Retractable steel screw pile and construction method

Abstract

The present invention provides a retractable steel spiral pile and a construction method. The steel spiral pile comprises a steel pipe pile, an inner shaft steel pipe and a retractable spiral steel sheet. The inner shaft steel pipe is located inside the steel pipe pile, and the spiral steel sheet is hinged to the outer surface of the inner shaft steel pipe; a spiral guide hole is provided on the pipe wall of the steel pipe pile, and before the inner shaft steel pipe is lifted, the spiral steel sheet is folded and stored inside the steel pipe pile; during the lifting process of the inner shaft steel pipe, the spiral steel sheet extends outward and protrudes out of the outer surface of the steel pipe pile. Compared with traditional spiral piles that are hammered or spirally entered into the soil layer, the pile body resistance of the present invention is greatly reduced, the speed of pile entry into the soil can be greatly increased, no waste soil is generated during the construction process, and construction costs are reduced. Traditional spiral piles are hammered into the soil or spirally descended into the soil, which continuously cuts and disturbs the soil around the pile, destroying the original state and mechanical properties of the soil around the pile. The present invention spirally enters the soil for one circle and then is grouting fixed, which has less impact on the soil around the pile, and the properties of the soil around the pile itself are better preserved and maintained.

Description

Technical Field

[0001] The invention belongs to the field of screw pile foundations, and in particular relates to a retractable steel screw pile and a construction method. Background Art

[0002] Steel screw piles, also known as ground screws, are made of hot-forged metal tubes with spiral blades wrapped around their surface. They are screwed into the ground using specialized ground screw tightening equipment, replacing the existing concrete foundation and connecting the load to the top. As underground foundations, ground screws offer advantages such as ease of construction, short construction times, minimal impact on the construction environment, environmental friendliness, and ease of relocation and recycling.

[0003] In 1833, British builder Alexander Mitchell used helical piles (called helical anchors) as the foundations for lighthouses on islands near England. However, due to the limitations of the technology at the time, their application was slow to expand.

[0004] Research on screw pile foundations began relatively early abroad. AB Chance used spiral steel pipe piles in transmission tower foundation projects and developed the first standard for spiral steel pipe piles, PISA (Power Installed Screw Anchors), in 1959. The 1979 Building Code, Part II, Design Standards, Chapter 17, Section 5, Clause 5.13, Screw Piles, specifies the design criteria for screw pile foundations. In 1992, Australia's INSTANT FOUNDATION invented a steel pipe spiral cast-in-place pile for foundation engineering. In 1995, Japan's Fukuei Kosan developed the SP-300, a fully prefabricated steel fiber reinforced concrete spiral pile.

[0005] In 1999, Chen Rihong et al. in China systematically studied precast concrete spiral piles. In 2002, the School of Urban Construction at Wuhan University developed fully threaded cast-in-place piles and demonstrated this type of pile in real-world projects, comparing its bearing capacity and economic benefits with traditional piles. They concluded that threaded piles require only 60% to 70% of the concrete used in linear cast-in-place piles of the same diameter, while their ultimate bearing capacity is more than double that of linear cast-in-place piles of the same diameter. In 2004, the Institute of Engineering Mechanics at Northeastern University, the MCC Shenyang General Survey and Research Institute, and the Liaoning Electric Power Survey and Design Institute jointly conducted research on precast spiral pile foundations. In 2011, the State Grid Corporation of China, drawing on nearly a decade of experimental research and engineering application experience with spiral pile foundations for transmission lines in Dandong, Yingkou, and Panjin, Liaoning Province, issued the corporate standard "Technical Specifications for the Design of Spiral Anchor Foundations for Overhead Transmission Lines."

[0006] Traditional steel screw piles are all equipped with spiral blades on the outer surface of the steel pipe. The spiral piles are generally driven into the soil by rotating or hammering the pile head. The external spiral blades directly shear the soil around the pile during the process of descending into the soil. The soil-entry process has the following technical problems and shortcomings:

[0007] (1) Mechanical cutting and segmentation of the soil around the pile destroys the integrity and continuity of the soil around the pile, affecting the original state and mechanical properties of the soil around the pile;

[0008] (2) It requires a large hammering force or rotational torque, which results in high construction costs. The larger the pile diameter, the greater the cost increase.

[0009] (3) Rotary drilling or hammering results in a higher porosity at the contact surface between the spiral blade and the soil, which reduces the bite effect and joint working performance of the “screw pile-soil layer” and reduces the bearing advantage of the spiral pile itself.

[0010] (4) The traditional method of burying piles in the ground will produce a certain amount of waste soil, which will increase construction costs. Summary of the Invention

[0011] The object of the present invention is to provide a retractable steel spiral pile and a construction method, which can solve the problems existing in the prior art of steel spiral piles, such as large disturbance to the soil around the pile, high porosity of the spiral blade-soil contact surface, which reduces the bearing advantage of the spiral pile itself; and large resistance of the pile body to entering the soil and generation of a certain volume of waste soil, resulting in high construction costs.

[0012] The present invention is achieved as follows: a retractable steel spiral pile comprises a hollow steel pipe pile, a hollow inner shaft steel pipe, a retractable spiral steel sheet, a steel pipe pile top connector and an inner shaft steel pipe top connector;

[0013] The top connector of the steel pipe pile is fixed to the top of the steel pipe pile. The top connector of the steel pipe pile has a threaded hole. The inner shaft steel pipe is located in the steel pipe pile. The inner shaft steel pipe passes downward through the threaded hole and is threadedly connected to the threaded hole. The bottom end of the inner shaft steel pipe is a free end.

[0014] The top of the inner shaft steel pipe is provided with a grouting port, and the wall of the pipe is provided with a plurality of grouting holes, and the spiral steel sheet is hinged to the outer surface of the inner shaft steel pipe;

[0015] A spiral guide hole is opened on the wall of the steel pipe pile. Before the inner shaft steel pipe is lifted, the spiral steel sheet is stored in the steel pipe pile in a contracted and folded manner. During the lifting process of the inner shaft steel pipe, the spiral steel sheet moves and stretches outward under the guidance of the spiral guide hole. When the spiral steel sheet is in the stretched state, its outer edge protrudes outward from the outer side surface of the steel pipe pile.

[0016] The top connector of the inner shaft steel pipe is fixed to the top of the inner shaft steel pipe; the inner space of the inner shaft steel pipe and the space between the outer periphery of the inner shaft steel pipe and the inner wall of the steel pipe pile are solidified by grouting.

[0017] Furthermore, the bottom end of the steel pipe pile is tapered.

[0018] Furthermore, a plurality of the retractable spiral steel sheets are hingedly connected to the outer periphery of the inner shaft steel tube along the axial direction of the inner shaft steel tube.

[0019] Furthermore, before the inner shaft steel pipe is lifted, the spiral steel sheet is embedded in the spiral guide hole, and the outer diameter line of the spiral steel sheet is flush with the outer side surface of the steel pipe pile.

[0020] Furthermore, the spiral steel sheet is an integral sheet structure.

[0021] Furthermore, the spiral steel sheet includes a plurality of dispersed strip structures, and each of the strip structures is hinged to the outer periphery of the inner shaft steel pipe.

[0022] To solve the above problems, the present invention further provides a construction method of the above steel screw pile, comprising the following steps:

[0023] S10. Positioning and setting out at the construction site;

[0024] S20, connecting the top of the steel pipe pile to a tightening machine or a ballast machine;

[0025] S30, tightening machine or ballast machine to carry pile into place;

[0026] S40, tighten or ballast the pile;

[0027] S50, after the sinking depth of the steel screw pile reaches the designed depth, stop sinking the pile;

[0028] S60, use a tightening machine to connect to the top of the inner shaft steel pipe;

[0029] S70: The tightening machine works to lift the inner shaft steel pipe by rotating. During the lifting process, the inner shaft steel pipe pulls the spiral steel sheet, so that the spiral steel sheet gradually stretches outward from the folded state and protrudes from the spiral guide hole to the outer side of the steel pipe pile.

[0030] S80: After the inner shaft steel pipe is lifted to the designed height, stop lifting;

[0031] S90, grouting the inner shaft steel pipe until the inner space of the inner shaft steel pipe and the steel pipe pile is filled with grout;

[0032] S100: Construction is completed, the next pile is moved for construction, and the above steps S10 to S90 are executed again.

[0033] Furthermore, the above construction method further comprises the following steps:

[0034] Before pile construction, trial pile driving should be carried out to determine the various construction quality control parameters during the construction process according to the design documents and standard requirements, and the ultimate bearing capacity of a single pile should be determined in combination with the trial pile driving.

[0035] Furthermore, the above construction method further comprises the following steps:

[0036] Select appropriate construction equipment based on the pile type, pile length, ground conditions and on-site construction conditions; verify the connection strength and grouting pressure between the construction equipment and the top of the steel pipe pile and the top of the inner shaft steel pipe, and adopt a stable and reasonable connection method to ensure the safety of the construction process.

[0037] Furthermore, the above construction method further comprises the following steps:

[0038] The allowable deviation of pile position layout is less than 10mm, and the verticality deviation of the pile when it is screwed in is less than 1%. If the rotation process encounters drill sticking, poor grouting, pile position offset or tilt, work must be stopped immediately, the cause must be identified, and appropriate measures must be taken before continuing the operation.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. Compared to traditional screw piles, the retractable steel screw piles provided by this invention have a cylindrical outer surface during the driving phase. They can be driven to the designed depth using static ballasting or hammering. Compared to traditional screw piles driven into the soil by hammering or spiraling, the pile's penetration resistance is significantly reduced, significantly increasing the speed of penetration and reducing costs.

[0041] 2. The steel spiral pile is screwed into the soil once and then fixed with grouting. Compared with the physical segmentation and cutting of the stratum by traditional spiral piles, the steel spiral of the present invention effectively protects the original state and continuity of the soil layer, reduces the disturbed area of ​​the original soil, and better preserves and maintains the properties of the soil around the pile. The steel spiral pile has a compacting effect on the soil around the pile. After the spiral steel sheet is extended, a "spiral pile-soil layer" load-bearing community is formed, which minimizes the vibration caused by traditional pile driving into the soil and the large void ratio at the pile-soil interface caused by the rotation of the spiral steel sheet into the soil, enhances the density of the pile-soil interface, and increases the stability of the pile body in the soil layer.

[0042] 3. After the spiral steel sheet is lifted and rotated to cut into the soil layer, solidifying slurry is poured into the pile through the inner shaft steel pipe. After filling the inner shaft steel pipe, the slurry diffuses into the internal space of the outer steel pipe pile to form an integrated solidification area of ​​"spiral pile-non-spiral pile (steel pile)-soil around the pile", effectively improving the overall anchoring capacity of the spiral pile. This process integrates the three major technical advantages of "spiral anchoring + rotation and expansion of the inner shaft spiral steel sheet + grouting solidification".

[0043] 4. Compared with cylindrical steel piles or spiral piles of the same size, the novel retractable steel screw piles of the present invention have significantly improved compressive bearing capacity and pull-out anchoring performance with a relatively small cost increase.

[0044] 5. The novel retractable steel screw pile of the present invention does not generate waste soil during the construction process, which is beneficial to reducing construction costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a central cross-sectional view of a retractable steel screw pile of this embodiment;

[0046] Figure 2 is an elevation view of a retractable steel screw pile according to the present embodiment;

[0047] Figure 3 1 is a cross-sectional view comparing the spiral steel sheet of a retractable steel spiral pile of this embodiment before and after lifting;

[0048] Figure 4 This is a construction flow chart of a retractable steel screw pile provided in this embodiment.

[0049] Reference numerals in the figures:

[0050] 1-steel pipe pile, 11-spiral guide hole, 2-inner shaft steel pipe, 21-grouting port, 22-slurry outlet hole, 3-spiral steel sheet, 3a-spiral steel sheet in folded state, 3b-spiral steel sheet in extended state, 4-top connector of steel pipe pile, 41-threaded hole, 5-top connector of inner shaft steel pipe. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0052] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "inside", "outside" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance; in addition, unless otherwise expressly specified and limited, the terms "installed", "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 direct connection, an indirect connection through an intermediate medium, or a communication between the internal parts of the two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] Please see Figure 1 , shows a retractable steel spiral pile provided by this embodiment, including a hollow steel pipe pile 1, a hollow inner shaft steel pipe 2, a retractable spiral steel sheet 3, a steel pipe pile top connector 4 and an inner shaft steel pipe top connector 5.

[0054] The top connector 4 of the steel pipe pile is fixed to the top of the steel pipe pile 1. The top connector 4 of the steel pipe pile has a threaded hole 41. The inner shaft steel pipe 2 is located in the steel pipe pile 1. The inner shaft steel pipe 2 passes downward through the threaded hole 41 and is threadedly connected to the threaded hole 41. The bottom end of the inner shaft steel pipe 2 is a free end. The steel pipe pile 1 is cylindrical as a whole, and its bottom end is conical.

[0055] The top opening of the inner shaft steel pipe 2 serves as a grouting port 21 , and a plurality of slurry outlet holes 22 are reserved on the wall of the inner shaft steel pipe 2 along its axial direction. The spiral steel sheet 3 is hinged to the outer surface of the inner shaft steel pipe 2 .

[0056] Please see Figure 2 , a spiral guide hole 11 is provided on the wall of the steel pipe pile 1. Figure 3 Before the inner shaft steel pipe 2 is lifted, the spiral steel sheet 3a is stored in the steel pipe pile 1 in a contracted and folded manner; during the lifting process of the inner shaft steel pipe 2, the spiral steel sheet 3a slides along the spiral guide hole 11 under the guidance of the spiral guide hole 11 and extends to the outside. When the spiral steel sheet 3b is in the extended state, its outer edge protrudes outward from the outer side of the steel pipe pile 1, so that it can cut the soil around the pile and embed into the soil around the pile.

[0057] The inner shaft steel pipe top connector 5 is fixed to the top of the inner shaft steel pipe 2; the inner space of the inner shaft steel pipe 2 and the space between the outer periphery of the inner shaft steel pipe 2 and the inner wall of the steel pipe pile 1 are solidified by grouting.

[0058] Specifically, a plurality of retractable spiral steel sheets 3 are hinged on the outer periphery of the inner steel pipe 2 along the axial direction of the inner steel pipe 2. Before the inner steel pipe 2 is lifted, the spiral steel sheets 3 are embedded in the spiral guide holes 11, and the outer diameter of the spiral steel sheets 3 is flush with the outer side surface of the steel pipe pile 1.

[0059] In practical applications, the spiral steel sheet 3 is an integral sheet structure, or the spiral steel sheet 3 can also be configured as a plurality of dispersed strip structures, each strip structure being hinged to the outer side surface of the inner shaft steel tube 2 .

[0060] The material of the steel pipe pile 1 should be Q235, Q345 ordinary steel or low alloy steel pipe, the pipe wall thickness of the steel pipe pile 1 should not be less than 4mm; the galvanized layer of the steel pipe pile 1 should not be less than 80μm.

[0061] Please see Figure 4 This embodiment also provides a construction method for the above-mentioned steel screw pile, comprising the following steps:

[0062] S10. Positioning and setting out at the construction site;

[0063] S20, connecting the top of the steel pipe pile 1 to a tightening machine or a ballast machine to ensure a firm connection;

[0064] S30, Use a screwing machine or ballast machine to carry the pile into place and ensure the verticality of the steel screw pile;

[0065] S40, tightening or ballasting the pile, and during the pile driving process, controlling the pile driving speed within the set range;

[0066] S50, after the sinking depth of the steel screw pile reaches the designed depth, stop sinking the pile;

[0067] S60, use a tightening machine to connect to the top of the inner shaft steel pipe 2 to ensure a firm connection;

[0068] S70: The tightening machine works to lift the inner shaft steel pipe 2 by rotating. During the lifting process, the inner shaft steel pipe 2 pulls the spiral steel sheet 3, so that the spiral steel sheet 3 gradually stretches outward from the folded state and protrudes from the outer side of the steel pipe pile 1 from the spiral guide hole 11;

[0069] S80, after the inner shaft steel pipe 2 is lifted to the designed height, the lifting is stopped;

[0070] S90, grouting the inner shaft steel pipe 2 until the inner space of the inner shaft steel pipe 2 and the steel pipe pile 1 is filled with grout. During the grouting process, pay attention to controlling the grouting pressure, flow rate and volume;

[0071] S100: After the construction is completed, the next pile is moved and the above steps S10 to S90 are executed again.

[0072] Preferably, the above construction method further comprises the following steps:

[0073] Before pile construction, trial pile driving should be carried out to determine the various construction quality control parameters during the construction process according to the design documents and standard requirements, and the ultimate bearing capacity of a single pile should be determined in combination with the trial pile driving.

[0074] Select appropriate construction equipment based on the pile type, pile length, ground conditions and on-site construction conditions; verify the connection strength and grouting pressure between the construction equipment and the top of the steel pipe pile 1 and the top of the inner shaft steel pipe 2, and adopt a stable and reasonable connection method to ensure the safety of the construction process.

[0075] The allowable deviation of pile position layout is less than 10mm, and the verticality deviation of the pile when it is screwed in is less than 1%. If the rotation process encounters drill sticking, poor grouting, pile position offset or tilt, work must be stopped immediately, the cause must be identified, and appropriate measures must be taken before continuing the operation.

[0076] Compared to traditional screw piles, the steel screw piles of this embodiment feature a cylindrical outer surface during the driving phase. This allows for driving the pile to the designed depth using static ballasting or hammering. Compared to traditional screw piles driven into the soil by hammering or spiraling, this significantly reduces the resistance to pile penetration, significantly increasing the speed of penetration and reducing costs.

[0077] The steel spiral pile of this embodiment is screwed into the soil once before being secured with grouting. Compared to the physical segmentation and cutting of the stratum by conventional screw piles, the steel spiral of this embodiment effectively preserves the original state and continuity of the soil, reduces the area of ​​disturbed undisturbed soil, and effectively preserves and maintains the inherent properties of the soil surrounding the pile. The steel spiral pile compacts the soil surrounding the pile, forming a "spiral pile-soil" load-bearing community after the spiral steel blades 3 extend. This minimizes the vibration caused by conventional pile driving and the high porosity at the pile-soil interface caused by the rotation of the spiral steel blades into the soil, thereby enhancing the compaction of the pile-soil interface and increasing the stability of the pile body in the soil.

[0078] After the spiral steel sheet 3 cuts into the soil layer by lifting and rotating, solidifying slurry is poured into the pile through the inner shaft steel pipe 2. After filling the inner shaft steel pipe 2, the slurry diffuses into the internal space of the external steel pipe pile 1, forming an integrated solidification zone of "spiral pile-non-spiral pile (steel pile)-soil around the pile", effectively improving the overall anchoring capacity of the spiral pile. This process integrates the three major technical advantages of "spiral anchoring + rotation and expansion of the inner shaft spiral steel sheet + grouting solidification".

[0079] Compared with cylindrical steel piles or spiral piles of the same size, the steel screw piles of this embodiment have significantly improved compressive bearing capacity and pull-out anchoring performance with a slightly higher cost.

[0080] The steel screw piles of this embodiment do not generate waste soil during the construction process, which is beneficial to reducing construction costs.

[0081] The retractable steel screw piles of this embodiment are suitable for use in soil fill, silt, clay, sand, loose to medium-dense gravel, fully weathered rock, and strongly weathered soft rock. They can be used in geotechnical and underground engineering, trenchless piles, foundation reinforcement, and prefabricated building foundations.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A retractable steel screw pile, characterized in that: It includes a hollow steel pipe pile, a hollow inner shaft steel pipe, a retractable spiral steel sheet, a top connector of the steel pipe pile and a top connector of the inner shaft steel pipe; The top connector of the steel pipe pile is fixed to the top of the steel pipe pile. The top connector of the steel pipe pile has a threaded hole. The inner shaft steel pipe is located in the steel pipe pile. The inner shaft steel pipe passes downward through the threaded hole and is threadedly connected to the threaded hole. The bottom end of the inner shaft steel pipe is a free end. The top of the inner shaft steel pipe is provided with a grouting port, and the wall of the pipe is provided with a plurality of grouting holes, and the spiral steel sheet is hinged to the outer surface of the inner shaft steel pipe; A spiral guide hole is opened on the wall of the steel pipe pile. Before the inner shaft steel pipe is lifted, the spiral steel sheet is stored in the steel pipe pile in a contracted and folded manner. During the lifting process of the inner shaft steel pipe, the spiral steel sheet moves and stretches outward under the guidance of the spiral guide hole. When the spiral steel sheet is in the stretched state, its outer edge protrudes outward from the outer side surface of the steel pipe pile. The top connecting piece of the inner shaft steel pipe is fixed on the top of the inner shaft steel pipe; the internal space of the inner shaft steel pipe and the space between the outer periphery of the inner shaft steel pipe and the inner wall of the steel pipe pile are solidified by grouting; the outer periphery of the inner shaft steel pipe is hinged with a plurality of retractable spiral steel sheets along the axial direction of the inner shaft steel pipe, and before the inner shaft steel pipe is lifted, the spiral steel sheet is embedded in the spiral guide hole, and the outer diameter line of the spiral steel sheet is flush with the outer side surface of the steel pipe pile.

2. The steel screw pile according to claim 1, characterized in that: The bottom end of the steel pipe pile is tapered.

3. The steel screw pile according to claim 1 or 2, characterized in that: The spiral steel sheet is an integral sheet structure.

4. The steel screw pile according to claim 1 or 2, characterized in that: The spiral steel sheet includes a plurality of dispersed strip structures, and each of the strip structures is hinged to the outer periphery of the inner shaft steel pipe.

5. A method for constructing a steel screw pile according to any one of claims 1 to 4; characterized in that: The following steps are involved: S10. Positioning and setting out at the construction site; S20, connecting the top of the steel pipe pile to a tightening machine or a ballast machine; S30, tightening machine or ballast machine to carry pile into place; S40, tighten or ballast the pile; S50, after the sinking depth of the steel screw pile reaches the designed depth, stop sinking the pile; S60, use a tightening machine to connect to the top of the inner shaft steel pipe; S70: The tightening machine works to lift the inner shaft steel pipe by rotating. During the lifting process, the inner shaft steel pipe pulls the spiral steel sheet, so that the spiral steel sheet gradually stretches outward from the folded state and protrudes from the spiral guide hole to the outer side of the steel pipe pile. S80: After the inner shaft steel pipe is lifted to the designed height, stop lifting; S90, grouting the inner shaft steel pipe until the inner space of the inner shaft steel pipe and the steel pipe pile is filled with grout; S100: Construction is completed, the next pile is moved for construction, and the above steps S10 to S90 are executed again.

6. The construction method according to claim 5, characterized in that: The following steps are also included: Before pile construction, trial pile driving should be carried out to determine the various construction quality control parameters during the construction process according to the design documents and standard requirements, and the ultimate bearing capacity of a single pile should be determined in combination with the trial pile driving.

7. The construction method according to claim 5, characterized in that: The following steps are also included: Select appropriate construction equipment based on the pile type, pile length, ground conditions and on-site construction conditions; verify the connection strength and grouting pressure between the construction equipment and the top of the steel pipe pile and the top of the inner shaft steel pipe, and adopt a stable and reasonable connection method to ensure the safety of the construction process.

8. The construction method according to claim 5, characterized in that: The following steps are also included: The allowable deviation of pile position layout is less than 10mm, and the verticality deviation of the pile when it is screwed in is less than 1%. If the rotation process encounters drill sticking, poor grouting, pile position offset or tilt, work must be stopped immediately, the cause must be identified, and appropriate measures must be taken before continuing the operation.

Images