Dynamic Compaction is a ground improvement solution primarily used to densify loose, or medium dense coarse-grained soils, such as sandy or gravelly deposits, through the repeated dropping of heavy weights.
This method enhances the in-situ density of the soil, leading to increased stiffness and reduced foundation settlements. In the UK it is commonly used to treat deep deposits of made ground or uncontrolled fill, reducing the need for more expensive foundation systems such as piling. The technique allows for the use of more economical shallow foundations and ground-bearing slabs.
Dynamic Compaction Process
Dynamic Compaction deploys a very similar construction process to Dynamic Replacement.
However, there is no requirement to compact imported stone in the formed dynamic compaction craters. Instead, the working platform is graded into the compaction craters, resulting in a global site level reduction.
Step 1: Site Preparation
Before beginning the compaction process, the client surveys the site for underground services and prepares a stable working platform at either the foundation or slab level. Compaction points are then marked by driving numbered pins into the working surface at the designated locations.
Step 2: Health & Safety Briefing
A comprehensive health and safety briefing is conducted for the workers on-site. The compaction rig is set up and moved to the first compaction point, ensuring that all safety protocols are in place. Crucially, a minimum 25m exclusion zone must be established to ensure no unauthorised pedestrian access into the working area.
Step 3: Initial Compaction Trial
A compaction trial is conducted at the start of the project to determine the depth of the drop weight’s penetration, and the saturation energy (number of consecutive drops) needed to compact the soil effectively. This is done by measuring the crater depth, and heave profile of the ground following each impact.
The results inform the procedure for the remaining compaction process. However, regular monitoring is required throughout the project, and the process adjusted wherever necessary to ensure the design requirements are achieved.
Step 4: Compaction Execution
Once the trial is complete, the crawler crane is moved to the first compaction point, the drop weight is positioned above the marked position and raised to the predetermined height.
The weight is then released in free fall, striking the ground with significant force. This process is repeated at each compaction point until the required crater depth or saturation energy level is reached, effectively increasing the soil density.
Step 5: Grading and Surface Treatment
After the initial compaction points have been treated, the surface is graded to fill the craters formed by the impacts, and, where the initial compaction pass has targeted deeper soil layers, a secondary pass of intermediate compaction points will be treated, targeting shallower soil layers. Finally, a low energy tamping phase is carried to re compact the surface layers disturbed during the high energy compaction process.
Benefits of Dynamic Compaction
- Cost-effective: Dynamic compaction can be significantly cheaper than traditional piling methods, especially for deep deposits of made ground or uncontrolled fill.
- Increased soil stiffness: By increasing the density of loose, coarse-grained soils, dynamic compaction improves the stiffness and bearing capacity of the ground.
- Reduced settlement: The technique helps minimise future settlements, ensuring more stable and reliable foundation conditions.
- Environmental benefits: Dynamic compaction often requires minimal imported materials, and in some cases, site-won material can be reused in the compaction process, reducing waste and the need for additional resources.
Contact Us
Are you looking for Dynamic Compaction assistance on your construction project? Contact our expert team of engineers for advice on your project and get a no obligation quote.
FAQs
Q – How much does dynamic compaction cost?
A – The cost of dynamic compaction can vary widely depending on factors such as site conditions, project size, and location. To get an idea on costs, speak to our ground improvement specialists to get a more accurate quote.
Q – What equipment is used in dynamic compaction?
A – Dynamic compaction and dynamic replacement is carried out using a 9.0t – 15.0t weight, dropped in free fall from heights of 10.0 – 20.0m using a 65.0t + tracked crawler crane. When using GeMech’s modified dynamic replacement system, the crane will be supplemented by a tracked excavator, which is used to place imported aggregate into the compaction voids.
Capabilities:
- Depth of influence up to 8.0m
