Seismic sounding / The detection of liquefying layers

Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

Seismic sounding The detection of liquefying layers

drs. RenĂŠ de Bruijn

Introduction • Ingenieursbureau Boorsma BV is a consultancy firm and knowledge partner of Royal Eijkelkamp and Hoogveld Sonderingen – We advice Eijkelkamp in the R&D process – We supply Hoogveld with essential (scientific) support and knowledge of geology in projects

• In this presentation: – Seismic sounding – The detection of liquefying layers

Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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Seismic sounding, why?

• Determine the ground conditions and sensitivity for earthquakes of: – buildings – railways – wind turbines, gas distribution stations, power plants.

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Goal • Buildings in earthquake zones are expected to be constructed by including an earthquake load.

• Seismic soundings can identify the required measures to prevent damage by earthquakes.

• They provide the parameters that are used in the calculations for earthquake-resistant constructions.

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What is liquefaction • When a sand layer is affected by vibrations (earthquake), the grains will settle and cause subsidence.

• Liquefaction is the process by which saturated soil undergoes severe shaking, causing it to turn to liquid.

• This is called liquefaction of the soil layer.

Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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Sand boils due to liquefaction

• •

Liquefaction causes major settlement and sand boils to occur.

Liquefaction is an important factor in the collapse of buildings and infrastructures.

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Magnitude 5,8 earthquake in the Netherlands 1992

Liquefaction in sand layer in river bank

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PageLandslide 7 because of liquefaction

river

subsidence of river bank due to liquefied layer Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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Kobe earthquake (magnitude 6,9) Page 10

Density increase due to earthquake Consequence: subsidence

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Kobe earthquake Page 12

Layer model of subsurface Tokyo red=Pleistocene green = weak mud (weakness determined by N-value)

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Damage in relation to mud thickness by: Geological Surveys of Japan and the Netherlands = Dutch/Japanese cooperation project

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How do we detect liquefying layers?

By seismic sounding!

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Theory of seismic sounding

Seismic cones are used to measure the shear wave velocity.

From the shear wave velocity we can calculate: • Shear modulus • Modulus of elasticity • Poisson ratio Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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In the shear wave (or S-wave), the particles move perpendicular to the direction of propagation.

The velocity depends on the rock type: Granite: Volcanic rock: Weathered rock: Clay: Sand & Gravel: Quicksand:

3000-7000 m/sec 1000-3000 m/sec 600-900 m/sec 900 m/sec 600 m/sec 0 m/sec

The S-waves cannot propagate through a liquid.

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Method The seismic sounding can be done in combination with the standard CPT. The seismic wave is generated by hammering a metal plate.

The seismic cone records the seismic wave in depth-intervals of 1 meter.

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The SCPT is developed by Hoogveld CPT Company and Sonic Sample Drill. state of the art software is used for processing and interpretation of seismic soundings.

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Example of seismic sounding The first-arrivals of the shear wave are plotted against depth, showing 3 layers with characteristic Vs values.

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3-layer ground model on the basis of seismic sounding Layer 2 has a potential for liquefaction

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Vs

combination of SCPT and CPT

Vs Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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Soil profile of SCPT

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Product The average shear wave velocity in the upper 30 meter (Vs,30) is used to determine the earthquake-load on buildings.

If Vs,30 >250 m/s and no individual layers with Vs<200 m/s, calculations of earthquake load using â&#x20AC;&#x2DC;normal conditions'.

If Vs,30 <250 m/s or individual layers with Vs<200 m/s, calculations based on â&#x20AC;&#x153;special conditions".

This is according to the design code for earthquake-resistant building Eurocode 7 / NPR9998 (applicable in the Netherlands).

For Japanese conditions and legislation, the required parameters will be calculated accordingly.

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Vs can also be used to calculate the following basic parameters for each layer:

Shear modulus

G = *Vs2

Poisson's ratio

Pr = ((Vp/Vs)2 – 2) / (2*(Vp/Vs)2 – 2)

Young's modulus

E

Bulk modulus

K = 1/3 * E/(1-2Pr)

in which:

Vp = primary (longitudinal) wave velocity  = density

= 2G*(1+Pr)

Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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The application of seismic sounding in railroads Railroad tracks are subject to static and dynamic loading: Static loading:

Ground settlement due to track ballast depends on geotechnical parameters (Shear modulus, Youngâ&#x20AC;&#x2122;s modulus).

Dynamic loading:

Due to the movement of the train.

The critical train velocity is the velocity of the Rayleigh wave.

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Rayleigh waves are surface waves, and can be produced by earthquakes, railway trains, or by a hammer impact (seismic sounding).

Rayleigh waves have a velocity slightly less than shear waves, by a factor dependent on the Poisson ratio: VR/Vs = (0.862 + 0.14Pr ) / (1 + Pr) VR = velocity of Rayleigh wave VS = velocity of shear wave Pr = Poisson ratio So: by measuring the shear wave velocity (Vs ) we determine the Rayleigh wave velocity (VR ) Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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If the train velocity is equal to the Rayleigh wave velocity - > problem !

The Rayleigh velocity is 50â&#x20AC;&#x201C;300 m/s (= 180-1080 km/hour).

The Japanese bullet trains have maximum speeds of 240â&#x20AC;&#x201C;320 km/h.

So: there may be problems!

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Example: new railway track in the Netherlands (Hanzelijn) Design speed of the train: 200 km/hour = 56 m/s Seismic sounding: VS,min = 60 m/s.

The criterium for the critical train speed is approximately 0.9 x VS,min = 54 m/s Problem : possible liquefaction

Depth(m)

shear wave velocity Vs (m/s)

Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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Seismic sounding on the railway track By a special vehicle it is possible to do seismic soundings on the track.

A special vehicle with rubber tyres ensures that there is no damage of the railway track.

The width (in Holland) of the vehicle is 2 meters, length is 4 meter, 6 meter including rail wheels.

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The rig is moved along the railway track, stopping for seismic soundings at intervals of 10-100 m.

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Treatment of liquefying layers

Passive Site Stabilization Method proposed for sites that are susceptible to liquefaction.

This non-invasive method uses injection wells at the edge of a site.

Distribution of the stabilizing material into the liquefiable layer using existing groundwater flow.

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Colloidal silica is nontoxic, biologically and chemically inert, has excellent durability characteristics, as well as viscosity and gel time characteristics.

This makes it a desirable stabilizer.

The grout is a solution of sodium silicate (Na2O3Si).

It solidifies on exposure to air and is used to make silica gel.

It is also called â&#x20AC;&#x2DC;water glassâ&#x20AC;&#x2122;.

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Silica Grouting

Colloidal silica is produced from saturated solutions of silicic acid that can be made to gel by changing the ionic strength and pH. In its liquid form, it has a viscosity similar to water. It replaces water in the soil pores, then solidifies over a specific gel time. The silica grout forms a permanent gel, which binds soil particles, strengthening the soil and providing deformation resistance during earthquake loading.

This increases the deformation resistance of loose sand to earthquakes and prevents collapse.

The strength of soil treated with colloidal silica grout depends primarily on the concentration of silica in the grout. Liquefiable sands treated with 5 weight% silica grout should provide adequate liquefaction resistance.

Strength increases for up to a year after treatment with silica grout. However, once the sample has cured for approximately 4 times the initial gel time, the majority of the strength has been gained. Gel times vary from minutes to months.

Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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Injection method The injection layer is built up by using a grid of injection tubes with predetermined depths.

Seismisch sonderen

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For succesful permeation grouting, the permeability of the layer has to be good.

Injection with silica grout (water glass) can therefore only be carried out in sand.

A quick test can be performed initially by examining the CPT sounding. If the friction number <1.2%, the grout injection can be considered.

Pressure and flow are monitored during injection. Control by injection computers results in uniform injection bodies.

During injection, the groundwater is pressed out of the pores and replaced by the injection fluid.

This technique is called "permeation groutingâ&#x20AC;?.

Due to grouting, the treated layer will not be liquefying in case of earthquakes.

Extra advantage: When the silica grouting is done before the construction of a new building, the subsurface becomes more or less impermeable for groundwater.

Building can take place in dry conditions. This is specifically interesting when building underground structures (cellars, subways, tunnels, parking garages).

Groundwater abstraction rates will be reduced significantly.

Presentation Sonic Samp Drill Seminar 2016 (Daiki Co.Ltd.)

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THANK YOU !!

Seismic sounding The detection of liquefying layers Feel free to contact drs. RenĂŠ de Bruijn Visit our website for more information.

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Gerben Sondermanstraat 2 9203 PV Drachten +31(0)512 580 300 +31(0)512 525 296 drachten@boorsma-consultants.nl http://www.boorsma-consultants.nl @IB_Boorsma

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