Excavation Support û Secant Wall

[GeoPerson]

I have two jobs that required shoring and sheeting. The 1st job is along the river and requires a 20 feet of excavations. The sheeting system will have to penetrate through till (N>50). The preliminary analysis shows that the minimum length of sheeting is 32. At 30 feet mudstone bedrock is encountered as well. I don’t think sheeting can be used or can be driven through the till. I’m thinking of a Secant Wall (cofferdams). The client is also requesting to take a look into soil cement mixing wall to act as a cutoff wall as well. What reference I could use to design these systems.

The 2nd job is for basement excavation and it’s surrounded by buildings and rail roads. drilled system is a must. What kind of system I should use in this situation where groundwater is an issue.

 

[jdonville]

Geoperson,

You will have to drill in your shoring for the first job. You may wish to consider a jet-grout cutoff in place of soil-cement mixing. In any event, you will have to ensure that windows between your piles are kept to a minimum. With a 20-foot excavation with only 10 feet of embedment, I suspect you might need some sort of lateral restraint (tieback, anchor, etc.) in addition to the plain wall section unless you key into the rock with the toe of you pilings.

In both cases, you don't really describe the geotechnical and hydraulic setting very well. Give us a better description of the soil and water conditions at each job.

Jeff

 

[GeoPerson]

Jdonvill,
The geotechnical Info for the job #1 is as follow:
0-10’ Fill/ 10'-22' Till (cf SAND, some Silt, some Gravel)/ 22'-30' weathered rock. Silty CLAY, some gravel, little Sand/ 30’ mudstone bedrock. Groundwater is at 10'. The river runs along the excavation and therefore I can’t use tieback or anchors.
The client for the Job#2 is talking about using Soldier Beam and Lagging system. I haven't got the geo report yet, but I know the GW is shallower than the bottom of the excavation.

I’m planning on using Secant wall for job#1, but if there is anyone knows of a good reference to use to guide me through the calc and specs.

 

[PEinc]

GeoPerson,

Call Moretrench in Rockaway, NJ (973-627-2100). They do dewatering, ground freezing, grouting, sheeting, tieback anchors, underpinning, etc.