Drilling and Sampling

Summary

Professor Kitch introduces geotechnical engineering webcasts focusing on soil drilling and sampling techniques. The presentation covers various drill rigs and methods like solid stem auger, hollow stem auger, wash boring, and casing methods. It explains how each technique operates, the types of soil they're suited for, and the process of obtaining and analyzing soil samples. Animations are used to illustrate subsurface activities, complementing photos and videos, and links to field operation videos are provided for further insight.

Takeaways

• 📚 Professor Kitch introduces a series of geotechnical engineering webcasts focusing on drilling and sampling techniques.
• 🔧 The presentation aims to complement visual materials by explaining what happens underground during drilling and sampling.
• 🚜 Different types of drill rigs are discussed, including large truck-mounted, off-road track-mounted, and trailer-mounted portable rigs, each suited for various site conditions.
• 🔩 The process of drilling involves positioning the rig, erecting the drilling boom, and using a drill head to apply torque and vertical thrust.
• ⚒️ The solid stem auger-open hole method is a simple technique using a continuous flight auger to bring soil cuttings to the surface, but it provides low-quality samples.
• 🧪 High-quality soil samples are collected by removing the auger and using a sampling tool, which is a hollow tube pushed into the soil to retrieve undisturbed samples.
• 🏗️ In stiff or dense soils, a heavy-walled sampler driven by a drop hammer is used instead of a push-type sampler.
• 🕳️ The hollow stem auger method is used in soils that cannot maintain an open hole, as it supports the hole with the auger stem while sampling.
• 💧 The rotary wash boring method uses a slurry or drilling mud to flush cuttings out of the hole, providing a quicker and deeper drilling method with added hydrostatic pressure for stability.
• 🛠️ The casing method involves driving a large diameter pipe into the ground to support the hole, allowing for sampling in unstable soil conditions.

Q & A

What is the main purpose of Professor Kitch's geotechnical engineering webcast?

The main purpose of the webcast is to provide an overview of common soil drilling and sampling techniques, supplementing presentations with animations to demonstrate what happens below the ground.

Why can't photos and videos of drilling and sampling operations show what is happening below ground?

Photos and videos can only show the equipment being used on the surface, but they cannot reveal the subsurface processes and interactions that occur during drilling and sampling.

What are the four most common drilling techniques mentioned in the presentation?

The four most common drilling techniques mentioned are: Solid stem auger-open hole method, Hollow stem auger method, Wash boring method, and the Casing method.

What types of drill rigs are commonly used in geotechnical engineering?

Commonly used drill rigs include large truck mounted rigs, off-road track mounted rigs, and trailer-mounted portable rigs.

How does the solid stem auger method with an open hole work?

In the solid stem auger method, a continuous flight auger with a cutting bit at the tip is rotated and pushed into the ground. The auger flights carry the loosened soil to the surface, and samples can be taken by replacing the auger bit with a sampling tool.

What are the limitations of the open hole method using a solid stem auger?

The open hole method is limited to situations where the soil is stiff or strong enough to remain open after the augers are removed. It is not suitable for soft soils or clean sands where the hole may squeeze or cave.

How does the hollow stem auger method differ from the solid stem auger method?

The hollow stem auger method uses a continuous flight auger with a retractable center bit. The auger remains in the ground to support the hole during sampling, allowing for the acquisition of samples through the hollow stem.

What is the rotary wash boring method, and how does it handle cuttings?

The rotary wash boring method uses a slurry or drilling mud to flush cuttings out of the hole. The mud is pumped down the drill stem, exits through the bit, and carries the cuttings to the surface, where they are separated from the mud in a holding tank.

What is the casing method, and how does it support the bore hole during sampling?

The casing method involves driving a large diameter pipe into the ground to support the hole. The hole is then cleaned using either auger or rotary wash methods, and samples can be taken from the undisturbed soil below the casing.

What factors influence the selection of a drilling method in geotechnical engineering?

The selection of a drilling method depends on factors such as the location and accessibility of the site, the type of project and its objectives, and the soil conditions.

Outlines

00:00

🔧 Introduction to Drilling and Sampling Techniques

Professor Kitch introduces a series of geotechnical engineering webcasts focusing on drilling and sampling. The presentation aims to provide an overview of common soil drilling and sampling techniques, complementing visual materials like photographs and videos. It emphasizes the importance of animations to illustrate subsurface activities that photos and videos cannot capture. The video will cover various drill rigs, four common drilling techniques (solid stem auger-open hole, hollow stem auger, wash boring, and casing method), and the basics of pushed and driven samplers. The rigs mentioned include large truck-mounted, off-road track-mounted, and trailer-mounted portable rigs, each suitable for different site conditions and methods. The process of drilling involves positioning the rig, erecting the drilling boom, and using a drill head to apply torque and vertical thrust. The open hole method with a solid stem continuous flight auger is detailed, explaining how soil cuttings are brought to the surface and can be collected as bulk samples, albeit of low quality due to disturbance and potential contamination.

05:03

🌐 Advanced Drilling Methods for Challenging Soil Conditions

This section discusses alternative drilling methods for soils that cannot maintain an open hole, such as soft clays or cohesionless sands. The hollow stem auger method is introduced as a solution for these conditions, where a hollow auger stem allows for sampling while supporting the hole. The rotary wash boring method is detailed, which uses a slurry or drilling mud to flush cuttings out of the hole, aided by special equipment like a holding tank, pump, and swivel head. This method offers advantages like quicker advancement and greater depths compared to auger borings, and also provides hydrostatic pressure to stabilize the hole. The casing method is also described, which involves driving a large diameter pipe into the ground to support the hole, allowing for sampling in undisturbed soil. The summary emphasizes that the choice of drilling method depends on site accessibility, project objectives, and soil conditions, and that samplers can be driven or pushed into the soil. The presentation concludes with references and links to additional online resources for further exploration of drilling and sampling techniques.

Keywords

💡Geotechnical Engineering

Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It involves the investigation, analysis, and improvement of soil and rock for engineering purposes. In the context of the video, geotechnical engineering is the overarching theme, as the presentation focuses on drilling and sampling techniques which are crucial for understanding soil conditions and for designing foundations and other earthworks.

💡Drilling

Drilling in geotechnical engineering refers to the process of making a hole in the ground to extract samples of soil or rock for analysis. It is a critical step in site investigation. The video script describes various drilling techniques such as solid stem auger, hollow stem auger, and rotary wash boring, each serving different purposes and soil conditions.

💡Sampling

Sampling in this context is the process of collecting soil or rock specimens from the ground for laboratory testing and analysis. The video emphasizes the importance of sampling for understanding subsurface conditions. It discusses different sampling methods, including push and driven samplers, which are used to retrieve undisturbed samples for accurate engineering assessments.

💡Solid Stem Auger

A solid stem auger is a drilling tool with continuous flights that run the full length of the auger. It is used for soil investigation in the open hole method. The script explains that the auger is rotated and pushed into the ground, with the cutting bit at the tip loosening soil and the flights carrying the cuttings to the surface. This method is simple but can be limited by soil conditions.

💡Hollow Stem Auger

A hollow stem auger is a variation of the solid stem auger where the stem is hollow, allowing for the use of a retractable center bit. This method is highlighted in the script as being useful in conditions where the soil might collapse or squeeze into the hole after the auger is removed, such as in soft clay or clean sands.

💡Wash Boring

Wash boring is a drilling method that uses a slurry or drilling mud to flush cuttings out of the hole instead of an auger. The script describes the use of a drilling mud, which is a mixture that increases the viscosity and helps carry the cuttings to the surface. This method is advantageous for its speed and ability to reach greater depths compared to auger borings.

💡Casing Method

The casing method involves driving a large diameter pipe into the ground to support the hole during sampling. As mentioned in the script, this method is used when soil conditions are unstable and might collapse without support. The casing prevents caving and allows for the collection of undisturbed samples.

💡Drill Rigs

Drill rigs are the machines used to perform drilling operations. The script outlines different types of drill rigs such as large truck-mounted rigs, off-road track-mounted rigs, and trailer-mounted portable rigs, each suited for different site conditions and drilling methods.

💡Drill Head

The drill head is the mechanism mounted on the drilling boom that performs the drilling and sampling operation. As described in the script, it provides two essential motions: torque to rotate the drill bit and vertical thrust to raise and lower the drill bits and other equipment.

💡Subsurface Conditions

Subsurface conditions refer to the physical and chemical properties of soil and rock beneath the ground surface. The video script discusses how drilling and sampling techniques are used to investigate these conditions, which are crucial for engineering design and construction projects.

💡Bulk Samples

Bulk samples are collected during the drilling process and consist of soil or rock cuttings brought to the surface. The script explains that while these samples can be collected, they are of lower quality because they are disturbed by the cutting process and can be contaminated by soil from upper layers.

Highlights

Introduction to drilling and sampling techniques in geotechnical engineering.

Use of animations to demonstrate subsurface activities during drilling.

Overview of common soil drilling and sampling techniques.

Types of drill rigs: Large truck mounted, off-road track mounted, and trailer mounted portable rigs.

Drilling process involves positioning the rig, erecting the drilling boom, and using a drill head.

Solid stem auger-open hole method for simple soil sampling.

Challenges with open hole method in soft or caving soils.

Hollow stem auger method to support bore holes during sampling.

Rotary wash boring method using slurry or drilling mud to flush cuttings.

Casing method for drilling in caving or squeezing conditions.

Importance of selecting the appropriate drilling method based on site conditions and project objectives.

Use of different samplers for various soil conditions.

Process of sampling with a push-type sampler in stiff or dense soils.

Use of a drop hammer for driving samplers in very stiff or dense soils.

Advantages of rotary wash boring for quick advancement and deep drilling.

Stabilizing the bore hole with drilling mud for moderate caving conditions.

Summary of the most common drilling and sampling methods and their applications.

Links to additional resources and videos for further learning.

Transcripts

Hello I'm Professor Kitch.

Welcome to my series of geotechnical engineering webcasts.

This web cast is an introduction to drilling and sampling.

The purpose of this presentation is to provide an overview of common soil drilling and sampling

techniques.

It is intended to supplement presentations using photographs or videos or drilling and

sampling operations.

While photos and videos of drilling and sample operations can show you equipment being used,

they can't show you what is going on below ground.

This presentation uses animations of drilling and sampling operations to demonstrate what

happens below the ground.

At the end of this video, I'll provide some links to other videos that show actually drilling

and sampling being done in the field.

The presentation will cover common types of drill rigs

The four most common drilling techniques Solid stem auger-open hole method

Hollow stem auger method Wash boring method

the casing method It will also cover the basics of pushed and

driven samplers There are a number of types of drill rigs

available.

Some of the most common are Large truck mounted rigs, sometimes called

a highway rigs Off road track mounted rigs

Trailer mounted portable rigs Different rigs are suited for different site

conditions and different drilling and sampling methods

The large truck mounted rig, is the most versatile and one of the most common rigs used.

However, it can only be used in situations where it can be driven onto the site.

The process of drilling is similar regardless of the type of rig used.

First we positioned the rig over the location where we wish to drill.

Then we erect the drilling boom, or mast, and make sure it is vertical.

A drill head mounted on the boom is the mechanism used to perform the drilling and sampling

operation.

The drill head provided two motions to aid in drilling.

A torque can be applied to rotate drill bit.

And a vertical thrust can be applied to raise and lower drill bits and other equipment.

There are many different drilling and sampling techniques we can use to investigate subsurface

conditions.

One of the simplest is the open hole method using a solid stem continuous flight auger.

The flights on a continuous flight auger run the full length of the auger.

At the tip of the auger is a cutting bit.

The inset photo show two different diameter solid stem augers with two different types

of cutting bits.

The auger is rotated and pushed into the ground by the drill head.

The bit at the tip of the auger loosens soil at the bottom of the hole and the flights

carry the cuttings to the ground surface.

An engineer or geologist can estimate when new soil layers are encountered by observing

changes in the cuttings as they are brought to the surface.

These cuttings can be collected as bulk samples.

However, they are low quality samples because they are completely disturbed by the cutting

process and because soil from upper layers can contaminate soil from lower layers as

the cuttings are carried up the auger flights.

When the boring reaches a depth where a higher quality sample is desired,

the auger is removed from the hole to make room for the sampling equipment.

In the this method the bore hole must be able to stand open without support, which is why

we call it the open hole method.

When we wish to take a sample, we replace the auger bit with a sampling tool,

or sampler.

Nearly all soil samplers consist of some sort a hollow tube which is inserted into the soil

to retrieve a sample.

There are many different designs of samplers to suit different soil conditions, but the

basic process of sampling is similar for most of these samplers.

The sample tool is lowered to the bottom of the boring.

And then pushed into the soil below the bottom of the boring.

When the sampler has reached its full depth, the rods are twisted to shear off the bottom

of the sample, and the sampler containing the soil sample

is retrieved from the boring.

The sample is then stored for later analysis and testing.

The sampling tool is then replaced with the auger

and the auger is lowered back down the hole.

Augering continues until we reach a new layer where we wish to take another sample.

The auger is again retracted from the hole, and replaced with the sampling tool.

Another sample is taken using the same process.

When the soil is very stiff or dense, it is not possible to use a push-type sampler.

In these circumstances we use a heavy walled sampler that can be driven into the soil using

a drop hammer.

The process is similar to retrieving a push type sample, but uses different equipment

and a different sampler.

The open hole method only works when the soil is stiff enough and strong enough to remain

open after the augers are removed.

While it is often possible to use the open hole method, many times the soil is not able

to maintain an open hole for sampling.

If the soil is soft, it may squeeze into the boring when the augers are removed.

This often happens is soft clay layer.

If the soil is a clean sand with little or no cohesion, the soil at the side of the hole

may cave or fall into the boring.

This is particular problem when drilling in sands below the water table.

When squeezing or caving conditions occur we must use a drilling method that will support

the bore hole during the sampling process.

One method that can be used in caving or squeezing conditions it the hollow stem auger method.

In this method, we use a continuous flight auger as the open hole method, but in this

case the auger stem is hollow.

The bit in the center of the auger is retractable and can be removed through the hollow stem.

The inset photo shows a hollow stem auger and its retractable center bit.

For illustration purposes the center bit has been removed and is shown next to the hollow

stem auger.

During drilling the center bit is inserted inside the hollow stem.

The augering proceeds in the same fashion as with the open hole method.

When we reach a depth at which we wish to take a sample, we stop the auger,

detach the center drill bit from the auger and remove it.

The auger remains in the ground and supports the hole.

We can now acquire a sample through the open hollow stem.

The sampling process is the same as we showed before.

After sampling the center drill bit is replace and auguring continues.

The rotary wash boring is another common drilling method.

Instead of using an auger to remove cutting from the hole,

this method uses a slurry or drilling mud to flush cuttings out of the hole.

The drilling mud or slurry is a mixture of either bentonite and water,

or a polymer and water.

The purpose of the bentonite or polymer is to increase the viscosity of the slurry which

makes it easier for the slurry to carry the cuttings to the surface.

Special equipment is needed to handle the drilling mud including a

holding tank a pump

and a swivel head.

The pump circulates the drilling mud from the holding tank through the swivel head into

the top of the drilling rod and then down the hollow inside of the drill rod toward

the toward the cutting bit.

The boring is advanced using a drill bit at the bottom of the hole

The drill bit or cutting bit is turned by the drilling head an loosens soil at the bottom

of the hole The drill bit contains ports that allow the

drilling mud being pumped down the hollow drill stem to exit out the side of the bit

into the annular space outside the drill rod.

The mud flows up the annular space and carries cuttings away from the bit and out the top

of the hole The cuttings settle out of the drilling mud

in the holding tank and the clean mud is recirculated back down the drill rod.

Driving the drill bit of a rotary wash boring takes much less energy than driving a long

continuous flight auger.

Therefore rotary wash borings can be advanced very quickly and reach depths much greater

than auger borings.

In addition to flushing cuttings from the boring, the drilling mud also provides a hydrostatic

pressure along the sides of the drill hole.

This can help to stabilize the hole and allow drilling in moderate caving conditions.

When we reach our desired sampling depth, drilling is stopped and all of the cuttings

are flushed out of the boring.

The pump is then shutdown, the hose disconnected from the swivel, and the drill rod removed

from the hole.

The drilling equipment is replaced with sampling equipment

and a sample is taken directly through the drilling mud.

Another method that can be used to advance a boring in caving or squeezing conditions

is the casing method.

In this method a large diameter pipe is driven into the ground below the depth of the boring

. The hole is then cleaned out using either

the auger method or rotary wash method The casing supports the hole and samples can

be taken in the undisturbed soil below the casing

So let's summarize.

There are many type of drilling and sampling methods.

In this presentation we have presented a few of the most common methods: the solid stem

auger method with an open hole, the hollow stem auger method, and the rotary wash boring

which can be used with or without a casing.

Each method has it pros and cons.

There is no one best method.

The drilling method selected will depend on a number of factors including.

Location and accessibility of the site.

Type of project and its objectives.

Soil conditions Samplers can either be driven in with a drop

hammer of pushed into the soil.

Here are some references and links to drilling and sampling videos online.