Compaction

[kxa]

Is there any other way of compacting the back fill behind bulkhead w/o dewatering

 

[dgillette]

Geotechnical engineers always answer a question with a question.

What kind of material? Working below standing water, or just in wet conditions with wet fill? What degree of compaction do you need? What size of space are you working in? How big is your budget for testing and analysis?

The real answer to almost any geotechnical question is "Well, that depends..."

 

[kxa]

The steel bulkhead is being installed to replace existing timber one. This in the bay with water about 10' deep. the ground is being sloped back for about 15' and then backfiled with sany material. finally the surface will be paved with asphalt.Top of bulkhead will be about 4' above MHWL.

 

[dgillette]

With sandy material (or silty or clayey), it's pretty hard to accomplish much compaction in saturated conditions. The pore water just can't escape fast enough. You probably can't tolerate a whole lot of settlement under the pavement (aggravated by wave loading), or just wait a couple years and refill the settled areas. I haven't got any good tricks up my sleeve, without going to clean +3/8" gravel or something that would be very pervious. Others may have more experience with this particular kind of project, but I don't see any way around unwatering the area to backfill. Good luck.

 

[USGeotech]

Many years ago I was involved with the construction of a new bulkhead in Vancouver. The bulkhead was backfilled with silty sand and was compacted using a vibratory Terraprobe.

 

[dgillette]

What kind of density were you able to get with the Terraprobe?

 

[Ron]

dgillette....I've been involved in a couple of Terraprobe projects. The last was the expansion of the Nassau harbor and cruise ship berths in the Bahamas. According to field reports, the increase in density of the material was about 10 percent. It works well, particularly in loose to medium dense sands.

 

[dgillette]

With the Terraprobe do you have to design the wall for much higher pore pressures than the usual? I didn't mention stone columns because I figured he would destroy any reasonably dimensioned wall in the process.

 

[Ron]

The wall needs to handle the liquifaction during the Terraprobe process, but after that just the increased density. Poor pressures should equilibrate without much difficulty, assuming granular material. If not granular the Terraprobe will not be nearly as effective, in my opinion.