Articles
Soil, Murrum & Backfilling in Construction Projects
· Published
In industrial construction, especially food factory design and infrastructure development, understanding soil characteristics and backfilling techniques is vital. This article explores the properties of soil, murrum, and the methodology of backfilling, with special focus on soil classification systems and compaction testing using the Core Cutter Method—a critical step in ensuring structural stability in food manufacturing plants and industrial facilities.
Understanding Soil and Murrum
What is Soil?
Soil is a complex mixture of minerals, organic matter, rock particles, and microorganisms. It forms the upper layer of the Earth’s crust and plays a vital role in supporting foundation structures for buildings, especially in food factory construction projects.
What is Murrum?
Derived from Tamil, Murrum means powdered rock. It is a granular type of soil, usually brown or red, commonly used for:
- Plinth filling
- Footing pit backfill
- Road and pavement base construction
- Trench backfilling
Its non-organic composition and compact nature make it highly suitable for industrial project execution in food and beverage plants.
Backfilling: Definition and Application
Backfilling involves replacing or reusing the excavated material to support the structure’s substructure. It is a key element in:
- Foundation protection
- Sub-base stabilization for roads and pavements
- Utility trench filling
Typical backfill materials include:
- Soil
- Sand
- Gravel
- Crushed stone
Soil Classification Systems for Engineering Applications
1. Geological Classification
Soils are categorized based on origin and formation process:
- Inorganic soil
- Organic soil
2. Structural Classification
Based on natural grain arrangements:
- Single-grained structure
- Honeycomb structure
- Flocculent structure
3. Classification by Grain Size
Used in civil and food industry projects, this method includes:
- Gravel
- Sand
- Silt
- Clay
Popular grain-size classification systems:
- U.S. PRA (Public Roads Administration)
- International Congress (Washington, 1927)
- MIT System
- IS:1498-1970 (Indian Standard)
4. Unified Soil Classification System (USCS)
Developed by A. Casagrande, it is widely used in airfield and industrial foundation design, including food plant layouts.
5. Preliminary Soil Type Classification
Identifies common soil types relevant to construction consultants:
- Boulders, Gravel, Sand, Silt, Clay
- Loam, Peat, Laterite, Murrum
- Black Cotton Soil, Topsoil, Varved Clay, etc.
Soil Compaction Testing: Core Cutter Method
Soil compaction is critical for structural durability in food processing plants. The Core Cutter Method is widely adopted to determine:
- ·Field Dry Density
- Bulk Density
- Compaction Percentage
Step-by-Step Parameters:
Volume of Core Cutter (Vc):
Vc =π r² x h
(or) Vc = πd²/4 x h
Weight Measurements:
- Core Cutter (Wc)
- Core Cutter + Soil (Ws)
- Soil Weight (Wa) = Ws - Wc
2.2. Weight of Core Cutter + Weight of Soil (Ws)
The weight of Core Cutter + weight of soil measures from Weighing balance machine and noted as Ws. And it is taken in grams.
2.3. Soil Weight (Wa)
The weight of soil (Wa) derives from ( Ws – Wc )
(Wa) = ( Ws – Wc )
2.4. Bulk Density (Yb)
Bulk Density derives from the formula,
(Yb)=(Ws-Wc / Vc)
where,
Wc = weight of Core Cutter,
Ws = weight of Core Cutter + weight of soil
Vc = Volume of Core Cutter
2.5. Moisture Content / Water Content (W) %
The Rapid Moisture Metre determines the moist soil's Moisture Content / Water Content. The formula determines the moisture/water content of wet soil.
W= (M/100-M) x 100
The moisture/water content is taken in Percentage.
2.6. Dry Density (Yd)
(Yd)= (100 x Yb / 100 + w)
Yb = Bulk Density,
W = Moisture Content / Water Content
2.7. Maximum Dry Density
The maximum value of Dry Density is taken, and it is noted in grams.
2.8. Compaction Percentage
Compaction Percentage calculates by dividing the dry density by maximum dry density.
Cp % = Dry Density / Maximum Dry Density
2.9. Table for Calculation of Soil Compaction using Core Cutter Method
Applications in Food Industry Projects
In the context of food factory design, proper soil evaluation and backfilling are essential for:
- Supporting heavy food processing equipment
- Preventing foundation failure
- Ensuring hygiene compliance by avoiding soil settlement under cleanroom floors
