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Bore holes and Saturation Zone

Beware of the gusher!

Test Boring

The elevation of a water table is indicated by the elevation at which, free water rises in a test hole. Consequently, it should be realized that it takes time for the water to accumulate in the hole. The amount of time depends on the rate of flow, of the groundwater from the adjacent soils. If the soil is pervious; the water in the test hole will rise to the water table within a very short time; but if it is relatively impervious, considerable time may be required for the water to rise to the true water-table elevation.

Don't get in a tizy

A good rule of thumb, is to allow the test hole to stand for 24 hours after the hole has been dug before the elevation of the water is measured. If the soil and the region of the water table is characteristically known to befreely pervious, this time-lag period is not necessary.

Big Surprise

If, while drilling a test bore and you make an unfortunate discovery like an artisan well. "Oh Boy," your day has just begun, and mandatory overtime for everybody; this is a horse of a different color, because the flow must be stopped and the hole plugged. It gets a little hairy at this point. A helical auger may be rotated in reverse, and soil packed back into the hole. If this is not possible or if flow continues; immediately after withdrawing the auger a bentonite clay plug may be driven in with a timber, which then is cemented with Portland cement. If the flow continues it will draw down the ground water level,dry up wells, and cause surface erosion, ponding, and flooding. The worst case scenario is, a rapidly flowing uncased artisan well that will quickly erode a gaping hole that may be exceedingly difficult to plug.

Even when there is no artisan pressure, boring's in sand below the aquifer tend to cave in if the drilling tools are withdrawn, and may even cave in during the drilling operation, oweing this unfortunate circumstance to seepage of water into the drill hole, which causes a "quick" condition. This may impede penetration of the drill and result in excavation of an underground cavern. The unexpected collapse of such caverns may endanger near by foundations or the driller.

Adjustments to the Water table

A water table can be lowered artificially by providing an outlet for the groundwater at a level below its natural outlet by means of open ditches or by tile under-drains. It must be realized however, that the new water table will not be lowered to the new elevation of the drains themselves, except right in the vicinity of the drains, because the natural tendency for a water table to rise as the distance from an outlet or point of release increases. The steepness of the water table in the vicinity of the drain depends on the characteristics of the soil, being relatively flat in a permeable soil and relatively steep in a impermeable soil. Thanks for the comments. Have a good day!!

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Posted in Drilling Equipment, OSHA, Safety, Subsurface Investigation, water table.

Tagged with artesian, ground water level, watertable, worst case scenario.

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By Keith Bray – February 18, 2010

Just tell me How Much

OSHA

Specific Excavation Requirements - 1926.651

Part Number: 1926
Part Title: Safety and Health Regulation for Construction
Sub-part: P
Sub-part Title: Excavations
Standard Number: 1926.651
Title: Specific Excavation Requirements

I'm not going to list the whole regulation, but here are some you need to know prior to excavating, and please do research the rest.

1926.651(a) Surface encumbrances; (b)(1) Estimate locations of utility installations; (b)(2) Contact utility companies; (b)(3) Determine safe acceptable distance from utilities; (b)(4) When excavation is open protect underground installations; (c) Access and Egress-; (c)(1) Structural ramps; (c)(1)(i) Access and Egress ramps shall be designed by a competent person; (c)(1)(ii) Two or more structural members must be connected to prevent displacement; (c)(1)(iii) Structural members used for ramps and runways shall be of uniform thickness; (c)(1)(iv) Cleats and other attachments for ramps shall be attached in a manner to prevent tripping.

For a start check these OSHA regulations. We will look some more later.

In October of 2008 thru September 2009 OSHA was giving out citations like passing out candy! This standard is Excavations

Standard 19260651;Cited 471; Number of Inspections 283; Penalty 518279.

(To figure the average penalty amount per standard cited, use this example.)

If #cited=120 and the inspections=40, the percentage of cited inspection=3

If the penalty is 60,000 average. The current penalty amount per standard cited is $500 (120 x 500 = 60,000).

* Here are some good OSHA Standards and Regulations that cover excavations

Soil Classification - 1926 Sub-part P App A

Part Number: 1926
Part Title: Safety and Health Regulation for Construction
Sub-part: P
Sub-part Title: Excavations
Standard Number: 1926 Sub-part P App A
Title: Soil Classification

And

Sloping and Benching - 1926 Sub-part P App B

Part Number: 1926
Part Title: Safety and Health Regulation for Construction
Sub-part: P
Sub-part Title: Excavations
Standard Number: 1926 Sub-part P App B
Title: Sloping and Benching

We will look at these.

The following table is taken from this standard and it might do us some good to take a quick look at it.

Maximum Allowable Slope

Soil or Rock Type Maximum allowable slope (H:V(1) For Excavations less than 20 feet deep

Stable Rock Verticle (90 Degree)

Type A (2) 3/4 : 1 (53 Degree)

Type B 1 : 1 (45 Degree)

Type C 1 1/2 : 1 (34 Degree)

Before the excavation begins, the cost for earth removal must be factored in the equation, this estimate should be based on cubic yards of materials to be dug and hauled away. Your building plans will show the structure and the area that it is occupied by and the depth the excavation must be carried to. Because additional space is required to work around the outside of the building or forms in an excavation, a line is drawn around this additional space requirement and dug out from this line. The distance is usually two feet to the outside of the forms or building line. This line is referred to as the pay-line. The excavation contractor is paid to excavate material to this line.

When the soil is taken from its compacted position and broken up, as in excavating, it increases in bulk. This increase is called soil swell.The volume of material to be removed from the site must therefore be increased by a percentage depending upon the type of material to be moved. Most soils will swell 20% and 50%.

Soil swell percentages for common soils

Soil type Percentage of swell from Compact State

Silt 20%

Clay 25%

Sand and gravel 50%

Loam 25%

Stone 50%

If the soil is cohesive enough or if some means of supporting the sides of the excavation are to be used, the compacted volume to be removed is simply a matter of length X width X depth. But for loose, sliding soils, the excavation must have sloping sides, usually with a 1 : 1 slope. This fact must be taken into account when estimating the volume of materials to be removed.

For figuring out the slope there is another equation for that, and that I have to figured out. And as it goes If you don't use it you loose it. I've been a stranger to my mathematical genius side for some time and I need to do some refreshing, so I'll get back to you with that, once I re familiarize myself and get reacquainted.