pavement design for nr-1 pavement design for national road … · 1.5 design cbr based on the above...

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G-3. Pavement Design for NR-1

PAVEMENT DESIGN

FOR

NATIONAL ROAD NO. 1 (PHNOM PENH – NEAK LOEUNG SECTION)

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PAVEMENT DESIGN

Pavement of the Study Road is designed following the procedures stipulated in AASHTO’S

Guide for Design of Pavement Structures. Also, Asphalt Pavement Manual of Japan Road Association and Road Design Standard; Part II “Pavement” of Cambodia are referred as appropriate. The strength of pavement, denoted as SNB (structure number), is determined with the following equation.

Log10 W18 = ZR*S0 + 9.36*log10 (SN+1) - 0.20 + + 2.32*log10 MR - 8.07

-------(Eq. 1)

Where W18 = predicted number of 18-kip equivalent single axle load

applications, ZR = standard normal deviate, S0 = combined standard error of the traffic prediction

and performance prediction, ⊿PSI = difference between the initial design serviceability index, p0,

and the design terminal serviceability index, pt, and MR = resilient modulus (psi) (of subgrade); calcualoted from CBR.

Figure 1-1 shows the general flow of design of pavement.

Figure 1-1 General Flow of Pavement Design

Equation 1

Estimation of Axle Load Equivalency Factors (ALEF)

Estimation of Traffic Volume

Estimation of MR

Design CBR

CBR Tests

Estimation of ESAL (W18)

Determination of ZR, S0 and ∆ PSI

Determination of SN

Log10 {⊿PSI/(4.2 - 1.5)} 0.40 + 1094/(SN+1)5.19

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The following sections describe the procedures to determine the factors used in designing of pavement.

1. Design CBR 1.1 Assessment of Bearing Capacity of the Existing Subgrade

1.1.1 Field CBR Test and Laboratory CBR Test Bearing capacity of the existing subgrade was assessed using three kinds of tests; field CBR test, laboratory CBR test on the samples taken from the test pits and dynamic cone penetrometer test (DCPT). Field CBR tests were conducted at w0 to 25 cm below the surface of the unpaved shoulder to avoid the influence of top soil which is often different from the subgrade material and also compacted to higher degree than ordinary material below. Laboratory CBR tests were conducted on the samples taken from the test pits excavated after the field CBR tests had been completed. The laboratory CBR tests were conducted on 4-day soaked samples. The locations of the test-pitting and field CBR tests are as follows:

Table 1-1 Location of Test Pitting, Field CBR and Laboratory CBR Values CBR Value No. Location(KP)

Field* Laboratory1 1+184 R 15.0 7.4 2 7+050 L 14.6 3.2 3 11+381 R 45.7 2.7 4 16+000 R 9.1 8.8 5 23+002 L 16.9 3.3 6 30+000 R 8.0 2.5 7 34+980 L 7.9 2.2 8 39+900 L 14.0 2.0 9 44+600 R 11.7 3.3

10 45+290 L 7.4 1.5 11 51+132 R 5.0 2.1

As can be seen in the above, the field CBR values vary from 5.0 to 45.7, while laboratory CBR values vary from 0.8 to 16.2. There are large differences between the filed CBR values and laboratory CBR values. In general, field CBR values are larger than laboratory CBR values.

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However, there is no apparently consistent relation between the field CBR values and laboratory CBR values. One way of interpreting the differences between the field CBR values and laboratory CBR values may be that field CBR values represent the CBR during dry season while laboratory CBR values represent CBR during high water level season. The field CBR tests were conducted in June 2002 when the water level in Mekong River was still far below the road surface, while the laboratory tests were conducted on the water-soaked specimens.

1.2 Dynamic Cone Penetrometer Test Dynamic cone penetrometer test (DCPT) is commonly used in Cambodia to assess in-situ CBR values because it does not require large test equipment, and, thus, can be easily conducted. In this Study, DCPTs were conducted at every 1 km to obtain supplementary data of field CBR. In DCPT, CBR values are estimated from the number of blow against the unit depth of penetration (usually recorded every 10 cm). Because of this test procedure, DCPT yield estimated CBR values at every 10 cm of penetration up to 1 m deep. Average CBR over 1 m depth at each test locationwas obtained by the following formula:

CBRAVE = [(h1 x CBR11/3 + h2 x CBR2

1/3 + · · · )/100]3 Where h1, h2: thickness of each layer in cm CBR1, CBR2: CBR of each layer

Figure 1-1 shows the CBR values obtained by the DCPT. As seen in the figure, the CBR values thus obtained considerably fluctuate, ranging from 3 to 20, which are similar values with those of the conventional field CBT tests. It is difficult to find any tendency in distribution of in longitudinal direction along the Study Road.

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1.1.3 CBR Values Obtained in the Previous Studies In the past, there were two surveys on CBR of the Study Road; one by JICA Expert (Mr. Kawamura) and another by ADB for the design of NR-1. (They are the result of laboratory CBR tests.)

Organization/Project ADB (Design of Improvement of NR-1)

JICA Expert (Mr. Kawamura) for Preliminary Design of NR-1

CBR 1.2 – 7 (Design CBR: 3.5) 1.3 - 9

These values are slightly higher than the result of laboratory tests of this Study. 1.1.4 Evaluation of CBR of the Existing Subgrade Considering the available information on CBR, as described above, the CBR of the existing

subgrade is assumed to be 2 in high water level season and 7 in other seasons.

1.3 Improvement of Subgrade When CBR of subgrade is smaller than 3, it is usually more economical to improve the subgrade rather than increase the strength of the pavement structure. There are two types of methods widely used for subgrade improvement; chemical (lime or cement) stabilization, and mechanical stabilization or usage of selected material. In case of the Study Road, preliminary cost comparison indicated that usage of selected material is less expensive than chemical stabilization. Therefore, usage of selected material is considered here. Based on the survey on the available materials, the following layers are assumed for the design subgrade.

Figure 1-2 Assumed Layer Structure of Subgrade Average CBR of combination of the layers with defferent CBR values is obtained by the

Selected Material CBR = 30; T = 30 cm

Additional Embankment CBR = 5; T = 20 cm

Existing Subgrade Dry Season: CBR = 7 High-water Season: CBR = 2 T = 50 cm

100

cm

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following formula:

CBRAVE = [(h1 x CBR11/3 + h2 x CBR2

1/3 + h3 x CBR31/3 )/100]3

CBR values for dry season and high water season are obtained as the following. From the result of the CBR tests, in-situ and in laboratory, showed that CBR of the existing subgrade is 7 in dry season and 2 in high water season. Fro dry season,

CBRAVE = [(30 x 301/3 + h2 x 81/3 + h3 x 71/3 )/100]3 = 11.99. For high water season, CBRAVE = [(30 x 301/3 + h2 x 81/3 + h3 x 21/3 )/100]3 = 7.55. From these results, the rounded values are as follows.

1.4 Estimation of Average CBR over a Year CBR values for dry season and high water season obtained in the above are considerably different. This fluctuation in CBR is considerably large and needs appropriate consideration in determining the design CBR value for the Study Road. If CBR of 7 is used in the design, it will underestimate the bearing capacity of the existing subgrade, and may result in over-conservative pavement design. On the other hand, if CBR value of 12 is used, the result would be insufficient pavement strength. Therefore, average CBR value over a year needs to be evaluated with an appropriate method. “AASHTO Guide for Design of Pavement Structure” (pp II-12 ~ 14) (AASHTO Guide) shows the method to evaluate average CBR over a year where CBR fluctuates under certain climate, such as freeze-thaw cycle. Using the CBR values of dry season and high water season, and following

the procedure described in AASHTO Guide, average CBR values over a year is estimated at

9.3 as shown in the following.

Season Dry Season High Water Season

CBR 12 7

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Roadbed Relative Month Soil Modulus Damage

CBR/MR Uf

Jan 12/18,000 0.016

Feb 12/18,000 0.016

Mar 12/18,000 0.016

Apr 12/18,000 0.016

May 12/18,000 0.016

Jun 12/18,000 0.016

Jul 12/18,000 0.016

Aug 7/10,500 0.055

Sep 7/10,500 0.055

Oct 7/10,500 0.055

Nov 7/10,500 0.055

Dec 12/18,000 0.016

Total Uf = 0.3848 Average Uf = 0.0290 � MR = 13,900 (psi) � CBR = 9.27 The table and chart in the following page shows the procedure of estimating average CBR presented in AASHTO Guide.

1.5 Design CBR Based on the above discussion, CBR = 9 is used as the design CBR. Since the measured CBR values of the existing subgrade show large fluctuation with no apparent tendency in longitudinal

direction, design CBR of 9 is used over the entire section of the Study Road.

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Figure 1-3 Chart for Calculating Average CBR over a Year (AASHTO)

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2. Estimation of Traffic Volume and Equivalent Single Axle Load (ESAL)

2.1 Estimation of Traffic Volume In designing pavement, vehicles with light weight, such as motorcycles, mot-remorks, cyclos and bicycles, are disregarded because of their very small influence on pavement life, and only motorized 4-wheel vehicles, such as heavy trucks, passenger cars, are considered. The types of vehicles were counted in the traffic surveys as the categories of “Light Vehicle” and “Heavy Vehicle”. Future traffic volumes of Light Vehicle and Heavy Vehicle were estimated in “Traffic Forecast” of the Study. They are shown in Table 2-1 (next page). The total traffic volume of light vehicles and heavy vehicles for years 2006 – 2015 are summarized below:

Table 2-2 Summary of Forecasted Traffic Volume (2 Directions)

Section A B C D E F G Station Start -3.5 3.5 - 7 7 -14 14 -25 25 - 36 36 - 47 47 - End

Pk (MPWT) 5.6 – 9.1 9.1 – 12.6 12.6 – 19.6 19.6 – 30.6 30.6 – 41.6 41.6 – 52.6 52.6 - EndDaily, 2005 11,234 5,530 3,613 2,080 1,875 1,722 1,691

Light Veh. 2006-2015

Total (mil) 65.73 32.31 22.14 12.98 11.63 10.65 10.36

Daily, 2005 1,197 969 739 482 439 399 389 Heavy Veh. 2006-2015

Total (mil) 6.81 5.52 4.35 2.84 2.57 2.33 2.26

2.2 Design Life In this Study, the design life of pavement is assumed to be same year with the target year of the Project (2006 – 2015), and, thus, set as 10 years. It is also usual to se the design life of pavement at 10 years.

2.3 Estimation of ESAL Equivalent single axle load (ESAL, or W18) for each section is estimated with multiplying the total traffic volume as described above by load equivalency factors (ALEF). ESAL (2006 – 2015) = Total Traffic Volume (2006 – 2915) x ALEF The values of ALEF have been determined using the axle load data obtained through the vehicle weight survey. The process of determining ALEF is presented in a separate paper (Woking Paper RD-1). ALEF values for light vehicles and heavy vehicles are as follws:

Vehicle Type Light Vehicle Heavy Vehicle

ALEF 0.00356 1.89

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Using these values of ALEF and the total traffic volume as described above, ESAL (W18) for each section is calculated as the following: Table 2-3 ESAL (W18) of Each Section (Unit: million)

In the urbanized section, 4-lane (2 directions) is proposed in the Study. In such case, the design ESAL is to be determined by dividing the ESAL of 2-direction by 4. Howecer, theactual traffic situation is that right lane is mostly used by motorcycles and moto-remorks, and 4-wheel vehicles concentrate on the left (center) lane. Therefore, it is considered to be more reasonable to use ESAL as half of the 2-direction ESAL. As indicated in the above table, Sections D and E, Sections F and G are combined for the purpose of pavement design with regard to ESAL. Thus, the section of pavement design are st as the following:

Table 2-4 Sections of Pavement Design and Design ESAL

Pavement Design Section

1 2 3 4 5

Station Start – 3.5 3.5 - 7 7 -14 14 – 36 36 - End

Pk (MPWT) 5.6 – 9.1 9.1 – 12.6 12.6 – 19.6 19.6 – 41.6 41.6 - End

Design ESAL (W18) 6.56 5.27 4.15 2.71 2.22

Light Vehicle Heavy Vehicle Total ESAL Total ESAL Design

Sect-

ion Sta. ~ Sta. Traffic Vol. ESAL Traffic Vol. ESAL (2 Direction) (1 Direction) ESAL

2006-2015 2006-2015 (W18)

A 0.0 ~ 3.5 65.732 0.234 6.812 12.876 13.110 6.555 6.56

B 3.5 ~ 7.0 32.314 0.115 5.516 10.424 10.539 5.270 5.27

C 7.0 ~ 14.1 22.143 0.079 4.345 8.212 8.291 4.146 4.15

D 14.1 ~ 25.2 12.975 0.046 2.841 5.370 5.416 2.708

E 25.2 ~ 36.3 11.627 0.041 2.575 4.866 4.908 2.454 2.71

F 36.3 ~ 46.8 10.653 0.038 2.333 4.409 4.447 2.223

G 46.8 ~ 55.4 10.362 0.037 2.262 4.275 4.312 2.156 2.22

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3. Calculation of Structure Number Structure Number (SN) is an index to indicate strength of pavement. SN is calculated with the following formula: Log10 W18 = ZR*S0 + 9.36*log10 (SN+1) - 0.20 + + 2.32*log10 MR - 8.07

-------(Eq. 1)

Where W18 = predicted number of 18-kip equivalent single axle load applications, ZR = standard normal deviate, S0 = combined standard error of the traffic prediction and performance prediction, ⊿PSI = difference between the initial design serviceability index, p0,

and the design terminal serviceability index, pt, and MR = resilient modulus (psi) (of subgrade); calculated from CBR.

In this formula, W18, or ESAL has been determined as described in Section 2 above, while MR is calculated from CBR. Design CBR has been described in Section 1 above. The formula to

calculate MR is given below: MR = CBR x 1,500 (psi) In case of the Study Road, MR = 9 x 1,500 = 13,500 (psi) ZR, S0 and ∆ PSI are assumed as follows:

ZR: - 0.674 (R = 75 %: typical value shown in AASHTO Design Guide)

S0: 0.450 (typical value shown in AASHTO Design Guide)

⊿PSI: 1.9 (= 4.4 - 2.5: typical value shown in AASHTO Design Guide)

Calculation of SN is made by trial-and error method in computer. The results are shown below:

Table 3-1 Required SN for Each Section

Section 1 2 3 4 5

Station Start – 3.5 3.5 - 7 7 -14 14 – 36 36 - End

Pk (MPWT) 5.6 – 9.1 9.1 – 12.6 12.6 – 19.6 19.6 – 41.6 41.6 - End

ESAL (W18) 6.56 5.27 4.15 2.71 2.22

CBR 9

Calculated SN 3.345 3.231 3.111 2.906 2.815

Log10 {⊿PSI/(4.2 - 1.5)}

0.40 + 1094/(SN+1)5.19

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4. Design of Pavement Structure

4.1 Structural Coefficients Structural coefficients and drain factors of each layer used in the design is assumed as shown below: Table 4-1 Structural Coefficient and Drain Factor of Each Layer

Examples of Structure Number of each layer for typical thickness are shown in the table below:

Table 4-2 Examples of Typical Thickness of Layers and Their Structure Numbers

Thickness (T) Layer

cm

in

Layer Coefficient

(a)

T*a

Drain Factor

(D)

T*a*

D

Remarks

5 1.969 0.83 0.83 Surface Course (AC) 10 3.937

0.42

1.65

1.0

1.65

10 3.947 0.51 0.41

15 5.906 0.77 0.62

20 7.874 1.02 0.82

Base Course (Crushed Stone)

25 9.843

0.13 (CBR=80)

1.28

0.8

1.02

15 5.906 0.68 0.54

20 7.874 0.91 0.72

25 9.843 1.13 0.91

30 11.811 1.36 1.09

Subbase Course (Granular Material)

35 13.779

0.115 (CBR=30)

1.58

0.8

1.27

Layer Structural Coefficient Drain Factor

Surface Course (AC)

0.42 1.0

Base Course (Crushed Stone)

0.13 (CBR = 80) 0.8

Subbase Course (Granular Material)

0.115 (CBR = 30) 0.8

Surface Course

Base Course

Subbase Course

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4.2 Minimum Thickness of Each Layer Design of pavement is done by combining these thicknesses to make the total of structural numbers of the layers equal to, or lager than, the required SN, with minimum cost. However, it is usual practice to decide the minimum thickness of layers. AASHTO Design Guide stipulates the following thicknesses for asphalt concrete and aggregate base course.

Table 4-3 Minimum Thickness (AASHTO) (inches)

Asphalt Aggregate Traffic, ESAL Concrete Base

Less than 50,000 1.0 (or surface treatment) 4 50,001 – 150,000 2.0 4

150,001 – 500,000 2.5 4 500,001 – 2,000,000 3.0 6

2,000.001 – 7,000,000 3.5 6 Greater than 7,000,000 4.0 6

In the case of theStudy Road, ESAL of the entire section fall in the category of “2,000,001 – 7,000,000”. Accordingly, the minimum thickness of 3.5 inches (approximately 8.9 cm) is recommended for surface course. Similarly, minimum thickness of 6 inches (approximately 15 cm) is recommended for base course. Asphalt Pavement Manual of Japan Road Association (JRO) stipulates the following minimum thicknesses for surface course (total of “wearing course” and “binder course”).

Table 4-4 Minimum Thickness of Surface Course (JRO)

Class of Design Traffic Volume Thickness (cm)

L, A 5 B 10 (5)* C 15 (10)* D 20 (15)*

* Thickness in ( ) can be used where the base course material is asphalt-stabilized. The classes of traffic volumes used in the above table are as defined in the following table.

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Table 4-5 Class of Traffic Volume

Traffic Volume of Heavy Vehicles Class of Design Traffic Volume (Vehicle/day/direction)

L Less than 100 A 100 – 249 B 250 – 999 C 1,000 – 2,999 D 3,000 or more

When these criteria are applied, the traffic volumes of Sections 4 and 5 are classified as “Class A” and those of other Sections are classified as “Class B”. Accordingly, minimum thickness of 5 cm recommended for Section 4 and 5, and 10 cm is recommended for other Sections. (Please note that the traffic volumes of heavy vehicles shown in Table 2-1 are for 2-directions, while the traffic volumes shown in Table 4-5 are for 1-direction.) JRO’s Asphalt Pavement Manual also gives minimum thickness of base course and subbase course as shown in the table below.

Table 4-6 Minimum Thickness of Base Course and Subbase Course

Material/Construction Method Minimum Thickness of Layer

Asphalt-stabilized 2 times of the maximum grain size and 5 cm

Other than above 3 times of the maximum grain size and 10 cm

4.2 Cost Comparison of Alternatives 4.2.1 Alternatives of Pavement Structure Considering the minimum thickness of each layer as described above, and required SN as described in Section 3, the following alternatives are examined.

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Table 4-7 Alternatives of Pavement Structure

Section Start - St.

3 St. 3 - 7 St. 7 - 14

St. 14 - 36

St. 36 - End

Required SN 3.345 3.231 3.111 2.906 2.815

Surface Thick. (cm) 10 10 10 5 5

SN 1.654 1.654 1.654 0.827 0.827

A Base Thick. (cm) 20 20 15 25 25

L SN 0.827 0.827 0.620 1.033 1.033

T Subbase Thick. (cm) 24 21 24 29 27

1 SN 0.869 0.761 0.869 1.050 0.978

Total SN 3.350 3.241 3.143 2.911 2.838

Total Thickness (cm) 54 51 49 59 57


SN 1.654 1.654 1.654 0.827 0.827

A Base Thick. (cm) 15 15 20 20 20

L SN 0.620 0.620 0.827 0.827 0.827


2 SN 1.087 0.978 0.688 1.268 1.159

Total SN 3.360 3.252 3.169 2.921 2.813


Surface Thick. (cm) 10 5 10 10

SN 1.654 0.827 1.654 1.654

A Base Thick. (cm) 25 25 15 15

L SN 1.033 1.033 0.620 0.620

T Subbase Thick. (cm) 19 35 18 15

3 SN 0.688 1.268 0.652 0.543

Total SN 3.375 3.128 2.926 2.817

Total Thickness (cm) 54 65 43 40

4.2.2 Comparison of Costs Preliminary cost estimates are made on the alternatives listed in Table 4-7. For the purpose of cost comparison, cost indices using the cost of AC surface course with thickness of 5 cm as 1.000 are used. The result of cost comparison is shown in the table below.

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Section Start - St.

3 St. 3 - 7 St. 7 - 14

St. 14 - 36

St. 36 - End


Cost 2.067 2.067 2.067 1.000 1.000

A Base Thick. (cm) 20 20 15 25 25

L Cost 0.766 0.766 0.544 0.926 0.926


1 Cost 0.813 0.727 0.813 0.956 0.898

Total Cost 3.646 3.560 3.423 2.882 2.824


Cost 2.067 2.067 2.067 1.000 1.000

A Base Thick. (cm) 15 15 20 20 20

L Cost 0.544 0.544 0.766 0.766 0.766


2 Cost 0.984 0.898 0.607 10128 1.041

Total Cost 3.595 3.509 3.440 2.894 2.808

Surface Thick. (cm) 10 5 10 10

Cost 2.067 1.000 2.067 2.067

A Base Thick. (cm) 25 25 15 15

L Cost 0.926 0.926 0.544 0.544

T Subbase Thick. (cm) 19 35 18 15

3 Cost 0.607 10128 0.578 0.493

Total Cost 3.600 3.054 3.190 3.104

As indicated by bold-face letters, the following alternatives are with the lowest costs. Section 1: Alternative 2 Section 2: Alternative 2 Section 3: Alternative 1 Section 4: Alternative 1 Section 5: Alternative 2 In case of Section 3, the estimated cost of Alternative 3 is the lowest. However, the thickness of surface course does not satisfy the recommended minimum thickness of AASHTO and JRO, and, thus, this alternative is not recommended. The recommended pavement structures are summarized in the table below.

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Table 4-9 Summary of Pavement Structure

Section 1 2 3 4 5

Station Start – 3.5 3.5 - 7 7 - 14 14 - 36 36 - End

Pk (MPWT) 5.6 – 9.1 9.1 – 12.6 12.6 – 19.6 19.6 – 41.6 41.6 - End

Pavement Type A B C D E


SN 1.654 1.654 1.654 0.827 0.827

Base Thick. (cm) 15 15 15 25 20

SN 0.620 0.620 0.620 1.033 0.827

Subbase Thick. (cm) 30 27 24 29 32

SN 1.087 0.978 0.869 1.050 1.159

Total SN 3.360 3.252 3.143 2.911 2.813


Required SN 3.345 3.231 3.111 2.906 2.815

Figure 4-1 Pavement Structure

Surface

Base

Subbase

10 cm

15 cm

30 cm

10 cm

15 cm

27 cm

10 cm

15 cm

24 cm

5 cm

25 cm

29 cm

5 cm

20 cm

32 cm

Type A Type B Type C Type D Type E

Total Thickness 55 cm 52 cm 49 cm 59 cm 57 cm

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4.2.3 Comparison of Costs for Various Design Life Periods Although design life period of pavement is set at 10 years in usual practice, life cycle cost (LCC) of design life of 5, 10 and 15 years are compared to verify the justification of design life period. Table 4-10 shows the design factors and price indices of pavement of Section 1 and 5 for design life of 5, 10 and 15 years.

Section 1 5

Design Life (Year) 5 10 15 5 10 15

Total ESAL 3.07 6.56 10.89 1.03 2.22 3.72

Required SN 2.965 3.345 3.621 2.487 2.815 3.057

Thck. (cm) 10 10 10 5 5 5 Surface

SN 1.654 1.654 1.654 0.827 0.827 0.827

Thck. (cm) 15 15 20 15 20 25 Base

SN 0.620 0.620 0.827 0.620 0.827 1.033

Thck. (cm) 19 30 32 29 32 33 Subbase

SN 0.688 1.087 1.159 1.050 1.159 1.195

Total SN 2.962 3.360 3.639 2.497 2.813 3.056

Total Thickness (cm) 44 55 62 49 57 63

Actual Design Life (Year) Price Index as Surface (T = 5 cm) = 1.000

Surface 2.067 2.067 2.067 1.000 1.000 1.000

Base 0.544 0.544 0.544 0.544 0.766 0.926

Subbase 0.607 0.984 1.012 0.927 1.041 1.070

Total 3.218 3.595 3.845 2.471 2.807 2.996

Tables 4-11 and 4-12 show the comparison of LCC for these pavement designs.

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Table 4-11 Comparison of Life Cycle Cost for Section 1

Section 1

Design Life (Year) 5 10 15

Discount Cost

Year Rate Nominal Disc'td Nominal Disc'td Nominal Disc'td

0 1.00000 3.2180 3.2180 3.5950 3.5950 3.8450 3.8450

1 0.89286 0.0322 0.0287 0.0322 0.0287 0.0322 0.0287

2 0.79719 0.0322 0.0257 0.0322 0.0257 0.0322 0.0257

3 0.71178 0.0322 0.0229 0.0322 0.0229 0.0322 0.0229

4 0.63552 0.0322 0.0205 0.0322 0.0205 0.0322 0.0205

5 0.56743 0.0322 0.0183 0.0322 0.0183 0.0322 0.0183

6 0.50663 1.0000 0.5066 0.0322 0.0163 0.0322 0.0163

7 0.45235 0.0322 0.0146 0.0322 0.0146 0.0322 0.0146

8 0.40388 0.0322 0.0130 0.0322 0.0130 0.0322 0.0130

9 0.36061 0.0322 0.0116 0.0322 0.0116 0.0322 0.0116

10 0.32197 0.0322 0.0104 0.0322 0.0104 0.0322 0.0104

11 0.28748 1.0000 0.2875 1.0000 0.2875 0.0322 0.0093

12 0.25668 0.0322 0.0083 0.0322 0.0083 0.0322 0.0083

13 0.22917 0.0322 0.0074 0.0322 0.0074 0.0322 0.0074

14 0.20462 0.0322 0.0066 0.0322 0.0066 0.0322 0.0066

15 0.18270 0.0322 0.0059 0.0322 0.0059 0.0322 0.0059

16 0.16312 0.0322 0.0052 0.0322 0.0052 1.0000 0.1631

17 0.14564 1.0000 0.1456 0.0322 0.0047 0.0322 0.0047

18 0.13004 0.0322 0.0042 0.0322 0.0042 0.0322 0.0042

19 0.11611 0.0322 0.0037 0.0322 0.0037 0.0322 0.0037

20 0.10367 0.0322 0.0033 0.0322 0.0033 0.0322 0.0033

21 0.09256 0.0322 0.0030 0.0322 0.0030 0.0322 0.0030

22 0.08264 1.0000 0.0826 1.0000 0.0826 0.0322 0.0027

23 0.07379 0.0322 0.0024 0.0322 0.0024 0.0322 0.0024

24 0.06588 0.0322 0.0021 0.0322 0.0021 0.0322 0.0021

25 0.05882 0.0322 0.0019 0.0322 0.0019 0.0322 0.0019

Salvage value 0.05882 0.9804 0.0577 0.7000 0.0412 0.4000 0.0235

Total 6.8812 4.4022 5.6030 4.1644 5.1851 4.2317

Cost of overlay = Surface (5 cm) = 1.000 Cost of Maintenance = 1 %of Cost of New Construction

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Table 4-12 Comparison of Life Cycle Cost for Section 5

Section 5

Design Life (Year) 5 10 15

Discount Cost

Year Rate Nominal Disc'td Nominal Disc'td Nominal Disc'td

0 1.00000 2.5850 2.5850 2.8070 2.8070 2.9100 2.9100

1 0.89286 0.0259 0.0231 0.0259 0.0231 0.0259 0.0231

2 0.79719 0.0259 0.0206 0.0259 0.0206 0.0259 0.0206

3 0.71178 0.0259 0.0184 0.0259 0.0184 0.0259 0.0184

4 0.63552 0.0259 0.0164 0.0259 0.0164 0.0259 0.0164

5 0.56743 0.0259 0.0147 0.0259 0.0147 0.0259 0.0147

6 0.50663 1.0000 0.5066 0.0259 0.0131 0.0259 0.0131

7 0.45235 0.0259 0.0117 0.0259 0.0117 0.0259 0.0117

8 0.40388 0.0259 0.0104 0.0259 0.0104 0.0259 0.0104

9 0.36061 0.0259 0.0093 0.0259 0.0093 0.0259 0.0093

10 0.32197 0.0259 0.0083 0.0259 0.0083 0.0259 0.0083

11 0.28748 1.0000 0.2875 1.0000 0.2875 0.0259 0.0074

12 0.25668 0.0259 0.0066 0.0259 0.0066 0.0259 0.0066

13 0.22917 0.0259 0.0059 0.0259 0.0059 0.0259 0.0059

14 0.20462 0.0259 0.0053 0.0259 0.0053 0.0259 0.0053

15 0.18270 0.0259 0.0047 0.0259 0.0047 0.0259 0.0047

16 0.16312 1.0000 0.1631 0.0259 0.0042 1.0000 0.1631

17 0.14564 0.0259 0.0038 0.0259 0.0038 0.0259 0.0038

18 0.13004 0.0259 0.0034 0.0259 0.0034 0.0259 0.0034

19 0.11611 0.0259 0.0030 0.0259 0.0030 0.0259 0.0030

20 0.10367 0.0259 0.0027 0.0259 0.0027 0.0259 0.0027

21 0.09256 1.0000 0.0926 1.0000 0.0926 0.0259 0.0024

22 0.08264 0.0259 0.0021 0.0259 0.0021 0.0259 0.0021

23 0.07379 0.0259 0.0019 0.0259 0.0019 0.0259 0.0019

24 0.06588 0.0259 0.0017 0.0259 0.0017 0.0259 0.0017

25 0.05882 0.0259 0.0015 0.0259 0.0015 0.0259 0.0015

Salvage value 0.05882 0.4000 0.0235 0.6000 0.0353 0.4000 0.0235

Total 7.5279 3.7869 6.0016 3.3447 4.9304 3.2481

Cost of overlay = Surface = 1.000 Cost of Maintenance = 1 %of Cost of New Construction

G - 65

As can be seen in the tables, 10-year life period design is most economical for Section 1, and 15-year design is slightly more economical than 10-year design for Section 5. As stated before, it is usual practice to set the design life period at 10 years. Considering that the difference between the 10-year design and 15-year design foe Section 5 is small and that the 10-year design is a little more economical for Section 1, it is considered to be reasonable to adopt wo years as the design life period of the pavement for the Study Road.

5. Summary Design traffic volume, ESAL, CBR and pavement type for each section are summarized in Figure 5-1.

N

ATI

NA

L R

OA

D N

o.1

HO

RIZ

ON

TAL

ALI

GN

MEN

TPr

inte

d 21

Oct

200

2A(

angl

e)AZ

(deg

.)AZ

IMU

THD

ISTA

NC

ER

Cr

XMe

Sde

gree

dm

sm

mA

IA (d

)TL

LSLC

Es%

m

0BP

1,27

4,76

2.45

249

2,89

5.69

376

.976

.976

553

14

1,27

4,77

9.58

549

2,96

9.42

081

.281

.281

1149

75.6

920

-4.

34

1645

0.00

00.

000

0.00

0N

C-

25

1,27

4,79

4.72

849

3,06

7.20

1-8

9.6

90.4

9022

4798

.946

700

-9.

29

1058

56.2

1511

2.18

92.

254

NC

-3

61,

274,

793.

830

493,

202.

784

-80.

699

.499

2119

135.

586

650

-9.

08

5833

51.0

1710

1.82

61.

999

NC

-4

71,

274,

641.

152

494,

129.

517

70.3

70.3

7019

4193

9.22

595

0-

29.0

291

3824

5.92

848

1.29

131

.316

NC

-5

81,

274,

961.

366

495,

025.

217

61.2

61.2

6110

995

1.21

82,

190

-9.

29

931

175.

409

350.

071

7.01

4N

C-

69

1,27

5,24

0.69

049

5,53

2.66

142

.942

.942

5121

579.

243

900

-18

.318

1849

145.

071

287.

669

11.6

17N

C-

710

1,27

5,70

6.10

949

5,96

4.48

6-6

6.3

113.

711

339

3263

4.89

149

5-

70.8

7048

1135

1.79

861

1.69

511

2.27

84

608

121,

274,

891.

368

497,

824.

150

86.0

86.0

861

62,

030.

309

970

-27

.627

3825

238.

617

467.

943

28.9

193

509

131,

274,

954.

395

498,

729.

669

-79.

010

1.0

101

029

907.

710

1,40

0-

15.0

1459

2318

4.18

636

6.26

812

.064

350

1014

1,27

4,83

5.64

449

9,34

0.12

7-7

1.8

108.

210

813

2462

1.90

11,

640

-7.

27

1255

103.

399

206.

526

3.25

6R

C40

1115

1,27

4,63

5.02

849

9,94

9.46

7-7

1.4

108.

610

833

1264

1.51

50

-0.

30

1948

0.00

00.

000

0.00

0N

C-

1218

1,27

3,94

3.71

750

2,00

9.20

6-5

5.2

124.

812

445

562,

172.

656

1,46

5-

16.2

1612

4420

8.65

941

4.53

014

.785

350

1319

1,27

2,38

9.75

550

4,24

7.94

283

.983

.983

5651

2,72

5.20

450

020

00.

533

39.9

9140

.840

495

226.

228

80.0

0027

6.20

434

.057

460

1420

1,27

2,51

7.86

350

5,45

6.15

1-5

7.5

122.

512

227

371,

214.

982

300

150

0.78

137

.480

38.5

3830

4614

2.55

675

.000

126.

653

18.6

06N

C-

1521

1,27

2,22

0.86

750

5,92

3.05

4-7

4.6

105.

410

525

155

3.35

740

017

00.

544

36.1

1517

.017

236

96.1

3272

.250

46.7

355.

015

460

1623

1,27

2,10

7.76

850

6,33

3.18

1-5

4.5

125.

512

527

2042

5.43

61,

300

-20

.020

219

229.

678

454.

663

20.1

333

5017

241,

271,

726.

743

506,

868.

234

-49.

613

0.4

130

2422

656.

857

1,65

0-

5.0

457

271

.326

142.

564

1.54

1R

C40

1825

1,27

1,35

8.19

950

7,30

1.17

7-7

2.5

107.

510

728

2256

8.56

41,

600

-22

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5560

324.

554

640.

418

32.5

85R

C40

1926

1,27

1,20

4.32

250

7,79

0.02

177

.877

.877

467

512.

491

410

175

0.56

737

.337

29.7

2942

1514

6.21

374

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137.

863

14.7

584

6020

271,

271,

269.

379

508,

090.

128

-81.

398

.798

4240

307.

077

450

180

0.48

035

.992

20.9

2056

3311

9.24

972

.000

92.4

818.

109

460

2128

1,27

1,13

8.78

650

8,94

2.45

989

.389

.389

2058

862.

278

700

250

0.47

444

.637

9.4

921

4210

1.99

189

.286

25.0

892.

819

350

2229

1,27

1,14

1.23

750

9,15

8.27

3-8

0.5

99.5

9931

221

5.82

770

025

00.

474

44.6

3710

.210

104

106.

996

89.2

8634

.940

3.24

13

5023

301,

270,

972.

199

510,

166.

527

-63.

611

6.4

116

2611

1,02

2.32

61,

270

-16

.916

559

188.

887

375.

025

13.9

703

5024

311,

270,

588.

415

510,

938.

419

-70.

710

9.3

109

1951

862.

037

2,82

0-

7.1

76

2017

5.08

934

9.73

05.

430

NC

-25

321,

269,

845.

783

513,

055.

395

-70.

910

9.1

109

834

2,24

3.45

50

-0.

20

1117

0.00

00.

000

0.00

0N

C-

2633

1,26

9,63

4.20

051

3,66

4.93

7-4

1.3

138.

713

843

2164

5.22

078

027

00.

467

46.7

2529

.629

3447

252.

786

93.4

6230

9.22

527

.211

350

2734

1,26

9,02

3.66

551

4,20

0.87

8-5

0.8

129.

212

912

1481

2.39

51,

740

-9.

59

317

144.

869

289.

072

6.02

0R

C40

2836

1,26

8,32

6.81

351

5,05

5.18

4-4

9.1

130.

913

054

51,

102.

470

5,00

0-

1.7

141

5174

.071

148.

132

0.54

9N

C-

2938

1,26

7,12

9.56

651

6,43

7.25

8-5

3.5

126.

512

627

571,

828.

532

2,03

0-

4.4

426

878

.616

157.

154

1.52

2R

C40

3039

1,26

6,71

7.60

151

6,99

4.69

4-6

8.8

111.

211

112

1269

3.14

51,

450

-15

.315

1544

194.

274

386.

248

12.9

573

5031

401,

266,

465.

153

517,

645.

427

-61.

611

8.4

118

2232

697.

986

1,64

0-

7.2

710

1910

2.77

920

5.28

93.

217

RC

4032

411,

266,

094.

073

518,

332.

428

-61.

611

8.4

118

256

780.

814

0-

0.0

02

340.

000

0.00

00.

000

NC

-33

421,

265,

563.

467

519,

313.

010

-40.

613

9.4

139

2621

1,11

4.93

71,

170

-21

.021

115

217.

067

429.

253

19.9

663

5034

441,

264,

378.

847

520,

326.

944

-40.

313

9.7

139

4421

1,55

9.29

00

-0.

30

180

0.00

00.

000

0.00

0N

C-

3545

1,26

4,14

4.54

752

0,52

5.37

0-5

0.0

130.

012

958

2830

7.03

32,

040

-9.

89

4553

174.

257

347.

670

7.42

9R

C40

3647

1,26

3,23

0.96

552

1,61

5.11

7-5

9.3

120.

712

044

191,

422.

034

2,00

0-

9.2

914

916

1.54

532

2.39

06.

514

RC

4037

501,

262,

372.

145

523,

059.

309

-70.

710

9.3

109

1740

1,68

0.25

61,

290

-11

.411

2639

129.

263

257.

666

6.46

03

5038

531,

262,

060.

637

523,

949.

112

-47.

413

2.6

132

3843

942.

755

980

-23

.423

213

202.

510

399.

398

20.7

053

5039

551,

260,

754.

348

525,

367.

439

-33.

214

6.8

146

456

1,92

8.22

31,

420

-14

.114

623

175.

691

349.

605

10.8

283

5040

561,

259,

406.

868

526,

250.

833

-8.5

171.

517

132

221,

611.

237

1,02

0-

24.8

2447

1622

4.14

844

1.28

324

.338

350

4157

1,25

7,43

8.52

752

6,54

3.61

8-8

.617

1.4

171

222

1,98

9.99

70

-0.

20

1020

0.00

00.

000

0.00

0N

C-

4258

1,25

6,52

4.45

952

6,68

2.39

25.

518

5.5

185

3216

924.

542

1,37

0-

14.2

1410

1417

0.28

433

8.83

110

.542

350

4363

1,25

2,69

0.46

952

6,31

0.67

35.

518

5.5

185

2752

3,85

1.96

80

-0.

10

424

0.00

00.

000

0.00

0N

C-

4464

1,25

1,94

2.52

052

6,23

9.12

2-4

0.7

139.

313

917

5475

1.36

499

0-

46.2

469

5842

1.92

579

7.69

486

.160

350

4566

1,24

9,91

3.22

152

7,98

4.69

9-1

1.1

168.

916

856

22,

676.

769

980

-29

.629

388

259.

253

506.

894

33.7

123

5046

681,

247,

633.

666

528,

430.

529

-7.4

172.

617

238

482,

322.

743

2,36

0-

3.7

342

4676

.490

152.

927

1.23

9R

C40

4769

1,24

6,78

4.89

752

8,54

0.06

2-1

5.4

164.

616

435

185

5.80

71,

680

-8.

18

347

118.

407

236.

423

4.16

8R

C40

4870

1,24

5,35

8.11

352

8,93

3.50

5-6

8.8

111.

211

112

601,

480.

038

490

190

0.46

136

.830

53.4

5322

128

3.32

973

.673

382.

726

58.9

214

6049

711,

245,

086.

892

529,

632.

152

-88.

591

.591

2713

749.

446

530

-19

.819

4547

92.3

2418

2.81

37.

981

460

5072

1,24

5,08

0.10

552

9,89

9.63

326

7.56

791

.591

2713

0.00

00.

000

0.00

00

00.

000

0.00

00.

000

CU

RVE

ELE

MEN

TsIA

(d,m

,s)

No.

PI N

o.N

OR

THIN

GEA

STIN

GG-4. List of Horizontal Alignment Data

G - 67

G - 68

G-5. General Consideration on Soft Ground The Study Road traverses the marshy hinterland of Mekong River, and existence of soft ground is strongly suspected. From viewpoint of highway embankment, problems and countermeasures are briefly explained below. 1. Problems of Highway Embankment on Soft Ground. Problems associated with construction of highway embankment on soft ground and are summarized in the table below.

Table 1-1 Problems of Highway Embankment on Soft Ground

Problem Typical Phenomena Basic Mechanism Typical Countermeasure

Stability (Failure of Embankment)

- Crack in embankment - Rise of the ground

surface of the adjacent land

- Shear rapture of the soils in foundation

ground due to the load of embankment

- Control speed of embankment

- Mild angle of slope for embankment - Stabilizing berm - Improve foundation with vertical drain

Settlement (During construction)

- Settlement of embankment

- Consolidation of soils in the ground - Lateral plastic flow of soils in the ground

- Additional embankment to compensate settlement

Post-construction Settlement

- Uneven road surface

- Residual consolidation of soil

- Pre-loading - Vertical drain etc

2. Types of Soft Ground and Their Nature From viewpoint of highway embankment, soft grounds are categorized into three as described below: (1) Soft ground consisting of marine deposit Characteristics of marine deposits can be summarized as follows. (i) Generally fine grained (rich of clay) compared with deposits of on land (river or lake)

because they deposited in quiet water in the sea.

G - 69

(ii) More uniform both vertically and horizontally than river/lake deposits. (iii) Less strength than river/lake deposits because of rich clay content. (iv) Longer time needed for consolidation (squeezing out of water in soil) when load is

applied: This is due to longer path of water squeezed out because of uniformity, or “homogeneity” in the geotechnical terminology, in both horizontal and vertical direction.

(v) As a result of (iv) above, longer time is needed to complete settlement. (vi) Slow increase in strength due to slow consolidation speed (vii) As a result of (vi) above, stability of embankment against the failure of ground is slow

to be improved. All of these facts make marine deposits unfavorable for highway embankment. (2) Soft ground consisting of deposits on land Contrary to marine deposits, deposits on land (river or lake) have the following characteristics. ( (i) Usually coarse grained (sand or silt) and contains less clay. (ii) Less uniform both horizontally and vertically because they are transported by flood

water and flow conditions changes every year. (iii) Layered structure with alteration of sand, silt and clay. (iv) Strength is relatively high because there is less clay. (v) Larger strength compared to marine deposits because of coarser grain size. (vi) Shorter time needed for consolidation because thin sand layers function as “drainage”

path. (vii) As a result of (vi) above, settlement is completed in relatively short period. (viii) As a consequence of (vi), increase in strength of soil is faster than in the case of marine

deposits and stability of embankment increases faster than in the case of marine clay. Because of the characteristics as described above, river/lake deposits are less unfavorable for highway embankment than marine deposits. On the other hand, properties of river deposits may drastically change in horizontal and vertical direction. Therefore, it is necessary to conduct appropriate sounding of ground condition and to take precaution in execution are indispensable for river deposits. (3) Soft ground consisting of highly organic soil This type of soft ground is typically encountered in cold region, such as Canada and northern Japan where dead plants in marshy land deposit without being dissolved. This type of soft

G - 70

ground is very unfavorable for highway embankment because of the following characteristics. (i) Very low strength and, thus, very low stability of embankment (ii) Large amount of post-construction settlement (iii) High water content which requires special preparatory works and equipment for

embankment. Very fortunately, it is rather rare to encounter this type of soft ground with large scale in tropical climate like Cambodia. 3. Definition of Soft Ground Usually, soft ground is defined as soil layer(s) with N-value of 4 or less exists for certain thickness, such as 10 m. However, past experience shows that the soil layer with N-value of 3 or larger usually does not pose serious problem for highway embankment unless the height of embankment is very high (for example higher than 10 m). 4. Position (depth) of soft layer Experience tells that serious problem of stability and settlement is generally anticipated where soft layers with N-value of 2 or less within some 10 m deep from the ground surface. For example, even if there is a soft layer with N-value of one (1) at 10 m or more below the ground surface, and the layers above this soft layer are relatively firm (say N-value 4 or more), then, highway embankment is safely constructed without serious problem of stability, unless the height of embankment is large (for example higher than 10 m). This is due to the fact that the load of the embankment is distributed by the relatively firm layers above the soft layer and becomes small enough when it reaches the soft layer.

G - 71

N = 5

N = 10

N = 7

N = 1 (Soft Layer)

Mor

e th

an 1

0 m

Figure 1-1-X Soft Layer in Deep Place and Decrease of Load

Decrease of Load

G - 72

G-6. Preliminary Analysis of Stability and Estimation of Settlement of Embankment on Soft Ground

1. Estimation of Settlement The conditions as shown in Figure 1-1 were assumed. Assumed e-log p curve is shown in Figure 1-2.

Figure 1-1 Condition Assumed for Estimation of Settlement Calculation of Settlement Using the data of the consolidation tests on the samples obtained from the soft layer, settlement due to consolidation is calculated with the following formula:

S = SHee

��

�

01

Where S: Settlement (m) ∆e: change in void ratio of soil due to loading of embankment, determined from the e-log p curve obtained by consolidation test e0: void ratio of soft soil before construction of embankment HS: thickness of soft layer (m).

3.6ｍ

3.

0 m

3.

5 m

γt = 2.0 t/m３

γt = 2.0 t/m３

γt = 1.8 t/m３1.75 m

G - 73

Figure 1-2 Assumed e-log p Curve

S = SHee

��

�

01

= 30095.01

05.0�

�

(cm)

= 7.7 cm Residual Settlement According to the past experience, 70 to 90 % of the total settlement occurs during the construction. Therefore, amount of residual settlement, SR, or post-construction settlement (settlement occurring after completion of embankment) is estimated as follows. SR = 7.7 x (1 – 0.8) = 1.5 cm Since the assumptions and calculation adopted in the estimation above is very simplified, the result of calculation should be interpreted as to show only the overall magnitude of the problem. Therefore, it can be said that the magnitudes of settlement and residual settlement are in the order of 10 and 2 cm, respectively. These values are considered to be relatively small. The calculation shown here is very preliminary and considers only one soft layer. The reason for

0.95

1.00

0.95

0.90

0.85

0.80

0.75

Void

Rat

io, e

Pressure, p (kN/m2)

0.90

10 100 1000

0.47

5 1.

05

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this simple calculation is that soils of other layers are relatively firm and it can be assumed that

the settlement due to consolidation of other layers are relatively small. The purpose of the

estimation made here is to show the magnitude of settlement and degree of difficultness of the problem. More detailed analysis needs to be made at design stage.

2. Analysis of Stability For the analysis of stability, the conditions as shown in Figure 2-1 were assumed. Factor of safety, Fs, against circular slip failure was calculated. Minimum Fs = 1.51 was obtained. This is considered to indicate sufficient stability against failure. (Usually minimum Fs of 1.2 to 1.3 are stipulated in the design manuals of highway. For example, Design Manual of Japan Highway Public Corporation stipulates Fs = 1.25.)

Similarly to the estimation of settlement, this stability analysis is for the purpose of show the

degree of seriousness of stability problem. More detailed analysis is needed at design and execution stages wherever soft ground is suspected or encountered.

Figure 1-3 Stability Analysis by Circular Slip Surface Method

14.00

γt = 2.0 tf/m C = 2.0 tf/mφ = 20°

γt = 2.0 tf/m C = 2.0 tf/mφ = 20°

γt = 1.8 tf/m C = 1.5 tf/mφ = 0°

γt = 2.0 tf/m C = 2.0 tf/mφ = 20°

3

2

2

3

3

2

2

3

Top Soil(old Fell Material)

Soft Clay/Silt

Sandy Silt

3.6

03.0

03.5

03.0

0

2.00

Fs min = 1.51

1:2.01:2.0

(0,0)

CL

St. 18+500

CAMBODIAN NATIONAL ROAD No.1

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G-7. Life Cycle Cost Analysis of Pavement To verify the economic justification of usage of AC pavement, Life Cycle Cost (LCC) analysis was made for AC pavement and DBST. This paper describes outline of the LCC analysis.

1. Example of Expenditure of Road Maintenance To estimate the cost of maintenance of the Study Road, actual expenditure of the maintenance of the existing national roads are desired. The rehabilitation of the principal national roads of Cambodia started after the end of Civil War in 1992, and many of them are still being implemented. Accordingly, there are only very few cases where the data on expenditure of road maintenance are available. The followings are the examples of expenditure of actual road maintenance.

1.1 NR-1; C1 Section (Study Road) Rehabilitation of the Study Road was implemented from 1994 to 1996 with financial assistance by ADB. In this improvement, many sections were widened to secure necessary width for 2-lane. Single-layer bituminous surface treatment (SBST) was adopted for the pavement. The civil work was executed by force account. In 1997, pot holes started to appear. However, practically no repair could be done because of lack of fund, until 2001. In 2001, urgent repair works were implemented with a fund of Cambodian Government. Total amount of actual expenditure was Riel 2.2 billion or approximately US$ 0.55 million. This amount corresponds very approximately 10 % of the cost of new construction of DBST for whole section of 55 km. Since this repair works were implemented as very urgent relief, the quality of the works was not high and the area of repair was limited. This fact implies the following:

Assumed Condition for DBST Construction

Length 55,000 m

Pavement Width 6.0 m

Total Area of Pave. 330,000 m2

Unit Cost $16.9/ m2

Total Cost $5.577 million

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(i) Condition of SBST pavement becomes intolerable 5 to 7 years from the time of new construction if no routine maintenance is done. (ii) The cost of minimum repair at this stage is approximately 10 % of the cost of new construction of DBST. In 2002, severe pot holes are to be repaired as a part of ADB’s Emergency Flood Relief Project. In the Bill of Quantity of the contract, total 2,000 m2 of repair of pot holes and 2,000 m2 of repair of edge break are listed for the 36 km-long section (KM 24 – 60). This corresponds approximately 2 % of the total area of pavement of this section. This figure was very provisionally decided for the purpose of tendering, based on the visual evaluation by the consultant for the Emergency Flood Relief Project. After the works were started, it was felt that the method repair of pot holes is not sufficient and MPWT is currently reviewing the repair method. Even after revision of repair method, this repair work is limited to very severe pot holes, and other less severe pavement defection will be left untouched. Therefore, new necessity of repair will arise from next year and afterwards. MPWT is planning to request the necessary budget allocation for these maintenance works. This implies the following: (i) One year after the minimum repair works, more than 2 % of the total pavement area needs to be repaired. Table below summarizes these maintenance works.

Table 1-1 Summary of Maintenance of the Study Road

Year of Implementation

Type of Works Total Cost ($ 1,000)

Fund Source

Remarks

1994 - 96 Road rehabilitation NA ADB Include widening

2001 Urgent repair of pavement 550 GOC* Approx. 10% of new construction of DBST

2002 Urgent repair of pavement (15)** ADB Approx. 2% of total pavement area

*GOC: Government of Cambodia ** This is the figure listed in the original contract and may vary depending on the actual conditions.

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It should be emphasized that the above record of maintenance does not mean that MPWT is satisfied with the situation of maintenance. MTWT had to accept this situation because of the shortage in the fund for maintenance. Therefore, better maintenance would have been implemented if appropriate fund had been available.

1.2. NR-4 This highway was rehabilitated under USAID program. Rehabilitation was implemented in year 1994 – 1995. The type of pavement was AC. In year 2000, small “dents” were observed on the pavement surface very sporadically. Some of them developed to pot holes and they were repaired by MPWT. The total expenditure for this repair was Riel 68 million, or approximately US$ 17,400. Compared to the total length of NR-4 (214 km), this amount of repair cost is considered to be very small. This figure becomes more impressive when the fact, that this highway is used by heavy trucks connecting Phnom Penh and Sihanoukville, is considered. The cost of AC pavement for entire 214 km-long section is very approximately estimated at US$ 21.7 million. The above-mentioned cost of repair represents less than 0.1 % (0.08 %) of the estimated cost of new construction of AC pavement. Overall condition of the pavement of NR-4 with these sporadic potholes was much better than that of NR-1. The present condition of pavement of NR-4 is still in fairly good and very little repair is observed to have been done up to today. Therefore, it is reasonable to assume that pavement of NR-4 is still in much better condition than that of NR-1 even without any repair. (Of course this will result in the necessity of earlier rehabilitation and larger amount of cost than those expected under present maintenance practice.) In 2001, GOC decided to give a private firm the concession of collecting the toll for maintenance in exchange of assigning the firm of responsibilities for maintenance. Since concessionaire of road maintenance was effective, the firm has been carrying out routine maintenance. The cost of maintenance was not available to the Study Team.

Assumed Condition of AC Construction

Length 214 km

Width 6.0 m

Total Area of Pave. 1,284,000 m2

Unit Cost $ 22.1/ m2

Total Cost $21.7 million

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From this fact, the following can be derived. (i) Routine maintenance cost of AC pavement is less than 0.1 % 5 to 6 years after construction. (ii) AC pavement is fairly intact under substantially heavy traffic

2. Scenario of Maintenance Expenditure Based on the facts of actual maintenance in Cambodia, two scenarios for future maintenance are assumed for the purpose of Life Cycle Cost Analysis of pavement as follows: (i) Scenario 1: Minimum Maintenance This scenario is a copy of what happened on the Study Road as described above. The assumptions are summarized below.

Table 2-1Minimum Maintenance Scenario of DBST

Period Maintenance Work 1st – 4th years after construction No maintenance work, no expenditure: Pavement

deteriorates to unacceptable level. 5th year Repair is implemented to recover the pavement condition to

lowest acceptable level: Expenditure = 10% of cost of new construction

6th – 9th year Minimum repair: Expenditure = 2% of the total area x $7.5 10th – 12th year Pavement deteriorates to the level that lowest acceptable

level can not be maintained by minimum maintenance: Rehabilitation is implemented for 3 years. Total cost is the cost for new construction.

13th year and after Repeat the cycle of 0 -14th year above

Table 2-2 Minimum Maintenance Scenario of AC Pavement

Period Maintenance Work 1st – 10th year after construction No maintenance work, no expenditure: Some pot holes

occur but overall condition still acceptable compared ordinary DBST.

11th year Pot holes repaired: Total cost is 0.5% of the new construction (0.1% x 5 years)

12th – 14th year New pot holes occur and repaired: Cost is 0.1% of new construction per year.

15th – 17th year Severely damaged pavement is rehabilitated by overlay: Unit cost of overlay is $9/ m2

18th – 22nd year No maintenance

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(ii) Scenario 2: Acceptable Maintenance Scenario 1 assumes almost what was actually implemented in the past for DBST. As for AC, the scenario assumed less maintenance than actually done to balance the condition of AC pavement with that of DBST, and worse than actually anticipated. In Scenario 2, maintenance of AC is assumed to be same to actual condition in the past case of NR-4. To balance the condition, better maintenance for DBST is assumed. It is usually agreed that practical life period of DBST with ordinary maintenance is 5 to 7 years. Therefore, 7 years is assumed to be life period of DBST here. As for practical life period of AC pavement, there are very limited data. One literature in Japan indicates that repair works increases when application of axle load in terms of ESAL exceeds 1 million. In case of Section 5 of the Study Road, estimated ESAL for design life of 10 yeas is approximately 2. Therefore, it is assumed that with ordinary maintenance, overlay becomes necessary 10 years after construction. Based on the above assumptions, the following scenario is assumed.

Table 2-3 Acceptable Maintenance Scenario for DBST

Period Maintenance Work

1st year after construction No maintenance work

2nd – 6th year 2% of total pavement area/year: Unit cost = $7.5/ m2

7th – 9th year Rehabilitation of entire pavement, Implemented over 3 year

10th year and after Repeat the cycle of 1st – 10th year above

Table 2-4 Acceptable Maintenance Scenario of AC Pavement

Period Maintenance Work

1st – 5th year after construction No maintenance work

6th – 10th year Repair of pot holes etc: Cost = 0.1% of new construction per year

11th – 13th year Overlay implemented: Unit cost = $ 9/ m2

14th and after Repeat the cycle of 1st -13th year above

3. Estimation of LCC 3.1 Assumed Conditions and Scenario LCC analysis was made on Section 5 of the Study Road. The reason for this was that the estimated traffic volume of Section 5 is the smallest among those of the five sections of the Study Road, and, thus, Section 5 is considered to be most suitable for adopting DBST. The conditions assumed and used in the analysis are summarized in the table below. Anayses were made for “Minimum Maintenance Scenario” and “Acceptable Maintenance Scenario” as

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described in Section 3 above.

Table 3-1 Assumed Conditions of LCC Analysis

Item Assumed Condition

or Value Remarks

Length of Road 18 km Section 5: St. 36 - 54 Width of Pavement 7.5 m @3.75 m x 2 Area of Pavement 135,000 m2 AC Pavement Structure Type F Refer Figure 13-2-2 of Main Text Unit Cost of New Construction $ 22.1/ m2 Based on the cost estimate used in

Subsection 13.2.1 of Main Text Total Cost of New Construction $ 2,983,500 Unit Cost of Overlay $ 9.0/ m2 Used for budget allocation by DPWT of

Phnom Penh Total Cost of Overlay $ 1,215,000 Unit Cost of Routine Maintenance $ 5.5/ m2 Repair of pot holes: figure used by

DPWT of Phnom Penh DBST Structure 19 mm surface treatment Base and subbase are same to AC Unit Cost of New Construction $ 16.9/ m2 Estimated for the above pavement

structure Total Cost of New Construction $ 2,281,500 Unit Cost of Rehabilitation $ 7.5 Base course and surface reconstructed Total Cost of Rehabilitation $ 1,012,500 Unit Cost of Routine Maintenance $ 5.5/ m2 Figure used for budget allocation by

DPWT, Phnom Penh

3.2 Calculation of LCC Tables 3-2 and 3-3 show the calculation of LCC for “Minimum Maintenance Scenario” and “Acceptable Maintenance Scenario”. The result of the calculation is summarized in the tablebelow.

Table 3-2 Summary of LCC Calculation LCC ($1,000)

AC DBST AC/DBST Minimum Maintenance 3,111 2,729 1.14 Acceptable Maintenance 3,328 2,867 1.16 As can be seen in the table above, LCC of AC is higher than that of DBST by 14 % for “Minimum Maintenance Scenario” and by 16 % for “Acceptable Maintenance Scenario”.

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Table 3-2 Comparison of LCC: Minimum Maintenance Scenario

(Unit: $ 1,000)AC DBST

YearConstructio

n &Maintenanc

DiscountRate*

Discounted Cost

Construction &

Maintenanc

DiscountRate*

Discounted Cost

0 2,984 1.00000 2,983.50 2,282 1.00000 2,281.501 0 0.89286 0.00 0 0.89286 0.002 0 0.79719 0.00 0 0.79719 0.003 0 0.71178 0.00 0 0.71178 0.004 0 0.63552 0.00 0 0.63552 0.005 0 0.56743 0.00 186 0.56743 105.336 0 0.50663 0.00 15 0.50663 7.527 0 0.45235 0.00 15 0.45235 6.728 0 0.40388 0.00 15 0.40388 6.009 0 0.36061 0.00 15 0.36061 5.36

10 0 0.32197 0.00 338 0.32197 108.6711 15 0.28748 4.29 338 0.28748 97.0212 0 0.25668 0.08 338 0.25668 86.6313 0 0.22917 0.07 0 0.22917 0.0014 0 0.20462 0.06 0 0.20462 0.0015 405 0.18270 73.99 0 0.18270 0.0016 405 0.16312 66.06 0 0.16312 0.0017 405 0.14564 58.99 186 0.14564 27.0418 0 0.13004 0.00 15 0.13004 1.9319 0 0.11611 0.00 15 0.11611 1.7220 0 0.10367 0.00 15 0.10367 1.54

Salvage value (729) 0.10367 -75.57 (74) 0.10367 -7.70Total 3,111.46 2,729.27

*Discount rate: 12 % / Yr

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Table 3-3 Comparison of LCC: Acceptable Maintenance Scenario

(Unit: $ 1,000)AC DBST

YearConstructio

n &Maintenanc

DiscountRate*

Discounted Cost

Construction &

Maintenanc

DiscountRate*

Discounted Cost

0 2,984 1.00000 2,983.50 2,282 1.00000 2,281.501 0 0.89286 0.00 0 0.89286 0.002 0 0.79719 0.00 15 0.79719 11.843 0 0.71178 0.00 15 0.71178 10.574 0 0.63552 0.00 15 0.63552 9.445 0 0.56743 0.00 15 0.56743 8.436 3 0.50663 1.51 15 0.50663 7.527 3 0.45235 1.35 338 0.45235 152.678 3 0.40388 1.20 338 0.40388 136.319 3 0.36061 1.08 338 0.36061 121.71

10 3 0.32197 0.96 0 0.32197 0.0011 1,215 0.28748 349.28 15 0.28748 4.2712 0 0.25668 0.08 15 0.25668 3.8113 0 0.22917 0.07 15 0.22917 3.4014 0 0.20462 0.06 15 0.20462 3.0415 0 0.18270 0.00 15 0.18270 2.7116 0 0.16312 0.00 338 0.16312 55.0517 3 0.14564 0.43 338 0.14564 49.1518 3 0.13004 0.39 338 0.13004 43.8919 3 0.11611 0.35 15 0.11611 1.7220 3 0.10367 0.31 15 0.10367 1.54

Salvage value (122) 0.10367 -12.60 (405) 0.10367 -41.99Total 3,327.97 2,866.59

*Discount rate: 12 % / Yr

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G-8. Further Study on Traffic Situation at Chbar Ampov Intersection 1. Present Condition of Chbar Ampov Area

Chbar Ampov Intersection is located at the eastern end of Monivong Bridge. It exists between National Road No.1 and National Road No.361, while at the western of the bridge, there is Kbal Ntal Intersection that is between National Road No.1 and National Road No.2 & 3. Chbar Ampov Intersection is located on the National Road No. 1 (NR-1) in Mean Chey District of Phnom Penh Municipality, and the name of road at this section is Viyadapuda Road.

Old Monivong Bridge had been constructed in 1929 on the extending line of Chbar Ampov

Intersection, and it had collapsed due to scouring of western abutment. Since the existing Monivong Bridge was constructed in 1960s about 50 m north from the position of old bridge, Chbar Ampov Intersection becomes staggered.

300 m stretch of Viyadapuda Road at the Phnom Penh side is divided 6 lanes road, and

concrete buildings and permanent residences exist along the road. Densely developed commercial and residential areas are spread in this district, and grid-pattern road network comprising local narrow streets sustain the development of this built-up area.

View from Kbal Ntal Intersection to Monivong Br. Crowded and congested Chbar Ampov Market

Fig. G-8-1 shows the built-up area and road network in the vicinity of Chbar Ampov Intersection.

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2. Problems related to Road Traffic

12 hrs (6:00 – 18:00) traffic volume on Monivong Bridge are of 168,000 vehicles (Motorcycle: 87%, Light vehicles: 11%), that is equivalent to 64,000 pcu, while 12 hrs traffic volume from all directions at Chbar Ampov Intersection is observed 128,000 vehicles or 44,000 pcu. These figures account for the saturation of traffic capacity quantitatively, and it incurs problems related to road traffic in this area where traffic congestion frequently occurs.

From physical and qualitative viewpoints, public facilities such as Chbar Ampov Market,

bus terminal, taxi terminal, ferry terminal and pagoda are scattered in the vicinity of Chbar Ampov Intersection. One of salient features related to road traffic in this area is found many turning traffic. East-westward through traffic at this intersection is predominant at Chbar Ampov Intersection, and it is considerably affected by turning traffic access to and egress from such public facilities.

Under such circumstances, this intersection has many disadvantages in the traffic

engineering aspect as follows:

1) Unbalanced number of lane occurs between western entrance and eastern exit at Chbar Ampov Intersection. NR-1 has 6 lanes at 300 m stretch of Viyadapuda Road, but it reduces up to 2 lanes on Monivong Bridge.

Divided 6-lane National Road No. 1 Undivided 2-lane Monivong Bridge

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2) It is basically 4-leg intersection, but entrance traffic is generated from more than four directions actually because there are additional local roads to connect to the intersection.

Undivided 2-lane National Road No.361 Narrow local road in Mean Chey District

3) Bus terminal, taxi terminals, public market and pagoda encompass Chbar Ampov Intersection, and accordingly many turning traffic are generated.

4) It is situated on the steep slope of approach section of the bridge, and moreover it is staggered. This intersection consists of two 3-leg intersections in the short distance theoretically.

Situated on the steep slope of bridge approach Congested bus terminal besides intersection

3. Issues on Improvement of Chbar Ampov Intersection

The improvement of Chbar Ampov Intersection has been studied in the past, namely the feasibility study of “Ho Chi Minh City to Phnom Penh Highway Improvement Project” funded by ADB. According to hearing from MPWT staff, some grade separation structures were examined to maneuver traffic effectively in the course of the study and the improvement by roundabout was proposed finally as shown in Fig. G-8-2. The study team

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examined the improvement plan of channelized intersection as shown in Fig. G-8-3.

However, it is obvious that the present traffic volume exceeds the traffic capacity at intersection considerably, and common issues were discussed technically to identify the following points:

1) The existing intersection is situated on the steep slope of approach section of the bridge as well as staggered shape, and it is inevitable defect of intersection design, that is to say, below standard.

2) Queue of waiting vehicles at entrance is long enough to cause traffic interlocking that is the most serious congestion at intersection.

Congested Chbar Ampov Intersection is one of major traffic bottlenecks on National Road No. 1 C-1 Section (Phnom Penh – Neak Loueng Section) together with Neak Loueng Ferry and Kokir Market. Accordingly, it is desirable to improve it simultaneously if NR-1 C-1 is improved a flood-free road to an all-weather standard. However, physical constraints such as close location to the bridge, steep slope, staggered shape and lack of land availability in the vicinity are so severe and complicated that it is difficult to solve the problems only by an engineering design without the construction of 2nd Monivong Bridge. 2nd Monivong Bridge is proposed in the Study on the Transport Master Plan of the Phnom Penh Metropolitan Area conducted by JICA in 2001 to relieve traffic bottleneck and increase the traffic capacity.

Besides intersection improvement, traffic management is also one of practical measures to cope with such problems. Making full use of existing road network in the area, one-way traffic control was examined in the course of the study. However, it is sure that traffic management can contribute facilitating east-westward traffic flow, but it does not contribute alleviating traffic congestion due to many turning traffic access to and egress from public facilities. Moreover, it may bring about adverse environmental impacts along local roads that will be selected as a part of National Road No. 1.

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4. Recommendation on Improvement of Chbar Ampov Intersection

It may conclude that the construction of 2nd Monivong Bridge is badly required to solve the problems related to road traffic as shown in Fig. G-8-4 even though it is out of the scope of work for the Study. However, the scheme of 2nd Monivong Bridge surely leads to the drastic change of Kbal Ntal Intersection where National Roads No.2 & 3 connect to National Road No. 1.

Accordingly it is necessary to conduct a comprehensive study on the spatial plan including traffic management in the area of Chbar Ampov Market and its surrounding because an improvement plan such as adoption of roundabout, channelization or grade separation structure is hard to be selected as practical and substantial measures.

It is recommended that the in-depth investigations and more comprehensive study covering Chbar Ampov Market, Kbal Ntal Intersection and its surroundings in Mean Chey District of Phnom Penh Municipality should be conducted for the improvement plan at Chbar Ampov Intersection.

pavement design for nr-1 pavement design for national road … · 1.5 design cbr based on the above...

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