Problematic Soils - Soil Testing - Boreholes

Understanding Problematic Soils for Residential Construction in the Philippines

Planning to build your dream home in the Philippines? Before breaking ground, it’s crucial to understand what lies beneath the surface. The soil under your future home can significantly impact its stability and longevity, especially in a country prone to natural disasters like earthquakes and typhoons. Let’s explore some challenging soil types and how to identify them.

The Importance of Soil Analysis

Soil isn’t just dirt; it’s a complex mixture of minerals, organic matter, and sometimes, hidden challenges. In the Philippines, where natural disasters are a reality, knowing your soil type is more than just a precaution—it’s a necessity. But how do you know what you’re dealing with? Let’s dive into some problematic soil types and their identification methods.

Expansive Soils

Expansive soils can cause significant foundation movement due to their tendency to swell when wet and shrink when dry. This constant movement can lead to structural damage over time.

Identification Methods:

• Visual Inspection: Look for cracks in existing structures or uneven ground surfaces.
• Atterberg Limits Test: Determines the soil’s plasticity index.
• Swell Test: Measures the soil’s volume change in response to moisture variations.

Question to Consider: Have you noticed any unusual cracks in nearby buildings or sidewalks?

Collapsible Soils

These soils appear stable but can suddenly compact when saturated or under pressure, potentially leading to rapid settlement.

Identification Methods:

• Dry Density Test: Collapsible soils typically have low dry density.
• Collapse Potential Test: Evaluates volume change upon loading and saturation.
• Soil Structure Analysis: Identifies loose, porous structures prone to collapse.

Organic Soils

High organic content in soils can lead to ongoing decomposition and settlement, compromising foundation integrity over time.

Identification Methods:

• Visual and Olfactory Inspection: Look for dark color, fibrous texture, and earthy odors.
• Loss on Ignition Test: Measures organic content by burning the soil sample.
• Organic Matter Content Test: Quantifies the percentage of organic material.

Question to Consider: Does the soil in your area have a distinctly earthy smell or dark appearance?

Liquefiable Soils

In earthquake-prone areas like the Philippines, these soils can lose strength during seismic events, behaving like a liquid and causing catastrophic foundation failure.

Identification Methods:

• Standard Penetration Test (SPT): Low N-values indicate high liquefaction potential.
• Cone Penetration Test (CPT): Assesses soil behavior under pressure.
• Grain Size Analysis: Identifies fine sands and silts prone to liquefaction.

Karst Topography

Karst regions, characterized by soluble rocks like limestone, are susceptible to sinkholes and underground voids that can undermine foundations.

Identification Methods:

• Geological Maps and Historical Records: Essential for identifying known karst areas.
• Ground Penetrating Radar (GPR): Detects subsurface voids and anomalies.
• Electrical Resistivity Imaging (ERI): Maps variations in subsurface resistivity.

Question to Consider: Are there any known sinkholes or caves in your area?

The Importance of Professional Assessment - The Soil Test

While understanding these soil types is crucial, it’s essential to engage professional geotechnical engineers for a comprehensive site assessment. They can perform detailed tests and provide expert recommendations tailored to your specific location.

Soil testing is usually mandatory for more than 2 stories, make sure that your company doing soil test is DPWH - BRS accredited.

You can get different costs depending on the location and the number of boroholes required for the building.

I’ve got quotations ranging from 53K to 235K pesos, the lower ones increased as I gave more details on movilization and soil types, also restrictions about staying overnight in the subdivision.

Check also the Soil testing groups in Facebook and ask for multiple quotations, then check reviews and accreditations.

Take into account that manual soil test and rotary is different the second one is more expensive, if your soil is rocky you will need a rotary soil test, you can check with your neighbours if possible.

Verify this yourself, but I was told that is one borehole per 200 SQM. Make your numbers!

Make sure that you check yourself the borehole how deep it is, make sure that they won’t say they found already hard strata even if your contractor just hit a small rock.

Remember, investing in proper soil analysis before construction can save you from costly repairs and structural issues in the future. It’s not just about building a house; it’s about creating a safe, stable home that will stand the test of time—and nature—in the beautiful but challenging landscape of the Philippines.

Disclaimer: This information is based on consumer research to understand the construction process, legal requirements, potential issues, and best practices. It is not professional advice. Please consult with qualified experts for specific project guidance. This information is subject to change and improvement.