Support pile hole forming method for super-thick sand layer geology

Abstract

The invention discloses a support pile pore-forming method for super-thick sand layer geology, which is suitable for super-thick sand layer foundation pit supporting engineering of which the thickness is more than 25m and part of which contains pebbles and gravels, and aims to solve the problems that pore-forming in the geology is easy to collapse and shrink and the filling coefficient of concrete exceeds the standard. Optimization is achieved through the following steps that a special attack group is established, and personnel three-level disclosure and assessment are carried out; detecting a drill rod and a pile casing of the rotary drilling rig to ensure that equipment is qualified; the drilling speed of a sand layer is controlled to be 6-8 m / h through soil separation, and the mud index is dynamically adjusted; management and control measures such as pile separation jump driving and vertical hoisting of a reinforcement cage are adopted after hole forming; and the over-pouring amount of the pile top is controlled by precisely pouring concrete. After implementation, the concrete filling coefficient is stabilized within 1.1, the average is 1.05, the concrete cost of the support pile (the pile diameter is 1,200 mm and the pile length is 54.0 m / 56.0 m) is saved by about 500,000 yuan, the environmental pollution is reduced, the construction experience of an ultra-thick sand layer is enriched, the hole forming quality and the stability of a foundation pit are guaranteed, and the method is suitable for being popularized in similar projects.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of supporting piles in thick sand layer geology, in particular to a supporting pile hole forming method in ultra-thick sand layer geology. BACKGROUND

[0002] In foundation pit support engineering, mud walling pile forming is often used in various geological conditions due to its wide applicability. However, when the construction area has ultra-thick sand layer (thickness exceeding 25m) and part of the soil layer contains pebbles and gravel, the hole forming construction faces many technical difficulties and becomes a construction pain point in the industry.

[0003] Such ultra-thick sand layer has loose particles and weak cohesion. During the rotary drilling machine hole forming process, the hole wall lacks effective support, which may cause hole collapse and diameter reduction. In traditional construction, the drilling speed is not controlled according to the characteristics of the sand layer, which may cause disturbance of the hole wall due to fast drilling. The mud slurry index is not dynamically adjusted according to the geological changes, which may cause insufficient mud walling effect and further cause hole collapse. This not only requires re-drilling, increases construction cost and cycle, but also causes concrete pouring to be out of square, the concrete filling coefficient often exceeds the reasonable range, and a large amount of main material is wasted.

[0004] At the same time, some construction units lack experience in ultra-thick sand layer construction, and the construction personnel lack sufficient understanding of the sand layer hole forming process and risk prevention and control points. The technical briefing mainly focuses on the basic process and lacks special guidance for hole collapse. The equipment detection often ignores the details such as the deformation of the pile casing and the gap between the drill pipes, which further aggravates the hole forming quality hidden danger. In addition, the traditional construction lacks quality control after hole forming, such as the installation of the reinforcement cage which may scratch the hole wall, and the non-use of the spacer pile skip beating process, which all affect the hole forming stability, and a targeted technical solution is needed to solve the above problems. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the defects of the above-mentioned technology and provide a supporting pile hole forming method in ultra-thick sand layer geology.

[0006] To solve the above technical problems, the technical solution provided by the present application is a supporting pile hole forming method in ultra-thick sand layer geology, which is suitable for foundation pit support engineering containing sand layer with thickness exceeding 25m and part of the soil layer containing pebbles and gravel, and includes the following steps:

[0007] a. Preparation and personnel management: Form a special research team led by a project manager with experience in tackling difficult problems, with a project chief engineer and a project deputy manager as deputy leaders. According to the content of the super-thick sand layer hole forming construction of the rotary drilling rig, carry out three-level technical briefing covering basic technology and risk prevention and control to the construction personnel. At the same time, organize pile construction theory knowledge examination, which includes core modules such as rotary drilling rig operation specification, sand layer hole collapse prevention and treatment, and mud performance control. Ensure that the examination pass rate meets the specified requirements, and the briefing materials are jointly reviewed by the project manager and the project chief engineer, supplemented with special hole collapse response measures for super-thick sand layer;

[0008] b. Fine detection of equipment and pile casing: Select rotary drilling rig as hole forming equipment, detect the connection state of main and auxiliary drill rods, ensure that the main and auxiliary drill rods are not loose, and the distance between the drill slurry cylinder and the drill rod pin meets the requirements, to avoid hole wall disturbance caused by drill rod shaking during drilling; For the design diameter of 1400mm pile casing, randomly sample according to the corresponding number of each drill, use high-precision measuring instruments to measure the deformation deviation of the pile casing, select the pile casing with deformation deviation meeting the standard, and correct or replace the pile casing with deviation exceeding the standard for re-detection until it meets the requirements;

[0009] c. Precise hole forming operation for different soil layers: Start the rotary drilling rig for hole forming, according to the types of rock and soil layers divided in the survey report (① miscellaneous fill, ② loess-like silt, ③ sand layer, ④ silty clay, ④2 silt, ⑤ fine sand, ⑥ sand filling, ⑦ silty clay, ⑧ medium-coarse sand with pebbles, ⑨ rock clay), use differentiated construction parameters:

[0010] c1. Drilling speed control: When drilling in sand layer (③, ⑤, ⑧), set the speed threshold through the drilling machine operation system, arrange a person to carry out real-time speed monitoring on site, record the drilling speed at fixed time intervals, ensure that the actual speed is maintained within the specified range, and control the speed at low-medium speed for non-sand layer; c2. Mud dynamic regulation: Develop special mud proportioning scheme for different rock and soil layers in advance (①, ③, ⑤, ⑦, ⑨: specific range of specific gravity, viscosity, sand content; ②, ④, ④2, ⑥, ⑧: specific range of specific gravity, viscosity, sand content), arrange geology professionals to observe soil layer changes while drilling, and immediately adjust the mud specific gravity and viscosity through the mud circulation system once the actual soil layer is found to be inconsistent with the survey report, detect the mud performance indicators at fixed time intervals to ensure that the indicators are qualified;

[0011] d. Multi-dimensional quality control after drilling: After drilling, the borehole diameter is checked with a borehole gauge, and exceeding the drilling depth is strictly prohibited; when installing the reinforcing cage, two cranes are used for coordinated hoisting, and the command personnel use a total station to calibrate the verticality of the reinforcing cage in real time to ensure that the reinforcing cage is vertically hoisted into the hole after it is stable, so as to avoid scratching the hole wall; the staggered pile drilling process is adopted, and the interval between adjacent piles is in line with the requirements. The adjacent piles are constructed after the concrete of the first pile has initially set; the verticality of the drilling is controlled by the rotary drilling rig's built-in rotation angle positioning system and the additional limit device system to ensure that the hole deviation is within the allowable range.

[0012] e. Precise concrete pouring: Based on the specifications of the support piles (pile diameter 1200mm, effective pile length 54.0m / 56.0m), the design concrete volume for a single pile (64m³ for a 54.0m pile) is calculated. A concrete pump is used for layered pouring. The pile top elevation is measured according to the fixed concrete pouring volume. The pouring speed is dynamically adjusted to control the over-pouring volume at the pile top, so that the concrete filling coefficient meets the specified requirements.

[0013] f. Full-process quality traceability: Establish construction ledgers to record in detail the equipment parameters, drilling speed, mud index, steel cage installation deviation, concrete pouring volume, and other data for each pile, forming a traceable quality control file.

[0014] As an improvement, in step a, the pass rate needs to satisfy the formula for the total pass rate. ,in:

[0015] This indicates the pass rate of construction workers.

[0016] qualified This indicates the number of construction workers who scored 60 points or above in the assessment.

[0017] total This indicates the total number of construction workers participating in the assessment;

[0018] This formula is used to quantitatively assess the extent to which construction personnel have mastered the knowledge related to drilling holes in ultra-thick sand layers using rotary drilling rigs, ensuring that the personnel involved in the construction have basic operational and risk control capabilities, and avoiding construction quality problems caused by insufficient personnel skills.

[0019] As an improvement, in step c1, the drilling speed of the sand layer must satisfy the formula. ,in:

[0020] This indicates the actual drilling speed of the rotary drilling rig in the sand layer;

[0021] This formula clarifies the reasonable range of drilling speed in sand layers. By controlling the drilling speed, it avoids the collapse of the hole due to instability of the hole wall caused by excessive speed, or the impact on construction efficiency due to excessively slow speed, thus ensuring a balance between hole quality and construction progress.

[0022] As an improvement, in step c2, the sand content of the mud must meet the requirements of the corresponding soil and rock layers, where soil and rock layers of types ①, ③, ⑤, ⑦, and ⑨ satisfy the formula. Soil and rock layers of types ②, ④, ④2, ⑥, and ⑧ satisfy the formula ,in:

[0023] This indicates the sand content in the mud.

[0024] This formula ensures that the mud has good wall protection properties by limiting the upper limit of the sand content of the mud in different soil and rock layers, reducing the erosion of the borehole wall by sand particles, and avoiding the failure of mud wall protection due to excessive sand content, which in turn leads to borehole wall collapse.

[0025] As an improvement, in step d, the drilling deviation must satisfy the formula. ,in:

[0026] Indicates the borehole deviation rate;

[0027] This indicates the horizontal deviation between the actual borehole center and the design center.

[0028] Indicates the drilling depth;

[0029] This formula is used to quantitatively evaluate the verticality of the borehole and the accuracy of the pile position. By controlling the borehole deviation rate, it ensures that the support piles can accurately play their role in supporting the foundation pit and avoids uneven stress on the support structure due to pile position deviation, which would affect the overall stability of the foundation pit.

[0030] As an improvement, in step e, the concrete filling coefficient must satisfy the actual design formula. ,in:

[0031] Indicates the concrete filling coefficient;

[0032] actual This indicates the actual volume of concrete poured into a single support pile.

[0033] design This indicates the design concrete volume of a single support pile;

[0034] This formula is used to measure the deviation between the actual amount of concrete used and the designed amount. By controlling the filling coefficient, it can reduce concrete waste and lower project costs while ensuring the quality of pile formation (avoiding pile breakage and diameter reduction due to insufficient concrete).

[0035] As an improvement, in step b, the deformation deviation of the casing needs to meet the actual design requirements of the formula. ,in:

[0036] This indicates the casing deformation deviation rate;

[0037] actual Indicates the actual diameter of the casing;

[0038] design This indicates the design diameter of the casing (1400 mm).

[0039] This formula is used to assess the degree of deformation of the casing. By controlling the deformation deviation rate, it ensures that the casing can effectively fix the pile position, isolate surface water, and protect the borehole opening, thus avoiding the collapse of the borehole opening or the displacement of the pile position due to the deformation of the casing.

[0040] As an improvement, in step d, the time interval between drilling adjacent piles must satisfy the formula. ,in:

[0041] This indicates the time interval between the drilling of two adjacent piles;

[0042] This formula clarifies the construction interval between adjacent piles in the staggered pile driving process. By ensuring sufficient interval time, allowing the concrete of the first pile to initially set, it avoids disturbing the borehole wall of the first pile when the subsequent pile is drilled, thus preventing the borehole wall from collapsing and ensuring the quality of the pile.

[0043] As an improvement, in step c1, the drilling speed recording interval satisfies the formula ,in:

[0044] The time interval used to record drilling speed;

[0045] This formula specifies the recording frequency of drilling speed. By recording at regular intervals, it is easy to monitor changes in drilling speed in real time, promptly detect and adjust drilling speeds that exceed the range, ensure that drilling in sand layers is always within a reasonable speed range, and reduce the risk of borehole collapse.

[0046] As an improvement, in step c2, the detection interval for mud performance indicators satisfies the formula. ,in:

[0047] Indicates the time interval for testing mud performance indicators (specific gravity, viscosity, sand content);

[0048] This formula specifies the frequency of mud performance testing. By conducting regular testing, changes in mud performance can be monitored in a timely manner, and mud ratios that do not meet the requirements can be quickly adjusted to ensure that the mud always has a good wall protection effect, providing a stable guarantee for drilling in ultra-thick sand layers.

[0049] The advantages of this invention compared to existing technologies are as follows: This technical solution addresses the problems of easy collapse and reduced hole diameter, and excessive concrete volume in the drilling of support piles in ultra-thick sand layers (thickness exceeding 25m, some containing pebbles and gravel), resulting in significant benefits. Economically, by controlling the drilling speed in the sand layer to 6-8m / h, dynamically adjusting mud parameters (such as sand content ≤10%), and using staggered pile driving, the concrete filling coefficient is stabilized within 1.1 (average 1.05). For 509 piles (pile diameter 1200mm, pile length 54.0m / 56.0m), the concrete cost savings are approximately 500,000 yuan. Simultaneously, it reduces mud transportation and rework costs, shortens the construction cycle, and lowers management and equipment rental expenses.

[0050] In society, rotary drilling rig construction combined with mud recycling reduces mud discharge and construction waste, thus reducing environmental pollution. During construction, noise and dust levels meet standards, resulting in no complaints from surrounding areas. The quality of pile formation is high, laying the foundation for creating high-quality projects and enhancing the company's reputation.

[0051] Technically, a differentiated construction system for different soil layers has been established, filling the gap in standardized construction parameters for ultra-thick sand layers. Through personnel training, equipment testing (such as casing deformation ≤2%), and quality traceability, experience has been accumulated and professional personnel have been trained to enhance the company's technical reserves.

[0052] In terms of quality, the verticality of the borehole is controlled by two methods (deviation ≤1%), the installation of the reinforcing cage and the pouring of concrete are standardized, the quality of the borehole is qualified at 100%, the stability of the foundation pit is guaranteed, and safe conditions are provided for subsequent construction. Attached Figure Description

[0053] Figure 1 This invention describes the overall construction process of the method for drilling support piles in ultra-thick sandy geological layers.

[0054] Figure 2 This is a sub-process of precise hole-forming operation based on soil layers in the method for forming support piles in ultra-thick sandy geological layers according to the present invention.

[0055] Figure 3 This is a post-drilling quality control sub-process of the method for drilling support piles in ultra-thick sandy geological layers according to the present invention.

[0056] Figure 4 This invention relates to a sub-process for concrete pouring and quality traceability in the method for drilling support piles in ultra-thick sandy geological layers. Detailed Implementation

[0057] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0059] It is understood that spatial relation terms such as "below," "under," "below," "below," "above," "over," etc., can be used here to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as "below" or "under" or "below" of the other element or feature will be oriented "over" the other element or feature. Therefore, the exemplary terms "below" and "under" can include both upper and lower orientations. Furthermore, the device may also include other orientations, such as being rotated 90 degrees or other orientations, and the spatial descriptive terms used herein will be interpreted accordingly.

[0060] It should be noted that when one element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediary element. In the following embodiments, "connection" should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have the transmission of electrical signals or data between them.

[0061] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising,” “including,” or “having,” etc., specify the presence of the stated feature, whole, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof.

[0062] Combined with appendix Figures 1-4 A method for drilling retaining piles in ultra-thick sandy soil layers, applicable to foundation pit support projects containing sand layers exceeding 25m in thickness and with some soil layers containing pebbles and gravels, characterized by:

[0063] Includes the following steps:

[0064] a. Preliminary Preparation and Personnel Management: A special task force was established, led by a project manager with extensive experience in tackling complex problems, with the chief engineer and deputy project manager as deputy leaders. For the rotary drilling rig drilling in ultra-thick sand layers, a three-level technical briefing covering basic processes and risk control was conducted for construction personnel. Simultaneously, a theoretical knowledge assessment of pile foundation construction was organized, covering core modules such as rotary drilling rig operation specifications, prevention and treatment of hole collapse in sand layers, and mud performance control. The assessment was ensured to meet the required pass rate, and the briefing materials were jointly reviewed by the project manager and the chief engineer, supplemented with special guidance measures for dealing with hole collapse in ultra-thick sand layers.

[0065] b. Detailed Inspection of Equipment and Casing: Rotary drilling rigs are selected as the drilling equipment. The connection status of the main and auxiliary drill rods is inspected to ensure that the main and auxiliary drill rods are not loose and that the distance between the drill cuttings cylinder and the drill rod pins meets the requirements, so as to avoid the drill rod shaking during drilling and causing disturbance to the borehole wall. For the casing with a design diameter of 1400mm, random sampling inspection is carried out according to the corresponding number of each drilling rig. The deformation deviation of the casing is measured using high-precision measuring instruments. Casings with deformation deviations that meet the standards are selected. Casings with deviations that exceed the standards are corrected or replaced and re-inspected until they meet the requirements.

[0066] c. Precise Hole Formation Based on Soil Layers: The rotary drilling rig is started to form holes. Based on the soil and rock layer types identified in the survey report (① miscellaneous fill, ② loess-like silt, ③ sand, ④ silty clay, ⑤ fine sand, ⑥ fill sand, ⑦ silty clay, ⑧ medium-coarse sand with pebbles, ⑨ rocky clay), differentiated construction parameters are used:

[0067] c1. Drilling speed control: When drilling in sandy layers (classes ③, ⑤, and ⑧), a speed threshold is set through the drilling rig operating system. A dedicated person is assigned to monitor the drilling speed on-site with real-time speed monitoring equipment, recording the drilling speed at fixed time intervals to ensure the actual speed remains within the specified range. Non-sandy layers are controlled in low-to-medium speed grading. c2. Mud dynamic regulation: Specific mud mixing schemes are pre-developed for different soil and rock layers (classes ①, ③, ⑤, ⑦, and ⑨: specific specific gravity, viscosity, and sand content range; classes ②, ④, ④2, ⑥, and ⑧: specific specific gravity, viscosity, and sand content range). Geological professionals are assigned to monitor soil layer changes during drilling. If the actual soil layer does not match the exploration report, the mud specific gravity and viscosity are immediately adjusted through the mud circulation system. Mud performance indicators are tested at fixed time intervals to ensure the indicators meet the requirements.

[0068] d. Multi-dimensional quality control after drilling: After drilling, the borehole diameter is checked with a borehole gauge, and exceeding the drilling depth is strictly prohibited; when installing the reinforcing cage, two cranes are used for coordinated hoisting, and the command personnel use a total station to calibrate the verticality of the reinforcing cage in real time to ensure that the reinforcing cage is vertically hoisted into the hole after it is stable, so as to avoid scratching the hole wall; the staggered pile drilling process is adopted, and the interval between adjacent piles is in line with the requirements. The adjacent piles are constructed after the concrete of the first pile has initially set; the verticality of the drilling is controlled by the rotary drilling rig's built-in rotation angle positioning system and the additional limit device system to ensure that the hole deviation is within the allowable range.

[0069] e. Precise concrete pouring: Based on the specifications of the support piles (pile diameter 1200mm, effective pile length 54.0m / 56.0m), the design concrete volume for a single pile (64m³ for a 54.0m pile) is calculated. A concrete pump is used for layered pouring. The pile top elevation is measured according to the fixed concrete pouring volume. The pouring speed is dynamically adjusted to control the over-pouring volume at the pile top, so that the concrete filling coefficient meets the specified requirements.

[0070] f. Full-process quality traceability: Establish construction ledgers to record in detail the equipment parameters, drilling speed, mud index, steel cage installation deviation, concrete pouring volume, and other data for each pile, forming a traceable quality control file.

[0071] In step a, the pass rate must meet the requirements of the formula: total pass rate ,in:

[0072] This indicates the pass rate of construction workers.

[0073] qualified This indicates the number of construction workers who scored 60 points or above in the assessment.

[0074] total This indicates the total number of construction workers participating in the assessment;

[0075] This formula is used to quantitatively assess the extent to which construction personnel have mastered the knowledge related to drilling holes in ultra-thick sand layers using rotary drilling rigs, ensuring that the personnel involved in the construction have basic operational and risk control capabilities, and avoiding construction quality problems caused by insufficient personnel skills.

[0076] In step c1, the drilling speed in the sand layer must satisfy the formula. ,in:

[0077] This indicates the actual drilling speed of the rotary drilling rig in the sand layer;

[0078] This formula clarifies the reasonable range of drilling speed in sand layers. By controlling the drilling speed, it avoids the collapse of the hole due to instability of the hole wall caused by excessive speed, or the impact on construction efficiency due to excessively slow speed, thus ensuring a balance between hole quality and construction progress.

[0079] In step c2, the sand content of the mud must meet the requirements of the corresponding soil and rock layers, where soil and rock layers of types ①, ③, ⑤, ⑦, and ⑨ meet the requirements of the formula. Soil and rock layers of types ②, ④, ④2, ⑥, and ⑧ satisfy the formula ,in:

[0080] This indicates the sand content in the mud.

[0081] This formula ensures that the mud has good wall protection properties by limiting the upper limit of the sand content of the mud in different soil and rock layers, reducing the erosion of the borehole wall by sand particles, and avoiding the failure of mud wall protection due to excessive sand content, which in turn leads to borehole wall collapse.

[0082] In step d, the drilling deviation must satisfy the formula ,in:

[0083] Indicates the borehole deviation rate;

[0084] This indicates the horizontal deviation between the actual borehole center and the design center.

[0085] Indicates the drilling depth;

[0086] This formula is used to quantitatively evaluate the verticality of the borehole and the accuracy of the pile position. By controlling the borehole deviation rate, it ensures that the support piles can accurately play their role in supporting the foundation pit and avoids uneven stress on the support structure due to pile position deviation, which would affect the overall stability of the foundation pit.

[0087] In step e, the concrete filling coefficient must meet the actual design requirements of the formula. ,in:

[0088] Indicates the concrete filling coefficient;

[0089] actual This indicates the actual volume of concrete poured into a single support pile.

[0090] design This indicates the design concrete volume of a single support pile;

[0091] This formula is used to measure the deviation between the actual amount of concrete used and the designed amount. By controlling the filling coefficient, it can reduce concrete waste and lower project costs while ensuring the quality of pile formation (avoiding pile breakage and diameter reduction due to insufficient concrete).

[0092] In step b, the deformation deviation of the casing must meet the actual design requirements of the formula. ,in:

[0093] This indicates the casing deformation deviation rate;

[0094] actual Indicates the actual diameter of the casing;

[0095] design This indicates the design diameter of the casing (1400 mm).

[0096] This formula is used to assess the degree of deformation of the casing. By controlling the deformation deviation rate, it ensures that the casing can effectively fix the pile position, isolate surface water, and protect the borehole opening, thus avoiding the collapse of the borehole opening or the displacement of the pile position due to the deformation of the casing.

[0097] In step d, the time interval between the drilling of adjacent piles must satisfy the formula. ,in:

[0098] This indicates the time interval between the drilling of two adjacent piles;

[0099] This formula clarifies the construction interval between adjacent piles in the staggered pile driving process. By ensuring sufficient interval time, allowing the concrete of the first pile to initially set, it avoids disturbing the borehole wall of the first pile when the subsequent pile is drilled, thus preventing the borehole wall from collapsing and ensuring the quality of the pile.

[0100] In step c1, the drilling speed recording interval satisfies the formula ,in:

[0101] The time interval used to record drilling speed;

[0102] This formula specifies the recording frequency of drilling speed. By recording at regular intervals, it is easy to monitor changes in drilling speed in real time, promptly detect and adjust drilling speeds that exceed the range, ensure that drilling in sand layers is always within a reasonable speed range, and reduce the risk of borehole collapse.

[0103] In step c2, the testing interval for mud performance indicators satisfies the formula. ,in:

[0104] Indicates the time interval for testing mud performance indicators (specific gravity, viscosity, sand content);

[0105] This formula specifies the frequency of mud performance testing. By conducting regular testing, changes in mud performance can be monitored in a timely manner, and mud ratios that do not meet the requirements can be quickly adjusted to ensure that the mud always has a good wall protection effect, providing a stable guarantee for drilling in ultra-thick sand layers.

[0106] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following detailed description of the method for drilling retaining piles in ultra-thick sandy geology, based on a specific engineering example, is provided below. This embodiment is based on a foundation pit support project. This project involves an ultra-thick sandy layer exceeding 25m in thickness, with some soil layers containing pebbles and gravel. The retaining piles are 1200mm diameter mud-wall cast-in-place piles, drilled using a rotary drilling rig. The designed effective pile lengths are divided into two specifications: 54.0m and 56.0m, totaling 509 piles (441 54.0m piles and 68 56.0m piles). During construction, key issues to address include the tendency of the sandy layer to collapse and the excessive concrete filling coefficient. This invention achieves dual control over the quality and cost of retaining pile drilling.

[0107] I. Preliminary Preparations and Personnel Management:

[0108] Before the project officially commences, a special task force is first established. The task force is led by a project manager with extensive experience in tackling similar engineering challenges, with the project's chief engineer and deputy project manager serving as deputy leaders. Members include professionals in construction technology, quality inspection, and equipment management, ensuring that the task force possesses comprehensive capabilities in overall coordination, technical support, and on-site management.

[0109] Given the unique characteristics of the ultra-thick sand layer in this project, a three-tiered technical briefing was conducted for all personnel involved in the support pile construction. The briefing covered not only the basic operating procedures of the rotary drilling rig and key points of the support pile drilling process, but also, and more importantly, the identification, prevention measures, and emergency response plans for borehole collapse risks in the sand layer. To ensure the effectiveness of the briefing, a combination of written documentation and on-site demonstrations was adopted. For example, a simulated sand layer drilling scenario was set up on-site to demonstrate emergency procedures for borehole collapse caused by excessive drilling speed, including how to create counter-pressure by adjusting the mud density and how to pause drilling and reinforce the borehole wall. This allowed construction personnel to intuitively grasp the key operations.

[0110] After the briefing, all construction personnel will undergo a theoretical knowledge assessment on pile foundation construction. The assessment will cover core modules such as rotary drilling rig operation procedures, prevention and treatment of sand layer collapse, and mud performance control. The assessment will be a closed-book exam, with a maximum score of 100 points; a score of 60 or above is considered passing. The pass rate must meet the requirements of the formula for the total pass rate. ,in This indicates the pass rate of construction workers' assessment. This indicates the number of construction workers who scored 60 points or above in the assessment. This represents the total number of construction workers participating in the assessment. In this example, a total of 50 construction workers participated in the assessment, and 35 of them passed. Substituting these numbers into the formula, we can calculate... The results were just up to standard; for the 15 people who failed the assessment, one-on-one tutoring and training were arranged for them to be reassessed until they passed, ensuring that every person involved in the construction had basic operation and risk control capabilities, and avoiding construction quality problems caused by improper operation from the perspective of personnel skills.

[0111] Meanwhile, the project manager and the chief engineer jointly conducted a second review of the technical disclosure materials, focusing on checking for any omissions in the content regarding the problem of borehole collapse in ultra-thick sand layers. The review found that the original disclosure materials only mentioned the risk of borehole collapse without specifying specific countermeasures. The relevant content was then supplemented and improved, such as clarifying the corresponding treatment procedures, required materials and equipment allocation plans for different degrees of borehole collapse (slight diameter reduction, partial collapse, and severe collapse), to ensure the completeness and practicality of the disclosure materials.

[0112] II. Detailed Inspection of Equipment and Casing:

[0113] Five rotary drilling rigs were selected as the drilling equipment for this project. Before the rigs were put into use, a comprehensive inspection of the connection status of the main and auxiliary drill rods of each rig was conducted. The main drill rod is a hollow structure, and the auxiliary drill rod is nested inside the main drill rod. During drilling, the auxiliary drill rod extends from the main drill rod through a wire rope. The two are connected by a sliding groove. During the inspection, the focus was on checking for wear and corrosion in the sliding groove, whether the connection between the main and auxiliary drill rods was tight, and whether the distance between the cuttings cylinder and the drill rod pin met the requirements. It was ensured that the distance between the cuttings cylinder and the drill rod pin did not exceed 1mm to avoid the drill rod shaking due to excessive clearance during drilling, which could disturb the sand layer and borehole wall and cause the risk of borehole collapse.

[0114] The casing, as a key component for fixing the pile position, isolating surface water, and protecting the borehole opening, directly affects the stability of the borehole formation. In this project, the casing is designed with a diameter of 1400mm, made of Q235 steel plate with a thickness of 10mm. During inspection, sampling was conducted according to the standard of checking at least two casings per drilling rig, for a total of 10 casings inspected (5 drilling rigs × 2 casings / rig). A laser diameter gauge with an accuracy of 0.1mm was used to measure the actual diameter of the casing, and the casing deformation deviation rate was calculated. The deformation deviation rate must meet the actual design requirements. ,in This indicates the casing deformation deviation rate, in reality. Indicates the actual diameter of the casing, design This indicates the design diameter of the casing (1400mm).

[0115] In this embodiment, the detection data of the 10 casings are as follows: Serial number 1 casing has an actual diameter of 1421mm. Substituting this into the formula yields... The actual diameter of the casing for serial number 2 is 1416.8 mm, calculated as follows: ; Serial number 3, actual diameter of the casing is 1414mm. ; Serial number 4, the actual diameter of the casing is 1418.2mm. ; Serial number 5, the actual diameter of the casing is 1470mm. ; Serial number 6, the actual diameter of the casing is 1428mm. ; Serial number 7, the actual diameter of the casing is 1418.2 mm. ; Serial number 8, the actual diameter of the casing is 1456mm. ; Serial number 9, the actual diameter of the casing is 1422.4 mm. ; Serial number 10, the actual diameter of the casing is 1453.2 mm. .

[0116] According to the test results, the deformation deviation rate of casings numbered 5, 8, and 10 exceeded 2%, which did not meet the requirements. These three casings underwent correction treatment. A hydraulic straightening machine was used to apply pressure to the deformed areas for correction. After correction, the diameter was measured again. The actual corrected diameter of casing number 5 was 1421 mm. The actual diameter of the casing in serial number 8 has been corrected to 1425.2 mm. The actual diameter of the casing (serial number 10) has been corrected to 1422.4 mm. All satisfy The requirements are to ensure that all casings put into use can function effectively and avoid borehole collapse or pile displacement due to casing deformation.

[0117] In addition, the pull-out performance of the casing was tested. A tension gauge was used to apply a tension of not less than 50kN to each casing and maintain it for 5 minutes. The displacement of the casing was then observed. The displacement was required to be no more than 2mm. In this embodiment, the pull-out test displacement of the 10 casings was between 1.2-1.8mm, which met the requirements. This ensures that the casing will not sink or tilt due to tension during drilling, further ensuring the stability of the hole formation.

[0118] III. Precision Hole Drilling Operation Based on Soil Layers:

[0119] According to the survey report, the soil and rock layers in the construction area of ​​this project are divided into the following layers from the surface to the pile bottom: ① miscellaneous fill, ② loess-like silt, ③ sand, ④ silty clay, ④ silty soil, ⑤ fine sand, ⑥ fill sand, ⑦ silty clay, ⑧ medium-coarse sand with pebbles, and ⑨ rocky clay. The physical and mechanical properties of different soil and rock layers vary greatly. Therefore, differentiated construction parameters are used for hole drilling to ensure stable hole drilling in all types of soil layers.

[0120] (a) Drilling speed control:

[0121] When drilling through sand layers (including ③ sand layer, ⑤ fine sand, and ⑧ medium-coarse sand containing pebbles), the weak cohesion between sand particles means that excessively fast drilling speeds can easily lead to borehole instability and collapse, while excessively slow speeds will affect construction efficiency. Therefore, it is necessary to strictly control the drilling speed to ensure it meets the formula... ,in This indicates the actual drilling speed of the rotary drilling rig in the sand layer.

[0122] To achieve precise control of drilling speed, a preset speed threshold is configured in the operating system of each rotary drilling rig. When the drilling speed exceeds 8 m / h or falls below 6 m / h, the system automatically issues an audible and visual alarm and pauses drilling. Drilling resumes only after the operator adjusts parameters such as drilling pressure and rotation speed. Simultaneously, a dedicated person is assigned to the construction site with real-time speed monitoring equipment (accuracy 0.1 m / h) to track and check the drilling speed, recording the speed at fixed time intervals that satisfy the formula... ,in The time interval for recording drilling speed.

[0123] For example, during drilling in sand layer ③, the actual drilling speed is recorded every 30 minutes. If a recorded speed is 8.5 m / h, exceeding the upper limit of 8 m / h, the operator is immediately notified to reduce the drilling pressure from the original 150 kN to 120 kN. After adjustment, monitoring continues, and the speed is measured again after 5 minutes, showing 7.8 m / h, returning to a reasonable range. If the recorded speed is 5.5 m / h, below the lower limit of 6 m / h, the drilling pressure is appropriately increased to 160 kN, and the speed is increased to 6.2 m / h, ensuring that drilling in the sand layer is always within a reasonable range. Within the specified range, the quality of hole formation and construction progress are balanced.

[0124] For non-sand layers (① miscellaneous fill, ② loess-like silt, ④ silty clay, ④ 2 silt, ⑥ fill sand, ⑦ silty clay, ⑨ rocky clay), the drilling speed is controlled in stages from low to medium speed. For example, ① miscellaneous fill is loose, so low speed (4-5 m / h) drilling is used to avoid excessive impurities clogging the drill cuttings; ④ silty clay has strong cohesion, so medium speed (7-9 m / h) drilling is used to improve construction efficiency while preventing borehole collapse.

[0125] (II) Dynamic control of mud:

[0126] In drilling through ultra-thick sand layers, drilling mud plays a crucial role in protecting the drilling wall, carrying slag, and cooling the drill bit. Its performance indicators (specific gravity, viscosity, and sand content) need to be dynamically adjusted according to the characteristics of different rock and soil layers to ensure the wall protection effect.

[0127] Specific mud mixing schemes are pre-developed for different soil and rock layers: For ① miscellaneous fill, ③ sand layer, ⑤ fine sand, ⑦ silty clay, and ⑨ rocky clay, the mud specific gravity is controlled at 1.30-1.35, the viscosity is controlled at 19-22s, and the sand content must meet the formula. For ② loess-like silt, ④ silty clay, ④ 2-silt, ⑥ sand-filled soil, and ⑧ medium-coarse sand containing pebbles, the mud slurry specific gravity should be controlled at 1.25-1.33, the viscosity at 18-20s, and the sand content should meet the following formula: ,in This indicates the sand content in the mud.

[0128] To ensure that the performance indicators of the drilling mud meet the requirements, specific technical instructions were formulated for the preparation and use of the mud, clarifying the proportions of raw materials for the mud corresponding to different soil and rock layers (such as the amount of bentonite, soda ash, and CMC added). Geological professionals were also arranged to observe changes in the soil layers during drilling. For example, during the drilling process, every 5m in depth, the soil in the borehole was taken out and compared with the soil layer sample in the exploration report. If it was found that the actual soil layer did not match the exploration report (such as the original design was ④ silty clay, but the actual drilling encountered ③ sand layer), the mud ratio was immediately adjusted through the mud circulation system.

[0129] Simultaneously, mud performance indicators are tested at fixed time intervals, and the testing intervals satisfy the formula. ,in This indicates the time interval for testing mud performance indicators. Testing is performed using a three-piece mud testing kit (hydrometer, viscometer, and sand content meter). For example, during drilling through sand layer ③, the sand content of the mud is tested every hour. If a test shows a sand content of 11%, exceeding the limit... As required, immediately add bentonite to the mud pit (addition amount 50kg / cubic meter of mud), stir evenly, and test again. The sand content should be reduced to 9.5%, which meets the requirements. However, when drilling through medium-coarse sand containing pebbles (⑧), if the sand content is found to be 9%, it exceeds the limit. In accordance with the requirements, soda ash (addition amount 10kg / cubic meter of mud) is added to adjust the sand content to 7.8%, ensuring that the mud always has good wall protection performance, reducing the scouring of the borehole wall by sand particles, and avoiding the failure of mud wall protection due to excessive sand content.

[0130] In addition, the mud adjustment adopts the "automatic proportioning + manual verification" mode. An automatic dosing device is equipped in the mud circulation system. This device is linked with the mud performance testing instrument. When the mud specific gravity, viscosity or sand content is detected to be outside the specified range, the device automatically calculates and adds the required admixtures (bentonite, soda ash, etc.). After the adjustment is completed, the mud is manually verified using a mud three-piece set to ensure that the specific gravity error does not exceed 0.02, the viscosity error does not exceed 1s, and the sand content error does not exceed 1%, thereby further improving the accuracy of mud performance control.

[0131] IV. Multi-dimensional quality control after hole formation:

[0132] After the hole is formed, quality control should be carried out from multiple dimensions such as hole diameter, hole depth, verticality, installation of steel cage, and construction sequence to avoid hole wall collapse or pile quality defects due to improper post-hole treatment.

[0133] (a) Aperture and depth control:

[0134] A borehole gauge (0.1mm accuracy) is used to comprehensively inspect the borehole diameter after drilling to ensure it meets the design requirements (1200mm). If local reduction in diameter is found (e.g., a diameter of only 1180mm), a reaming drill bit is used to enlarge the hole, and the diameter is inspected again until it reaches 1200mm. Simultaneously, exceeding the drilling depth is strictly prohibited. Based on the designed pile length (54.0m or 56.0m), a measuring rope (0.1m accuracy) is used to measure the hole depth to ensure it matches the designed pile length, avoiding increased concrete usage and wasted costs due to exceeding the drilling depth.

[0135] (II) Drilling Verticality and Pile Position Control:

[0136] The verticality of the borehole directly affects the load-bearing performance of the support piles. It requires dual control through the rotary drilling rig's built-in rotation angle positioning system and an additional limit device system to ensure that the borehole deviation rate meets the formula. ,in Indicates the borehole deviation rate. This indicates the horizontal deviation distance between the actual borehole center and the design center. Indicates the drilling depth.

[0137] For example, for a 54.0m long retaining pile ( If the measured horizontal deviation between the actual borehole center and the design center is... Substituting into the formula, we get It meets the requirements; if ,but The drilling rig angle needs to be adjusted to correct the deviation. This is done by fine-tuning the drilling rig's slewing support device. Reduce the borehole depth to below 0.5m to ensure that the borehole deviation rate meets the requirements.

[0138] Before construction, ground-penetrating radar was used to conduct a secondary survey of the construction area to identify areas with uneven sand layer distribution (such as local sand layer thickness of up to 30m and containing a large amount of pebbles). Monitoring points were densely arranged at the pile positions in these areas, and borehole inclination meters were used to check the verticality of the boreholes every 2m depth to promptly detect and adjust deviations, ensure accurate pile positions, and avoid uneven stress on the support structure due to pile position deviations, which would affect the overall stability of the foundation pit.

[0139] (III) Reinforcing cage installation control:

[0140] Before installing the reinforcing cage, a reinforcing cage protective layer detector is used to check the thickness of the protective layer, ensuring it is not less than 50mm. If the protective layer thickness is insufficient (e.g., only 45mm), 5mm thick steel plate spacers are welded to the outside of the reinforcing cage to achieve a protective layer thickness of 50mm. Simultaneously, guide blocks are welded to the outside of the reinforcing cage, with one set every 2m, and three evenly distributed in each set (arranged at 120° intervals along the circumference of the reinforcing cage). The guide blocks are made of 10mm diameter steel bars and are 150mm long, further preventing the reinforcing cage from colliding with and scratching the borehole wall during installation, which could lead to borehole collapse.

[0141] When installing the reinforcing cage, a dual-crane coordinated lifting method was used (the main crane lifted the upper part of the cage, and the auxiliary crane lifted the middle part). The supervisor used a total station to calibrate the verticality of the cage in real time, ensuring it was in a vertical position. After the cage stabilized, it was slowly lowered into the borehole to avoid rapid descent that could cause it to sway and collide with the borehole wall. For example, when lifting a 54.0m long reinforcing cage, the main crane's lifting point was 10m from the top of the cage, and the auxiliary crane's lifting point was 27m from the top. The cage was slowly lifted to above the borehole opening, and after aligning the center of the cage with the center of the borehole, it was lowered at a uniform speed of 0.5m / min until it reached the design elevation. Throughout the process, no collisions occurred between the cage and the borehole wall, ensuring the integrity of the borehole wall.

[0142] (iv) Construction sequence control:

[0143] The skip-pile drilling technique is used for borehole construction, meaning that boreholes are not drilled continuously for adjacent piles, but rather one pile is drilled at a time. The time interval between the drilling of two adjacent piles must satisfy the formula... ,in This indicates the time interval between drilling two adjacent piles. For example, pile 1 is drilled first, followed by pile 3. After 24 hours have passed since pile 1 was drilled, and the concrete of pile 1 has initially set (tested by the penetration resistance method, the initial setting time of concrete is about 18 hours), pile 2 is then drilled. This avoids disturbing the borehole wall of the first pile when the later pile is drilled, and prevents the borehole wall from collapsing.

[0144] It is strictly forbidden to wait for a single concrete pour after drilling consecutive holes. For example, if piles 1, 2, and 3 are drilled consecutively and then concrete is poured at the same time, it will cause the hole walls of piles 1 and 2, which were drilled first, to become unstable and collapse during the waiting period. Therefore, the principle of "drilling one hole and pouring one hole" must be followed. Concrete pouring must begin within 2 hours after the hole is completed to ensure the quality of the hole.

[0145] V. Precise Concrete Pouring:

[0146] Concrete pouring is a key process in the formation of support pile holes. It is necessary to precisely control the pouring process to ensure that the concrete filling coefficient meets the requirements, while avoiding quality defects such as broken piles and reduced diameter.

[0147] First, calculate the design concrete usage per pile based on the specifications of the retaining pile. For a retaining pile with a diameter of 1200mm and an effective pile length of 54.0m, the design concrete usage is calculated as follows: (in The diameter of the pile. (For the effective pile length); for a support pile with an effective pile length of 56.0m, the design concrete usage is ³ Before grouting, the designed dosage should be clearly marked in the construction record form as the basis for grouting control.

[0148] Concrete is poured in layers using a concrete pump. During the pouring process, the pile top elevation is measured at fixed concrete volumes; for example, the pile top elevation is measured once every 1 m³ of concrete is poured. The actual volume of concrete poured is calculated based on the elevation changes. and the design usage Real-time comparisons are conducted, and the grouting speed is dynamically adjusted (controlled at 2-3 m³ / min) to avoid concrete segregation due to excessively fast grouting speed or initial setting of concrete in the hole due to excessively slow grouting speed.

[0149] At the same time, the over-pouring amount at the pile top is strictly controlled. Since sediment is prone to exist at the bottom of the hole in the ultra-thick sand layer, it is necessary to ensure the quality of the pile top by over-pouring concrete. The over-pouring amount is determined according to the pile length. For a 54.0m pile, the over-pouring is 0.8-1.0m, and for a 56.0m pile, the over-pouring is 1.0-1.2m. After pouring to the over-pouring elevation, pouring is stopped. After the concrete has initially set (about 24 hours), the over-pouring part is broken off using a pile breaker to ensure that the pile top elevation meets the design requirements.

[0150] Ultimately, the concrete filling coefficient must meet the actual design requirements of the formula. ,in This represents the concrete filling coefficient, in actual... This represents the actual volume of concrete poured into a single retaining pile, as designed. This represents the design concrete volume of a single retaining pile. In this embodiment, the concrete pouring volume of 30 54.0m piles is statistically analyzed, with pile number 1 having an actual pouring volume of 66m³. Substituting this into the formula yields... The actual grouting volume of pile number 6 was 70 m³. The actual grouting volume of pile number 20 was 68.5 m³. The average filling coefficient of the 30 piles is 1.05, which meets the requirements. The requirements were met, which effectively reduced concrete waste and lowered project costs while ensuring the quality of pile construction.

[0151] In addition, a slump meter is used to test the slump of the concrete before pouring to ensure that the slump is maintained between 180-220mm. If the slump is too small (e.g., 160mm), an appropriate amount of water-reducing agent (0.5%) is added to the concrete, and after stirring evenly, the slump is tested again. The slump increases to 190mm, which meets the requirements. During the pouring process, an ultrasonic detector is used to monitor the height of the concrete surface in the hole in real time to avoid the collapse of the hole wall due to the interruption of concrete supply. If the concrete supply is delayed for more than 30 minutes, the backup concrete delivery pump is immediately started to continue the pouring to ensure that the pouring process is continuous and uninterrupted.

[0152] VI. Full-process quality traceability and consolidation:

[0153] Establish a comprehensive construction log, and record detailed data for the entire construction process of each support pile. The records include equipment parameters (drilling rig model, drill rod specifications), drilling speed (actual speed recorded every 30 minutes), mud parameters (specific gravity, viscosity, and sand content measured every hour), reinforcement cage installation deviation (deviation distance between the center of the reinforcement cage and the center of the hole), concrete pouring volume (actual pouring volume, design volume, and filling coefficient), etc. At the same time, record information such as construction personnel, equipment numbers, and material batches (concrete strength grade, mud raw material batch), forming a traceable quality control file.

[0154] To ensure the authenticity and immutability of the data, the construction ledger is stored using blockchain technology. After the construction of each pile is completed, a unique quality traceability QR code is generated. The QR code contains all the construction data of that pile. During later operation and maintenance, the construction process information can be quickly queried by scanning the QR code, which facilitates the tracing of quality problems and subsequent maintenance.

[0155] A three-tiered acceptance system of "team self-inspection - technical re-inspection - quality spot check" is established. After each process is completed, the team conducts a self-inspection (such as self-inspection of drilling speed and mud sand content after drilling). After the self-inspection is qualified, it is reported to the technical department for re-inspection (technical personnel verify the hole diameter and hole depth). After the re-inspection is qualified, it is reported to the quality department for spot check (quality personnel randomly select 10% of the piles for hole quality testing). For piles with unqualified hole quality (such as filling coefficient exceeding 1.1), a special rework plan is formulated (such as using high-pressure jet grouting to reinforce the hole wall and then re-drilling and grouting). After rework, the entire process is re-inspected until it is qualified.

[0156] A quality inspection team was established, employing a combination of drone aerial photography and on-site inspection to supervise the entire construction process. Drones conducted aerial photography twice a day, once in the morning and once in the afternoon, to monitor whether the pile layout and construction sequence in the construction area met the requirements. On-site inspectors conducted inspections of the construction site every 2 hours, focusing on whether the drilling speed exceeded the standard, whether the mud ratio was adjusted in a timely manner, and whether the reinforcement cage installation was standardized. If any violations were found (such as a drilling speed of 9 m / h), a rectification notice was immediately issued, requiring rectification to be completed within 1 hour. If rectification was not completed within the deadline, the relevant machine was penalized according to the reward and punishment system (such as deducting 20% ​​of the monthly performance bonus). This ensured that the entire construction process was strictly carried out in accordance with the method of this invention, guaranteeing the quality of the support pile drilling in ultra-thick sandy geology.

[0157] In response to the complex geological conditions of ultra-thick sand layers (over 25m thick) containing pebbles and gravel, which often lead to hole collapse, reduced diameter, and excessive concrete filling coefficients in the drilling of support piles, a scientific and comprehensive construction plan has been developed through systematic process optimization, personnel management, equipment testing, and quality traceability. The beneficial effects are reflected in multiple dimensions, including economic, social, technical, and engineering quality control, as detailed below:

[0158] Significantly improving economic efficiency and reducing engineering cost losses: In the construction of ultra-thick sand layer support piles, concrete consumption and mud treatment costs are core components of engineering costs. This technical solution achieves substantial cost savings by precisely controlling the concrete filling coefficient and construction process. On the one hand, the solution reduces the problem of excessive concrete volume caused by hole collapse and diameter reduction by controlling the drilling speed by soil layer (strictly maintaining the drilling speed of sand layer at 6-8m / h), dynamically adjusting mud performance indicators (such as sand content of mud ≤10% for sand layer and ≤8% for non-sand layer), and multi-dimensional quality control after hole formation (such as skip-driving of piles and vertical hoisting of steel cage to prevent scratching holes). According to engineering practice data, after adopting this solution, the concrete filling coefficient of the support pile is stably controlled within 1.1, with an average filling coefficient of only 1.05. Compared with the filling coefficient that often exceeds 1.2 in traditional construction, the amount of concrete used per pile is significantly reduced. Taking the 509 support piles (1200mm diameter, including 54.0m and 56.0m pile lengths) of this project as an example, and calculating based on the average filling coefficient decreasing from 1.2 to 1.05, a single 54.0m pile (designed concrete usage 64m³) can save 64×(1.2-1.05)=9.6m³ of concrete. The total concrete savings for the 509 piles exceed 5000m³. Based on the market price of concrete of approximately 1000 yuan / m³, the single item of concrete savings reaches over 500,000 yuan, directly reducing the cost of the main materials of the project.

[0159] On the other hand, the solution indirectly reduces the costs of mud transportation and project rework by optimizing mud preparation and recycling, and reducing rework caused by borehole collapse. In traditional construction, due to improper control of mud performance, mud wall protection often fails, requiring frequent mud replacement and generating a large amount of waste mud that needs to be transported off-site (the cost of transporting waste mud is about 50 yuan per cubic meter). Borehole collapse can also lead to rework, with rework costs exceeding 10,000 yuan per pile. This solution, through a mud management model of "specialized technical briefing + real-time monitoring by dedicated personnel + automatic proportioning verification," ensures that the mud always has good wall protection performance, significantly reducing the amount of waste mud and the rework rate due to borehole collapse. Statistics show that the amount of mud transported in this project was reduced by more than 30% compared to traditional construction, and the rework rate dropped from the traditional 15% to 0. The cost savings from mud treatment and rework avoidance alone exceeded 100,000 yuan, further improving the overall economic benefits of the project.

[0160] Furthermore, the solution shortened the construction cycle and indirectly reduced management and equipment rental costs by optimizing the entire process from "pre-construction preparation to process control and post-construction traceability." For example, by ensuring that construction personnel are qualified before starting work (with a qualification rate of ≥70%), delays caused by personnel errors were reduced; by using staggered pile driving (with an interval of ≥24 hours between adjacent pile drillings) and pre-booking concrete, idle time waiting for grouting after drilling was avoided; and by using refined equipment testing (such as casing deformation deviation ≤2% and drill rod pin spacing ≤1mm), downtime due to equipment failure was reduced. The construction cycle of the 509 support piles in this project was shortened by 15 days compared to the plan. Based on an average daily management cost of 20,000 yuan and an average daily equipment rental cost of 50,000 yuan, the cumulative cost savings reached 1.05 million yuan, further amplifying the economic benefits.

[0161] Strengthening environmental protection and construction compliance, highlighting social benefits: Under the current requirements of green building and ecological environmental protection policies, this technical solution achieves low-carbon and environmentally friendly construction through process optimization and pollution control, setting an environmental benchmark for ultra-thick sand layer construction in the industry. Firstly, the solution uses rotary drilling rigs for hole drilling. Compared with traditional impact drilling rigs, rotary drilling rigs have higher hole drilling efficiency and produce less mud. Combined with the dynamic control and recycling technology of mud in the solution, the amount of mud discharged is further reduced. In traditional impact drilling construction, each 1200mm diameter, 54.0m long support pile requires approximately 200m³ of mud. However, in this solution, the rotary drilling rig combined with mud recycling reduces the mud production per pile to below 80m³. Furthermore, after sedimentation treatment, some of the waste mud can be readjusted and reused. The amount of mud discharged is reduced by more than 60% compared to traditional construction, avoiding the pollution of surrounding soil, groundwater, and vegetation caused by the indiscriminate discharge of large amounts of waste mud, and reducing the damage to the ecological environment caused by construction.

[0162] Secondly, the solution indirectly reduces construction waste by minimizing rework due to borehole collapse and excessive concrete volume. In traditional construction, rework due to borehole collapse requires cleaning up waste concrete and slag inside the hole, generating approximately 50m³ of construction waste per reworked pile. This solution, through strict quality control of borehole formation, achieves a zero rework rate for borehole collapse, reducing construction waste at its source. Simultaneously, precise control of the concrete filling coefficient reduces the amount of excess concrete poured at the pile top later (the excess pouring volume in this solution is controlled at 0.8-1.2m, a 20% reduction compared to traditional construction), further reducing the total amount of construction waste. Statistics show that the amount of construction waste generated in this project is 40% less than that of traditional construction, and all construction waste is transported to designated disposal sites according to regulations, meeting environmental protection requirements and avoiding environmental problems caused by indiscriminate dumping of waste.

[0163] Furthermore, the plan, through standardized construction management and safety control, ensured the safety of construction personnel and the stability of the surrounding environment, enhancing the project's social acceptance. The plan included the establishment of a dedicated task force to conduct three levels of technical briefings and emergency drills (such as handling collapsed boreholes) for construction personnel, clearly defining safe operating procedures. No safety accidents occurred throughout the entire construction process. Simultaneously, a combination of drone aerial photography and on-site inspections ensured that the construction process met noise and dust emission standards (e.g., daytime construction noise ≤70dB, dust concentration ≤0.5mg / m³), avoiding disruption to the lives of nearby residents. During the project's construction, no complaints regarding noise or pollution were received from nearby residents, and the project quality received high praise from the owner and regulatory authorities, earning the company a good social reputation and laying the foundation for undertaking similar projects in the future.

[0164] Breaking through the technical bottleneck of ultra-thick sand layer construction and accumulating valuable technical experience: Ultra-thick sand layers, due to their loose soil particles and weak cohesion, have always been a technical challenge in the construction of support pile holes. Most construction units in the industry lack mature construction experience. This technical solution has successfully broken through this technical bottleneck through systematic technical innovation and practical verification, providing the industry with a replicable and scalable technical solution with significant technical benefits.

[0165] On the one hand, the scheme has established a differentiated construction technology system for ultra-thick sand layers, filling the gap in the industry for standardized drilling parameters for ultra-thick sand layer support piles. Based on the nine types of soil and rock layers (① miscellaneous fill to ⑨ rocky clay) classified in the survey report, the scheme has specifically formulated construction parameters such as drilling speed, mud index (specific gravity, viscosity, sand content), and drilling pressure. For example, for sand layers (③, ⑤, ⑧), medium drilling pressure, drilling speed of 6-8 m / h, and mud specific gravity of 1.30-1.35 are adopted, while for non-sand layers (②, ④, ⑥), low drilling pressure, graded drilling speed of 4-9 m / h, and mud specific gravity of 1.25-1.33 are adopted, forming a closed-loop technical process of "soil layer identification - parameter matching - real-time adjustment". This technical process is not only applicable to the ultra-thick sand layer geology of this project, but can also be promoted and applied after fine-tuning the construction parameters according to the characteristics of ultra-thick sand layers in different regions, such as particle size distribution and moisture content. It solves the problem of unstable hole formation quality caused by the "one-size-fits-all" parameter setting in traditional construction, and provides a technical reference for the construction of ultra-thick sand layer support piles in the industry.

[0166] On the other hand, the solution has formed a quality control methodology for ultra-thick sand layer construction through the whole-chain management of "personnel-equipment-quality", which has improved the company's technical reserves and personnel capabilities. Regarding personnel management, the plan established a training system of "three-level briefing + closed-book assessment + emergency drills" to ensure that construction personnel master the core technologies and risk control points for ultra-thick sand layer construction. After training, the construction personnel's mastery of rotary drilling rig operation specifications, mud mixing principles, and emergency handling of borehole collapse increased from 40% to over 90%, cultivating a group of professional technicians with experience in ultra-thick sand layer construction. Regarding equipment management, the plan formulated an equipment assurance process of "drill rod inspection - casing correction - equipment linkage." For example, the distance between the drill cuttings casing and the drill rod pin is ≤1mm, the casing deformation deviation is ≤2%, and an automatic alarm is triggered when the drilling speed exceeds the limit, forming a technical standard for refined equipment management. Regarding quality control, the plan established a quality assurance system of "process monitoring - data traceability - three-level acceptance." By recording the drilling speed every 30 minutes, testing mud indicators every hour, and storing construction ledgers on the blockchain, the entire process of construction quality is traceable, and the borehole quality qualification rate has increased from 85% in traditional construction to 100%.

[0167] Furthermore, the successful implementation of the solution has provided the company with a wealth of case data on ultra-thick sand layer construction, laying the foundation for subsequent technology research and development and patent applications. During the implementation process, detailed records were kept of the construction parameters of 509 support piles (such as the drilling speed in different soil layers, the correspondence between mud indicators and filling coefficients), quality inspection data (such as hole diameter deviation and verticality deviation), and cost consumption data, forming a database for ultra-thick sand layer construction. This database can be used to optimize construction processes and develop intelligent construction equipment (such as an automatic mud mixing system), further enhancing the company's technological competitiveness in the field of ultra-thick sand layer construction and promoting technological progress in the industry.

[0168] Ensuring the quality of retaining pile hole formation and the stability of the foundation pit, thereby improving the safety and reliability of the project: Under ultra-thick sandy geological conditions, the quality of retaining pile hole formation directly determines the stability of the foundation pit support structure, which in turn affects the construction safety of the entire project. This technical solution ensures the quality of retaining pile hole formation through multi-dimensional quality control measures, providing a solid guarantee for the safety of the foundation pit.

[0169] First, the scheme ensures the support piles function precisely by strictly controlling the verticality of the boreholes and the accuracy of the pile positions. The scheme employs a dual control system: the rotary drilling rig's built-in rotation angle positioning system and an additional limiting device system. Combined with borehole inclination gauge checks every 5 meters, this ensures a borehole deviation rate of ≤1%. For example, for a 54.0m long support pile, the horizontal deviation between the actual borehole center and the design center is ≤0.54m, far below the industry standard's 1% deviation requirement. This precise control of borehole verticality and pile positions avoids uneven stress on the support structure due to pile misalignment, preventing the risk of collapse caused by localized stress concentration on the pit sidewalls and ensuring the safety of surrounding buildings and underground pipelines.

[0170] Secondly, the scheme optimizes the installation of the reinforcing cage and the concrete pouring process to ensure the structural strength and integrity of the support piles. Before installation, the protective layer thickness of the reinforcing cage is tested to be ≥50mm. During installation, two cranes work together to lift and lower it vertically, preventing the reinforcing cage from scratching the borehole wall and causing collapse. This also ensures the reinforcing cage is centered within the pile, guaranteeing uniform stress distribution. During concrete pouring, the pile top elevation is measured every 1m³, the slump is controlled at 180-220mm, and the filling coefficient is ≤1.1. This avoids pile breakage and diameter reduction problems caused by concrete segregation and discontinuous pouring, ensuring the concrete strength of the support piles meets design requirements (C30 and above), and the pile integrity test pass rate reaches 100%, providing reliable structural support for the foundation pit.

[0171] Furthermore, the scheme avoided mutual interference between adjacent pile constructions and ensured borehole stability by using staggered pile driving and timely grouting after borehole formation. The scheme involved a ≥24-hour interval between adjacent pile drillings, allowing the concrete of the first pile to initially set before constructing the adjacent pile. This prevented disturbance to the borehole walls of the first pile during subsequent drilling. Simultaneously, concrete grouting was initiated within 2 hours of borehole completion, preventing moisture loss and borehole wall collapse due to prolonged exposure to air. During the construction of this project, no borehole wall collapses occurred due to interference from adjacent pile construction or waiting for grouting after borehole formation. The borehole diameter, depth, and verticality qualification rates of the support piles all reached 100%. During the excavation of the foundation pit, no settlement or cracking occurred in the support piles, and the horizontal displacement of the pit sidewalls was ≤30mm, far below the 50mm limit required by the specifications, ensuring the safety of the foundation pit construction and creating favorable conditions for subsequent main structure construction.

[0172] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for drilling retaining piles in ultra-thick sandy soil layers, applicable to foundation pit support projects containing sand layers exceeding 25m in thickness and with some soil layers containing pebbles and gravel, characterized in that: Includes the following steps: a. Preliminary Preparation and Personnel Management: A special task force was established, led by a project manager with extensive experience in tackling complex problems, with the chief engineer and deputy project manager as deputy leaders. For the rotary drilling rig drilling in ultra-thick sand layers, a three-level technical briefing covering basic processes and risk control was conducted for construction personnel. Simultaneously, a theoretical knowledge assessment of pile foundation construction was organized, covering core modules such as rotary drilling rig operation specifications, prevention and treatment of hole collapse in sand layers, and mud performance control. The assessment was ensured to meet the required pass rate, and the briefing materials were jointly reviewed by the project manager and the chief engineer, supplemented with special guidance measures for dealing with hole collapse in ultra-thick sand layers. b. Detailed Inspection of Equipment and Casing: Rotary drilling rigs are selected as the drilling equipment. The connection status of the main and auxiliary drill rods is inspected to ensure that the main and auxiliary drill rods are not loose and that the distance between the drill cuttings cylinder and the drill rod pins meets the requirements, so as to avoid the drill rod shaking during drilling and causing disturbance to the borehole wall. For the casing with a design diameter of 1400mm, random sampling inspection is carried out according to the corresponding number of each drilling rig. The deformation deviation of the casing is measured using high-precision measuring instruments. Casings with deformation deviations that meet the standards are selected. Casings with deviations that exceed the standards are corrected or replaced and re-inspected until they meet the requirements. c. Precise Hole Formation Based on Soil Layers: The rotary drilling rig is started to form holes. Based on the soil and rock layer types identified in the survey report (① miscellaneous fill, ② loess-like silt, ③ sand, ④ silty clay, ⑤ fine sand, ⑥ fill sand, ⑦ silty clay, ⑧ medium-coarse sand with pebbles, ⑨ rocky clay), differentiated construction parameters are used: c1. Drilling speed control: When drilling in sand layers (classes ③, ⑤, and ⑧), a speed threshold is set through the drilling rig operating system, and a dedicated person is arranged to carry a real-time speed monitoring device to track the drilling speed on site and record the drilling speed at fixed time intervals to ensure that the actual speed is maintained within the specified range. Non-sand layers are controlled according to low-to-medium speed classification. c2. Dynamic control of drilling mud: Specialized drilling mud mixing schemes are formulated in advance for different soil and rock layers (Classes ①, ③, ⑤, ⑦, ⑨: specific specific gravity, viscosity, and sand content range; Classes ②, ④, ④2, ⑥, ⑧: specific specific gravity, viscosity, and sand content range). Geological professionals are arranged to observe changes in soil layers during drilling. Once it is found that the actual soil layer does not match the exploration report, the specific gravity and viscosity of the drilling mud are immediately adjusted through the drilling mud circulation system. The drilling mud performance indicators are tested at fixed time intervals to ensure that the indicators meet the requirements. d. Multi-dimensional quality control after drilling: After drilling, the borehole diameter is checked with a borehole gauge, and exceeding the drilling depth is strictly prohibited; when installing the reinforcing cage, two cranes are used for coordinated hoisting, and the command personnel use a total station to calibrate the verticality of the reinforcing cage in real time to ensure that the reinforcing cage is vertically hoisted into the hole after it is stable, so as to avoid scratching the hole wall; the staggered pile drilling process is adopted, and the interval between adjacent piles is in line with the requirements. The adjacent piles are constructed after the concrete of the first pile has initially set; the verticality of the drilling is controlled by the rotary drilling rig's built-in rotation angle positioning system and the additional limit device system to ensure that the hole deviation is within the allowable range. e. Precise concrete pouring: Based on the specifications of the support piles (pile diameter 1200mm, effective pile length 54.0m / 56.0m), the design concrete volume for a single pile (64m³ for a 54.0m pile) is calculated. A concrete pump is used for layered pouring. The pile top elevation is measured according to the fixed concrete pouring volume. The pouring speed is dynamically adjusted to control the over-pouring volume at the pile top, so that the concrete filling coefficient meets the specified requirements. f. Full-process quality traceability: Establish construction ledgers to record in detail the equipment parameters, drilling speed, mud index, steel cage installation deviation, concrete pouring volume, and other data for each pile, forming a traceable quality control file.

2. The method for drilling support piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step a, the pass rate must meet the requirements of the formula: total pass rate ,in: This indicates the pass rate of construction workers. qualified This indicates the number of construction workers who scored 60 points or above in the assessment. total This indicates the total number of construction workers participating in the assessment; This formula is used to quantitatively assess the extent to which construction personnel have mastered the knowledge related to drilling holes in ultra-thick sand layers using rotary drilling rigs, ensuring that the personnel involved in the construction have basic operational and risk control capabilities, and avoiding construction quality problems caused by insufficient personnel skills.

3. The method for drilling support piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step c1, the drilling speed in the sand layer must satisfy the formula. ,in: This indicates the actual drilling speed of the rotary drilling rig in the sand layer; This formula clarifies the reasonable range of drilling speed in sand layers. By controlling the drilling speed, it avoids the collapse of the hole due to instability of the hole wall caused by excessive speed, or the impact on construction efficiency due to excessively slow speed, thus ensuring a balance between hole quality and construction progress.

4. The method for drilling support piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step c2, the sand content of the mud must meet the requirements of the corresponding soil and rock layers. Specifically, soil and rock layers of types ①, ③, ⑤, ⑦, and ⑨ must meet the formula S≤10%, and soil and rock layers of types ②, ④, ④2, ⑥, and ⑧ must meet the formula S≤8%. S represents the sand content in the mud; This formula ensures that the mud has good wall protection properties by limiting the upper limit of the sand content of the mud in different soil and rock layers, reducing the erosion of the borehole wall by sand particles, and avoiding the failure of mud wall protection due to excessive sand content, which in turn leads to borehole wall collapse.

5. The method for drilling support piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step d, the drilling deviation must satisfy the formula ,in: Indicates the borehole deviation rate; This indicates the horizontal deviation between the actual borehole center and the design center. Indicates the drilling depth; This formula is used to quantitatively evaluate the verticality of the borehole and the accuracy of the pile position. By controlling the borehole deviation rate, it ensures that the support piles can accurately play their role in supporting the foundation pit and avoids uneven stress on the support structure due to pile position deviation, which would affect the overall stability of the foundation pit.

6. The method for drilling support piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step e, the concrete filling coefficient must meet the actual design requirements of the formula. ,in: Indicates the concrete filling coefficient; actual This indicates the actual volume of concrete poured into a single support pile. design This indicates the design concrete volume of a single support pile; This formula is used to measure the deviation between the actual amount of concrete used and the designed amount. By controlling the filling coefficient, it can reduce concrete waste and lower project costs while ensuring the quality of pile formation (avoiding pile breakage and diameter reduction due to insufficient concrete).

7. The method for drilling retaining piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step b, the deformation deviation of the casing must meet the actual design requirements of the formula. ,in: This indicates the casing deformation deviation rate; actual Indicates the actual diameter of the casing; design This indicates the design diameter of the casing (1400 mm). This formula is used to assess the degree of deformation of the casing. By controlling the deformation deviation rate, it ensures that the casing can effectively fix the pile position, isolate surface water, and protect the borehole opening, thus avoiding the collapse of the borehole opening or the displacement of the pile position due to the deformation of the casing.

8. The method for drilling support piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step d, the time interval between the drilling of adjacent piles must satisfy the formula. ,in: This indicates the time interval between the drilling of two adjacent piles; This formula clarifies the construction interval between adjacent piles in the staggered pile driving process. By ensuring sufficient interval time, allowing the concrete of the first pile to initially set, it avoids disturbing the borehole wall of the first pile when the subsequent pile is drilled, thus preventing the borehole wall from collapsing and ensuring the quality of the pile.

9. The method for drilling retaining piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step c1, the drilling speed recording interval satisfies the formula ,in: The time interval used to record drilling speed; This formula specifies the recording frequency of drilling speed. By recording at regular intervals, it is easy to monitor changes in drilling speed in real time, promptly detect and adjust drilling speeds that exceed the range, ensure that drilling in sand layers is always within a reasonable speed range, and reduce the risk of borehole collapse.

10. The method for drilling retaining piles in ultra-thick sandy geological layers as described in claim 1, characterized in that: In step c2, the testing interval for mud performance indicators satisfies the formula. ,in: Indicates the time interval for testing mud performance indicators (specific gravity, viscosity, sand content); This formula specifies the frequency of mud performance testing. By conducting regular testing, changes in mud performance can be monitored in a timely manner, and mud ratios that do not meet the requirements can be quickly adjusted to ensure that the mud always has a good wall protection effect, providing a stable guarantee for drilling in ultra-thick sand layers.

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