Interactive Soil Bearing Capacity Simulator

Soil Bearing Capacity Simulator

Created By : Ir. MD Nursyazwi

How to Use This Simulator

This interactive tool allows you to simulate the behavior of a foundation under load and determine if it is stable. Simply follow these steps to run a geotechnical analysis:

1. Select a Design Standard: Choose the engineering standard you want to use for the calculation. Different standards have slightly different factors and methodologies.
2. Input Foundation Dimensions: Enter the width, length, height, and burial depth of your foundation. These values are crucial as they define the contact area and the surcharge pressure on the soil.
3. Input Soil Properties: Provide the soil's key properties:
   • Soil Unit Weight (gamma): The weight of a unit volume of the soil.
   • Soil Cohesion (c): The soil's ability to stick together.
   • Angle of Internal Friction (phi): The soil's resistance to shearing.
4. Set the Factor of Safety (FoS): This is a critical design value that provides a safety margin against uncertainties in the soil properties and applied load. A higher value means a more conservative design.
5. Add Applied Loads: Enter the Dead Load and Live Load that the foundation must support. The simulator will automatically combine these to get the total load.
6. Run the Simulation: Click the "Calculate Capacity & Simulate" button. The simulator will perform calculations, run a virtual load test, and show a 3D animation of the foundation's behavior.
7. Analyze the Results: The results section will display the ultimate and allowable bearing capacities and a final verdict of "STABLE" or "UNSTABLE". Pay close attention to the graph, which visualizes the applied load against the safe load limit. If your result is unstable, you can adjust the inputs to find a stable solution.

Design Standard: Terzaghi's (General) Malaysia Standard (MS) Indian Standard (IS) British Standard (BS) Eurocode 7 (EN 1997) American Standard (IBC/ACI)

Foundation Width (B) (m):

Foundation Length (L) (m):

Foundation Height (m):

Foundation Depth (Df) (m):

Select Soil Type: Sand (Cohesionless) Clay (Cohesive) Silt Gravel

Soil Unit Weight (gamma) (kN/m³):

Soil Cohesion (c) (kN/m²):

Angle of Internal Friction (phi) (degrees):

Factor of Safety (FoS):

Dead Load (P_dead) (kN):

Live Load (P_live) (kN):

0%

Calculation Results

Design Standard:

Foundation Dimensions: m (W) x m (L) x m (H)

Foundation Depth: m

Soil Properties: gamma = kN/m², c = kN/m², phi = °

Factor of Safety:

---

Ultimate Bearing Capacity (q_ult): kN/m²

Allowable Bearing Capacity (q_all): kN/m²

Simulated Safe Load: kN

Total Applied Load: kN

Test Result:

---

Load Test Graph

Understanding the Graph

The blue line on the graph represents the Simulated Load that is gradually applied to the foundation over the course of the test. The green dashed line represents the Safe Load, which is the maximum load your foundation can safely bear based on the soil properties and the factor of safety you selected. The **orange line** indicates your **Total Applied Load** (Dead + Live Loads).

A successful test occurs when your **Total Applied Load** (the orange line) stays below the Safe Load (green dashed line). If the orange line crosses above the green line, the test result is UNSTABLE, indicating that the load has exceeded the foundation's safe capacity.

Solutions for an Unstable Foundation

If your simulation results in an UNSTABLE foundation, you can make several adjustments to improve its stability:

• Increase Foundation Size: By increasing the side length of the foundation, you increase the surface area that distributes the load onto the soil. This reduces the contact pressure and improves stability.
• Change Soil Type: If possible, you could compact the existing soil or replace the weak soil with a stronger, denser material. This directly increases the soil's ultimate bearing capacity.
• Adjust Factor of Safety: If your design allows, you can lower the factor of safety. This is generally not recommended as it reduces the safety margin against uncertainties, but it will increase the allowable capacity.
• Reduce Applied Load: In some cases, reducing the total load on the foundation (e.g., by using lighter building materials) can be a viable solution.

Science Explanation

Soil bearing capacity is the maximum average contact pressure between the foundation and the soil before shear failure occurs. This simulator uses Terzaghi's Bearing Capacity Equation to calculate the ultimate bearing capacity (q_ult) of the soil, which is a fundamental principle in geotechnical engineering.

The general form for a rectangular foundation is given by a formula with three key components:

• A term related to the soil's cohesion (c) and a bearing capacity factor (Nc).
• A term related to the surcharge (q) from the soil above the foundation, the unit weight of the soil (gamma), the depth of the foundation (Df), and a bearing capacity factor (Nq).
• A term related to the foundation width (B), the soil's unit weight (gamma), and a bearing capacity factor (Ngamma).

These terms are combined with shape factors (Fcs, Fqs, and FgammaS) that account for the foundation's geometry. All bearing capacity factors and shape factors depend on the angle of internal friction (phi) of the soil.

A Factor of Safety (FoS) is then applied to the ultimate bearing capacity to get the Allowable Bearing Capacity (q_all), ensuring a safety margin against uncertainties. The simulation visually demonstrates the concept of the soil failure wedge and how excessive load causes this wedge to push the soil outwards and the foundation to sink and tilt, representing a shear failure.

References

This simulator is based on principles from various national and international standards, including Indian Standard (IS) 6403, British Standard (BS 8004), Eurocode 7 (EN 1997), American Standard (IBC/ACI), and Malaysia Standard (MS). For more detailed information on soil bearing capacity, you can refer to these standards or geotechnical engineering textbooks on foundation design.

Here are some recommended books for a deeper understanding:

• Geotechnical Engineering: Principles & Practices (2nd Edition) - This book is a great introductory textbook that covers both the theoretical principles of soil mechanics and their practical applications in engineering.
• Principles of Geotechnical Engineering (10th Edition) - This comprehensive textbook provides a solid foundation in soil mechanics and soil properties, while also incorporating the latest field practices.
• Fundamentals of Geotechnical Engineering (5th Edition) - A concise text that combines key components of both soil mechanics and foundation engineering, focusing on fundamental concepts and providing many worked-out examples.

Other Simulators

While this simulator focuses on soil bearing capacity, there are many other great online resources for engineering students and professionals:

• The Transformative Role of Online Simulators in Engineering: This article explores how online simulators and tools are changing the way engineering is taught and practiced.
• Free Online Engineering Courses from Alison: Alison offers a wide range of free online courses in various engineering disciplines, including civil, mechanical, and electrical engineering.