Category: Cement Treated Base

General         

Soil cement stabilization is a construction method which is  used to increase the strength of subgrade soil by mixing it with cement as well as water.  This method statement pertains to usually construction of top 150mm of subgrade and earthen shoulders with 2% (two percent) cement by weight mixed with approved soil including all leads and lifts as per Technical Specifications modified Clause 403.

1.CONSTRUCTION EQUIPMENT:

The following equipment shall be used:

1. Disc Harrows with tractor for scarifying , pulverizing and mixing
2. Motor Grader for leveling
3. Vibratory Compactor for compaction
4.  Water tanker with sprinkler for mixing of water as well as curing

2.DESIGN  : The mix design shall be done on the basis of 7 days unconfined compressive strength and durability test and the laboratory strength shall be at least 1.5 times the minimum field  UCS value stipulated in the contract. The cement to be used is of grade 43 and the quantity to be used is 2% by weight & is of dry density of soil.

3.CONSTRUCTION SEQUENCE:  

Mix in place method will be adopted. In this method the mixing of the soil – cement is done at the place where it will be finally placed. It consists of the following steps:

1.   The Sub grade is cleared of all undesirable materials such as boulders, debris, stumps etc. It is then leveled to the required formation level and true to the camber.
2. The leveled sub grade is scarified to a depth equal to the proposed thickness of the soil cement mix i.e 150 mm. This will be done by disc harrows pulled by the tractors.
3. The scarified soil is then pulverized till all the particles pass through 26.5 mm sieve and 80% pass through 5.6mm sieve. (Refer table 400.7 MORT&H Specification). This will be achieved by using disc harrows pulled by tractors.
4. The pulverized soil is properly shaped to require grade and cement is spread uniformly over surface. The cement to be used is of grade 43 and the quantity to be used is 2% by weight & is of dry density of soil. It is then intimately dry mixed till the mixture gets uniformly mixed.
5.   The required quantity of water is sprinkled over the surface and the wet mixing is done till the mixture is uniform in the colour. However the mixing should not be continued after the cement has started hydrating, as it would result in a loss of strength. The moisture content compaction is checked vide IS 2720 (Part 2) shall neither be less than the OMC corresponding to IS 2720 (Part 8) not more than 2% above it.
6. The operation (d) & (e) should be completed within 3 hours of spreading the   cement.
7. The surface is properly graded using the grader.
8. Compaction immediately after the grading of the mixed material, compaction will be carried out with smooth drum vibratory rollers. Rolling shall commence at the edges and progress towards the center except at super elevated portions where it shall commence at the inner edge and progress towards outer edge. During rolling the surface shall be frequently checked for grades and cross fall any irregularity corrected by loosening the material and removing / adding fresh material. Compaction is to continue until the density achieved is at least 98% of the maximum dry density for the material determined is accordance with IS 2720  (Part 8 )
9. Care is to be taken to see that the compaction of the mix is completed within two hours of its mixing.
10. The compacted soil- cement is most cured for 7 days by keeping it damp water will be sprinkled every four hours for the first 3 days and every 8 hours for the balance four days.

4.THE FOLLOWING QUALITY CONTROL TESTS ARE PROPOSED:        

1.  Quality of cement                               – One test for each consignment of 50 MT
2. Cement content                                    –   Regularly through procedural check.
3.  Degree of pulverization                   – As considered necessary
4.  Moisture content                                –   One set of 2 tests for per 500 sqm
5. Density of compacted layer             -One set of 2 tests per 500 sqm
6. CBR or Unconfined strength test  – On a set of 3 specimen  Drawn from 1 Km
7. Deleterious Material                           – As required
8. Surface finish                                        – As per MORT&H Specification Clause 902

5.TRAFFIC ARRANGEMENT:

No traffic of any kind will ply over completed Sub base except the water truck used for sprinkling of water