designing and construction of roads, subways, airfields

Scientific Herald of the Voronezh State University of Architecture and Civil Engineering. Construction and Architecture

60

DESIGNING AND CONSTRUCTION OF ROADS, SUBWAYS,

AIRFIELDS, BRIDGES AND TRANSPORT TUNNELS

UDC 625.717 Military Air Engineering University (Voronezh)

Ph. D. in Engineering, Assoc. Prof., Head of 32 department of Engineering Airfield Maintenance A. N. Popov

Ph. D. student of 32 department of Engineering Airfield Maintenance I. G. Shashkov

Voronezh State University of Architecture and Civil Engineering

D. Sc. in Physics and Mathematics, Prof. of Dept. of Building Machinery and Engineering Mechanics

A. V. Kozlov

Russia, Voronezh, tel.: 8-919-243-32-17; e-mail: [email protected]

A. N. Popov, I. G. Shashkov, A. V. Kozlov

A TECHNIQUE OF ESTIMATION OF TECHNICAL CONDITION OF RIGID

AIRFIELD PAVEMENTS IN THE CONTEXT OF RISK THEORY

Problem statement. To provide for safe takeoff and landing of modern aviation complexes, special

attention is given to technical condition of artificial pavements of runways which can be serviceable

or faulty, efficient or limiting. Available standard methods of an expeditious estimation of an opera-

tional-technical condition of airfield pavements are based on general principles of defect graduation

and of definition of integrated total generalized indicator of pavement condition and often yield the

results contradicting each other, which complicate making decision in relation to operation.

Results and conclusions. The classification of linear constructions of airfields by responsibility

level is proposed. Theoretical basics and practical recommendations on estimation of a technical

condition of rigid airfield pavements by permissible level of are formulated with respect to level of

risk with the use of principals of reliability theory and of risk theory. The recommendations pro-

posed rest on new principles of technical regulation established by Federal Law N 184-FZ “On

technical regulation”.

Keywords: airfield pavement, reliability, risk, runway.

Introduction

Airfield pavements in modern aerodromes are complex engineering structures that have to

meet so many high requirements imposed on them, among them particularly operational ones.

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The advancing level of technical operation involves first of all more rational organizational

patterns that would assist in creating a maintenance system allowing for timely and efficient

rehabilitation with minimum cost and labour.

Critical to the technical operation of aerodrome structures are the following:

adherence to the operational code during design process;

creating a pavement control system and related structures at different stages of their

operation.

There are two methods in which paving is maintained – by searching and eliminating dis-

tresses and by carrying out planned inspection and test activities. The first method is disad-

vantageous in the sense that it puts limits to its actual use. First, as aerodrome pavement is

routinely and normally used, a likelihood of identifying distresses is numerically small espe-

cially when such massive structures as a runway are in operation, thus resulting in a signifi-

cant drop in the efficiency achieved by searching and eliminating distresses at this point. Fur-

thermore, in practice, technical operation is organized with no sufficient information available

or none at all. This being the case, searching and eliminating distresses allows for assump-

tions to be made. A likelihood of identifying pavement failures and their timely removal de-

pends on whether these turn out true or false.

The second issue that is detrimental to the efficiency of the operational system in question is

that searching and eliminating distresses involves a series of events where in order for any

technical measures to be taken, there first should be an ongoing defect to be removed and on-

ly then can they act on its elimination. Since there should be some time delays between these

steps for proper preparations to be in place, searching and eliminating defects allows for a

time delay in their removal. In some cases, this may not meet the safety requirements for air-

port runways.

The third issue offsetting the efficiency of this method of the technical operation is that it does

not enable scheduling of repair and maintenance works as there is not a whole lot of variety of

pavements resulting in all of their present applications to a certain point under the same con-

ditions show the same likelihood of failure.

The above suggests that the major system of operating airport pavements that ensures its fre-

quency and aircraft safety is a system of inspection and test activities. This system means works


62

associated with restoring operational characteristics of runways are conducted not after defects

occur but so that to prevent them doing so. At the core of this united system of repair and main-

tenance works on airport facilities is a system of timely scheduled inspection and test activities.

The major challenge this system poses especially given its poor funding is that it provides no

comprehensive methods of analyzing the outcome of a study that would potentially enable not

only to assess the pavement condition but also to make predictions as to changes that might

happen and therefore sensibly allocate funding.

1. Analyzing current methods of the assessment of the technical condition of aerodrome

pavements

The assessment of the technical condition of aerodrome pavements of state aviation in accor-

dance with the regulatory documents [8, 9] includes the qualitative and quantitative assessment.

The qualitative assessment is performed to determine whether a pavement is fit to use in terms

of its load-bearing capacity in a specified type of aircraft by comparing aircraft classification

numbers ACN and a load-bearing capacity of РCN with the same subgrade strength [9].

A pavement classification number should not be lower than an aircraft classification number

operating on this very pavement [3, 9]:

,K ACN PCN (1)

where К is a coefficient considering the intensity of air traffic flows.

If the condition (1) is not met, it is necessary that the aircraft mass limits are introduced and

intensity of take-offs and landings is decreased.

The method ACN—РCN found a range of applications and is adopted as a regulatory docu-

ment in the Russian Federation [9, 10].

The quantitative assessment defines the operational suitability of pavements based on the

analysis of the nature and number of distresses [9]. The criteria describing the condition of the

pavement surface are the parameters describing the defects and wears (the width of exposure,

area, etc.) revealed during inspection. These are also quantitative indices of the technical con-

dition of a pavement surface and deterioration rate that reflect a number of ongoing defects

and wears and intensity of their manifestation.

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In practice, a whole range of Russian and foreign methods of operational assessment of the

technical condition of rigid aerodrome pavements are put into use [4, 5, 8, 12]:

of signal assessment Sk (FGUP GPI and NII GA “Aeroproject”);

determining the pavement condition index Ik (Ministry of Aviation Industry);

assessment of the technical and operational pavement performance using

N. V. Sviridov’s method;

determining the pavement integrity index MI (26 CSRI MR RF);

a standard method of determining an aerodrome pavement condition index PCI (USA);

determining a complex index Кк (26 CSRI MR RF).

The index Sk is computed based on cracks occurring on the pavement plates, spalling and

slabbing and is calculated using the formula

0

1005.00 (0.10 0.05 0.03 ),к ск тр шS N N NN

(2)

where Nск, Nтр, Nш is a respective number of the surface plates experiencing cracks, spalling

and slabbing; Nо is a total number of the plates on the pavement surface.

The method of signal assessment Sk is to be in compliance with the requirements set for an

airport performance [5].

The index Ik makes provisions for a close relation between “a weight” of defects and areas of

the pavement under our estimation as well as for a range of an influence major structural in-

dices have on the pavement condition index. The pavement is subdivided into sections for

which we calculate individual condition indices:

4 7

1 1

100k j ik i ij

j ik

I W V b aS

, (3)

where Sk is the area of the k-th section; Wj is a factor weight: W1 is a service life cycle, W2 is

an adhesion coefficient, W3 is an evenness, W4 is clogging; Vik is a percentage of the plates

with the failures of the i-th type obtained as a result of the survey of the k-th section; bi is a

weight of the i-th failure type; aij is the assessment of the influence of the i-th failure type on

the j-th factor.


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The weight of the i-th failure type bi and effect assessment aij are defined by the method of

expert poll.

N. V. Sviridov came up with the method of the assessment of technical and operational condi-

tion of pavements according to which a number of plates subjected to a certain type of distress

is divided into a total number of the plates in this area and as a result a density of distress is

obtained which is then multiplied by the weight of distress. Thus an average distress weight is

obtained for each its type and their sum also yields a total average distress weight whose val-

ue further guides the judgment as to what condition a pavement is currently in.

The general disadvantage underlying the methods of signal assessment Sk of the pavement

condition index Ik and N. V. Sviridov’s method is the assessment of the technical pavement

condition according to a number of distressed plates with no respect to the value of distresses

(height, area, etc.). A typical feature of the pavement integrity index МI is that it gives the

consideration to a number of distresses and the effect ‘a weight’ of distress has on the flying

safety. The pavement integrity index is determined using the following formula:

1,

ki i

i

n aMIn

(4)

where n, ni is a total number of plates and distresses of the i-th type; аi is the weight of dis-

tresses of the i-th type; k is a number of the identified distress types. If distresses and failures

of different types occur in one plate, when determining the index MI.

Abroad they use a US-developed method ASTM D5340-93 of quantitative and qualitative as-

sessment of the aerodrome pavement condition which is routinely used to determine the aero-

drome pavement condition index (PCI). This method is based on the same approach as the

Russian methods are, i. e. on visual identification of distresses in pavements, classification of

these distresses according to their weight and their severity, determining the integral assess-

ment of the pavement condition with regard to the density of distress propagation in the

pavement area. The index of the aerodrome pavement condition PCI was determined using

the formula

PCI = 100 – MaxCDV, (5)

where MaxCDV is the greatest value of the altered reduced value.

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In order to define the value of failures in rigid pavements, this method utilizes the already de-

termined weight functions for each distress. The functions are presented as graphs with vary-

ing degrees of distress (low, average, high) and its volume considered.

Similar to the index PCI in its essence and the algorithm of the assessment of the pavement

condition is the complex index Кк that is defined as described in [4]:

100 100,кA A Б Б В В Г ГK K P K P K P K P (6)

where РА, РБ, РВ, РГ are weight coefficients for the pavement areas, КА, КБ, КВ, КГ are the

values of the quality indices of the pavement area.

Depending on the value of the complex index, it is recommended that operational mainten-

ance, routine or major repairs be in place. A peculiar thing about the Кк is that it takes the

quality of the surface into special account.

Despite the common principles, each of these methods are particular in its own individual

way and are fundamentally different:

1. A varying approach to the algorithm of visual observation:

the method of determining the index PCI and the complex index Кк implies that the

elements of the airfield are divided into areas which are in turn are divided into samples;

N. V. Sviridov’s method, the method of determining the pavement condition index Ik

and the method of determining the pavement integrity index MI: the elements of the pavement

are divided into areas (sections);

the method of signal assessment Sk: the pavement is assessed element-wise.

2. A varying set of distresses of artificial pavements:

according to the method of determining Кк, 18 types of distresses are taken into ac-

count;

according to the method PCI — 15;

according to the method MI — 9;

according to N. V. Sviridov’s method — 12;

according to the method Ik — 12;

according to the method of signal assessment Sk — 3.


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3. Varying indices and ambiguity of the category of the technical condition of aerodrome

pavement.

Table 1 presents the resulting assessments of the condition of a part of the artificial runway

obtained using various methods.

Table 1

Example of the pavement condition assessment

Calculation method Index Value Pavement condition

Using the pavement condition index PСI 9.3 Poor

Using the complex index Кк 58.0 Good

Using the method of signal assessment Sк 4.0 Fit to operate

Using the pavement integrity index MI 3.1 Restricted operation

Using N. V. Sviridov’s method

1.2 Satisfactory

The analysis shows that the conclusions made as to the pavement condition are at odds with

one another, which obviously poses extra challenges on making operation-related decisions.

4. A common disadvantage of all the methods considered is that the pavement condition can

only be assessed at the moment of its monitoring which makes it impossible to forecast

changes in its technical condition.

2. Theoretical principles and practical guidelines on the assessment of the reliability of

the pavement areas using the major regulations and the risk theory

“Technical Regulation’ law was enacted in 2002 that established the risk management as a

characteristic shared by all structures. Its authors propose the assessment of the aerodrome

pavement condition in terms of a reliability level accepted and a degree of risk based on the

new principles of technical regulation and of the reliability theory. The subjects of the tech-

nical regulation in [15] were buildings and structures of any purpose (as well as networks of

engineering and technical provision and systems of engineering and technical provision) as

well as processes associated with buildings and structures and project designs (including ex-

amination), construction, installation, remedy works, operation and recycling (demolition).

The principles provided in [15] hold for all life cycles of a building or a structure. The docu-

ment in question sets out minimum necessary requirements for buildings and structures as

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67

well as for processes associated with buildings and structures and project designs (including

examination), construction, installation, remedy works, operation and recycling (demolition).

Following the identification process, a building or a structure is referred to an appropriate lia-

bility level which is a characteristic of a building or a structure defined according to the scope

of economical, social and environmental consequences that may follow their deterioration:

I — high. These are buildings and structures in compliance to the Urban Design Code

of the Russian Federation deemed overly hazardous, technically complex or unique objects;

II — normal: buildings and structures, except for buildings and structures of the high

and low liability levels;

III — low: these are buildings and structures for a temporary (seasonal) use as well as

buildings and structures for secondary use involved in the construction or reconstruction of a

building or a structure or those located on lands granted for individual housing construction.

The values of the reliability coefficient as related to buildings and structures of all liability

levels are given in Table 2.

Aerodrome pavements which following the construction are thus linear construction systems

with building above ground levels consisting of load-bearing structures are referred to struc-

tures with the high liability level whose failure is highly likely to have a heavy economic, so-

cial and environmental impact.

According to the regulations [8], aerodrome pavements are divided into groups of areas based

on the effect of the aircraft load and load-bearing capacity (Fig. 1).

Hence the fundamental principles [15] can apply to the pavement classification according to a

liability level:

high — areas Б (runways areas adjacent to the edges);

normal — areas A, Б (aircraft ramps), В and Г;

low — areas Б (terminal and junction helipads).

The overall feature of aerodrome pavement is its reliability. The reliability of aerodrome

pavement is knowingly a figure that describes the system’s ability to deliver unfailing per-

formance thus ensuring a safe take-off, landing and taxiing. Depending on the specification of

a system and its operation conditions, the regulations and guidelines defines the following in-


68

dicators of a system’s reliability. They are unfailing performance, durability, maintenance and

repairability, a longer service life and variability.

To provide an unbiased assessment of the operational suitability of aerodrome pavements, it

would make sense to introduce another indiсator of operational durability that describes its

ability to retain its working capacity till some boundary condition.

Table 2

Classification of linear aerodrome structures according

to the liability levels with consideration to [15]

According

to [15]

Considering

the structure [17]

According to the

guidelines [2] According to [16]

A st

ruct

ure

liabi

lity

leve

l

Rel

iabi

lity

coef

ficie

nts

A g

roup

of r

unw

ay a

reas

Aerodrome

element

Acc

epta

ble

relia

bilit

y

valu

es P

acce

ptab

le

Mar

gina

l fai

lure

coef

ficie

nt (t

oler

able

risk

)

Into

lera

ble

risk

Coe

ffic

ient

of v

aria

tion

of th

e qu

ality

of a

erod

rom

e pa

vem

ent

A d

egre

e of

risk

and

dam

age

I ≥1.1 Б

Areas of the run-

way adjacent to the

edges

0.9 0.1 > 0.05 ≤0.1 Low

II ≥1.0

В Middle of a runway 0.85 0.15 > 0.05

≤0.15 Average

А Edges of a runway 0.8 0.2 > 0.05

Main helipad 0.8 0.2 > 005

Г

Edges of the mid-

dle of a runway

except those adja-

cent to the junction

helipads

0.8 0.2 > 0.05

Б Aircraft parking 0.7 0.3 > 0.05

III ≥0.8 Б Junction helipads 0.7 0.3 > 0.1

≤0.2 High Terminal helipads 0.6 0.4 > 0.1

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69

Fig. 1. Groups of aerodrome pavement areas:

А — main helipads; runway edges; Б — runway areas adjacent to its edges; auxiliary and junction helipads;

bridge structures, ramps and similar structures used for aircraft parking; В — middle of the runway;

Г — width edges of the middle of the runway except those adjacent to the junction helipads

These all comply with the requirements for the load-bearing capacity but fail to provide flying

safety. It is recommended in [16] that tolerable risk be used as a measure of a level of flying

safety required. Risk is a probability of a damage to life or health of people, property of indi-

viduals and corporations, municipal and state property, environment, life or health of animals

and plants with respect to damage done.

The reasons causing disruptions in flying safety are distress and damage of aerodrome pave-

ments that are to be inspected and monitored within the framework of the risk theory. Opera-

tional durability thus defines a life cycle of the aerodrome pavement Т with certain damage of

a tolerable risk level. Their total number can be found based on the conditions of flying safety

and is established using the acceptable reliability level Рacceptable (see Table 2).

With respect to the analysis performed we propose a classification of linear aerodrome struc-

tures (see Table 2) that is not at odds with the current legislation of the Russian Federation

considering:

liability levels and reliability coefficients according to the requirements [15];

minimum reliability levels for aerodrome pavements consistent with the surveys pre-

sented in [2];

intolerable risk and coefficient of variation of aerodrome quality according to the re-

quirements [16].

Г

Г

В ББb

L

1 4 b1 4 b

1 2 b

1 50

12 L 1

4 L14 L

1 50

А А

Б

А А


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Let us look at a pavement as a system of N0 plates. related to the system, a plate failure is a

damage to it. In order to disrupt the performance of the entire pavement, a runway for exam-

ple, it is necessary that there is a number of distresses that overall lead to an event making fur-

ther flying operation impossible.

The system reliability equals a probability of its unfailing performance which is calculated

using the known formula [2]:

0

0( ) lim О Ot

t ON

N NP t

N

, (7)

where N0 is a total number of plates; Nоt is a number of failed plates in a calculating time in-

terval; t is time.

A more simple formula can be used in practical calculations:

( ) ,Н Н

О Н Ot

N NP tN N N

(8)

where NН is a number of intact plates.

Obviously, just as there can be no absolutely reliable technical systems, there cannot be any

pavements like that either. In the process of the operation of a pavement with Nо plates, by the

time t there is usually NН intact plates and Not failed ones.

Hence

No = NН+Not

is a constant value.

Assumingly, the failed plates are not substituted. A number of failed plates is

NН = No–Not,,

then the expression of reliability can be written as follows:

( ) 1 ,О Ot Ot

O O

N N NP tN N

(9)

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71

0

0

( ) ,tND tN

(10)

where D(t) is a pavement damage defined with a ratio of a number of the failed (distresses)

plates to a total number of plates on the runway area.

Reliability can also be as follows

( ) 1 ( ).P t D x (11)

Fig. 2 gives a graph of the reliability function that illustrates a probable behaviour of a pave-

ment during its operation.

Fig. 2. Reliability and failure of the pavement

We should not forget, though, that during the pavement operation there may come a moment

when its reliability is less than Pacceptable, i. e. there are distressed plates with distresses with

the values unacceptable according to the safe flying conditions based on [8, 9].

Hence the expression (11) for the pavement area can be written as follows:

0

0

( ) 1 ( ) 1 .tдоп

NP t D x PN

(12)

The formula (12) allows one to determine the reliability of areas of aerodrome pavements

which are classified in Fig. 1.

A degree of a plate’s distress is defined by distresses and their severity. How accurate the as-

sessments of the operational condition are depends on a set of distresses available to be ana-


72

lyzed. In the above methods of the assessment of the technical condition of a pavement sur-

face, a number of the distresses considered varies from 3 (the method of signal assessment

using the index Sk) to 18 (the method of determining the complex quality index Кк), which in

turn are divided into groups depending on a degree and effect they have on the operational

condition. Beyond any doubt, an infinite increase in a number of distresses allows for a more

accurate assessment of the technical condition of aerodrome pavements.

However, this approach results in increasing labour costs incurred in the inspection and main-

tenance of pavement and complexity of mathematical analysis. Other than that, the effect cer-

tain distresses have on operational durability (flying safety) is not significant and thus can be

left out of consideration. At the same time, minimizing a number of the parameters (n0) is

also unacceptable, since the result obtained does not reflect the actual condition of aerodrome

pavements. The paper [11] defines a set of distresses that exert a direct influence on flying

safety. They are namely spalling of the edges of the plates, deep raveling, rutting, potholes

and depressions, reinforcement stripping, cracking of the edge of the plates, failure of patch-

ing material.

Therefore, in order to calculate the reliability of a pavement area, it is necessary to determine

a number of distressed plates Not.

A degree of the development of these distresses of a certain plate is estimated from the pers-

pective of the risk theory:

( ) 1 ,P t r (13)

where r is a degree of risk.

A degree of risk of disrupting flying safety due to distresses occurring in aerodrome pave-

ments is evaluated using the ratio [14]

max

2 2max

0,5 ф

ф

Н Нr

, (14)

where Нa is the actual value of distresses; ф is a root-mean-square deviation of the actual

value of distresses; Нmax is a maximum value of distresses when a probability of non-desired

Issue № 1 (13), 2012 ISSN 2075-0811

73

effects is 50 %; max is a root-mean-square deviation of the maximum value of distresses;

Ф(и) is a Laplace function.

Following the results of the statistical calculations, the indices НФ and σф are defined based on

a sufficient number of measurements of the values of distresses occurring in aerodrome

pavements.

The coefficient of the variation of the actual value of a distress фHVC is evaluated using the

following formula:

фН фV

ф

СН

. (15)

The maximum value of a distress Нmax and its root-mean-square deviation max is determined

using the following:

max

max maxН

VС Н , (16)

where maxН

VС is a coefficient of the variation of the maximum value of a distress determined

using

max фН фV

ф

НVС С

Н

, (17)

max

max

22 2 2

max 2

25 1 252 ,

25 1

Ндоп V доп доп доп

доп НV

Н С Н НН Н

С

(18)

where Нacceptable is a maximum permissible value of a distress; доп is a root-mean-square dev-

iation of a maximum permissible value of a distress.

A root-mean-square deviation of the value of a distress is determined using the following

formula:

допН

доп V допС Н . (19)


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In order to assess the reliability of the pavement in areas A, Б, В or Г, it is necessary that risks

ri of the i-th distress on a certain plate is estimated and the obtained value of the reliability for

this area is compared to Pacceptable using Table 1:

( ) 1 .i i допP t r P (20)

If the condition (12) is not met, a plate is deemed distressed.

The value of pavement reliability is generally determined using the ratio

0

0

1 .tдоп

NP PN

(21)

Conclusions

1. Linear structures of aerodromes are classified according to a liability degree in com-

pliance to the Federal Law № 384-ФЗ ‘Technical Safety Regulations for Buildings and Struc-

tures’.

2. It is proposed that the index of operational durability is used as the indicator of opera-

tional and technical condition for time interval of continuous operation of aerodrome pave-

ments Т with certain damages of tolerated risks. Their total number may be found in pave-

ments based on flying safety conditions.

3. Theoretical principles of the assessment of reliability of areas of aerodrome pavements

using the fundamental principles of the reliability and risk theories.

References

1. State Standard (GOST) Р 51901.1-2002. Risk Management. The Analysis of Risk of

Technological Systems (Moscow, 2002) [in Russian].

2. A. P. Vinogradov, Reliability and Certification of Cement Concrete Pavements of Air-

fields (Moscow, 1994) [in Russian].

3. Technique of Determination of Classification Numbers of Aircrafts and Rigid Pave-

ments Airfields of Armed Forces Aviation (Moscow, 1992) [in Russian].

Issue № 1 (13), 2012 ISSN 2075-0811

75

4. Technique for Estimation of Operational Suitability of Pavements of Airfields of Armed

Air Forces (Moscow, 2007) [in Russian].

5. Serviceability Regulations of Civil Airfield Operation (Moscow, 1993) [in Russian].

6. А. N. Popov, I. G. Shashkov, A. V. Kochetkov, “Mathematical Modeling of Dynamics

of Change of Working Capacity of Rigid Airfield Pavements”, Building Materials, N 11

(2009), 69—73.

7. Directions on Inspection of the Elements of Airport Airfield of Armed Air Forces of

Russian Federation (Moscow, 2002) [in Russian].

8. Order of the Minister of Defense of Russian Federation N 455 “on the Statement of

Federal Aviation Rules “Serviceability Regulations of Airdromes Operation” (Moscow,

2008) [in Russian].

9. Order of the Minister of Defense of Russian Federation N 460 “On the Statement of

Federal Aviation Rules “Guidelines on Airdrome Operation” (Moscow, 2008) [in Russian].

10. Guidelines on Civil Airdrome Operation in Russian Federation (Moscow, 1995) [in

Russian].

11. E. N. Smirnov, V. S. Sokolov, G. Ya. Klyuchnikov, Diagnostics of Damages of Air

Field Pavements (Moscow, 1984) [in Russian].

12. A. P. Stepushin, “Estimation of Operational and Technical Conditions of Airfield

Pavements” (Moscow, 2008) [in Russian].

13. A. P. Stepushin, V. A. Saburenkova, Methodical Instructions on Probabilistic Calcula-

tion of Rigid Airfield Pavement Structures (Moscow, 1998) [in Russian].

14. V. V. Stolyarov, “Design of Highways with Consideration for Risk Theory” (Saratov,

1994) [in Russian].

15. The Federal Law N 384-ФЗ “Technical Regulations on Safety of Buildings and Con-

structions” (Moscow, 2009) [in Russian].

16. The Federal Law N 184-ФЗ “On Technical Regulation”, Moscow, 2002, 89 pp.

17. Sanitary Code (SNIP) 32-03-96. Aerodromes (Moscow, 1998) [in Russian].

designing and construction of roads, subways, airfields

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