Provide a summary of the subgrade, subbase and base properties that are needed a

ID: 1710145 • Letter: P

Question

Provide a summary of the subgrade, subbase and base properties that are needed as input in the ME design method. An engineer wants to determine if a certain asphalt would be graded as PG58-28. At what temperatures should he or she run the following tests? a. DSR for rutting analysis b. DSR for fatigue cracking analysis c. BBR Plot the following relationships considering ranges of compressive strength and density for normal weight concrete a. Flexural strength vs compressive strength b. Tensile strength vs compressive strength c. Modulus of elasticity vs compressive strength Calculate the required layer thicknesses for a new asphalt pavement on a fiat draining base and subgrade (the water drains out of the pavement within a period of two days). The pavement structure is expected to be saturated less frequently than 5% of the time. Following data is also given: a. Estimated ESAL over 15 year performance period=3 million b. Subgrade resilient modulus =25000 psi c. Reliability=95% d. Std error=0.45 e. Change In PSI= 2.5 (from 4.5- 2.0)

Explanation / Answer

SUBGRADE

The granular material provided between the soil sub grade and base course layer to increase the thickness pavement at a low cost is termed as sub base. It consists of preparation of subgrade to final level .the thickness of subgrade is 500 mm, which is laid in three layers.

After spreading mechanical compaction is done using soil compactor of 11.6 ton, but with vibrator weight get double. The roller shall commence from lower edge and move towards upper edge. Rolling is done with 1/3rd overlapping

Function:

To provide uniform support pavement.

To distribute the load on the pavement on layer below it.

To provide good drainage for this purpose, subgrade should be given a proper camber may constructed.

CBR should not less than 10%.

Rolling pattern:

The Sub-base provided under the concrete slabs comprises Granular Sub base (GSB) as lower sub-base

The material to be used for the work shall be natural sand, crushed gravel, crushed stone, or combination thereof depending upon the grading required. The material shall be free from organic or other deleterious constituents and shall conform to the quality standards as prescribed in the specifications.

The water absorption value of the coarse aggregate shall be determined as per IS 2386 (Part III). If this value is greater than 2 percent, the soundness test shall be carried out on the material delivered to site as per IS 383.

Strength of Sub-Base: It shall be ensured prior to actual execution of sub-base that the material used in the sub-grade satisfies the requirements of minimum CBR of 8 percent along with other physical requirements like density (98 percent of the modified Proctor lab MDD) when compacted and finished.

Properties

Limits

Max liquid limit

25%

Max plastic limit

Min CBR

Percentage 10 fines

50kn

Water absorption

FOR BASE MATERAIAL WE GENERALLY USE WET MIX MACADAM

WET MIX MACADAM

Wet Mix Macadam is a pavement layer wherein crushed graded aggregates and granular material, like, graded course sand arc mixed with water in mixing plant and rolled to a dense mass on a prepared surface. It has many advantages over the WBM construction. These include superior gradation of aggregate, faster rate of construction, higher standard of densification that can be achieved, less consumption of water and stricter standards of quality achievable. The specification can be adopted for sub-base and base courses. The work may be done in many layers. The thickness of an individual layer shall not be less than 75 mm and can be up to 2(X) mm provided suitable type of compacting equipment is used.

Coarse aggregates shall be crushed stone/crushed gravel/shingle, not less than 90 per cent by weight of gravel/shingle pieces retained on 4.75 mm sieve and shall have at least two fractured faces. The aggregates shall conform to the physical requirements set forth in Table

The aggregates shall conform to the grading given in table Material finer than 425 micron shall have Plasticity Index (PI) not exceeding 6. The nominal size of aggregate to be used in a given case would depend on availability. The final gradation within the limits set forth in Table 2 shall be well graded from coarse to fine and shall not vary from the lower limit on one sieve to the higher limit on the adjacent sieve or vice versa.