Construction method for gravel pile of thick dyke layer

Abstract

The invention provides a construction method for a gravel pile of a thick embankment layer, which comprises the following steps of: in a field after backfilling and flattening gravel materials, starting a down-the-hole hammer to lead a whole riprap layer above a hole in a construction area, lifting a drill bit after a steel casing follows up to the bottom of the riprap layer, and backfilling and pulling out a sleeve to complete the hole lead; pile forming construction of the gravel pile is completed through material supplementing; and after the pile machine moves, a cushion layer is laid on the gravel pile, and the compactness effect of the gravel pile is detected through a dynamic penetration method. The down-the-hole hammer and the steel pile casing are combined, so that the interior of the hole is kept stable, the time of repeated drilling of the down-the-hole hammer and auxiliary sinking of the pile casing by a vibratory hammer is saved, the hole forming construction progress is accelerated, and the down-the-hole hammer pile casing follow-up construction method can achieve the efficiency of forming a pile and leading 5-9 holes in one day.

Description

Technical Field

[0001] The invention relates to the technical field of gravel pile construction, in particular to a construction method of gravel piles for thick embankment layers in an embankment environment. Background Art

[0002] In the prior art, gravel pile construction is usually carried out in a small site by punching and crushing stones on land. Specifically, the seawall blocks are first excavated and then backfilled with stones to +4.0m to form a construction platform. Now 20 piles are selected as typical construction. The diameter of the gravel piles is 1m, the replacement rate is 20% (pile spacing is 1.95m×1.95m), and the construction site elevation is +4.0m.

[0003] However, part of the gravel pile construction needs to be carried out in the dike head area. At this time, the original location of the construction area is low-level treated by installing plastic drainage boards, and has a complete dike structure. At the same time, there is a 10m to 12m riprap layer on the silt layer in the onshore gravel pile construction area. Below it are mainly silt layers, silty clay, clay and other soil layers, which are difficult to complete directly through onshore punching and crushing. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a construction method for gravel piles in thick embankment layers. The casing is kept sinking synchronously with the down-the-hole hammer to keep the hole stable, eliminating the time of repeated drilling by the down-the-hole hammer and the time of sinking the casing with the assistance of a vibrating hammer, thereby accelerating the progress of hole construction. The down-the-hole hammer casing follow-up method can achieve an efficiency of 5-9 pile drillings per day.

[0005] In order to solve the above technical problems, the technical solutions provided by the present invention are as follows: The method for constructing gravel piles in thick embankment layers comprises the following steps: in a site that has been backfilled and leveled with sand material, a down-the-hole hammer is used to start drilling holes in the construction area, all the riprap layers are laid on top, a steel casing is followed to the bottom of the riprap layer, and the drill bit is lifted, and the casing is backfilled and pulled out to complete the drilling; The construction of gravel piles is completed by filling materials; After the pile driver is moved, a cushion layer is laid on the gravel pile, and the compactness of the gravel pile is tested by the dynamic penetration method.

[0006] Furthermore, the sand backfill is specifically carried out by backfilling the quarry rocks to a height of 4m to form a working platform for the borehole construction.

[0007] Furthermore, the working platform is formed to cover the construction area, and a protection area located outside the construction area is formed at the working platform.

[0008] Furthermore, the down-the-hole hammer forms a drill hole with a down-the-hole depth greater than 600 mm.

[0009] Furthermore, when the down-the-hole hammer is drilling down a hole, compressed air is used as a power to drive the drill bit to impact the rock, and the compressed air is used as a well-washing medium to carry out the rock cuttings in the down-the-hole hammer.

[0010] Furthermore, the pressure of the compressed air is 0.3-0.5 MPa.

[0011] Furthermore, the steel casing is in effective contact with the hammer head of the down-the-hole hammer through the follower pipe, so that the steel casing always sinks synchronously with the down-the-hole hammer.

[0012] Furthermore, the pipe shoe ring body located at the bottom of the steel casing forms a contact cavity located at the outer periphery of the down-the-hole hammer.

[0013] Furthermore, one of the tube shoe ring body and the pituitary body forms a plurality of protrusions, and the other forms a plurality of recessed portions corresponding to the protrusions.

[0014] Furthermore, the material supplement is specifically completed by reverse insertion and retained vibration to complete the pile formation. When the crushed stone in the pile driving pipe is insufficient to retain vibration, the hammer is stopped to supplement the stone until it is pulled out of the ground, and vibration is retained at the hole mouth for 20 seconds to ensure the pile formation.

[0015] The present invention has the following beneficial effects: The present invention solves the problem of following casing in a 10mm thick rock-filled layer. The conventional process is to follow up with the casing by punching, which is slow and takes 3 days to form one hole. In addition, the large rocks at the bottom will damage the surrounding holes due to the squeezing of the punching hammer. In the present invention, when the down-the-hole hammer process is adopted, the casing is kept sinking synchronously with the down-the-hole hammer, so that the inside of the hole remains stable, eliminating the time of repeated drilling of the down-the-hole hammer and the time of the vibrating hammer to assist in sinking the casing, speeding up the progress of hole-forming construction, and the down-the-hole hammer casing follow-up method can achieve the efficiency of 5-9 piles per day. The pile-forming speed is twice or more than that of impact drilling or other conventional means. After the down-the-hole hammer construction and hole-forming, an excavator should be used to fill soil or sand into the steel casing, and then the steel casing should be pulled out to meet the subsequent pile driver construction operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A construction flow chart of a thick embankment gravel pile construction method provided by the present invention; Figure 2 The present invention provides a construction flow chart of the lead hole. DETAILED DESCRIPTION

[0017] The present invention is described in detail below in conjunction with the various embodiments shown in the accompanying drawings, but it should be noted that these embodiments are not limitations of the present invention, and any equivalent transformations or substitutions in functions, methods, or structures made by ordinary technicians in the field based on these embodiments are all within the scope of protection of the present invention.

[0018] Refer to the attached Figure 1-2 As shown, it is a case of applying the present invention to a certain confidential project, which is described in detail as follows: First, the construction environment of the riprap layer of the embankment is introduced.

[0019] In this project, the construction area is the dike head area of ​​the West Second District. The original location has been treated with foundation by installing plastic drainage boards, and a complete dike structure has been formed. At present, there is a 10m to 12m riprap layer on the silt layer in the onshore gravel pile area, and the main soil layers below are silt layers, silty clay, clay, etc., which makes it face the following main problems during construction: It is difficult for the gravel pile pipe to penetrate the thick riprap layer of the embankment, and the required gravel pile body cannot be formed.

[0020] Secondly, the construction process is introduced.

[0021] In the present invention, after the punching section uses a full casing and pipe down-the-hole hammer drill to lead the hole, the vibration pipe sinking construction is carried out according to the non-punching section. The specific construction method is as follows: (1) Site backfill The original slope embankment is backfilled with quarry rock to +4.0m. The quarry rock is naturally graded and weighs 10-100kg of medium and slightly weathered quarry rock mixture. The quarry rock is mined from Xiaoshulanghu Island and then transported to the filling site by truck. The riprap is used on land to form an operating platform. To ensure the safety of the construction work, the top of the platform should be about 15 meters wider than the gravel pile construction area.

[0022] (2) Drilling hole construction plan After the site is leveled, down-the-hole hammer drilling is carried out on the +4.0 working platform. The drilling construction is planned to use the down-the-hole hammer to drill the entire riprap layer, and the long steel casing will follow to the bottom of the riprap layer. Then the drill bit will be lifted, backfilled with sand or plain fill, the casing will be pulled out, and then the gravel pile construction will be carried out.

[0023] Large-diameter down-the-hole hammers can effectively break up boulders, isolated rocks, moderately weathered and slightly weathered hard rocks in the gravel pile area where the project is located; long steel casings follow up to the bottom of the riprap layer to effectively avoid water leakage, hole collapse, and tidal washing; lifting the drill bit and backfilling with sand can effectively avoid the collapse of the hole wall after pulling out the casing, while reducing the resistance of the gravel pile to sink, creating good conditions for the construction of gravel piles.

[0024] (3) Down-the-hole hammer drilling process Pneumatic down-the-hole hammer is also called pneumatic impactor. Under the action of air compressor, large-diameter down-the-hole hammer uses compressed air as power medium to drive its work, and performs high-frequency crushing impact on hard rock. During the drilling process of pneumatic down-the-hole hammer, high-pressure air drives the piston in the impactor to make high-frequency reciprocating motion, and continuously transfers the kinetic energy generated by the motion to the drill bit, so that the drill bit obtains a certain impact work. Under the action of the impact work, the drill bit continuously impacts the rock at the bottom of the hole. Under the action of the impact work, the rock forms volume crushing. At the same time, the compressed air generated by the air compressor also serves as a well washing medium to carry the rock cuttings crushed by the down-the-hole hammer out of the hole. Large-diameter down-the-hole hammer has achieved good results in the drilling of block stone, isolated stone, medium-weathered and slightly weathered hard rock formations, meeting the smooth pile formation of subsequent equipment to solve the pile sinking problem in complex embankment layers of this project. The down-the-hole in this embodiment has a diameter greater than 500 mm, which is a large diameter compared with the conventional down-the-hole diameter less than 500 mm.

[0025] (3) Drilling hole construction 1) Working principle of casing and pipe drilling Its working principle is to establish a follow-pipe structure, that is, through the setting of the down-the-hole hammer head and the design of the casing follow-pipe drilling boot structure, so that the down-the-hole hammer can maintain effective contact with the steel casing during drilling, keep the steel casing from separating from the down-the-hole hammer, and always sink synchronously with the down-the-hole hammer, thereby effectively protecting the wall of the hole drilled by the down-the-hole hammer, avoiding the phenomenon of hole collapse, and facilitating the drilling of the down-the-hole hammer.

[0026] 2) Follow-up structure The ring body of the pipe shoe is placed entirely at the bottom of the full casing and embedded in the inner surface of the full casing. The pipe shoe ring body forms a protruding structure on the inner ring of the bottom of the casing. This protruding structure will contact the down-the-hole hammer to form a part of the follow-up pipe structure; the outer ring surface of the pipe shoe ring body in contact with the steel casing, and the groove formed by the pipe shoe ring body and the casing are welded together to form a whole.

[0027] 3) Connection and use of pipe shoe structure and down-the-hole hammer drill bit When the full casing is sleeved on the outer periphery of the down-the-hole hammer, the pipe shoe ring is placed on the outer periphery of the drill bit, and the protruding structure formed cooperates with the concave structure of the drill bit. When the full casing of the down-the-hole hammer follows the pipe for drilling, the full casing is in contact with the down-the-hole hammer body under the cooperation of the protruding structure and the concave structure, and it will not separate from the down-the-hole hammer, but always keeps sinking synchronously with the down-the-hole hammer.

[0028] 4) High construction efficiency This process solves the problem of casing following pipe in deep rock-filled layers. The casing keeps sinking synchronously with the down-the-hole hammer, so that the hole remains stable, eliminating the time of repeated drilling of the down-the-hole hammer and the time of sinking the casing with the assistance of the vibrating hammer, speeding up the construction progress of the hole. The casing following method of the down-the-hole hammer can achieve the efficiency of 5-9 piles per day. The pile speed is twice or more than that of impact drilling or other conventional methods. After the down-the-hole hammer construction, an excavator should be used to fill the steel casing with soil or sand, and then pull out the steel casing to meet the subsequent pile driver construction operations.

[0029] 5) Down-the-hole hammer punching construction method For the mountain stones, embankment slope protection and bottom protection stones of the embankment, pneumatic down-the-hole drilling rigs are used for drilling and punching construction, with a drilling diameter of 1.0m, a vacancy deviation of ±10cm, a verticality of ≤1%, and a drilling length of ≥10m. The down-the-hole hammer uses a DW640 series impactor, with an outer diameter of 1012mm for the casing, and a closed diameter of 950mm for the impact drill bit and an open diameter of 1054mm.

[0030] Backfilling the rock is done by punching holes with a double rotary rock drilling rig and following up with full casing. After penetrating the rock layer, the drill bit is lifted, sand or plain fill is backfilled, the casing is pulled out, and then the gravel pile is constructed by vibration sinking. The drilling equipment consists of a Bada pile frame JB-168, an upper power head, a down-the-hole hammer, and a steel casing. Among them, the down-the-hole hammer uses a DW-640 down-the-hole hammer with an outer diameter of 1012mm and an exhaust volume of 140m3 / minute.

[0031] Punching construction method: (a) Measure and stake out the gravel pile positions according to the construction drawings and mark the pile positions with lime; (b) Move the punching equipment to the pile position, align the pile tip with the center of the gravel pile position, and adjust the verticality of the drill rod; (c) Start the power equipment and submersible drilling equipment, start drilling, and adjust the verticality at any time according to the drilling project; (d) After drilling through the sand blowing layer and the rock filling layer according to the geological conditions, the drill rod is pushed out and the steel pipe is backfilled with soil or sand using an excavator; (e) After pulling out the steel casing, move the gravel pile equipment to that location to carry out gravel pile operations.

[0032] 6) Analysis of technical parameters of down-the-hole hammer drilling At present, the down-the-hole hammers used in China are mainly below φ500-φ600, and the holes larger than 500mm belong to the large-diameter down-the-hole hammer drilling range. There are two main parameters of the pneumatic down-the-hole hammer drilling process: air pressure and air volume.

[0033] These two parameters mainly meet two requirements: ①Meet the requirements of rock-breaking power of driving impactor; ② To discharge the cuttings in the hole out of the well to avoid repeated crushing. Different hydrogeological conditions, drilling structures, hole depth and diameter parameters have different requirements for air volume and air pressure. The parameters of the down-the-hole hammer can be selected as follows: (a) Air volume.

[0034] The rated air volume of the impactor selected for this project is 30m³ / min. With the increase of hole depth and hole diameter, the discharge of rock cuttings at the bottom of the hole is guaranteed, the repeated crushing of rock powder is reduced to achieve the ideal drilling efficiency. Usually, the upward return speed of the air volume in the hole is required to be ≥15m / s. At this time, the air flow speed is greater than the suspension speed of the rock cuttings. According to the conditions such as the borehole diameter, the outer diameter of the drill pipe, and the upward return wind speed on the slag discharge channel, the air volume can be calculated as follows: Q=47.1×K1×K2×(D2-d2)×V Where: Q——air supply volume m³ / min; K1——hole depth correction coefficient K1=1~1.1; K2—— water inflow system in the hole K2=1~1.5; D——drilling diameter; d——Drill pipe outer diameter; V——return wind speed (15~25m / s).

[0035] According to the formula, the return wind speed at the hole mouth is 15m / s, the drilling correction coefficient of the drilling depth is K1=1.0, and the water inflow coefficient in the hole is K2=1.5; it can be concluded that the down-the-hole hammer uses DW-640 down-the-hole hammer casing with an outer diameter of 1012mm and an exhaust volume of 140m3 / minute.

[0036] (b) Wind pressure. The down-the-hole hammer is a low-pressure down-the-hole hammer, and the required wind pressure is 0.5-0.7 MPa. However, the drilling efficiency is directly affected by the wind pressure. The greater the wind pressure, the greater the impact work and the higher the rock crushing efficiency.

[0037] Therefore, to complete large-diameter pneumatic down-the-hole hammer drilling, the working pressure requirements of the impactor must be met first so that it can work at full load. At the same time, it is also necessary to meet the along-the-hole pressure (0.0015MPa / m) brought about by the increase in drilling depth, overcome the water column pressure below the water level, and remove the pressure difference in the hole.

[0038] 6) Handling of main technical problems in down-the-hole hammer and pipe drilling construction (a) Insufficient drilling air volume Countermeasures: According to the requirements of the borehole diameter and the air volume of the selected air compressor, the down-the-hole hammer and casing drilling process are used to drill the hole. According to the drilling diameter capacity and casing specifications that the air compressor meets. After actual application, the down-the-hole hammer and casing drilling process solved the problem of insufficient air volume and achieved a relatively ideal effect during the drilling process.

[0039] (b) Cuttings holes Countermeasures: The reason why the cuttings are stuck in the hole is that the distance between the two pile guide holes is small. Under the action of high-pressure air, the high-pressure air passes through the pores in the stratum, and the boreholes are connected, resulting in a decrease in the pressure of the high-pressure air. During the construction of prestressed pipe piles with down-the-hole hammers, due to the problem of cuttings sticking in the hole, the air volume at the guide hole outlet is less than 15m / s, and the purpose of chip removal cannot be achieved. Instead, the cuttings pass through the pores into another hole, and a certain thickness of sediment is formed in the adjacent holes. Research and analysis have found that the sediment in the hole has little effect on the sinking of prestressed pipe piles. The main reasons are two aspects: On the one hand, the sediment in the hole has small particles and loose structure, which has little effect on the pile driving resistance. On the other hand, the sediment forms a saturated sand layer under the action of water in the hole. During the pipe pile construction, under the action of vibration force, the saturated sand layer produces sand liquefaction, which makes the sediment in the hole have little effect on the pile driving. Therefore, during the construction process, no special treatment was performed on the lead hole of the pile hole. Through actual construction, it was found that the phenomenon of rock cuttings stringing through the hole did not have a significant impact on the lead hole pile driving.

[0040] In this embodiment, the problem of sinking steel pipe piles is solved by introducing 0.3-0.5 MPa compressed air and adding water at the same time.

[0041] 7) How to control the verticality of down-the-hole hammer and casing drilling Countermeasures: Start the air compressor to drive the down-the-hole hammer to start drilling. During the initial drilling, the drilling speed should be low, the verticality of the drill pipe should be checked frequently, and the down-the-hole hammer and casing drilling process should be adjusted in time to guide the hole, which can not only solve the problem of insufficient outlet air volume but also control the verticality of the guide hole.

[0042] In this project, by adopting the down-the-hole hammer drilling technology, the rocks at the bottom of the casing are broken up by the down-the-hole hammer, and then rotated and ground into stone powder. The stone powder is discharged out of the hole by wind pressure, and then the casing follows and sinks, which improves construction efficiency.

[0043] In this embodiment, after the gravel pile completes the thick embankment layer, the density effect of the gravel pile can also be detected by the dynamic penetration method. At this time, a 63.5 kg core hammer is used to drive into the soil with a drop distance of 76 cm, and the number of hammer strikes per 10 cm is recorded. The heavy-duty dynamic penetration test is a conventional method, and the average hammer strike of a single pile is not less than 10, the minimum is not less than 7, and the number of detection points within the range of 7 to 10 is less than 20% of the total number of inspection points.

[0044] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0045] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A construction method for gravel piles in thick embankment layers, characterized in that: The following steps are included: in the site after the sand and gravel are backfilled and leveled, the down-the-hole hammer is used to start drilling holes in the construction area, all the riprap layers are laid on top, the steel casing is followed to the bottom of the riprap layer, and the drill bit is lifted, and the casing is backfilled and pulled out to complete the drilling; The construction of gravel piles is completed by filling materials; After the pile driver is moved, a cushion layer is laid on the gravel pile, and the density of the gravel pile is tested by the dynamic probing method.

2. The construction method for thick embankment gravel piles according to claim 1, characterized in that: The sand backfill is specifically performed by backfilling the quarry rocks to a height of 4m to form a working platform for the borehole construction.

3. The construction method for gravel piles in thick embankment layer according to claim 1, characterized in that: The working platform is formed to cover the construction area, and a protection area located outside the construction area is formed at the working platform.

4. The construction method for gravel piles in thick embankment layers according to claim 1, characterized in that: The down-the-hole hammer forms a drill hole with a down-the-hole diameter greater than 600 mm.

5. The construction method for gravel piles in thick embankment layer according to claim 1, characterized in that: The down-the-hole hammer uses compressed air as a driving force to drive the drill bit to impact the rock while the compressed air is used as a well-washing medium to carry out the rock cuttings in the down-the-hole hammer.

6. The construction method for gravel piles in thick embankment layers according to claim 5, characterized in that: The pressure of the compressed air is 0.3-0.5 MPa.

7. The construction method for gravel piles in thick embankment layers according to claim 5, characterized in that: The steel casing is in effective contact with the hammer head of the down-the-hole hammer through the follower pipe, so that the steel casing always sinks synchronously with the down-the-hole hammer.

8. The construction method for thick embankment gravel piles according to claim 7, characterized in that: The pipe shoe ring body located at the bottom of the steel casing forms a contact cavity located at the periphery of the vertical body of the down-the-hole hammer.

9. The construction method for gravel piles in thick embankment layer according to claim 8, characterized in that: One of the tube shoe ring body and the pituitary body is formed with a plurality of protrusions, and the other is formed with a plurality of recessed parts corresponding to the protrusions.

10. The construction method for gravel piles in thick embankment layer according to claim 1, characterized in that: The material supplement is specifically completed by reverse insertion and retained vibration. When the crushed stone in the pile sinking pipe is insufficient, the hammer is stopped and the stone is supplemented until it is pulled out of the ground, and the vibration is retained at the hole mouth for 20 seconds to ensure the pile is formed.

Images