activities in soil

7/29/2019 activities in soil

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Contents

CUT AND FILL: ......................................................................................................................................... 2

ROCK EXCAVATION ............................................................................................................................... 13

CLEARING AND GRUBBING ................................................................................................................... 16

WASTE MATERIAL ............................................................................................................................. 16

BORROW EXCAVATION ......................................................................................................................... 17

COMPACTION ........................................................................................................................................ 18

REFERENCE ............................................................................................................................................ 20


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CUT AND FILL:

The objectives of routine road cuts and fills are:

To create space for the road template and driving surface; To balance material between the cut and fill; To remain stable over time; To not be a source of sediment; and To minimize long-term costs.

Landslides and failed road cuts and fills can be a major source of sediment, they can close the

road or require major repairs, and they can greatly increase road maintenance costs (Photo

1.1). Vertical cut slopes should not be used unless the cut is in rock or very well cemented

soil. Long-term stable cut slopes in most soils and geographic areas are typically made with

about a 1:1 or :1 (horizontal: vertical) slope (Photo 1.2). Ideally, both cut and fill slopes

should be constructed so that they can be vegetated (Photo 1.3), but cut slopes in dense,

sterile soils or rocky material are often difficult to vegetate.

Photo 1.1 Over-steep slopes, wet areas, or existing slide areas can cause instability problems

for a road and increase repair and maintenance costs, as well as sediment production.


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Photo 1.2 Construct cut slopes at a 3/4:1 or flatter slope in most soils for long-term stability.

In well-cemented soils and rock, a 1/4:1 cut slope will usually be stable.

Photo 1.3 A well-stabilized cut slope, with about a 1:1 slope, that is well covered with

vegetation.

Fill slopes should be constructed with a 1 1/2:1 or flatter slope. Over-steep fill slopes (steeper

than a 1 :1 slope), commonly formed by side-casting loose fill material, may continue toravel with time, are difficult to stabilize, and are subject to sliver fill failures (Photo 1.4). A


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rock fill can be stable with a 1 1/3:1 slope. Ideally, fills should be constructed with a 2:1 or

flatter slope to promote growth of vegetation and slope stability (Photo 1.5). Terraces or

benches are desirable on large fill slopes to break up the flow of surface water. Table1.1

presents a range of commonly used cut and fills slope ratios appropriate for the soil and rock

types described. Also Figure 1.1 and Figure 1.2 show typical cut slope and fill slope design

options, respectively, for varying slope and site conditions. Note, however, that local

conditions can vary greatly, so determination of stable slopes should be based upon local

experience and judgment. Groundwater is the major cause of slope failures.

Photo 1.4 Avoid loose, overstep fill slopes (steeper than 1 1/5:1), particularly along streams

and at drainage crossings.


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Photo 1.5 Construct fill slopes with a 1 1/2:1 or flatter slope (to promote vegetation growth)

and stabilize the fill slope surface. Use benches (terraces) on large fill slopes to intercept any

flow of surface water.

Table 1.1

COMMON STABLE SLOPE RATIOS FOR VARYING SOIL/ROCK CONDITIONS

Soil/Rock Condition Slope Ratio (Hor:Vert)

Most rock :1 to :1

Very well cemented soils :1 to :1

Most in-place soils :1 to 1:1

Very fractured rock 1:1 to 1 :1

Loose coarse granular soils 1 :1

Heavy clay soils 2:1 to 3:1

Soft clay rich zones or wet seepage areas 2:1 to 3:1

Fills of most soils 1 :1 to 2:1

Fills of hard, angular rock 1 1/3:1

Low cuts and fills (


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Figure 1.1 Cut slope design options.


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Figure 1.2 Fill slope design options


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Figure 1.3 Slope problems and solutions with stabilization measures.

A wide range of slope stabilization measures is available to the engineer to solve slope

stability problems and cross an unstable area. In most excavation and embankment work,

relatively flat slopes, good compaction, and adding needed drainage will typically eliminate

routine instability problems (Photo 1.6). Once a failure has occurred, the most appropriate

stabilization measure will depend on site-specific conditions such as the size of the slide, soil

type, road use, alignment constraints, and the cause of the failure. Here are a range of


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common slope stabilization options appropriate for low-volume roads, presented roughly

from simplest and least expensive, to the most complex and expensive:

Simply remove the slide material. Ramp over or align the road around the slide. Replant the slope and add spot stabilization. Flatten or reconstruct the slope. Raise or lower the road level to buttress the cut or remove weight from the slide,

respectively.

Relocate the road to a new stable location. Install slope drainage such as deep cut off trenches or dewater with horizontal drains. Design and construct buttresses (Photo 1.7), retaining structures, or rock anchors.

Retaining structures are relatively expensive but necessary in steep areas to gain roadway

space or to support the roadbed on a steep slope, rather than make a large cut into the hillside.

They can also be used for slope stabilization. Figure 1.4 (a and b) presents information on

common types of retaining walls and simple design criteria for rock walls, where the base

width is commonly 0.7 times the wall height (Photo 1.8). Figure 1.4c presents common

gabion gravity wall designs and basket configurations for varying wall heights. Gabion

structures are very commonly used for walls up to 6 meters high, particularly because they

use locally available rock and are labour intensive (Photo 1.9).


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Photo 1.6 Simple hand compaction behind a low rock wall. Compaction is important behind

any retaining structure or fill. It can be achieved by hand or, preferably, using equipment such

as a wacker or small compactor.

Photo 1.7 A drained rock buttress can be used to stabilize a cut slope failure area.


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Figure 1.4 Construction of various types of retaining structures. (Adapted from Gray &

Leiser, 1982)


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Figure 1.4 Continued. (Adapted from Gray & Leiser, 1982)


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ROCK EXCAVATION

Reviews standard excavation practices used to construct and modify rock slopes and provides

current design and construction guidelines for their use in context sensitive areas. Several of

these practices have been used for many years, while others are new techniques or recent

modifications of established methods. The most common are blasting (which includes drilling

the holes to be filled with explosives), ripping, and breaking. Table 1 provides a brief

description of these procedures, along with the advantages and limitations of each. Each

procedure is discussed in detail below.

BLASTING

Blastingthe controlled use of explosives to excavate rockhas been part of construction

engineering for hundreds of years. In any blasting situation, the geologic structure of the rock

mass will be the most important consideration. Other considerations include the degree of

scarring that would be acceptable (some areas can tolerate more blasting scars than others),

cost, and safety (blasting cannot be performed in close proximity to populated areas).

Effect of Geologic Structure on Blasting Procedure

The first consideration when designing a blasting operation should be the local geologic

conditions. Rock competency and fracture patterns can have a significant impact on the

success of a blasting operation.

Discontinuity Sets

When discussing blasting, the single most important geologic factor is fracture: the spacing

and orientation of any breaks, or discontinuity sets, in the rock. In particular, the orientation

of the discontinuity sets with respect to the cut slope angle will influence any slope failures

that may occur along the slope face. The modes of failure can be grouped into four primary

mechanisms, shown left to right in Figure 1

Planar failure (a), Wedge failure (b), Circular failure (c), and Toppling failure (d).


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Figure 1. Illustration. The four primary mechanisms of slope failure.

Table 1. Description, advantages, and limitations of common excavation practices.

PROCEDURE DESCRIPTION ADVANTAGES LIMITATIONS

Presplit

Blasting

Presplit holes are blasted

before production blasts.

Procedure uses smalldiameter holes at close

spacing and lightly

loaded with distributed

charges.

Protects the final cut by

producing a fracture plane

along the final slope face

that fractures fromproduction blasts cannot

pass. Can produce steeper

cuts with less maintenance

issues.

Performs well in hard

competent rock.

The small diameter

borings limit the

blasting depth to 15 m

(50 ft). Borehole tracesare present for entire

length of boring. Does

not perform well in

highly fractured, weak

rock.

Smooth

Blasting

Smooth blast holes are

blasted after production

blasts. Procedure uses

small diameter holes at

close spacing and lightly

loaded with distributed

charges.

Produces a cosmetically

appealing, stable perimeter.

Can be done on slopes yearsafter initial construction.

Drill hole traces are less

apparent than presplitting.

Performs best is hard,

competent rock.

The small boring

diameter limits blasting

depth to 15 m (50 ft).

Borehole traces are

present for much of theboring length. Does not

protect the slope from

damage caused by

production blasting.

Does not perform well

in highly fractured,

weak rock.

Cushion

Blasting

Cushion blasting is done

after production blasts.

Larger drill holes areused with small diameter,

lightly loaded distributed

loads. Space around the

explosive is filled with

crushed rock to cushion

the explosive force.

Reduces the amount of

radial fracturing around the

borehole and also reducesborehole traces. The large

diameter holes allow

blasting depths up to 30 m

(100 ft). Produces a ragged

final slope face. Performs

well in all rock types.

Radial fractures are

more abundant than

presplit and smooth

blasting. Slope face ismore prone to raveling.

A catchment area is

recommended at slope

base. More demanding

on the driller. Borehole

traces still apparent in

hard, competent rock.

Step Drilling

Larger diameter drill

holes, drilled vertically

and used as production

blasting (although spaced

If properly designed the

final slope face shows

minimal signs of blasting.

Can be used when sloped

Can produce extensive

damage to slope or

inadequate base

fracturing if not


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closer and loaded lighter

to minimize radial

fractures). Slope face is

formed along base of

blast holes.

controlled blasting cannot.

Best used in moderately to

highly fractured rock.

designed properly.

Should only be used

with experienced driller

and blasting engineer.

Only applicable for

slopes between 0.7:1and 1:1 (H:V). Does not

perform well in hard

competent rock.

Horizontal

Drilling

Larger diameter, closely

spaced, lightly loaded

horizontal borings are

used for production style

blasting. Used in massive

rock to eliminate drillholes or in areas of poor

access.

Eliminates bore hole traces

when drilled perpendicular

to the slope face. Good in

massive rock where traces

are not acceptable.

Demanding on the

driller and explosives

engineer. Can produce

extensive radial

fractures or inadequate

base fracturing if not

loaded properly.

Requires complicatedloading and timing

procedures, and special

stemming procedures.

Ripping

Uses a tractor with an

attached tooth or teeth

that is lowered into the

rock and dragged to

break up material for

excavation.

Much cheaper and safer

than blasting. Can be done

in close proximity to

development without

disturbance. Is effective on

a variety of angled cuts and

an excavator can be used

after ripping to slope

sculpting.

The tooth of the ripper

can leave scars on the

rock surface. The

tractor cannot be used

on steep slopes because

of risk of overturning.

Ripping is limited to

relatively low density

rocks.


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CLEARING AND GRUBBING

The clearing and grubbing topics addresses clearing and grubbing, the first of several

operations that are required to bring the construction site to subgrade. Clearing and grubbing

is the satisfactory removal of materials that cannot be used in the work. These materials

include trees, stumps, shrubs, topsoil, buildings, fences, and other obstacles interfering with

the work.

Material & Equipment

There is no material required for this operation, but the contractor may be required to

stockpile topsoil that is stripped from the site for later use. There are various types of

equipment used in clearing and grubbing, including chain saws, log skidders, wood chippers

and grinders, harvesters, fellers and bunchers, delimbers, bulldozers, scrapers and pans,

excavators, and dump trucks.

Construction Methods

Clearing and grubbing is usually the first construction operation performed. The process for

clearing and grubbing involves cutting and removing trees (clearing) or other obstructions

within the project site, removing stumps and brush, and removing topsoil and organic

material (grubbing). The work also includes disposal of removed material, salvaging and

storing material, stockpiling topsoil, and chipping and stockpiling wood waste material. The

demolition of structures, such as buildings, garages, sheds, sign stone, fences, signs, markers,

and guide rails, is also performed during this phase. The contract may require that certain

items, such as guide rails, signs, and posts, be reserved for PennDOT reuse.

WASTE MATERIAL

This chapter addresses the satisfactory disposal of waste material from earthwork operations.

Material and Equipment

Equipment used in the disposal of waste material includes bulldozers, excavators, dump

trucks, rollers, compactors, and seeding and mulching equipment.


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The contractor loads waste material from the project into dump trucks or other hauling

equipment and hauls the waste to a designated waste area. The material is placed and

compacted in the same manner as for embankment construction. Once all material is in the

waste area, it is graded for positive drainage. The appropriate seeding formula and mulch is

then applied. At on-site waste disposal areas, frequent moisture-density tests are performed to

ensure the soils placed meet specification requirements. The contractor may be required to

perform other items if required by DEP permits.

BORROW EXCAVATION

This chapter addresses excavation required to supply material needed on a project in addition

to the material available from project operations. These excavations are called borrow

excavations. Borrow excavation is classified as common, foreign, or selected, depending on

where the material is obtained.

Common borrow excavation occurs when extra material, measured before and after

excavation, is obtained from a location within the limits of the project or outside of the right

of way limits. Foreign borrow excavation occurs when extra material cannot be obtained

from within the project limits, must be obtained elsewhere, and cannot be measured before or

after excavation. Selected borrow excavation occurs when material for the work is obtained

from sources outside the project limits that cannot be measured before or after excavation and

is used for specific items of work due to quality or size requirements.


Equipment typically used to excavate and load material includes bulldozers, backhoes,

excavators, scrapers, drag lines, clamshell buckets, and front-end loaders. Dump trucks,

scrapers, and off-road trucks are used to transport and dump the excavated material. Rollers

and compactors are used to compact the material and to seal the surface of the excavation at

the end of the workday. Seeding and mulching equipment is used to see and mulch borrow

areas.


All required permits and agreements must be obtained before the work begins. Borrow pits

should be identified early enough to allow sufficient time for sampling and laboratory testing.


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Test results must be forwarded to the District soils engineer before the material is

incorporated into the project. If more than one type or classification of material is obtained

from the same borrow pit, samples must be taken and submitted for each type of material.

These separate materials must be removed consecutively rather than concurrently should not

be mixed.

When borrow excavation is required, excavation cannot begin until the material and

placement sequence has been accepted in writing, and an erosion and sediment control plan

has been submitted and accepted by the county conservation district, the Pennsylvania DEP,

and by PennDOT. The Department also requires a signed agreement with the property owner.

The inspector should make certain the borrow pit is cleared of vegetation, debris, unsuitable

material, topsoil, and overburden before production work begins. The removed topsoil is

stockpiled for reuse in restoring the pit.

During excavation, the material is monitored for changes. The District soils engineer must be

notified of changes and if previously unsampled material is found during the course of

borrow pit excavation (in which case additional sampling and testing is required).

Final cross sections must be taken after the last of the material has been removed from the

borrow pit. After completion of the cross sections, the borrow pit should be restored

according to the approved restoration plan.

COMPACTION

This chapter addresses compaction methods and equipment, and applies to embankment,

benches, and subgrade compaction.

Compaction is the process of making particles of a given material fit together in the smallest

possible space. Proper compaction is important because it makes material more stable and

increases its supporting or load bearing capacity.

Materials are comprised of different grain sizes and physical compositions; hence, each

material has unique compaction characteristics. When a given material is fully compacted,


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the spaces or voids between particles are limited to their smallest possible configuration. The

greatest density obtainable through compaction is the maximum density. The moisture

content of a given material directly correlates to the materials ability to be compacted to

maximum density. The maximum water content needed to achieve maximum density is

known as optimum moisture content. Every material has its own optimum moisture content,

determined by conducting proctor tests. Too little or too much moisture inhibits adequate

compaction.

In general, there are five different methods used to compact materials.

The first method is to allow the material to settle and compact on its own with no mechanical

assistance. This method is time consuming and the results are unpredictable; therefore, it is

rarely used.

The second method, known as surcharging, involves placing of the excess material to a given

height above the plan elevation. This material is kept in place for a certain amount of time.

Compaction is obtained by the weight of the excess material, which is removed after the

required amount of time.

The third method involves forcing the particles together, much the same as a snowball is

formed by squeezing snow in the hands. Most non-vibratory rollers and compactors compact

material in a similar manner.

The fourth method of compaction involves applying weight and vibration. This method is

used for broken stone or sandy material that is difficult to compact. Generally speaking, these

materials are not compacted, they are consolidated. Vibratory rollers and plate tampers

achieve compaction through consolidation. The amount of compaction achieved depends

upon the amplitude (frequency) of machine vibration, how fast the machine is moved forward

and backward, and the weight of the machine.

The fifth compaction method incorporates tampers. Tampers are usually gasoline powered

and used in areas that are inaccessible to large rollers. Hand tampers are also used, but are

often not as effective as mechanical tampers.


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Materials used for compaction are those specified for embankment and/or backfill of the

various types.

Equipment typically used includes vibratory compactors, vibratory rollers, tandem rollers,

three-wheel rollers, rubber tired rollers, sheeps foot rollers, and tampers. Equipment

requirements vary by the type of material and its application.

The contractor also needs equipment, including sand cone and nuclear testing equipment, for

testing the compaction and moisture of the material used.


Material used for embankment structure backfill or other work is placed in appropriate layers

per specifications and standards. Compaction is applied using the appropriate equipment,

depending on the material and its application.

After compaction, the contractors certified materials technician performs compaction testing

using either the sand cone or nuclear procedures. If appropriate (as noted in the contractors

approved quality control plan), the visual non-movement under equipment procedure may be

used.

Test results are obtained, evaluated, and accepted prior to placing the next layer.

REFERENCE

Document

Section 200Earthwork. PennDOT Publication 8. PDF Document. Slope Stabilization and Stability of Cuts and Fills. LOW-VOLUME ROADS BMPS.

PDF Document.

Chapter 3Rock Excavation Methods. PDF Document.

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