Settlement & Subsidence Monitoring

Settlement and subsidence monitoring are critical aspects of geotechnical engineering, designed to maintain the stability and safety of structures or infrastructure. Atlas Engineering & Technology Group (AETG) utilises advanced monitoring techniques to track changes in ground or foundation levels over time, allowing for the early detection of any movement or displacement. By identifying such shifts promptly, AETG can take proactive measures to prevent potential structural damage or failure, ensuring long-term performance and safety. Continuous monitoring helps engineers make informed decisions about foundation repairs or ground stabilisation measures.

Factors Influencing Settlement and Subsidence

• Soil Properties: Cohesion, friction angle, and compaction of soil influence its ability to resist settlement. Saturation, consolidation, and drainage conditions also affect the degree of settlement.
• Groundwater Levels: Fluctuations in groundwater levels can lead to differential settlement, as soils may shrink or expand depending on moisture content.
• Load Increases: Construction, particularly heavy buildings or infrastructure, may induce additional loads on the ground, leading to settlement.
• Mining and Excavation: Activities such as underground mining, tunnelling, or large excavations can lead to void formation, causing ground subsidence.
• Hydro compaction: Some soils, particularly certain clays, can undergo significant settlement when wet.
• Natural Events: Earthquakes, landslides, and other natural events can lead to significant subsidence or settlement.

AETG Methods of Analysis

Inclinometers: Inclinometers measure the tilt or inclination of a vertical reference line. They are often installed in boreholes and can provide real-time data on lateral movements. Inclinometers are especially useful for detecting slope movements or lateral shifts in soils that could lead to settlements or instability in structures. Used for monitoring embankments, retaining walls, or large excavations to prevent slope failures.

Borehole Monitoring: Boreholes are drilled into the ground, and instruments like piezometers or settlement gauges are installed to monitor changes in pore pressure or vertical displacement at various depths. This process helps assess subsurface settlement caused by factors such as soil consolidation or groundwater withdrawal. It is particularly useful in areas where significant settlement or subsidence may occur due to changes in soil properties or fluctuations in groundwater levels.

Piezometers: Piezometers are used to measure pore water pressure in the soil at different depths. A reduction in pore pressure can result in soil compaction and settlement. These instruments are employed to monitor variations in groundwater pressure or hydraulic head, which could contribute to subsidence or settlement. They are commonly used to assess the effects of dewatering or groundwater extraction, particularly in areas susceptible to subsidence.

Geotechnical Instrumentation (Geophones, Strain Gauges, etc.): Geophones and strain gauges are installed in the soil or on structural elements to measure vibrations, strain, and stress, which may indicate ground movements. These instruments are capable of detecting dynamic changes or movements in real time and are frequently used to monitor infrastructure subjected to dynamic loads. They are commonly deployed in seismic risk zones or large-scale infrastructure projects, such as tunnels or dams.

AETG Remediation Capabilities

• Foundation Repair: If significant settlement is detected, foundation repairs, such as underpinning, can be implemented to stabilise the structure.
• Soil Stabilisation: Techniques such as grouting, soil compaction, or the use of geosynthetics may be employed to reduce settlement.
• Groundwater Management: If groundwater changes are causing settlement, dewatering or artificial recharge systems may be implemented.
• Surface Reinforcement: For large areas of subsidence, soil or surface reinforcement using techniques like soil nailing or geotextile installation may be needed.

Why Choose AEGT for Settlement and Subsidence Issues

At AEGT, we have a deep understanding that settlement monitoring and subsidence detection is crucial for maintaining the stability and safety of structures. A combination of surface-based techniques and subsurface monitoring allows for accurate detection and early intervention. By monitoring settlement and subsidence over time, our engineers can assess the behaviour of the ground and implement necessary remedial actions to prevent damage to foundations, structures, infrastructure and the surrounding environment.

Successfully Completed Jobs by AETG to Date

✔ Proposed Multi-Story Development - Ewan Street, Mascot NSW

The Geotechnical Investigation Report at Ewan St, Mascot NSW aims to provide geotechnical design parameters and settlement analysis for the proposed pile foundations. The report includes a review of existing geology maps, determination of in-situ soil conditions, subsurface soil profile and geotechnical parameters, bearing capacity, groundwater, bedrock level, and proposed screw pile foundation settlement. AETG conducted the investigation by reviewing DBYD drawings, drilling boreholes, conducting DCP tests, logging onsite boreholes, performing settlement modelling in PLAXIS, and preparing a geotechnical report.

✔ Proposed Landslip Remediation - Guy Pl, Emu Plains NSW

The Geotechnical Investigation Report for Guy Place, Emu Heights NSW outlines a comprehensive assessment conducted by AETG in response to a significant slope subsidence event near a residential dwelling. The report identifies that the site is underlain primarily by silty clay soils with highly dispersive properties (Emerson Class 1), contributing to instability. Field investigations included borehole drilling, DCP testing, and laboratory analyses of soil properties such as plasticity and particle size distribution. The investigation confirmed that the slope, which failed, consists of un-engineered fill with foreign debris, steep gradients (~66°), poor compaction, and inadequate drainage – factors exacerbated by extreme rainfall and a high groundwater table (~4.1m bgl). Finite element modelling revealed a critical factor of safety (FoS) of just 1.35, well below acceptable levels, indicating a high risk of further failure. AGS recommended a suite of remediation measures including staged excavation, sheet piling, retaining wall construction, use of non-dispersive backfill, geotextiles, soil anchors, and vegetation (e.g. Vetiver grass), with final modelling showing an improved FoS of 3.18. These findings and recommendations aim to ensure long-term slope stability and mitigate future risks to the adjacent property.