Types of Earth Retaining Systems For Deep Excavations
Types of Earth Retaining Systems For Deep Excavations
Types of Earth Retaining Systems For Deep Excavations
2. Ground condition
3. Groundwater level
5. Displacement criteria
d. Soils with some cohesion and without water table are suitable
e. Often limited to small dimension shafts and trenches with and without
penetration below base (mostly without)
e. Projects: above water table and soils with some cohesion, otherwise soil
treatment like; dewatering, grouting, soil mixing
f. Very popular in European cities and economic, but not yet practiced in this
country
3. SHEET PILE WALLS (SHEETPILING)
a) Their use is often restricted in urbanized areas due to environmental
problems: effect of vibrations, driving difficulties in case of hard layers and
boulders, presence of buried pipes, public utilities etc.
b) Struts or anchors are used. They are usually constructed in water bearing
soils. Sheet pile discontinuities constitute the risk for water tightness.
Light vs. heavy sections. (Sheet pile and H sections are imported to Turkey,
not manufactured.)
4. PILE WALLS
i. Intermittent (Contiguous) Bored Pile Walls
a Cohesive Soils or soils having some cohesion are suitable.
b No water table.
d Common diameters : 60 , 80 cm
Material:
I. Soil-Bentonite
II. Cement-Bentonite
§ Quide Wall
§ panel dimensionas and arrangements thickness : 50, 60, 75, 80, 90,
100, 120, 150 (cm) (60-80 cm most common)
– plasticizers, water reducing agents, air entrainment agents & fly ash
recommended
o Bentonite slurry:
– Fresh bentonite upon mixing Gs = 1.03
PH : 7 to 11
– Should be stored at least one day for hydration in tanks, pits etc.
o Before tremie
Concreting : Gs £ 1.10 .
b. Then prefabricated panels are placed inside the trench and the slurry
mixture is set.
c. The panels are excavated to the depth required for tightness, while the
prefabricated elements are placed only to the depth required for ground
retaining.
d. Drainage
Cofferdams are used in the following areas;
i. Bridge piers and abutments in rivers, lakes etc.
Diameter safe, quick and cheap method especially in poor soils (no water
lowering and soil improvement, grouting).
8. Jet Grout walls or other soil methods like deep soil mixing
a. Experiences with one line of vertical columns were not always satisfactory
due to their small bending stiffness, when no steel reinforcing element is
placed inside the column.
Problems;
Deep columns in water-bearing sands: If 1-2 % deviation of the borings
occurs ( may be unavoidable) or discontinuities (mainly at the interfaces
between hard and soft layers) occur sand-bearing flows into the excavation
are potential. (Highly specialized contractors needed.)