Creep

Test Your Knowledge

Creep Quiz

Instructions: Choose the best answer for each question.

1. Which of the following is NOT a contributing factor to creep? a) Gravity b) Wind c) Water d) Frost Heave

2. What is the most common way to measure creep? a) Feet per minute b) Meters per second c) Millimeters or centimeters per year d) Kilometers per hour

3. Which of these is NOT a sign of creep? a) Bent or tilted trees b) Curved fences or walls c) Rapidly flowing water d) Cracked pavement or foundations

4. What is one potential consequence of creep on structures? a) Increased structural strength b) Damage to foundations and walls c) Enhanced insulation properties d) Reduced seismic vulnerability

5. Which of the following is a strategy for managing creep? a) Increasing water infiltration b) Removing vegetation from slopes c) Implementing drainage systems d) Constructing unanchored retaining walls

Creep Exercise

Imagine you are a geotechnical engineer tasked with assessing a hillside for potential creep. The hillside has several houses built on it. You observe the following:

• Several trees have curved trunks and are leaning downslope.
• Some fences and retaining walls along the hillside are showing signs of tilting.
• A few houses have developed cracks in their foundations.
• The hillside is composed of clay-rich soil and has a high water table.

Task:

1. Based on your observations, what evidence suggests creep is occurring on this hillside?
2. Explain how the composition of the soil and the high water table contribute to the likelihood of creep.
3. What recommendations would you make to the homeowners regarding potential mitigation strategies to address the creep?

Techniques

Chapter 1: Techniques for Investigating and Measuring Creep

Creep, due to its slow and subtle nature, requires specialized techniques for investigation and measurement. These techniques generally focus on either direct measurement of ground movement or indirect assessment through observation of surface features.

Direct Measurement Techniques:

• Inclinometers: These instruments measure the tilt or inclination of the ground at various depths. By regularly monitoring the inclinometer readings, the rate and extent of creep can be quantified. Multiple inclinometers installed at different locations provide a comprehensive picture of the creep movement.

• Extensometers: Extensometers measure changes in the distance between two fixed points. These are commonly used to monitor the deformation of soil or rock masses susceptible to creep. They provide highly accurate measurements of displacement over time.

• GPS (Global Positioning System): High-precision GPS surveys can track changes in the horizontal and vertical positions of points on a slope over time. The accuracy of modern GPS equipment makes it suitable for detecting even small creep displacements.

• Total Stations: Total stations use electromagnetic distance measurement (EDM) technology to precisely measure distances and angles. Repeated surveys over time can reveal subtle ground movements characteristic of creep.

Indirect Assessment Techniques:

• Photogrammetry: Analysis of repeated aerial or ground photographs can reveal changes in slope geometry and surface features over time, providing evidence of creep. Digital image correlation (DIC) techniques enhance the accuracy of this approach.

• Geophysical Techniques: Methods like ground penetrating radar (GPR) can provide subsurface information on soil layering and moisture content, which influence creep behavior. Resistivity surveys can also help identify zones of higher water content.

• Observation of Surface Features: As mentioned previously, monitoring features like bent trees, tilted fences, and cracked pavements can provide qualitative indications of creep. While not providing precise quantitative data, these observations can be valuable indicators of potential creep problems.

Chapter 2: Models for Creep Analysis

Several models exist to predict and analyze creep behavior in geotechnical engineering. These models range from simple empirical relationships to complex numerical simulations. The choice of model depends on the complexity of the problem, the available data, and the desired level of accuracy.

Empirical Models:

• Power-law models: These models express creep rate as a power function of stress and time. They are relatively simple to use but may not accurately capture the complex behavior of all soil types.

• Logarithmic models: These models describe creep rate as a logarithmic function of time, reflecting the decelerating nature of creep observed in many materials.

Constitutive Models:

• Viscoelastic models: These models treat soil as a material that exhibits both viscous and elastic properties. They account for the time-dependent deformation behavior characteristic of creep. Examples include the Burgers model and the generalized Maxwell model.

• Viscoplastic models: These models incorporate both viscous and plastic deformation, allowing for the consideration of irreversible creep deformation that can occur under sustained stress.

Numerical Modeling:

• Finite element analysis (FEA): FEA is a powerful technique for simulating the creep behavior of slopes and other geotechnical structures. It allows for the consideration of complex geometries, material properties, and boundary conditions.

• Finite difference methods: These methods can also be employed to simulate creep behavior, particularly in situations with simpler geometries.

Chapter 3: Software for Creep Analysis

Several software packages are available for performing creep analysis. The choice of software depends on factors such as the type of model used, the complexity of the problem, and the user's experience.

• Specialized Geotechnical Software: Packages like PLAXIS, ABAQUS, and Rocscience Slide are examples of software packages with capabilities for simulating creep behavior using various constitutive models and numerical techniques. These often include pre- and post-processing tools for model creation, analysis, and visualization of results.

• General-Purpose FEA Software: Programs like ANSYS and COMSOL Multiphysics also offer modules that can be used for creep analysis, but often require greater expertise in numerical modeling.

• Spreadsheet Software: Simple empirical models can be implemented in spreadsheet software like Microsoft Excel or LibreOffice Calc for preliminary estimations. However, these are limited in their ability to handle complex scenarios.

The software typically requires input parameters such as soil properties (shear strength, elastic modulus, creep parameters), geometry of the slope, and boundary conditions. The output will include predictions of displacement, stress, and strain over time.

Chapter 4: Best Practices for Creep Mitigation and Management

Effective management of creep requires a multi-faceted approach that combines careful site investigation, appropriate design considerations, and ongoing monitoring.

Site Investigation:

• Detailed geological mapping: Understanding the soil stratigraphy, material properties, and geological history is essential for assessing creep potential.
• Geotechnical testing: Laboratory and in-situ tests are necessary to determine soil properties relevant to creep behavior.
• Hydrogeological investigations: Assessing groundwater conditions and drainage patterns is crucial, as water content significantly influences creep.

Design Considerations:

• Slope stabilization: Techniques such as terracing, retaining walls, rock anchors, and soil nailing can reduce slope instability.
• Drainage control: Installing effective drainage systems to intercept and divert surface and subsurface water is critical.
• Vegetation management: Appropriate vegetation can help stabilize slopes and reduce erosion.

Monitoring and Maintenance:

• Regular monitoring: Implementing a program for regular monitoring of creep indicators (e.g., inclinometers, extensometers, GPS surveys) is essential to detect early signs of movement.
• Early intervention: Prompt response to early warning signs can prevent small movements from escalating into larger, more damaging events.
• Maintenance: Regular maintenance of drainage systems and slope stabilization measures is necessary to ensure their continued effectiveness.

Chapter 5: Case Studies of Creep and Mitigation Efforts

Several case studies illustrate the impact of creep and the effectiveness of different mitigation measures. (Note: Specific case studies would be included here, drawing upon real-world examples of creep incidents and their remediation. These would likely include details such as location, geology, triggering factors, implemented mitigation strategies, and the outcomes). Examples could include:

• Case Study 1: A case study detailing the creep affecting a hillside residential area, highlighting the signs of creep observed, the investigations undertaken, and the mitigation measures implemented (e.g., retaining walls, improved drainage).

• Case Study 2: An example showing creep impacting a transportation infrastructure (road or railway), detailing the monitoring techniques used, the design of the remedial works (e.g., slope stabilization using rock bolts), and the cost-effectiveness of the intervention.

• Case Study 3: A case study of a historical structure affected by slow, long-term creep, focusing on the challenges in assessing the extent of the damage and the strategies adopted for preservation or reinforcement.

These case studies would offer valuable lessons learned and best practices in understanding, managing, and mitigating the effects of creep in various geotechnical settings.