Dynamic Compaction

Dynamic Compaction is a ground improvement method that involves dropping a heavy tamper in a grid pattern to densify loose soil particles.

Dynamic compaction is only available when Horizontal Soil Layers is selected from the Project Settings dialog:

When dynamic compaction is selected as the ground improvement method, the following options will appear in the Ground Improvement Region dialog:

Drop Point Layout

Define the grid for the primary pass by selecting one of two patterns:

• Square Pattern
• Triangular Pattern

The chosen pattern will affect the influence area () used when computing the applied energy per unit area.

Where s is the drop spacing.

Square Drop Pattern	Triangular Drop Pattern

Tamper Properties

In addition to the weight of the tamper, the user will choose the geometry of the tamper’s base then specify its size:

• Circular: specify the diameter
• Square: specify the width

Dynamic Compaction Settings

The Calculation Method radio buttons allow the user to select between correlating the applied energy from dynamic compaction to improved SPT-N and CPT qc values presented in Lukas 1995 (see below):

SPT – N after improvement	CPT qc after improvement

The improved modulus of elasticity is calculated by multiplying the correlation ratio by the improved SPT-N or CPT qc.

• For CPT:
• For SPT:

If the applied energy exceeds the bounds of the graphs shown above, the value of improved SPT-N or CPT qc will be capped by the maximum or minimum.

• Number of Passes: How many high-energy passes the tamper will make over the drop grid
• Number of Drops per Pass: The number of blows delivered at each drop point during a single pass
• n_c : Empirical constant

Settle3 provides a table of recommended values of n_c adopted from Han (2015). To access this table, click the icon to open the input box:

Settle3 automatically calculates D_i from the dialog inputs and updates the 3D view to ensure the displayed region always reflects the energy-based calculation.

To further densify loose soil particles at the surface of the impact craters, engineers often opt to include a final lower energy ironing pass. To include an ironing pass in Settle3:

1. Tick the Ironing Pass checkbox
2. Enter the same tamper setting used for the high-energy pass: pattern, spacing, drop height tamper weight and number of drops

The additional applied energy contribution from the ironing pass will be added to the cumulative applied energy when estimating the post-improvement SPT-N or CPT qc.

Peak particle velocity (PPV) is an indicator of vibration-induced risk, representing the maximum instantaneous speed at which soil particles travel during a vibration event.

To calculate PPV:

1. Tick the Calculate PPV checkbox.
2. Specify the distance to the nearest affected structure.

The peak particle velocity will be calculated as follows:

Where:

• PPV = Peak Particle Velocity (mm/s)

• W_t = tamper weight (ton)

• H_d = drop height (m)

• x_dp= distance to drop point (m)

Results

After drawing the ground improvement region, the following list of empirical results will appear next to the ground improvement region:

• Depth of Improvement
• Applied Energy from Ironing Pass
• Applied Energy from High Energy Pass
• Total Applied Energy
• CPT qc or SPT N After Improvement
• Elastic Modulus After Improvement
• Depth of Crater
• Estimated Induced Settlement
• Peak Particle Velocity

For further details on the calculations of the output results, please refer to the example presented in the Settle3: Dynamic Compaction Verification Manual.