Project Insights: Castel di Lama - IT
Survey in Castel di Lama, IT
Client: Special Office for Reconstruction (USR), Marche Region - ITALY
Location: Castel di Lama, Italy
Coordinates
Latitude: 42.8560° N
Longitude: 13.6915° E
The geotechnical and geophysical investigation project in Castel di Lama was commissioned by the Special Office for Reconstruction (USR) of the Marche Region. The primary objective was to assess the landslide risks and develop a detailed geophysical and geotechnical model of the area. This report synthesizes the findings from the field activities, data processing, and interpretation stages of the project.
Surveyed Areas
This map illustrates the precise locations of the boreholes and geophysical survey spreads, providing a comprehensive overview of the surveyed areas.
1. Data Acquisition in the Field
Field activities were conducted to gather essential geotechnical and geophysical data. The following tasks were completed:
Borehole Drilling:
2 continuous core drilling boreholes up to -20.00 m with Standard Penetration Tests (SPT).
Sampling of 2 undisturbed samples per borehole.
Geophysical Surveys:
9 Electrical Resistivity Tomography (ERT) 2D spreads for subsurface resistivity characterization.
7 Seismic Refraction Tomography (SRT) 2D spreads for subsurface velocity characterization.
2. Data Processing
The collected data were processed using software like ERTLab and AutoCAD Civil 3D. The interpretation phase revealed significant resistivity and seismic velocity variations, indicating potential zones of instability. These findings were crucial in developing effective mitigation strategies.
Key Findings:
Identification of critical zones of instability
Visualization of resistivity variations and seismic velocity changes
Recommendations for slope stabilization, improved drainage, and continuous monitoring
3. Data Interpretation
The processed data were interpreted to construct a comprehensive geophysical and geotechnical model of the region. This interpretation was essential for identifying key subsurface features and understanding the geological dynamics of the area.
The 3D models generated from the interpretation of the data provided a clear visualization of the subsurface structure, highlighting areas of potential instability and other geological features of interest.
Key Findings:
Blue Volume: Zone of new formation of fractures and/or slip surfaces due to the retrogradation of the landslide movement.
Red Volume: Shallow landslide areas.
Purple Volume: Deep landslide areas.
Examples of Interpretation of the 2D Resistivity Model (ERT)
ERT7/SRT7
This figure illustrates the interpretation of the 2D resistivity model (ERT3), identifying a "Zone of possible formation of fractures and/or sliding surfaces due to the retrogradation of the landslide movement." This zone is characterized by heterogeneous resistivity values associated with areas of extremely low resistivity (<5 ohm*m), indicating potential instability.
ERT4/SRT4
This figure shows marked vertical resistivity variations, suggesting the presence of a shallow sliding surface (red line) between the active landslide deposits (unit B) and the underlying quiescent landslide deposits (layer C).
Final 3D model of the landslide risk analysis conducted in Castel di Lama, Italy.
5. Detailed Analysis and Interpretation
Geological Context of Castel di Lama:
The region of Castel di Lama is characterized by complex geological formations and a history of landslides. The primary geological units include:
Alluvial Deposits: Predominantly composed of clay, silt, sand, and gravel. These deposits are prone to liquefaction and sliding, particularly during heavy rainfall or seismic events.
Colluvial Deposits: These are unconsolidated, loose sediments deposited by gravity-driven processes such as landslides. They exhibit varying degrees of consolidation and strength, influencing slope stability.
Bedrock: The underlying bedrock consists of marl and limestone, which provide a relatively stable foundation but can be fractured and faulted, influencing overlying deposits.
Phenomena Observed:
Several phenomena were observed during the investigation:
Vertical and Horizontal Resistivity Variations: These variations were critical in identifying sliding surfaces and areas of potential weakness. Low resistivity zones often indicate saturated or clay-rich soils, which are prone to sliding.
Seismic Velocity Inversions: Inversions in seismic velocity data suggest the presence of weak layers or fault zones. These inversions are indicative of areas where the subsurface materials change abruptly, such as at the interface between loose colluvial deposits and more competent bedrock.
Mechanisms of Landslide Formation:
The landslides in Castel di Lama are primarily triggered by a combination of factors:
Rainfall Infiltration: Heavy rainfall infiltrates the soil, increasing pore water pressure and reducing soil strength. This process is particularly critical in clay-rich and poorly drained soils.
Seismic Activity: The region is seismically active, and ground shaking can destabilize slopes, especially those already weakened by rainfall infiltration or previous sliding.
Human Activities: Construction, deforestation, and other human activities can alter the natural drainage patterns and add load to slopes, contributing to instability.
Risk Mitigation Strategies:
Based on the findings, several strategies are recommended to mitigate landslide risks:
Slope Stabilization: Techniques such as retaining walls, soil nailing, and terracing can be used to stabilize slopes. These methods enhance the mechanical strength of the soil and provide support to prevent sliding.
Improved Drainage: Installing drainage systems such as French drains or surface water channels can help manage excess water and reduce pore water pressure in the soil.
Reforestation: Planting trees and vegetation can enhance slope stability by increasing root strength and reducing surface runoff.
Regular Monitoring: Implementing a monitoring system with inclinometers, piezometers, and GPS can help detect early signs of slope movement and trigger timely interventions.
6. Comprehensive Conclusion
The geotechnical and geophysical investigation in Castel di Lama has provided a detailed understanding of the subsurface conditions and the mechanisms driving landslide formation. The use of advanced geophysical techniques, coupled with thorough geotechnical analysis, has enabled the identification of critical zones of instability and the development of effective mitigation strategies.
Recommendation for Further Action:
To ensure the safety and stability of the Castel di Lama region, it is recommended that the proposed mitigation strategies be implemented promptly. Additionally, continuous monitoring and periodic reassessment of the slopes are essential to address any changes in conditions and ensure the long-term effectiveness of the interventions.
