In the construction of any building, a good foundation is extremely crucial. One of the techniques applied to prepare the grounds for foundations is known as rubble soling. You can create a strong base for your building by using rubble soling. It is the crucial concept followed by civil engineers in India. In this blog, you will come to understand what rubble soling is, why it is required, what its advantages and disadvantages are, and how it is done step by step.
What is Rubble Soling?
Rubble soling in civil construction is one of the ground improvement techniques used in construction to maximise the stability and bearing capacity of soil. In this process, coarse aggregates are laid and compacted over the prepared subgrade.
Rubble soling is most effective on medium to well-drained soils such as sandy gravel or dense sandy soils, where it improves load distribution. The soling layer typically consists of stones of sizes ranging from 75 mm to 150 mm, hand-packed closely with minimal voids. The general purpose of rubble soling is to improve the bearing capacity and to stop the soil beneath from moving or settling too much. It also distributes the load from the building evenly, so it will not crack and damage the structure.
However, for very soft or expansive soils, rubble soling may not be sufficient alone. Alternatives like PCC (Plain Cement Concrete) layers, soil stabilisation with lime or cement, or geotextile reinforcement are recommended to improve bearing capacity and reduce settlement.
Importance of Rubble Soling in Construction
Rubble soling is also responsible for keeping your building safe and strong. The following are the reasons why it is essential:
- Efficient Ground Improvement: For low-bearing-capacity soils, it improves performance without any expensive soil stabilization.
- Resists Soil Movement: Loose or soft soil will change position when weight-loaded. Rubble soling prevents this by establishing a solid layer on the ground.
- Aids Drainage: The gaps between stones allow water to pass through easily. It reduces the risk of water accumulation and damage.
- Supports Heavy Loads: Rubble soling distributes the structural load uniformly over the subgrade and reduces stress concentrations and prevents differential settlement.
- Protects Foundations: By keeping water away and supporting the soil, it prevents cracks and other foundation problems.
- Economical: It uses local rubber or stones. Therefore, it is less expensive than some other foundation-based preparation processes.
Applications of Rubble Soling in Construction
Rubble soling is used in various parts of construction work. Here are some applications:
- Under Foundations: It is placed below the foundation for a solid base.
- Under Floors: It is used for underground floors to provide a firm surface.
- Road Construction: It is used in roadbeds to stabilise the ground.
- Temporary Roads or Paths: It is used to create rough and stable paths on construction sites.
- Drainage Layers: It helps improve water flow in some works.
Due to its strength and drainage, rubble soling is often preferred for buildings on loose or wet soil.
Materials Used for Rubble Soling
The materials typically used for rubble soling include:
- Rubbles: For rubble soling, granite, basalt, or any other strong rocks are chosen. The preferred size and shape are 75mm to 150mm.
- Crushed Stone: In case larger stones are unavailable, gravel fill or crushed stones are used to reduce voids and provide dense packing between the rubble.
- Sand or Quarry Dust: To fill the space among the rocks, sand or quarry dust are used.
- Binding Material: Like moram sand or moorum for better interlocking.
- Water: For compaction during laying.
Pros and Cons
When there are advantages, there would be some disadvantages too. Similarly, rubble soling has both pros and cons, which you should be aware of to make a wise decision.
Pros:
- Long-lasting: It provides a strong foundation that will last for several decades.
- Sufficient Drainage: The gaps between stones allow water to drain through. It helps avoid water damage.
- Budget-Friendly: For rubble soling, you can make use of stones that are available locally and cheaper.
- Ease of Use: No specialised equipment or skilled labour is needed.
- Stop Settlement: It minimises soil movement below the foundation.
Cons:
- Not Suitable for Very Soft Soils: Rubble soling can be sufficient in very weak soil.
- Labour-Intensive: Pressing down the stones and placing them right takes time and hard work to do it properly.
- Irregular Surface: Stones are not regular in shape. Therefore, extra steps must be taken to create an even surface.
- May Require Additional Layers: Sometimes, you must put another layer of concrete on the surface for support.
- Needs Proper Drainage Design: In case of inadequate drainage. Water may still be a problem underneath the rubble layer.
Step-by-Step Process of Rubble Soling
Rubble soling is the process of laying stones in a layer to create a strong foundation for walls and floors. Below is the step-by-step procedure:
- Step 1: Ground Preparation – Level the ground upon which rubble soling will be carried out before starting. Clear the ground of grass, roots, loose soil, or waste.
- Step 2: Layout Marking – Mark the area of soling with chalk lines, ropes, or wooden stakes according to the foundation plan.
- Step 3: Position the Rubble Stones – Place big stones (150 mm size) side by side without any gap. Start from one end and continue row by row. Ensure that the flat surface is facing upwards.
- Step 4: Hammering and Setting the Stones – Use a hand hammer to adjust and fix the stones firmly in place. Ensure they are tightly packed with minimal voids.
- Step 5: Fill the Gaps with Smaller Stones or Chips – To strengthen the layer, fill the gaps between large pieces of rubble with small stones or stone chips. The minimum stone gaps can be filled with murum. This gives stability. (Note: Murum is a disintegrated form of rocks used for filling the plinth gap in construction lines, roads, footings, and drains etc. It is red in colour but rich in aluminium.)
- Step 6: Watering the Surface – Water over the surface of the stones laid. This compacts the small pieces and makes them stronger.
- Step 7: Compact the Layer Properly – Use a hand hammer or plate compactor to press the stones tightly into place. This step is important for strengthening and levelling.
- Step 8: Final Surface Check – After compaction, check if the surface is even. Add more stone chips or gravel to fill gaps, then compact again if needed.
Estimation & Rate Analysis of Rubble Soling Cost in India
To calculate the exact rate of rubble-soling work, you need to know actual market rates. As the material and labour costs differ from one location to another.
Example Rubble Soling Cost Calculation:
Let us assume you are calculating for
Rubble soling length = 16 ft
Width of the rubble soling = 7 ft.
The thickness of the rubble soling = 0.75 ft.
The total volume of the rubble soling
= [length x width x thickness]
= [16 ft. x 7 ft. x 0.75 ft.]
= 84 cu ft.
We will calculate the material and then labour required for the stone soling.
A) Material calculation:
1) Volume of rubble stone:
The required vol. of stone
= [1.25 x the vol. of rubble soling]
= [1.25 x 84 cu ft.]
= 105.00 cu ft.
2. Volume of murum:
The required volume of murum.
= 15% of the vol. of rubble stone.
= (15 x 105)/100
= 15.75 cu ft.
B. Labour calculation:
The labour rate per cu ft. of the rubble soling work ranges from INR 8/- to 15/- depending upon the region.
Let us consider an average rate of INR 12/- per cu ft.
The total cost of labour for rubble soling
= Total vol. of rubble soling in cu ft. x labour rate/ cu ft.
= 84 cu ft. x 12
= ₹ 1,008/-
Now, let us calculate the total cost of rubble soling in table format.
| Sl No. | Feature | Qty (cu ft.) | Rate(₹) | Unit | Cost(₹) |
| 1. | Rubble Stone | 105.00 | 40 | cu ft. | 4200 |
| 2. | Murum | 15.75 | 13 | cu ft. | 204.75 |
| 3. | Rent of a compactor | Lump-sum | 200 | ||
| 4. | Water for Flooding | Lump-sum | 100 | ||
| 5. | Miscellaneous | Lump-sum | 100 | ||
| The material Cost= | 5004.75 | ||||
| 5% of wastage= | 250.23 | ||||
| Total material cost= | 5,254.98 | ||||
| Labour cost= | 1,008 | ||||
| Total cost of Rubble soling work= | 6,262.98 | ||||
a. The cost of rubble soling /cu ft.
= [total rubble soling cost/total soling vol. in cu ft.]
= (6,262.98/84)
= INR 74.55 /cu ft.
b. The cost of rubble soling /cu meter.
= [74.55 x 35.3147] {since 1cum = 35.31 cu ft.}
= INR 2,632.36/cum.
Note: When preparing the bill of quantities for the project, keep in mind to add an extra 10% to 15% for the contractor’s profit.
Rubble Soling vs. PCC (Plain Cement Concrete) Layer: Key Differences
| Aspect | Rubble Soling | PCC (Plain Cement Concrete) |
| Material | Broken stones, boulders | Cement, sand, aggregate, water |
| Role | Subbase; improves soil bearing capacity | Base/flooring; creates a uniform surface |
| Placement | On compacted earth, beneath PCC | Above rubble soling or prepared surface |
| Thickness | 150–300 mm typical | 75–150 mm typical |
| Cost | Lower, uses local stone | Higher, uses manufactured materials |
| Drainage | Good, permeable | Poor, impermeable |
| Strength | For supporting load; uneven surfaces | For distributing loads evenly |
| Application Area | Foundations, roads, leveling uneven ground | Flooring, slabs, base for foundations |
Key Takeaways and Conclusion
And here you go! Rubble soling may seem like a simple step, but it plays a prominent role in building a strong foundation. The right soling execution minimises soil movement and spreads the weight of structural loads evenly. Additionally, it reduces the risk of water accumulating under the foundation. The ease of use and affordable cost make it a popular choice for residential and basic commercial construction projects. In any case, hire a reputable construction company that supplies high-quality stone, conducts proper layering, and applies careful compaction to ensure its long-term effectiveness.
Frequently Asked Questions (FAQs)
What is the purpose of rubble soling?
The layer acts as a strong base that supports the foundation of a building. The primary purpose of rubble soling is to enhance the bearing capacity and prevent the soil beneath from excessive movement or settlement.
What is the rate of rubble soling?
Labour rates can vary regionally, roughly around INR 8 to 15 per cubic foot depending on location and project conditions.
What size material is used for rubble soling?
Typically, soling stones size ranges from 75 mm to 150 mm for rubble soling, placed closely to minimise voids.
Is rubble soling necessary beneath the foundation?
Yes, rubble soling acts as a subbase that enhances soil strength, provides level ground, and prevents differential settlement below the foundation, ensuring structural stability.
Apoorva H P Achar