Tattla, Prabhjot Kaur
Engr. Mikami
CE 162P – E04
Homework
Soil Improvement and Ground Modification methods
 Deep Dynamic Compaction (DDC)
This method of ground improvement uses cranes to drop heavy weights (10 to 170
tons) from a height of up to 85ft onto the ground. The weights are dropped in a
grid pattern typically spaced anywhere from 6 to 40ft apart. The impact of the
weight on the ground creates low frequency energy waves which move and shake
the soil causing compression and densification.
DDC is most suitable for saturated sands and silty sands though improvements can
still be made on certain fine grained soils if they are located above the groundwater
table. DDC can also help with collapsible soils or soil strata that have large void
spaces (like Karst).
 Vibrocompaction/Vibroflotation
This method of ground improvement uses a large crane/truck to lower vibrating
probes into the ground. The probes vibrate with a cyclical action in order to cause
granular soils to rearrange themselves into a more dense configuration.
Vibrocompaction cannot be used on silts or clays and is generally more expensive
then deep dynamic compaction. Some advantages to vibrocompaction are that it is
easier to use than many other compaction methods and that you can more easily
achieve a uniform and densified soil surface. Vibrations felt on the ground are
often significantly less than those caused by deep dynamic compaction or blasting.
 Penetration/Pressure Grouting
With this method of ground improvement a very fluid, cementicious grout is
pumped into the ground under high pressure. The high pressure forces the grout to
fill the void spaces in granular materials resulting in higher density soils, improved
strength and stiffness and a lower hydraulic conductivity.
Typical application pressures are on the order of 1psi per foot of depth. Usually
only coarse grain soils can be treated however if micro-fine cement grout is used,
fine sands may also be able to be treated. Penetration/Pressure grouting is a widely
available construction technique and is commonly used to repair damaged
foundations.
 Compaction Grouting
Compaction grouting injects stiffer grout into the ground at a specified depth using
medium to high pressure. The grout injection process creates and expands a grout
cavity (e.g. a grout bulb) near the bottom of the column which presses against the
surrounding soil increasing its density.
Compaction grouting is best used on loose granular soils or collapsible soils
though it has been used with some success for certain fine grained soils. The
improvement in soil characteristics is related to the type of soil being treated and
the spacing and pattern of the compaction grouted columns. The cost of this
method can be moderate to high depend on equipment availability and application
techniques.
 Jet Grouting
When jet grouting is used a special drilling rig with a jet nozzle is used to drill a
hole into the earth to a specified depth. The nozzle ejects water and/or air to erode
the soil at depth creating a cavity that can be filled with grout.
Jet grouting can be used in most soil types, although it works best in soils that are
easily eroded like sands and gravels. Cohesive soils, especially highly plastic clays,
can be difficult to erode and may require lengthy drilling times to create the soil
cavity. Improvement results are also less noticeable for cohesive soils.
 Deep Soil Mixing
When deep soil mixing is used, a drill rig with one or multiple counter rotating
augers drills down into the ground to mix the soil with additives. Typically grout,
lime, flyash, or even some other additives such as montmorillinite clay are added
to the soil during the mixing process to improve strength and stiffness. The soil's
compressibility as well as its hydraulic conductivity are reduced during the
process.
 Blasting
Blasting is the use of explosives to compact/consolidate soils. This technique
works well for gravels and mild sands but is not effective on silts or clays. Blasting
is best used to densify hydraulic or dredged fill materials. Blasting typically
consists of drilling several holes to depth below the groundwater table, placing
explosives at the bottom of the hole, backfilling and tamping and then blowing it
up.
 Soil Replacement/Chemical Treatment
Soil replacement is a technique that can be used to simply remove the poor quality
soil and replace it with good or engineered soil. The advantage with this technique
is that it is easy to do, requires no specialized equipment, and most general
contractors can do this work. However, this method does have a few major
disadvantages. Primarily, deep excavations can be economically nonviable and
may also require a lengthy time to complete as application of new soil layers can
only be done in relatively small lifts.
 Lime stabilization
Lime provides an economical way of clayey soil stabilization. Selection of the
suitable lime concentration for clay stabilization is based on achieving a target pH
value. Stabilization can be ineffective if the concentration of admixture is not
adequate to ensure strength and durability.it is usually in the range from 5 to 10%.
 Sand drains
These are constructed by drilling holes through the clay layer by using rotary
drilling, continuous flight auger or driving down hollow mandrels into the soil. The
holes are then filled with sand. When a surcharge is applied at the ground surface,
the pore water pressure in the clay will increase, and it will be dissipated by
drainage in both vertical and horizontal directions.
 Soil freezing
This involves lowering the temperature of the soil until the moisture in the pore
spaces freezes. Freezing of pore water acts as a cementing agent between the soil
particles causing significant increase in shear strength and permeability