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Soil, Murrum & Backfilling in Construction Projects

By PMG Engineering ·

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

References:

Frequently asked
Why does soil evaluation matter so much in food factory construction?
In food factory design, proper soil evaluation and backfilling are essential for supporting heavy food processing equipment, preventing foundation failure, and ensuring hygiene compliance by avoiding soil settlement under cleanroom floors. Soil forms the upper layer of the Earth's crust and directly supports foundation structures, so its characteristics govern the structural stability of the entire food manufacturing plant.
What is murrum and where is it used on a food plant site?
Murrum, from the Tamil word meaning powdered rock, is a granular soil that is usually brown or red. On food and beverage plant sites it is commonly used for plinth filling, footing pit backfill, road and pavement base construction, and trench backfilling. Its non-organic composition and compact nature make it highly suitable for industrial project execution.
What materials are acceptable for backfilling around foundations?
Backfilling replaces or reuses excavated material to support a structure's substructure. Typical backfill materials include soil, sand, gravel and crushed stone. In food factory and industrial projects, backfilling is applied for foundation protection, sub-base stabilization for roads and pavements, and utility trench filling.
Which soil classification systems should our consultant reference?
Soil classification for engineering applications covers geological classification (inorganic and organic soil), structural classification (single-grained, honeycomb, flocculent), and grain-size classification into gravel, sand, silt and clay. Popular grain-size systems include U.S. PRA (Public Roads Administration), the International Congress (Washington, 1927), the MIT System and IS:1498-1970. The Unified Soil Classification System (USCS), developed by A. Casagrande, is widely used in industrial foundation design including food plant layouts.
How is field compaction checked using the Core Cutter Method?
The Core Cutter Method determines field dry density, bulk density and compaction percentage. Core cutter volume is Vc = pi r squared x h (or Vc = pi d squared / 4 x h). The core cutter weight (Wc) and core cutter plus soil weight (Ws) are taken in grams on a weighing balance, giving soil weight Wa = Ws minus Wc. Bulk density Yb = (Ws minus Wc) / Vc.
How do you arrive at dry density and compaction percentage from the core cutter readings?
Moisture content of the wet soil is found with a Rapid Moisture Metre using W = (M / 100 minus M) x 100, expressed as a percentage. Dry density is then Yd = (100 x Yb) / (100 + W), where Yb is bulk density. The maximum value of dry density is recorded, and compaction percentage is Cp % = Dry Density / Maximum Dry Density.
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PMG Engineering. (2024). Soil, Murrum & Backfilling in Construction Projects. PMG Engineering. https://pmg.engineering/Article/363/soil-murrum-backfilling-in-construction-projects/

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