A base-enlarged pile for pre-watering and compaction treatment of collapsible loess

Abstract

The invention discloses a pre-immersion and compaction treatment of collapsible loess with an expanded bottom pile, the expanded bottom pile comprises a prefabricated concrete pipe pile, the bottom and side of the pile body are provided with a immersion port for water seepage grouting, and a loading frame is installed on the pile top; the pile bottom is a bottom sealing plate and a water inlet plate connected to a stainless steel pipe, and a first sealing ring, a bottom spring and a bottom air bag are installed between the bottom sealing plate and the water inlet plate; the pile side is a side sealing plate and a steel cover plate, and a second sealing ring, a third sealing ring, a side spring and a side air bag are installed between the two. The present invention combines the compaction effect of the pile body and the pre-immersion treatment, and can quickly eliminate the collapsibility of the loess on the pile side and the pile bottom, shortening the construction period. At the same time, the pile side and the pile bottom can be immersed in water with different or the same water pressure, greatly reducing the pile end and pile side resistance during pile sinking, accelerating the pile sinking speed, and improving the construction efficiency. After the pile sinking is completed, the pressure grouting at the pile bottom forms a cement slurry enlarged head, which can greatly improve the bearing capacity of the pile foundation.

Description

Technical Field

[0001] The invention relates to a foundation treatment technology for construction projects in collapsible loess areas, in particular to a bottom-enlarged pile for pre-watering and compacting the collapsible loess. Background Art

[0002] Loess is widely distributed in my country, covering more than 10 provinces and regions including Gansu, Shaanxi, Ningxia, and Qinghai, with an area of ​​about 635,000 square kilometers, accounting for about 6.6% of the country's land area, of which collapsible loess accounts for about 3 / 4. As a result, industrial and civil infrastructure will be increasingly built in vast loess areas. The collapsibility of loess can cause significant settlement, cracks, and even collapse of buildings. Therefore, the treatment of collapsible loess foundations has always been a common and difficult problem in geotechnical engineering.

[0003] At present, the most commonly used methods for treating collapsible loess foundations at home and abroad include dynamic tamping, cushioning, lime soil compaction, chemical reinforcement, pre-immersion, etc. Although these technologies are relatively mature and widely used, they also have some common defects. For example, most of them can only treat shallow collapsible loess foundations, and the collapsibility of deep loess is usually difficult to eliminate. In addition, these technologies also have their own limitations. For example, the dynamic tamping method has high vibration and noise, and disturbs surrounding buildings; the chemical reinforcement method has high construction costs; and the pre-immersion method has a long construction period.

[0004] When the building settlement requirements are high or the thickness of collapsible loess is deep, pile foundation is usually used for foundation reinforcement. The treatment thickness of traditional soil piles, gray soil piles, etc. for collapsible loess foundations generally does not exceed 15m. Even if the impact method or bored pile compaction method is used for construction, the treatment thickness is also limited. In its natural state, loess has a low moisture content, strong structure, low compressibility, and high strength. In this way, when using pipe piles or prefabricated piles to treat collapsible loess foundations, due to the large pile end resistance and pile side friction resistance, it is difficult to sink the piles, the construction efficiency is low, and the collapsible nature of deep loess cannot usually be eliminated.

[0005] Chinese patent CN102995637A discloses a patented technology entitled "Equipment and method for constructing pipe-sinking compaction piles in thick backfill or self-weight collapsible loess sites". It mainly adopts an inner and outer pipe combination structure to achieve the purpose of using pipe-sinking compaction piles to treat thick self-weight collapsible loess. Although this treatment technology is easy to operate and economical, the pile end resistance and the friction resistance around the pile are large during pile sinking, making pile sinking difficult. In addition, it is difficult to completely eliminate the collapsible nature of loess by only using the compaction method for loess foundation treatment.

[0006] Chinese patent CN109914458A discloses a patented technology entitled "A steel pipe pile suitable for collapsible loess", which includes a pile body, an electric heating film, a control center, a water flow duct, an air flow duct and a filter device. It realizes the function of water seeping out from the collapsible loess foundation when the water level rises, reduces the negative friction of the pile foundation after the collapsible loess is deformed, and improves the bearing capacity of the pile foundation. However, it is not specially designed to handle the function of collapsible loess, so it is impossible to completely eliminate the impact of the collapsible nature of the loess. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the above-mentioned thick collapsible loess foundation treatment technology, and to provide a base-enlarged pile and a construction method thereof that can quickly eliminate the collapsible nature of loess and has convenient construction, good economy, and high bearing capacity.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A base-enlarged pile for pre-watering and compacting collapsible loess comprises a precast concrete pipe pile, a conical head is formed at the bottom of the precast concrete pipe pile, a detachable lower plugging structure is installed on the top of the conical head, and a detachable upper plugging structure is installed in the precast concrete pipe pile; a cavity is formed in the conical head, and a plurality of pile end water outlets connected with the cavity are formed on the surface of the conical head; a plurality of pile side water outlets are formed in sequence from top to bottom in the circumference of the precast concrete pipe pile; an upper water injection cavity is formed between the detachable lower plugging structure and the detachable upper plugging structure; the cavity of the conical head is connected with a pile end water inlet pipe, and the upper water injection cavity is connected with a pile side water inlet pipe; a pile side water outlet is formed on the side of the precast concrete pipe pile;

[0010] After the conical head and the precast concrete pipe piles above the conical head enter the loess, the position of the detachable upper sealing structure is adjusted so that the bottom of the detachable upper sealing structure is flush with the loess surface, and then water is injected into the cavity of the conical head and the upper water injection cavity respectively, so that the loess below and around the conical head and the loess around the precast concrete pipe piles above the conical head reach saturation at the same time.

[0011] A further improvement is that the detachable upper blocking structure is an annular side airbag, and a stainless steel tube connected to the detachable lower blocking structure is slidably connected to the middle part of the side airbag; the side airbag is connected to the side air inlet pipe; the detachable lower blocking structure is a bottom airbag, and the bottom airbag is connected to the bottom air inlet pipe.

[0012] As a further improvement, a bottom sealing plate is installed at the bottom of the bottom air bag, and a water inlet plate is installed at the top. The water inlet plate is sealed and connected to a stainless steel pipe, and the stainless steel pipe is connected to the cavity in the conical head; the pile end water inlet pipe is connected to the stainless steel pipe through a bottom water inlet valve; the bottom air inlet pipe is connected to the bottom air bag after passing through the bottom air inlet valve on the stainless steel pipe, and a top plug is installed on the top of the stainless steel pipe.

[0013] As a further improvement, a bottom spring is installed on the outside of the bottom air bag, and a first sealing ring is installed on the outside of the bottom spring; the bottom spring and the first sealing ring are both located between the bottom sealing disk and the water inlet disk; the bottom spring is always in a tensile stress state, and the bottom air bag lifts up the bottom sealing disk after being inflated.

[0014] As a further improvement, a steel cover plate is installed on the top of the side airbag, and a side sealing plate is installed on the bottom; a connecting column is fixedly connected to the top of the steel cover plate, and a loading frame is installed on the top of the precast concrete pipe pile.

[0015] A further improvement is that a side spring is installed on the outside of the side airbag, a second sealing ring is installed on the outside of the side spring, and a third sealing ring is installed on the inside of the side airbag; the side spring, the second sealing ring and the third sealing ring are all located between the steel cover plate and the side sealing plate; the side spring is always in a tensile stress state, and the side sealing plate is lifted up after the side airbag is inflated.

[0016] As a further improvement, the loading frame is provided with a limiting cap cooperating with the precast concrete pipe pile and a through hole d cooperating with the connecting column. The connecting column is provided with pairs of limiting holes with a spacing of 0.5m to 1.5m along the axial direction, and the spacing of each pair of limiting holes is 2cm to 4cm larger than the thickness of the limiting cap.

[0017] As a further improvement, the pile side of the precast concrete pipe pile is provided with a plurality of groups of pile side water outlets with a longitudinal spacing of 0.3m to 1.0m and a diameter of 2cm to 4cm from top to bottom; each group of pile side water outlets includes 4 to 8 pile side water outlets evenly arranged along the circumference of the precast concrete pipe pile 1.

[0018] As a further improvement, 3 to 5 groups of pile end water outlets with a diameter of 3 cm to 6 cm are arranged longitudinally on the conical head, and each group of pile end water outlets includes 4 to 8 pile end water outlets evenly arranged along the radial section of the pile body.

[0019] Further improvement, the single pile bearing capacity R a Design according to needs, where R a Obtained by the following formula:

[0020] Where d1 is the outer diameter of the precast concrete pile; L1 is the length of the pile body; L2 is the length of the pile end; d p is the diameter of the designed cement slurry expansion head; τ cs is the pile side resistance of collapsible loess after pre-watering and compaction treatment; q pa is the pile tip resistance of collapsible loess after pre-watering and compaction treatment; c is the pile side resistance correction factor, which is determined based on the field test results of the test pile;

[0021]

[0022] The beneficial effects of the present invention are:

[0023] 1. During the static pressure pile sinking process, the precast concrete pipe pile of the present invention quickly eliminates the collapsibility of the loess around and at the bottom of the pile through the compaction effect and pre-immersion treatment of the precast pile. In this way, there is no need to perform other methods of collapsibility elimination treatment on the loess in the construction site, which significantly shortens the construction period and greatly saves the project cost.

[0024] 2. The present invention performs water immersion treatment during the static pressure pile sinking process, destroying the structure of the pile bottom and the soil around the pile, thereby greatly reducing the pile end resistance and pile side friction resistance, accelerating the pile sinking speed and improving the construction efficiency;

[0025] 3. The present invention uses two sets of immersion sealing systems to achieve different immersion pressures at the pile bottom and pile side during pre-immersion treatment, and can treat thick collapsible loess. In addition, it also accelerates the water penetration rate, thereby more quickly eliminating the collapsible loess of the foundation, further improving the construction efficiency;

[0026] 4. The water-immersed sealing system at the bottom of the pile of the present invention can also be used for pressure grouting. One system has multiple functions, thereby simplifying the system structure and facilitating operation.

[0027] 5. The present invention eliminates the collapsible loess of the foundation and improves the strength of the soil through compaction. A cement slurry enlarged head is formed at the bottom of the precast concrete pipe pile, which can greatly improve the bearing capacity of the pile foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural principle diagram of the present invention.

[0029] Figure 2 This is a structural principle diagram of the precast concrete pipe pile 1 of the present invention.

[0030] Figure 3 It is a schematic diagram of the connection of various components at the pile top of the present invention.

[0031] Figure 4 It is a schematic diagram of the connection between the middle stainless steel pipe 11, the side sealing plate 16 and the precast concrete pipe pile 1 of the present invention.

[0032] Figure 5 It is a schematic diagram of the connection of various components at the bottom of the pile of the present invention.

[0033] Figure 6 The invention discloses the arrangement of pile foundation and the zoning of collapsible loess treatment.

[0034] Figure 7 The pile body after the cement slurry enlarged head 24 is formed during construction of the present invention.

[0035] Figure 8 It is a partial dimension diagram of the cement slurry enlargement head 24 of the present invention.

[0036] Fig. 9 It is a flow chart of the construction method of the present invention.

[0037] The labels in the figure are:

[0038] 1-precast concrete pipe pile; 1a-side water outlet of pile; 1b-side water outlet of pile end; 1c-receiving platform; 2-side water inlet pipe of pile; 3-side water inlet pipe of pile end; 4-side air inlet pipe; 5-bottom air inlet pipe; 6-water inlet plate; 7-bottom sealing plate; 8-bottom spring; 9-bottom air bag; 10-first sealing ring; 11-stainless steel pipe; 12-top plug; 13-bottom water inlet valve; 14-bottom air inlet valve; 15-steel cover plate; 15a-side air inlet valve; 16-side sealing plate; 16a-side water inlet valve; 17-side spring; 18-side air bag; 19-second sealing ring; 20-third sealing ring; 21-connecting column; 21a-limiting hole; 22-limiting pin; 23-loading frame; 23a-loading platform; 23b-limiting cap; 23c-loading column; 23d-through hole; 24-cement slurry enlargement head. DETAILED DESCRIPTION

[0039] The following is a further description of the embodiments of the present invention in conjunction with the accompanying drawings and examples. It should be noted that the examples do not limit the scope of protection claimed by the present invention.

[0040] A pre-water-impregnated and compacted expanded bottom pile for treating collapsible loess mainly comprises a precast concrete pipe pile 1. In this embodiment, the precast concrete pipe pile 1 has a pile length L1=10m, a pile end length L2=0.5m, an outer diameter d1=0.6m, an inner diameter d2=0.45m, and is made of C30 concrete. Figure 1 and Figure 2As shown, the pile side of the precast concrete pipe pile 1 is provided with pile side water outlets 1a with a longitudinal spacing of 0.3m to 1.0m and a diameter of 2cm to 4cm. In this embodiment, the longitudinal spacing of the pile side water outlets 1a is 0.5m and the diameter is 3cm. 4 to 8 pile side water outlets 1a are evenly arranged along the radial cross section of the pile body, and 4 are arranged in this embodiment; the pile end (conical head) of the precast concrete pipe pile 1 is conical, and 3 to 5 layers of pile end water outlets 1b with a diameter of 3cm to 6cm are arranged in the longitudinal direction. In this embodiment, the pile end water outlets 1b are arranged in 4 layers in the longitudinal direction with a diameter of 4cm. 4 to 8 pile end water outlets 1b are evenly arranged along the radial cross section of the pile body, and 4 are arranged in the 1st and 2nd layers at the bottom of the embodiment, and 4 are arranged in the 3rd and 4th layers. 6 layers are arranged; a receiving platform 1c is set at the pile end to limit the position of the bottom sealing plate 7; a bottom sealing plate 7 is set at the bottom of the precast concrete pipe pile 1, the water inlet plate 6 is sealed and connected to the stainless steel pipe 11, and the pile end water inlet pipe 3 is connected to the stainless steel pipe 11 through the bottom water inlet valve 13, which is used to soak the collapsible loess at the pile end; the bottom air inlet pipe 5 passes through the bottom air inlet valve 14 and the stainless steel pipe 11 and is connected to the bottom air bag 9; a side sealing plate 16 is set at the pile body of the precast concrete pipe pile 1, and the top surface of the steel cover plate 15 is welded or threadedly connected to the connecting column 21. The present embodiment is a threaded connection, and the pile side water inlet pipe 2 passes through the steel cover plate 15 and is connected to the side sealing plate 16; the side air inlet pipe 4 passes through the steel cover plate 15 and is connected to the side air bag 18.

[0041] like Figure 3 As shown, a loading frame 23 is installed on the top of the precast concrete pipe pile 1, and the loading frame 23 is provided with a loading platform 23a and a loading column 23c, which are convenient for the pile driver to perform static pressure pile sinking. A limiting cap 23b cooperating with the precast concrete pipe pile 1 is provided at the bottom of the loading frame 23 to limit the shaking of the loading frame 23 during static pressure pile sinking. The loading frame 23 is also provided with a through hole 23d cooperating with the connecting column 21; a top plug 12 is installed on the top of the stainless steel pipe 11, and a bottom water inlet valve 13 and a bottom air inlet valve 14 are provided; the connecting column 21 is axially provided with pairs of limiting holes 21a with a spacing of 0.5m to 1.5m, which is 1.0m in this embodiment, and the spacing of each pair of limiting holes 21a is 2cm to 4cm larger than the thickness of the limiting cap 23b, which is 3cm in this embodiment, and the connecting column 21 is fixed to the loading frame 23 by a limiting pin 22.

[0042] like Figure 4As shown, a side spring 17, a side airbag 18, a second sealing ring 19 and a third sealing ring 20 are installed between the side sealing disk 16 and the steel cover disk 15; the side spring 17 is always in a tensile stress state, ensuring that the second sealing ring 19 fits against the inner wall of the precast concrete pipe pile 1 and the third sealing ring 20 fits against the outer wall of the stainless steel pipe 11, thereby realizing the pile side sealing; the side airbag 18 can lift the side sealing disk 16 after being inflated through the side air inlet pipe 4, ensuring that the second sealing ring 19 is disengaged from the inner wall of the precast concrete pipe pile 1 and the third sealing ring 20 is disengaged from the outer wall of the stainless steel pipe 11, thereby realizing the removal of the pile side sealing system after the foundation pile construction is completed.

[0043] like Figure 5 As shown, a bottom spring 8, a bottom air bag 9 and a first sealing ring 10 are installed between the bottom sealing plate 7 and the water inlet plate 6. The bottom spring 8 is always in a tensile stress state to ensure that the first sealing ring 10 fits against the inner wall of the precast concrete pipe pile 1 to achieve pile bottom sealing; after the bottom air bag 9 is inflated, it can lift the bottom sealing plate 7 to ensure that the first sealing ring 10 is separated from the inner wall of the precast concrete pipe pile 1, thereby realizing the removal of the pile bottom sealing system after the foundation pile construction is completed.

[0044] After pre-watering and compaction treatment, the collapsibility of loess is basically eliminated, and the negative friction on the pile side is also eliminated. a It is composed of pile side friction and pile end resistance, which can be calculated by the following formula:

[0045]

[0046] Where, d1 is the outer diameter of the precast concrete pile 1; L1 is the length of the pile body; L2 is the length of the pile end; d p is the diameter of the designed cement slurry enlargement head 24; τ cs is the pile side resistance of collapsible loess after pre-watering and compaction treatment; q pa is the pile tip resistance of collapsible loess after pre-watering and compaction treatment; c is the pile side resistance correction factor, which can be determined based on the field test results of the test pile; according to the geometric relationship, such as Figure 8 ,

[0047] In this embodiment, the enlarged head diameter d is designed p =0.8m, calculated l b =0.15m, take ξ c =0.9, τ cs =10kPa,q pa = 80 kPa, the single pile bearing capacity R of the expanded pile is calculated a =229.9kN.

[0048] A construction method for enlarged bottom piles for pre-watering and compaction treatment of collapsible loess, such as Fig. 9 , the steps are as follows:

[0049] 1) Construction preparation: Survey the natural void ratio e and natural water content w of the collapsible loess at the construction site c and specific gravity d s Basic physical and mechanical indicators such as e = 0.95 and w c =12%, d s =2.7, site leveling, surveying and setting out, marking the position of foundation piles according to the design plan, and assembling precast concrete piles 1;

[0050] 2) Putting the pile driver in place: Using a pile driver, the assembled prefabricated concrete pipe pile 1 is driven into the collapsible loess foundation by static pressure pile sinking.

[0051] 3) Pile bottom immersion: water with a pressure of p1 is injected into the collapsible loess at the pile bottom through the pile end water inlet pipe 3, the stainless steel pipe 11, the water inlet plate 6 and the pile end water outlet 1b to eliminate the collapsible loess at the pile end and facilitate static pressure pile sinking. The water pressure p1 in this embodiment is set to 120 kPa;

[0052] 4) Static pressure pile sinking and pile side immersion: Continue to use the pile driver to press the precast concrete pipe pile 1 into the foundation by static pressure pile sinking. After the first row of pile side outlets 1a at the bottom enter the foundation, adjust the side sealing plate 16 to the middle of the first and second row of pile side outlets 1a, and then inject water with a set pressure p2 through the pile side water inlet pipe 2, the side sealing plate 16 and the pile side outlet 1a into the stratum at the pile side to eliminate the collapsibility of the loess on the pile side and facilitate static pressure pile sinking. The water pressure p2 in this embodiment is Set to 80kPa; after the second row of pile side outlets 1a at the bottom enter the foundation, use the connecting column 21 to cooperate with the limit pin 22 to adjust the side sealing plate 16 to the middle of the second and third row of pile side outlets 1a; repeat this step until the precast concrete pipe pile 1 is completely sunk into the foundation; during the static pressure pile sinking process, the pile side outlets 1a below the side sealing plate 16 and the second sealing ring 19 are below the ground, and the pile side outlets 1a above the ground are above the ground, ensuring that the water on the pile side does not flow out of the ground;

[0053] 5) Foundation soil soaking treatment: Increase the water pressure p1 and p2 at the bottom and side of the pile, and monitor the flow rate q of the pile end water inlet pipe (3) and the pile side water inlet pipe (2). b and q c , observe the settlement of the stratum and the surface at the same time, and wait until the collapsible loess on the pile side and pile bottom reaches saturation at the same time or the water infiltration reaches the design value Q c and Q b After that, Q c is the designed water infiltration volume of the pile side, Q b The water infiltration volume is designed for the pile bottom, water injection is stopped, and the water in the precast concrete pipe pile 1 is pumped out.

[0054] Specifically, according to the principle of soil mechanics, the water seepage radius d of the precast concrete pile 1 is e for:

[0055]

[0056] In the formula, Figure 6 As shown, s is the center distance of the piles. In this embodiment, s = 2.0m, the piles are arranged in a plum blossom shape, and d is calculated. e =2.1m;

[0057] The collapsible loess on the pile side is treated by the water leaching from the pile side outlet 1a, while the collapsible loess at the pile bottom is treated by the water leaching from the pile end outlet 1b. The volume of collapsible loess that needs to be treated on the pile side and pile bottom of each pile is V c and V b They are:

[0058]

[0059] In the formula, Figure 6 As shown, L1 is the length of the pile body; h0 is the treatment thickness below the pile end. In this embodiment, L1 = 10m, h0 = 3m;

[0060] The air volume V of the collapsible loess on the pile side and bottom before pile sinking ca and V ba They are:

[0061]

[0062] After the pile is sunk, the air volume V of the collapsible loess on the pile side and bottom is ca ′ and V ba ′ is equal to the designed water infiltration volume Q at the pile side and pile bottom c and Q b , respectively:

[0063]

[0064] Wherein, L2 is the length of the pile end. In this embodiment, L2 = 0.5m, Q c =8.3m 3 , Q p =3.3m 3 .

[0065] In order to ensure that the collapsible loess on the pile side and pile bottom can be saturated at the same time, thereby avoiding oversaturation or undersaturation of some collapsible loess, the designed water infiltration volume Q of the pile side and pile bottom is c and Q b Must be achieved simultaneously, namely:

[0066]

[0067] Where t is the required immersion time, q b and q c are the flow rates of the pile end water inlet pipe 3 and the pile side water inlet pipe 2 respectively.

[0068] The flow rate q b and q c The following relationships must be satisfied:

[0069]

[0070] In this embodiment, the pile side water immersion pressure p2 is increased to 300 kPa, and the flow rate q of the pile side water inlet pipe 2 is monitored by a flow meter. c =8.0L / s. The required flow rate q of the pile end water inlet pipe 3 is calculated by formula (6): b is 3.2L / s, adjust the pile bottom water pressure p1 until q b =3.2L / s. Further, the required immersion time t=17.3min is estimated.

[0071] 6) Pressure grouting: After the immersion treatment is completed, the cement slurry is injected into the collapsible loess at the bottom of the pile through the pile end water inlet pipe 3, the stainless steel pipe 11, the water inlet plate 6 and the pile end water outlet 1b at a set pressure p3. In this embodiment, the pressure p3 is set to 500 kPa, the water-cement ratio of the cement slurry is 0.45, and the amount of grouting to be injected / volume Q cs After reaching the set value, stop grouting.

[0072] Grouting quantity / volume Q cs The diameter of the enlarged head is d p Calculated from the design parameters, specifically, Figure 8 As shown, according to the geometric relationship, l b and l c It can be calculated by formula (8). In this embodiment, the enlarged head diameter d is designed p =0.8m, d1=0.6m, L2=0.5m, we can calculate l b =0.15m,l c =0.1m.

[0073]

[0074] Assuming that the cement slurry enlarged head 24 is a sphere with the pile end center as the sphere center, according to the geometric relationship, the grouting amount / volume Q required to form the cement slurry enlarged head 24 is cs It can be calculated according to formula (9). In this embodiment, Q cs =0.24m 3 .

[0075]

[0076] 7) Dismantling of the sealing system: dismantle the loading frame 23; inject pressure air into the side pressure bag 18, lift up the side sealing disc 16, disengage the second sealing ring 19 from the inner wall of the precast concrete pile 1, disengage the third sealing ring 20 from the outer wall of the stainless steel pipe 11, and further dismantle the steel cover plate 15, the side sealing disc 16 and the connecting column 21; inject pressure air into the bottom pressure bag 9, lift up the bottom sealing disc 7, disengage the first sealing ring 10 from the inner wall of the precast concrete pile 1, and dismantle the stainless steel pipe 11, the water inlet plate 6 and the bottom sealing disc 7;

[0077] 8) Construction is completed: Use pressure water to clean the stainless steel pipe 11, water inlet plate 6 and bottom sealing plate 7 to ensure that the sealing system can be used again; Figure 7 and Figure 8 As shown, after a certain period of curing, the cement slurry injected into the pile bottom hardens to form a cement slurry enlarged head 24, and the cement slurry enlarged head 24 and the precast concrete pipe pile 1 form a whole, thereby improving the bearing capacity of the pile foundation.

Claims

1. A base-enlarged pile for pre-watering and compaction treatment of collapsible loess, characterized in that: The precast concrete pipe pile (1) comprises a conical head formed at the bottom of the precast concrete pipe pile (1), a detachable lower plugging structure installed at the top of the conical head, and a detachable upper plugging structure installed inside the precast concrete pipe pile (1); a cavity is formed inside the conical head, and a plurality of pile end water outlets (1b) connected to the cavity are formed on the surface of the conical head; a plurality of pile side water outlets (1a) are formed in sequence from top to bottom in the circumference of the precast concrete pipe pile (1); an upper water injection cavity is formed between the detachable lower plugging structure and the detachable upper plugging structure; the cavity of the conical head is connected to a pile end water inlet pipe (3), and the upper water injection cavity is connected to a pile side water inlet pipe (2); and a pile side water outlet (1a) is formed on the side of the precast concrete pipe pile (1); After the conical head and the precast concrete pipe pile (1) above the conical head enter the loess, the position of the detachable upper plugging structure is adjusted so that the bottom of the detachable upper plugging structure is flush with the loess surface, and then water is injected into the cavity of the conical head and the upper water injection cavity respectively, so that the loess below and around the conical head and the loess around the precast concrete pipe pile (1) above the conical head are simultaneously saturated; the detachable upper plugging structure is an annular side airbag (18), and the middle part of the side airbag (18) is slidably connected to the detachable lower plugging structure. The invention relates to a stainless steel pipe (11) connected to the structure; the side air bag (18) is connected to the side air inlet pipe (4); the detachable lower blocking structure is a bottom air bag (9), and the bottom air bag (9) is connected to the bottom air inlet pipe (5); the pile side of the precast concrete pipe pile (1) is provided with a plurality of groups of pile side water outlets (1a) with a longitudinal spacing of 0.3m to 1.0m and a diameter of 2cm to 4cm from top to bottom; each group of pile side water outlets (1a) includes 4 to 8 pile side water outlets (1a) uniformly arranged along the circumference of the precast concrete pipe pile (1).

2. The expanded bottom pile for pre-watering and compaction treatment of collapsible loess according to claim 1, characterized in that: The bottom of the bottom air bag (9) is provided with a bottom sealing plate (7), and the top of the bottom air bag (9) is provided with a water inlet plate (6), the water inlet plate (6) is sealedly connected to a stainless steel pipe (11), and the stainless steel pipe (11) is connected to the cavity in the conical head; the pile end water inlet pipe (3) is connected to the stainless steel pipe (11) through a bottom water inlet valve (13); the bottom air inlet pipe (5) is connected to the bottom air bag (9) after passing through a bottom air inlet valve (14) on the stainless steel pipe (11), and a top plug (12) is provided on the top of the stainless steel pipe (11).

3. The expanded bottom pile for pre-watering and compaction treatment of collapsible loess according to claim 2, characterized in that: A bottom spring (8) is installed on the outside of the bottom air bag (9), and a first sealing ring (10) is installed on the outside of the bottom spring (8); the bottom spring (8) and the first sealing ring (10) are both located between the bottom sealing plate (7) and the water inlet plate (6); the bottom spring (8) is always in a tensile stress state, and the bottom air bag (9) lifts up the bottom sealing plate (7) after being inflated.

4. The base-enlarged pile for pre-water-impregnated and compacted collapsible loess according to claim 1, characterized in that: The side airbag (18) is provided with a steel cover plate (15) on the top and a side sealing plate (16) on the bottom; a connecting column (21) is fixedly connected to the top of the steel cover plate (15), and a loading frame (23) is provided on the top of the precast concrete pipe pile (1).

5. The base-enlarged pile for pre-water-impregnated and compacted collapsible loess according to claim 4, characterized in that: A side spring (17) is installed on the outside of the side airbag (18), a second sealing ring (19) is installed on the outside of the side spring (17), and a third sealing ring (20) is installed on the inside of the side airbag (18); the side spring (17), the second sealing ring (19), and the third sealing ring (20) are all located between the steel cover plate (15) and the side sealing plate (16); the side spring (17) is always in a tensile stress state, and the side sealing plate (16) is lifted up after the side airbag (18) is inflated.

6. The expanded bottom pile for pre-watering and compaction treatment of collapsible loess according to claim 4, characterized in that: The loading frame (23) is provided with a limiting cap (23b) matched with the precast concrete pipe pile (1) and a through hole (23d) matched with the connecting column (21). The connecting column (21) is provided with a pair of limiting holes (21a) with a spacing of 0.5m to 1.5m along the axial direction, and the spacing of each pair of limiting holes (21a) is 2cm to 4cm larger than the thickness of the limiting cap (23b).

7. The base-enlarged pile for pre-water-impregnated and compacted collapsible loess according to claim 1, characterized in that: The conical head is provided with 3 to 5 groups of pile end water outlets (1b) with a diameter of 3 cm to 6 cm in the longitudinal direction, and each group of pile end water outlets (1b) includes 4 to 8 pile end water outlets (1b) evenly arranged along the radial cross section of the pile body.

8. The base-enlarged pile for pre-water-impregnation and compaction treatment of collapsible loess according to claim 1, characterized in that: The single pile bearing capacity R a Design according to needs, where R a It is obtained by the following formula: Where d1 is the outer diameter of the precast concrete pile; L1 is the length of the pile body; L2 is the length of the pile end; d p is the diameter of the designed cement slurry expansion head; τ cs is the pile side resistance of collapsible loess after pre-watering and compaction treatment; q pa is the pile tip resistance of collapsible loess after pre-watering and compaction treatment; c is the pile side resistance correction factor, which is determined based on the field test results of the test pile;

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