ge 343 subsurface exploration instructional objectives ch ...web.mst.edu/~norbert/ge5443/class...

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GE 343 SUBSURFACE EXPLORATIONCH 6 – Drilling in Overburden

Text Ch. 7.

Dr. Norbert H. Maerz

Missouri University of Science and Technology

(573) 341-6714

[email protected]

Instructional Objectives

1. List the rules of thumb for boring spacing and depths.

2. Explain the requirements for locating underground services before you dig.

3. Select and justify a drilling method for a given design use and geological scenario.

4. Select and justify a sampling method and strategy for a given design use and geological scenario.

5. Select and justify an insitu testing method and strategy for a given design use and geological scenario.

Exploration Program

• Evaluate the variety of methods and procedures available

• Depends on the type of construction and the geological conditions encountered

AASHTO Man. Sub. Inv.

Exploration Plan

1. Key locations to clarify the geological interpretation as a whole.

2. Key location that could lead to relocation or redesign.

3. Bridges or other structures.4. Deep cuts and high embankments.5. Areas of engineering difficulty or complicated

ground surface.6. Off-line investigations for geological hazards or

borrow surveys.


Exploration Plan

7. Points of Interpolation (function of complexity of the geology).

8. Least expensive methods of investigation should be used first. These may provide sufficient information by themselves, or will indicate where more detailed and expensive investigations may be required.

9. In areas of intense, complex, or expensive construction activity, it may be necessary to conduct very sophisticated and expensive which include horizontal boring, inspection shafts or pilot tunnels.


Types of Borings

1. Pilot borings

2. Control borings

3. Verification borings


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Exploration Spacing

1. Narrow right of ways 150 m2. Uniform conditions for subgrade 60-90

m, up to 300 m in the Midwest3. With increasing complexity 60-90 m4. Highly erratic critical foundations 8-15 m5. High embankments and deep cuts 60 m,

in compressible materials 30 m6. Specific structure borings, 30 m or at

each end of the structure


Exploration Spacing

7. Critical Areas (irregular bedrock, bogs, caverns 15 m grid

8. Tunnels: soft ground adverse conditions 15-30 m, favorable conditions 90-150 m

9. Tunnels: mixed-face adverse conditions 8-15 m, favorable conditions 15-23 m

10.Tunnels: hard ground adverse conditions 15-60 m, favorable conditions 150-300 m


Exploration Depths

1. Subgrade borings 2-3 meters below profile elevation

2. High embankments, 2-4 times the height of the embankment

3. Excavations > 5 m, 2 times depth

4. Specific structure borings- to depth of “where net increase in soil stress due to structural load is less than 10 of effective stress. Minimum 10 m below footing (3 m into rock) AASHTO Man. Sub. Inv.

Exploration Depths

5. Critical Areas – deep enough to evaluate their extent

6. Tunnel borings: 1 to 1.5 time tunnel diameter below grade. If alignment is subject to modifications, then 2 to 3 times


Sampling Requirements

• Every change in soil strata

• At interval not to exceed 1.5 m

• Rock core continuously

Right of Way, Permits, Utilities

• Permission from property owners, preferably written

• Formalized permits for certain access

• Underground utilities

• Overhead utilities


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1-800-Dig-Rite

http://mo1call.com/http://mo1call.com/excavmanual.pdf

Color codes

http://mo1call.com/codes_index.php

Soil Drilling Methods

• Displacement boring

• Wash boring

• Percussive drilling (rock)

• Rotary drilling (rock)

• Auger boring

• Sonic Drilling


Displacement BoringMethod where a piston or plug-type sampler is forced into the soil to the

desired depth, displacing all the material on its path. Upon reaching the desired depth, the sampler is retracted and "grabs' a sample on its way back to the surface.

• PROS: – Does not require heavy equipment (by hand or lightweight equipment); – Clean method for shallow well installation;

• CONS: – Method limited to shallow depths; – Method limited to soft soils and boulder, cobble-free zones; – Not efficient if necessary to install several wells; – Practical limitation up to ~ 2" diameter sampler. – Similar to the above method is "Direct Push Technology" or DPT. A

common trade name is GeoProbe. DPT does not require heavy equipment, most units are pickup mounted or ATV mounted for easy accessibility.

http://technology.infomine.com/hydromine/topics/Site_Assessment/Drilling.asp#b1

Wash Borings


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Continuous Flight Augers

• Construction Augers

• Solid stem

• Hollow stem

• Truck mounted

• Track mounted


Construction Auger

Solid Stem Continuous Flight Augers

FHWA NHI-01-031 AASHTO Man. Sub. Inv.

Solid-stem augerMethod consists of drilling a continuous helix into the ground. The

torque is provided by a top drive auger drilling machine, which permits both downward push and retraction. Individual flights are normally 5 feet long. Different drill bits can be attached to the bottom of the auger to meet the formation requirement, which cut a hole ~10 % greater in diameter than the diameter of the auger.

• PROS:– Rapid and low-cost drilling in clayey formations; – Clean method, does not require circulation fluids; – No casing necessary where the formation is stable; – Allows collection of representative sample in semi-consolidated

formations; • CONS:

– Practical limitation to 24" diameter; – Inefficient in loose, sandy material (depends on the depth); – Inefficient below the water table (depends on the depth).


Hollow Stem Continuous

Flight Augers

FHWA NHI-01-031

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AASHTO Man. Sub. Inv. AASHTO Man. Sub. Inv.

Hollow-stem augerThis is a form of continuous-flight auger where the helices are wound around

and welded to a tubular center stem or axle. Drilling proceeds essentially as in solid-stem drilling. When the sections are connected however, the hollow-stem auger will present a smooth, uniform bore throughout its length thus providing an open, cased hole in which samplers can be used or well installation can be performed. Other drilling methods can also proceed within the hollow stem, which can be used as temporary casing to prevent caving.

• PROS: – Allows collection of uncontaminated sample in unconsolidated formation; – Can be used as temporary casing to prevent caving; – Relatively rapid, especially in clayey formations;

• CONS: – Ineffective through boulders; – Limited drilling in loose, granular soils, particularly below the water table

where sample recovery can be compromised; – Difficult to retrieve a sample in loose, granular soil because cuttings don't

always want to come to the surface. Samples must be collected with a split spoon or a continuous corer, either of which can provide excellent samples if done correctly;

– Limited to rather shallow depths.http://technology.infomine.com/hydromine/topics/Site_Assessment/Drilling.asp#b1

Hollow stem auger drilling

Hollow stem auger drilling Rotary Wash Boring

FHWA NHI-01-031

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Rotary Wash BoringThis method makes use of a constantly rotating bit to penetrate any type of

formation to depths that can exceed 1,000 feet. As drilling proceeds, cuttings are removed by a continuous circulation of fluid (either air or water based) that flows down inside the pipe string and up-hole along the annular space between the borehole walls and the pipe string. The penetration rate is often faster and the bit life longer when using air as compared with water based drilling fluids. A drag bit is normally used to penetrate unconsolidated to semi-consolidated sediments; while a cone-type or roller bit is used to drill consolidated rock.

• PROS: – High penetration rate; – Drilling operation requires a minimum amount of casing; – Rapid mobilization and demobilization;

• CONS: – Use of a drilling fluid, both in terms of sample contamination and water

management (in the case of water-based fluids and air injected by gasoline compressors);

– Circulation of drilling fluid may be lost in loose/coarse formations, hence making difficult to transport drill cuttings;

– Difficult to collect accurate samples, i.e. a sample from a discrete zone since the cuttings accumulate at surface around the rim of the borehole.


MODOT Rig

Sonic Drilling

• Faster speed (2-3x)

• Better core recovery

• Less waste (70-80%)

• Up to 12” core

• Up to 500’ deep

• No drilling mud

• Less collapse problems

http://www.wdcexploration.com/what_we_do/pdf/sonic_drilling_methodology.pdfhttp://www.slopeindicator.com/stories/sonicdrill.html

Boart Longyear rig

Rotosonic Video

http://www.prosoniccorp.com/PDF/HTML/Leader_in_Sonic_Drilling/

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Other “Tools”• Test pits (backhoe,

bulldozer)

• Hand dug test pits

• Hand Augers

• Portable powered auger

http://www.equipmentland.com/products/general/general330.shtml

AASHTO Man. Sub. Inv. Home Depot

Franklin

Horizontal Drilling

• Horizontal drilling in rock

• Horizontal drains and tiebacks

• Ditch Witch

• Coil tubing drilling

Ditch Witch

http://www.ditchwitch.com/dwcom/Product/ProductView/10883

Coil Tubing Drilling

http://www.canadian-wellsite.com/images/Photo%20Gallery/Calfrac_Coil_Unit.JPG

Drilling Fluids/Stabiliztion

• Water stabilization

• Drilling mud

• Air stabilization

• Casing stabilization

• Grout stabilization

• Freezing Stabilization

Soil Sampling

• Disturbed Samples– Wash sampling– Auger cuttings– Bulk– Modified California– Split spoon

• Undisturbed Samples– Thin walled sampling

tube (Shelby Tube)– Piston sampler – Bishop sand sampler– Continuous push

(Geoprobe)– Pitcher– Denison– Block– Core barrel (rock)

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Undisturbed Sampling

ASCEFHWA NHI-01-031

Split Spoon

FHWA NHI-01-031


Thin Walled Samplers/Shelby Tube

FHWA NHI-01-031

Sampling tools inside

augers

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Piston Samplers

FHWA NHI-01-031

Osterberg sampler


Mechanical StationaryPiston Sampler


Retractable Piston Sampler

Hydraulic Piston Sampler


Bishop Sand Sampler


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Pitcher Tube

FHWA NHI-01-031

Pitcher Tube

Sampler

Insitu Tests in Soil

FHWA NHI-01-031

Standard Penetration Test (STP)

FHWA NHI-01-031


• Driven by a 140 lb hammer dropping 30”, multiple blows (counts) = standard penetration test


• ADVANTAGES

– Obtain both a sample & a number

– Simple & Rugged

– Suitable in many soil types

– Can perform in weak rocks

– Available throughout the U.S.

• DISADVANTAGES

– Obtain both a sample & a number *

– Disturbed sample (index tests only)

– Crude number for analysis

– Not applicable in soft clays & silts

– High variability and uncertainty

FHWA NHI-01-031

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Standard Penetration Test (STP)videos

Cone Penetrometer Test (CPT)

FHWA NHI-01-031


FHWA NHI-01-031


FHWA NHI-01-031


• ADVANTAGES

– Fast and continuous profiling

– Economical and productive

– Results not operator-dependent

– Strong theoretical basis in interpretation

– Particularly suitable for soft soils

• DISADVANTAGES

– High capital investment

– Requires skilled operator to run

– Electronic drift, noise, and calibration

– No soil samples are obtained

– Unsuitable for gravel or boulder deposits

FHWA NHI-01-031

Flat Plate Dilatometer (DMT)

FHWA NHI-01-031

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FHWA NHI-01-031


• ADVANTAGES

– Simple and Robust

– Repeatable & Operator-Independent

– Quick and economical

• DISADVANTAGES

– Difficult to push in dense and hard materials

– Primarily relies on correlative relationships

– Need calibrations for local geologies

FHWA NHI-01-031

Pressuremeter Test (PMT)

FHWA NHI-01-031


FHWA NHI-01-031


• ADVANTAGES

– Theoretically sound in determination of soil parameters

– Tests larger zone of soil mass than other in-situ tests

– Develop complete σ-ε-τcurve.

• DISADVANTAGES

– Complicated procedures; requires high level of expertise in the field

– Time consuming and expensive (good day gives 6 to 8 complete tests)

– Delicate, easily damaged

FHWA NHI-01-031

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Vane Shear Test (VST)

FHWA NHI-01-031


FHWA NHI-01-031


• ADVANTAGES

– Assessment of undrained strength

– Simple test and equipment

– Measure in-situ clay sensitivity

– Long history of use in practice

• DISADVANTAGES

– Limited application to soft to stiff clays

– Slow and time-consuming

– Raw undrained strength needs (empirical ) correction

– Can be affected by sand lenses and seams

FHWA NHI-01-031

Downhole Geophysics

• ADVANTAGES

– Nondestructive and/or non-invasive

– Fast and economical testing

– Theoretical basis for interpretation

– Applicable to soils and rocks

• DISADVANTAGES

– No samples or direct physical penetration

– Models assumed for interpretation

– Affected by cemented layers or inclusions

– Results influenced by water, clay, & depth

FHWA NHI-01-031

Relevance of In-situ Tests to Different Soil Types

FHWA NHI-01-031

Obstructions


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Taking samples (extruding from Shelby Tube)

Cutting the

sample

Cutting a sample to testing size Testing a sample with Torvane

Sample Preservation

• Clearly, permanently and accurately labeled, and position recorded on drill log

• Sealed against moisture loss if appropriate

• Put in appropriate container/box

• Not left in unattended vehicles to freeze or over heat, taken to office/lab in a timely fashion


Waxing samples

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AASHTO Man. Sub. Inv.AASHTO Man Sub Inv

Boring Logs1. Description and classification of each

layer of soil

2. Depth for each

3. Depths and results of field tests

4. Informationa) Boring (hole) number

b) Start and finish date

c) Name of driller and logger

d) Elevation at top of hole

e) Depth of hole and reason for terminatioinAASHTO Man. Sub. Inv.

Boring Logsf. Diameter of any casing usedg. Size of hammer and free fall distanceh. Blows per 0.3 mi. Description and size of samplerj. Size of drive hammer and free fall distancek. Blow count (SPT) each 150 mm drive of

samplerl. Type of drilling machine usedm. Drilling time for each core runn. Sample recoveryo. Project identificationp. Client name


Boring Logs5. Notes regarding any other pertinent info

a) Dept of observed groundwater, time, conditions

b) Artesian condition

c) Obstructions

d) Drilling difficulties (caving, coring boulders, surging of sands, caverns)

e) Loss of circulation

f) Drilling mud and casing as needed

g) Odor of sample

6. Any other information requiredAASHTO Man. Sub. Inv.


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Borehole Sealing

• Cement grout from the bottom

• Bentonite

• Remove casing


Bad Actors

• Organic Soils• Normally consolidated clays• Metastable soils (loess, alluvial, mud

flows)• Caliche• Expansive soils• Loose granular soils• Sensitive clays


Bad Actors• Noxious or explosive gasses

• Slope movements

• Kettle holes

• Meander loops and cutoffs

• Artificial fill

• Karst

• Weathered shale

• Abandoned mines

• Frozen soils


SLIDE SHOW:Geological Environments

Fluvial / Breccia

Images from Monro and Wicander

Fluvial Variability


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Braided River / Point Bars


Oxbow Meanders


River Terrace / Delta


Aluvial Fans / Talus


Glacial Variability


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Till / Moraine Eskers


Esker Cross section of an esker

Outwash


Buried Valleys

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Beach Deposit


Raised beach ridges

Raised beach ridges (air photo)

Aolean: Desert Pavements


Desert Pavement


Salt Flats / Dunes


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Tropical Regions: Weathering Products


Drilling gone wrong

ge 343 subsurface exploration instructional objectives ch ...web.mst.edu/~norbert/ge5443/class...

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