Building on Sand

An earth quake propagates as a p and a S-curve.

Displacement in sand may already be caused by the vibration of the mild first stage.

A plastic pipe in sand tends to "climb" out of the ground if the water is pumped by a reciprocating pump. Disturbed grain by grain.

...in sand may already be caused by the vibration...

Yes, but what would make it different than say a rock-bed, during the transfer of the "wave"?

Yuval,

To a large extent it depends on the earthquake and the actual way the building is constructed and "anchored", along with the geology beneath the sand. Wood frame or reinforced buildings can do quite well on sand or sandy soils. Unreinforced brick and mortar buildings will suffer severe damage/collapse on any soil.

Typically the worst soils are the water saturated clays, and/or loose soil with a high moisture content because they can undergo "liquefaction" and loose their weight bearing capacity when shook.

Regards, Greg

Greg, have you seen those huge elastomeric building mounts and also dynamic absorbers for quakeproofing?

Have you seen the counter-acting pendulum, in the middle of the Malay Tower (I think it was)?

I New Orleans, if you dig a small hole 1-2 meters it will fill up w/water

the soil is mostly sand & mud.

Your basic building tech for say a strip mall is

drive in a bunch of pilings

pour a slab w/pipes running end to end, the pipes have lg cables strung through them w/tensioning bolts @ the ends

after the concrete cures, the cables are tightened

this minimizes slab sagging/cracking when the pilings start to subside indivually

Hi Greg,

...undergo "liquefaction" and loose their weight bearing...

This was what I read about the San Francisco bay area, and I can understand that Damage per-se has a lot to do with the foundation and flexibility of the structure built, however, this "liquefaction" thing is what I'm interested about: If you were to stand near a highway or rails built on sand you'd feel an "exaggerated" movement during on-going traffic, so, there goes, what?

Israel and Liquifaction of the soil?

Not likely- as far as we know-- where is the soggy water?

Regarding Sound travel along earth from a passing train--

• Will be maximum through soggy wet,(liquified )soil.
• Will be minimum through sand/sandy loam.

If you look up a book on Seismology/Seismic Survey -- you can be sure.

The whole West Coast (ashore the Mediterranean) of Israel is dotted with settlements (cities, towns, kibbutzim, etc) and infrastructure, above and below ground, all built on sand. Loose sand. Sometimes miles into the country. It is mostly dry, except those structures built right above the waterfront.

Having had first hand experiance of an earth quake with a house built on sand with no foundations and the bonding between the bricks gone to a dry powder I can say for certain it is the water that is the killer when the ground liquifies. the sand its self is not a danger. This is because unless the earth quake is directly under the building or the structure is weak to begin with the sand particles have too much of a coeficient of friction to move very far and it is the water that over comes this and lubricates the ground causing the sand to go like a sloppy jelly. We survived our quake with just a rumbling and a little shaking.

The question is: given the exact same construction, and the exact same seismic wave, one upon dry sand, and one upon wet sand, where is the greatest kinetic transfer?

This can be observed in a commercially made neighborhood, where the housing units are the exact same, located on the same sandy ground.

Where? Good question. Japanese and Californian beaches?

If the house is designed primarily as an ultra-stiff frame with walls /roof having minimum-possible weights:

Then the house with strong/stiff bottom frame resting on loose sand will only shift/sink a little through a Richter8+ 'quake while other STRONG Masonry houses would have collapsed!

In Assam on 15 Aug 1950 I could not stand vertical throughout the ~8 Richter 'quake which kept shaking for good 5 minutes.

Yet the Bamboo walled ,thatch roofed Assam-type homes remained intact.We can supply such light prefab bamboo walls (appropriate for any climate including Polar)in large quantity.

Interesting since bamboo is a great renewable building material. What is your company name and/or web site. xdesign@pacbell.net

"Liquification" takes place when particles are moved about or compacted by cyclic pressures or movement. Almost like flowing awway.

In water it is much more noticeable. (quick sand effect)

The same effect can be seen in dry sand but more force is needed.

Foundations can be designed and materials can be selected to withstand the required forces.

For this question 2 identical houses should be considered. the result will change due to design and material.

My impression with brick & mortar houses is that sand will be the loser.

Thank you Hendrik,

This confirms what I described near highways and rails built on (dry) sand. It would even make some kind of (weird) sense that dry sand is subject to greater liquefaction than wet, because of a weaker bond or cohesion between particles, other than the occurring drag or friction between particles.

Does this make any mechanical sense at all?

See my post .

...See my post...

Which of those?

Post 17.

O.K, but the previous posts hint that dry sand is more likely to liquefy than wet sand.

"Liquefy" not in the sense of being wet or dry (as such), but in the sense of it's structural-behaviour during a shockwave.

It's ability to transfer momentum as in: "grain-to-grain".

Not unlike billiard balls knocking each other, transferring their momentum, from one to another.

Maybe the grain-to-grain bond, being somewhat firmer when wet, upscales the viscosity of a body of sand, absorbing some of the momentum (transfered from grain-to-grain), thus acting to restrain the liquefaction phenomenon.

No No think liquid liquify liquifaction. Water lubricates the sand grains and lets them move much more freely. It also coducts energy much better than dry sand. I should know having lived it. Who are these idiots.

Yes it's true. Buildings without the appropriate damping measures will suffer significant damage. Read about liquefaction.

Here is the ultimate example from Mexico City in '85.

http://en.wikipedia.org/wiki/Great_Mexican_Earthquake

I believe that Mexico City sits on a very thick layer of swelling clay. Liquifaction in sand is fundamentally different from the somewhat similar failures that occur in cohesive soils.

liquefaction in sand can be seen in some old photos from Japanese earthquakes,, essentially the soil foundation material loses all shear strenght and bearing capacity, your build can sink as a unit, and do so differentially (fall over like leaning tower), all in one earthquake. This is caused by the increased pore pressure in the sand. The finer and more poorly graded the sand the more susceptible. Additionally, saturation by water must be present in the sand. Clays and very fine grained cohesive materials resist this liquefaction due to the cohesion of the particles. However, these fine grained materials are subject to an accelerated settlement during seismic events (seismic settlement), eventual the clays are consolidated and this becomes minimal (after a load is applied from a new building the clays will begin to settle under this lod on a curve similar to a decay curve). Damage directly from the seismic wave propigation is typically worse, in areas of underconsolidated silts, fine sands and clayey silts, like bay muds. This soil can amplify local wave effects, and settle substantially during an event.

what if you build on sand dunes where there is no threat of earthquakes?