Vibrocompaction Construction Technology – Full Densification Process of Sandy Soil Foundation

In ground improvement engineering, vibrocompaction, commonly known as filler-free vibroflotation, serves as the core technology for loose sandy ground to resist liquefaction, boost relative density and enhance bearing capacity.

Unlike stone-column vibroflotation which requires backfilled crushed stone, the biggest feature of filler-free vibroflotation is no extra filling materials. It only relies on high-pressure water jetting and high-frequency vibration to liquefy and recompose in-situ sand for compaction. Featuring higher construction efficiency and lower cost, it is the preferred treatment method for hydraulically filled sand and medium-coarse sand foundations.

I. Core Working Principle

To put it simply: Jet drilling, vibration liquefaction, in-situ compaction, settlement and consolidation.

With high-frequency vibration from a vibroflotator combined with high-pressure water flow, saturated loose sand underground instantly liquefies. Soil voids shrink rapidly and particles rearrange for mutual compaction. After excess pore water pressure dissipates, the overall foundation density and bearing capacity are greatly improved, thoroughly solving two major hazards of sandy ground: post-construction settlement and seismic liquefaction.

Applicable Strata (Key Points to Memorize)

✅ Optimal Application: Medium-coarse sand, loose hydraulically filled sand; soil clay content ＜15%, abundant groundwater and good permeability

⚠️ Conditional Application: Silty fine sand (trial vibroflotation test is mandatory when clay content ranges from 10% to 15%)

❌ Prohibited Application: Silt, silty clay, soft clay and low-permeability cohesive soil

II. Supporting Construction Equipment

The complete equipment set features simple assembly and strong versatility:

The set includes mobile crane, high-power vibroflotator (75kW / 100kW / 180kW), high-pressure water pump, intelligent power distribution cabinet, measuring tape, level instrument and total station.

Current readings from the power distribution cabinet act as the core on-site quality control indicator to directly judge whether soil compaction meets design standards.

III. Standard Complete Construction Procedures

1. Pre-construction Preparation

First, clear and level the construction site: thoroughly remove weeds, construction waste and surface silt. Backfill and level low-lying areas, and dig surface drainage ditches to prevent ponding from softening native soil and compromising construction quality.

Next, conduct precise layout survey via total station to mark vibroflotation hole positions, normally arranged in equilateral triangles with standard hole spacing of 2.0–3.0 m. All marking stakes shall be reviewed and approved by supervisors before construction commencement.

Trial vibroflotation test is an indispensable critical step. Select representative zones on site to carry out test vibroflotation, and confirm five core parameters matching local strata: water pressure, penetration rate, compaction current, sectional vibration retention time and lifting interval. These parameters shall serve as the sole construction standard for mass production.

2. Precise Equipment Positioning

Adjust the crane to align the vibroflotator vertically with the hole center, strictly controlling verticality deviation ≤1.5%. Connect water and power supply, calibrate instrument readings to zero, and ensure stable equipment operation and accurate data monitoring.

3. High-pressure Water Jet Drilling & Penetration

Follow the operating sequence: turn on water supply first, then activate vibration. Rely on high-pressure water flow for drag reduction and high-frequency vibration for soil cutting to drive the vibroflotator down at a uniform speed.

Standard penetration rate is controlled at 0.5–2.0 m/min. Slower penetration is required for looser strata to avoid hole offset and excessive soil disturbance. For local hard interlayers, moderately raise water pressure to assist penetration; forced downward pressurization is forbidden to prevent equipment overload damage.

After the vibroflotator reaches the designed bottom elevation for improvement, over-penetrate by 0.3–0.5 m, then close the water jet valve. Retain vibration at the hole bottom for 30–60 s until operating current stabilizes at the compaction current determined in trial tests, before starting upward densification.

4. Sectional Lifting & Densification (Core Working Procedure)

The essence of filler-free vibroflotation: zero filling materials, sectional lifting, sectional vibration retention and layer-by-layer compaction.

Control vibroflotator lifting speed at 0.3–1.0 m/min. Pause lifting every 0.3–0.5 m (one compaction interval) and maintain continuous vibration in-situ for 30–60 s. Monitor power cabinet current throughout the whole process; upward lifting can only resume after the current of the current soil segment stabilizes above the specified compaction standard. Repeat until the vibroflotator is lifted out of the ground to complete a single hole.

5. Zonal Secondary Vibroflotation for Reinforcement (Optional)

For locally extremely loose sand layers, conduct secondary compaction by alternate-hole vibroflotation after full-area primary construction to eliminate weak compaction zones and guarantee uniform foundation performance.

6. Surface Finishing Treatment

Upon completion of all vibroflotation works, level and roller-compact the entire site, then lay a 300–500 mm thick graded crushed stone bedding course on the surface. It functions as horizontal drainage layer, disperses foundation stress and prevents surface sand outflow.

IV. Key On-site Control Parameters (Practical Reference)

✅ Water supply pressure: 200–600 kPa

✅ Penetration rate: 0.5–2.0 m/min

✅ Lifting rate: 0.3–1.0 m/min

✅ Compaction interval per lift: 0.3–0.5 m

✅ Sectional vibration retention time: 30–60 s

✅ Quality acceptance criterion: Operating current ≥ compaction current confirmed by trial test (core acceptance indicator)

V. Quality Inspection & Acceptance Standards

Full traceability during construction: Record construction depth, water pressure, operating current, vibration retention time and other data hole by hole, archive all documents synchronously as acceptance records.

Delayed post-construction testing: Carry out standard penetration test (SPT) and cone penetration test (CPT) 7–14 days after construction to allow complete dissipation of pore water pressure. Verify soil relative density, foundation bearing capacity and liquefaction resistance of sand to meet design requirements.

VI. Common On-site Issues & Countermeasures

Excessively fast penetration & low operating current: Indicates extremely loose native sand. Slow down lifting speed and extend vibration retention time to strengthen compaction effect.

Difficult penetration & sudden current overload: Encounter dense hard interlayer. Temporarily raise water pressure to assist soil cutting; forced downward pressurization is prohibited.

Severe surface sand outflow & water gushing: Reduce water supply pressure and slow penetration rate to lessen lateral erosion on hole walls, avoiding hole collapse and sand backflow.

Conclusion

Filler-free vibrocompaction boasts core advantages of low cost, high efficiency, zero filling materials and minor ground disturbance, making it the mainstream liquefaction mitigation technology for sand and hydraulically filled ground.

On-site construction quality can be fully controlled by managing four critical factors: trial test parameters, vibration retention time, compaction current and lifting interval.

If you have ground improvement demands for your project, please contact SUNZO. We will deliver customized solutions tailored to project conditions to support safe and efficient project delivery.