RÉGIMEN DE INHABILIDADES PARA LOS CARGOS DE PRESIDENTE Y VICEPRESIDENTE

SUB-GRADE SUB-GRADE OPTIONAL GEOTEXTILE

Type of Formation Layer Minimum Required CBR Value

Blanket / Sub-ballast Layer 50 %

Prapared Sub-grade/ Top Layer 8 % of Formation

Sub-grade/Embankment Fill 5 %

Explanatory Notes : 1. Categories of soil Quality :

Sl. Soil Description w.r.t. Fine- IS Classifiacation Quality Particles (size less than to Referred Soil

75 micron) Quality (Suggestive)

1. SQ 1 Soils containing fines CL, ML, CL,ML,CI,MI

> 50 %

2. SQ2 ** Soils containing fines from GM, GC, SM, SC 12 % to 50 %

3. SQ3*** Soils containing fines GW, GP, SW, GW-

< 12 % GM, GW-GC, SW-

SM, GP-Gm, GP-GC, SP-SM, Sp-SC, etc.

Proposed Two Layers System Of Blanketing On Track Formation For Adoption On Indian Railways

(Reference Calculations based on UIC practices in terms of UIC Code 719R-1994)

SL Soil Quality Top Layer of Recommended Remarks Category in Formation Thickness lareal of

Sub grade (prepared Blanket for lute leads need in Subgrade)

embankment

Quality Thick- 20 T 22.9T 25 T 30T 32.5 T (CC+ (For 8+2) D.F.C.)

1 SQI SQ1 - 300 350 400 600 750 Geo-synthetiks to be used 2 SQ1 SQ2 500 150 200 250 450 600 Geo-synthetiks to be used 3 SQ1 S03 5OO 150 150 200 350 500 Goo-synthetics is optional 4 SQ2 SQ2 - 150 200 250 450 600 Geo-synthetiks to be used 5 SQ2 SQ3 350 150 150 200 350 500 Geo-synthetics is optional 6 SQ3 SQ3 - 150 150 200 350 500 Goo-synthetics is optional

Particle Size Distribution :

Material shall be well graded with typical particle size distribution as follows :

IS Sieve Percentage Passing Nominal Size (20mm) 53 mm 100 37.5 mm 100 26.5 mm 100 19.0 mm 95-100 9.5 mm - 4.75 mm - 2.36 mm 30-80 0.075 mm 6-10 Atterberg Limits :

• Liquid Limit : Maximum 30 (35 for and areas)

• Plastic Limit : Maximum 20

• Plasticity Index : 2 -10 (2 -IS for and areas)

• Linear Shrinkage : Maximum 3%

Maximum Dry Density : Minimum 2.0 t/cum

Soaked CBR : Minimum 50%, determined on material compacted

to 95% (min.) of Maximum Dry Density

General Soil Type USC Soil Type CBR Range

GW 40 - 80 GP 30 - 60 GM 20 - 60 GC 20 - 40 Coarse-grained soils SW 20 - 40 SP 10 - 40 SM 10 - 40 SC 5 - 20 ML 15 or Less CL LL < 50 % 15 or Less OL 5 or Less

Fine grained soils MH 10 or Less

CH LL > 50 % 15 or Less

14.0 Conclusion:

• The problem of formation failure is going to gain much importance in view of increased axle load, demand for increasing line capacity by reducing PSR and TSR, and need to bring economy in operation as well as to bring down asset life cycle cost.

• Formation even made of soil with sufficient bearing capacity may fail in punching and will need blanket cover.

• Blanketing is the only reliable method for formation rehabilitation having symptoms of ballast penetration.

• Depending on the traffic pattern selection of blanketing method can be done.

• It is possible to lay any thickness of blanketing layer.

• With reduced blanket thickness requirement and with use of geo grid reasonable progress can be achieved even in busy routes.

• Use of Ameca crane can be tried in RE area.

• Multiple working units is going to increase the progress in the same block.

• Apart from strengthening the top layer, widening of bank/provision of sub-bank will address the problem of sub grade weakness.

15.0 Recommendations:

1. The present specification for blanketing material is stricter than the previous specification. As per present specification blanketing material should have CBR of 50 and above with MDD of 2.0 ton per cum. It is very difficult to get a naturally occurring material of this specification. In fact only well graded gravel will meet the above specification. The guidelines issued by RDSO do not specify the method by which a blanketing material of above specification can be obtained. It will be useful to the field staff if RDSO comes with the blending proportions of different materials like quarry dust and gravel of different sizes up to 20 mm which are to be mixed to achieve the above specification.

2. In field blanketing of new formation during construction of new lines or doubling is much easier than blanketing of formation of running

track. The RDSO guidelines has not specified if any relaxation can be given wherever rehabilitation of formation is to be done for running track due to difficult circumstances at the field level in carrying out the work. These relaxations can be in the form of thickness of blanketing material etc. It is recommended that based on the studies, the minimum thickness of blanketing for rehabilitation of track may be advised separately.

3. It will be also useful if guidelines are issued as done for bridges regarding rehabilitation of formation whereby the horizon axle load is prescribed based on the future traffic for different routes for rehabilitation of formation.

4. The rehabilitation/renewal of formation should be treated as track renewal and wherever rehabilitation is to be done it should be considered as overdue track renewal arrear. These track renewal arrear should be wiped out in a time bound programme as it was done for TRR, TSR etc. duly making rout wise plan and fixing targets. 5. For running heavier axle load a strategy for preventive rehabilitation should be made even for those stretches where there is no PSR/ TSR at present, based on present track parameters, frequency of track attention, ballast penetration, type of sub grade soil etc in a particular stretch. Based on these parameters works of formation rehabilitation should be taken up for catering to future axle load.

Impact & Experience of Heavier Axle Load on