Slurry Walls / Deep Soil Mixing Criteria for Offset 1

[InDepth]

For Slurry Walls and Deep Soil Mixing, is there a technical guideline or rules of thumb for selecting a) offsets from existing structures and b) panel sizes (width, not thickness). I have three cases, and I assume that the criteria will be different for each.

1) Continous footings
2) Isolated footings
3) Friction pile foundations


What I am after is preventing collapse of the excavation for the panel when it is surcharged by building loads. For continous footings I would assume there is greater redundancy because the load can redistribute (either side of panel excavation). For friction piles, I'm worried that if you get too close you loose friction capacity.

In my mind, the criteria would be based on the lateral load that a bentonite or polymer fluid (and concrete later) can exert laterally on the side of the excavation.

i.e. Soil pressure + Surcharge pressure <= Polymer/Bentonite Fluid pressure

......in order to prevent collapse of excavation and/or loss of bearing/friction of foundations adjacent.

Any insight would help. I've read papers and talked to contractors installing these system 1-3 feet away from foundations, and I'm looking for logical reasoning.

 

[InDepth]

Just an update:

It appears that for slurry walls, the stability of the trench is dependent on a) Specific Gravity of the bentonite (1.03-1.5) and b) a slope stability analysis. There also appears to be methods to account for arching of soil around the panel.

Another interesting aspect is the formation of a filter cake on the edges of the trench and the permeability of this filter cake. i.e. if the permeability is high, the actual fluid pressure exerted to conteract soil pressure and surcharge pressure is lower.

The following appear to have good info:
"Slurry Walls as Structural Systems" by Xanthakos
Construction Dewatering and Groundwater Control by Powers
ASCE also has a few journal papers of interest.

 

[BigHarvey]

InDepth

Obviously things will be better with deep soil mixing than with diaphragm wall just because there is no soil extraction with the first method.

The most important parameter is the quality of the adjacent structure and it ability to sustain settlements and more particularly differential settlements.

There is nothing else to cope with this situation than reduce the length of some of the panels ( shortened to single bites of 2.8 m ) and organize the construction sequence strategically to "block" the adjacent foundations.

If this not enough you can think of underpinning the shallow foundations with jet grouting.

There is no theoretical approach of this kind of problem but you need an experienced D-wall contractor to tackle it.

 

[BigHarvey]

I forgot one point : mud density cannot be 1.5 ( it wouldn't be mud ). It is between 1.03 and 1.05 for new mud and it can reach 1.2 with hydraulic cutters during excavation.