Slope Stability Excavation Slopes - Blue Ridge Servicesblueridgeservices.com/wp-content/uploads/2015/01/Slo… · · 2015-01-15Slope Stability Excavation Slopes Blue Ridge Services,

Slope Stability

Excavation Slopes

Blue Ridge Services, Inc. 7204 Hites Cove Rd Mariposa, CA 95338

209-742-2398 www.blueridgeservices.com

Landfill Safety Training Series

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http://www.blueridgeservices.com/

Safety is not a plan …it’s an attitude

When it comes to landfill operations …We Wrote the book

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This booklet or any portion thereof may not be copied

or reproduced in any form, except as permitted under the United States Copyright Act of 1976, nor

distributed in any form or by any means, or stored in a data base retrieval system, without the express, prior,

written permission of the author.

This book is intended to assist the reader in

understanding how to work safely in a variety of situations that may occur at a landfill. It is not

intended to replace common sense or judgment. The author(s) and publisher(s) of this manual shall not be

held responsible in any way for the safety of those using this material for training purposes. Safe

operation of every landfill is the responsibility of that facility’s owner, manager, operators and laborers and

other staff.

Printed in the United States of America World Rights Reserved

Copyright 2014 by Neal Bolton

Copyrighted 2014

Published by: Blue Ridge Services, Inc. 7204 Hites Cove Rd Mariposa, CA 95338




INTRODUCTION Slope stability is one of those things that we don’t spend much time thinking about. Oh sure, it may be whispering a warning in the back of your mind as you work along a steep bank or trim the edge of a big stockpile, but you probably won’t lose any sleep over it. Much like earthquakes or tornados, slope stability doesn’t really become an important issue for operators until something bad happens. Landfill slopes are designed to be stable, even in the event of an earthquake – this is a requirement. And without question, most of the concern and most of the effort are directed toward landfill liners and landfill caps. The emphasis on liner and cap stability is in large part due to the important role they play in protecting our environment – mainly groundwater. But it is also because the components used in their construction can be very slippery. Clay soil and plastic have- what an engineer would refer to as - a low coefficient of friction. With the increased use of composite liners and caps throughout the industry, slope stability is a major concern for all landfills. There are lots of issues related to liner and cap stability, and we’ll discuss them in detail another time, but today we’re going to talk about the stability of excavation slopes. Excavation slopes are created whenever soil is removed or “excavated.” Most landfills operate at one time or another




as a cut/fill operation and the “cut” almost always creates an excavation slope. There are many terms for an excavation, all of which refer to the same thing. They include: cut, borrow area, excavation, or perhaps simply, the “pit.” But no matter what you call it, when a dozer, scraper, loader, excavator or other machine removes soil, it creates an excavation slope.

Excavation slopes pose a common, and very real threat to landfill workers, and anyone else who may be nearby. But unlike liners and caps, excavation slopes often do not receive the respect and caution they deserve.




Perhaps that’s because working around excavation slopes is commonplace. Or maybe it’s because it’s usually handled by the operations staff and is seen more as the operator’s responsibility. In any event, the risks associated with excavation slopes are often greater than the attention they receive.

Risks There are many risks associated with excavation slopes. These risks can range from minor erosion to machine rollover, from rolling rocks to catastrophic slope failure. Here’s a look at some of the more common risks, including:

1. Machine Roll-over 2. Erosion and Falling Rocks, and 3. Slope Failure

Machine Rollover It is, of course, common practice for heavy equipment to work on or near the slopes of excavation areas. And in most cases, the work can be performed safely and without incident, but sometimes conditions can become dangerous. Excavation slopes that are unstable or too steep can cause a machine to rollover. Here are few things that safety-minded operators should watch for when working near excavation slopes:




Steep Vertical Banks When soil is excavated, the operator should avoid creating a vertical bank. This is a common tendency when working with a loader or excavator, but dozers and scrapers can also create vertical banks. Even small vertical banks just a few feet high, can and often do collapse, causing machine damage or operator injury. When soil is excavated, the operator should avoid creating a vertical bank.

Loose Soil The loose soil, often present along the edge of haul roads or at the top of an excavation slope, can create a hazard for vehicles and heavy equipment. When driving or operating near the edge of an excavation slope, stay back from the edge. Slow down and limit your travel to the established roadway. If an excessive amount of loose soil




creates a hazard, use a bulldozer or motor grader to cast it aside. Slippery Conditions Rain, snow or ice can make excavation slopes very slippery and create a serious hazard for heavy equipment and other vehicles. When slippery conditions exist, use extreme care when working or traveling near excavation slopes. If possible, avoid working on excavation slopes at these times. If you must work when conditions are slippery, move slowly, especially when operating rubber-tired machines such as loaders or scrapers. Often, slippery areas can be stabilized by trimming off a few inches of saturated mud or by placing a layer of dry soil or processed wood waste on the operating surface.




Know your Machine Every machine has limitations in regard to its ability to work on a steep slope. In general, a bulldozer can handle a steeper slope than a scraper or loader. However in certain situations a scraper can handle a very steep slope as long as it’s headed directly uphill or downhill and the bowl is kept very low. For maximum stability, all machines should be operated with the bowl, blade or bucket kept as low as possible. For specific information on the limitations of individual machines, you should refer to the Operation and Maintenance Manual provided by the machine manufacturer.




Erosion and Falling Rocks Erosion is a potential problem with excavation slopes. Erosion occurs when soil particles are loosened and removed through the action of wind or water. We most often think of the erosion in terms of very small soil particles, however, falling rocks are also a form of erosion. If the soil in your excavation area contains rocks, take extra precautions to prevent possible injury. Constructing a small soil berm, ditch or fence along the toe of the excavation slope might control small rocks. Larger rocks may require larger control systems.

It’s important to note that while rocks could fall at any time, the likelihood increases during wet weather or during freeze-thaw periods.




Aside from the threat of falling rocks, erosion usually presents a relatively minor threat to landfill workers. Although if ignored, erosion can, over time, lead to more serious conditions. The Grand Canyon is an example of erosion on a very grand scale. On a smaller scale, erosion can weaken slopes or undercut haul roads, culverts or other structures. In a round-about way, uncontrolled erosion can also lead to surface water intrusion which can in lead to massive slope failure. Let’s look at some of the more common contributors to slope failure.

Slope Failure

Slope failure occurs when the force of gravity acting on the slope exceeds the internal strength of the soil of which the slope is comprised. In other words: a slope can fail when the weight increases and/or the strength decreases.




There are many factors that can contribute to slope failure and the entire issue can become pretty complex. But rather than get too scientific, let’s look at some of the basic factors that can contribute to slope failure. Soil Type The type of soil is an obvious and important factor when it comes to slope stability. Loose soil, such as sand, is typically weak. So too are soils that consist predominately of one size rather than a range of particle sizes. For example, consider the difference between a poorly graded material such as pea gravel, where all the particles are more or less the same size, and a well-graded material like road base, where the particle size varies. A well-graded soil can be very strong, especially if it contains some fine silt or clay. On the other hand, any soil with particles of similar size is usually weak. The strength of a sedimentary soil like shale can vary depending on how thick it is, the type of soil and the slope of soil layers. Occasionally, the layers can be tilted just enough to slide on - what is often referred to as - a “slip-plane.” Fine-grained soils, such as clay and silt, can appear to be strong, and in fact, may be, depending on the moisture content. Soils that contain some coarse material, such as gravel, are also usually quite strong.




OSHA provides some guidelines for excavation slopes, based on soil type and excavation depth: Soil Origin In some cases, the origin of the soil also plays a part in how stable it is. Windblown soils are typically weak because the soil particles are arranged in a random pattern. Conversely, sedimentary soils (placed in layers as lake or ocean sediment) are better able to align themselves tightly together and thus may be stronger.

Moisture content The amount of water present in the soil, referred to as “moisture content”, is perhaps the most important factor related to slope stability. Many of the landslides and slope failures visible along highways are a result of excessive water.




A moment ago we learned that slopes could fail when the weight increases or the strength decreases. Along those lines, consider what happens when an excavation slope becomes wet or saturated: Soil can act as a sponge to varying degrees and depending on the soil type, can retain 2-4 inches of water per vertical foot of soil. That means that very wet soil could weigh 300-600 pounds per cubic yard more than it weighs dry. When applied across a large excavation slope, this added moisture represents a tremendous weight. Soil can also become weak if the moisture content gets too high. This is due in part to the attraction that water molecules have for each other and for the surface of the soil particles. As the moisture content increases, the




individual soil particles become surrounded by more and more water until they lose contact with each other. This loss in friction between the particles translates into a loss of strength. Clay soil has a particularly strong appetite for water because the clay particles themselves have an electrical charge, they have the ability to become very wet and very weak. Because water plays such a vital role in slope stability, it is critical that excavation slopes be protected from water in every possible way. The simplest - and most effective - is to maintain good drainage ditches to carry storm-water and snowmelt away from the excavation area. It is also important not to allow water to pond at the toe of the slope where the weight of the slope creates the greatest stress. But even with good drainage practices, excavation slopes can become very wet and unstable due to underground springs, excessive rainfall or other factors that are out of your control.

Steepness of Slope The steepness of the slope is something that you can control by periodically checking grade as you excavate the soil. It’s likely that the engineer who designed your landfill




could provide some basic guidelines on maximum allowable slope. Length of slope The length of a slope has an effect on its stability. Remember, for a slope to be stable, the weight of the soil must be supported. Longer slopes represent more weight and higher stresses at the base. Constructing periodic benches in the excavation slope can help reduce weight-related stresses. Building to a flatter slope can do the same thing.

Loading Loading on or near the edge of an excavation also plays a role in the stability of the slope. Loading is a term used by




engineers and geologists and simply refers to additional weight that may be placed on or near the slope. One example is a tractor that is operated too near the edge of a steep bank. Another is soil stockpile placed too near the edge of an excavation slope. In both cases, the added weight imposes additional stresses on the slope and could cause a slope failure. Always be alert to the potential problems associated with placing any type of load on or near an excavation slope. If it ever becomes necessary to do so, be sure to check with your engineer to make sure it’s safe.

Types of Slope Failure There are many ways that excavation slopes can fail. Here’s a look at some of the more common ones.




Rotational Rotational slides occur when a section of the slope rotates down and out. These generally are the result poor drainage.

Lateral Slide Lateral slides occur along a particular stratum or slip plane. These are most common where soil is layered. They may result from water intrusion or from undercutting a slope where the layers are tilting steeply. Flow A flow occurs when soils become fluid, (acts like a fluid). This type of failure is almost always associated with poor drainage that allowed portions of the slope to become saturated. Flows can travel a considerable distance.




Working Safely Let’s review some ways to keep yourself and others safe while working on excavation slopes. Follow the Plan Every landfill is unique and there are many different types of soil. Become familiar with your landfill’s characteristics and the limitations established by your engineer. These may include: the allowable slope for all excavation areas; the maximum vertical spacing between benches for the excavated slope; methods for controlling water; limitations for loading on or adjacent to the slope; as well as any other pertinent information. Know Your Slope In order to comply with your engineer’s guidelines you must monitor the grade of the slope. To do this, you’ll need to hire a surveyor or use some basic tools for checking grade. Watch for Warning Signs Slope failures can occur at any time and without warning. But more often than not there will be some prior indicators of a problem. Here are some things to watch for:

1. Cracks in the slope or near the top edge of the slope 2. Bulges in the slope, especially in the bottom half of the

slope 3. Seeps or wet spots, especially in the bottom half of

the slope




4. Loose soil along haul roads or near the top edge of the slope that could cause machine instability

5. Exposed rocks that could loosen and roll down the slope

6. Additional loads imposed by machines or stockpiles placed on or near the excavated slope

Manage Water To minimize the risk of slope failure, carefully control surface water and keep it away from the excavated slope through the use of ditches, culverts, down-drains or berms. Do not allow water to pond at the toe of the slope.




Are You Safety Savvy? We’ve discussed many of the concerns relating to excavation slopes. Now let’s see if you are Safety Savvy. We’re going to take the safety test. The questions are simple and are intended to help you think about how to work safely around excavation slopes. Please take them seriously, because knowing the right answer could help you work safely. Look at these photographs, listen to the questions and see if you know the correct answers.

Question 1

It rained last night and the haul road across the excavation slope is very wet and slippery. What is your advice to the

operator?




Question 2 You are picking up litter along the toe of this slope and you notice several large rocks that have rolled down the slope.

What should you do?

Question 3 You are working near the toe of an excavation slope and

notice water seeping out of the ground. It looks like a spring. What should you do?




Question 4 It’s Friday and a major rainstorm is expected this weekend. Your supervisor instructs you to prep the excavation area.

What should you do?




Summary Working near excavation slopes is a normal part of operating a landfill. If managed properly, excavation slopes need not pose a risk.

It’s never too soon to start thinking about safety.




Answers No. 1

Wait for the road to dry out before working

Use a dozer to strip off the top few inches of mud to expose dry soil

Haul in a few loads of dry soil or processed wood waste to provide some traction to the road

Anything else? No. 2

Leave the area immediately

Ask the supervisor how to stabilize the area before you return to work there

Any other ideas? No. 3

You recognize a potential indicator of pending slope failure

Evacuate all workers from the excavation slope area

Notify your supervisor

What else could you do?




No. 4

Make sure the ditches, culverts and other drainage structures around the excavation slope are in good condition

Make sure the area at the toe of the slope is graded to drain away from the slope

Try to repair any areas that appear prone to erosion

Any other ideas?

Note: These are only some of the more obvious issues. You

may find more.




Notes:




Notes:




This is Your Book.

It is a valuable reference.

Keep it handy and refer to it often.

2014 © Blue Ridge Services, Inc.

Documents

Slope Stability Excavation Slopes - Blue Ridge Servicesblueridgeservices.com/wp-content/uploads/2015/01/Slo… · · 2015-01-15Slope Stability Excavation Slopes Blue Ridge Services,