WO2024074130A1

WO2024074130A1 - Construction method for prefabricated hollow internally-rammed carrier pile

Info

Publication number: WO2024074130A1
Application number: PCT/CN2023/123165
Authority: WO
Inventors: 王继忠; 张力霆; 张连喜; 徐彤; 张少雄; 王光亮; 杨启安; 李湘明
Original assignee: 北京波森特岩土工程有限公司
Priority date: 2022-10-08
Filing date: 2023-10-07
Publication date: 2024-04-11
Also published as: CN115288131B; CN115288131A

Abstract

The present application relates to the technical field of civil engineering foundation piles, in particular to a construction method for a prefabricated hollow internally-rammed carrier pile, the method comprising the following steps: mounting a bottom sealing steel plate at a lower end of a hollow pile body to seal the bottom of the hollow pile body; and slowly humping a slender heavy hammer into an inner cavity of a sealed isolation cavity through a pile opening at an upper end of the hollow pile body, wherein a filler and airflow channel is provided between the slender heavy hammer and a side wall of the sealed isolation cavity, such that cement sand mixture is tamped with low tamping energy, and whether the bottom sealing steel plate is opened or not is determined. When the cement sand mixture reaches a preset height in the sealed isolation cavity or the filled amount of the cement sand mixture reaches a preset value, the cement sand mixture is continuously filled through the channel, the tamping energy is properly increased, the cement sand mixture and the soil body below the pile end within a certain depth and range are driven to be reinforced and compacted to form a pile end carrier. According to the present application, the influences of underground water on engineering foundation pile construction can be overcome, and the yield in an actual foundation pile construction process is improved.

Description

A construction method for prefabricated hollow internal rammed carrier piles

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 202211229263.0 filed in China on October 8, 2022, the entire contents of which are incorporated herein by reference.

Technical Field

The present application relates to the technical field of civil engineering foundation piles, and in particular to a construction method of prefabricated hollow internally rammed carrier piles.

Background technique

With the rapid development of infrastructure and the widespread deployment of basic infrastructure, the construction technology and construction requirements of construction projects have also been greatly improved, especially large-scale construction projects such as super-large bridges and buildings have been built in recent years. On the other hand, it has also prompted construction technology to make great progress in infrastructure construction and super-difficult construction production.

In the process of construction engineering, the foundation construction of the construction engineering is often the most basic and most crucial step; in the current field of construction engineering foundation treatment, precast piles are a type of pile often used in foundation treatment. At this stage, prestressed pipe piles are the most extensive, most mature and least expensive construction method in the field of precast piles, and they play a vital role in infrastructure construction.

However, under the premise that the volume and weight of infrastructure construction are getting bigger and bigger and the construction environment is getting more and more complex, the original prestressed pipe piles have gradually exposed their inevitable defects. After a large number of experimental practices, it was found that the pile body of the prestressed pipe pile was damaged when it was subjected to a heavy load-bearing matrix. The prestressed pipe piles are installed under high pressure by the diesel hammer hammering method. The tensile stress generated during the transmission of the pile body stress wave often cracks the pile body concrete. When encountering hard plastic clay, interlayer silt, silt sand and pebble soil layers, the prestressed pipe pile itself is difficult to enter the pile. In addition, it is necessary to increase the pile driver counterweight or hammer weight to drive the prestressed foundation pile to reach the construction requirements. When the pressure and kinetic energy used exceed the strength that the pile body can withstand, it will cause the pile head to break and the pile body to crack. In the presence of groundwater or corrosive minerals, such damaged prefabricated piles will inevitably cause the corrosion of the prestressed tendons and the strength of the concrete to be damaged, which will bring great hidden dangers to construction. In addition, the bearing capacity of precast pipe piles is mostly derived from the friction on the pile side, and the pile end resistance value is relatively low. Under the construction background of increasing volume and weight of construction buildings, the foundation bearing capacity of prestressed piles will also highlight certain bearing risks.

Based on this, on the basis of the prestressed pipe piles in the relevant technology, in order to overcome the technical defects highlighted by the above-mentioned prestressed pipe piles, a Chinese patent with publication number CN100375820C discloses a construction method of concrete piles. Specifically, it fills the bottom end of the pile pipe with bulk filler through the middle hole of the prestressed pipe pile, and then compacts the bulk filler with a rammer to compact and reinforce the foundation soil within a certain depth and range below the pile end until the optimal compacted soil that meets the required requirements is formed.

However, based on the above concrete pile construction, there are still corresponding technical defects:

(1) The production technology of prefabricated pipe piles is relatively backward. The inner wall of the hole in the pipe piles shipped from the factory is irregular and not smooth, and there is a lot of residual concrete. It is very easy to cause problems during the tamping process, and it is difficult to achieve the tamping action of the tamping hammer;

(2) Using bulk filling materials such as broken bricks and tiles, dry and hard concrete, and the central hole of the precast pipe pile is relatively small, so the rammer must be completely lifted out of the upper mouth of the precast pipe pile before filling, which leads to low construction efficiency;

(3) Bulk fillers are very likely to clog the middle hole (especially the bottom of the middle hole) of the precast pipe pile. After measuring the penetration, a certain amount of dry hard concrete must be added. As a result, the bottom of the precast pipe pile is often cracked or exploded, resulting in waste piles.

Finally, in related fields, infrastructure construction has expanded substantially, such as in coastal areas, mountainous areas, etc., where the groundwater content is relatively rich and the soil is relatively soft. On the one hand, it is difficult for prestressed pipe piles to obtain the best stress tolerance. Secondly, groundwater also drives the middle hole of the above-mentioned existing concrete piles to enter water during construction, making it impossible to continue to fill and tamp the piles, forming waste piles. This is not only a serious waste, but also seriously restricts the progress of the project and causes quality problems.

In summary, under the premise of pipe pile construction in the relevant technology, in order to meet the needs of high bearing capacity and be applicable to various geological soil layers, as well as cost control, there is still room for improvement in the pipe piles and the construction technology of the pipe piles in the relevant technology.

Summary of the invention

The present application provides a construction method for prefabricated hollow internal rammed carrier piles, which can meet the needs of high bearing capacity, can be applied to pipe piles in various geological soil layers, and has low cost.

A construction method for prefabricated hollow internal rammed carrier piles, comprising the following construction steps:

Step S1, installing a bottom sealing steel plate at the lower end of the hollow pile body to perform bottom sealing treatment on the hollow pile body, the bottom sealing steel plate and the inner wall of the hollow pile body form a sealed isolation cavity, the upper side of the bottom sealing steel plate is also installed with a waterproof rubber pad that fits and seals the lower end of the hollow pile body, and the bottom sealed hollow pile body is placed in the area of the project site selection;

Step S2, slowly slide a slender weight along the pile mouth at the upper end of the hollow pile body into the inner cavity of the sealed isolation chamber, and leave fillers and air flow channels between the slender weight and the side wall of the sealed isolation chamber, feed a small amount of cement sand mixture into the sealed isolation chamber along the fillers and the air flow channels, and simultaneously use a steel wire rope to lift the slender weight, tamp the cement sand mixture with a relatively low tamping energy, drive the cement sand mixture downward to squeeze the bottom steel plate, and judge whether the bottom steel plate has been opened by observing the height of the position marked by the steel wire rope;

Step S3, repeating step S2 multiple times, and ensuring that the slender heavy hammer is continuously controlled with a relatively low tamping energy so as not to hit the bottom of the hollow pile body, until the forming height of the formed dense cement sand mixture or the filling amount of the cement sand mixture reaches a preset value;

Step S4, when the cement-sand mixture reaches a preset height in the sealed isolation chamber or the cement-sand mixture filling amount reaches a preset value, continue to fill the cement-sand mixture through the channel, appropriately increase the tamping energy, drive the cement-sand mixture and the soil within a certain depth and range under the pile end to be reinforced and compacted, and form a pile end carrier;

Step S5, after step S4, stop filling the cement-sand mixture, tamp the pile end carrier by dropping a slender heavy hammer three times in succession, measure the penetration of the three blows, stop tamping when the penetration measurement value meets the design value, and continue filling the cement-sand mixture and tamping operations in step S4 when the penetration measurement value does not meet the design value, until the penetration measurement value meets the design value.

Optionally, when construction is carried out in a geological type with a low groundwater content at the construction site, in the above step S1, a waterproof rubber pad is installed on the upper side of the bottom steel plate, and in step S2, after the filler and the air flow channel are left between the slender weight and the side wall of the sealed isolation cavity, the slender weight is lifted to a certain height and then directly dropped to tamp the bottom steel plate, so as to knock the bottom steel plate away from the bottom end of the prefabricated hollow pile;

Then repeat step S3 to step S5, and in the process of performing step S3 to step S5, a method of not considering low-energy tamping and a method of not considering whether the slender heavy hammer hits out of the bottom of the hollow pile body can be used for construction.

Optionally, the method further comprises step S6, wherein a certain amount of bentonite or clay is wrapped with linen or cotton sack and placed into the hollow pile body through the upper opening of the hollow pile body;

The step S6 is located between step S1 and step S2. In addition, when water enters the hollow pile body during step S3 or step S4, this step can also be used to remove water and stop water.

Optionally, the method further comprises the following steps:

Step S7, after step S5, continue to fill the cement sand mixture or concrete into the sealed isolation cavity, and use a slender heavy hammer to tamp it to form a dense body of a certain height in the sealed isolation cavity.

Optionally, the method further comprises the following steps:

Step S8, pouring a certain amount of concrete into the center hole of the hollow pile body, or placing a steel cage in the center hole of the hollow pile body and then pouring a certain amount of concrete, after completion, processing the pile head of the hollow pile body to increase the pile body load.

Optionally, the area of the bottom steel plate and the waterproof rubber pad is larger than the area of the central channel of the hollow pile body, and the bottom steel plate is fixed to the flange at the bottom end of the hollow pile body by bolts or welding. The strength of the bolt or welding fixation is appropriately reduced to facilitate driving the bottom steel plate away from the bottom end of the hollow pile body in subsequent processes.

Optionally, the size of the filler and the air flow channel in step S2 is 2 cm to 4 cm;

In step S5, a certain amount of cement sand mixture is continuously added with a content greater than 0.1 m ³ .

In step S2 to step S4, the amount of cement sand mixture or concrete filled in each time does not exceed 0.05 m ³ , and the number of tamping after each filling does not exceed 5 times.

Optionally, in step S5, the penetration refers to the sinking value of the slender hammer after it freely falls from the same height to hit the bottom filler, that is, the penetration of each tamping, and the penetration of the latter time is not greater than the penetration of the previous time;

When measuring the penetration of a slender hammer, the impact energy of the slender hammer should be close to 2100kN/ ^m2 (unit area). The impact energy calculation formula is: the weight of the hammer multiplied by the drop distance divided by the bottom area of the hammer.

Optionally, when performing steps S2 to S5, the buoyancy value of the hollow pile body is synchronously observed. When the hollow pile body rises, the prefabricated pipe pile is re-driven or re-pressed. Re-driving or re-pressing means that the prefabricated hollow pile is sunk by hammering or static pressure. The sinking value does not exceed the buoyancy value of the prefabricated hollow pile. If the prefabricated hollow pile does not float or the buoyancy is very small, there is no need to re-drive or re-press.

In summary, the present application includes at least one of the following beneficial technical effects:

1. Fully combine the respective advantages of hollow piles and pile end carriers: Hollow piles are commonly used conventional pile types with mature construction technology. The advantages are simple process, fast speed, and no fear of groundwater, etc. However, since its bearing capacity mainly comes from The friction force on the pile side and the resistance value at the pile end are small, so the overall bearing capacity of the pile is limited and the quality is unstable. Based on the prefabricated hollow pile, this application cleverly uses the center hole of the prefabricated hollow pile to make the pile end carrier through reasonable and efficient technical means. In this way, the prefabricated hollow pile is equivalent to a casing, which not only greatly improves the bearing capacity of ordinary prefabricated hollow piles, but also solves the difficulties of drilling and blocking groundwater during the construction of ordinary carrier piles, and avoids the common problems of pile body shrinkage in soft soil layers or soil layers rich in groundwater, achieving twice the result with half the effort.

2. The pile end carrier is composed of rammed cement sand mixture, compacted soil and impact soil. The strength and modulus gradually decrease from the inside to the outside. When subjected to force, the pressure diffuses step by step during the load transfer process, which is equivalent to a multi-level extended foundation. The bearing capacity of the pile end foundation soil is fully utilized, so that the stress borne by the pile body can be diffused, reduced and reduced layer by layer, thereby significantly improving the bearing capacity of the pile. Its ultimate bearing capacity can generally be increased by more than 2 times compared with conventional prefabricated hollow piles. The better the soil properties of the pile end bearing layer, the greater the increased bearing capacity of the pile end carrier and the higher the characteristic value of the single pile bearing capacity.

3. Because the pile end carrier provides a high bearing capacity and the pile end carrier can be set in the shallow soil layer in the foundation, the length and diameter of the prefabricated hollow pile can be effectively shortened under the condition of providing the same bearing capacity, so that the overall cost of the foundation project can be reduced by more than 30%. At the same time, it is more suitable for buildings or structures with larger upper loads.

4. According to different geological conditions, especially according to the amount of water content in the foundation soil, targeted construction technology is designed. The different water content in the foundation soil directly affects the success and efficiency of the construction, as well as the engineering quality of the pile foundation, and it is especially important to pay attention to the soil layer with higher water content. Since the present application needs to add a carrier at the bottom of the prefabricated hollow pile, it is even more necessary to prevent water from entering the central channel. Therefore, in the entire technical solution, basically every step has waterproof technical measures, such as the bottom sealing of the pile body, the provision of waterproof rubber pads, the slender heavy hammer never hitting the bottom of the prefabricated hollow pile, the use of cement sand filler to seal the central channel of the prefabricated hollow pile, and the gradual increase of the tamping energy of the slender heavy hammer after the cement sand mixture filled in reaches a certain amount, etc. These waterproof technical measures can ensure the engineering quality of the pile foundation and the pile completion rate of the construction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a construction process diagram of embodiment 1 a-f of the present application;

FIG2 is a construction process diagram of Example 1 g-i of the present application;

FIG3 is a construction process diagram of a-f of Example 2 of the present application;

FIG4 is a construction process diagram of g-h of Example 2 of the present application;

Explanation of the reference numerals: 1: hollow pile body; 2: bottom steel plate; 3: sealed isolation cavity; 4: waterproof rubber pad; 5: slender weight; 6: filler and air flow channel; 7: cement sand mixture; 8: pile end carrier; 11: dense body; 12: steel cage; 13: flange; 14: concrete; 15: compacted soil; 16: affected soil.

Detailed ways

The present application is further described in detail below in conjunction with Figures 1-4.

The embodiment of the present application discloses a construction method of a prefabricated hollow internal ramming carrier pile, which is mainly used in the engineering pile foundation construction of the related technology, and overcomes the technical defects of the engineering foundation piles in the related technology that the construction is difficult and the construction quality is low in areas with high groundwater levels, and has the effects of convenient construction, good molding quality, and high bearing weight.

Embodiment 1:

In this embodiment, referring to FIG. 1 a, a construction method of a prefabricated hollow internal ramming carrier pile is disclosed, which is mainly used in areas with a high groundwater level; specifically, in the actual construction process, first, in order to prevent the groundwater from affecting the construction of the hollow pile body 1, a bottom sealing steel plate 2 is installed at the lower end of the hollow pile body 1 to perform bottom sealing treatment on the hollow pile body 1, and the bottom sealing steel plate 2 and the inner wall of the hollow pile body 1 form a sealed isolation cavity 3; it should be noted that the hollow pile body 1 is an existing prestressed pipe pile, a prefabricated hollow bamboo pile, a prefabricated hollow square pile, etc., and the bottom sealing steel plate 2 is fixed to the flange 13 at the bottom end of the hollow pile body 1 by bolts or spot welding, and the strength of the bolts or welding fixation is appropriately reduced to facilitate the bottom sealing steel plate 2 to be driven away from the bottom end of the hollow pile body 1 in the subsequent process.

By setting the bottom sealing steel plate 2, it can be ensured that when the hollow pile body 1 sinks into the soil, the groundwater in the soil will not affect the hollow pile body 1. In addition, in order to further improve the actual waterproof effect, a waterproof rubber pad 4 is installed on the upper side of the bottom sealing steel plate 2 to fit and seal with the lower end of the hollow pile body 1. The area of the bottom sealing steel plate 2 and the waterproof rubber pad 4 is larger than the area of the central channel of the hollow pile body 1. The waterproof rubber pad 4 is used to further waterproof and improve the actual sealing effect.

Referring to FIG. 1 b , after the bottom sealing and sealing operation is performed on the hollow pile body 1, the bottom sealed prefabricated hollow pile body 1 is sunk into the soil to a set depth by one of the methods such as hammering, vibration, and static pressure, so as to complete the installation of the hollow pile body 1 in the area with a high groundwater content.

Referring to FIG. 1 c and FIG. 1 d, after the installation of the hollow pile body 1 is completed, the slender weight 5 is lifted by a steel wire rope and slowly slid into the inner cavity of the sealed isolation chamber 3 along the pile mouth at the upper end of the hollow pile body 1, and a filler and an air flow channel 6 are left between the slender weight 5 and the side wall of the sealed isolation chamber 3, and a small amount of cement sand mixture 7 is fed into the sealed isolation chamber 3 along the filler and the air flow channel 6. In this embodiment, the size of the filler and the air flow channel 6 is 2 cm to 4 cm, and the height of the position of the slender weight 5 to the bottom steel plate 2 is marked on the steel wire rope for suspending the slender weight 5.

Continuing, after the cement-sand mixture falls from the filler and the air flow channel 6 onto the waterproof rubber pad 4, the slender heavy hammer 5 is lifted to tamp the cement-sand mixture 7 with a drop distance not exceeding 2 m, driving the cement-sand mixture 7 to squeeze the bottom steel plate 2 downward. By observing the height of the position marked with the above-mentioned wire rope, it is determined whether the bottom steel plate 2 has been opened. If not, the number of tamping times can be appropriately increased or the drop distance of the hammer can be slightly increased until the bottom steel plate 2 is opened.

Referring to e in Figure 1, continue to fill in a small amount of cement-sand mixture 7 and use the slender heavy hammer 5 to tamp the cement-sand mixture 7. During this process, the slender heavy hammer 5 is controlled with a lower tamping energy to never hit the bottom of the central channel, ensuring that the central channel is always blocked by the cement-sand mixture 7 to prevent water from entering the hollow pile body 1.

As shown in FIG. 1 f, when the cement sand mixture 7 reaches a preset height in the sealed isolation chamber 3 or the amount of cement sand mixture 7 filled reaches a preset value, after the cement sand mixture 7 filled in this embodiment exceeds ^0.1m3 , a waterproof layer with a certain compaction range is formed at the bottom of the hollow pile body 1, and the tamping energy is appropriately increased to drive the cement sand mixture and the soil within a certain depth and range under the pile end to be reinforced and compacted to form a pile end carrier 8. In the process of forming the pile end carrier 8, according to the actual construction situation, in order to ensure the quality of the pile end carrier 8, the slender heavy hammer 5 may not be knocked out from the lower end of the hollow pile body 1 during the tamping process, or it may be knocked out from the lower end of the hollow pile body 1, depending on the actual situation. In addition, in the process of forming the pile end carrier 8, the amount of cement sand mixture 7 filled in each time does not exceed ^0.05m3 , and the number of tamping times after each filling does not exceed 5 times.

Referring to g in FIG. 2 , when there is no filling material, that is, the cement sand mixture is stopped, and the pile end carrier 8 is rammed by dropping the slender weight 5 three times in a row, and the penetration of the three hits is measured. When the penetration measurement value meets the design value, the ramming is stopped. When the penetration measurement value does not meet the design value, the cement sand mixture 7 and the ramming operation are continued until the penetration measurement value meets the design value. At the bottom end of the hollow pile body 1, a carrier composed of the filled cement sand mixture 7 and the compacted, impact soil 16 is formed from the inside to the outside. When measuring the penetration of the slender weight 5, the impact energy of the slender weight 5 should be close to 2100kN/m ² (unit area), and the impact energy calculation formula is: the weight of the hammer multiplied by the drop distance divided by the bottom area of the hammer.

2h, a small amount of cement-sand mixture 7 is then filled into the central channel of the hollow pile body 1, and a slender heavy hammer 5 is used to tamp with a relatively low tamping energy to form a dense body 11 of cement-sand mixture 7 with a height of 2m in the central channel.

Finally, as shown in Fig. 2 i, a steel cage 12 is sunk into the central hole of the hollow pile body 1, and then concrete 14 is poured to the top of the precast hollow pile, or concrete 14 is directly poured to the top. After completion, the pile head of the hollow pile body 1 is processed to increase the pile body load.

In addition, it needs to be explained that after the hollow pile body 1 is placed underground in the construction site, the buoyancy value of the hollow pile body 1 is observed synchronously during the above-mentioned construction steps. When the hollow pile body 1 rises, the prefabricated pipe pile is re-driven or re-pressed. Re-driving or re-pressing means that the prefabricated hollow pile is sunk by hammering or static pressure. The sinking value does not exceed the buoyancy value of the prefabricated hollow pile. If the prefabricated hollow pile does not float or the floating amount is very small, there is no need to re-drive or re-press.

Embodiment 2:

Based on the first embodiment, this embodiment discloses the construction and installation of the foundation in an area with less groundwater content, as follows:

Referring to a, b, c, d, e, f in Figure 3, and g and h in Figure 4, when the groundwater content is low, the bottom of the hollow pile body 1 is also installed with a bottom sealing steel plate 2 by welding or bolting, etc., as in Example 1, but there is no need to additionally install a waterproof rubber pad 4, and after the hollow pile body 1 passing through the bottom sealing is placed under the soil, a slender weight 5 is placed and a filler and an air flow channel 6 are left. After the slender weight 5 is lifted to a certain height, it is directly dropped to tamp the bottom sealing steel plate 2, so as to knock the bottom sealing steel plate 2 away from the bottom end of the prefabricated hollow pile.

Moreover, in the process of forming the pile end carrier 8, the construction can be carried out without considering the low-energy tamping method, or without considering whether the slender heavy hammer 5 hits out of the bottom of the hollow pile body 1, so as to complete the construction quickly.

Similarly, finally, a steel cage 12 is sunk into the central hole of the hollow pile body 1, and then concrete 14 is poured to the top of the prefabricated hollow pile, or concrete 14 is directly poured to the top. After completion, the pile head of the hollow pile body 1 is processed to increase the pile body load.

Embodiment three:

Since water leakage may occur in the hollow pile body 1 during the actual construction process, in order to overcome the construction problems caused by this situation, in the present embodiment, during the construction of the foundation pile, a certain amount of bentonite or clay can be wrapped with linen or cotton sack 1, and then put into the hollow pile body 1 through the upper end opening of the hollow pile body 1, and then the extruded material after the bentonite is wrapped with linen is squeezed by a slender heavy hammer 5, so that the water inside the hollow pile body 1 is squeezed out, and Linen and bentonite also have a certain water absorption effect, thereby improving the actual water removal and water stopping effect.

Moreover, if water overflow occurs during the process of forming the dense body 11 and the pile end carrier 8, this step can also be used to remove water and stop water, thereby improving the qualification rate of actual construction piles and reducing the generation of waste piles.

Therefore, based on the above-mentioned implementation mode, pile foundation construction operations can be performed when there is more groundwater, less groundwater, or when water overflows from the pile body or during the construction process, without being affected by groundwater.

In the above embodiments, the construction process steps of the integral foundation piles are described, which are explained based on the first embodiment, the second embodiment and the third embodiment as a whole. Therefore, according to the conventional means of those skilled in the art, how to select the construction process when there is sufficient or less groundwater and when the pile body overflows, it should be covered in the protection scope of this application.

The embodiments of this specific implementation method are all optional embodiments of the present application, and are not intended to limit the protection scope of the present application. Therefore, all equivalent changes made based on the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

A construction method for a prefabricated hollow pile inner rammed carrier pile, the method being applicable to geological types with a high groundwater content, and comprising the following steps:

1) At the bottom of the prefabricated hollow pile, a bottom steel plate or a bottom steel plate plus a waterproof rubber pad is used to seal the central channel of the prefabricated hollow pile;

2) At the pile position, the prefabricated hollow pile with the sealed bottom is sunk into the soil to a set depth by hammering, vibration, or static pressure; or a pile hole is pre-formed in the soil by hammering, auger drilling, or rotary drilling, and then the prefabricated hollow pile with the sealed bottom is placed in the pile hole;

3) In the central hole of the precast hollow pile, slowly slide a slender weight to the bottom of the pile, leaving a certain gap between the outer wall of the slender weight and the inner wall of the central hole to form a filling channel and an air flow channel, mark the height of the position when the bottom of the slender weight hits the bottom steel plate on the steel wire rope for suspending the slender weight, fill a small amount of cement sand mixture in the central hole of the precast hollow pile, lift the slender weight to tamp the cement sand mixture with a low tamping energy to press the bottom steel plate downward, and judge whether the bottom steel plate has been opened by observing the height of the position marked on the steel wire rope;

4) Continue the above operation of filling a certain amount of cement-sand mixture and tamping the cement-sand mixture with a slender heavy hammer. During this process, the slender heavy hammer is controlled with a relatively low tamping energy so as not to hit the bottom end of the prefabricated hollow pile.

5) When the cement-sand mixture filled in reaches a certain amount, gradually increase the tamping energy of the slender weight, continue to fill in a certain amount of cement-sand mixture and tamping the cement-sand mixture with the slender weight, during which the slender weight can knock out the bottom of the prefabricated hollow pile, so that the soil within a certain depth and range under the pile end is reinforced and compacted, and gradually form a pile end carrier;

6) Under the unfilled state, measure the penetration of the slender hammer after three consecutive drops. When the penetration value meets the design value, stop tamping. When the penetration value does not meet the design value, continue to fill the cement sand mixture and tamping operation in step 5) above until the penetration value meets the design value;

7) Continue the above-mentioned filling of cement-sand mixture and tamping operation with the slender heavy hammer to form a cement-sand mixture compact body of a certain height in the central hole of the precast hollow pile, or pour a certain amount of concrete in the central hole of the precast hollow pile;

8) Carry out pile body treatment according to geological conditions and load requirements, including pouring concrete or cement mortar into the central hole of the precast hollow pile, or placing a steel cage in the central hole of the precast hollow pile and then pouring concrete or cement mortar, and also including the treatment of the pile head of the precast hollow pile.
A construction method for a prefabricated hollow pile inner rammed carrier pile, the method being applicable to geological types with low groundwater content, and comprising the following steps:

1) At the bottom of the prefabricated hollow pile, a bottom steel plate is used to seal the central channel of the prefabricated hollow pile;

2) At the pile position, the prefabricated hollow pile with the sealed bottom is sunk into the soil to a set depth by hammering, vibration, or static pressure; or a pile hole is pre-formed in the soil by hammering, auger drilling, or rotary drilling, and then the prefabricated hollow pile with the sealed bottom is placed in the pile hole;

3) A slender weight is placed in the central hole of the prefabricated hollow pile, with a certain gap between the outer wall of the slender weight and the inner wall of the central hole to form a filler channel and an air flow channel. The slender weight is lifted to a certain height and then dropped to tamp the bottom steel plate, thereby knocking the bottom steel plate away from the bottom end of the prefabricated hollow pile;

4) Fill a certain amount of cement-sand mixture into the central hole of the prefabricated hollow pile, lift a slender heavy hammer to a certain height and then drop it to tamp the cement-sand mixture;

5) Repeat the operation of step 4) to reinforce and compact the soil within a certain depth and range under the pile end, and gradually form a pile end carrier;

6) Under the unfilled state, measure the penetration of the slender hammer after three consecutive drops. When the penetration value meets the design value, stop tamping. When the penetration value does not meet the design value, continue to fill the cement sand mixture and tamping operation in step 5) above until the penetration value meets the design value;

7) Continue the above-mentioned filling of cement-sand mixture and tamping operation with the slender heavy hammer to form a cement-sand mixture compact body of a certain height in the central hole of the precast hollow pile, or pour a certain amount of concrete in the central hole of the precast hollow pile;

8) Carry out pile body treatment according to geological conditions and load requirements, including pouring concrete or cement mortar into the central hole of the precast hollow pile, or placing a steel cage in the central hole of the precast hollow pile and then pouring concrete or cement mortar, and also including the treatment of the pile head of the precast hollow pile.
According to the construction method of prefabricated hollow pile internal ramming carrier piles according to claim 1 or claim 2, the prefabricated hollow piles include prestressed pipe piles, prefabricated hollow bamboo piles, and prefabricated hollow square piles.
According to the construction method of ramming carrier piles in prefabricated hollow piles as described in claim 1 or claim 2, the area of the bottom steel plate is larger than the area of the central channel of the prefabricated hollow pile, the bottom steel plate is fixed to the flange at the bottom end of the prefabricated hollow pile by bolts or welding, and the strength of the bolt or welding fixation is appropriately reduced to facilitate the bottom steel plate to be driven away from the bottom end of the prefabricated hollow pile in the subsequent process.
According to the construction method of prefabricated hollow pile internal rammed carrier piles as described in claim 2, in some cases, such as when a pile hole is pre-formed in the soil and then a prefabricated hollow pile is placed in the pile hole, it is not necessary to perform bottom sealing treatment on the prefabricated hollow pile.
According to the construction method of prefabricated hollow pile internal ramming carrier piles according to claim 1 or claim 2, the gap left between the outer wall of the slender weight and the inner wall of the central channel is 2 cm to 4 cm.
According to the construction method of ramming carrier piles in prefabricated hollow piles as described in claim 1, using lower ramming energy means reducing the drop distance of the slender heavy hammer or the weight of the hammer, whereas gradually increasing the ramming energy of the slender heavy hammer in step 5) means increasing the drop distance of the slender heavy hammer or the weight of the hammer.
According to the construction method of prefabricated hollow pile internal ramming carrier piles according to claim 1 or claim 2, the materials of the cement sand mixture include cement, sand, water, small-size crushed stone, slag, and steel slag.
According to the construction method of prefabricated hollow pile internal ramming carrier piles as described in claim 1, wherein the cement sand mixture reaches a certain amount greater than 0.1m3.
The construction method of prefabricated hollow pile internal ramming carrier pile according to claim 1 or claim 2, wherein: The amount of cement-sand mixture filled in each time shall not exceed 0.05m3, and the number of tamping times after each filling shall not exceed 5 times.
According to the construction method of rammed carrier piles in prefabricated hollow piles as described in claim 1 or claim 2, the penetration refers to the sinking value of a slender heavy hammer after it freely falls from the same height to hit the bottom filler, that is, the penetration of one hit, and the penetration of the latter is not greater than the penetration of the previous one; when measuring the penetration of the slender heavy hammer, referring to the requirements of the specifications, the impact energy of the slender heavy hammer should be close to 2100kN/m2 (unit area), and the impact energy calculation formula is: the weight of the hammer multiplied by the drop distance divided by the bottom area of the hammer.
According to the construction method of prefabricated hollow pile internal ramming carrier piles as described in claim 1 or claim 2, it is observed whether the prefabricated hollow piles are floating, and the prefabricated pipe piles are re-driven or re-pressed according to the floating value of the prefabricated pipe piles. The re-driving or re-pressing means that the prefabricated hollow piles are sunk by hammering or static pressure, and the sinking value does not exceed the floating value of the prefabricated hollow piles. If the prefabricated hollow piles do not float or the floating amount is very small, there is no need to re-drive or re-press.
According to the construction method of rammed carrier piles in precast hollow piles as described in claim 1 or claim 2, a cement-sand mixture compact of a certain height is formed in the central channel of the precast hollow pile or a certain amount of concrete is poured, the purpose of which is to seal the bottom of the precast hollow pile and increase the contact area between the pile bottom and the carrier, while preventing the soil at the bottom of the pile from surging upward in the central channel under the surrounding pressure.