The first episode of Cold Facts about Impact Ramming: For impact ramming to "press firmly", it doesn't rely on "great force", but on "matching the impact frequency with the amplitude"

Many people think that "the heavier the impact ram weight, the greater the power, the better the compaction effect" - but in the actual construction, the 100kg heavy impact ram in the backfill operation, the effect may not be as good as the 60kg medium type, the core problem is in the "matching degree of impact frequency and amplitude", rather than the simple "strength".

Principle breakdown

The compaction principle of impact compaction is that "the eccentric block rotates at high speed to generate centrifugal force, driving the machine body to impact the ground up and down", which transfers kinetic energy to soil particles, reducing the gaps between particles and increasing their density.

Here are two key parameters:

Impact frequency: It refers to the number of times the ground is impacted per minute (unit: times per minute), which determines the "frequency at which soil particles are shaken" - if the frequency is too low, the particles will not have enough time to fully fill the gaps.

If the frequency is too high, the particles will rebound due to "excessive vibration", and thus cannot be compacted.

Amplitude: It refers to the maximum distance of the up and down impact of the fuselage (unit: mm), which determines the "impact depth" - if the amplitude is too large, it is easy to compact the surface soil, but the deep soil remains loose.

The amplitude is too small and it cannot reach the deep layers, resulting in "the surface meeting the standards but the bottom layer sinking".

The "frequency-amplitude combination" required by different soils is completely different:

Backfill soil and sandy gravel soil (with coarse particles and large gaps) : It requires "low frequency + large amplitude" (such as 450-500 times per minute, amplitude 10-12mm), and through a relatively large impact depth, allow the deep particles to fully interbite.

Plain soil and lime soil (with fine particles and strong viscosity) : It requires "high frequency + small amplitude" (such as 550-600 times per minute, amplitude 6-8mm).

Through high-frequency vibration, the soil viscosity is broken, and the fine particles are closely arranged.

Practical verification

During the construction of a certain municipal road, the backfill soil was treated with an impact tamper with a power of 800W, a frequency of 500 times per minute, and an amplitude of 10mm.

Within 10 minutes, the soil compaction degree reached 95% (meeting the standard).        However, when the heavy-duty model with "1200W power, 600 times per minute frequency, and 6mm amplitude" was used, after the same 10 minutes, the compaction degree was only 88% (not meeting the standard) - the reason was that the "frequency-amplitude combination" of the latter did not match the characteristics of the backfill soil.