Compaction - Memory Anchors
Memory techniques transform abstract geotechnical formulas and concepts into vivid, retrievable images stored in long-term memory. For the PRC CE Board Exam, where you must retrieve γ_dry, RC, and γ_zav formulas under pressure in minutes, these anchors act as mental shortcuts — a quick trigger floods your working memory with the full concept. Use each anchor during your review: read it once, close your eyes and replay the image, then test yourself. The goal is automatic, stress-free retrieval on exam day.
Memory anchors
Compaction expels air (not water) to increase dry unit weight
Memory aid
Think of compaction like packing a BAON box (lunchbox) tighter. You push the rice grains closer together — the rice is the soil solids, the air gaps between grains disappear as you press down. The moisture (ulam sauce) stays in the box. You didn't drain the box; you just removed the air pockets. The box (same volume) is now heavier because more solid rice fills it.
Why it works
The familiar Filipino lunchbox analogy converts an abstract soil-mechanics concept into a concrete, sensory-rich image. Associating 'rice grains = soil solids' and 'air pockets = expelled air' makes the distinction between compaction and consolidation (which expels water) immediately clear.
Example usage
Question: 'What does compaction remove from soil?' Trigger the baon box. Answer: AIR is expelled. Dry unit weight rises because more solids occupy the same space.
Recall trigger
Packing a baon box of rice — pushing out air, not draining it.
Formula: γ_dry = γ_moist / (1 + w)
Memory aid
Say it as a Filipino math teacher would: 'DIVIDE by ONE PLUS W.' The acronym is 'D-O-P-W' — Dry Over Plus W. Or simply: γ_dry = γ / (1 + w). Remember it as 'you must PAY 1 plus W to GET the dry value' — like a tax: the moist weight is the gross price, (1+w) is the tax factor, and what remains after dividing is the pure dry value.
Why it works
The 'tax analogy' frames the formula as a real-life transaction. Students instinctively know you divide the total (gross) by the tax factor to get the net — reinforcing the division operation and the (1+w) denominator.
Example usage
Given γ = 19.5 kN/m³, w = 12%: γ_dry = 19.5 / (1 + 0.12) = 19.5 / 1.12 = 17.41 kN/m³. Trigger: 'divide by one plus w — the tax formula.'
Recall trigger
'Gross price ÷ tax factor = net price' → γ ÷ (1+w) = γ_dry
Proctor test gives γ_d,max at OMC (bell-shaped compaction curve)
Memory aid
Picture a MOUNT MAYON silhouette — a perfectly symmetric, bell-shaped volcano. The peak of Mount Mayon IS the OMC (the sweet spot of moisture), and the peak elevation IS γ_d,max. Too little water (dry side, left flank) = friction resists compaction. Too much water (wet side, right flank) = water pushes soil apart, reducing dry density. The volcano ALWAYS peaks at exactly one optimum point.
Why it works
Mount Mayon is the most iconic volcano in the Philippines and is famous for its near-perfect cone shape — identical to a Proctor compaction curve. Linking the curve shape to a nationally recognized landmark creates a powerful, culturally specific visual anchor.
Example usage
When asked to sketch a compaction curve, visualize Mayon: label left flank 'dry of optimum,' peak 'OMC / γ_d,max,' right flank 'wet of optimum.' The ZAV line sits above and to the left of the peak.
Recall trigger
Mount Mayon's perfect cone = Proctor compaction curve. Peak = OMC and γ_d,max.
Modified Proctor → HIGHER γ_d,max and LOWER OMC than Standard Proctor
Memory aid
Imagine two laborers compacting a road fill. STANDARD Samuel uses a lighter hammer and fewer blows — medium effort. MODIFIED Mario uses a heavier hammer (4.54 kg vs 2.49 kg) and more blows (5 layers, 25 blows each) — maximum effort. Mario's soil reaches a HIGHER peak density (γ_d,max ↑) but needs LESS moisture to do it (OMC ↓) because the extra energy itself forces grains together, reducing dependence on water lubrication. 'More muscle = less water needed, but higher peak.'
Why it works
Assigning distinct characters (Samuel = Standard, Mario = Modified) personalizes the comparison. The logical chain 'more energy → less water needed → lower OMC but higher γ_d,max' is embedded in the story, making both shifts memorable simultaneously.
Example usage
Board question: 'Compare OMC and γ_d,max for Standard vs Modified Proctor.' Recall Mario vs Samuel: Modified → γ_d,max higher, OMC lower. Standard → γ_d,max lower, OMC higher.
Recall trigger
Mario (Modified) muscles his way to a HIGHER peak with LESS water.
Formula: RC = (γ_d,field / γ_d,max) × 100%
Memory aid
RC is your GRADE in a quiz. Your score (γ_d,field) divided by the perfect score (γ_d,max) times 100 gives your percentage grade. The professor (project specifications) requires at least 90–95% to pass. If your field dry unit weight is 17.41 and the lab max is 18.5, it's like scoring 17.41 out of 18.5 — your grade is 94.1%. Just barely passed the 90% cut but not yet 95%.
Why it works
Every Filipino student has experienced the anxiety of a quiz grade — mapping RC to a familiar academic scoring system makes the formula intuitive and emotionally anchored. The pass/fail threshold mirrors real specification requirements.
Example usage
γ_d,field = 17.41, γ_d,max = 18.5 → RC = (17.41/18.5) × 100 = 94.1%. Passes 90% spec; fails 95% spec.
Recall trigger
RC = your quiz score percentage. γ_d,field = your score; γ_d,max = perfect score.
Specification: RC ≥ 90–95% (modified Proctor) for fills and subgrades
Memory aid
Remember '90-95 FILLS THE ROAD.' The sentence tells you: the range (90–95%), what it applies to (fills, roads/subgrades), and the test basis (Modified Proctor implied by 'fills the road' = highway construction uses Modified). Think: a road that is 90–95% compacted FILLS the gap between failure and perfection.
Why it works
The phrase combines the numerical values with their application context in a short, rhythmic sentence. Philippine infrastructure context (road fills, subgrades) makes it relevant to board exam problems.
Example usage
Question: 'What RC is typically required for highway subgrades?' → Recall '90–95 fills the road.' Answer: RC ≥ 90–95% (Modified Proctor).
Recall trigger
'90–95 FILLS THE ROAD' — RC requirement for fills and subgrades.
Formula: γ_zav = G_s × γ_w / (1 + w × G_s)
Memory aid
ZAV = 'Zero Air Voids.' For the formula, remember the phrase 'G-W over ONE-plus-WG' → G_s·γ_w / (1 + w·G_s). The structure mirrors γ_dry = γ / (1+w) but replaces the numerator with 'G times gamma_water' and the denominator's w with 'w times G.' Think of it as: 'the DRY formula UPGRADED by multiplying both numerator and denominator by G_s when you reach theoretical zero air.'
Why it works
Connecting ZAV's formula structure to the already-known γ_dry formula creates a relational memory — students only need to remember the 'upgrade' (multiply by G_s), not an entirely new formula. This reduces cognitive load.
Example usage
G_s = 2.68, w = 15%, γ_w = 9.81: γ_zav = (2.68 × 9.81) / (1 + 0.15 × 2.68) = 26.29 / 1.402 = 18.75 kN/m³.
Recall trigger
'G-W over ONE-plus-WG' — ZAV formula rhythm.
The compaction curve always lies BELOW the ZAV line (real soil retains some air)
Memory aid
Visualize Mount Mayon (the compaction curve) looking UP at a cloud (the ZAV line) floating above it. The cloud is ALWAYS above the peak. The volcano can never reach the cloud because real soil can never achieve 100% saturation through compaction alone — there's always some trapped air. The cloud is the theoretical limit; the volcano is reality.
Why it works
Building on the established Mount Mayon anchor (A3) and adding a cloud above it creates a spatial hierarchy — the visual now encodes both the shape of the curve AND its relationship to the ZAV boundary in one image.
Example usage
If a calculated γ_dry at a given w exceeds γ_zav, it's WRONG — recheck. The curve cannot pierce the cloud. Use this as a sanity check in board problems.
Recall trigger
Mount Mayon (curve) always below the cloud (ZAV line).
Compaction improves: strength ↑, settlement ↓, permeability ↓
Memory aid
SSP — 'Soil's Super Powers' from compaction: Strength ↑, Settlement ↓, Permeability ↓. Or reverse it: remember 'compaction gives Strength and kills Settling and Seeping' → SSS: Strength goes up, Settling goes down, Seeping goes down. The three S's of compaction benefits.
Why it works
Alliteration (S-S-S) groups the three benefits under one sound, making them easy to list rapidly. The up/down arrows are attached to each S during encoding, so the direction is retrieved automatically.
Example usage
Board question: 'What are the engineering benefits of compaction?' → Recall SSS. List: increases shear strength, reduces settlement, reduces hydraulic conductivity (permeability).
Recall trigger
Three S's of compaction: Strength ↑, Settling ↓, Seeping ↓.
Dry of optimum (left of OMC): soil is stiffer, flocculated structure, higher strength but susceptible to swell
Memory aid
Imagine molding CLAY the morning after it rained but the sun already dried the surface. The clay is stiff and crumbly — hard to press together because there's not enough moisture to lubricate the grains. You're DRY of optimum. The grains huddle in clumps (flocculated), strong but brittle — like dried bibingka that cracks when you press it. Add more water and it softens to the perfect mold-able state (OMC).
Why it works
The bibingka analogy is culturally familiar to Filipino students. The texture change (dry/crumbly to moist/pliable) physically mirrors the transition from dry-of-optimum to OMC, creating a tactile memory.
Example usage
Question on compaction behavior dry vs wet of optimum: Dry side → flocculated, stiff, susceptible to swell if wetted later. Wet side → dispersed, lower strength, less permeable.
Recall trigger
Dry bibingka (dry of optimum) — stiff, flocculated, crumbly.
Wet of optimum (right of OMC): dispersed structure, lower permeability, more workable for liners
Memory aid
Think of overwatered lugaw (rice porridge). Too much water makes it flow easily (dispersed, workable) but less 'solid.' For compacted clay liners (like dam cores or landfill liners), you WANT wet of optimum because the dispersed structure has lower permeability — the water-filled pores block seepage. Too much water = lower γ_dry but excellent liner. The overly watery lugaw 'seals' better but has less substance.
Why it works
The lugaw analogy gives a tangible texture to 'dispersed' and explains WHY engineers deliberately compact wet of optimum for liner applications — a practical application that is frequently tested on boards.
Example usage
Board question: 'For a compacted clay liner, on which side of OMC should you compact?' → Wet of optimum (dispersed structure → lower hydraulic conductivity).
Recall trigger
Overwatered lugaw = wet of optimum = dispersed = low permeability liner.
Relative compaction (RC) is for cohesive/general soils; Relative density (Dr) is for granular soils
Memory aid
RC vs Dr — 'Rich Clay, Dense Rock.' RC = Relative Compaction → used for Rich (cohesive) Clay. Dr = Relative Density → used for Dense (granular) Rock/sand. The alliterative pair 'Rich Clay — Dense Rock' locks the correct pairing of test type to soil type.
Why it works
Direct pairing mnemonics exploit the brain's preference for parallel structure. 'R-C = Rich Clay' and 'D-r = Dense Rock' share their initials with the formula symbols, creating a two-way retrieval link.
Example usage
If a problem gives you e_max, e_min, e_field → use Dr (granular). If it gives γ_d,field and γ_d,max → use RC (cohesive/general).
Recall trigger
'Rich Clay, Dense Rock' — RC for clay soils, Dr for sandy/granular soils.
Compaction mechanism: mechanical energy, not hydraulic — no drainage occurs
Memory aid
COMPACTION = pressing a sponge that still has air pockets but keeping all the water inside (mechanical squeeze, air out). CONSOLIDATION = pressing a waterlogged sponge over time until water drains out (hydraulic, slow, time-dependent). Compaction is fast (field rollers in minutes), consolidation is slow (clay under load over months). Same action, different fluid expelled.
Why it works
The sponge analogy is universal and tactile. Distinguishing which fluid is expelled (air vs water) and the time scale (fast vs slow) gives two independent ways to remember the distinction — redundancy improves retention.
Example usage
Board pitfall: never confuse compaction with consolidation. Compaction = air expelled, no drainage, quick. Consolidation = water expelled, drainage required, time-dependent.
Recall trigger
Sponge squeeze: compaction expels air (fast), consolidation expels water (slow).
Standard Proctor test parameters: 2.49 kg hammer, 305 mm drop, 3 layers, 25 blows/layer, 944 cm³ mold
Memory aid
Chunk the numbers as a phone number pattern: '2-3-25' — hammer is about 2 (2.49 kg), layers are 3, blows are 25. The drop height (305 mm = 30.5 cm ≈ 'one foot') gives another anchor. Mold volume 944 cm³ ≈ 'almost 1 liter.' Phone number: CALL STANDARD → dial 2-3-25 (2.49kg, 3 layers, 25 blows).
Why it works
Phone number chunking is a well-established memory strategy that reduces five separate facts to one three-digit pattern. The 'almost 1 liter' approximation for the mold also provides a quick sanity-check anchor.
Example usage
If the board asks for Standard Proctor specifications: recall the phone number 2-3-25 → 2.49 kg, 3 layers, 25 blows. Drop ≈ 305 mm. Mold ≈ 944 cm³.
Recall trigger
Dial STANDARD: 2-3-25 (2.49 kg, 3 layers, 25 blows/layer, ~1 ft drop, ~1 L mold).
Modified Proctor test parameters: 4.54 kg hammer, 457 mm drop, 5 layers, 25 blows/layer, 944 cm³ mold
Memory aid
Dial MODIFIED: '4-5-25' — hammer is about 4 (4.54 kg), layers are 5, blows are 25 (same as standard). The drop is 457 mm (18 inches ≈ 'one and a half feet'). Same mold volume as Standard (944 cm³). MODIFIED = MORE (heavier hammer 4.54 vs 2.49 kg, more layers 5 vs 3, taller drop 457 vs 305 mm) — only the blows per layer stay the same.
Why it works
Building on the Standard Proctor chunking (A14), Modified becomes 'the upgraded version' — everything bigger except blows/layer. The word MORE (More layers, More mass, More drop) serves as a retrieval cue for every parameter that changes.
Example usage
Board asks Modified Proctor parameters: 4.54 kg, 5 layers, 25 blows/layer, 457 mm drop, 944 cm³ mold. Recall: MORE in everything except blows.
Recall trigger
Dial MODIFIED: 4-5-25. Everything MORE than Standard except blows/layer.
Adding water past OMC LOWERS dry unit weight
Memory aid
Pedro is filling a palengke box with soil. He adds water drop by drop — each drop helps grains slide closer together (γ_dry rises). Then he goes PAST OMC — now the water is occupying so much space that it pushes grains APART instead of helping them pack. The water is now an intruder, not a lubricant. γ_dry drops because the same volume now has LESS solid and MORE water. 'Too much water is the enemy of density.'
Why it works
The story arc (water helps → water hurts) builds intuitive logic rather than memorized fact. The phrase 'lubricant vs intruder' provides a two-word recall for dry-side vs wet-side behavior.
Example usage
Board question: 'Why does dry unit weight decrease on the wet side of OMC?' → Excess water occupies void space, displacing solid particles — γ_dry falls. Recall Pedro's palengke box.
Recall trigger
Water: lubricant before OMC (γ_dry ↑), intruder after OMC (γ_dry ↓).
ZAV line bounds the curve from ABOVE because S = 100% is theoretically impossible through compaction
Memory aid
Rhyme to remember: 'ZAV is high, curve stays low — 100% sat you cannot go. Compact all day, compress all night — some air remains, that's always right.' The ZAV line is the SKY LIMIT — the compaction curve is the GROUND — you can jump (improve compaction) but never reach the sky (full saturation through mechanical means alone).
Why it works
Rhymes exploit phonological memory loops in working memory, making the rule stick through rhythm. The sky/ground metaphor reinforces the spatial relationship (ZAV always above the curve) with a physical image.
Example usage
If a computed γ_dry exceeds γ_zav at the same w, the answer is mathematically impossible — flag it as an error. ZAV is an upper bound that cannot be crossed.
Recall trigger
Rhyme: 'ZAV is high, curve stays low.' Sky (ZAV) above, ground (curve) below.
G_s for typical soils is approximately 2.65–2.70
Memory aid
G_s = 'God's constant for soil' — almost always 2.65 to 2.70 for quartz-dominated soil. Think of it as the Philippine average: just like the Philippine average height is reliably in a narrow range, G_s for most soils is reliably near 2.68. When a problem doesn't give G_s, assume 2.65–2.70 and proceed. '2.68 — the default Filipino soil.'
Why it works
Anchoring G_s to a cultural 'average' concept makes the number feel familiar rather than arbitrary. The phrase 'Philippine average' also signals to students that this is a default assumption value — practical exam advice embedded in the anchor.
Example usage
Problem gives no G_s but asks for γ_zav: assume G_s = 2.68 (or 2.70 if not stated). This is standard practice in board problems.
Recall trigger
'Default G_s = 2.68, the Philippine soil average.' Range: 2.65–2.70.
Compaction curve: plotting γ_dry vs w produces a single-hump bell curve with unique peak
Memory aid
See the compaction curve as a Philippine CARABAO (water buffalo) back when viewed from the side — a single hump in the middle (OMC, γ_d,max), sloping down on both sides. The left leg (dry side) is stiffer, the right leg (wet side) is softer and flatter. The ZAV line is the fence above the carabao that it can never jump over. Plot it: x-axis is water content (%), y-axis is γ_dry (kN/m³).
Why it works
The carabao is the Philippine national animal — a deeply familiar, culturally resonant image. Mapping the single hump to the peak of the compaction curve and the animal's posture to the curve shape creates a memorable visual that is uniquely Filipino.
Example usage
When drawing a compaction curve on the board exam: sketch the carabao hump, label peak as γ_d,max at OMC, draw ZAV line above, label dry and wet sides.
Recall trigger
Carabao's back hump = compaction curve peak. Fence above = ZAV line.
Relative density Dr used for granular soils: Dr = (e_max - e) / (e_max - e_min)
Memory aid
Dr formula — 'MAX minus ME, over MAX minus MIN.' Think of a leaderboard: e_max is the loosest state (worst/maximum), e is your current state (ME), e_min is the densest state (best/minimum). Dr = how far you've come from the worst, divided by the total range. Dr = 0% = loosest (e = e_max); Dr = 100% = densest (e = e_min). 'How far FROM WORST relative to the FULL RANGE.'
Why it works
The 'leaderboard from worst to best' framing makes the formula's numerator and denominator logically meaningful rather than arbitrary symbols. Students can re-derive the formula from the concept even if they forget the exact form.
Example usage
e_max = 0.80, e = 0.60, e_min = 0.50: Dr = (0.80-0.60)/(0.80-0.50) = 0.20/0.30 = 66.7% (medium dense).
Recall trigger
'MAX minus ME over MAX minus MIN' = Dr. How far from worst, over full range.
Revision game
I am the soil parameter you MAXIMIZE in a Proctor test. I measure how dense the SOLIDS are per unit volume. What am I?
Answer
Dry Unit Weight (γ_dry or γ_d,max)
Memory link
Anchor A2: 'Net price after removing the water tax = γ_dry = γ / (1+w)'
I am the mount where γ_d,max lives. I peak at exactly one perfect moisture content. Filipino engineers know me well. What engineering concept am I?
Answer
The Proctor Compaction Curve peak at OMC
Memory link
Anchor A3: 'Mount Mayon silhouette = compaction curve. Peak = OMC and γ_d,max.'
Mario uses more energy than Samuel, achieves a higher peak, but surprisingly needs LESS water. Who are Mario and Samuel?
Answer
Modified Proctor (Mario) and Standard Proctor (Samuel)
Memory link
Anchor A4: Mario (Modified) = heavier hammer, more layers → higher γ_d,max, lower OMC.
I am the percentage grade of field compaction. Engineers need me to be at least 90–95% to pass inspection. What am I?
Answer
Relative Compaction (RC)
Memory link
Anchor A5: 'Quiz grade analogy — RC = (field score / perfect score) × 100%'
I am the theoretical upper ceiling of the compaction curve. I assume 100% saturation. The curve can approach me but never touch me. Who am I?
Answer
Zero-Air-Voids (ZAV) Line
Memory link
Anchor A8 and A17: 'Mount Mayon (curve) always below the cloud (ZAV). ZAV is high, curve stays low.'
I am used for granular soils instead of Relative Compaction. My formula involves e_max, e_min, and current void ratio e. What am I?
Answer
Relative Density (Dr)
Memory link
Anchor A12: 'Rich Clay → RC; Dense Rock → Dr' and Anchor A20: 'MAX minus ME over MAX minus MIN.'
My formula is G_s × γ_w / (1 + w × G_s). I tell you the dry density if no air existed in the soil at all. What am I?
Answer
Zero-Air-Voids dry unit weight (γ_zav)
Memory link
Anchor A7: 'G-W over ONE-plus-WG' — the ZAV formula rhythm.
I am the moisture content at which a soil achieves its maximum dry unit weight during Proctor testing. Too little or too much of me reduces density. What am I?
Answer
Optimum Moisture Content (OMC)
Memory link
Anchor A3 and A16: OMC = peak of the carabao's hump / Mount Mayon's peak. Water is lubricant before me, intruder after me.
Formula mnemonics
γ_dry = γ_moist / (1 + w)
Mnemonic
TAX FORMULA: Net = Gross ÷ (1 + tax rate). Dry = Moist ÷ (1 + w). 'DOPW: Dry Over Plus W.'
When to use
Whenever you have a moist unit weight and water content and need dry unit weight. This is the most commonly used compaction formula on the board exam. Also used to check field compaction results.
What each part means
γ_dry = dry unit weight (kN/m³) — unit weight of solids only; γ_moist = moist/total unit weight (kN/m³) — includes both solids and water; w = water content (decimal form, NOT percent) — e.g., 12% → 0.12. The (1+w) factor removes the water contribution from the total.
RC = (γ_d,field / γ_d,max) × 100%
Mnemonic
QUIZ GRADE: Score / Perfect Score × 100. RC = your soil's quiz grade. Pass = 90–95%.
When to use
Field quality control of earthfill, road subgrade, embankments. Use with Modified Proctor for highway fills (AASHTO T99/T180). Board problems typically give both γ values and ask for RC, or give RC and one γ value to find the other.
What each part means
RC = Relative Compaction (percent); γ_d,field = dry unit weight achieved in the field (kN/m³) — obtained by nuclear density gauge or sand cone test; γ_d,max = maximum dry unit weight from Proctor test in lab (kN/m³). RC tells you how close field performance is to lab maximum.
γ_zav = G_s × γ_w / (1 + w × G_s)
Mnemonic
'G-W over ONE-plus-WG.' ZAV upgraded from γ_dry formula: numerator × G_s, denominator w becomes w·G_s. 'Multiply everything by G_s to reach zero air.'
When to use
Plotting the ZAV line on a compaction curve graph. Used as a CHECK: if computed γ_dry > γ_zav at the same w, there is an error. Also used when given w and G_s to find the theoretical maximum dry density at that moisture.
What each part means
γ_zav = zero-air-voids unit weight (kN/m³) — theoretical dry unit weight at S=100%; G_s = specific gravity of soil solids (typical: 2.65–2.70); γ_w = unit weight of water = 9.81 kN/m³; w = water content (decimal). Result is always ABOVE the actual compaction curve at the same w.
Dr = (e_max - e) / (e_max - e_min)
Mnemonic
'MAX minus ME over MAX minus MIN' — leaderboard from worst (e_max) to best (e_min). ME is where you are now.
When to use
Granular soils (sands, gravels) where Proctor compaction is not applicable. Board problems give e_max, e_min, and current e (or unit weights) and ask for Dr or field condition description.
What each part means
Dr = Relative Density (0 to 1, or 0% to 100%); e_max = void ratio at loosest state; e = current in-situ void ratio; e_min = void ratio at densest state. Dr = 0 → very loose; Dr = 15–35% → loose; Dr = 35–65% → medium; Dr = 65–85% → dense; Dr > 85% → very dense.
e = G_s · γ_w / γ_dry - 1
Mnemonic
'G times W over dry MINUS ONE gives e.' Derived from γ_dry = G_s·γ_w/(1+e). Rearranging: e = G_s·γ_w/γ_dry - 1. Remember: 'dry unit weight and G_s give you the void ratio minus one.'
When to use
When you need void ratio from dry unit weight for subsequent Dr calculations, or to verify ZAV-line consistency. Bridges the Proctor test world (γ_dry) and the phase diagram world (e).
What each part means
e = void ratio (dimensionless); G_s = specific gravity of solids; γ_w = 9.81 kN/m³; γ_dry = dry unit weight (kN/m³). This links compaction results (γ_dry) back to the fundamental void ratio needed for Dr calculation or ZAV verification.
Quick recall chains
Steps to Solve a Standard Proctor/RC Board Problem
Recall test
Cover the chain. Can you write all 7 steps from 'Read moist unit weight' to 'State pass or fail' without looking?
Memory chain
Think of it as a 7-step baon preparation: (1) Get the raw ingredients (read γ and w). (2) Prep the ingredients (convert w). (3) Cook it down (compute γ_dry). (4) Find the target recipe (identify γ_d,max). (5) Grade the dish (compute RC). (6) Check the passing grade (compare to spec). (7) Announce pass or fail (state result). 'BAON PREP: Read-Convert-Compute-Find-Grade-Check-State.'
Items to remember
- 1. Read moist unit weight γ and water content w
- 2. Convert w to decimal (e.g., 12% → 0.12)
- 3. Compute γ_dry = γ / (1 + w)
- 4. Identify γ_d,max from Proctor data
- 5. Compute RC = γ_d,field / γ_d,max × 100%
- 6. Compare RC to specification (90% or 95%)
- 7. State pass or fail
Compaction Curve Key Points (Left to Right)
Recall test
Draw the compaction curve and the ZAV line. Label: dry side characteristics, OMC peak, wet side characteristics, and ZAV line. Do it from memory in 2 minutes.
Memory chain
Walk from LEFT to RIGHT along the carabao's back: (1) Left hoof = dry, stiff, crumbly, swelling risk. (2) Hump peak = OMC = best density. (3) Right hoof = wet, soft, flows, good liner. (4) Fence above = ZAV — never touchable. 'Left-Hoof → Hump → Right-Hoof → Fence (ZAV).'
Items to remember
- Dry side (left of OMC): flocculated structure, high strength, high permeability, susceptible to swell
- OMC: optimum moisture content — peak of curve — γ_d,max achieved here
- Wet side (right of OMC): dispersed structure, lower strength, lower permeability, less swell
- ZAV line: always above the curve, asymptotically
Standard vs Modified Proctor Comparison
Recall test
Without notes: list all parameters for both Standard and Modified Proctor. State the difference in γ_d,max and OMC between the two. Time yourself — target: 30 seconds.
Memory chain
Phone numbers: STANDARD = dial 2-3-25 (2.49 kg, 3 layers, 25 blows). MODIFIED = dial 4-5-25 (4.54 kg, 5 layers, 25 blows). Same mold for both. Mario (Modified) muscles up → peak HIGHER, water LESS. Samuel (Standard) takes it easy → peak LOWER, water MORE. 'Same phone area code (944 cm³ mold), different extension (2-3-25 vs 4-5-25).'
Items to remember
- Standard: 2.49 kg, 3 layers, 25 blows, 305 mm drop
- Modified: 4.54 kg, 5 layers, 25 blows, 457 mm drop
- Same: 944 cm³ mold, 25 blows per layer
- Modified result: HIGHER γ_d,max, LOWER OMC
- Standard result: LOWER γ_d,max, HIGHER OMC
Benefits of Compaction (Engineering Properties Improved)
Recall test
List all 5 engineering properties improved by compaction and the direction of change (↑ or ↓). Recall the five S-words.
Memory chain
Remember 'SSP-VB': Strength ↑, Settlement ↓, Permeability ↓, Volume change ↓, Bearing capacity ↑. Or say it as: 'COMPACTION: Strengthens, Stops Settlement, Seals, Stops Swell, and Supports Bearing.' Five S-words: Strength, Stops settlement, Seals, Stops swell, Supports bearing.
Items to remember
- Shear strength increases
- Compressibility/settlement decreases
- Permeability (hydraulic conductivity) decreases
- Volume change potential (swell/shrink) decreases
- Bearing capacity increases
Relative Density Classification for Granular Soils
Recall test
Fill in the blanks: Dr < ___% = Very Loose; Dr = ___–___% = Medium Dense; Dr > ___% = Very Dense.
Memory chain
Remember the 5-level JEEPNEY LOAD classification: 'Very light load (empty jeep) → Light load → Medium load → Heavy load → Very heavy load (overloaded).' Very Loose (empty) → Loose (few passengers) → Medium Dense (half full) → Dense (full) → Very Dense (beyond capacity). The Dr percentages are the seat counts: 0, 15, 35, 65, 85.
Items to remember
- Dr < 15%: Very Loose
- Dr = 15–35%: Loose
- Dr = 35–65%: Medium Dense
- Dr = 65–85%: Dense
- Dr > 85%: Very Dense
Diagrams
Compaction — Master Concept Map
A comprehensive mind map showing all major topics in the Compaction chapter: the definition, Proctor test variants, compaction curve characteristics, key formulas, ZAV line, and engineering benefits. Use this as a navigation map during review — cover branches one at a time and test recall.
Step-by-Step Problem Solving: Compaction Board Exam
A decision-tree flowchart for solving board exam compaction problems. Follow the branches based on given data: (1) if moist unit weight and water content are given → compute γ_dry → then RC; (2) if field and max dry densities are given → go straight to RC; (3) if G_s and w are given → compute ZAV. Includes spec check (90% vs 95%) and ZAV validity check (γ_dry must be below γ_zav). Use this flowchart as a problem-solving checklist during the exam.
Compaction vs Consolidation — Key Distinction Flowchart
A side-by-side flowchart comparing compaction and consolidation. The key branching question is 'which fluid is expelled?' — air for compaction (fast, mechanical, no drainage) vs water for consolidation (slow, time-dependent, drainage required). Each path lists the mechanism, time scale, drainage condition, and resulting parameter change. Prevents the most common board exam mix-up.
Soil State Changes Along the Compaction Curve
A state diagram showing the three distinct soil behavioral states along the compaction curve. As water content increases from left to right: Dry of Optimum (flocculated, stiff, swelling risk) → At OMC (peak density, best packing) → Wet of Optimum (dispersed, low permeability, good liner). Each state box lists the key engineering characteristics. Understanding state transitions helps answer 'dry vs wet side' behavior questions on the board exam.
Modified Proctor vs Standard Proctor — Energy Ratio
A pie chart showing the relative compaction energies of Modified Proctor (~2700 kJ/m³) vs Standard Proctor (~600 kJ/m³). Modified Proctor applies approximately 4.5× more energy, which directly explains why it produces higher γ_d,max and lower OMC. The visual proportion reinforces why Mario (Modified) achieves so much more than Samuel (Standard).
History and Development of Compaction Testing
A timeline showing the evolution of compaction testing from Proctor's original 1933 test to modern Philippine practice under NSCP 2015. Highlights the 1945 development of Modified Proctor (originally for heavy military aircraft runways), the adoption of Relative Compaction for field control, and the formalization of ZAV theory. Provides board exam context for why two Proctor standards exist.