2009 MSHA Coal Refuse Disposal Facilities Manual - Blasting

7/29/2019 2009 MSHA Coal Refuse Disposal Facilities Manual - Blasting

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Chapter 6

A 9

disparity in the weights and foundation conditions between the two structures. If both structures

Either situation can lead to excessive deformation of the conduit joints in the vicinity of the intakestructure. Under such circumstances, provisions to allow for relative movement may need to beincorporated into the design.

6.6.7 Blasting Impacts

Blasting must be conducted in such a manner as to prevent injury to site personnel and unaccept-able impacts to structures associated with a coal refuse disposal facility, including refuse or earthenbe limited in accordance with applicable guidelines. Typically, embankment dams have very low natu-ral frequencies (on the order of 1 hz) and thus are not particularly susceptible to damage due to blast-tion method), the impact of ground motion for the anticipated magnitude and frequency range of blastvibrations can be considered using the procedures for seismic stability described in Chapter 7. Somestructures associated with fresh water dams, such as large concrete spillway channels, tall riser intake-quencies and thus be impacted by blasting. However, typical concrete structures and pipelines used atcoal refuse facilities are normally not very susceptible to damage from blasting vibrations.

mine

NA C

A AAC .

NA AAC .

NN-Z( ) CN

NAC

ESTIMATED SETTLEMENT PROFILE

ACTUAL SETTLEMENT PROFILE BASEDON MEASURED DISPLACEMENT OFCONDUIT JOINTS)

DISTANCE (FEET)

SETTLE

MEN

T(IN

CHES

)

(A, 5a)

.5 CAN C AN B CN N

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Geotechnical Engineering, Material Testing, Engineering Analysis and Design

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the charge size relative to the horizontal distance to the monitoring point in order to meet accept-able motion (velocity) criteria. One such relationship for the peak particle velocity Vresulting from

VK(D/W)

where:

K

D distance to blast (length)

W weight of charge (force)

Topographic and geologic variations between the blast location and observation point and the posi--

Acceptable vibration criteria are published in a number of sources: state regulatory programs typi-cally provide guidance for peak particle velocity for common structure types, and general guidancecan be found in Nichols et al. (1971), second for mass concrete structures (Hartman, 1992) and to 2 inches per second for typical steel andto the possible onset of visible cosmetic damage. The noted structure types can typically tolerate much shows acceptable limits of vibration

and Reclamation Act of 1977 requires approval of an operators blasting plan by OSM, or the appro-

AB .57 CN NA C CA AN C

elocity amage evel

.5 in/sececommended limit to prevent threshold damage in plaster-on-lath construction near surface

mines due to long-term, large-scale blasting operations (B, 19).

.75 in/sececommended limit to prevent threshold damage in sheetrock construction near surface

mines (B, 19).

1. in/sec2IFHRI6XUIDFH0LQLQJ260UHJXODWRU\OLPLWIRUUHVLGHQFHVQHDUVXUIDFHPLQHRSHUDWLRQVDW

distances of 3 to 5, ft (long-term, large-scale blasting).

. in/secidely accepted limit for residences near construction blasting and quarry blasting. Also

allowed by for frequencies above 3 hz (B; 1971, 19).

5.4 in/sec 0LQRUGDPDJHWRWKHDYHUDJHKRXVHVXEMHFWHGWRTXDUU\EODVWLQJYLEUDWLRQV86%0

9. in/secAbout 9 percent probability of minor damage from quarry blasting. tructural damage to some

houses, depending on vibration source, characteristics and house construction.

. in/secor close-in construction blasting, minor damage to nearly all houses, structural damage to

some. or low-frequency vibrations, structural damage to most houses.

(AA , 199)

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NC (Z)

PARTICLE

VELOCITY

(IN/SE

C)

(AA N A., 19)

111.1

1.

1.

4 15 4

A

. N/C

A

.5 N/C

.75 N/C

-cerns when an impoundment is present include fracturing of abutments, impacts to pipes and otherrigid structures, and possibly impacts to upstream construction. The potential impacts should beevaluated, and monitoring of particle velocity with a seismograph may be appropriate. Monitoringembankment crests and slopes for evidence of cracks or displacements, review of piezometer data forgeneral integrity and to note any movements.

. ACCAB BAN

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Chapter 7

SEISMIC DESIGN: STABILITY

AND DEFORMATION ANALYSES

7-1A 9

7.1 GENERAL

7.1.1 Design Approach

Under certain conditions, seismic loadings from an earthquake or other source can cause embank-ment or foundation materials to lose strength, potentially causing a structure to become unstable.Coal refuse embankments constructed using the upstream construction method may be particularlyloose saturated, hydraulically-placed material. Designers should perform an evaluation (commensu-an adequate margin of safety against seismically-induced instability.

The methods of exploration, testing, and analysis presented in this chapter are based on research

and practice, publications, and experience on a variety of projects. They provide a variety of optionsfor design. These methods, ranging from basic to sophisticated, have generally been applied on coalrefuse disposal sites. Commentary is provided in the text to help explain the basis for the methodsmethods, as well as new methods, may be developed in the future. Designers are encouraged to eval-substantial research and investigation, as well as input from geologists, seismologists, geotechnicalengineers, and other professionals.

This chapter refers to dams and embankments interchangeably. Also, references to soil or mate-dcoal refuse, mixed refuse, coarse coal refuse, and amended refuse). As there have been no reportedstudies of strength loss due to seismic loading are predominantly from sites that contain natural soilsor other mine tailings. Thus, the physical behavior of coal refuse materials must be inferred from cor-relations, supported by laboratory testing.

The following published papers, studies and ongoing research on coal refuse materials and seismicpotential information on testing and parameters that may be available:

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Chapter 7

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present an overview of challenges in evaluating strength lossat coal refuse disposal facilities from MSHAs perspective. They summarize the avail-cone penetration testing) and strain-based laboratory methods (undrained steady-state shear strength approach based on triaxial compression tests) for evaluation ofpotential strength loss at coal refuse disposal impoundments.

tests on undisturbed samples and laboratory-consolidated slurry samples. Thesesteady-state strength values are typically between one-half and one-fourth of thepeak undrained strength. The paper also provides cyclic-triaxial test data for undis-the degradation of peak undrained strength with strain during cyclic loading.

present the undrained steady-state shear strength approach forIsotropically-consolidated, undrained triaxial compression tests of undisturbed and

vertical stress.

discuss pore-pressure-based empirical methods for trig-gering of strength loss at coal refuse dams and provide standard penetration testsa summary of cyclic-triaxial test results from four disposal sites.

presents engineering properties for northern Appalachian coal

shear testing used for determining undrained shear strength.

at the University of Kentucky concerning development of dynamic properties of coal-seismic testing are to be performed. Complementary laboratory cyclic-triaxial testingand resonant-column testing are also proposed for determining dynamic propertiesof coal refuse materials.

cyclic-triaxial tests) for determining dynamic properties (damping ratio and shear

modulus) performed on Appalachian coal refuse at Case Western Reserve University.

Seismic design of dams and embankments involves two separate requirements:

1.

2.

7.1.1.1 Seismic Instability

The ground motion from an earthquake can result in a reduction in the shear strength of loose, satu-rated materials. Seismic instability may occur when post-earthquake shear strength is less than the

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Seismic Design: Stability and Deformation Analyses

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pThe driving force of the seismic instability is the static (gravity) weight of the embankment. Seismicinstability is a particular concern for dams with substantial upstream construction because a portionconditions must develop:

1. The earthquake shaking must be strong enough to trigger undrained strength loss in

one or more zones of material.2.

strengths are less than the static driving shear stresses.

The location and amount of the material that experiences strength loss must be suf-

stability problem, using post-earthquake shear strengths for the materials in the embankment andfoundation. The earthquake shaking causes the material in the embankment or foundation to losestrength, but the static gravity shear stresses drive the failure. Some instability failures have been

caution and care.

7.1.1.2 Excessive Deformations

If seismic stability analyses indicate that an embankment is unstable, then deformations should beconsidered to be unacceptably large. However, if seismic stability analyses indicate that an embank-

ment is stable, then potential seismic deformations should be assessed. Seismic deformations occurprimarily during earthquake shaking. The cyclic-shear stresses induced by the earthquake contrib-ute directly to the deformations. This contrasts with the primary mechanisms of instability. In seis-mic instability, the earthquake shaking causes undrained strength loss, but the static gravity stressesdrive the instability failure.

and sometimes underlying the embankment, and the natural soil below the embankment must all beevaluated as part of stability and deformation analyses.

The basic elements for seismic design and analysis require evaluation of:

7.1.2 Seismic Design Considerations and Flow Chart

The following points were considered in developing the guidance and recommendations presentedin this chapter:

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-ity and the consequences of failure. So, for example, no seismic analysis is requiredstability and deformation analyses are required for high-hazard-potential dams.

earthquake and for evaluating the degree of strength loss depend partly on whethersoil deposits in the foundation, might include zones of both sand-like and clay-likematerial. Therefore, methods for evaluating both sand-like and clay-like material areprovided. These methods apply to both coal refuse materials and soil.

are potentially susceptible to seismically-induced strength loss from zones that arethe potentially-susceptible zones. This chapter presents screening methods for bothclay-like and sand-like material that require only the basic information provided by

well as methods that are more sophisticated. The more sophisticated methods mayallow for less conservatism in the design and might be worthwhile for achieving amore economical design. However, the more sophisticated methods are optional, notto estimate post-earthquake strength, as well as more sophisticated, optional, labora-tory methods. Another example is that seismic-stability analyses can be performed bysimply assuming that the design earthquake triggers strength loss in materials that arepotentially susceptible to strength loss, or an optional triggering analysis can be per-formed to evaluate whether the design earthquake is in fact strong enough to triggerstrength loss. The authors of this chapter note that triggering analyses are not con-sidered to be appropriate for sand-like materials for design earthquakes that exceed

-forward methods rather than using more sophisticated methods to justify a design.

on the level of seismic hazard at the site. Many coal mining regions in the U.S. are inareas of low seismic hazard. Minimum parameters for the design earthquake in these

in the seismic design of dams should be available for use. Therefore, this chapter

presents three methods for analyzing the triggering of strength loss in loose, sand-like material: (1) the pore-pressure-based approach developed by Seed and updatedand laboratory methods and correlations for estimating post-earthquake strength ofmaterials that are susceptible to strength loss and several methods for performingdeformation analyses are also presented.

based on a static stability analysis using post-earthquake material strengths. Thissafety factor is intended to account for uncertainties in the geometry of the structure,

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in the shear strength, and in the delineation of zones that are potentially susceptibleto strength loss, and it also helps achieve designs for which predicted seismic defor-mations are within acceptable limits.

design criteria can be relaxed. Examples of these special cases include minor modi-will eventually improve seismic stability, and interim improvements for addressing-board).

in , 7.1b and 7.1c. These steps are described in detail in Section 7.4.4. A relatively straight-sophisticated laboratory testing, and seismicity evaluations are avoided) is described in Section 7.1.5.

can be summarized as follows:

1. Classify the structure and foundation based on type, size, downstream hazard po-

tential, and anticipated performance under seismic loading, per the criteria indicated

2. -tion as either (1) further seismic evaluation is not needed (go to Box 4) or (2) poten-tially susceptible to seismic instability such that additional analysis is required (goto Box 7).

and spatial distribution of the refuse materials can be variable. Identify zones in the

structure and foundation that may be susceptible to strength loss due to earthquakeshaking (Section 7.4.4.2).

4. Analyze the stability of the embankment using post-earthquake strengths (Sec-strengths for zones that are susceptible to strength loss. This analysis may be rela-large enough to allow design of massive (wide) embankments with broad crests,employing the basic and more straightforward methods are recommended becauseof their relative simplicity in design and regulatory review and their conservatism.-mates of post-earthquake strength, and relatively complex triggering analyses can be

performed to evaluate whether the earthquake shaking is actually strong enough totrigger strength loss in the materials that are potentially susceptible to strength lossSections 7.4.2 and ). A seismic hazard evaluation (Sec-tion 7.7 and ) may be needed as part of these more sophisticated testingdesign earthquake and to obtain representative time histories of acceleration. Thesebasic and more straightforward methods. The added costs of the more sophisticated

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Chapter 7

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Classify structure

and foundation

nitial xploration and ite Characterization

or existing structures this will include review of construction records, some subsurface exploration and some lab-

oratory testing. enerally more exploration and testing will be required for structures in Box 3 than in Boxes 1 and .

or new structures, properties of proposed materials must be estimated. ee 3 C 77.1 for structures requiring a

design plan approved by A.

Non-mpounding mbank-

ments hat Clearly ave No

oose Zones of ignificance

with espect to eismic

tability.

Coarse Coal efuse

mbankments

Combined efuse

mbankments

solated lurry Cells/

ilter Cake Cells

ow-azard-otential ams

Non-mpounding mbankments hat ay ave or Clearly ave ignificant

oose Zones

egregated efuse mbankments

tacked, verlapping or igh lurry Cell/ilter Cake Cell mbankments

mbankments with potentially ensitive oundations

pstream-Constructed mbankments or mbankment tages

mall, ignificant-azard-otential ams

ams less than 4 feet high or impoundments with less than 1, acre-feet

capacity that are well constructed and are unlikely to have issues with respect to

seismic stability.

valuate ost-arthquake tability

or sand-like material, use conservative estimates of us for any suspect zones. orsand-like material with N

(1,)> 15, use the drained strength. or soft clay-like

material (N < ) use us

. or stiff clay-like material use up

. ifferentiate clay-like

material from sand-like material based on gradation, Atterberg limits, and (ifavailable) C.

or existing embankments and dams, it may be necessary to obtain field data

related to the level of the phreatic surface, piezometric levels within the dam or

embankment, the geometry of fine and coarse refuse within the dam or embank-

ment, and material properties, particularly the degree to which fine refuse may have

consolidated due to the weight of overlying material. nly limited data are requiredat this point, as the evaluation is intended as a conservative screening analysis.

he purpose of this step is to decide whether analysis of the structure should start at

Box 1 or Box 3. his step may be skipped, in which case the analysis of the

structure starts at Box 3.

igh-azard-otentialams

arge, ignificant-azard-

otential ams

efinition of roblem eometry and aterial Characterization

f necessary, perform additional subsurface investigations to define the geometry of

embankment zones, obtain and/or C data, identify the phreatic surface and

piezometric levels within the refuse to estimate the degree of fine refuse consolid-

ation, and obtain samples for index testing. Classify materials as clay-like or sand-like. or zones of clay-like refuse, it may be desirable to obtain undisturbed tube

samples for laboratory tests to measure up

and to perform field vane shear testing

for estimating up

and us

.

nitial eismic tability Analysis

valuate static stability using post earthquake strengths. or loose sand-likematerial, use

usvalues based on and/or C data. or sand-like material with

N(1,)

> 15, use the drained strength. or soft clay-like material (N < ) use us

. orstiff clay-like material use

uequal to to 1 percent of

up(ection 7.4.4.3).

econfigure cross section to

obtain > 1., or perform

triggering and seismic stability

analysis (igure 7.1b)

tability is acceptable. erform

eformation creening and

Analysis (igure 7.1c).

Confirm that tatictability is Adequate

riggering and eismic

tability Analysis and

eformation creening

steps and eformation

Analysis are not required.

A (7) cites that

an impounding structure

should normally have a

minimum seismic stabilityfactor of safety of 1. and

allows for pseudo-static

analysis where embank-

ment or foundation

materials are not subject

to significant strength loss

as a result of seismic

loading.

s > 1.?

s > 1.5?

N

N

1 3

4

5

7

7A

7.1a C AB CNN

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teady-tate aboratory esting rogram

or loose, sand-like materials and N(1,)

< 15 or qt1

< 75, consider performing a steady-state laboratory testing programon undisturbed and reconstituted samples to refine values of

us.

his step and Box 1 may be deferred or skipped entirely, especially if loose, sand-like zones are not significant with

respect to stability. to skip to Box 11.

erform cyclic tests followed by static

tests to obtain better estimates of

strength reduction due to earthquake.

equires esign arthquake number

of cycles and seismic shear stresses.

(Correlations of earthquake-induced

strain to post- strength may be

developed in the future.)

Alternatively, use us

.

erform riggering Analyses

erform analyses to evaluate if earthquake will trigger strength loss. A seismic hazard assessment will be required forevaluating the agnitude and A for the esign arthquake and possibly for obtaining ground motion records.

Alternatively, assume that the post-earthquake strength for loose sand-like zones and soft clay-like zones isus

and skip

to Box 1.

f A < .g or C in loose zone

< .15

se oud et al. (1) to determine if

earthquake will trigger strength loss.

> 1.4 - No strength loss

< 1. - trength loss to us

1. < 1.?

e-analyze post-

stability with new

information from Boxes 11

through 15.

s > 1.?

valuate A and magnitude and

compute C

f A > .g and C in loose zone> than .15

Assume that earthquake will triggerstrength loss.

tability is Acceptable

erform eformation

creening and

Analysis (igure 7.1c)

or oose and-ike Zones

or oft Clay-ike Zones

N

N

1

17

1

1

1 1514

13

7.1b N AN C-AB ANA

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7-8

Chapter 7

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equires seismic hazard assess-

ment (A) for evaluation of

agnitude and A for esign

arthquake and possibly obtaining

ground motion records.

s the site in an area of low

seismic hazard

(ection 7.7.3.7)?

s the predicted pore-

pressure buildup in sand-

like materials small (C/

C > 1.)?

s the safety factor for post-

earthquake stability > 1.

for failure surface through

clay-like material?

AN

ANA

Are criteria for use of thepseudo-static procedure for

preliminary screening met?

oes the pseudo-static

meet required criteria?

eformations are consideredacceptably small. No further

analysis is required.

A

AN

ANA

Are the computed

deformations acceptable?

New and xisting tructures

odify design to reduce deformations and/or to increase available freeboard. e-evaluate modified design as

necessary.

n Certain Cases, Consider elaxing esign Criteria1. f making interim improvements to address a specific deficiency (e.g., adding an interim stage to improve freeboard).

. or modifications as part of closure activities in cases where the closure activities will improve the seismic stability.

3. or relatively minor modifications to existing structures in areas of low seismic hazard,

AN ANA

AN CNN

erform either:

1. Newmark Analysis if

C/C > 1., or

. Numerical Analysis withoutCyclic obility if

C/C > 1., or

3. Numerical Analysis with

Cyclic obility if

C/C < 1..

N

N

N

N

N

N

1

3

4

5

7

9

5. If stability is acceptable (safety factor of 1.2 or higher), evaluate potential deforma-tions (Step 7).

If stability is not acceptable, redesign or modify the embankment until stability is ac-ceptable (Box 17).

7. Evaluate potential deformations of the embankment caused by the earthquake shak-Section 7.5). The deformation analysis may involve a

7.1c AN CNN AN ANA

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relatively simple screening analysis or may require sophisticated computer model-ing. If not performed as part of Step 4, a seismic-hazard evaluation (Section 7.7 and) will be needed as part of the deformation analysis.

If the estimated deformations are within an acceptable range, accept the design. Oth-erwise, redesign or modify the embankment (Box D9).

7.1.3 Sand-Like Versus Clay-Like Material

as sand-like or clay-like depending on whether they exhibit monotonic and cyclic undrained shearloading behavior that is fundamentally more similar to that of either sand or clay. The methods for

the purposes of seismic stability and deformation analyses, are the strain at peak undrained strength peak. Loose sands and highly sensitive clays can reach peak undrained strength Sup at small strains,

Sup at higherthe boundary of these two types of behavior.

Loose material with shear strain at peak strength of less than 2 percent in an undrained monotonic- illustrates the associated stress-straincurves for these materials. Material with strain behavior between these descriptions is considered

borderline. It should be noted that shear strain in an undrained triaxial test is 1.5 times axial strain.1 3).

categorize materials as sand-like or clay-like. Laboratory stress-strain testing should be used to helpcategorize borderline materials.

The following criteria are recommended:

-7 or less.

Material should be considered clay-like if all of the following criteria are met:

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2009 MSHA Coal Refuse Disposal Facilities Manual - Blasting

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Transcript of 2009 MSHA Coal Refuse Disposal Facilities Manual - Blasting