Risk assessment method and system for cast-in-situ bored pile construction

Abstract

The invention provides a risk assessment method and system for cast-in-situ bored pile construction, and belongs to the field of building construction.The method comprises the following steps that a WBS-RBS risk identification coupling matrix for cast-in-situ pile construction in a karst cave area is constructed; calculating risk values of different risk factors in the risk identification coupling matrix; calculating weight coefficients of different risk factors in the risk identification coupling matrix by using a subjective empowerment G1 sequence method; and the risk value of a construction unit in the risk identification coupling matrix is determined through the risk value and the weight coefficient, and the potential risk in the cast-in-place pile construction process in the karst cave area is evaluated through the risk value of the construction unit. According to the method, the WBS-RBS coupling matrix is constructed, so that risk identification factors are more comprehensive; the weight coefficient and the risk value of each risk factor are calculated by adopting the G1 method, qualitative analysis and quantitative evaluation can be effectively fused, the calculation amount and subjective factors are reduced, and the calculation precision is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of building construction, and in particular relates to a risk assessment method and system for bored pile construction. Background Art

[0002] Karst caves refer to soluble rock formations, such as dolomite, limestone, dolomitic limestone, gypsum, and rock salt, which are formed through the chemical and mechanical action of water. These formations include grooves, cracks, and cavities, as well as surface sinkholes and depressions caused by the collapse of the cave roof. my country has a vast territory, complex and diverse geology, and widespread limestone distribution. Because karst caves are generally underground and hidden, they are not intuitively visible. While geological exploration techniques can be used to study them, they can only confirm their existence and approximate location, making it difficult to avoid the many challenges karst caves present during construction. The greatest challenge in pile foundation construction is encountering karst caves, which pose a significant risk and seriously threaten the quality of the project and the safety of construction workers. Therefore, effective risk assessment of pile foundation treatment involving karst caves, especially during bored pile construction, is crucial.

[0003] Chen Guoliang believes that the hazards of karst to underground projects can be roughly categorized into three categories: karst caves pose instability to structures and their foundations; karst groundwater can trigger mud and water inrush, impacting underground project construction; and karst ground collapse can cause subsidence and tilting damage to surrounding buildings. Kampmann J. (1998) used risk assessment techniques to propose 10 risk types for the Copenhagen Metro Project, encompassing over 40 hazards. He developed a specific classification system for the likelihood of occurrence and the consequences of these events, and proposed 48 risk mitigation measures. He then used Monte Carlo methods and computer spreadsheets to construct a risk model for calculations. Woude S. (2012) conducted an extensive risk analysis of the Betuweroute shield tunnel during its design phase and used risk analysis and construction monitoring to control risks during tunnel construction. Huang Ping (2013) summarized the various risks encountered during bored pile construction from a technical perspective and proposed preventive measures. Yu Jiexu (2018) used a fuzzy hierarchical comprehensive evaluation model to assess the risks of water and mud inrush and surrounding rock stability in karst tunnels. Sha Mengyi (2021) proposed a composite risk assessment method of gridded statistical law analysis of cave distribution-numerical calculation-hierarchy analysis method.

[0004] In summary, many researchers often use the Analytic Hierarchy Process (AHP), the Fuzzy AHP, or the Fault Tree Analysis (FTA) method for risk assessment. These methods share a common drawback: their high subjectivity. When applying the AHP to solve practical problems, the construction of the judgment matrix often fails to meet consistency requirements. While many researchers have proposed numerous correction methods, such as optimizing with eigenvectors and genetic algorithms, to ensure that the corrected matrices meet consistency requirements, the weights of risk factors calculated using different methods are inconsistent. Some risk factors may even contradict each other due to different methods, resulting in inaccurate results. Bored pile construction in karst areas is a complex project with numerous risk factors. Systematically and accurately identifying potential risks is crucial. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a risk assessment method for bored pile construction, comprising the following steps:

[0006] Establish a WBS construction unit decomposition structure based on the construction process of bored piles in karst cave areas; establish an RBS risk factor decomposition structure based on the risk factors in the construction process of bored piles in karst cave areas; construct a WBS-RBS risk identification coupling matrix with WBS as columns and RBS as rows;

[0007] Calculate the risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix;

[0008] The weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix are calculated using the subjective weighted G1 sequence method;

[0009] The risk values ​​of the construction units in the risk identification coupling matrix are determined by the risk values ​​and weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix, and the potential risks in the cast-in-place pile construction process in the cave area are evaluated by the risk values ​​of the construction units.

[0010] Preferably, the WBS construction unit decomposition structure includes steel casing construction W1, hole-forming construction W2 and pile-forming construction W3. The steel casing construction includes steel casing processing and manufacturing W11, steel casing hoisting and transportation W12 and steel casing positioning and inserting W13; the hole-forming construction includes drilling with a drill rig W21, drilling and backfilling W22, lowering of a steel cage W23 and hole cleaning W24; the pile-forming construction W3 includes guide tube installation W31 and concrete pouring W32.

[0011] Preferably, the RBS risk factor decomposition structure includes construction risk factors R1, surrounding environment risk factors R2 and personnel and management risk factors R3.

[0012] Preferably, the risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix are calculated by the following formula:

[0013] D = L·E·C;

[0014] Where L is the probability of an accident occurring, E is the probability that a worker is in a risky environment, and C is the loss caused by the accident.

[0015] Preferably, the method of using the subjective weighted G1 sequence method to calculate the weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix includes the following steps:

[0016] Sort the risk factors in WBS-RBS by importance;

[0017] Assign weights based on the importance ratios between adjacent risk factors;

[0018] Calculate the weight coefficient based on the assigned weight.

[0019] Preferably, the weight coefficient λ k The calculation formula is:

[0020]

[0021] Where n is the number of experts, r ki is the value assigned by expert i to risk factor k, j is the jth risk factor, and s is the number of risk factors.

[0022] Preferably, the calculation formula of the risk value of the construction unit is:

[0023]

[0024] Where D i represents the risk value of the i-th construction unit; λ ij represents the weight coefficient of the jth risk factor of the i-th construction unit; D ij represents the weight coefficient and risk value of the jth risk in the i-th construction unit; n represents the number of risks in the i-th construction unit, and x represents the risk factor of the construction unit.

[0025] The present invention also provides a risk assessment system for bored pile construction, comprising:

[0026] The risk identification coupling matrix construction module is used to establish a WBS construction unit decomposition structure based on the construction process of bored piles in karst cave areas; establish an RBS risk factor decomposition structure based on the risk factors in the construction process of bored piles in karst cave areas; and construct a WBS-RBS risk identification coupling matrix with WBS as columns and RBS as rows.

[0027] Risk value calculation module, used to calculate the risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix;

[0028] The weight coefficient calculation module is used to calculate the weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix using the subjective weighted G1 sequence method;

[0029] The risk assessment module is used to determine the risk value of the construction unit in the WBS-RBS risk identification coupling matrix based on the risk values ​​and weight coefficients of different risk factors in the risk identification coupling matrix, and to assess the potential risks in the construction process of cast-in-place piles in the cave area based on the risk value of the construction unit.

[0030] The risk assessment method for bored cast-in-place pile construction provided by the present invention has the following beneficial effects:

[0031] The present invention establishes a WBS construction unit decomposition structure according to the construction process of bored cast-in-place piles in karst cave areas; establishes an RBS risk factor decomposition structure according to the risk factors in the construction process of bored cast-in-place piles in karst cave areas; uses WBS as columns and RBS as rows to construct a WBS-RBS risk identification coupling matrix, and this process can make the identified risk factors more comprehensive and detailed; by calculating the risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix and calculating the weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix through a sequence method, the risk values ​​of the construction units in the risk identification coupling matrix can be determined, thereby quantitatively evaluating the potential risks in the construction process of cast-in-place piles in karst cave areas, reducing the influence of subjective factors, and greatly improving the accuracy of calculation and the reliability of risk assessment; the method does not need to construct a judgment matrix, can avoid the occurrence of inconsistent consistency tests, can effectively evaluate risks, improve the accuracy of results, and provide a basis for risk identification and evaluation reference of bored cast-in-place piles in karst cave areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the embodiments of the present invention and its design, the following briefly introduces the drawings required for this embodiment. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0033] Figure 1 Flow chart of a risk assessment method for bored pile construction according to an embodiment of the present invention;

[0034] Figure 2 This is the Struts framework hierarchy diagram;

[0035] Figure 3 This is the SSH architecture association diagram;

[0036] Figure 4 This is the WBS breakdown diagram for bored cast-in-place pile construction in cave areas. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solution of the present invention and to be able to implement it, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are not intended to limit the scope of protection of the present invention.

[0038] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the technical solutions of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0039] In addition, the terms "first", "second", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance. In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meaning of the above terms in the present invention can be understood according to the specific circumstances. In the description of the present invention, unless otherwise specified, "plurality" means two or more, which will not be described in detail here.

[0040] Example 1

[0041] The present invention provides a risk assessment method for bored pile construction, comprising the following steps: Figure 1 As shown:

[0042] Step 1: Construct a WBS-RBS risk identification coupling matrix for cast-in-place pile construction in karst areas. The construction process includes the following steps:

[0043] Establish a WBS construction unit decomposition structure based on the construction process of bored piles in karst areas;

[0044] Establish an RBS risk factor decomposition structure based on the risk factors in the construction process of bored piles in karst areas;

[0045] With WBS as columns and RBS as rows, a WBS-RBS risk identification coupling matrix is ​​constructed.

[0046] Step 2: Calculate the risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix.

[0047] The risk value (D) is determined by the probability of an accident occurring (L), the probability of workers being in a risky environment (E), and the loss caused by the accident (C). The formula for calculating the risk value is:

[0048] D=L·E·C(1);

[0049] Where L is the probability of an accident occurring, E is the probability that a worker is in a risky environment, and C is the loss caused by the accident.

[0050] Step 3: Use the subjective weighted G1 sequence method to calculate the weight coefficients of different risk factors in the risk identification coupling matrix.

[0051] The basic principle of the subjectively weighted G1 sequence method is to rank risk factors by importance based on the subjective perception of evaluation experts and assign weights based on the importance ratios of adjacent risk factors. This evaluation method has the advantage of effectively addressing the problem of considering too many risk factors, making direct and effective analysis impossible. It simplifies the process of determining risk factor weights, reduces computational workload, and eliminates the need for consistency testing, thereby improving the accuracy of the evaluation of each risk factor.

[0052] The subjective weighted G1 sequence method is used to calculate the weight coefficient of each risk factor in the risk identification coupling matrix, which specifically includes the following steps:

[0053] (1) Sort the risk factors in WBS-RBS according to their importance.

[0054] Let X1, X2, ..., X m (m≥2) represents m extremely large risk factors that have been processed by risk factor type consistency and dimensionlessness.

[0055] (2) Determine the order relationship: According to X1>X2>…>X m Sort the evaluation risk factors, with the relatively important risk factors placed first.

[0056] (3) Determine two adjacent risk factors X k-1 With X k The ratio between k-1 With X k The ratio is denoted as r k =X k-1 / X k (k=m,m-1,…,2),rk The specific assignment and numerical meaning of are shown in Table 1:

[0057] Table 1 Assignment Reference

[0058] <![CDATA[r k ]]> Assignment Description 1.0 Equally important 1.2 Relatively important 1.4 Obviously important 1.6 Strongly important 1.8 Extremely important 1.11.31.51.7 Importance is between two adjacent values

[0059] (4) Calculate the weight coefficient based on the assigned weight.

[0060] Suppose n experts give consistent rankings, and expert i ranks r k The value of r ki ,but r k Indicates that n experts give r ki The average value of the risk factor k weight coefficient λ k The calculation formula is as follows:

[0061]

[0062] r k Indicates that n experts give r ki The average value of .

[0063] Step 4: Determine the risk value of the construction unit in the risk identification coupling matrix using the risk value and the weight coefficient, and evaluate the potential risks in the construction process of cast-in-place piles in the cave area using the risk value of the construction unit.

[0064] The calculation formula for the risk value of a construction unit is:

[0065]

[0066] Where D i represents the risk value of the i-th construction unit; λ ij represents the weight coefficient of the jth risk of the i-th construction unit; D ij represents the weight coefficient and risk value of the jth risk in the i-th construction unit; n represents the number of risks in the i-th construction unit, and x represents the risk factor of the construction unit.

[0067] The present invention also provides a risk assessment system for bored pile construction, comprising a risk identification coupling matrix construction module, a risk value calculation module, a weight coefficient calculation module and a risk assessment module.

[0068] The risk identification coupling matrix construction module is used to establish a WBS construction unit decomposition structure according to the construction process of bored cast-in-place piles in karst cave areas; establish an RBS risk factor decomposition structure according to the risk factors in the construction process of bored cast-in-place piles in karst cave areas; construct a WBS-RBS risk identification coupling matrix with WBS as columns and RBS as rows; the risk value calculation module is used to calculate the risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix; the weight coefficient calculation module is used to calculate the weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix using the subjective weighted G1 sequence method; the risk assessment module is used to determine the risk value of the construction unit in the risk identification coupling matrix through the risk values ​​and weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix, and assess the potential risks in the construction process of cast-in-place piles in karst cave areas through the risk values ​​of the construction units.

[0069] Specifically, the risk assessment system for bored pile construction of the present invention includes the development model, technology platform, development method, etc. in terms of technology selection. The system is selected based on the user requirements of bored pile construction, and this requirement is addressed from a technical perspective. In addition, relevant technical methods should be compared and contrasted in a scientific and fair manner to select one that meets their own requirements.

[0070] 1. Development model selection.

[0071] C / S and B / S are two common application methods. Bored pile construction users can compare these two development methods based on their needs, considering resources, applications, performance, and post-maintenance, to decide which method to choose for system development. In the 1980s, the C / S model saw rapid development and widespread use. Since the 21st century, the rapid development of the Internet, Java, network distributed objects, and information publishing and querying on the Internet have promoted the transition of most application system architectures from the C / S architecture to the multi-tiered distributed B / S architecture, which offers greater flexibility and wider adaptability.

[0072] 1) System development.

[0073] The C / S model features mature components and offers high system development efficiency. However, when the system runs on multiple operating systems, it requires tailored development based on system requirements, increasing development time and costs. However, when developing a B / S system, there's no need to worry about version inconsistencies caused by clients using multiple operating systems. Furthermore, after more than a decade of development, the B / S model has become more mature and reliable in terms of technology, software design, and the number of developers involved.

[0074] While the C / S model's components are mature and development efficiency is high, its service objectives are maintenance and customer service. Therefore, adopting a C / S approach requires installing client software on every maintenance terminal and customer service staff's office terminal. However, because maintenance and customer service work in different areas, and the number and types of terminals are complex, it is very difficult to get users to install client software, which makes system development more difficult. Furthermore, drawing on the example of related gateways developed using a B / S approach, the bored pile construction risk management system was also implemented using a B / S approach.

[0075] 2) Application of the system.

[0076] The system uses a B / S model, making it easy to use. Users can log in through a web page and complete various actions by clicking and checking boxes. This is very helpful for the system's large-scale application and popularization. Because maintenance and customer service work is complex and involves different levels, and there are many systems to maintain and use, a B / S architecture will make this work more convenient. Therefore, the application and popularization of this system has important practical significance.

[0077] 3) System performance.

[0078] The advantages of the B / S model include remote browsing, flexible data collection, and the ability to break geographical limitations. However, users are limited to basic browsing, querying, and data entry, while the server handles most of the work, placing significant pressure on the server. In situations where massive data throughput and a large number of concurrent users are unavailable, a B / S architecture can effectively address this issue.

[0079] 2. Selection of technology platform.

[0080] Currently, the two primary platforms used are J2EE and .NET. Their architectures are similar, and both offer mature and reliable enterprise-level application solutions. Depending on the development content and enterprise needs, developers can choose a platform based on their preferences and language proficiency. This article compares and analyzes these two systems from the perspective of digital supervision, ultimately determining the architecture required.

[0081] 1) Portability.

[0082] J2EE's greatest strength is its cross-platform support. All software and services that adhere to J2EE standards can be customized to meet specific needs, without relying on specific hardware, middleware, or operating system support. Third-party components that are consistent with J2EE can also be used. Web services are a cross-platform technology based on .NET. By integrating XLM and SOAP technologies, they can establish connections across multiple platforms and in multiple languages.

[0083] The portability advantage of the J2EE platform lies primarily in its core concept of "write once, run anywhere." The platform decouples code from the underlying hardware through the Java Virtual Machine (JVM), enabling applications to run in any JVM-supported environment without recompilation. This feature is particularly important for the bored pile construction risk management system, as it must run on a variety of devices, including construction workstations, professional equipment used by management agencies, government office systems, and users' personal mobile devices.

[0084] J2EE's enterprise-level component model further enhances the system's portability. Enterprise Java Beans (EJB) provides a distributed component architecture, enabling business logic to be independent of specific implementations; Java Servlet and Java Server Pages (JSP) provide a platform-independent web application framework. This componentized design allows the system to be flexibly deployed in different environments. For example, deployment strategies can be adjusted based on regional resource availability, employing full-featured deployments in resource-rich urban areas and lightweight configurations in rural areas with weak infrastructure. With the development of cloud computing technology, the portability advantages of J2EE applications have become even more significant. This system can be seamlessly migrated between different cloud service providers (such as Alibaba Cloud, Tencent Cloud, and Huawei Cloud), avoiding vendor lock-in. This flexibility enables the system to dynamically adjust resource allocation strategies based on actual operating conditions and cost considerations.

[0085] 2) Security.

[0086] The above non-functional requirements analysis indicates that the digital supervisory perspective system requires greater security. Therefore, compared to the .NET-based Windows system, host operating systems like Linux offer exceptional anti-virus capabilities, and their security also aligns with the system's needs. Since J2EE is typically built on Linux, I prefer the J2EE architecture.

[0087] 3. 2SSH framework design.

[0088] (1)Struts framework.

[0089] The implementation basis of Struts framework is JSPModel2, which is a kind of MVC framework. Figure 2 As shown, the Struts framework consists of three parts: model, view and controller. It decouples presentation logic and business logic through the controller in order to improve the maintainability, scalability and reusability of the system.

[0090] (2) SSH architecture relationships and applications.

[0091] The relationship between SSH frameworks is mainly as follows Figure 3 As shown in the figure, the reactive architecture specifically utilizes a front-end framework based on Bootstrap and Vue.js, and a responsive grid system enables adaptive layouts from large-screen workstations to mobile devices. The system design takes into account that many users may use older devices or have poor network conditions. Therefore, a progressive enhancement strategy is adopted to ensure that core functions can still function normally in low-configuration environments, while providing a richer interactive experience on high-performance devices. The front-end code adopts a component-based development approach, breaking down complex interfaces into reusable independent components, which not only improves development efficiency but also ensures consistent interactions between different pages.

[0092] The humanized information reminder mechanism is dynamically adjusted according to user habits and needs. The system will record the user's usage patterns and intelligently adjust the reminder frequency and method. For example, after the system finds that the user often ignores a certain type of notification, it will try to change the reminder method or increase the significance of the reminder. For important information, the system provides multi-channel push, including in-app notifications, SMS and phone voice reminders, to ensure that the information is effectively delivered. At the same time, the system can also intelligently switch the reminder method according to the user's current environment. For example, when it detects that the user is using voice interaction, it automatically switches to voice broadcast of the notification content.

[0093] In this embodiment, the system uses the SpringBoot microservices architecture to implement business layer encapsulation, breaking down complex functions into independently deployable microservice modules. The dependency injection model is implemented using the Spring framework, effectively resolving coupling issues between components. The system defines standardized service interfaces, with specific implementation classes dynamically injected via configuration files. This loosely coupled architecture enables the system to flexibly replace service implementations based on the specific needs of different regions and institutions without modifying the core code. The ORM layer uses the MyBatis framework, mapping the domain model to the relational database and simplifying data access operations. A flexible data model is designed for different types of construction conditions and risk records, supporting diverse risk control schemes and progress record formats. The system uses an optimistic locking mechanism to handle concurrent access conflicts, ensuring data consistency when multiple stakeholders are simultaneously operating on a set of data. For sensitive personal information, the system implements field-level encrypted storage, ensuring that only authorized roles can view the complete information, and detailed operation logs are recorded for all sensitive data access. The multi-agent collaborative workflow is implemented based on the BPMN 2.0 standard, precisely defining the responsibilities and collaborative processes of different roles (construction personnel, managers, government staff, etc.) during the construction process. The system supports dynamic workflow definition, allowing for automatic adjustment of subsequent processes based on construction status and progress, enabling personalized risk path management. Each process node is equipped with complete permission control and timeout reminder mechanisms to ensure timely processing of tasks and avoid disconnections and delays in the execution of risk management plans.

[0094] In this embodiment, the system uses a PostgreSQL distributed cluster as the main storage engine, and distributes data across multiple nodes through horizontal sharding technology, ensuring the performance and reliability of the system when facing a large number of concurrent accesses. A hybrid storage strategy is adopted for different types of data: structured basic construction information and risk management records are stored in a relational database; unstructured construction images, risk management training videos and other multimedia data are stored in a distributed file system; and rapidly changing monitoring data such as real-time construction equipment indicators are stored in a time series database to optimize query efficiency and storage space utilization. The system implements a complete ETL process, which can convert heterogeneous data from different construction equipment into a standard format, solving the problem of data silos. Standardized interfaces support automatic acquisition of relevant information from external data sources such as construction management systems, construction unit databases, and supervisory supervision systems, reducing repeated data entry and improving work efficiency.

[0095] A high degree of reusability is achieved through a domain-driven design approach. The system defines core domain objects such as risk management plans, risk assessments, and resource matching. These objects encapsulate complete business rules and data operation logic. For example, the same risk assessment model can be used for initial assessments, phased progress evaluations, and final impact assessments, enabling vertical reuse of data models. The same data model structure can also be used for cross-project group analysis, enabling horizontal reuse and significantly reducing system maintenance costs.

[0096] Construction progress monitoring relies on the use of image processing technology to automatically identify key construction nodes, such as whether concrete pouring of bored piles is complete, and calculate the construction progress percentage based on the number of completed key construction nodes. The specific steps are as follows: Data preparation: image data of different key construction nodes is prepared and labeled; model training: the labeled construction node image data is fed into the model for training; model application: the system's real-time image data is fed into the model, which automatically detects key construction nodes.

[0097] The present invention also discloses a construction method for constructing cast-in-place piles in a karst cave area, comprising the following steps:

[0098] The construction site is surveyed and steel casing is laid. A standard drill bit is used to drill and extract soil to the karst cave. The soil removed by the rotary drilling rig is backfilled. The standard drill bit of the rotary drilling rig is replaced with a special karst cave drilling bit, which compacts the soil in the pile hole downwards. The drill rod of the rotary drilling rig drives the special karst cave drilling bit from the top of the karst cave downwards, continuously compacting the soil inside the karst cave. Backfill is then completed to the top of the karst cave, and the soil inside the karst cave is compacted again. After the karst cave is treated, the steel cage is lowered and concrete is poured. After the concrete is poured, the steel casing is removed using a puller. The karst cave is compacted using the rotary drilling process to ensure that the subsequent drilling and grouting process can proceed.

[0099] Step 1: Survey the construction site, check the engineering survey report, and understand the depth and size of the cave.

[0100] Step 2: After leveling the site, perform measurement and positioning. Once qualified, transport the drilling rig to the designated location. For construction progress, image processing technology can be used to identify key construction nodes. Progress percentages are calculated for each key construction node.

[0101] Step 3: Use a steel casing drill to bury the steel casing.

[0102] Step 4: Use a rotary drilling rig with an ordinary drill bit to drill and take soil to the cave location.

[0103] Step 5: Use an excavator to backfill the soil removed by the rotary drilling rig to a position 2m above the top of the cave.

[0104] Step 6: The rotary drilling machine replaces the ordinary drill bit with a rotary drilling bit for treating caves, and the rotary drilling bit compacts the soil in the pile hole downwards.

[0105] Step 7: Repeat steps 5 and 6 at least once, and then use the drill rod of the rotary drilling machine to drive the rotary drilling bit for processing the cave from the top of the cave to continuously compact the soil in the cave from top to bottom.

[0106] Step 8: After compacting to the bottom of the cave, take out the drill and backfill to the top of the cave, then use the drill rod of the rotary drilling rig to drive the rotary drilling bit to compact the soil in the cave.

[0107] Step 9: After the cave is treated, the rotary drilling rig replaces the soil drill bit and drills normally until it reaches the pile top elevation, lowers the steel cage and pours concrete.

[0108] Step 10: When the concrete is poured to 2m above the top of the cave, the conduit port is left in the middle of the cave for pouring, and the buried pipe depth is maintained at 6m. The side pressure of the concrete is used to further compact the cave backfill soil.

[0109] Step 11: After the concrete pouring is completed, use a puller to pull out the steel casing and pay close attention to the elevation of the concrete at the hole. If there is any sinking, replenish it in time to ensure the integrity of the pile concrete.

[0110] Example 2

[0111] This paper takes the residential building of Chujiang County City Project in Ezhou as an example to illustrate the risk assessment method of bored pile construction. The residential building of Chujiang County City Project in Ezhou has 23 to 27 floors and a construction area of ​​about 74,800 m 2 According to the initial survey report, the foundations of the residential buildings all have a certain number of karst cavities. The foundation of this project uses impact bored cast-in-place piles, designed as end-bearing piles with post-grouting at the pile ends, with a pile diameter of 600mm.

[0112] Based on drilling, standard penetration tests, static cone penetrations, and indoor geotechnical tests, the strata within the survey depth of the project site are divided into six layers: Layer 1 is Quaternary Holocene artificial accumulation (Q4ml) plain fill, Layers 2-5 are Quaternary Upper Pleistocene alluvial (Q3al) clay, and Layer 6 is Middle Triassic (T2) slightly weathered limestone. Drilling revealed that the karst subsurface primarily consists of caves, which partially contain small amounts of plastic clay and original rock fragments. The caves in the drill holes are partially filled, mostly with clay, and connectivity is average. Karst is strongly developed at the site, with 231 drill holes encountering caves.

[0113] 1. Technical solution is determined.

[0114] Due to the complex terrain, the project pile diameter was only 600mm, making it difficult for large rotary drilling rigs to operate. The drill bit was also prone to getting stuck in karst caves and inclined rock faces, causing drill bits to drop, become stuck, or even break the drill rod. Impact-drilled cast-in-place piles, on the other hand, were ineffective, time-consuming, and expensive, with mud splashing on site. Analysis of the actual site conditions led to the decision to add a rotary drilling process to compact the soil filling the karst caves.

[0115] 2. Construction preparation.

[0116] 2.1 Advance drilling survey.

[0117] For foundations with karst caves, a professional surveying company must conduct advance drilling surveys on a pile-by-pile basis (larger diameter piles require multiple drillings per pile, as per design requirements). The drilling depth should be 8.0m into slightly weathered limestone. If a karst cave is encountered during drilling, 8m of stable limestone must be ensured beneath the cave.

[0118] 2.2 Construction preparation.

[0119] (1) Detect optical cables and other pipelines, take protective measures for important pipelines in advance, and communicate with designers in advance to relocate the foundation piles within the prohibited construction area of ​​the pipeline.

[0120] (2) Determine the pretreatment plan for the piles at the cave location based on the geological histogram data. Conduct cave treatment related technical and safety briefings for the construction team before construction. Distribute the geological histogram and cave treatment plan to relevant personnel, so that specific operators, technicians, and work team leaders are familiar with the location, size, filling conditions, and cave treatment plan to be adopted.

[0121] (3) Spare mud should be provided for cave pile foundations. The selection of clay should be strictly controlled. Good clay for slurry preparation should be selected and prepared. The specific gravity of the mud entering the hole should be 1.1-1.3. The viscosity of the mud entering the hole should be 16-22s for general formations and 19-28s for formations close to caves. At the same time, the amount of mud prepared should be increased to cope with the phenomenon of slurry loss that may occur at any time.

[0122] (4) 30m of steel casing was reserved on site to deal with emergencies. The steel casing was made of steel plates with a thickness of not less than 10mm and an inner diameter of 610mm. At the same time, 80m3 of stone and 100m3 of clay were reserved on site to deal with the collapse of the hole.

[0123] (5) When installing the drilling rig, the contact area with the ground should be maximized and sufficient sleepers should be placed. Cables should be used to secure the rig. During construction, the access road should be kept clear. Ensure that the road for moving the equipment is smooth and unobstructed, so that people and equipment can be evacuated quickly in an emergency.

[0124] (6) Excavators, cranes and other types of machinery required for cave processing should be prepared in advance and be on standby.

[0125] (7) The main construction machinery and equipment selected are: XCMG 360 rotary drilling rig; ZZ-6A punching drilling rig; BW150 mud pump; cross-shaped hammer with a diameter of 600mm and a weight of 3 tons.

[0126] 2.3 Risk identification.

[0127] Risk identification of bored pile construction in cave areas:

[0128] The Chujiang County City Project in Ezhou comprises residential buildings. Its foundation utilizes impact bored cast-in-place piles, designed as end-bearing piles with post-grouting at the ends. The pile diameter is 600mm. Drilling revealed that the underground karst formations primarily consist of caves, which partially contain small amounts of plastic clay and fragments of the original rock. The caves in the drilled holes are partially filled with clay, and connectivity is average. This indicates a strong karst development at the site. Through research and analysis of the aforementioned construction projects, combined with actual construction characteristics and reference to construction specifications and procedures, this study identified and analyzed potential risk accidents and identified the underlying risk factors.

[0129] (1) Steel casing deformation accident.

[0130] The project's piles are located in a shallow overburden area, and the rock face is severely tilted. This reduces the contact area between the bottom of the steel casing and the rock surface. Upon entering the bedrock, it will be subjected to significant axial pressure, resulting in excessive local stress at the bottom and axial buckling deformation. This construction accident makes it difficult to drive the steel casing to the designed elevation and later makes it difficult to lower the drilling rig. In reality, the wall thickness of steel casing is limited. Increasing the wall thickness will increase the weight of the steel casing, making it difficult to transport and hoist the steel casing. However, when the wall thickness is small, the bottom of the steel casing is very likely to buckle during the driving process, making it difficult to drive to the designed elevation.

[0131] Based on the above analysis, the wall thickness design, ovality control and hammer energy output of large-diameter steel casing will become important risk factors for deformation construction accidents of steel casing.

[0132] (2) Slurry leakage accident.

[0133] The construction area has complex geological conditions. The strata are filled with partially weathered limestone and overburden of uneven thickness, which can easily lead to insufficient burial depth of the steel casing into the rock. The rock surface at the pile position has a certain inclination angle, which means that during the construction phase, the bottom of the steel casing is not anchored to the bedrock, preventing a tight connection and the presence of large cracks. Overall, the insufficient burial depth of the steel casing reduces the stratum fracture pressure, and the mud column pressure is greater than the stratum fracture pressure. In addition, the presence of cracks ultimately leads to slurry leakage at the bottom of the steel casing, which will further trigger construction accidents such as hole collapse.

[0134] (3) Accidents of drill falling or buried.

[0135] During drilling operations, when a drill rig penetrates complex, hard formations, especially those with uneven hardness and softness, the drill often experiences shaking or sticking. This forces the drill pipe to withstand asymmetric alternating torque and frequent overloads. This torque generates alternating shear stresses on the drill pipe, which has a greater impact on drill pipe fatigue strength than steady torque. The drill pipe of a large-diameter drill rig is subjected to complex alternating stresses due to the lever arm. If these stresses are not relieved, they can damage the drill tool. Stress is most concentrated at the connection between the weight and the drill pipe, ultimately leading to drill pipe fracture and damage, resulting in drill drop and buried accidents.

[0136] (4) Accidents of inclined holes and collapsed holes.

[0137] Backfilling measures slowed down the progress of drilling and prolonged borehole drilling, impacting the overall progress of the project. The construction area was characterized by uneven rock formations with a steep inclination at the interface. The weight of the drill bit and drill rod forced the drill centerline to deviate from the borehole axis. For example, the steel casing was buried at a shallow depth, and early drilling and piercing caused stress release in the rock formation. Fractures developed in some weakly weathered rock formations, and the borehole drilling cycle was long. These factors were the primary causes of the borehole collapse accident.

[0138] (5) Accidents caused by infusion quality defects.

[0139] The risk of quality accidents during the pouring of bored pile foundation concrete in karst cave areas is also increasing. During the bottom concrete sealing process, improperly settling of bottom hole sediment and the setting of the suspended conduit can easily cause mud to be trapped in the concrete at the pile bottom and spread throughout the pile bottom, reducing the strength of the concrete at the pile bottom. The unique geographical environment of the karst cave can change the pouring flow pattern of the concrete at the bottom of the hole, resulting in a change in the way the concrete rises, which in turn affects the bond between the poured concrete and the pile side. As the pile diameter increases, the pouring volume will also continue to increase, and the diameter of the conduit used will also increase, affecting the fluidity of the concrete at the bottom of the hole. However, during the pouring process, the setting of the conduit burial depth can play a role in controlling the flow pattern of the concrete at the bottom of the hole.

[0140] 2.4WBS-RBS method.

[0141] (1) Establish a WBS construction unit decomposition structure. According to the construction process of bored piles in the cave area, the main construction excavation is decomposed into three main processes: steel casing construction W1, hole construction W2, and conduit installation W3. The main processes are further broken down into lower-level process sub-items to form its WBS process decomposition structure, such as Figure 4 shown.

[0142] (2) Establish an RBS risk factor decomposition structure.

[0143] The risk factors involved in bored pile construction in karst areas are broken down into primary and secondary risk factors, as shown in Table 2. A total of 17 risk factors are included. Risk factors are represented by Rij (i = 1, 2, 3, j = 1, 2, ..., 17).

[0144] (3) Construct the WBS-RBS matrix. With WBS as the columns and RBS as the rows, create the matrix shown in Table 3.

[0145] 2.5 Determine the risk value.

[0146] The construction of bored piles in the cave area involves many different types of professionals.

[0147] Table 2 Risk factors for bored pile construction in cave areas

[0148]

[0149] The project involved numerous underground pipelines. Based on the actual circumstances of the case, the LEC risk assessment method proposed by Graham and Kinney was adopted. Experts were invited to score and determine the values ​​of L, E, and C. The risk value, D, was calculated using Equation (1). The results are shown in Table 3. Different values ​​indicate the magnitude of the risk of a risk event occurring in that construction unit. Table 3 clearly shows the degree of impact of different risk factors in the matrix on each construction unit. The risk level classification is shown in Table 4.

[0150] Table 3 WBS-RBS matrix

[0151]

[0152]

[0153] Table 4 Risk levels

[0154] Score Risk level classification grade >320 Extremely dangerous, cannot continue working Ⅰ 160～320 Highly dangerous, immediate rectification is required Ⅱ 70～160 Significant danger, need to be corrected Ⅲ 20～70 General danger, please be careful Ⅳ <20 A little dangerous, but acceptable Ⅴ

[0155] 2.8 Risk response measures.

[0156] Personnel Management:

[0157] (1) Strengthen pre-job training and safety education knowledge training for construction workers to improve their risk awareness.

[0158] (2) Carefully carry out technical briefings and strictly require operators to construct according to the drawings.

[0159] Technology Management

[0160] (1) Control of steel casing deformation risk accidents.

[0161] The steel casing deformation construction accident was rated as a comprehensive III risk level in the risk assessment, among which the steel casing wall thickness, vertical impact output energy and ovality factors are all key risk factors, all of which need to be taken

[0162] Table 5 Risk factor weights and risk values ​​for bored pile construction in karst areas

[0163]

[0164] Targeted prevention and control measures should be implemented. If the steel casing does not reach the design elevation during installation, the drill rig should be used to re-drill and follow up with the casing to the design elevation. If the bottom of the steel casing in this project deforms, the foundation plan should be promptly revised and the casing should be removed and re-installed.

[0165] (2) Control of risk accidents caused by infusion quality defects.

[0166] Based on risk analysis and research on accident patterns, the risk factors for underwater concrete pouring quality defects include the height of the suspended conduit, bottom sediment at the hole, pouring depth, conduit diameter, and conduit burial depth. These factors were identified as key risk factors in the risk assessment results.

[0167] The diameter of the conduit affects the total pouring time and flow pattern. A smaller conduit diameter significantly increases the total pouring time. A mismatch between the effective radius of the conduit diameter and the pile diameter affects the pouring fluidity, resulting in an inclined surface rise and quality defects on the pile side. An overly large conduit diameter exacerbates mud inclusion in the pile body. Therefore, it is necessary to rationally set the conduit diameter and implement secondary hole cleaning for the pile foundation, in compliance with regulatory requirements, with enhanced monitoring and over-pouring of any defective initial concrete that is ultimately jacked up.

[0168] (3) Control of risk accidents of inclined holes and collapsed holes.

[0169] After risk identification and estimation for inclined boreholes and collapsed boreholes, it was determined that the risk factor for rock fracture development reached Level III, and the risk factors for large rock formation inclination, unstable drill rods, and long drilling cycles reached Level III. Based on previous cases where the single-stage full-section drilling method had resulted in inclined boreholes, collapsed boreholes, and low drilling efficiency, a secondary drilling process was adopted to meet construction requirements. For this project, the secondary drilling process is also recommended for construction risk control. Based on this, a combined method of rotary drilling rigs and rotary drilling rigs is proposed.

[0170] From the above description, it can be seen that the present invention has the following effects:

[0171] (1) The WBS-RBS coupling matrix analysis method is used to make risk identification and risk factors more comprehensive and detailed.

[0172] (2) Using the G1 method to calculate the weight value of each risk factor can effectively integrate qualitative analysis and quantitative evaluation, reduce the amount of calculation and subjective factors, and greatly improve the reliability of the calculation.

[0173] (3) Through application in actual engineering projects, it is shown that the use of this model for risk assessment is effective and feasible, and can provide a reference for risk identification and evaluation of bored cast-in-place piles in cave areas in the future.

[0174] The above-described embodiments are only preferred specific implementation methods of the present invention, and the protection scope of the present invention is not limited thereto. Any simple changes or equivalent replacements of the technical solutions that can be obviously obtained by any technician familiar with the field within the technical scope disclosed in the present invention fall within the protection scope of the present invention.

Claims

1. A risk assessment method for bored pile construction, characterized in that: The steps include: Establish a WBS construction unit decomposition structure based on the construction process of bored piles in karst cave areas; establish an RBS risk factor decomposition structure based on the risk factors in the construction process of bored piles in karst cave areas; With WBS as columns and RBS as rows, a WBS-RBS risk identification coupling matrix is ​​constructed; Calculate the risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix; The subjective weighted G1 sequence method is used to calculate the weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix; The risk values ​​of the construction units in the risk identification coupling matrix are determined by the risk values ​​and weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix, and the potential risks in the cast-in-place pile construction process in the cave area are evaluated by the risk values ​​of the construction units.

2. The risk assessment method for bored pile construction according to claim 1, characterized in that: The WBS construction unit decomposition structure includes steel casing construction W1, hole construction W2 and pile construction W3. The steel casing construction includes steel casing processing and manufacturing W11, steel casing hoisting and transportation W12 and steel casing positioning and insertion W13; the hole construction includes drilling with a drill rig W21, drill removal and backfilling W22, lowering of the steel cage W23 and hole cleaning W24; the pile construction W3 includes guide tube installation W31 and concrete pouring W32.

3. The risk assessment method for bored pile construction according to claim 1, characterized in that: The RBS risk factor decomposition structure includes construction risk factors R1, surrounding environment risk factors R2 and personnel and management risk factors R3.

4. The risk assessment method for bored pile construction according to claim 1, characterized in that: The risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix are calculated specifically by the following formula: D = L·E·C; Where L is the probability of an accident occurring, E is the probability that a worker is in a risky environment, and C is the loss caused by the accident.

5. The risk assessment method for bored pile construction according to claim 1, characterized in that: The method of using the subjective weighted G1 sequence method to calculate the weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix includes the following steps: Sort the risk factors in WBS-RBS by importance; Assign weights based on the importance ratios between adjacent risk factors; Calculate the weight coefficient based on the assigned weight.

6. The risk assessment method for bored pile construction according to claim 1, characterized in that: The weight coefficient λ k The calculation formula is: Where n is the number of experts, r ki is the value assigned by expert i to risk factor k, j is the jth risk factor, and s is the number of risk factors.

7. The risk assessment method for bored pile construction according to claim 1, characterized in that: The calculation formula of the risk value of the construction unit is: Where D i represents the risk value of the i-th construction unit; λ ij represents the weight coefficient of the jth risk factor of the i-th construction unit; D ij represents the weight coefficient and risk value of the jth risk in the i-th construction unit; n represents the number of risks in the i-th construction unit, and x represents the risk factor of the construction unit.

8. A risk assessment system for bored pile construction, characterized in that: include: The risk identification coupling matrix building module is used to establish the WBS construction unit decomposition structure based on the construction process of bored piles in karst areas; Establish an RBS risk factor decomposition structure based on the risk factors in the construction process of bored piles in karst areas; With WBS as columns and RBS as rows, a WBS-RBS risk identification coupling matrix is ​​constructed; Risk value calculation module, used to calculate the risk values ​​of different risk factors in the WBS-RBS risk identification coupling matrix; The weight coefficient calculation module is used to calculate the weight coefficients of different risk factors in the WBS-RBS risk identification coupling matrix using the subjective weighted G1 sequence method; The risk assessment module is used to determine the risk value of the construction unit in the WBS-RBS risk identification coupling matrix based on the risk values ​​and weight coefficients of different risk factors in the risk identification coupling matrix, and to assess the potential risks in the construction process of cast-in-place piles in the cave area based on the risk value of the construction unit.

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