This standard outlines detailed recommendations for choosing and preparing building sites in mountainous regions, emphasizing the reduction of slope stabilization and protective measures. It covers aspects such as geotechnical surveys, slope safety evaluation, terrace construction, retaining wall design, drainage solutions, and erosion control to facilitate secure and economical building practices on hillsides.
Overview
This standard outlines detailed recommendations for choosing and preparing building sites in mountainous regions, emphasizing the reduction of slope stabilization and protective measures. It covers aspects such as geotechnical surveys, slope safety evaluation, terrace construction, retaining wall design, drainage solutions, and erosion control to facilitate secure and economical building practices on hillsides.
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Frequently Asked
Before choosing a building site in hill regions, comprehensive geotechnical assessments must be carried out. These include identifying soil and rock types (weathered or intact), analyzing bedding plane orientations, evaluating drainage and shear planes, and inspecting for cracks and vegetation characteristics. Additionally, soil strata thickness and shear strength parameters should be determined, along with permeability and drainage studies. Identification of any potential slip zones is crucial. Field tests such as test pits or auger borings, and wetting tests on rock samples help in understanding site stability. Avoidance of unstable geological formations like heavily fractured or faulted rocks is recommended, and the final site stability must be certified by qualified geotechnical engineers.
The standard advises maintaining stable cut slopes based on soil and rock types, with specific vertical to horizontal ratios outlined for slopes with and without protective structures like breast walls. For example, soil or soil-mixed boulder slopes without protection should be at 1:1 (V:H), while with breast-wall support they can be as steep as 6:1. Hard rock slopes with inward dip are stable at 1:0.25 to 0.1 or vertical, requiring no protection. Proper drainage restoration, controlled ground slope, adequate soak pit placement, and limiting retaining wall heights are critical. Avoidance of steep sites and successive retaining walls further enhances stability. These measures, combined with drainage management and protective works, ensure slope safety for foundations.
Retaining and breast walls should be constructed with a maximum height of 4 meters, with an additional 1 meter allowed if there is a risk of falling boulders. Economical wall designs feature vertical front faces and sloping backs. Drainage provisions such as weep holes are essential to avoid water pressure buildup. Materials commonly used include dry stone masonry complemented by masonry bands of 400–600 mm thickness spaced every 3 to 5 meters vertically. Impervious compacted silty soil layers about 300 mm thick should be placed behind walls to minimize seepage. Clearance between walls and buildings should be maintained between 1.0 and 1.5 meters to ensure ventilation and dampness control. Blasting should be avoided unless strictly supervised, and proper drainage must be incorporated to divert water away from foundations.
Effective drainage involves both surface and subsurface systems to prevent water accumulation that could destabilize slopes. Surface drainage should disperse rainwater over wide areas using lined or unlined drains to avoid concentrated flows that cause erosion. Subsurface drainage with holes and filters safely evacuates groundwater behind slopes and foundations. Maintaining appropriate ground slope around structures ensures rapid runoff. Soft soil surfaces should be protected with vegetation, stone pitching, or grouting to prevent erosion. Stormwater must be collected and disposed of within the premises without affecting natural streams. Sewage and wastewater should be prevented from percolating behind retaining walls by installing surface drains and placing soak pits at a safe distance from foundations. Community involvement is encouraged to design drainage respecting natural watercourses.
To reduce landslide hazards, clearances of at least 1.5 meters between cut slope toes and building walls are recommended, with greater distances on valley sides. Sites near gullies, rivers, quarries, or slopes steeper than 35° should be avoided. Foundations must rest on firm soil or rock, not on filled or unstable ground. Cutting heights should be limited to 4 meters per terrace step, and retaining walls should not exceed 4 meters in height with a foundation slope of 3:1 towards the hillside. Successive retaining walls are discouraged due to collapse risks. Natural drainage systems must be restored and water diverted away from foundations. Soak pits should be located at building sides with at least 2 meters clearance and avoided in front or rear if slopes exceed 30°. Blasting should only be done under strict supervision. Vertical cracks indicative of instability need immediate investigation and monitoring.
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