What is dynamic replacement?

Dynamic compaction replacement method refers to the use of heavy hammer to tamp away the soft soil, backfill the tamping pit with block stone, gravel, sand or other granular materials, and finally form a block (gravel) pier. The block (gravel) pier forms a composite foundation with the tamped soil mixed with sand and gravel around. Its bearing capacity and deformation modulus are greatly improved, and the gap in the block (gravel) pier provides a good channel for the discharge of pore water of soft soil. The foundation treated by dynamic compaction replacement method not only improves the foundation strength, but also improves the drainage conditions, which is conducive to the consolidation of soft soil.

Classification

In engineering practice, dynamic compaction replacement method has a lot of successful experience in dealing with cohesive soil fill with high water content and silt and muddy soil foundation with small thickness. It can overcome the limitations that the excavation and soil replacement cannot be too deep (generally 3M deep) and the powder jet grouting pile cannot be too shallow (generally more than 6m), and has the characteristics of low cost and short construction period. Therefore, it is used to treat the soft foundation in the shallow layer (less than 6m) of the Yellow River alluvial plain.

Dynamic compaction replacement is divided into: ① single point compaction replacement forms an independent pier replacement form; ② The replacement of group points with sufficient spacing forms the replacement form of orderly arranged group pier composite foundation; ③ There are three types of densely arranged group point ramming, forming the form of overall replacement. The replacement depth of single point compaction is generally 5 ~ 7m, and the deepest is 8.5m; Generally, the depth of integral replacement will not exceed that of single point tamping replacement. The depth of silt squeezing replacement in silt is generally 6m and the deepest is 10m (special process is adopted).

Replacement method and effect of dynamic compaction

The depth of the tamping pit formed by one replacement is generally 1 ~ 2 times the diameter of the tamping hammer. When the replacement body is deep, it must be replaced for many times to achieve the goal. For the first replacement, tamp a tamping pit with a depth of 1 ~ 2 times the hammer diameter, fill it with replacement materials such as crushed (block) stones, and then carry out the second replacement in exactly the same steps as the above until the "second replacement" achieves the expected purpose or replacement depth.

The shape and size of the replacement body formed by multiple replacement are related to many factors such as replacement technology. According to the indoor model test and field in-situ test, the dynamic compaction replacement process and replacement effect of high saturation soil are discussed below.