construction of the steel sheet pile supporting wall, a guide frame is arranged before the Larsen steel sheet piles are driven to ensure the verticality of the Larsen steel sheet piles. The guide frame is mainly composed of a guide beam and surrounding purlin piles.

5. The construction method for overlapping two support systems in a soft soil deep foundation pit according to claim 3, characterized in that: When a construction cold joint is formed at the joint of the construction method pile support wall and the steel sheet pile support wall, supplementary piles are driven outside the construction method pile support wall at the construction cold joint position, and the overlap thickness of the supplementary piles and the construction method pile support wall is 10 cm.

6. The construction method for overlapping two support systems in a soft soil deep foundation pit according to claim 3, characterized in that: When carrying out the construction of pile support wall, H-shaped steel is driven into the piles in the method of inserting two and jumping one.

7. The construction method for overlapping two support systems in a soft soil deep foundation pit according to claim 3, characterized in that: The friction reducer is cold primer oil.

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