--- title: "Site investigation for road construction" subject: "Engineering Geology I" chapter: 1 key: "semester_3/engineering_geology_i:site-investigation-for-road-construction" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/site-investigation-for-road-construction site: BCT Engineering --- # Site investigation for road construction Engineering Geology I · Chapter 1: Geology and Civil Engineering - Asked in: 2064 Jestha (old course), 5 marks - Video: [What is Geotechnical Investigation or Soil Investigation?](https://www.youtube.com/watch?v=ClCUdEyqm4Q) — Civil Mentors - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/site-investigation-for-road-construction - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-1 ## Question Describe the various methods of site investigation for road construction. ## Short answer Site investigation for a road involves desk study and reconnaissance, followed by detailed engineering geological mapping, test pits, boreholes, and geophysical surveys to determine ground conditions. In-situ tests, slope stability analysis, and material surveys for aggregates and fill are conducted, with findings documented in strip maps and geological sections. ## Answer Site investigation for a road finds the ground conditions along the alignment so that the road is safe, economical and stable. It is done in stages. #### 1. Reconnaissance and desk study - Collect topographic maps, geological maps, aerial photographs, satellite images and earlier reports. - Walk over possible routes to compare them and avoid landslides, steep slopes, marshes and fault zones. #### 2. Preliminary survey - Detailed **engineering geological mapping** of the corridor: rock types, structures, weathering, slope angles, springs, existing landslides. - Aerial photograph interpretation for lineaments, drainage and unstable areas. - A few test pits and shallow boreholes at key locations. #### 3. Detailed investigation of the chosen alignment - **Test pits and trenches** every 200 to 500 m or at changes in soil type to find soil type and depth of rock; sample for laboratory tests (grain size, Atterberg limits, CBR, compaction). - **Boreholes (auger/rotary)** at bridge sites, high embankments, deep cuttings and landslide areas to get strata, groundwater and rock quality. - **Geophysical methods**: electrical resistivity and seismic refraction for depth of bedrock, water table and buried slide surfaces. - **In-situ tests**: SPT, plate load test, field CBR. - **Slope stability study** by kinematic analysis of joints and bedding relative to the cut face. #### 4. Material survey - Locate quarries for stone and aggregate, borrow pits for fill, and sand and gravel sources; test for quality and quantity. #### 5. Reporting - Prepare strip maps, longitudinal geological sections, and recommendations on cut slopes, retaining structures, drainage and bioengineering. #### 6. Construction stage - Inspect cuttings and foundations, and revise treatment if conditions differ. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Detailed engineering geological mapping of the corridor is done in: A. Reconnaissance only B. Preliminary survey C. Construction stage only D. Reporting only Answer: B. Mapping the corridor is part of preliminary survey. (Key point: Stages) 2. Boreholes in road investigation are placed mainly at: A. Every metre of the road B. Only flat plains C. Bridge sites, high embankments, deep cuttings and landslide areas D. Quarry roofs only Answer: C. Boreholes target critical locations. (Key point: Boreholes) 3. Kinematic analysis checks: A. Soil colour B. Aggregate size C. Bridge loads D. Joints and bedding orientation relative to the cut face Answer: D. It shows whether blocks can slide out of the cut. (Key point: Slope stability) 4. Soil samples from test pits are tested for: A. Grain size, Atterberg limits, CBR and compaction B. Fossil age C. RQD D. Lugeon value Answer: A. These are road subgrade tests. (Key point: Lab tests) ## Related in Engineering Geology I - [Methods of surface and subsurface site investigation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Amethods-of-surface-and-subsurface) — Engineering Geology I, chapter 1, asked 4× - [Engineering geological map and site investigation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-geological-map-and-site) — Engineering Geology I, chapter 1, asked 3× - [Site investigation for dam and reservoir](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Asite-investigation-for-dam-and) — Engineering Geology I, chapter 1, asked 2× - [Objectives of investigation for hill road](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aobjectives-of-investigation-for-hill) — Engineering Geology I, chapter 1 ## Related in other subjects - [Purposes of site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asite-investigation-purposes) — Engineering Geology II, chapter 4, asked 7× - [Types and methods of site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asite-investigation-methods) — Engineering Geology II, chapter 4, asked 7× - [Contents of site investigation report](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asite-investigation-report) — Foundation Engineering, chapter 2, asked 5× - [Detail stage of EG site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Adetail-stage-investigation) — Engineering Geology II, chapter 4