Debris impact on wall
Debris impact on wall
(OP)
Hi all -
Looking to see if anyone has a method that would help with assessing how much impact enery is gerated and potentially transferred through a compacted bund of soil. Client is looking to build into th etow of teh bund and it'd be great to provide an indication on what the structural engineer would need to consider as some sort of impact load on their 1.5m high concrete wall.
Sketch attached, not to scale though. Previous assessment with respect to the bund determines that the bund is high enough to collect debris behind it.
Landslip would be fine grained, not rock fall. Maybe 2m high, and relatively fluidised given high sensitivity of the ground.
The filling has an undrained shear strength of 75kPa.
Thanks in advance
Looking to see if anyone has a method that would help with assessing how much impact enery is gerated and potentially transferred through a compacted bund of soil. Client is looking to build into th etow of teh bund and it'd be great to provide an indication on what the structural engineer would need to consider as some sort of impact load on their 1.5m high concrete wall.
Sketch attached, not to scale though. Previous assessment with respect to the bund determines that the bund is high enough to collect debris behind it.
Landslip would be fine grained, not rock fall. Maybe 2m high, and relatively fluidised given high sensitivity of the ground.
The filling has an undrained shear strength of 75kPa.
Thanks in advance
RE: Debris impact on wall
1) If you trust the design of the berm to be adequate, you could just make sure that the new foundation could support at least the strength lost by the excavated soil plus the pressure of the soil on the berm side of the foundation. I would think that given a normal concrete foundation and its supported weight that it wouldn't need to be much larger than a normal retaining wall type of application.
2) Otherwise you need to find an equation that gives you the energy of impact of a debris flow. You will have to assume a flow cross-section (height and length), speed, mass and impact angle. These things are very speculative, and that is why if you can go back to the design of the berm that should give some clues. Was any analysis used in the berm design?
RE: Debris impact on wall
RE: Debris impact on wall
RE: Debris impact on wall
RE: Debris impact on wall
The questions are difficult in that several methods have been used (older & newer) yet all require validation, usually backfiguring from events and the associated failures. The geology, topography, debris source (surface debris, slope failure or rockfall), climate & storm patterns have enormous influences on the catastrophes. What I am going to provide is some guidance from regions of Western Colorado, USA. Much of the following has undergone little change from the mid 1970's. The real changes have been much better mapping and definition of potential events. You MUST Understand your situation.
Debris Flow Hazard means low, moderate and severe debris flow activity, to include mudflows.
• Low debris flow hazard poses possible minor damage to structures and slight risk to life. Mitigation is usually limited to site grading and slight elevation of the building foundation.
• Moderate debris flow hazard poses possible moderate damage to structures and risk to life. The building site location, relative to the Debris Flow Feature determines the mitigation criteria, as described in Hazard Mitigation. Mitigation is recommended and major cleanup is probable.
• Severe debris flow hazard poses possible severe damage to structures and risk to life.. The building site location, relative to the Debris Flow Feature, determines the necessary mitigation criteria, as described in Hazard Mitigation, (3)a. The building site or parcel may include areas which should be avoided for some types of construction or in extreme circumstances, placed in a Hazard Avoidance District.
In the case of moderate to severe debris flow hazard the following criteria is applied:
a. Within six hundred (600) feet of gully mouths, as shown on the geologic hazards mapping, the following performance specifications shall be met unless a report by a qualified geologist and a qualified engineer which provides computations supporting other performance specifications for the specific area in question. Protection walls or constructions may be implemented which are separate from the building walls and meet the appropriate design criteria.
1. Within three hundred (300) feet (90 m) of gully mouths, all buildings shall have the uphill wall designed and constructed to resist a horizontal force of 900/lbs/ft2 (43kPa) to a height of six (6) feet above undisturbed or finished ground level, whichever is higher.
2. Between three hundred (300) and six hundred (600) feet (90-180 m) from gully mouths, all buildings shall have the uphill wall designed and constructed to resist a horizontal force of 400/lbs/ft2 (19kPa), to double the anticipated debris height ( six [6] feet maximum) above the undisturbed or finished ground level, whichever is higher.
3. The uphill wall shall be considered that wall most likely vulnerable, in terms of direction, to debris flow.
Building design which places sleeping quarters on the downhill or less vulnerable side is recommended within hazard mitigation districts with a high Hazard Zone designation.
RE: Debris impact on wall
RE: Debris impact on wall
As I noted above ' You MUST Understand your situation'
There are areas in Western Colorado which I would not commit to 'report values', far too little historic information to properly define the events.