Introduction

The Project has encountered significant challenges due to the environmental setting of the project area. This article provides an in-depth analysis of the geotechnical and hydrogeological conditions affecting the site, the impact on vehicle operations, and the corrective measures implemented to ensure safe and efficient project execution.

Geology

The soil in the project area is primarily composed of red clay and mud. This type of soil is fine-grained and exhibits significant plasticity and cohesion. The presence of mudstone and clay as backfilling materials indicates a substantial amount of sedimentary rock, which affects the stability and compaction properties of the soil. The fine-grained nature of the soil can lead to challenges in maintaining a stable surface for heavy machinery operations.

Hydrogeology

The hydrogeological conditions are influenced by high tides, causing water to infiltrate the clay. This infiltration leads to variations in moisture content, affecting the soil's compaction and stability. The clay's ability to retain water results in a higher risk of vehicles, such as tippers, getting stuck, especially when the soil is saturated. The periodic flooding and waterlogging due to tidal movements further exacerbate these issues.

Surface Waters

Surface waters in the area are affected by tidal movements, leading to periodic flooding and waterlogging of the soil. The infiltration of water into the clay during high tides causes the soil to become soft and less stable, posing challenges for construction activities and the use of heavy machinery. These conditions necessitate careful planning and implementation of drainage systems to manage water infiltration and prevent waterlogging.

Incident Analysis

On December 16, 2024, at the Project, a three-axle trailer overturned during offloading due to the rear left tire sinking into unstable, uneven soil. Preliminary findings suggest the incident was caused by the undulated and loose soil surface in the Basin-1 area. There have been no previous land site investigations or assessments at the site, but daily inspections and site visits have observed that approximately five three-axle trailers were stuck in the soil.

Engineering Considerations

Given the soil conditions and environmental factors, several engineering considerations must be addressed:

California Bearing Ratio (CBR) Test Results

The standard forces for 2.5 mm and 5 mm penetrations are 1370 kg and 2055 kg, respectively. These values indicate the soil's bearing capacity and its ability to support loads.

The penetration of tires, typically around 5-7 inches, suggests that the soil may have a lower bearing capacity, which can be problematic for heavy vehicles.

Vehicle Movement and Soil Stability

The increasing frequency of three-axle trailers and the penetration depth of tires indicate that the soil may not be able to support heavy loads effectively.

The risk of tippers getting stuck in the clay is high, especially during periods of high moisture content.

Compaction and Surface Stability

The drying of infiltrated water can affect the compaction and stability of the surface, making it challenging to maintain a stable offloading platform.

Proper drainage and soil stabilization techniques may be required to mitigate these issues.

Corrective Actions Taken

To address the challenges posed by the soil conditions and environmental factors, several corrective actions have been implemented:

Buffer Zone Implementation

It has been permitted to offload the material 10 meters away from the waterlogged area (Buffer Zone) as suggested corrective actions.

Drainage Systems

Effective drainage systems have been implemented to manage water infiltration and prevent waterlogging.

Regular Monitoring

Regular monitoring of soil moisture content and compaction levels is conducted to ensure the stability of the offloading platform.

Soil Stabilization Techniques

Techniques such as mixing Gatch material with the clay have been implemented to improve bearing capacity and reduce the risk of machinery getting stuck.

Backfilling materials with better compaction properties are used to enhance the stability of the offloading platform.

Load-Bearing Capacity Determination

The load-bearing capacity for the tippers that can endure the ground conditions at a +1.3m level has been determined.

Stable Working Platform

A proper stable working platform has been made to ensure that the offloading process can be done safely.

Conclusion

The Project faces significant geotechnical and hydrogeological challenges due to the soil composition and tidal influences. By implementing effective corrective measures, including buffer zones, drainage systems, regular monitoring, and soil stabilization techniques, the project aims to ensure safe and efficient operations. Continuous assessment and adaptation of engineering solutions are crucial to overcoming the environmental challenges and achieving project success.