Tunnels, as a crucial part of modern transportation infrastructure, play an irreplaceable role in connecting regions and promoting economic development. However, tunnel construction faces numerous challenges, with one of the most severe being tunnel collapse. So, why don't tunnels collapse? This is mainly due to advanced design concepts, scientific construction methods, and strict quality control, among other efforts.

　　Advanced Design Concepts

　　Advanced design concepts are key to ensuring tunnel stability. During the tunnel design phase, engineers comprehensively consider factors such as geological conditions, hydrological conditions, and traffic demands to formulate a reasonable tunnel plan. For example, they conduct geological surveys to understand the strata around the tunnel, predict possible geological disasters, and take corresponding measures to avoid these risks. Additionally, designers use advanced calculation software and simulation technology to accurately model and analyze the tunnel structure, optimizing its design to enhance stability and load-bearing capacity.

　　Scientific Construction Methods

　　Scientific construction methods are also crucial for ensuring tunnel stability. During construction, engineers choose appropriate methods based on geological conditions, such as the shield method or the cut-and-cover method. The shield method is an advanced technique that allows continuous advancement in underground tunnels while forming a stable structure. The cut-and-cover method involves mechanically or manually excavating the tunnel section, followed by support and reinforcement. Key factors like blast parameters and support spacing must be strictly controlled during construction to ensure safety and stability.

　　Methods to Ensure Stability

　　Various methods are employed during tunnel construction to ensure stability. For example, pre-reinforcement, grouting, and rock bolting are used to enhance the stability of the surrounding rock. Concrete lining and steel arches are used to strengthen the tunnel structure's strength and stability. Monitoring and forecasting methods, such as stress sensors and displacement monitors, are used to detect and resolve issues promptly during construction.

　　Advanced Monitoring and Warning Systems

　　Modern tunnel engineering extensively uses advanced monitoring technologies and warning systems. By installing devices like stress sensors and displacement monitors, the stress state and deformation of the tunnel can be monitored in real-time. Fiber optic sensing technology and wireless communication technology enable real-time data collection and remote monitoring inside the tunnel. These technologies not only help identify potential safety hazards promptly but also provide accurate data support for emergency rescue, significantly enhancing tunnel safety.

　　Conclusion

　　The ability of tunnels to remain stable and effectively prevent collapse incidents is due to the combined efforts of advanced design concepts, scientific construction methods, strict quality control, and advanced monitoring technologies. With continuous technological progress and innovation, we have reason to believe that future tunnel engineering will be safer, more efficient, and more sustainable.

　　The arch frame trolley, also known as a tunnel arch installation trolley, is a multifunctional mechanical device specifically used for installing steel arches, laying steel mesh, and other high-altitude tasks in tunnel construction. It integrates various high-altitude work platforms, offering strong adaptability and reliability. This significantly enhances work efficiency and reduces labor intensity.

　　The arch frame trolley mainly consists of an automotive chassis, front and rear support legs, subframe, sliding platform, mechanical arm, working platform, manipulator, auxiliary arm, hydraulic winch, and other components. These components work in synergy, enabling the arch frame trolley to perform various complex tasks. For example, in tunnel construction, the arch frame trolley can easily grab and install steel arches, lay steel mesh, and carry out quality inspections, ventilation pipe installation, defect repairs, grouting, and explosive charge setups.

　　Depending on the application scenario, arch frame trolleys can be divided into general and special types. General arch frame trolleys are mainly suitable for environments without significant danger factors, such as road tunnels and urban subways. Special arch frame trolleys, on the other hand, are primarily used in more hazardous environments, such as coal mine tunnels. Regardless of the type, all arch frame trolleys must adhere to relevant national standards to ensure equipment safety and stability.

　　In addition to tunnel engineering, arch frame trolleys also find wide applications in high-rise building and bridge engineering. In high-rise building projects, arch frame trolleys can be used to transport heavy construction materials like concrete, reducing manual handling labor and increasing work efficiency. In bridge engineering, arch frame trolleys are mainly used to transport and handle large and heavy materials such as steel beams and plates. Due to the varied shapes of bridges, materials need to be moved at different heights and angles, so arch frame trolleys feature adjustable heights and angles to better adapt to different work environments.

　　The use of arch frame trolleys not only improves construction efficiency but also enhances construction quality. With advanced mechanical arm and gripper designs, they can precisely grasp and install various materials, reducing human error. Additionally, arch frame trolleys are equipped with auxiliary devices like extendable baskets, hammers, and welding machines, ensuring various tasks in the construction process are well-executed.

　　Moreover, arch frame trolleys significantly reduce the number of personnel required. Traditional tunnel construction often requires a large number of workers for manual handling and installation, which is labor-intensive and poses safety risks. The advent of arch frame trolleys allows the entire construction operation to be completed by just 3-4 people, greatly lowering labor costs and improving work safety.

　　During TBM construction, a series of stringent safety measures must be taken to handle emergencies and ensure the safety of personnel and equipment. Here are some key safety measures:

　　1. Risk Assessment: Conduct a comprehensive risk assessment before construction to identify potential hazards, such as geological conditions, surrounding environment, and equipment status, and develop corresponding preventive measures.

　　2. Safety Training: Provide professional safety training to all operators, ensuring they are familiar with equipment operation, emergency response procedures, and personal protective measures.

　　3. On-site Monitoring: Install real-time monitoring systems to monitor the construction site 24/7, allowing for the timely detection of abnormal situations and the implementation of appropriate measures.

　　4. Emergency Plans: Develop detailed emergency plans, including response procedures for incidents such as fires, explosions, equipment failures, and collapses, and conduct regular drills.

　　5. Safety Equipment: Provide necessary safety equipment, such as helmets, safety belts, dust masks, and protective glasses, and ensure all personnel wear them during construction.

　　6. Regular Inspection and Maintenance: Perform regular inspections and maintenance on the TBM and related equipment to ensure they are in good condition and reduce the likelihood of failures.

　　7. Ventilation and Drainage: Ensure the construction site has adequate ventilation and drainage systems to prevent the accumulation of harmful gases and water, thereby reducing the risk of collapses.

　　8. Signal and Communication Systems: Establish effective signal and communication systems to ensure timely communication between operators and with the ground command center.

　　9. Emergency Evacuation Routes: Design reasonable emergency evacuation routes and ensure all personnel are familiar with escape methods and assembly points.

　　10. Rescue Preparation: Equip the site with necessary rescue equipment, such as first aid kits and firefighting equipment, and ensure that a professional rescue team is on standby at all times.

　　11. Environmental Protection: Take measures to prevent construction processes from polluting the surrounding environment, such as noise, dust, and wastewater.

　　12. Compliance with Laws and Regulations**: Strictly adhere to relevant safety regulations and standards to ensure all operations comply with legal requirements.

　　By implementing these safety measures, risks during the construction process can be minimized, ensuring the safety of personnel and equipment. Additionally, it is crucial to continuously monitor new safety technologies and management methods to continually improve construction safety levels.

　　What is Foam Concrete?Foam concrete is a type of concrete material formed by mixing water, cement, and a foaming agent in a specific ratio, then using specialized equipment to foam, mix, and convey it. After solidification, it forms concrete with numerous closed foam pores inside. Its notable characteristics include excellent thermal insulation, light weight, integrity, sound insulation, and durability. Additionally, foam concrete offers quick construction and lower costs.

　　I. Uses of Foam Concrete

　　Foam concrete is primarily used in China for in-situ roof insulation layers, foam concrete blocks, lightweight wall panels, and foundation compensation. However, its excellent properties continuously expand its application fields, enhancing project quality and construction efficiency. Here are some specific applications:

　　1. Retaining Walls:

　　Foam concrete is commonly used for backfilling harbor retaining walls. Its lightweight nature reduces vertical load and lateral pressure, thus minimizing wall settlement and maintenance costs. Additionally, it improves the stability of embankment slopes.

　　2. Sports Fields and Tracks:

　　Permeable foam concrete is used for sports field foundations, covered with gravel or artificial turf, making it suitable for hockey, football, and tennis courts. When covered with porous asphalt and plastic layers, it can also be used for athletic tracks.

　　3. Sandwich Components:

　　In prefabricated reinforced concrete components, foam concrete serves as the core material, enhancing the components' light weight and thermal insulation. Typically, foam concrete with a density of 400-600 kg/m? is used.

　　4. Pipeline Backfill:

　　Foam concrete is used to backfill abandoned underground oil tanks, pipelines, and sewage pipes, preventing fire and collapse issues. The density depends on pipe diameter and groundwater level, generally ranging from 600-1100 kg/m?.

　　5. Filling Applications:

　　Due to its high workability and adaptability, foam concrete is often used for lean concrete fillings. For lower thermal insulation requirements, a density of about 1200 kg/m? is used; for higher insulation requirements, a density of 500 kg/m? is used.

　　6. Roof Slopes:

　　Foam concrete is used for roof slopes, offering light weight, quick construction, and low cost. Typically, materials with a density of 800-1200 kg/m? are used, with a slope of 10 mm/m and a thickness of 0.03-0.2 m.

　　7. Tank Footing Support:

　　Foam concrete is poured under steel tank footings to form a convex foundation, ensuring optimal stress conditions for welding and facilitating cleaning. Commonly used materials have a density of 800-1000 kg/m?.

　　8. Other Applications:

　　Foam concrete can also be used for fireproof wall insulation filling, soundproof floor filling, tunnel lining backfill, and isolation of power and water pipelines.

　　II. Main Uses in Building Energy Conservation

　　Currently, foam concrete is most widely used in building energy conservation, including:

　　1. Roof Thermal Insulation:

　　Examples include foam concrete roof insulation bricks, insulation boards, magnesia foam sandwich corrugated tiles, and in-situ thermal insulation layers.

　　2. Wall Thermal Insulation:

　　This includes foam concrete blocks, insulation blocks, various insulation interior and exterior wall panels, and in-situ foam concrete walls.

　　3. Wall Surface Insulation:

　　Examples include external wall insulation systems, foamed cultural stone, and spray-type foam concrete wall insulation layers.

　　4. Floor Insulation:

　　This includes floor insulation bricks, insulation boards, and in-situ floor heating insulation layers.

　　Foam concrete, with its excellent properties, is continuously expanding its applications in construction projects, significantly contributing to improved project quality and construction efficiency.

　　What is the compressive strength of foamed concrete?The compressive strength of foamed concrete varies depending on factors such as its density, mix ratio, and curing conditions. Generally, the compressive strength of foamed concrete ranges from 0.5 MPa to 30 MPa.

　　Lightweight foamed concrete (with lower density) typically has a compressive strength between 0.5 MPa and 3 MPa, while heavyweight foamed concrete (with higher density) can reach compressive strengths of 10 MPa to 20 MPa, or even higher.

　　It is important to note that the compressive strength of foamed concrete is not its only performance indicator. Its thermal insulation, sound absorption, and sound insulation properties are also very important and should be comprehensively evaluated based on the specific application and requirements.

　　What safety hazards might be encountered during TBM construction? When using a TBM for construction, the following safety hazards may be encountered:

　　1. Complex geological conditions: Encountering unstable strata, faults, karst caves, etc., can lead to severe consequences such as collapses or water inrushes.

　　2. Equipment failure: Due to prolonged high-load operation or improper maintenance, the TBM may experience mechanical failures such as cutterhead jamming or hydraulic system leaks.

　　3. Operational errors: Operators may make mistakes due to fatigue, negligence, or lack of experience, such as mishandling that leads to equipment loss of control.

　　4. Fire and explosion: Electrical short circuits or oil and gas leaks can trigger fires or explosions, posing threats to personnel and equipment safety.

　　5. Collapse accidents: Improper support measures or changes in geological conditions can cause local or overall collapses.

　　6. Toxic and harmful gases: In enclosed or semi-enclosed environments, toxic and harmful gases may be present, posing health hazards to operators.

　　7. Noise and vibration: Prolonged exposure to high noise and vibration environments can lead to hearing loss and physical discomfort for operators.

　　8. Limited visibility: Under complex geological conditions, operators’ visibility may be restricted, making it difficult to accurately judge the situation ahead.

　　9. Improper handling of emergencies: If emergency measures are improperly executed in the face of sudden situations such as mud bursts or equipment failures, the situation may worsen.

　　10. Poor personnel safety management: Lack of adequate safety training, insufficient protective equipment, or failure to implement strict safety management systems can increase the risk of accidents.

　　To ensure construction safety, effective preventive measures must be taken, including but not limited to, enhancing geological surveys, improving operators’ professional skills, strictly enforcing safety operating procedures, regularly inspecting and maintaining equipment, and establishing comprehensive emergency response mechanisms. Additionally, on-site supervision and management should be strengthened to ensure all safety measures are effectively implemented.

　　Compared to traditional manual or mechanical excavation methods, tunnel boring machines (TBMs) have many significant advantages. Firstly, they possess powerful rock-breaking capabilities and high work efficiency, greatly shortening project durations and reducing costs. Secondly, they can adapt to various complex and changing construction environments, easily handling both hard rock and soft soil. Additionally, they offer high safety and reliability, effectively reducing the occurrence of accidents and casualties. So, in which fields are TBMs widely used?

　　Fields of Application for Tunnel Boring Machines

　　1、Mining Industry:

　　TBMs are used to open new mining passages in underground coal and metal mining, improving extraction efficiency.

　　2、Tunnel Construction:

　　For the excavation of tunnels for railways, highways, and urban rail transit, TBMs are crucial equipment ensuring the safety and speed of tunnel construction.

　　3、Water Conservancy Projects:

　　TBMs are employed in the construction of dams, canals, and irrigation systems, used for excavating channels and building structures.

　　4、Urban Construction:

　　In the development of subways, underground malls, parking lots, and other urban infrastructure, TBMs are used to create underground spaces.

　　5、Geological Exploration:

　　Specialized drilling TBMs are used to obtain underground information in mineral resource exploration and geological hazard assessment.

　　6、Defense Engineering:

　　For the construction of military facilities and underground bunkers, TBMs provide the necessary excavation capabilities.

　　7、Environmental Engineering:

　　In environmental projects such as soil remediation and the construction of waste treatment facilities, TBMs are used for land restoration and waste excavation.

　　8、Energy Development:

　　Specific types of drilling TBMs are used for well drilling in the exploration and development of oil, natural gas, and other energy resources.

　　9、Aerospace and Deep-Sea Exploration:

　　Specially designed TBMs are used in extreme environments for detecting and collecting geological samples.

　　These fields share the common characteristic of requiring efficient and precise excavation work in complex and harsh environments, and TBMs are the ideal tools designed for such tasks. With technological advancements, the application scope of TBMs continues to expand, providing robust support for human engineering projects and scientific exploration.

　　Monitoring and preventing the leakage of toxic and harmful gases during TBM operations is crucial for ensuring the health and safety of the workers. Below are some effective monitoring and prevention measures:

　　I. Effective Monitoring of Toxic and Harmful Gas Leaks

　　1. Use of Gas Detection Equipment: Install fixed or portable gas detectors in the construction area. These devices can monitor the concentration of toxic gases in real-time, such as methane, carbon monoxide, and hydrogen sulfide. Once the gas concentration exceeds the safety threshold, an alarm will be triggered immediately.

　　2. Optimization of Ventilation Systems: Ensure that the construction area has a good ventilation system. This can be achieved through natural or mechanical ventilation to dilute and remove harmful gases. Special attention should be paid to the ventilation setup in enclosed or semi-enclosed spaces.

　　3. Environmental Monitoring: Monitor the environment around the construction area to assess the impact of external gas sources, such as nearby industrial emissions or underground reservoirs.

　　4. Application of Technological Innovations: Explore the use of new monitoring technologies, such as fiber optic sensing technology and wireless sensor networks, to improve monitoring accuracy and coverage.

　　II. Measures to Prevent Toxic and Harmful Gas Leaks

　　1. Regular Detection and Maintenance: Conduct regular gas detection at the construction site, especially before entering new work faces. Additionally, regularly calibrate and maintain gas detection equipment to ensure its accuracy and reliability.

　　2. Safety Training: Provide safety training to workers on the hazards of toxic and harmful gases, so they understand the potential risks and know how to correctly use personal protective equipment (PPE) and handle emergency situations.

　　3. Use of Personal Protective Equipment (PPE): Provide appropriate PPE, such as respirators and gas masks, and ensure that workers wear them correctly when entering potentially hazardous areas.

　　4. Adjustment of Work Plans: Adjust work plans based on geological conditions and existing monitoring data to avoid prolonged operations in high-risk areas, or adopt segmented construction and alternating work patterns to reduce risks.

　　5. Development of Emergency Plans: Develop detailed emergency plans, including evacuation routes, assembly points, and emergency contact information. Conduct regular drills to ensure all personnel are familiar with emergency response procedures.

　　By implementing these measures comprehensively, it is possible to effectively monitor and prevent the leakage of toxic and harmful gases during TBM operations, thereby ensuring the health and safety of workers.

　　The engineering piles are excavated mechanically to the design elevation. During excavation, care should be taken to avoid the machinery from touching the pile body, and the soil within 200mm around the pile is manually removed. For support piles, due to their dense spacing and proximity to slopes, they are excavated mechanically to a distance of 200mm from the pile, and the remaining portion is manually excavated.

　　Process:

　　1、Removal of upper concrete

　　2、Determination of elevation and cutting of protective piles

　　3、Opening of gap

　　4、Removal of reinforcement bars

　　5、Deepening of gap

　　6、Drilling of top break

　　7、Hoisting of broken part

　　8、Removal of residue

　　9、Cleaning of pile head

　　Technical Requirements:

　　1、Before the removal of the pile head, the surveyor must accurately mark the design elevation of each pile.

　　2、During construction, the construction team should densely mark around the pile base according to the markings made by the survey team, with at least four markings per pile, marked with conspicuous red paint lines.

　　3、During the pile head removal operation, in order to protect the effective pile body, a ring cut and subsequent processes should be carried out 10cm above the pile top position, reserving the final 10cm for manual chiseling to ensure the accurate height and elevation of the pile head entering the bearing platform.

　　4、After lifting the broken pile head out of the pit, the construction team should inspect each pile top to ensure its flatness. If there are any uneven areas, they should be smoothed with a steel chisel.

　　5、Before the pile head removal operation, consult with technical personnel to confirm the presence of sonic tubes inside the pile base. When removing the pile head, be careful not to damage the sonic tubes. If the sonic tubes extend too far into the pile or are too long, causing difficulty in lifting after the pile is broken, use gas welding to cut the sonic tubes. Immediately after cutting, plug the opening of the sonic tube with cotton cloth to prevent debris from falling into the tube and blocking it, affecting the pile foundation testing.

　　6、After lifting the pile head with sonic tubes out of the pit, the construction team should inspect each pile top to ensure that the sonic tubes are exposed. If they are not exposed, continue excavating the pile head until the sonic tubes are exposed. If the sonic tubes extending from the pile base are pressed down or deformed during lifting or pile head removal, they should be corrected promptly.

　　7、When the height of the bearing platform or cap beam is less than the anchorage length of the longitudinal bars, the longitudinal bars at the pile top can be raised to the top of the bearing platform or cap beam and bent into a straight hook to ensure the anchorage length.

　　The above is the information provided by the construction channel regarding the understanding of the construction process for pile head removal in geotechnical engineering. The construction channel shares more construction knowledge to help you learn construction techniques, discover the beauty of architecture, and explore the path of construction.

　　Tunnel engineering, as a crucial part of transportation construction, has a decisive impact on the success of the project. Taking the Qinling Zhongnanshan Highway Tunnel—the longest twin-bore, one-way highway tunnel in the world—as an example, this tunnel spans 18.02 kilometers and fully showcases advanced construction techniques and strict construction principles.

　　When discussing tunnel construction, the Qinling Zhongnanshan Highway Tunnel, the world's longest twin-bore, one-way highway tunnel, often comes to mind. This tunnel starts in Qingcha, Chang'an District, Xi'an City, and ends in Yingpan Town, Zhashui County, Shangluo City, spanning 18.02 kilometers. With a design speed of 80 kilometers per hour, it takes only 15 minutes to traverse the Qinling Mountains, which form the natural dividing line between northern and southern China. Notably, this world record was entirely designed and constructed by China, incorporating highly human-centric design concepts. This article will detail the construction techniques and principles of tunnel construction.

　　Principles of Tunnel Construction

　　Before commencing tunnel construction, a thorough investigation of the weak surrounding rock on-site is essential, with a deep understanding of the design intentions. Based on different geological conditions, practical construction plans are developed. During construction, the following principles must be strictly adhered to:

　　1. Attention to Geological Conditions:** Accurately understand geological conditions, particularly the characteristics of weak surrounding rock areas.

　　2. Proactive Control： Maintain proactive control during construction to prevent potential problems.

　　3. Strict Grouting： Perform grouting reinforcement of the geology to ensure stability.

　　4. Short Advances： Conduct construction in segments to ensure the quality of each section.

　　5. Strong Support： Implement effective support measures to ensure the stability of the tunnel structure.

　　6. Frequent Measurements： Regularly measure and monitor various tunnel parameters to promptly detect and resolve issues.

　　7. Early Closure： Timely closure of the excavation face to reduce the risk of collapses.

　　Tunnel Construction Techniques

　　The techniques used in tunnel construction vary depending on the classification of the surrounding rock:

　　- Full-face Method： Suitable for Class III rock sections, involving one-time full-face excavation to ensure construction efficiency.

　　- Step Method Excavation： Suitable for Class IV and V rock sections, involving step-by-step excavation and gradual support to ensure safety.

　　For support, initial support measures include rock bolts, steel meshes, and shotcrete, with advanced construction of the invert to ensure tunnel stability. The arch walls are constructed in a single pass to ensure structural integrity and durability.

　　In sections with active fault zones or requiring seismic fortification, full-circle steel arch frames and double-layer φ42 small guide pipes for the arch are used for advanced support to enhance seismic performance. Lining inside the tunnel employs lining trolleys to ensure construction precision and efficiency.

　　Technological Applications in Construction

　　During construction, advanced geological prediction and forecasting are crucial. Techniques such as deep blast hole detection and infrared detection confirm the geological conditions ahead and detect differences between design and actual geology. In critical geological hazard sections, advanced horizontal drilling techniques ensure accurate geological understanding. Meticulous measurements are conducted throughout the construction process, analyzing settlement observation data to adjust construction plans in a timely manner.

　　Tunnel construction is a complex and precise engineering task requiring scientific planning and strict management. By adhering to scientific construction principles and adopting advanced construction techniques, the smooth progress of tunnel construction and the long-term safe operation of tunnels can be ensured. The successful construction of the Qinling Zhongnanshan Highway Tunnel is a powerful testament to this approach.