Falling Speed and Buffer Design of Construction Waste Chutes

Construction waste falls by gravity inside the pipe, with speed increasing as height rises. An excessively high falling speed can cause pipe rupture, increased noise and bottom splashing. Buffer design is the key technology for controlling falling speed. This article explains falling speed calculation and buffer design methods in detail.

1. Falling Speed Calculation

Waste falls inside the pipe under the influence of gravity and air resistance:

1. Ideal free-fall speed
   v = √(2gh)

• h: falling height (m)
• g: 9.8m/s²

Free-fall speeds at different heights:

2. Actual falling speed
   In an actual pipe, waste is subject to pipe wall friction and air resistance, so its speed is lower than free fall:

• Friction coefficient 0.25
• Air resistance increases with the square of the speed
• Actual speed is approx. 70%–80% of free fall
• Actual speed at 20m height is approx. 15–18 m/s

3. Impact energy
   E = ½mv²

• 10kg waste falling from 20m: E≈1500J
• Equivalent to a 1.5kg object falling from 1m height and striking the pipe wall

1. Buffer Design Principles

The purpose of buffering is to dissipate the kinetic energy of falling waste and reduce the final speed:

1. Turning buffer

• Waste changes direction when passing through a 45° elbow section
• Collision with the pipe wall dissipates energy
• Speed reduced by 30%–40%
• Longkang standard buffering method

2. Friction buffer

• Spiral flow deflectors are provided on the inner wall
• Waste falls along a spiral path
• Longer path, increased friction
• Speed reduced by 20%–30%

3. Expansion buffer

• Local pipe diameter expanded
• Vortex formed, dissipating kinetic energy
• Speed reduced by 20%–30%

4. Multi-stage buffering

• Buffer sections installed at regular height intervals
• Speed reduced at each stage
• Final speed controlled within the safe range

III. Principles for Buffer Section Placement

1. Low-rise (≤20m)

• No intermediate buffer sections needed
• 1 turning buffer at the bottom
• Final speed ≤10m/s

2. Mid-rise (20–60 m)

• 1 buffer section every 25m
• 1 buffer at the bottom
• Total 2–3 buffer sections
• Final speed ≤12m/s

3. High-rise (60–100 m)

• 1 buffer section every 15–20 m
• Double-layer buffer at the bottom
• Total 4–6 buffer sections
• Final speed ≤15m/s

4. Super high-rise (>100m)

• 1 buffer section every 10–15 m
• Multi-stage buffering, triple-layer buffer at the bottom
• Total 7–10 buffer sections
• Final speed ≤15m/s

1. Buffer Section Structural Design

Longkang 45° buffer section:

• Angle: 45° bend
• Length: approx. 800mm
• Reinforced inner wall: 12mm (wear-resistant)
• Wear-resistant liner: optional rubber liner
• Interface: standard socket-and-spigot connection

Buffer section working principle:

1. Waste enters vertically from above
2. Strikes the outer wall of the elbow
3. Direction changes by 45°
4. Enters the next section along the inclined surface
5. Kinetic energy loss approx. 35%
6. Buffer Effect Verification

Based on engineering measurements:

• Without buffering: bottom speed at 50m height approx. 25m/s
• With buffering (one every 25m): bottom speed approx. 12m/s
• Buffer sections reduce speed by approx. 50%
• Impact energy reduced by approx. 75%

1. Buffer Design Considerations
2. Buffer angle should not be too small: <30° turns easily cause blockage
3. Buffer angle should not be too large: >60° turns generate high impact force
4. 45° is the optimal buffer angle: balancing buffering effect and blockage risk
5. Buffer section inner wall is reinforced: withstands repeated impacts
6. Buffer sections are wear parts: inspect regularly, replace when severely worn
7. Mortar-type waste: buffer sections are prone to clogging and require regular cleaning

VII. Bottom Discharge Buffering

The bottom discharge outlet is where impact is most concentrated:

1. Double-layer buffer

• Both the last two sections have 45° turns
• Waste passes through two turns
• Speed reduced to below 10m/s

2. Wear-resistant liner

• Inner wall of the bottom 1–2 sections lined with rubber
• Thickness 5mm
• Absorbs impact, wear-resistant

3. Buffer hopper

• Buffer hopper connected at the bottom
• Baffle plate provided inside the hopper
• Waste first falls into the buffer layer
• Then slides into the collection hopper

VIII. Longkang Buffer Design Service

1. Calculate the number of buffer sections based on building height
2. Design buffer section positions
3. Provide buffer section selection
4. Provide dedicated buffer calculations for super high-rise projects
5. Buffer sections supplied separately as wear parts