Reducing noise from tunnel lining equipment is crucial for worker health and safety, environmental compliance, and maintaining good relations with nearby communities. Noise in tunnels is often amplified due to the confined space and hard, reflective surfaces. Here’s a breakdown of strategies, following the hierarchy of controls (elimination/substitution, engineering controls, administrative controls, PPE).

How to Reduce Tunnel Lining Equipment Noise

1. Source Control (Elimination, Substitution & Engineering Modifications): This is the most effective approach.

Equipment Selection (Procurement):

Specify Low-Noise Equipment: When purchasing or renting equipment (TBMs, segment erectors, grout pumps, ventilation fans, locomotives), specify maximum noise emission levels in the tender documents. Request noise data from manufacturers (sound power levels).

Choose Quieter Technologies: Opt for electric or hydraulic systems over noisier pneumatic ones where feasible. Use variable speed drives (VSDs) for fans and pumps so they only run as fast as needed. Consider modern, quieter engine designs for diesel equipment.

Engineering Modifications to Existing Equipment:

Engine/Motor Enclosures: Install well-sealed acoustic enclosures around noisy engines, motors, and pumps (e.g., grout pumps, generators). Ensure adequate ventilation for cooling, often requiring silenced air inlets and outlets.

Silencers/Mufflers: Fit high-performance silencers to engine exhausts and ventilation fan inlets/outlets. Ensure they are correctly sized and maintained.

Vibration Isolation: Mount noisy components (engines, pumps, gearboxes) on vibration isolators (rubber mounts, springs) to prevent vibration from transferring into the equipment structure or tunnel lining, which then radiates noise.

Hydraulic System Noise: Use low-noise hydraulic pumps, accumulators to dampen pulsations, and flexible hoses instead of rigid pipes where possible to reduce vibration transmission.

Conveyor Systems: Use low-noise rollers, belt materials, and ensure proper alignment and tension to minimize noise. Enclose drive units.

Grouting Equipment: Use pulsation dampeners on pumps. Enclose mixers and pumps if possible.

Segment Erectors: Ensure smooth hydraulic operation. Maintain components to prevent jerky movements or impacts.

Damping Materials: Apply damping materials (e.g., constrained layer damping) to large vibrating panels on equipment (like enclosures or guards) to reduce noise radiation.

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More detailed information on how to reduce noise from tunnel lining trolleys can be found at: https://www.gf-bridge-tunnel.com/a/blog/how-to-reduce-tunnel-lining-equipment-noise.html

Tunnel lining trolleys, also known as tunnel formwork systems or tunnel shuttering machines, are essential equipment used for in-situ concrete lining in tunnel construction. Depending on tunnel structure, size, and construction methods, tunnel lining trolleys can be classified into several types. These are large, mobile structures used inside tunnels to support the formwork for cast-in-place concrete linings or to install precast concrete segments.

Tunnel Lining Trolley Type

The primary categorization is based on the type of lining they are designed for:

Formwork Trolleys (for Cast-in-Place Concrete Lining):

These trolleys carry large sections of steel formwork. They position the formwork against the excavated tunnel profile, concrete is pumped behind it, and once the concrete cures sufficiently, the trolley lowers (strips) the formwork and moves forward (travels) to the next section.

Sub-types based on Formwork Configuration:

Full-Round Formwork Trolley: Carries formwork for the entire tunnel cross-section (invert, walls, and arch) allowing for a single pour. Complex and heavy, often used for circular or near-circular tunnels.

Arch (or Crown/Sidewall) Formwork Trolley: Carries formwork only for the upper arch and sidewall sections. This is used when the invert (floor) is cast separately first (often using simpler screeding or a dedicated invert form). This is very common for horseshoe or D-shaped tunnels.

Invert Formwork Trolley: Specifically designed to carry the formwork for casting the tunnel floor (invert). Often used in conjunction with an Arch Formwork Trolley.

Telescopic Formwork Trolley: The formwork sections are designed to retract inwards (like a telescope) after stripping. This allows the entire trolley to move forward through the previously cast lining section without needing extensive dismantling. This is the most common type for longer tunnels due to efficiency.

Non-Telescopic (Collapsible) Formwork Trolley: Sections may hinge or collapse, but might not fully telescope. Movement might require more clearance or partial dismantling. Less common for continuous tunnel drives.

Portal Formwork: While not strictly a “trolley” in the travelling sense, specialized formwork systems are used at the tunnel entrances/exits (portals).

Segment Erector Trolleys (for Precast Concrete Segments):

These are used primarily in tunnels excavated by Tunnel Boring Machines (TBMs), although variations exist for conventional tunnels installing precast linings.

Their main function is to pick up precast concrete segments (delivered usually by multi-service vehicles or segment cars), rotate them to the correct orientation, and precisely place them to form a complete ring against the TBM’s shield or the previously installed ring.

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More detailed information about tunnel lining trolley types can be found at: https://www.gf-bridge-tunnel.com/a/blog/tunnel-lining-trolleys-type.html

Repairing weld cracks in steel structures is a critical task that requires careful planning, execution, and inspection to ensure the structural integrity is restored and the crack doesn’t return. This is a job for critical structures and should ALWAYS be performed by qualified welders following approved procedures under the supervision of experienced engineers or inspectors.

Repairing Cracks in Steel Structure Welds

1. Assessment and Planning:

Safety First: Implement all necessary safety precautions. This includes proper PPE (welding mask, gloves, leathers, respirator if needed), fire watch, ventilation, hot work permits, lockout/tagout procedures if near machinery, and securing the area.

Identify the Crack: Locate the crack precisely. Determine its full extent (length, depth, and whether it extends through the thickness). Non-Destructive Testing (NDT) methods like Magnetic Particle Testing (MT), Liquid Penetrant Testing (PT), or Ultrasonic Testing (UT) are often essential to find the crack tips accurately.

Determine the Cause (Crucial!): This is the MOST important step to prevent recurrence. Why did the crack form?

Fatigue: Cyclic loading leading to crack initiation and propagation.

High Residual Stress: From the original welding or fabrication process.

Hydrogen Embrittlement: Hydrogen trapped in the weld/Heat Affected Zone (HAZ). Often causes delayed cracking (hours or days after welding).

Poor Weld Quality: Lack of fusion, lack of penetration, porosity, slag inclusions acting as stress risers.

Incorrect Weld Procedure: Wrong consumables, incorrect preheat/interpass temperature, wrong parameters.

Poor Joint Design: Creates stress concentrations.

Overload: The structure was subjected to loads beyond its design capacity.

Base Metal Defects: Laminations or inclusions in the steel itself.

Consult Codes and Standards: Refer to relevant welding codes (e.g., AWS D1.1 Structural Welding Code – Steel, Eurocode 3, etc.) and project specifications for requirements regarding crack repair.

Develop a Repair Procedure: Based on the cause, material type, thickness, location, and code requirements, a detailed Welding Procedure Specification (WPS) for the repair must be developed or selected. This specifies:

Method of crack removal.

Joint preparation details.

Welding process (SMAW, FCAW, GMAW, SAW).

Filler metal type and size.

Preheat requirements.

Interpass temperature control.

Post-Weld Heat Treatment (PWHT) if required.

NDT requirements before, during, and after repair.

Qualified Personnel: Ensure the welders performing the repair are qualified according to the specific WPS and relevant codes. Ensure qualified NDT technicians and inspectors are involved.

2. Repair Execution:

Crack Removal: The entire crack, including its tips, must be completely removed. This is typically done by:

Gouging: Air Carbon Arc Gouging (CAC-A) is common and efficient but requires care not to introduce excessive carbon into the base metal (usually followed by grinding). Plasma Arc Gouging (PAG) is another option.

Grinding: Using abrasive wheels. More controlled but slower, suitable for smaller cracks or finishing after gouging.

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For more detailed information on how to repair steel structure welding cracks, please click here: https://www.meichensteel.com/a/news/repairing-cracks-in-steel-structure-welds.html

Steel structure construction is a widely adopted method in modern architecture and engineering due to its strength, durability, and efficiency. From high-rise buildings and industrial warehouses to bridges and stadiums, steel provides a versatile solution for a wide range of construction needs.

The steel structure construction process involves a series of systematic steps that ensure the structural integrity and safety of the final build. These steps typically include planning and design, material procurement, fabrication, transportation, site preparation, and on-site erection. Each phase plays a crucial role in transforming raw steel components into a fully functional, load-bearing framework.

Steel structure construction process

Phase 1: Planning and Design

Conceptual Design & Feasibility: The client, architect, and engineers define the project requirements, budget, and overall building concept. Initial studies determine if a steel structure is the most suitable option.

Structural Engineering & Analysis: Structural engineers perform detailed calculations to determine loads (dead load, live load, wind, seismic, etc.) and design the steel frame. This includes selecting appropriate steel grades, member sizes (beams, columns), connection types (bolted, welded), and bracing systems for stability.

Detailed Drawings & Specifications: Architects and engineers produce detailed construction drawings (plans, elevations, sections, connection details) and technical specifications. These documents outline exactly how the structure should be built, the materials to use, and the quality standards required.

Shop Drawings: The steel fabricator (selected later) will create highly detailed shop drawings based on the engineering drawings. These drawings specify exact dimensions, cuts, hole locations, weld types, bolt types, surface finishes, and assembly marks for each individual steel member. These must be reviewed and approved by the structural engineer before fabrication begins.

Erection Plan: Often developed collaboratively between the engineer, fabricator, and erector, this plan outlines the sequence of lifting and assembling the steel members on site, crane locations, safety procedures, and temporary bracing requirements.

Phase 2: Fabrication (Off-Site)

This happens in a controlled factory environment (the fabrication shop):

Material Procurement: The fabricator orders the required raw steel shapes (I-beams, W-sections, channels, angles, plates, hollow sections) from steel mills based on the approved shop drawings and material specifications.

Cutting & Shaping: Steel members are cut to precise lengths using saws, shears, or thermal cutting (plasma, oxy-fuel).

Drilling/Punching: Holes for bolts are accurately drilled or punched according to the shop drawings.

Fitting & Welding: Components (e.g., base plates, connection plates, stiffeners) are fitted together and welded as specified in the shop drawings. Skilled, certified welders perform this work.

Surface Treatment: Steel members are cleaned (usually by shot blasting) to remove mill scale and rust. Then, a primer paint or other specified coating (like galvanizing) is applied for corrosion protection.

Quality Control (QC): Throughout fabrication, QC checks are performed (dimensional checks, weld inspection using visual or non-destructive testing methods like UT/MT/PT, coating thickness checks).

Marking & Labeling: Each finished piece is clearly marked with an identification number/code corresponding to the shop drawings and erection plan, ensuring it can be easily identified on site.

Phase 3: Transportation

Loading & Logistics: Fabricated steel members are carefully loaded onto trucks or trailers in a sequence that often aligns with the planned erection sequence on site.

Shipping: Steel is transported from the fabrication shop to the construction site. Special permits and escorts may be required for oversized loads.

Phase 4: Site Preparation

This happens concurrently with or before fabrication/transportation:

Foundation Construction: Concrete foundations (footings, pile caps, raft foundations) are constructed based on the engineering design. Crucially, anchor bolts are accurately embedded into the concrete where steel columns will be placed. Their position and elevation are critical.

Site Logistics: The site is prepared with clear access roads, designated laydown areas for storing steel deliveries, and stable pads for crane setup.

Phase 5: Erection (On-Site Assembly)

This is the process of assembling the steel frame on site:

Receiving & Sorting: Steel deliveries are received, checked against delivery tickets, and sorted in the laydown area according to their erection marks and the erection plan.

Crane Setup: Mobile or tower cranes capable of lifting the heaviest steel members are positioned strategically on site.

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For more detailed information about the steel structure construction process, please click here: https://www.meichensteel.com/a/news/steel-structure-construction-process.html

Adjusting the clearance of a slewing bearing is crucial for ensuring smooth operation, reducing wear, and extending its service life. The process varies depending on the bearing type (single-row ball, double-row ball, or cross-roller) and the manufacturer’s specifications.

Slewing Bearing Clearance Adjustment Method

1. Initial Assessment

Before adjusting the slewing bearing clearance, it’s important to assess the condition of the bearing and machinery:

Inspect the Bearing: Look for signs of wear, damage, or corrosion. If the bearing is significantly worn or damaged, it may require replacement.

Check Manufacturer Specifications: Ensure you know the recommended clearance values provided by the bearing manufacturer. These values are essential for setting the correct adjustment.

2. Required Tools

To adjust slewing bearing clearance, you will need the following tools:

Dial indicator or laser measurement tool

Feeler gauges

Torque wrench

Shims or spacers (if applicable)

Jack (if lifting the structure is necessary)

Lubrication (specific grease or oil for the bearing)

3. Measuring Existing Clearance

Before making any adjustments, it is important to measure the current clearance. This will help determine whether the bearing is within the desired tolerance or if adjustments are needed.

Axial Clearance:

Place a dial indicator perpendicular to the raceway.

Lift the upper structure (if applicable) slightly using a jack or lifting mechanism.

Measure the axial movement along the bearing’s axis.

Radial Clearance:

Attach the dial indicator parallel to the bearing’s radial surface.

Apply side force to the structure to check the movement in the radial direction.

Tilting Clearance:

Measure the angular clearance by placing the dial indicator at multiple points along the bearing. Check for any tilting or angular movement.

Record the measurements and compare them with the specifications. If the clearance is out of the acceptable range, proceed to adjustment.

4. Adjusting the Clearance

The adjustment process will vary depending on the bearing design. There are two main types of slewing bearings: adjustable bolt-type and gear-type.

For Adjustable Bolt-Type Bearings:

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For more detailed information on how to adjust the slewing bearing clearance, please click here: https://www.mcslewingbearings.com/a/news/slewing-bearing-clearance-adjustment-method.html