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RE: Road Repair Advice Needed

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Unless the stones of the existing wall are very BIG, as described by Ralph, my guess is that they are not acting as a retaining wall, but are acting as slope protection and erosion control.  If that is the case, you may destabilize them by trying to trench behind them.  Installing veneer ties into dry-stacked stone may be pretty risky – I would not want to be the one installing anchors between all that rock and the hard place behind it.


Nels Roselund, SE

South San Gabriel, CA


From: Dennis S. Wish, PE [mailto:dennis.wish(--nospam--at)]
Sent: Tuesday, March 15, 2005 5:04 PM
To: seaint(--nospam--at)
Subject: Road Repair Advice Needed


I have a client who is purchasing two lots for two custom  homes in the foothills of a mountain overlooking a golf course in Palm Springs. There is an old road about 300 feet long that makes the climb to the property; one side of the road is a rock hillside cut for the road years ago. The other side that is seen from below is simply stacked stone slabs retaining soil. The maximum height of the unsupported roadway (or that which is supported by the gravity wall of stacked stone slabs) was determined by the geotechnical engineer to be insufficient for heavy utility vehicles such as a fire truck that must be allowed access to the lots above.
I have not seen the road but the City is adamant about keeping the appearance of the stone wall. I discussed some choices with soil engineer but will not have any design values until sometime next week. His thoughts followed mine, but these seem rather expensive solutions for access to the two custom home lots:

1. Install Soldier Piles behind the existing stacked rock that would need to be drilled at the most, ten feet into bedrock and would be tied by one or more beams that would help retain and support the roadway. The potential down side is that the coring of the soldier piles may "blow out" the stone wall in which case it would need to be repaired.
2. design a retaining wall behind the existing stone wall that sets on embedded piles and grade beams and then work some veneer ties into the stacked stone. Again, the piles would be about ten feet deep into bedrock at this time and the wall would need to transfer rotation to the grade beam and top of piles.
3. Trench behind the existing stacked stone and shore sufficiently to allow a conventional "L" shaped retaining wall to be constructed, backfill and compact. This would avoid the need to core piles but would require the removal of more soil to allow the design of a more conventional wall with an adjacent surcharge for the road and heavy trucks. The stone would be veneered tied if possible and the face of the new wall would be constructed close enough to flow in a grout or mortar to help tie the stone to the wall.

The owner prefers number 3 above as the soldier piles would be very expensive for a 300-foot stretch of road.

There must be some other ideas out there. I thought we might be able to work in a corrugated sheet "pile" idea and then tie it back to the hillside bedrock using rock anchors.

Can anyone give me some ideas to search out that might help me make an intelligent choice as to the most economical solution to the problem?

Dennis S. Wish, PE


Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant


760.564.0884 (office - fax)

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