soil liquefaction and quicksand condition
Download as PPTX, PDF4 likes5,513 views
Soil liquefaction occurs when water-saturated soils lose strength during earthquakes or other vibrations, causing the soil particles to separate and behave like a liquid. This happens because earthquake shaking increases water pressure between soil particles. Buildings and structures can sink or collapse into liquefied soils. Techniques to prevent liquefaction include compacting soils or setting deep foundations below unstable layers. Quick sand conditions occur when upward seepage flow reduces effective stress in loose soils like sand, causing a floating effect with little weight-bearing capacity.
soil liquefaction and quicksand condition
- 1. Soil Liquefaction and quick sand
- 2. Soil liquefaction can be defined as the phenomenon by which the strength of the soil is lost either due to dynamic or static loading. Most of the earthquake forces are the major causes of soil liquefaction. The vibrations of earthquake shockwaves in water-saturated soils trigger the phenomenon.
- 3. Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water. This water exerts a pressure on the soil particles that influences how tightly the particles themselves are pressed together. Prior to an earthquake, the water pressure is relatively low. However, earthquake shaking can cause the water pressure to increase to the point where the soil particles can readily move with respect to each other.
- 4. WHY IS IT A PROBLEM? During an earthquake or other vibration in the ground, the liquid consistency of the ground cannot support objects. Buildings, bridges, trees and other objects collapse or sink into the soil. In most countries, modern building codes require builders and architects to analyze the viscosity of the soil before developing the land. Flotation of buried objects, such as pipelines, fuel tanks and more Landslides Lateral spreads, or landslides on gentle slopes Quicksand Sand boils, or sand volcano Sinkholes
- 5. HOW CAN WE PREVENT SOIL LIQUEFACTION? Builders can set the footings of the foundation deeper than the layer of unstable soil. Wherever possible, builders try to set the footings onto bedrock. This is especially important for bridges, dams and other building sites near water. However, this is not always practical or possible. Technicians insert vibrating probes into the soil at deep levels, and the trembling shakes the loose soil. The compression of the loose soil particles lessens the number of air pockets where water can settle.
- 6. Liquefied soil also exerts higher pressure on retaining walls, which can cause them to tilt or slide. This movement can cause settlement of the retained soil and destruction of structures on the ground surface
- 7. QUICK SAND Quick sand condition or boiling Quick sand condition is a condition of flow, not a type of soil, in which a vertical upward seepage flow causes floating condition of a particle in cohesion less soil such as Sand and fine gravel. In such cases, cohesion less soils lose all of their shear strength and bearing capacity and a visible agitation of soil grains is observed. This phenomenon is known as boiling or a quick sand condition.
- 8. EFFECTIVE STRESS (Σ') ACTING ON A SOIL IS CALCULATED FROM TWO PARAMETERS, TOTAL STRESS (Σ) AND PORE WATER PRESSURE (U) ACCORDING TO: Σ ´ = Σ - U WHERE, Σ = TOTAL STRESS U = PORE WATER PRESSURE
- 9. WHEN OCCUR SUCH CONDITION WHEN SEEPAGE FLOW TAKES PLACE IN AN UPWARD DIRECTION, THE SEEPAGE PRESSURE ALSO ACTS IN THE UPWARDS DIRECTION AND THE EFFECTIVE PRESSURE IS REDUCED. THERE IS ALSO A PRESSURE IN DOWNWARD DIRECTION DUE TO SUBMERGED WEIGHT OF SOIL. IF SEEPAGE PRESSURE BECOMES EQUAL TO THE PRESSURE DUE TO SUBMERGED WEIGHT OF SOIL, THE EFFECTIVE PRESSURE IS REDUCED TO ZERO.
- 10. QUICK SAND CAN NOT SUPPORT THE WEIGHT OF MAN OR ANIMAL AND IT BEHAVES LIKE A LIQUID WITH A UNIT WEIGHT ABOUT TWICE THAT OF WATER. A PERSON CAN EASILY FLOAT IN IT WITH ABOUT ONE THIRD OF HIS BODY OUT OF QUICK SAND IN CLAYS THE SHEAR STRENGTH OF SOIL DOES NOT GET REDUCED TO ZERO EVEN WHEN THE EFFECTIVE STRESS BECOMES ZERO, DUE TO ITS COHESION. HENCE, QUICKSAND CONDITION DOES NOT OCCUR IN CLAYS
- 11. AS THE PRESSURE OF THE ESCAPING WATER EXCEEDS THE WEIGHT OF THE SOIL AND THE SAND GRAINS ARE FORCED APART. THE RESULT IS THAT THE SANDY SOIL HAS NO CAPABILITY TO SUPPORT THE LOAD. BUT PEBBLES OR GRAVELLY SOILS CANNOT HAVE BECAUSE IT HAS TO EXCEED THE SELF WEIGHT THAN THOSE OF ESCAPING WATER WEIGHTS.