Special cases are designed for road projects where extremely low quality of existing material is present at the specific locations, especially for subgrades. However, it is recommended that selection of such modules (where necessary) shall be made with the approval of competent authorities.

Each of the 882 road design cases are based on combination of various bins (6 TL x 7 SG x 7 SB x 3 BS), as shown below:

TL - Traffic Load Bins:

0.000-0.05 Million ESALs (represents best)

0.051-0.15 Million ESALs

0.151-0.50 Million ESALs

0.501-2.00 Million ESALs

2.001-7.00 Million ESALs

7.001-10.00 Million ESALs (represents worst)

SG - Subgrade Bins in terms of CBR/MR:

1-3.999%/(1500-5999 psi) (special case) (represents worst)

4-6.999%/(6000-10499 psi) (special case)

7-9.999%/(10500-14999 psi)

10-25.998%/(15000-20557 psi)

26-45.998%/(20558-29617 psi)

46-70.998%/(29618-39101 psi)

71-100%/(39102-48685 psi) (represents best)"

SB - Subbase Bins in terms of CBR/Esb: 30-34.99%/(15000-15999 psi) (special case) (represents worst)

35-39.99%/(16000-16999 psi) (special case)

40-49.99%/(17000-17999 psi) (special case)

50-69.99%/(18000-18999 psi)

70-84.999%/(19000-19999 psi)

85-99.99%/(20000-20999 psi)

100-100%/(21000-45000 psi) (represents best)

BS - Base Bins in term of CBR/Ebs:

80-89.99%/(28500-29249 psi)

90-99.99%/(29250-29999 psi)

100-100%/(30000-45000 psi)"

Each modular design case requires a careful selection of designated bins. This designated bin , as any error/wrong selection of the input data can result in design errors and wastage of public money. The concerned department must establish a protocol of using these modules by taking into consideration the roles and powers of various officers involved.  

It is important to note that selection of bins for traffic and material properties (subgrade, subbase, base and AC) shall be based on authentic testing protocols for ascertaining material property bins, and traffic counts data for traffic count bin.

In this regard, a facilitation worksheet is provided for selection of Modular Case (refer to worksheet named 'Selection of Modular Case'). This worksheet shall be used to extract the file of the specific modular case number via entering material property bins, and traffic count bin by the SDO concerned and must be verified by the XEN concerned. This will avoid wastage of public money as well as to ensure safety/convenience to the road users.

Additional protocols may be devised involving higher ranking officers such as SEs and CEs while optimizing the specific module that will involve actual properties and traffic load."

ESALs - Equivalent Single Axle Loads (ESALs) is a cumulative traffic load summary statistic. The statistic represents a mixed stream of traffic of different axle loads and axle configurations predicted over the design or analysis period.

In this repository, the Traffic load bins contain Cumulative "Equivalent Single Axle Loads (ESALs)". This bin can be directly selected based on cumulative ESALs for entire design life. It has to be calculated by entering the current traffic counts data in the seperately provided Excel sheet. Please note that the design process will consider the upper value of the selected load bin.

The subgrade modulus of resilience is a design parameter of the road pavement structure, which is significantly affected by the overlying load and traffic load.

In this repository, after selection of Traffic Load bin, an appropriate Subgrade bin must be selected on the basis of subgrade modulus of resilience (MR). In the absence of MR values calculated from lab/field tests, the actual CBR value can be entered. Though it is strongly recommended that MR values calculated from lab/field tests shall be used instead of CBR-based MR values.

Please note that the design process will consider the lower value of the selected material bin.

A subbase is a layer of crushed aggregate which bears the load of paving and provides a strong base for paving to be laid onto. Subbases evenly distribute the weight of both the paving and any weight placed onto the paving afterwards. In this repository, after selection of Subgrade bin, an appropriate Subbase bin must be selected based on the subbase elastic modulus (Esb).

In the absence of Esb values calculated from lab/field tests, the actual CBR value shall be entered. Though, it is strongly recommended that Esb values calculated from lab/field tests shall be used instead of CBR-based Esb values. Please note that the design process will consider the lower value of the selected material bin.

Base Course in pavements refers to the sub-layer material of an asphalt roadway and is placed directly on top of the undisturbed soil (Sub-Grade) so as to provide a foundation to support the top layers of the pavement. 

In this repository, after selection of Subbase bin, an appropriate Basecourse bin must be selected on the basis of basecourse elastic modulus (Ebs). In the absence of Ebs values calculated from lab/field tests, the actual CBR value shall be entered. Though, it is strongly recommended that Ebs values calculated from lab/field tests shall be used instead of CBR-based Ebs values. Please note that the design process will consider the lower value of the selected material bin.

Based on the combination of Traffic Load bin, Sub-grade bin, Subbase bin, Basecourse bin, a unique nomenclature is developed for each modular design in the form:

Case #_(TL_Bin)_(SG_Bin)_(SB_Bin)_(BS_Bin)

For example, considering 1st options from each bin, the unique nomenclature will be as follows.

Case 1_(TL_0.000-0.05)_(SG_(CBR_71-100)_(MR_39102- 48685))_(SB_(CBR_100)_(MRsb_21000-45000))_(BS_(CBR_100)_(MRbs_30000- 45000))

When “(S)” appears in the Specific Design Case Number, it will mean that it is a special case. In this case, the design will be based on Subgrade CBR less than 7%, and/or Subbase CBR less than or equal to 50%. For such cases, keep the following points in mind;

Subbase material having CBR less than 30% is to be rejected.

Special case “(S)” will result in extra-ordinary layer thickness.

Rate adjustment/analysis is to be performed if either of these or both appears in the Specific Design Case Number, since the MRS rates corresponding to these values are not available as of MRS 2022.

For the given road designs, the material and thickness of Base and Subbase layers were computed in the Design Output sheet considering the required design SN, AASHTO recommendation for minimum thicknesses for various load ranges, and practical considerations to optimize the cost.

In these designs, the values of material coefficients are based on AASHTO Fig. 2.5, 2.6 and 2.7 along with their minimum and maximum range defined.

Coefficient for Asphalt layer (a1) is recommended between 0.43 and 0.44 for corresponding Eac value of 417,000 and 445,000 psi respectively (reference: AASHTO 1993 Design Guide Section 2.3.5, and https://www.fhwa.dot.gov/engineering/geotech/pubs/05037/alt.cfm#f067).

For modular design cases, a value of 0.43 is considered to stay on safe side. This value can be reviewed using actual design sheet if a value of Eac is higher than 417,000 psi.

The values of coefficient for base (a2) and subbase (a3) are linked with their elastic modulus values (reference: AASHTO 1993 Design Guide Section 2.3.5, and https://www.fhwa.dot.gov/engineering/geotech/pubs/05037/alt.cfm#f067)

Minimum thickness for AC and Base are based on AASHTO guideline (Reference: AASHTO 1993 Design Guide Section 3.1.4).

Subbase thickness is kept as minimum 4"" (100mm) for small roads for practical reasons, where needed."

The costs mentioned in the Design Output sheet are primarily used for optimizing the design SN for layer thicknesses. These values are assumed for a 3.7m wide lane and are tentative only. The actual cost for each module is given in the 'Quantities & Cross-Section' sheet.