Short answer: a landslide survey finds which slopes may fail, why, and what will hold them. In India it normally combines four things: a drone LiDAR terrain model, seismic refraction and boreholes for the ground below, geological mapping of rock and joints, and a stability analysis in dry, monsoon and earthquake conditions. The result is a hazard map, a priority list and the design inputs for drainage, soil nails, anchors, mesh and rockfall barriers.
Why landslide surveys matter in India
The Geological Survey of India estimates that about 12.6% of India's land area, outside snow-covered ground, is prone to landslides, across the Himalaya, the Northeast, the Western Ghats and the Nilgiris. Heavy monsoon rain, steep cut slopes beside new roads and railways, weathered rock and earthquakes combine to trigger failures every year. A survey before protection works are chosen puts money where the risk actually is.
The four parts of a landslide survey
1. Terrain: drone LiDAR and 3D models
Slopes beside hill roads are usually under trees. Drone LiDAR records the ground through gaps in the canopy, giving a bare-earth terrain model, contours, slope-angle maps and cross-sections. It also shows cracks, scarps, old slide scars and drainage paths. Repeat flights compare surfaces over time to measure movement. See LiDAR vs photogrammetry.
2. Subsurface: seismic refraction and boreholes
Seismic refraction tomography measures how fast sound travels through the ground to show the thickness of loose cover, the depth to weathered and fresh rock, and weak or saturated zones, continuously along each profile. Boreholes give samples and laboratory strength at chosen points. See seismic refraction survey.
3. Material: engineering geological mapping
Geologists map rock types and joints, measure joint orientations, test strength in the field and classify the rock mass with RMR, GSI and SMR. Kinematic analysis on stereonets shows whether planar sliding, wedge sliding or toppling is possible.
4. Stability analysis and hazard zonation
Geometry from LiDAR, layering from seismic refraction and strength from geology go into a limit-equilibrium analysis that gives a factor of safety for each critical section: dry, saturated (monsoon) and earthquake (pseudo-static, using the IS 1893 seismic zone). Stretches are then ranked Low, Medium, High or Critical.
Which method answers which question
| Question | Method | Output |
|---|---|---|
| How high and steep is the slope? Where are cracks and scarps? | Drone LiDAR, orthophoto | DTM, contours, slope-angle map, sections, 3D model |
| How thick is the loose material? Where is rock? | Seismic refraction tomography | Velocity section, depth to competent strata |
| How strong is the soil and rock? | Geological mapping, field tests, boreholes, laboratory | RMR, GSI, SMR, c′ and φ′ |
| How will it fail? | Kinematic analysis | Planar, wedge or toppling; shallow slide; toe scour |
| How close is it to failure? | Limit-equilibrium analysis | Factor of safety: dry, saturated, earthquake |
| Is it moving? | Repeat LiDAR, survey prisms, inclinometers | Change maps, displacement over time |
| Where do we act first? | Hazard zonation | Low / Medium / High / Critical map and priority list |
Indian standards and guidelines
- NDMA guidelines on the management of landslides and snow avalanches: the national framework for hazard assessment and mitigation
- IS 14496 (Part 2): preparation of landslide hazard zonation maps in mountainous terrain
- IS 1893: seismic zones and design seismic coefficients
- IS 11315: quantitative description of rock discontinuities
- IS 13365: rock mass rating (RMR)
- IS 8764: point-load strength of rock
- IS 15681: seismic refraction method
- IRC:SP:55: traffic management in road work zones; Drone Rules, 2021 for drone operations
What you should receive
- LiDAR point cloud, DTM, contours, orthophoto, slope maps, cross-sections and 3D models
- Seismic refraction field data, tomograms and interpreted sections
- Geological maps and sections, joint data, stereonets, RMR/GSI/SMR, strength parameters
- Stability analysis for each critical section, hazard zonation map and priority list
- Remedial recommendations and protection design inputs, or the protection design itself
Common protection measures
| Failure type | Typical measures |
|---|---|
| Water-driven shallow slides | Surface and sub-surface drainage, re-grading, vegetation, erosion-control mats |
| Slides in soil and weathered rock | Soil nails with flexible high-tensile mesh |
| Rock blocks on joints | Rock bolts and anchors, cable nets, rockfall drapes |
| Rockfall from above | Rockfall barriers and catch fences located by trajectory analysis |
| Toe erosion beside rivers | Toe walls, gabions, river training |
What decides the cost
- Length or area: kilometres of corridor or hectares of slope.
- Access and vegetation: remote hill roads, forest and traffic slow field work.
- Number of seismic profiles and boreholes: often one profile per kilometre plus extra at critical slopes.
- Detailed geology: how many locations need mapping and testing.
- Accuracy and deliverables: point density, section spacing, 3D models.
- Design scope: design inputs only, or full protection design with drawings and quantities.
An example: 66 km of road-side slopes in Assam
DATA PKT investigated about 66 km of road-side slopes in Assam, in seismic Zone V with heavy monsoon rain: drone LiDAR of the full corridor, 66 seismic refraction profiles, geological mapping at 7 critical locations and a stability report with stretch-wise hazard ranking and protection design inputs, in about nine weeks. Read the case study or see our landslide and slope stability service.