Introduction

Poor site investigation and unstable soil conditions led to several fatal building collapses in India. Inadequate geotechnical assessment often leads to structural failures, financial losses, and loss of lives.

For example, In 2013 in Mumbra Maharashtra, a 7-story building collapsed due to poor construction practices coupled with inadequate site investigation, killing 74 people. 

Similarly, In 2020, the collapse of a building in Bhiwandi, Maharashtra led to the deaths of 39 individuals due to poor site evaluation.

Let’s first understand about Site Investigation:

Site Investigation is a construction is a crucial process involving the collection of data and analysis of the physical, chemical, and geotechnical properties of a site. This helps in understanding the conditions of the land, soil, groundwater, and surrounding environment before any construction project begins. Site investigation are critical for ensuring the safety, feasibility, and stability of the project.

• Understanding the Site Conditions: Find out what is like, how strong it is, and what it's made of. Also, check things like water levels underground and any other factor that could affect construction.
• Ensuring Safe Design: Make sure the construction design is based on accurate information. This helps guarantee that the building or project will be safe and stable.
• Estimating Costs and Time: Help predict how much the project will cost and how long it will take, based on the conditions of the site and the work that needs to be done.
• Identifying Risks: Find out if there are any risks, like the soil shifting, flooding, or landslides, that could cause problems during or after construction.
• Following Rules and Regulations: Make sure the project follows all local building codes and laws, which may require a site investigation report before getting permission to build.

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Step 1: Initial Consultation:

The client (either the landowner or developer) talks to a geotechnical engineering company or contractor about their project. They discuss what needs to be done, the goals of the project, and any special challenges the site might have, like if it’s on a hill, near water, or in a flat area.

Step 2: Scope of Work:

The client decides what kind of investigation is needed (like how deep or shallow the tests should go), how many holes should be drilled, and what types of tests should be done (like soil tests or checking the strength of the ground). They also figure out where the tests should happen based on the type of project (like what kind of foundation will be used). For getting this information, refer to IS code 1892-2021.

Step 3: Site Visit & Preparation: 

A visit is made to the site to check out the land, see where the equipment can go, and figure out how to do the tests.

Step 4: Conducting the Investigation: 

The investigation is conducted according to the plan, which may involve drilling holes, digging test pits, and collecting surface samples. Below is the detailed procedure or methodology used to carry out the investigation.

Technical Tests in Site Investigation

• ‍Soil Sampling (Borehole Drilling):
  • ‍Test: Soil samples are taken from various depths of the borehole. ‍
  • Data: Soil type, grain size, moisture content, compaction characteristics. ‍
  • Results: Information on soil layers, their consistency, and bearing capacity. 

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• Standard Penetration Test (SPT): 
  • Test: A sampler is driven into the soil using a hammer to measure resistance.
  • ‍Data: Soil resistance at different depths. 
  • Results: N-values (blow counts), which indicate soil compaction, consistency, and potential for settlement.

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• Cone Penetration Test (CPT): 
  • Test: A cone is pushed into the soil while measuring resistance to penetration. 
  • Data: Tip resistance, sleeve friction, and pore water pressure. 
  • Results: Information on soil stratigraphy, soil type, and bearing capacity.

• Plate Load Test: 
  • Test: A plate is loaded on the ground surface to measure its settlement under load. 
  • Data: Settlement behavior under load. 
  • Results: Provides bearing capacity and load-settlement relationship for foundations.

• Water Table Measurement:
  • Test: Measure groundwater level during borehole drilling. 
  • Data: Groundwater depth and fluctuations. 
  • Results: Understanding the effects of groundwater on foundation stability, drainage needs, and potential for flooding.

Step 5: Soil Laboratory Testing & Data Analysis: 

The samples (soil, rock, water, etc.) are sent to a lab for testing. Geotechnical engineers then review the results to understand the properties of the soil and groundwater at the site. The laboratory tests are outlined below.

Soil Laboratory Tests in Site Investigation:

• Shear Strength Test:
  • ‍Test: Measures the soil's ability to resist shear forces using a direct shear test, triaxial test, or vane shear test. ‍
  • Data: Cohesion, internal friction angle. ‍
  • Results: Shear strength of the soil under different conditions, crucial for foundation design.

• Grain Size Analysis & Triaxial Tests:
  • Tests: Grain size analysis, Atterberg limits, consolidation tests, permeability tests. 
  • Data: Soil texture, plasticity, moisture content, consolidation behavior.
  • ‍Results: Helps assess soil compaction, drainage properties, and suitability for foundations. 

Test Results and Data Insights

After completing the necessary steps, we can derive the following key insights from the gathered data:

• Soil Type and Classification: Identifies the various soil layers and their characteristics (sand, clay, silt, etc.).
• Soil Strength: Data on shear strength, cohesion, and friction angle, important for foundation design.
• Bearing Capacity: The load the soil can safely support before failure.
• Settlement Behavior: Prediction of how much the soil will compress under load.
• Groundwater Conditions: Depth of the water table and potential seasonal fluctuations.
• Compaction and Density: Information on the compaction state of the soil, which impacts foundation stability.

Step 6: Preparation of Site Investigation Report:

After the tests are analyzed, a detailed report is created. This report explains the characteristics of the site, any possible risks, and gives recommendations for designing the foundation and structure of the project. (Sample Report)

Step 7: Review of Report:

The report is given to the client and other important people (like engineers, architects, and contractors) to review. If needed, more tests or investigations might be done to answer any additional questions or concerns.

In conclusion, a thorough site investigation is crucial for ensuring the safe, efficient, and cost-effective design and construction of any project. The data collected through detailed testing enables informed decision-making, minimizing the risk of unforeseen challenges during construction. The client’s involvement is key in defining the scope, reviewing the results, and ensuring that the report’s recommendations are followed.

Stay tuned for our upcoming blogs in this series, where we will share more detailed insights into technical information and concepts of civil engineering.

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