## Trenching for pipelines - Settlement Calculation

## Trenching for pipelines - Settlement Calculation

(OP)

Could someone kindly let me know one of the best practical codes/manuals to calculate the settlement due to well point de-watering in soft silty sandy soils.

Trenching is for 20 m piles to a depth of approximately 4 m at relatively silt-sand soils.

Trench width is 2 m at the bottom. The tench sides are supported by steel sheeting and a cage.

They are using well points to 6 m at one side of the trench to de-water the area and avoid sand boil at the bottom of trench.

As the engineer, I want to calculate the settlement due to groundwater lowering by well point.

I would appreciate guidance on the above.

Trenching is for 20 m piles to a depth of approximately 4 m at relatively silt-sand soils.

Trench width is 2 m at the bottom. The tench sides are supported by steel sheeting and a cage.

They are using well points to 6 m at one side of the trench to de-water the area and avoid sand boil at the bottom of trench.

As the engineer, I want to calculate the settlement due to groundwater lowering by well point.

I would appreciate guidance on the above.

## RE: Trenching for pipelines - Settlement Calculation

pipesnot piles. Sorry for typo.## RE: Trenching for pipelines - Settlement Calculation

dewatering settlement calculation## RE: Trenching for pipelines - Settlement Calculation

That chart was uploaded to a former topic. Today a search for "Hough" and some other key words came up with it. I'll attach a link with some on my former input comments. Those charts-then will show up if one opens those links shown. Using that method the spread sheet creations are significantly simplified.

http://www.eng-tips.com/viewthread.cfm?qid=395862

It's not a code or manual, but once created, it would serve for most of these sites.

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

Herer is one version. The reason for the "fixed" in the title apparently was some error in setting up one section. the broad column B was only for being to put the text there. I'd proof it by following the vatious steps. Note the place for outputting some basic data is way down the sheet. I have not used this (of similar sheets) in a few years now. The units are English but I think you can change over to metric. Maybe input in English and change your answer to metric.

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

The depression cone in the example excel file is arbitrary. Can the slope of the cone sides be estimated - without field pumping test? Thank you again for your valuable feedback.

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

In this case, your comps assume that settlement from soil below 22 ft. is not expected (Rock, dense soil, etc.). In a soil of infinte depth, we usually stop the comps when added pressure is 1`0% of existing. For submerged unit weight this goes a long ways down.

Observations of settlement from a loaded embankment in California showed the Hough supplied chart method probably did not allow for submergence. They observed twice the measured settlements compared to non saturated soil. So, I'd simply use half the value of C for saturated soil below the dewatered depth.

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

I didn't use all the old parts.

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

I think the bearing coefficient is the mail drive in settlement calculation. Yet its estimation is very rough and I did not quite understood how you obtained Houg these values in your spreadsheet.

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation

## RE: Trenching for pipelines - Settlement Calculation