RJP construction method for ultra-thick and dense sand layers in offshore areas

Abstract

The invention discloses a RJP construction method for ultra-thick dense sand layers in offshore areas, comprising the following steps: 1: after the construction of cast-in-place piles (1), deep dry mixing is performed between adjacent cast-in-place piles; 2: a prestressed cable body is mounted on the drill bit of an RJP drilling rig and drilled along with the drill bit; 3: the prestressed cable body is anchored after the drill bit drills to a designed depth; 4: the drill rod is lifted and grouting is performed using an RJP high-pressure jet grouting process to form an RJP high-pressure jet grouting anchoring section (21), which is engaged with the cast-in-place pile to form a retaining pile; 5: grouting is stopped, sand and gravel are backfilled in the hole to form an RJP high-pressure jet grouting free section (22), and the RJP drilling rig is moved to the next pile position; 6: steps 1-5 are repeated until the retaining pile is completed; 7: the retaining pile heads are connected to form a whole through a crown beam (3), and the other end of the prestressed cable body is anchored on the crown beam. The invention can solve the problem of easy leakage at the interlocking joints of the mortar pile and the cast-in-place pile in the prior art.

Description

Technical Field

[0001] The present invention relates to a foundation pit support construction method, in particular to a Rodin Jet Pile (RJP) construction method for ultra-thick and dense sand layers in offshore areas. Background Art

[0002] When constructing deep foundation pits using open-cut methods in areas with thick sand layers and abundant groundwater, a rigid, water-stopping peripheral support structure is often required to ensure stability and safety. Furthermore, excavation is performed to the bottom of the pit using a support-before-excavation approach, with dynamic monitoring. The main structure is then constructed from the bottom up. Upon completion of the structural work, the temporary support system is removed.

[0003] Among them, bored cast-in-place interlocking piles are a commonly used support structure system, characterized by high rigidity and excellent soil-retaining and water-stopping properties. However, during construction, the pile diameter and pile position can vary significantly. The interlocking areas between piles are particularly disturbed by the cast-in-place pile construction, making construction quality difficult to ensure and often becoming a major potential source of water leakage. Bored cast-in-place interlocking piles are divided into concrete cast-in-place piles B with reinforced cages and unreinforced mortar cast-in-place piles A. During construction, mortar piles A must be constructed first, and bored cast-in-place piles B must be completed before they begin to set. The drill bit is then used to cut the sides of mortar piles A before concrete is poured to achieve the interlocking effect.

[0004] As a crucial sealing and connecting structure in bored cast-in-place interlocking piles, the construction quality and integrity of mortar piles are of paramount importance, impacting the water-stopping effect of the retaining structure. However, due to the construction sequence, as interlocking piles require mortar piles to be constructed first, followed by reinforced concrete cast-in-place piles, the mortar piles are inevitably disturbed and subject to defects during construction, making it impossible to guarantee the quality of the joints. Therefore, the joints between the mortar piles and cast-in-place piles become the most vulnerable points in bored cast-in-place interlocking piles, which are prone to leakage. Furthermore, large voids caused by vertical deviations between the pile bodies, if not densely filled with concrete during the cast-in-place pile pouring process, can lead to leakage during later excavation. Larger voids are often accompanied by water and sand gushing, and in severe cases, can even cause foundation pit instability.

[0005] Therefore, it is necessary to provide a RJP construction method for ultra-thick and dense sand layers in offshore areas, which can solve the problem of easy leakage at the bite joints of mortar piles and cast-in-place piles in the existing technology. Summary of the Invention

[0006] The purpose of the present invention is to provide a RJP construction method for ultra-thick and dense sand layers in offshore areas, which can solve the problem of easy leakage at the bite joints of bored cast-in-place mortar piles and cast-in-place piles in the prior art.

[0007] The present invention is achieved in that:

[0008] A RJP construction method for ultra-thick and dense sand layers in offshore areas is characterized by comprising the following steps:

[0009] Step 1: After the bored piles are constructed, deep dry mixing is carried out at the location where the RJP high-pressure jet grouting piles are to be constructed between two adjacent bored piles.

[0010] Step 2: Make a prestressed cable body, install one end of the prestressed cable body on the drill bit of the RJP drilling rig, and drill synchronously with the drill bit of the RJP drilling rig;

[0011] Step 3: The drill bit of the RJP drilling rig carries the prestressed cable body and drills synchronously between two adjacent cast-in-place piles. After drilling to the designed depth, the prestressed cable body is anchored.

[0012] Step 4: Lift the drill rod of the RJP drilling rig, and during the lifting process, use the RJP high-pressure jet grouting process to spray grout into the hole and around the hole wall to form the RJP high-pressure jet grouting pile anchoring section. The RJP high-pressure jet grouting pile anchoring section and the adjacent cast-in-place piles are engaged to form a retaining pile;

[0013] Step 5: After the drill rod of the RJP drilling rig is lifted to the top elevation of the RJP high-pressure rotary jet grouting pile anchoring section, grouting is stopped; the hole is backfilled with sand and gravel and compacted to form the free section of the RJP high-pressure rotary jet grouting pile. The RJP high-pressure rotary jet grouting pile anchoring section and the free section of the RJP high-pressure rotary jet grouting pile form the RJP high-pressure rotary jet grouting pile, and the RJP drilling rig is moved to the next pile position to continue construction;

[0014] Step 6: Repeat steps 1 to 5 until the retaining piles of the foundation pit are completed;

[0015] Step 7: Construct the crown beam. The heads of the retaining piles are connected into a whole through the crown beam. After the strength of the crown beam reaches a certain level, the prestressed cable body is tensioned and the other end of the prestressed cable body is anchored on the crown beam.

[0016] In the step 1, according to the construction method of the cast-in-place pile, a pilot hole is made at the pile position where the RJP high-pressure rotary jet grouting pile is to be constructed for subsequent drilling by the drilling rig; if the cast-in-place pile is a bored cast-in-place pile, the pilot hole construction is carried out; if the cast-in-place pile is constructed using the SMW method, no pilot hole is required.

[0017] If the cast-in-place piles are bored cast-in-place piles, they are constructed by an interval jump driving method; if the cast-in-place piles are SMW method piles, they are constructed by a one-steel jump-one method.

[0018] The depth of the guide hole is 0.5-1m lower than the bottom elevation of the retaining pile, and the diameter of the drill bit of the guide hole is larger than the outer ring diameter of the prestressed cable body.

[0019] The construction time of the guide hole is at least 7 days after the construction of the bored pile adjacent to the guide hole is completed.

[0020] One end of the prestressed cable body is movably mounted on the drill bit of the RJP drilling rig through the anchor cable end plate. The drill bit carries the prestressed cable body through the anchor cable end plate to drill together. After reaching the final hole depth, the drill bit separates from the anchor cable end plate by reverse rotation. The diameter of the anchor cable end plate expands outward and embeds into the surrounding soil layer, so that one end of the prestressed cable body is anchored in the soil at the bottom of the hole.

[0021] The outer full-length of the prestressed cable body is wrapped with a sleeve.

[0022] In the step 4, the anchoring section of the RJP high-pressure jet grouting pile uses P.O42.5 grade ordinary Portland cement, the cement slurry pressure is greater than 40Mpa, the flow rate is greater than 90L / min, and the air pressure is not less than 0.7Mpa. After the jet grouting parameters reach the specified values, the grouting pipe is lifted and sprayed from bottom to top.

[0023] In the step 4, during the lifting process of the drill rod of the RJP drilling rig, the rotary grouting lifting speed is less than 6 cm / min, the rotation speed is less than 15 r / min, the lap length of the grouting pipe segments is greater than 100 mm, the verticality deviation does not exceed 1 / 200h, where h is the hole depth, and the 28d unconfined compressive strength standard value is not less than 1.0 MPa.

[0024] The bottom elevation of the free section of the RJP high-pressure jet grouting pile must be above the groundwater level.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention combines cast-in-place piles and RJP high-pressure rotary jet grouting piles to form retaining piles. The retaining piles have the characteristics of high rigidity and strict waterproofing of interlocking pile support, and have the advantages of simple construction, recyclability and low cost of SMW construction method piles. They can be used not only for inter-pile interlocking of concrete cast-in-place piles, but also for soil reinforcement and interlocking between SMW steel piles and between precast concrete piles and steel sheet piles. The retaining piles serve as a rigid retaining structure + water-stop curtain while having good flexibility and rigidity, good anti-leakage effect, and economical and reasonable cost. They can meet the construction conditions of ultra-thick and dense sand layers in offshore areas.

[0027] 2. The present invention adopts a prestressed cable body and RJP high-pressure rotary spraying process. The RJP high-pressure rotary spraying process combines high-pressure sprayed cement slurry with the ultra-thick and dense sand layer in the offshore area. The high-pressure sprayed cement slurry penetrates and consolidates into the soil between the piles to form a rigid pile body, fully filling the pores between the piles, achieving a better bite effect, so that the surface of the medium and fine aggregate at the bite pile position is coated with high-strength cement slurry, thereby forming a rigid body with relatively large rigidity. Then, prestressed anchor cables are used to apply pre-tension to the rigid body, greatly improving the rigidity and bending resistance of the retaining pile as a supporting structure, so that it has performance similar to that of reinforced concrete bored piles, and the bite structure of the retaining pile forms a whole with better stress and water-stopping effects.

[0028] 3. In the present invention, since the bored piles are constructed first and then the RJP high-pressure rotary grouting process is used to construct the RJP high-pressure rotary grouting piles between adjacent bored piles, the construction sequence is more reasonable, the damage to the surrounding structure is minimized, and a certain deviation in the verticality of the pile body during construction is allowed. Pile body defects caused by mud inclusion, high sand content, etc. during the bored pile construction process can also be grouting reinforced by RJP high-pressure rotary grouting cement slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of the RJP construction method for ultra-thick and dense sand layers in offshore areas of the present invention;

[0030] Figure 2 This is a construction plan of the RJP construction method for ultra-thick and dense sand layers in offshore areas of the present invention (the cast-in-place piles are bored cast-in-place piles);

[0031] Figure 3 This is a construction plan of the RJP construction method for ultra-thick and dense sand layers in offshore areas of the present invention (the cast-in-place piles are SMW method piles);

[0032] Figure 4 This is a vertical view of the connection between the RJP high-pressure jet grouting pile and the crown beam in the RJP construction method for ultra-thick and dense sand layers in offshore areas of the present invention;

[0033] Figure 5 This is a schematic diagram of the installation of the anchor cable end plate and the drill rod in the RJP construction method for ultra-thick and dense sand layers in offshore areas of the present invention;

[0034] Figure 6 yes Figure 5 Cross-section of AA.

[0035] In the figure, 1 cast-in-place pile, 101 bored cast-in-place pile, 102 SMW method pile, 2 RJP high-pressure rotary grouting pile, 21 RJP high-pressure rotary grouting pile anchoring section, 22 RJP high-pressure rotary grouting pile free section, 3 crown beam, 4 anchor cable end plate, 401 limit groove, 5 spring device, 501 limit part, 6 drill rod, 601 enlarged head, 602 drill bit, 7 anchor cable, 701 anchor head. DETAILED DESCRIPTION

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

[0037] Please see the attached Figure 1 A RJP construction method for ultra-thick and dense sand layers in offshore areas comprises the following steps:

[0038] Please see the attached Figure 2 and attached Figure 3 , Step 1: After the construction of the bored pile 1 is completed, deep dry mixing is carried out at the pile position where the RJP high-pressure rotary jet grouting pile 2 is to be constructed between two adjacent bored piles 1.

[0039] Preferably, deep dry mixing can be performed using an auger, and deep dry mixing can make the texture and particles of the sand layer at the pile position where the RJP high-pressure jet grouting pile 2 is to be constructed more uniform.

[0040] In step 1, based on the construction method of the cast-in-place pile 1, a pilot hole is constructed at the location where the RJP high-pressure jet grouting pile 2 is to be constructed, facilitating subsequent drilling by the drilling rig. This facilitates smoother pile drilling. Preferably, if the cast-in-place pile 1 is a bored cast-in-place pile 101, a pilot hole construction may be performed. If the cast-in-place pile 1 is constructed using the SMW (Soil Mixing Wall) method 102, a pilot hole is not required.

[0041] If the bored pile 1 is a bored pile 101, the bored pile 101 is constructed by using an interval skipping method, which can avoid the occurrence of a hole-in-place phenomenon and improve construction safety.

[0042] If the bored pile 1 is an SMW method pile 102 , the SMW method pile 102 is constructed by using an H-shaped steel insert-one jump-one method.

[0043] The depth of the pilot hole is 0.5-1 m below the bottom elevation of the retaining pile, and the diameter of the drill bit for the pilot hole is slightly larger than the outer diameter of the prestressed cable body. Preferably, the depth of the pilot hole can be increased according to actual working conditions, and the diameter of the drill bit for the pilot hole can be 5-10 cm larger than the outer diameter of the anchor cable to avoid damaging the pile body of the bored pile 101.

[0044] The construction time of the pilot hole is at least 7 days after the construction of the bored pile 101 adjacent to the pilot hole is completed, so as to ensure the structural safety of the bored pile 101.

[0045] Step 2: Make the anchor cable end plate and prestressed cable body, install one end of the prestressed cable body on the drill bit of the RJP drilling rig through the anchor cable end plate, and drill synchronously with the drill bit of the RJP drilling rig.

[0046] The drill bit for the RJP drill rig was modified to meet the following requirements: one end of the prestressed cable is flexibly connected to the drill bit via an anchor cable end plate. The drill bit can carry the anchor cable end plate and the prestressed cable together during drilling. After reaching the final hole depth, the drill bit rotates in the opposite direction to separate from the anchor cable end plate. Furthermore, after reaching the final hole depth, the diameter of the anchor cable end plate expands outward and embeds into the surrounding soil, allowing it to be smoothly separated from the anchor cable when the drill rod of the RJP drill rig is lifted. This also serves to expand the pile diameter and anchor the prestressed cable.

[0047] For preference, please see the attached Figure 5 and attached Figure 6 The anchor cable end plate 4 can adopt the existing spring-type telescopic plate structure. Several circumferentially arranged anchor cable end plates 4 can be rotatably mounted on the enlarged head 601 of the drill rod 6 via a rotating shaft through a spring device 5. Several obliquely extending stoppers 501 are formed at intervals along the edge of the spring device 5. The anchor cable end plates 4 are formed with obliquely extending stopper grooves 401. The stoppers 501 can be inserted into the stopper grooves 401. The extension direction of the stoppers 501 and the stopper grooves 401 is opposite to the drilling rotation direction of the drill rod 6. Multiple anchor cables 7 are fixed to the several anchor cable end plates 4 via anchor heads 701.

[0048] Drill rod 6 drives drill bit 602 along the Figure 6 During forward rotation in the direction of the middle arrow, the spring device 5 simultaneously rotates forward and compresses, and the limiting portion 501 positively impacts the limiting groove 401, causing the anchor cable end plate 4 to rotate forward and be installed above the drill bit 6, without hindering the drilling of the drill rod 6. When the drill bit 602 reaches the set depth and begins to rotate in the opposite direction to be pulled out, the spring device 5 simultaneously rotates in the opposite direction and expands in the opposite direction of the withdrawal, causing the limiting portion 501 to rotate in the opposite direction to collide and abut against the limiting groove 401 of the anchor cable end plate 4, and push the anchor cable end plate 4 to rotate in the opposite direction about the rotation axis, causing the end of the anchor cable end plate 4 to rotate outward relative to the expansion head 601 to expand to the maximum and embed into the surrounding soil layer, realizing the telescopic function. As the drill rod 6 is pulled out, the multiple anchor cable end plates 4 simultaneously move upward, and the pile diameter is expanded by the multiple anchor cable end plates 4 inserted into the soil.

[0049] The rotation and expansion of the end plate 4 drive the simultaneous outward expansion of the anchor cables 7, forming a reinforced concrete cage structure. This creates a rigid structure within the effective range of the high-pressure jet grouting pile, significantly improving the bending resistance and integrity of the jet grouting pile. The pile diameter is expanded overall, and the top can be fixed and straightened when the anchor cables 7 are anchored to the crown beam 3 to achieve the overall expansion effect.

[0050] The exterior of the prestressed cable body can be wrapped with a sleeve along its entire length, which facilitates the recovery of the prestressed cable body. When recovery is not a concern, the sleeve may not be used.

[0051] Step 3: The drill bit of the RJP drilling rig carries the prestressed cable body through the anchor cable end plate and drills synchronously between two adjacent cast-in-place piles 1. After the anchor cable end plate is drilled to the designed depth, the drill bit of the RJP drilling rig is rotated in the opposite direction. The anchor cable end plate is separated from the drill bit of the RJP drilling rig and expanded and anchored in the surrounding soil layer, so that one end of the prestressed cable body is anchored in the soil at the bottom of the hole.

[0052] If there is a pilot hole, the drill bit of the RJP drill rig drills through the pilot hole.

[0053] Step 4: Lift the drill rod of the RJP drilling rig, and during the lifting process, use the RJP high-pressure jet grouting process to spray grout into the hole and around the hole wall to form the RJP high-pressure rotary jet grouting pile anchor section 21, and the RJP high-pressure rotary jet grouting pile anchor section 21 is engaged with the adjacent cast-in-place pile 1 to form a retaining pile.

[0054] Preferably, the RJP high-pressure jet grouting pile anchoring section 21 can be made of P.O42.5 grade ordinary Portland cement. The cement slurry pressure should be greater than 40 MPa, the flow rate should be greater than 90 L / min, and the air pressure should be no less than 0.7 MPa. The pressure can be adjusted accordingly depending on the pile diameter. After the jet grouting parameters reach the specified values, the grouting pipe is raised and the grouting is sprayed from bottom to top.

[0055] Preferably, during the lifting process of the drill rod of the RJP drilling rig, the rotary grouting lifting speed should be less than 6 cm / min, the rotation speed should be less than 15 r / min, the lap length of the grouting pipe segments should be greater than 100 mm, the verticality deviation should not exceed 1 / 200 h (h is the hole depth), and the 28d unconfined compressive strength standard value should not be less than 1.0 MPa.

[0056] By combining RJP high-pressure rotary jet cement slurry with ultra-thick and dense offshore sand layers, the in-situ thick sand is utilized as pile aggregate to the maximum extent. Combined with prestressed anchor cables and high-strength cement slurry, a rigid body with relatively high rigidity is formed, greatly improving the rigidity and bending resistance of the retaining piles.

[0057] The diameter of the bored pile 101 is preferably 1000 mm, with a construction spacing of 1500 mm; the diameter of the RJP high-pressure jet grouting pile anchoring section 21 is preferably 700 mm, with a construction spacing of 1500 mm.

[0058] The SMW construction piles 102 can be H700*300*13*24 construction piles, preferably with a diameter of 850 mm and a construction spacing of 600 mm; the diameter of the RJP high-pressure jet grouting pile anchoring section 21 is preferably 500 mm and a construction spacing of 1200 mm.

[0059] Please see the attached Figure 4Step 5: After the drill rod of the RJP drilling rig is lifted to the top elevation of the RJP high-pressure rotary jet pile anchoring section 21, the grouting is stopped, the hole is backfilled with sand and gravel, and compacted and leveled to the bottom elevation of the crown beam 3 to form the RJP high-pressure rotary jet pile free section 22. The RJP high-pressure rotary jet pile anchoring section 21 and the RJP high-pressure rotary jet pile free section 22 form the RJP high-pressure rotary jet pile 2, and the RJP drilling rig is moved to the next pile position to continue construction.

[0060] The length of the prestressed cable body of the free section 22 of the RJP high-pressure jet grouting pile must meet the elongation requirement corresponding to the designed prestress.

[0061] The bottom elevation of the free section 22 of the RJP high-pressure jet grouting pile needs to be above the groundwater level, and the height of the free section 22 of the RJP high-pressure jet grouting pile can be adjusted according to actual construction conditions.

[0062] Step 6: Repeat steps 1 to 5 until the retaining piles of the foundation pit are completed.

[0063] Step 7: Construct the crown beam 3. Connect the pile heads of the retaining piles into a whole through the crown beam 3. After the strength of the crown beam 3 reaches a certain level, tension the prestressed cable and anchor the other end of the prestressed cable on the crown beam 3 with a clamp.

[0064] Prestressed anchor cables are used to apply pre-tension to the inter-pile rigid body, i.e., the RJP high-pressure jet grouting pile anchoring section 21, to form an overall structure of a rigid enclosure + water-stop curtain. This can be used as the pile body for the interlocking and connecting parts of the commonly used support structures in deep foundation pit projects (such as SMW method piles, concrete pouring or prefabricated pile rows, steel sheet piles, etc.), which can greatly reduce the leakage risk of the structure; it can also be used directly as a reinforced water-stop curtain.

[0065] The present invention breaks the limitations of constructing foundation pit support structures in ultra-thick and dense sand layers and rich groundwater environments near the coast, greatly improves construction efficiency and construction accuracy of the retaining structure, reduces the later repair work caused by intrusion, and at the same time has better water-stopping effect and better economy.

[0066] The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A RJP construction method for ultra-thick and dense sand layers in offshore areas, characterized by: The following steps are involved: Step 1: After the bored piles (1) are constructed, deep dry mixing is performed at the location where the RJP high-pressure jet grouting piles (2) are to be constructed between two adjacent bored piles (1); Step 2: Make a prestressed cable body, install one end of the prestressed cable body on the drill bit of the RJP drilling rig, and drill synchronously with the drill bit of the RJP drilling rig; The drill bit of the RJP drilling rig should be improved. The drill bit structure should meet the following requirements: one end of the prestressed cable body is movably connected to the drill bit of the RJP drilling rig through the anchor cable end plate. The drill bit can carry the anchor cable end plate and the prestressed cable body for drilling together. After reaching the final hole depth, the drill bit separates from the anchor cable end plate through reverse rotation. At the same time, after reaching the final hole, the diameter of the anchor cable end plate can expand outward and embed into the surrounding soil layer, so that it can be smoothly separated from the anchor cable when the drill rod of the RJP drilling rig is lifted. At the same time, it also serves to expand the pile diameter and is used for anchoring the prestressed cable body. A plurality of circumferentially arranged anchor cable end plates (4) are rotatably mounted on the enlarged head (601) of the drill rod (6) via a rotating shaft through a spring device (5); a plurality of obliquely extending limiting portions (501) are formed at intervals on the edge of the spring device (5); an obliquely extending limiting groove (401) is formed on the anchor cable end plate (4); the limiting portion (501) can be inserted into the limiting groove (401), and the extending direction of the limiting portion (501) and the limiting groove (401) is opposite to the drilling rotation direction of the drill rod (6); a plurality of anchor cables (7) are fixed to the plurality of anchor cable end plates (4) via anchor heads (701) respectively; Step 3: The drill bit of the RJP drilling rig carries the prestressed cable body and drills synchronously between two adjacent cast-in-place piles (1). After drilling to the designed depth, the prestressed cable body is anchored; Step 4: lift the drill rod of the RJP drilling rig, and during the lifting process, use the RJP high-pressure jet grouting process to spray grout into the hole and around the hole wall to form the RJP high-pressure jet grouting pile anchoring section (21), and the RJP high-pressure jet grouting pile anchoring section (21) is engaged with the adjacent cast-in-place pile (1) to form a retaining pile; Step 5: after the drill rod of the RJP drilling rig is lifted to the top elevation of the RJP high-pressure jet grouting pile anchoring section (21), stop grouting; backfill the hole with sand and gravel and compact it to form the RJP high-pressure jet grouting pile free section (22), the RJP high-pressure jet grouting pile anchoring section (21) and the RJP high-pressure jet grouting pile free section (22) form the RJP high-pressure jet grouting pile (2), and the RJP drilling rig moves to the next pile position to continue construction; Step 6: Repeat steps 1 to 5 until the retaining piles of the foundation pit are completed; Step 7: construct the crown beam (3), connect the pile heads of the retaining piles into a whole through the crown beam (3), and after the strength of the crown beam (3) reaches a certain level, tension the prestressed cable body and anchor the other end of the prestressed cable body on the crown beam (3).

2. The RJP construction method for ultra-thick and dense sand layers in offshore areas according to claim 1 is characterized in that: In the step 1, according to the construction method of the cast-in-place pile (1), a pilot hole is made at the pile position where the RJP high-pressure jet grouting pile (2) is to be constructed for subsequent drilling by a drilling rig; if the cast-in-place pile (1) is a bored cast-in-place pile (101), the pilot hole construction is carried out; if the cast-in-place pile (1) is constructed using the SMW method pile (102), the pilot hole is not required.

3. The RJP construction method for ultra-thick and dense sand layers in offshore areas according to claim 1 or 2, characterized in that: If the cast-in-place pile (1) is a bored cast-in-place pile (101), the bored cast-in-place pile (101) is constructed by an interval jump driving method; if the cast-in-place pile (1) is an SMW construction method pile (102), the SMW construction method pile (102) is constructed by a steel section inserting and jumping method.

4. The RJP construction method for ultra-thick and dense sand layers in offshore areas according to claim 2 is characterized by: The depth of the guide hole is 0.5-1m lower than the bottom elevation of the retaining pile, and the diameter of the drill bit of the guide hole is larger than the outer ring diameter of the prestressed cable body.

5. The RJP construction method for ultra-thick and dense sand layers in offshore areas according to claim 2 or 4, characterized in that: The construction time of the guide hole is at least 7 days after the construction of the bored pile (101) adjacent to the guide hole is completed.

6. The RJP construction method for ultra-thick and dense sand layers in offshore areas according to claim 1 is characterized by: The outer full-length of the prestressed cable body is wrapped with a sleeve.

7. The RJP construction method for ultra-thick and dense sand layers in offshore areas according to claim 1 is characterized by: In step 4, the RJP high-pressure jet grouting pile anchoring section (21) uses P.O42.5 grade ordinary Portland cement, the cement slurry pressure is greater than 40 MPa, the flow rate is greater than 90 L / min, and the air pressure is not less than 0.7 MPa. After the jet grouting parameters reach the specified values, the grouting pipe is lifted and sprayed from bottom to top.

8. The RJP construction method for ultra-thick and dense sand layers in offshore areas according to claim 1 or 7, characterized in that: In the step 4, during the lifting process of the drill rod of the RJP drilling rig, the rotary grouting lifting speed is less than 6 cm / min, the rotation speed is less than 15 r / min, the lap length of the grouting pipe segments is greater than 100 mm, the verticality deviation does not exceed 1 / 200h, where h is the hole depth, and the 28d unconfined compressive strength standard value is not less than 1.0 MPa.

9. The RJP construction method for ultra-thick and dense sand layers in offshore areas according to claim 1 is characterized by: The bottom elevation of the free section (22) of the RJP high-pressure jet grouting pile needs to be above the groundwater level.

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