FEExam # 82 Geotechnical Time at 50% consolidation скачать в хорошем качестве

FEExam # 82 Geotechnical Time at 50% consolidation

This video explains soil consolidation, primary vs secondary consolidation, drainage path length (Hdr), and how to solve FE Civil Exam consolidation problems easily 00:00 Introduction to the Problem Statement 00:33 Understanding Consolidation 02:46 Primary Consolidation Explained 03:16 Secondary Consolidation Explained 03:40 Consolidation in Construction 04:10 Time Factor (Tv) and Degree of Consolidation (U) 05:09 Drainage Path Length (Hdr) 06:20 Calculating Hdr for Double Drainage 07:20 FE Reference Manual and Tv Values 08:18 Solving the Consolidation Problem Stage 1: Load Is Applied A new load (called a surcharge) is placed on the ground, such as: A building A pavement An embankment At this instant: Clay particles cannot rearrange immediately Clay has very low permeability Water trapped in pores cannot escape quickly So initially: Water carries most of the load Excess pore water pressure develops Stage 2: Primary Consolidation Begins Over time: Water slowly drains out of the clay Drainage occurs toward permeable layers (sand, gravel) Excess pore water pressure dissipates As water leaves: Load transfers from water to soil particles Clay particles move closer together Settlement occurs gradually This time-controlled settlement is called: PRIMARY CONSOLIDATION Settlement Definitions Settlement: Vertical downward movement of a foundation due to soil compression Total settlement: Overall drop Differential settlement: Uneven drop (often more damaging) Primary Consolidation (Exam Definition) Primary consolidation is the time-dependent volume reduction of saturated clay caused by the dissipation of excess pore water pressure. Key FE facts: Occurs in low-permeability soils (clay, silt) Depends on drainage conditions Controlled by coefficient of consolidation (cv) Stops when excess pore pressure = 0 What Is Secondary Consolidation? (Simple Definition) Secondary consolidation is the continued settlement of soil after all excess pore water pressure has dissipated, caused by creep and rearrangement of soil particles. Key phrase to remember: No more water leaving — soil itself is slowly deforming. Why Clay Consolidates Slowly (But Sand Does Not) Clay Very small particles Very small pores Low permeability Water escapes slowly Consolidation takes months or years Sand Large particles Large pores High permeability Water escapes almost instantly Settlement is immediate, not consolidation This is why consolidation problems almost always involve clay. Single vs Double Drainage (The Game Changer) Consolidation speed depends on how far water must travel to escape. Drainage Path Length (Hdr) Hdr = maximum distance water must travel to drain This is the most important variable in consolidation time problems. Single Drainage Clay drains from one side only Example: Clay over bedrock Clay under an impermeable layer Drainage path: Hdr = H Double Drainage Clay drains from top and bottom Example: Clay between two sand layers Drainage path: Hdr = H / 2 This drastically reduces consolidation time. Why Hdr Matters More Than H Consolidation time is proportional to: time ∝ Hdr² This means: Cut Hdr in half Time becomes (1/2)² = 1/4 Consolidation is 4 times faster That’s why recognizing double drainage is an easy FE point. H vs Hdr (Common Exam Trap) H Total clay thickness Physical soil layer thickness Hdr Drainage path length Distance water must travel You use: H to understand soil profile Hdr in the time equation Role of cv and Tv (Why Time Can Be Calculated) Coefficient of Consolidation (cv) Describes how fast consolidation occurs Depends on soil permeability and compressibility Time Factor (Tv) Dimensionless number Corresponds to a percentage of consolidation Example: Tv = 1.4 → 50% consolidation The Consolidation Equation (Big Picture) Tv = (cv × t) / (Hdr²) This equation combines: Soil behavior (cv) Drainage condition (Hdr) Time (t) When Does Primary Consolidation End? Primary consolidation ends when: All excess pore water pressure has dissipated Soil skeleton carries the full load Settlement stops (for primary consolidation) After this, secondary consolidation (creep) may continue, but it is not time-factor based. #FECivil #GeotechnicalEngineering #SoilMechanics #Consolidation #CivilEngineering #FEExam #EngineeringStudents #ClaySoil #FoundationEngineering