What causes soil liquefaction?

Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid.

How does soil liquefaction happen?

Liquefaction occurs when the structure of a loose, saturated sand breaks down due to some rapidly applied loading. As the structure breaks down, the loosely-packed individual soil particles attempt to move into a denser configuration.

What soil conditions lead to liquefaction?

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.

What factors affect liquefaction?

What factors are necessary for liquefaction to occur?

• Loose, granular soil – typically artificial fill (landfill) and beach or stream deposits that are loosely compacted.
• Saturation of the soil by ground water (water fills the spaces between the soil particles).
• Strong shaking.

How can liquefaction of soil be prevented?

The most common way of preventing the occurrence of liquefaction are foundation soil improvement methods. One type of improvement is to replace the susceptible soil with the appropriate amount of gravel. A more favourable form of the granulometric soil curve in a narrower location is obtained in this way.

What are the effects of soil liquefaction?

Liquefaction of soil causes structural instability in buildings. This occurs due to various instances of structural failure. The liquefied ground cannot sustain the stresses of its load from the foundations. Foundations will sink into the sand deposit and cause the building to lean and eventually collapse.

What damage did liquefaction cause?

Damage from liquefaction

The overlying ground can also sink, spread and crack. Underground pipes and tanks float and break. Power poles fall and break cables. During the Canterbury earthquakes, over 400 000 tonnes of silt came to the surface, covering streets and gardens in several suburbs.

Why is Christchurch prone to liquefaction?

Groundwater levels move up and down over time. Earthquake shaking – Stronger earthquake shaking causes more of the soil profile to liquefy and causes more severe ground damage.

Why was Christchurch susceptible to liquefaction?

Christchurch is very familiar with liquefaction, with parts of the city experiencing significant liquefaction as a result of the 2010/2011 Canterbury Earthquakes. Following the earthquakes, a lot of information has been collected about the city’s ground conditions.

What damage did liquefaction cause in Canterbury?

The earthquake caused 182 fatalities, collapse of two multi-storey reinforced concrete buildings, collapse or partial collapse of many unreinforced masonry structures including the historic Christchurch Cathedral.

Is liquefaction primary or secondary?

primary effect

Liquefaction, because it is a direct result of ground shaking, is a primary effect.

In what ways can liquefaction damage man made structures?

The shaking from an earthquake can turn loose soil into a liquid during an earthquake. Liquefaction can undermine the foundations and supports of buildings, bridges, pipelines, and roads, causing them to sink into the ground, collapse or dissolve.

How might heavy rain before an earthquake affect the danger of liquefaction?

How might heavy rain before an earthquake affect the danger of liquefaction? it would fill the soil with moisture, where liquefaction is most likely. This would make the liquefaction very severe.

What are aftershocks when can they occur?

Aftershocks are smaller earthquakes that occur in the same general area during the days to years following a larger event or “mainshock.” They occur within 1-2 fault lengths away and during the period of time before the background seismicity level has resumed.

What happens in a liquefaction zone?

In liquefaction zones, saturated sand and silt take on the characteristics of a liquid during the intense shaking of an earthquake, according to the U.S. Geological Survey. During violent quakes, seemingly solid ground can turn into the consistency of cake batter, collapsing overhead buildings and infrastructure.

What two factors do geologist take into account when they determine earthquake risk?

What two factors help geologists determine earthquake risk? Geologists can determine earthquake risk by locating where faults are active and where past earthquakes have occured.

Why do scientists use shake tables?

Earthquake shaking tables are used extensively in seismic research, as they provide the means to excite structures in such a way that they are subjected to conditions representative of true earthquake ground motions.

How can earthquakes cause fire and flooding?

Earthquakes cause fires when they damage residential and business gas and electrical lines, creating natural gas leaks and downing power lines coursing with current.

What are four instruments that are used to detect movement along faults?

Four instruments that are used to monitor faults are creep meters, laser-ranging devices, tiltmeters, and satellites. A creep meter uses a wire stretched across a fault to measure sideways movement of the ground. A laser-ranging device uses a laser beam bounced off a reflector to detect even slight fault movements.

What do Strainmeters do?

A strainmeter is an instrument used by geophysicists to measure the deformation of the Earth. Linear strainmeters measure the changes in the distance between two points, using either a solid piece of material (over a short distance) or a laser interferometer (over a long distance, up to several hundred meters).

What does a creep meter do?

Creepmeters. A creepmeter measures fault slip by recording the displacement between 2 piers or monuments located on opposite sides of the fault, spaced 30 meters apart. Typically, an invar wire (or a graphic rod) is anchored to one pier and is stretched across the fault.

What is the point beneath Earth’s surface where rock breaks?

The point beneath Earth’s surface where rock under stress breaks to cause an earthquake is called the focus. The point on the surface directly above the focus is called the epicenter.

What is the name of the point above the focus?

The epicenter is the point on the earth’s surface vertically above the hypocenter (or focus), point in the crust where a seismic rupture begins.

What do you call the trace of the fault on the surface of the Earth?

The fault trace is the intersection of a fault with the ground surface; also, the line commonly plotted on geologic maps to represent a fault. Fault surface trace of the Hector Mine fault after the October 16, 1999 M7.1 rupture. ( Photo by Katherine Kendrick, U.S. Geological Survey)

What is the fastest seismic waves?

P waves travel fastest and are the first to arrive from the earthquake. In S or shear waves, rock oscillates perpendicular to the direction of wave propagation. In rock, S waves generally travel about 60% the speed of P waves, and the S wave always arrives after the P wave.

What does P in AP wave stand for?

primary

Compressional waves are also called P-Waves, (P stands for “primary“) because they are always the first to arrive.

What is the slowest wave?

Surface waves

Surface waves travel along the surface. There are two types of body waves: P-waves travel fastest and through solids, liquids, and gases; S-waves only travel through solids. Surface waves are the slowest, but they do the most damage in an earthquake.