A comprehensive construction method for cast-in-place piles in deep rock-fill and sand layers

Abstract

The application belongs to the technical field of pile foundation construction, and particularly relates to a comprehensive construction method of a cast-in-place pile for deep thick stone filling layer and sand layer, which comprises the following construction steps: determining a pile position, and positioning a large power rotary drilling pile machine; the large power rotary drilling pile machine drills downwards while a long casing follows; the large power rotary drilling pile machine retreats, and a conventional rotary drilling machine is positioned; the conventional rotary drilling machine is matched with special mud to continue drilling downwards to a design elevation; the conventional rotary drilling machine retreats; after cleaning the sediment in the hole, a reinforcing cage is hoisted into the hole and concrete is poured, and finally the pile is formed. The long casing follows the stone filling layer to effectively control the drilling quality of the stone filling layer, and the special mud effectively controls the hole collapse of the sand layer, effectively solving the problems of difficult hole forming and poor pile forming quality during the pile foundation construction in the deep thick stone filling layer and sand layer area, and reducing the comprehensive cost.

Description

Technical Field

[0001] This invention belongs to the field of pile foundation construction technology, specifically a comprehensive construction method for cast-in-place piles in deep rock-fill and sand layers. Background Technology

[0002] In infrastructure fields such as urban renewal, transportation hub construction, and large-scale building projects, pile foundations, as the core foundation form bearing the load of the superstructure, directly determine the overall safety and economy of the project through their construction quality and efficiency. However, when a project needs to traverse deep layers of rock and sand, pile foundation construction faces extremely complex technical challenges. Drilling holes is difficult and quality control is challenging in such geological conditions, and traditional construction techniques have revealed many insurmountable limitations in these geological environments.

[0003] Specifically, the constraints of such complex geological conditions on pile foundation construction are mainly reflected in the following aspects:

[0004] The process of drilling pile foundations carries extremely high stability risks. For deep rock-fill layers, typical characteristics include a loose, unconsolidated structure, significant variations in rock particle size, severely poor gradation, and numerous irregular voids and cavities. When using traditional rotary drilling techniques, drill bit cutting and disturbance easily cause rocks to roll and shift, leading to borehole instability and collapse. Simultaneously, the random distribution of rocks hinders casing advancement, frequently resulting in stuck drill bits, drill bit deviation, borehole displacement, and even failure to complete the hole. For deep sand layers, the cohesion of soil particles is extremely low, even approaching zero, and permeability is high. Conventional mud-wall techniques struggle to form a complete and resilient mud cake on the borehole wall. During drilling, the borehole wall is affected by dynamic water pressure, drill bit disturbance, and water level fluctuations, making it highly susceptible to quicksand and sand inrush, potentially leading to large-scale borehole collapses and drill bit burial accidents.

[0005] The quality of pile foundation construction is difficult to guarantee effectively. First, frequent borehole collapses can lead to irregular deformations such as local enlargement, narrowing, or necking of the pile hole. This not only obstructs the lowering of the reinforcing cage and causes positioning deviations, but also results in an abnormally high filling coefficient during concrete pouring, seriously affecting the structural integrity of the pile. Second, sediment at the bottom of the hole (including collapsed rocks, sand, and disturbed soil) is difficult to remove completely using conventional hole cleaning processes. This sediment forms a weak interlayer at the pile tip, significantly reducing the bearing capacity of the pile tip and the frictional resistance of the pile side. Third, the concrete overfilling caused by borehole collapses not only results in a large waste of cement, sand, and other materials, but may also lead to serious defects such as mud inclusions and broken piles due to the continuous collapse of the borehole wall during concrete pouring, causing the bearing capacity and durability of the pile foundation to fail to meet design requirements.

[0006] The construction process is inefficient and costly. Handling unexpected incidents such as borehole collapse and drill bit burial requires significant manpower and resources, with single incidents typically taking several days to weeks to resolve. Frequent borehole cleaning operations and secondary or even multiple drilling operations severely slow down the construction progress, leading to project delays. To ensure borehole stability, the project often resorts to the full-depth steel casing follow-up process (i.e., full-casing construction process). While this process can solve the wall protection problem to some extent, it requires extremely powerful equipment, and the placement and extraction of the casing are extremely time-consuming. Furthermore, the consumption of steel is enormous, and equipment rental costs and material costs rise sharply, making it highly uneconomical. In addition, rework and subsequent pile repairs due to unstable pile quality further increase the overall project cost, compress the effective construction window, and pose a serious threat to the overall project schedule.

[0007] Therefore, developing a comprehensive pile foundation construction method suitable for complex geological conditions involving deep rock-filled layers and sand layers has become an urgent need to solve such engineering and technical problems. It is of great practical significance for improving the quality of engineering construction, ensuring construction safety, and reducing overall costs. Summary of the Invention

[0008] To address the problems mentioned above, this invention provides a comprehensive construction method for cast-in-place piles in deep rock-fill and sand layers. By using a long casing to follow the rock-fill layer, the drilling quality of the rock-fill layer is effectively controlled, and by using specially formulated mud, the collapse of the hole in the sand layer is effectively controlled. This method effectively solves the problems of difficult hole formation and poor pile quality that occur during the construction of foundation piles in deep rock-fill and sand layers, and also reduces the overall cost.

[0009] This invention provides a comprehensive construction method for cast-in-place piles in deep rock-fill and sand layers, comprising the following construction steps:

[0010] S1. Determine the pile location and position the high-power rotary drilling rig;

[0011] S2. The high-power rotary drilling rig drills downwards, while the long casing follows.

[0012] S3. The high-power rotary drilling rig is removed and replaced with a conventional rotary drilling rig.

[0013] S4. The conventional rotary drilling rig, combined with special mud, continues to drill downwards to the design elevation;

[0014] S5. The conventional rotary drilling rig is withdrawn;

[0015] S6. After cleaning the sediment in the hole, hoist the steel cage into the hole and pour concrete to finally form the pile.

[0016] Furthermore, in the construction step S2, while the long casing moves downward following the high-power rotary drilling rig, the verticality of the long casing is measured.

[0017] Furthermore, in the construction step S2, the high-power rotary drilling rig drills downward to the bottom of the rock-fill layer, and the long casing passes through the rock-fill layer to form rigid support.

[0018] Furthermore, in the construction step S3, after the high-power rotary drilling rig drills down through the rock filling layer, it is replaced by the conventional rotary drilling rig to drill down into the sand layer. The high-power rotary drilling rig and the conventional rotary drilling rig are used alternately to save equipment costs.

[0019] Furthermore, in the construction step S4, the special mud slurry comprises the following components by weight: 2.5-3.5 parts of caustic soda (industrial sodium hydroxide), 1.0-1.2 parts of cellulose (sodium carboxymethyl cellulose), 200-230 parts of bentonite, and 700-800 parts of water. The overall specific gravity of the special mud slurry is 1.02-1.03.

[0020] Furthermore, in the construction step S4, the special mud forms a mud cake on the hole wall of the sand layer as the conventional rotary drilling rig drills downwards, in order to ensure the stability of the hole wall of the sand layer.

[0021] Furthermore, in the construction step S6, when pouring concrete into the long casing, the long casing is pulled upwards while pouring concrete.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The present invention adopts the drilling method of "high-power rotary drilling rig with long casing drilling into deep rock filling layer + conventional rotary drilling rig with special mud drilling into sand layer". Thanks to the physical isolation of the deep rock filling layer by the long casing and the effective protection of the sand layer by the special mud, the hole wall stability is high throughout the drilling process, which effectively avoids irregular hole shape problems such as hole diameter reduction and expansion caused by hole collapse. In addition, the sediment at the bottom of the hole is easy to remove, which ensures the effective performance of the pile end bearing capacity and pile side friction, thereby improving the drilling stability and pile quality. Moreover, the efficient and reliable wall protection system greatly reduces the occurrence rate of accidents such as hole collapse and drill bit burial, avoiding the high costs and time delays caused by additional hole cleaning, secondary or even multiple drilling, handling of drill bit burial, and pile repair due to quality defects. With fewer accidents and a smooth drilling process, the overall construction cycle is effectively shortened, and indirect costs such as project management, labor and equipment idleness are reduced.

[0024] (2) The present invention only requires the use of long casing in the deep stone filling layer stage. Compared with the traditional “full casing construction process” (i.e. the casing is used for the entire hole depth), the consumption of steel is greatly reduced. Moreover, it does not require the use of large power equipment throughout the process, and can be used only in the deep stone filling layer. The equipment rental and usage costs are significantly reduced.

[0025] (3) While the conventional rotary drilling rig is drilling into the sand layer, the special mud can effectively form a tough and dense mud skin on the hole wall of the sand layer. This mud skin significantly reduces water permeability, balances the pressure difference between the inside and outside of the hole wall, and strongly inhibits the sand flow, sand surge and hole collapse of the sand layer, thereby ensuring the stability of the hole wall in this stage of the sand layer.

[0026] (4) The stable borehole wall provides an ideal environment for the smooth lowering of the reinforcing cage and the pouring of concrete. When pouring concrete, the method of simultaneously pouring and pulling out the long casing can ensure that the concrete is continuously and densely filled under the protection of the long casing. This effectively prevents quality defects such as broken piles, mud inclusions and concrete segregation caused by pulling out the long casing too early or too late, thus forming a complete and dense high-quality pile body, thereby improving the pile formation quality of cast-in-place piles. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a process flow diagram of a comprehensive construction method for cast-in-place piles used in deep rock-fill and sand layers; Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0030] The following is in conjunction with the appendix Figure 1 The invention is described in detail with specific embodiments.

[0031] Reference Figure 1 The present invention provides a comprehensive construction method for cast-in-place piles in deep rock-fill and sand layers, comprising the following construction steps:

[0032] S1. Determine the pile location and position the high-power rotary drilling rig;

[0033] S2. The high-power rotary drilling rig drills downwards, while the long casing follows.

[0034] S3. The high-power rotary drilling rig was removed and replaced with a conventional rotary drilling rig.

[0035] S4. The conventional rotary drilling rig, combined with special mud, continues to drill downwards to the design elevation;

[0036] S5, conventional rotary drilling rig is dismantled;

[0037] S6. After cleaning the sediment in the hole, hoist the steel cage into the hole and pour concrete to finally form the pile.

[0038] This invention employs a drilling method that combines a high-power rotary drilling rig with a long casing for drilling into deep rock-filled layers with a conventional rotary drilling rig with specially formulated mud for drilling into sand layers. Benefiting from the physical isolation of the deep rock-filled layers by the long casing and the effective wall protection of the sand layers by the specially formulated mud, the borehole wall maintains high stability throughout the drilling process. This effectively avoids irregular borehole shapes caused by borehole collapse, such as diameter reduction or expansion. Furthermore, the sediment at the bottom of the borehole is easily removed, ensuring the effective utilization of the pile tip bearing capacity and pile side friction, thereby improving drilling stability and pile quality. Moreover, the highly efficient and reliable wall protection system significantly reduces the incidence of accidents such as borehole collapse and drill bit burial, avoiding the high costs and time delays associated with additional borehole cleaning, secondary or even multiple drilling operations, handling of burial drill bits, and re-piling due to quality defects. With fewer accidents and a smoother drilling process, the overall construction cycle is effectively shortened, and indirect costs such as project management, labor, and equipment downtime are reduced.

[0039] Specifically, in construction step S2, while the long casing moves downward with the high-power rotary drilling rig, the verticality of the long casing is measured, thereby effectively reducing the occurrence of hole deviation and ensuring the quality of hole formation. In addition, the method of verticality measurement is a conventional method in the field, and this invention does not describe or limit it in detail, as long as it can achieve verticality measurement.

[0040] In construction step S2, the high-power rotary drilling rig drills down to the bottom of the rock-fill layer, and the long casing penetrates the rock-fill layer to form rigid support. With its superior torque and pressurization capabilities, the high-power rotary drilling rig can efficiently and quickly penetrate deep, loosely structured, and easily collapsible rock-fill layers. As the rig drills downwards, the long casing follows, precisely sinking to the bottom of the rock-fill layer. This physically isolates the loose rocks from directly impacting the borehole wall, effectively reducing the risk of borehole collapse due to falling rocks. The long casing provides reliable rigid support and a barrier for the borehole wall in this stage of the deep rock-fill layer.

[0041] In construction step S3, after the high-powered rotary drilling rig penetrates the rock-fill layer, a conventional rotary drilling rig is used to drill into the sand layer. The high-powered rotary drilling rig and the conventional rotary drilling rig are used alternately to save equipment costs. This invention only requires the use of long casings in the deep rock-fill layer stage. Compared to the traditional "full casing construction process" (i.e., using casings throughout the entire hole depth), this greatly reduces steel consumption and eliminates the need to rely on high-powered equipment throughout the entire process; it is only required for the deep rock-fill layer, significantly reducing equipment rental and usage costs.

[0042] In construction step S4, the special mud comprises the following components by weight: 2.5-3.5 parts caustic soda (industrial grade sodium hydroxide), 1.0-1.2 parts cellulose (sodium carboxymethyl cellulose), 200-230 parts bentonite, and 700-800 parts water. The overall specific gravity of the special mud is 1.02-1.03. Based on the characteristics of the sand layer, the special mud developed according to the above weight ratio possesses high viscosity, high colloid content, good filtration loss, and appropriate specific gravity.

[0043] In construction step S4, the specially formulated drilling mud forms a mud cake on the borehole wall of the sand layer as the conventional rotary drilling rig drills downwards, ensuring the stability of the borehole wall in the sand layer. While the conventional rotary drilling rig drills downwards into the sand layer, the specially formulated drilling mud effectively forms a tough and dense mud cake on the borehole wall. This mud cake significantly reduces permeability, balances the pressure difference between the inside and outside of the borehole wall, and strongly inhibits sand flow, sand inrush, and borehole collapse, thereby ensuring the stability of the borehole wall during this stage of the sand layer drilling.

[0044] In construction step S6, when pouring concrete up to the long casing, the long casing is pulled upwards while pouring concrete. The stable borehole wall provides an ideal environment for the smooth lowering of the reinforcing cage and the pouring of concrete. By pouring concrete while simultaneously pulling out the long casing, it is ensured that the concrete is continuously and densely filled under the protection of the long casing. This effectively prevents quality defects such as broken piles, mud inclusions, and concrete segregation caused by pulling out the long casing too early or too late, thus forming a complete, dense, and high-quality pile body, thereby improving the pile formation quality of the cast-in-place pile.

[0045] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A comprehensive construction method for cast-in-place piles in deep rock and sand layers, characterized in that, The construction steps include: S1, determining a pile position, and positioning a large power rotary pile machine; S2, the large power rotary pile machine drills downward while a long casing follows; S3, the large power rotary pile machine retreats, and a conventional rotary drilling machine is positioned; S4, the conventional rotary drilling machine continues to drill downward to the design elevation with special mud; S5, the conventional rotary drilling machine retreats; S6, after cleaning the hole sediment, hoisting a reinforcement cage into the hole and pouring concrete, and finally forming a pile; In the construction step S2, the large power rotary pile machine drills downward to the bottom of the rock filling layer, and the long casing forms a rigid support through the rock filling layer; In the construction step S3, after the large power rotary pile machine drills through the rock filling layer, the conventional rotary drilling machine is used to drill downward into the sand layer, and the large power rotary pile machine and the conventional rotary drilling machine are used alternately to save equipment cost; In the construction step S6, when pouring concrete to the long casing, the long casing is pushed upward while pouring concrete; In the construction step S4, the special mud includes the following components by weight: caustic soda 2.5-3.5 parts, cellulose 1.0-1.2 parts, bentonite 200-230 parts, and cubic water 700-800 parts, and the overall specific gravity of the special mud is 1.02-1.

03.

2. The method according to claim 1, characterized in that, In the construction step S2, while the long casing follows the downward movement of the large power rotary pile machine, the long casing measures the perpendicularity.

3. The method according to claim 1, characterized in that, In the construction step S4, when the special mud drills downward with the conventional rotary drilling machine, a mud skin is formed on the hole wall of the sand layer to ensure the stability of the hole wall of the sand layer.

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