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How to Improve Soft Ground

Quiz Questions

1. Compaction for foundation is techniques that typically are used to
Compact or densify the soil
Before spreading the grouting
2. Reinforcement is techniques that typically construct a reinforcing element within the soil mass without necessarily changing the soil properties. The performance of the soil mass is improved by the inclusion of the reinforcing elements.
3. Fixation – techniques that fix or bind the soil particles together thereby increasing the soil’s _________ and __________ its compressibility and permeability.
Strength     decreasing
Volume        increasing
4. According to table 12.1, typical energy required to compact sand with 10-80%silt and <20% clay, pI<8 is in the range of:
2-2.5 tons ft/cf
2.5 -3.5 tons ft/cf
6-11 tons ft/cf
5. The Vibro Compaction is a process that involves the use of a down-hole vibrator (vibroflot), which is lowered into the ground to compact the soils at depth (Figure 12.3). The method is used to increase bearing capacity, reduce foundation settlements, reduce seismic subsidence and liquefaction potential, and permit construction on loose granular fills.
6. Compaction grouting, one of the few US born ground improvement techniques, was developed by Ed Graf and Jim Warner in California in the 1950s. This technique densifies soils by the injection of a _________________ . The grout bulb expands as additional grout is injected, compacting the surrounding soils through compression. Besides the improvement in the surrounding soils, the soil mass is reinforced by the resulting grout column, further reducing settlement and increasing shear strength. The method is used to reduce foundation settlements, reduce seismic subsidence and liquefaction potential, permit construction on loose granular fills, reduce settlements in collapsible soils, and reduce sinkhole potential or stabilize existing sinkholes in karst regions.
Low mobility low slump mortar grout
High mobility active mortar grout
7. Surcharging consists of placing a temporary load (generally soil fill) on sites to pre consolidate the soil prior to constructing the planned structure (Figure 12.9). The process improves the soil by compressing the soil, increasing its stiffness and shear strength. In partially or fully saturated soils, prefabricated vertical drains (PVDs) can be placed prior to surcharge placement to __________ the drainage, _______ the required surcharge time.
accelerate the drainage, reducing
Slow down the drainage, increasing
8. Columns of compacted, gravel size stone particles constructed vertically in the ground to improve the performance of soft or loose soils are called:
Stone columns
Gravel columns
9. The stone can be compacted with impact methods, such as with a falling weight or an impact compactor or with a vibroflot, the more common method. The method is used to increase bearing capacity (up to 5 to 10 ksf or 240 to 480 kPa), reduce foundation settlements, improve slope stability, reduce seismic subsidence, reduce lateral spreading and liquefaction potential, permit construction on loose/soft fills, and precollapse sinkholes prior to construction in karst regions.
10. Soil nailing is an in situ technique for reinforcing, stabilizing, and retaining excavations and deep cuts through the introduction of relatively small, closely spaced inclusions (usually steel bars) into a soil mass, the face of which is then locally stabilized in the United States. A zone of reinforced ground results that functions as a soil retention system. Soil nailing is used for temporary or permanent excavation support/retaining walls, stabilization of tunnel portals, stabilization of slopes, and repairing retaining walls.
11. Figure 12.19 is:
Micropile load test
Soil nailing
Installation of vibro concrete columns.
12. In Fig. 12.21, Injection rig is for treatment of
Expansive soil
Slow moving soil
13. Jet grouting (Figure 12.24) was conceived in the mid-1970s and introduced in the United States in the 1980s. The technique hydraulically mixes soil with grout to create in situ geometries of soilcrete. Jet grouting offers an alternative to conventional grouting, chemical grouting, slurry trenching, underpinning, or the use of compressed air or freezing in tunneling.
14. Dry soil mixing (Figure 12.30) is a low-vibration, quiet, clean form of ground treatment technique that is often used in very soft and wet soil conditions and has the advantage of producing very little spoil.
15. Bearing capacity of foundation soils can be improved using geogrids and geosythetics placed as a continuous single layer, closely spaced continuous multilayer set or mattress consisting of three-dimensional interconnected cells.