P otential Liquefaction of a silt deposit due to rock blasting

[georam]

I would like to get some information on the effect of rock blasting/excavation to potential liquefaction of soil deposits in the area.&nbsp;&nbsp;The soil deposits are generally 10 to 15m thick,consisting of varved clay and with frequent thick layers of silt (up to 2-3 m thick).&nbsp;&nbsp;The CPTU readings suggested that the tip resistance of this soil is almost uniform, about 1 to 1.5 MPa. Undrained shear strengths are about 50 to 100 kPa.<br><br>I went through a paper by Dr. Olson on the subject of liquefaction (also visited his website <A HREF="

http://www.liquefaction.com"

TARGET="_new">

http://www.liquefaction.com</A>),

as well as additional research on the effects of vibrations during blasting, etc.&nbsp;&nbsp;<br>Based on the above :<br>- There are relationships between liquefaction potential of a soil deposit and CPT or “N” values ,<br>or between “N” or CPT values and depth of deposit.&nbsp;&nbsp;These relationships are always connected to<br>an M -7.5 earthquake.....&nbsp;&nbsp;SSR vs normalized CPT or SPT<br>- Blasting causes vibrations and may effect nearby deposits which are susceptible to liquefaction.There are connections of damages to structures from certain blast (velocity versus damage), etc<br><br>My questions are :<br>- I have not found the relation of the two above (earthquake and blasting effect to liquefaction).<br>They seems to be treated as “different” world/field.&nbsp;&nbsp;Should there be ?&nbsp;&nbsp;<br>- How to relate the effect of vibration by blasting to SSR (Seismic Shear Stress Ratio) in the SSR vs normalized CPT relationship ?<br>- How to determine or estimate “a” (particle acceleration as a percentage of g) in the SSR equations for a blasting . I saw a blasting chart which came from one of our projects (it was from effect of pile driving), and showed 0.01 to 0.03g. What typical a is for blasting ?<br>SSR = 0.65 x amax/g x sigmavo/sigma’vo x rd (Seed and Idriss 1971)&nbsp;&nbsp;&nbsp;&nbsp;<br>rd = 1 - (0.012z)&nbsp;&nbsp;&nbsp;z= depth (Kayen et al,&nbsp;&nbsp;1992)<br>- Does vibration /shock from blasting has same effects as in earthquake ?... May be not on the same scale, but I think there is a connection here.&nbsp;&nbsp;(Most blasting info I know generally only discusses&nbsp;&nbsp;velocity and “scaled” distance.&nbsp;&nbsp;Blast Specs limits the velocity to avoid damages to existing structures).&nbsp;&nbsp;<br><br>Any comments which can shade some “light” on this subject is appreciated.&nbsp;&nbsp;Thanks<br><br>Regards<br><br>

 

[DougA]

Blasting is used specifically to densify materials, in principle, to effect liquefaction.&nbsp;&nbsp;At present, to my knowledge, this is a rather &quot;ad hoc&quot; field.&nbsp;&nbsp;Clearly research would be helpful, but as a first cut, the acceleration assumed in the SSR equations is NOT applicable.<br>The duration and frequency for blast vibration is very different, and has strong implications for liquefaction, which requires pore pressure changes that generally are accentuated by low-frequency vibration.&nbsp;&nbsp;<br><br>Doug A