Rock Slope Mapping (RSM) Pemetaan Cerun Batuan

Rock Slope Mapping (RSM) – Pemetaan Cerun Batuan

In the monsoon-dominated and tropical regions, landslides and slope failures often occur in areas characterized by steep hillslopes, high rainfall intensities, seasonally dry periods, unstable slopes and under forests. With these set of climates combined with the inherent geological conditions, landslides often cause extensive damage to infrastructure and many casualties. Landslides from massive rock slope failure are one of the major geological hazards. Hazard assessment is made difficult by a variety of complex initial failure processes and unpredictable post-failure behavior, which includes transformation of movement mechanism and changes in the characteristics of the moving mass.

When dealing with rock slopes, the failure mode is different compared to a soil slope whereby the instability mechanism is structurally controlled. Geologically, any type of rocks is subjected to at least a primary structure (i.e. beddings, unconformities, etc.) and/or secondary structures (i.e. foliation, joint, faults etc.). These structures usually were generalized as planes of discontinuities where it is classified as weak region of the rock mass. In worst case, intersections of any of these structures may lead to rock slope failures by either falls or/and rock slides. Massive rock slope failures include rockslides, rock avalanches, catastrophic spreads and rockfalls. Debris flows can also be triggered by massive rock slope failure. Hence, it is important to map out all relevant structures that attributed to the rock mass integrity.

Why RSM is important?

Rock Slope Mapping involves a visual inspection of the slope which employs several techniques including the traditional traverses, walk-over surveys, studying the exposures, outcrops and landforms. In the advancement of technology, traditional survey of Rock Slope Mapping nowadays often couples with airborne and ground imaging analysis such as LiDAR and Photogrammetry which has emerged as a powerful solution for enhancing the details of unreachable massive slope that is often limited by human vision.

A visual survey is used to classify major discontinuity planes observe randomly on the rock slopes as well as sign of distresses present. Orientation of all visible discontinuities will be measured and recorded/traced on the prepared base map (i.e. photomosaics, topography map) while its characteristics (such as length, roughness and infilling materials) were recorded. In general, the Rock Slope Mapping can be divided into 5 phases:

1. Desktop Assessment:
It is one of the essential items to provide overview and understanding of the site background such as lithology, bedrock profile as well as to identify area of weak zones are present within the study area. Desktop assessment includes reviewing existing data, satellite imageries, geological maps, drawings etc.

2. Data Acquisition, Processing & Analysis:
This phase dealt with multi sensor active remote sensing data collection, pre- and post-processing coupling with reconstruction of historical data and associated events and compilation of archived data.

3. Field Mapping:
This phase involves discontinuity survey by trained and qualified geologists. In order to establish a refined data collection, field mapping is usually performed using standard rock proforma developed by Jabatan Mineral & Geosains (JMG) and Jabatan Kerjaraya Malaysia (JKR). All pertinent geological features such as lithological type, structural discontinuities, degree of weathering, and the existing and anticipated geotechnical problems were noted and recorded during field mapping.

4. Slope Data Analysis:
This phase involves several important components such as kinematic stability and rock fall analysis. The outcome of these analyses is to identify the potential mode of failure which can either be one or combination of planar, wedge, toppling failure. Further statistical approach of rock fall trajectory will be analyzed to estimate the run-out distance of a failure towards the desired elements at risk such as highways or pipeline. A hypothetical cross section is then constructed to visualize the likely orientation of the geological discontinuities and potential worst-case scenario for any presence potential failures.

5. Recommendation for Mitigation:
This phase provides a detailed analysis and assessment of landslide risk covering geotechnical aspect, proposed conceptual and/or detail mitigation measures with spatial development planning.

For more info:

https://onlinepubs.trb.org/Onlinepubs/sr/sr247/sr247-015.pdf
https://geotechnica.com.my/services/