subsoil sites with poor strength Flashcards
What is the initial recommendation for subsoil sites with poor strength?
Not to build; potentially find a new site unless poor ground is localized.
If poor ground is localized, proposed foundations can be designed around these spaces with the remainder of the structure bridging these positions.
What is one method to address poor ground in renovation and replacement?
Excavate, remove, and replace with compacted fills.
This method presents risks of differential settlement and is not suitable for depths over 4 meters.
What is surcharging in the context of poor ground?
Preloading the poor ground with a surcharge of aggregate to speed up settlement and increase load bearing.
This method is expensive and can cause building delays.
How does vibration work as a method for compacting soil?
Vibrates granular soil into compacted stone columns using natural course soil or replacement.
A larger poker vibration and crane is used, with a compacting radius of 1.5-2.7 meters and centers placed 1.5-3.0m apart in a triangular grid pattern.
What types of soils can be compacted using vibration?
Coarse grained soils, clay, and other fine soils.
The vibrator is surged up and down for water tolerance, surrounding soft material, with boreholes filled with coarse granular material.
What is the range of increased bearing capacity achievable through compaction methods?
200-500 kN/m².
What is ground vibration used for?
Applied to non-cohesive soil where granular soils are rearranged into a denser condition.
This involves using a suspended vibrating poker that water jets into the ground.
What is dynamic compaction?
Improves soil bearing capacity by dropping a heavy weight from a considerable vertical distance to compact soil.
The drops pattern, size of weight, and height of drop are designed to suit the site.
What should be done if water is present in subsoil during excavation?
Excavate trenches to allow water to escape.
What is jet grouting used for?
Used for all types of soil, with spacing and depth designed depending on land conditions.
It involves a rotating probe with two jets: an upper jet that blasts water and a lower jet that fills the void with cement slurry.
What does the upper jet in jet grouting do?
Blasts water, concentrated by compressed air to force loose material up.
What does the lower jet in jet grouting do?
Fills the void with a cement slurry which sets into a solid mass.
