Without being too detailed, we will now list ground improvement and foundation improvement /repair techniques other than grouting and compaction below.
- Injection Systems: various aqueous solutions are injected into the ground, for treatment of collapsible and expansive soils, railroad subgrades, certain slopes.
- Rigid Inclusions: involves transferring of loads from weak to firm soil by using stiff columns made of concrete or grout.
- Deep Soil Mixing: blending of soil materials by mixing with slurry grout, to improve its properties. It can be done as dry or wet mixing. Dry mixing uses dry cement binder, while wet mixing involves liquid cement binder slurry.
- Stone Columns: Construction of aggregate columns in the soil, by first opening a hole and then filling it with aggregate and then compacting with vibrator.
- Compaction Pile: This is a common ground improvement method, which involves building piles made of compacted sand, in order to densify loose cohesionless soils (loose sands), but it is can also applicable to clay soils as well. The improvement not only results from the dense compacted sand pile itself, but also because while making the sand pile, the surrounding soil is pushed and therefore densified. This method improves load carrying capacity and liquefaction resistance of the ground.
- Slurry Walls: Slurry walls are used to support open excavations. Slurry is usually made of water and bentonite but various materials are possible. It serves as a non permeable, groundwater blocking wall for preventing its flow into another area.
- Soil Reinforcement: This is done by using geotextile materials, which are laid in layers or flat and long stripes, to improve tensile and shear strength of soil. This is not used below foundations, but behind retaining walls, to stabilize earth that is supported, which can also mean stabilizing slopes. We will talk about it more, under retaining structures and slopes section. They are laid to intercept a failure surface, and through its tensile strength, reinforces the slope or retained earth. They can also be used under embankments. Reinforcements can be made of steel or geosynthetics. Geosynthetics is a general term that includes polymeric materials used in geotechnical engineering for various purposes, such as geonets, geotextiles, geomembranes, geogrids. Because of the variety of materials and the applicability to many different situations such as soil reinforcing and drainage, geosynthetics is one of the heavily studied subjects in geotechnical engineering.
- Ground freezing: Water in the soil can deliberately be frozen temporarily, as a seepage control technique, not only to prevent that water body from flowing, but also because ice is totally impermeable and does not allow any water to pass through. Ground freezing can also be used for temporary underpinning, soil support, slope stabilization and similar applications. Even entire excavations can be supported, by forming a circular or square area made of icy soil around a proposed excavation area. In addition, frozen soils have greater strength, for both coarse and fine grained soils, although the strength gain rates and amounts are different. The process of soil freezing is similar to dewatering except now the water is being frozen, instead of being sucked. The water is frozen through metal pipes inserted to the ground, in which a fluid solution is circulated though pumps located on the ground. This liquid solution in the pipes, draw heat from the surroundings. One advantage of ground freezing is that no foreign materials are injected into the ground, and apart from the possibility of frost and heave, the ground usually returns to its original state.
In the next post of this series, we will discuss “Foundation Strengthening and Repair (underpinning) methods”