excavation question for contractors

[tsek]

Let's say an excavation is proposed. Prior to excavating, secant pile walls are installed to create a bathtub. Proposed depth of excavation is 30'. Water table is at 10' depth, but dewatering with wellpoints is expected. The excavation will be performed in the middle of a multi-lane local road. The excavation will be 55' long, measured in the direction of traffic.

What type(s) of excavator would you use? How much time would it take you if the cut took up one lane only? What if it took up three lanes?

Please spell out the sub-tasks. This is the excavation portion only. No dewatering, no installing support of excavation.

Thanks.
Kevin

 

[dicksewerrat]

One with a 100 ft extendable boom on it.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[tsek]

Please clarify? Dredge line with 100-ft boom? What's the expected cycle time?

 

[SlideRuleEra]

Crawler crane, using a clam shell bucket. This equipment can dig straight down and deposit the equipment easily into dump trucks or a stockpile for removal from the site.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[tsek]

Sliderule, thanks for the reply. I'm estimating that the crane would be able to carry up to 13-CF (3.9-CY) of soil without tipping over. What do you think is an approximate cycle time for lowering, excavating, raising, rotating, unloading, and repositioning altogether?

Thanks,
Kevin

 

[SlideRuleEra]

Kevin - IMHO, don't go with a maximum sized bucket. You don't want the crane to be operating anywhere near its allowable tipping load. The force required for the bucket to break the soil free and get it moving can easily exceed the soil dead weight. The force to do this is not predictable, either. Also a 4 CY bucket won't be light in weight, even empty. A 1 CY bucket, or so, should be well sized for what you have described. You need the flexibility that a smaller bucket offers to get into corners, clean out the final part of the excavation, etc. Also, a smaller bucket will cycle faster than a maxed out size that has to be "treated with kid glove" to keep it from overloading the crane. A good crane operator with properly matched equipment excavating favorable soil can probably make 2 or 3 cycles per minute.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[SlideRuleEra]

I need to amplify my estimated cycle rate. Two to three cycles per minute is maximum; that is when the excavation is shallow and the crane has to swing only a short arc, say 30 degrees, to unload into a stockpile.

As the excavation gets deeper, wet soil is more likely to resist digging, if the crane has to swing full arc (180 degrees) to unload (carefully) into dump trucks, the rate will slow down significantly. Maybe 1 cycle per minute.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[cvg]

ramp down and use a track hoe. a cat 385 long boom could do it with max digging depth of over 38 feet. it can dig a max vertical wall of just under 30 feet. buckets up to 6 cubic yards. cycle times would be less than a clamshell

http://s7d2.scene7.com/is/content/Caterpillar/C400866

 

[tsek]

Would it fit into an urban area? See photos. Better production rate is great. Sliderule, what is your thought on this?

Thanks.

 

[SlideRuleEra]

tsek - I see that this project has limited working space. Working totally from the surface (whether with a crane or a long-reach track hoe) has definite schedule advantages - this means larger equipment. With the other constraints that appear in the photo, I would NOT focus ONLY on the speed of the excavating equipment. The essential question for you is:

Does traffic have to be maintained?

The answer will determine whether large, speedy equipment is practical for this project.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[tsek]

Doing the math, it's not going to take more than 2 days to perform the excavation anyway. So I just went with the conservative 2 days.

 

[dicksewerrat]

It will take 2 days to layout the project and set up traffic control. 5 days to get dewatering set up and running. Probably 5 days to set piling and 5 more days to dig. Provided every thing works perfectly. However, you are in an urban area that has many things buried that few people know exist underground. this will IMHO take 35 to 45 days start to finish if there is only 2 days to install whatever goes in the hole.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[miningman]

Once again , old age and experience seems to trump youthful optimism , and dare I say it, unrealistic computer modelling

 

[tsek]

I appreciate all the responses, but you guys jumped to conclusions too quickly on my youthful optimism (not trying to sound defensive). I actually estimated a total of 76 days (including 9 days of building the structure), so 65 days to complete the excavation. There were 41 secant piles, so estimated 42 days to install all of them assuming 10-12 hour shifts. 2 days to relocate utililties, 1 day to jackhammer the concrete island (of course performed prior to pile installation). 20 days to perform jet grouting, to tie in with existing structure, 5 days overlap equals 15 extra days. 2 days to set up well point system, 2 more days to dewater. 3 days to excavate accounting for swell and crane shift. This is assuming zero equipment breakdowns, and no thunderstorms or high wind.

Thanks for all the input, the schedule has already been submitted.

 

[dicksewerrat]

OK. would have been good to include that info first. Good luck.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[tsek]

Dicksewerrat, I couldn't tell by looking at your message. Do you mean that you disagree strongly with my estimate, or were you just wishing me luck?

 

[bridgebuster]

Kevin.

What are you building, a sewer for DDC? Out of curiosity, is the city giving you long term lane closures of the usual daytime & nighttime hours?

Two days to move an oil static line might be optimistic.

 

[bridgebuster]

Forgot one thing: did you factor in time for the TA review? Hopefully their inspector shows up when you need him.

 

[dicksewerrat]

I was actually wishing you good luck. I used to dig up urban roads. My stress level almost bottomed out when I got out of that work. But when you post, give us all the info you have. you will get better, quicker answers.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com