## Rate of water rise in drilled shaft versus adjacent boring

## Rate of water rise in drilled shaft versus adjacent boring

(OP)

Question:

If a 6" diameter soil boring 135' deep that is generally dry during excavation down to rock has water rise up to 35' below grade in 8 hours, how fast would the water rise up if a 4' diameter drilled shaft is installed at the same location? Would the rate of rise be the less, the same or greater?

The site conditions are stratified clays and sands with 40' of shale at base of shaft. For a 1' layer of permeable sand within this overburden stratigraphy, the exposed wall area to liberate groundwater is 1.58 sq ft. The wall area in the 4' diameter shaft is 8 times the area of the 6" boring (12.56 sq ft).

Please furnish an authoritative reference such as an engineering journal citation or textbook to validate their answer.

Thank you,

Len

If a 6" diameter soil boring 135' deep that is generally dry during excavation down to rock has water rise up to 35' below grade in 8 hours, how fast would the water rise up if a 4' diameter drilled shaft is installed at the same location? Would the rate of rise be the less, the same or greater?

The site conditions are stratified clays and sands with 40' of shale at base of shaft. For a 1' layer of permeable sand within this overburden stratigraphy, the exposed wall area to liberate groundwater is 1.58 sq ft. The wall area in the 4' diameter shaft is 8 times the area of the 6" boring (12.56 sq ft).

Please furnish an authoritative reference such as an engineering journal citation or textbook to validate their answer.

Thank you,

Len

## RE: Rate of water rise in drilled shaft versus adjacent boring

Source: formulas for volume and surface area of a cylinder.

## RE: Rate of water rise in drilled shaft versus adjacent boring

## RE: Rate of water rise in drilled shaft versus adjacent boring

Did the water level rise at a constant rate (12.5 ft/hr) over an elapsed time of 8 hours?

Eight hours after the "start" water was 35 ft.below grade?

(Both rate of rise and time to reach 35 ft. below grade unknown. Also unknown, did the water rise at a constant rate or did it vary - likely slow down)

It makes a difference.

www.SlideRuleEra.net

## RE: Rate of water rise in drilled shaft versus adjacent boring

Question: Given the flow observed from the rock that created the rise in the 6" boring, would the water rise in 4' shaft exceed the 0.25 inch per minute criteria?

## RE: Rate of water rise in drilled shaft versus adjacent boring

Do the math:

For the 6" boring:Total inflow volume known: 6" dia. x 100'

Elapsed time assumed: 8 hr.

Calculate Inflow rate in ft

^{3}/ minute.For the 4' shaft:Inflow rate of flow is assumed: 8 x (6" diameter inflow rate)

Using this inflow rate, calculate distance (inches) water will rise in the 4' shaft in one minute. This is the "answer"... for the

assumeddata, which is not necessarily realistic.www.SlideRuleEra.net

## RE: Rate of water rise in drilled shaft versus adjacent boring

## RE: Rate of water rise in drilled shaft versus adjacent boring