PE civil exam – Geotechnical Prep Questions And Correct Answers With Detailed Rationales.

Void Ratio, e - correct answer or Vv/Vs Porosity, n - correct answer or Vv/Vt Saturation, S - correct answer or Vw/Vv Dry unit weight (Ɣd) - correct answer Wet unit weight (Ɣw) - correct answer Specific Gravity (Gs) - correct answer dry density (ρd) - correct answer Ws/Vt OR ρ / (1+w) Water content, w - correct answer Ww/Ws Truss - correct answer A truss is an assemblage of straight members connected at their ends by flexible connections (pin-jointed) to form a rigid configuration. Use of Truss - correct answer Trusses are widely used for applications such as supporting bridge decks, roofs of buildings, floor slabs, electricity pylons, towers, domes etc. Simple Truss (2D) - correct answer 2D plain trusses e.g. bicycle frame Planar truss - correct answer Consist of joining plane trusses Space Frame Truss - correct answer 3D framework Pitched Truss - correct answer A truss having inclined top chords. Flat truss - correct answer Truss Members - correct answer Types of connections in timber trusses - correct answer Metal plate and bolts Nail plate Traditional method using Hardwood pegs Types of connections in steel trusses - correct answer Bolts and nuts (also rivets, but they are now rarely used) Welded joint Plane truss determinacy calculations - correct answer m = 2j - r m = number of members in the truss j = number of joints in the truss r = number of external reactions Assumptions for analysis of Trusses - correct answer i. All members are connected only at their ends by frictionless hinges ii. All loads and support reactions are applied only at the joints iii. The centroidal axis of each member coincides with the line connecting the centers of the adjacent joints iv. The dead weight of the truss members is distributed along its length; hence it is ignored Characteristics of engineering soils - correct answer Gravel (2mm - 75mm) Sand (0.05mm - 2mm) Silt (0.002mm - 0.05mm) Clay ( 0.002mm) boulders ( 256 mm) cobbles (64 mm - 256 mm) pebbles (4 mm - 64 mm) granules (4 mm - 2 mm) Mechanical Weathering - correct answer The process by which rocks are broken into smaller pieces by physical forces e.g. running water, wind, ocean waves, glacier ice, frost, and expansion and contraction caused by the gain and loss of heat. Chemical Weathering - correct answer The process of chemical decomposition of the original/parent rock. In the case of mechanical weathering, the rock breaks down into smaller pieces without a change in its chemical composition. However, in chemical weathering, the original material may be changed into something entirely different. Residual soils - correct answer These soils stay where they were formed and cover the rock surface from which they were derived The rate of weathering is higher in warm and humid regions compared to cooler and drier regions and, depending on the climatic conditions, the effect of weathering may vary widely Common in the tropics. The nature of a residual soil deposits will generally depend on the parent rock. Transported soils - correct answer Soil produced by the weathering of rocks can be transported by physical process to other places. Peats and organic soils - correct answer These are derived from decomposition of organic matter Residual Soil - Hard Rocks - correct answer such as granite and gneiss, undergo weathering, most of the material are likely to remain in place. These soil deposits generally have a top layer of clayey or silty clay material, below which are silty or sandy soil layers. These layers in turn, are generally underlain by a partially weathered rock, and then sound bedrock. Residual Soil - chemical rocks - correct answer such as limestone that are chiefly made up of calcite (CaCO3 ) mineral, chalk and dolomite have large concentrations of dolomite minerals [CaMg(CO3 )2 ]. These rocks have large amounts of soluble materials, some of which are removed by groundwater, leaving behind the insoluble fraction of the rock Residual Soil - Gravity transported soils - correct answer Residual soils on a steep natural slope can move slowly downward, and this is usually referred to as creep. When the downward movement is sudden and rapid, it is called a landslide. The soil deposits formed by landslides are called colluviums Mud flows are one type of gravity transported soil. In this case, highly saturated, loose sandy residual soils, on relatively flat slopes, move downward like a viscous liquid and come to rest in a more dense state. The soil deposits derived from past mud flows are highly heterogeneous in composition Gravity transported soils -Braided Streams Deposit - correct answer Braided streams are high-gradient, rapidly flowing streams that are highly erosive and carry large amounts of sediment. Because of the high bed slope, a minor change in the velocity of flow will cause sediments to deposit. By this process, these streams may build up a complex triangle of converging and diverging channels, separated by sandbars and islands. Gravity transported soils- Meander Belt Deposits. - correct answer The valley floor in which a river meanders is referred to as the meander belt. In a meandering river (Figure 5a), the soil from the bank is continually eroded from the points where it is concave in shape and is deposited at points where the bank is convex in shape, as shown in Figure 5b, 6a. These deposits are called point bar deposits, they usually consist Gravity transported soils - Lacustrine deposits - correct answer Water from rivers and springs flow into lakes. In arid regions, streams carry large amounts of suspended solids. Where the stream enters the lake, granular particles are deposited in the area forming a delta. Some coarser particles and the finer particles; that is, silt and clay, which are carried further into the lake are deposited onto the lake bottom in alternate layers of coarse grained and fine- grained particles. The deltas formed in humid regions usually have finer grained soil deposits compared to those in arid regions. Gravity transported soils - Aeolian deposits - correct answer The grain-size distribution of the sand at any particular location is surprisingly uniform. The uniformity can be attributed to the sorting action of the wind. • The general grain size decreases with distance from the source, because the wind carries the small particles further than the large ones. • The relative density of sand deposited on the windward side of dunes may be as high as 50 to 60%, decreasing to about 0 to 15% on the leeward side. Geotechnical site investigation - Category 1 - correct answer Typically the foundations of relatively small and simple structures (e.g. lightly loaded 1-2 storey buildings) for which the ground conditions (confirmed by simple procedures such as trial holes) are known from experience to be uncomplicated with no loose or compressible strata and no significant groundwater problems.