Foundations (Shallow and Deep) - Memory Anchors
For PRC board exam preparation, where you must recall dozens of formulas and concepts under pressure, memory anchors are your secret weapon. This collection uses mnemonics, analogies, micro-stories, and vivid visual associations to wire every key concept of Foundations (Shallow and Deep) permanently into your long-term memory. Each anchor connects an abstract geotechnical concept to something familiar — making retrieval automatic, even during exam stress. Science backs this up: the more emotionally vivid and personally relevant a memory is, the stronger the neural pathway. So let's make geotechnical engineering unforgettable!
Memory anchors
Two types of foundations: Shallow vs. Deep
Memory aid
Think of a BAMBOO HOUSE (bahay kubo) versus a SKYSCRAPER in Makati. A bamboo house sits lightly on the ground — that's a SHALLOW foundation, spreading load near the surface. A skyscraper drives its steel columns deep into bedrock far below — that's a DEEP foundation. One rests on the surface like a plate of rice; the other drives down like a chopstick into a bowl.
Why it works
Filipino students instantly relate to the bahay kubo vs. Makati skyscraper contrast. The plate-of-rice vs. chopstick image encodes the physical behavior of each foundation type as a sensory memory.
Example usage
When a board exam asks 'which foundation type reaches firm strata below weak soil?' — picture the Makati skyscraper chopstick driving down. That's DEEP (piles/drilled shafts).
Recall trigger
Bahay kubo = shallow; Skyscraper chopstick = deep
Shallow foundation area formula: A = P / q_a
Memory aid
Remember 'APQ' — think of a Filipino student saying 'APO ko, Q-PA!': Area equals P over Q-sub-a. 'APO' sounds like ancestor (footing carries the load of the whole structure above), and 'Q' is the soil's question: 'How much can I carry?' The formula A = P/q_a answers it.
Why it works
The Filipino expression 'APO ko!' (my goodness!) combined with Q-PA creates a phonetic hook for the formula A = P/q_a. Emotional and cultural relevance boosts encoding.
Example usage
Exam: 'A column carries 600 kN; q_a = 150 kPa. Find footing area.' Trigger: 'APO ko, Q-PA!' → A = 600/150 = 4.0 m². Square side = √4 = 2.0 m.
Recall trigger
APO ko, Q-PA! → A = P / q_a
Pile ultimate capacity: Q_u = Q_p + Q_s (end bearing + skin friction)
Memory aid
A pile is like a BALUT egg seller carrying a heavy tray overhead: the POINTED TIP of the balut (egg tip = end bearing Q_p) pokes into the firm ground below, while the SKIN of the egg (the shell surface = skin friction Q_s) grips the surrounding clay as he pushes down. Total load carried = tip grip + skin grip.
Why it works
Balut is a universally recognized Filipino cultural icon. Mapping the tip and skin of the egg to Q_p and Q_s creates a concrete physical image that encodes the formula components simultaneously.
Example usage
When asked for pile ultimate capacity, picture the balut: Q_u = Q_p + Q_s = (tip contribution) + (skin contribution). Never forget either term.
Recall trigger
Balut: tip = Q_p (end bearing), skin = Q_s (skin friction)
End bearing in clay: Q_p = 9·c_u·A_p (with N_c* = 9)
Memory aid
Use the phrase: 'NINE cats UNDER the Area Plate.' N_c* = 9 is the magic clay number. Nine cats sit under the area plate. Q_p = 9 × c_u × A_p. The nine cats (9) are undrained (c_u) and stand on the area of the pile tip (A_p). WARNING: this 9 is ONLY for deep piles — not for shallow footings!
Why it works
The image of nine cats under a plate is absurd and vivid, making it sticky. The warning embeds the critical pitfall distinction directly into the anchor.
Example usage
Exam: 'Find end-bearing capacity of a pile in clay with c_u = 60 kPa, D = 0.4 m.' → Picture 9 cats under a plate. A_p = π/4(0.4²) = 0.1257 m². Q_p = 9 × 60 × 0.1257 = 67.9 kN.
Recall trigger
NINE cats UNDER the Area Plate → Q_p = 9·c_u·A_p
Skin friction in clay (α-method): Q_s = α·c_u·(π·D)·L
Memory aid
Imagine ALPHA (α), a gecko (butiki) clinging to the side of a cylindrical post. The gecko's grip strength = α times how sticky the clay is (c_u). The post's surface area = its perimeter (π·D) times its length (L). So Q_s = α × c_u × πDL. Alpha the gecko clings to the cylinder's full surface — that's your skin friction.
Why it works
A gecko clinging to a cylindrical post is a vivid kinesthetic image. Filipino students are very familiar with geckos (butiki) on walls, making the analogy culturally sticky. The surface-area concept maps naturally to skin friction.
Example usage
Exam: 'Pile: D = 0.4 m, L = 12 m, c_u = 60 kPa, α = 0.9.' → Alpha gecko: Q_s = 0.9 × 60 × π(0.4) × 12 = 814.5 kN.
Recall trigger
Alpha gecko clinging to a cylinder: Q_s = α·c_u·π·D·L
Pile group capacity: Q_group = η·n·Q_single
Memory aid
Think of a basketball team (PILIPINAS 3×3). Each player alone can jump 1 meter. But in a small court, when they all jump together, they BUMP INTO each other — so the team doesn't jump as high as 3 × 1 m = 3 m. The team efficiency η is less than 1. Group capacity = η (efficiency) × n (number of players) × Q_single (one player's jump).
Why it works
Gilas Pilipinas basketball is a beloved Filipino cultural reference. The concept of players bumping into each other in a crowded space perfectly mirrors overlapping stress zones in pile groups. Efficiency less than 1 is intuitive.
Example usage
Exam: '3×3 pile group, η = 0.80, Q_single_ult = 882.4 kN.' → Basketball: Q_group = 0.80 × 9 × 882.4 = 6,353 kN. Q_allowable = 6,353/2.5 = 2,541 kN.
Recall trigger
Gilas 3×3 bumping in small court → Q_group = η·n·Q_single, η < 1
Negative skin friction (downdrag) — soil dragging pile down
Memory aid
Picture a JEEPNEY (pile) stuck in a MUDSLIDE (consolidating fill). The mud (soft soil) is sinking faster than the jeepney can move. So instead of the mud holding the jeepney up, the mud GRABS the jeepney's sides and PULLS IT DOWN. This downward drag = NEGATIVE SKIN FRICTION. It adds to the load the pile must carry, reducing effective capacity. It's friction that works AGAINST you.
Why it works
Jeepneys stuck in mud during typhoon season is a vivid, emotionally resonant image for Filipino students. The reversal of friction direction (from support to drag) is captured by the sinking mud grabbing and pulling downward.
Example usage
Exam: 'A pile is driven through recently placed fill over soft clay. What additional load consideration is needed?' → Jeepney in mud! Negative skin friction / downdrag adds to the structural load — deduct it from capacity.
Recall trigger
Jeepney in sinking mudslide = negative skin friction pulling down
Mat/raft foundation — use when footings would overlap or soil is weak
Memory aid
A MAT foundation is like a BANGKA (outrigger boat) hull. A single stilts (isolated footing) would sink into the soft water (weak soil). But a wide flat hull (mat) spreads the weight over the entire boat bottom — no sinking! Rule: Switch to a mat when individual footings would cover MORE than 50% of the building footprint — like switching from stilts to a bangka hull.
Why it works
The bangka is an iconic Filipino watercraft. The transition from stilts to a full hull captures the concept of distributing load over a larger area. The 50% rule is embedded as the tipping point for the switch.
Example usage
Exam: 'Individual footings calculated to cover 60% of the building area. What foundation type should be used?' → Bangka hull! Switch to mat/raft foundation.
Recall trigger
Stilts sinking → switch to bangka hull = use a mat foundation at >50% footprint coverage
N_c* = 9 is for DEEP piles in clay, NOT shallow footings (where N_c ≈ 5.14 or 5.7)
Memory aid
Use the RULE OF NINES: 'NINE is for DEEP — if you go deep, use NINE. Five is for the SURFACE — shallow footings stay at FIVE.' Remember: 9 goes DOWN (deep), 5 stays UP (surface). You can also think: 9 > 5 just like DEEP > SHALLOW. Bigger number, deeper foundation.
Why it works
The simple greater-than comparison (9 > 5 = deep > shallow) creates a logical hook. The direction metaphor (9 goes down, 5 stays up) encodes the spatial concept directly.
Example usage
Exam: 'Find end-bearing for a 12 m pile in clay, c_u = 60 kPa.' → 9 goes DOWN: Q_p = 9 × c_u × A_p. Do NOT use 5.14 here — that's for shallow footings.
Recall trigger
9 goes DOWN (deep pile), 5 stays UP (shallow footing). N_c* = 9 for piles.
Skin friction uses SURFACE AREA (π·D·L); end bearing uses TIP AREA (π/4·D²)
Memory aid
Visualize a PENCIL: the SIDE of the pencil (lateral surface) = π·D·L = skin friction area (rub the side on paper = friction). The TIP of the pencil (circular cross-section) = π/4·D² = end bearing area (poke it into the paper = end bearing). Every time you pick up a pencil on exam day, remember: SIDE = skin friction surface area; TIP = end bearing tip area.
Why it works
Students use pencils during board exams. The physical object they hold creates a real-time kinesthetic memory anchor. The side-rubbing vs. tip-poking action encodes the different area calculations through physical sensation.
Example usage
Exam: 'D = 0.4 m pile.' → Pick up your pencil mentally. Side: A_s = π(0.4)(L). Tip: A_p = π/4(0.4²) = 0.1257 m². Never mix them up again.
Recall trigger
Pencil: SIDE surface = π·D·L (skin); TIP circle = π/4·D² (end bearing)
Factor of Safety for piles: FS = 2.5 to 3.0 → Q_a = Q_u / FS
Memory aid
Chant this: 'Two-point-five to three, that's where piles must be! Divide the ultimate load — that's the allowable code!' Q_a = Q_u ÷ FS. For piles, FS is between 2.5 and 3.0, never less. Safety first — in piles, you always divide by at least two and a half!
Why it works
Rhythmic chanting activates auditory memory pathways. The rhyme is short, board-exam focused, and pairs the range (2.5–3.0) with the operation (divide Q_u) in a single memorable phrase.
Example usage
Exam: 'Q_u = 882.4 kN, FS = 2.5.' → Chant the rhyme: divide! Q_a = 882.4 / 2.5 = 353 kN.
Recall trigger
'Two-point-five to three, piles must be!' → Q_a = Q_u / FS, FS = 2.5 to 3
β-method for sand skin friction: f_s = K·σ'_v·tan(δ)
Memory aid
Remember 'KST' — 'Kanina Siyang Tangis' (she was crying earlier). K = lateral earth pressure coefficient, S = σ'_v (effective vertical stress), T = tan(δ) (friction angle tangent). f_s = K × σ'_v × tan(δ). In sand, the pile 'cries' against the wall of soil — K tells how hard the soil pushes sideways, σ'_v how heavy the soil above is, and tan(δ) how rough the interface is.
Why it works
The Filipino phrase KST provides a phonetic acronym anchored in colloquial language. The 'crying against a wall' image encodes lateral pressure (K) as the soil pushing sideways on the pile surface.
Example usage
Exam: 'K = 0.8, σ'_v = 60 kPa, δ = 28°, D = 0.4 m, L = 10 m.' → KST: f_s = 0.8 × 60 × tan(28°) = 0.8 × 60 × 0.5317 = 25.5 kPa. Q_s = f_s × π × D × L = 25.5 × π × 0.4 × 10 = 320.4 kN.
Recall trigger
KST (Kanina Siyang Tangis) → f_s = K·σ'_v·tan(δ)
Block failure check for pile groups in clay
Memory aid
A pile group in clay can fail like a BLOCK OF TOCINO being pulled out of a pan. Instead of each tocino strip (pile) sliding out individually, the whole block (group + trapped clay) moves as ONE unit. If the 'block' is weaker than the sum of individual piles, the block governs. Always check BOTH: individual piles and block failure — use whichever capacity is LOWER.
Why it works
Tocino (cured pork) in a pan is a familiar Filipino breakfast image. The visual of the whole block of tocino lifting out together (vs. individual strips) captures the block failure mechanism intuitively.
Example usage
Exam: 'A 3×3 pile group in soft clay. Compute group capacity.' → Check (1) η·n·Q_single and (2) block failure capacity. The lower value governs.
Recall trigger
Block of tocino = pile group block failure; individual strips = individual pile failure. Use the LOWER capacity.
Square footing side length: B = √(A_req)
Memory aid
After computing A = P/q_a, picture UNFOLDING a square BANIG (woven mat). The area of the banig is known — you just need to find how long one side is. For a square banig, side = √Area. B = √(P/q_a). The banig perfectly covers the soil below the column.
Why it works
A banig (Philippine woven mat) is square and culturally familiar. The act of unfolding a square mat and finding its side from its area makes the square root operation intuitive and spatially memorable.
Example usage
Exam: 'P = 600 kN, q_a = 150 kPa.' → APO ko: A = 600/150 = 4.0 m². Banig side: B = √4 = 2.0 m. Use 2.0 m × 2.0 m footing.
Recall trigger
Square banig unfolded: B = √(A_req) = √(P/q_a)
Group efficiency η is always ≤ 1 — group never stronger per-pile than individual
Memory aid
OVER-LAPPING = UNDER-PERFORMING. When pile stress zones OVERLAP, piles UNDERPERFORM. η ≤ 1 always. Think: 'Group hugs weaken grip — personal space = peak performance.' Individual piles with space = full capacity. Grouped too tight = efficiency drops. η < 1 in reality; η = 1 only in textbook idealization.
Why it works
The 'group hug weakening grip' metaphor humorously encodes the geotechnical principle that overlapping stress zones reduce individual pile effectiveness. The alliteration 'overlap = underperform' aids recall.
Example usage
Exam: 'A student multiplies single-pile capacity by 9 for a 3×3 group.' → Wrong! Group hug weakens grip — multiply by η (< 1) first: Q_group = η × 9 × Q_single.
Recall trigger
Group hug = weakened grip → η ≤ 1 always
α-method adhesion factor range: α ≈ 0.5 to 1.0
Memory aid
Chunk it: 'ALPHA stays between HALF and WHOLE: 0.5 to 1.0.' If the clay is very stiff (high c_u), α is smaller (closer to 0.5) — stiff clay is harder to grip. If clay is soft (low c_u), α is larger (up to 1.0) — soft clay grips better. Think: stiff rubber eraser = hard to grip (low α); soft mud = hands sink in easily (high α).
Why it works
The chunk 'half to whole' (0.5 to 1.0) is easy to memorize. The rubber eraser vs. soft mud physical analogy encodes the inverse relationship between clay stiffness and α through tactile experience.
Example usage
Exam: 'α = 0.9 given.' → This is near 1.0 = soft clay good adhesion. Use directly in Q_s = α·c_u·π·D·L.
Recall trigger
Alpha: half to whole (0.5–1.0); stiff clay = low α; soft clay = high α
Negative skin friction occurs in consolidating fills — it ADDS to load, REDUCES net capacity
Memory aid
Engineer Dading drove piles through a new fill at a reclaimed area in Manila Bay. He was proud — piles looked strong. Then the fill started to CONSOLIDATE (compress). The settling soil grabbed the pile shafts and PULLED THEM DOWN. Suddenly, the pile had to carry both the column load AND the dragdown force. Dading realized: in consolidating areas, FRICTION BECOMES AN ENEMY. He had to add the negative skin friction to the applied load before checking against capacity.
Why it works
A narrative with a named Filipino engineer (Dading) in a relatable Philippine context (Manila Bay reclamation) creates an episodic memory. The emotional twist — friction becoming an enemy — makes the concept sticky through surprise.
Example usage
Exam: 'Pile in recently placed fill over soft clay. State additional load consideration.' → Remember Dading! Negative skin friction (downdrag) must be added to the applied axial load. Net capacity = Q_a minus downdrag.
Recall trigger
Dading's Manila Bay reclamation — friction became enemy → negative skin friction adds to load
Pile capacity components: Tip (Q_p) vs. Shaft (Q_s) — never confuse their area formulas
Memory aid
Use 'TIPS': T = Tip area (π/4·D²) = end bearing; I = Is at the bottom; P = Perimeter area (π·D·L) = skin friction; S = Surrounds the shaft. TIPS = Tip Is Perpendicular to top (end bearing), Skin is around the shaft. If you see Q_p → Tip area. If you see Q_s → Perimeter × Length.
Why it works
The acronym TIPS is short and alliterative. The geometric distinction (perpendicular tip area vs. surrounding perimeter area) is encoded into each letter, preventing the most common board-exam calculation error.
Example usage
Exam: 'D = 0.4 m, L = 12 m pile.' → TIPS: A_p = π/4(0.4²) = 0.1257 m²; Perimeter = π(0.4) = 1.257 m; A_s = 1.257 × 12 = 15.08 m².
Recall trigger
TIPS: Tip = π/4·D² (end bearing); Perimeter = π·D·L (skin friction)
Combined, strap, and isolated footings — classification of shallow foundations
Memory aid
Think of FOOD SHARING at a Filipino fiesta table: (1) ISOLATED footing = one person, one plate (single column, single footing). (2) COMBINED footing = two people sharing one big plate (two columns, one footing). (3) STRAP footing = two plates connected by a wooden stick/strap (two footings connected by a beam). (4) MAT = one giant bilao (round tray) for everyone (one slab under the whole structure).
Why it works
Filipino fiesta culture and food sharing is deeply familiar. Mapping each footing type to a recognizable food-sharing arrangement creates multiple distinct visual memories that prevent confusion between types.
Example usage
Exam: 'Two closely spaced columns near property line — which footing type?' → Fiesta: two columns share a plate but one is near the edge (property line) — use a STRAP footing to balance the eccentricity.
Recall trigger
Fiesta table: isolated=solo plate, combined=shared plate, strap=plates with stick, mat=giant bilao
Mat foundation trigger: use when individual footing area > 50% of building footprint
Memory aid
Chant: 'Fifty percent is the line — cross it, mat is fine! Footings crowd the floor, use one slab, nothing more!' When your calculated footing areas, added together, exceed half the building plan area — stop designing individual footings. Switch to a mat. 50% is the magic threshold.
Why it works
The rhyme locks in the 50% rule as a catchy threshold. 'Cross it, mat is fine' is a decision rule in rhyme form, making it easier to recall the action (switch to mat) alongside the criterion (>50%).
Example usage
Exam: 'Individual footings would cover 55% of the building footprint.' → Rhyme says: 55% > 50% = crossed the line → Switch to MAT FOUNDATION.
Recall trigger
Fifty percent is the line — cross it, mat is fine!
Revision game
I am the factor that tells you how much of a single pile's capacity the whole group can claim per pile. I am always ≤ 1. What am I?
Answer
Group efficiency factor η (eta)
Memory link
Anchor A6 — Gilas basketball team bumping in small court. Their per-player performance drops when crowded.
I look like a pile helping, but I actually hurt. When soil settles faster than the pile, I drag it down and add to its load. I am the villain of foundation design.
Answer
Negative skin friction (downdrag)
Memory link
Anchor A7 and A17 — Jeepney in sinking mudslide; Engineer Dading's Manila Bay reclamation problem.
I am the magic number for end-bearing capacity of a deep pile in clay. I am NOT 5.14 or 5.7 — those belong to shallow footings. What am I?
Answer
N_c* = 9
Memory link
Anchor A4 and A9 — Nine cats under the area plate; 9 goes DOWN (deep), 5 stays UP (shallow).
A column carries 850 kN on soil with q_a = 180 kPa. If I am a square, what is my side length?
Answer
B = √(850/180) = √4.72 ≈ 2.17 m → use 2.20 m × 2.20 m
Memory link
Anchor A2 (APO ko Q-PA formula) and Anchor A14 (square banig side = √Area).
A 3×3 pile group with single-pile Q_u = 700 kN and η = 0.85, FS = 2.5. What is the allowable group capacity?
Answer
Q_group_ult = 0.85 × 9 × 700 = 5,355 kN; Q_group_allowable = 5,355 / 2.5 = 2,142 kN
Memory link
Anchor A6 — Gilas team formula: η × n × Q_single, then divide by FS.
I am the surface area formula for skin friction on a circular pile. I involve the circumference of the pile multiplied by its embedded length.
Answer
A_s = π · D · L (lateral surface area of pile shaft)
Memory link
Anchor A10 — Pencil SIDE surface = πDL for skin friction; pencil TIP = πD²/4 for end bearing.
You calculated that your spread footings would cover 60% of the building plan area. What foundation type must you use instead?
Answer
Mat (raft) foundation — individual footings exceed the 50% rule
Memory link
Anchor A8 (bangka hull) and Anchor A20 (rhyme: 'Fifty percent is the line — cross it, mat is fine!').
In the α-method for clay, I relate undrained shear strength to unit skin friction. I range from 0.5 to 1.0, and I get smaller as clay gets stiffer. Who am I?
Answer
α (alpha) = adhesion factor
Memory link
Anchor A16 — 'ALPHA stays between HALF and WHOLE.' Anchor A5 — Alpha the gecko gripping a cylinder.
Formula mnemonics
A_req = P / q_a
Mnemonic
APO ko, Q-PA! (Area = P over Q-sub-a)
When to use
When sizing a spread (isolated) footing for a given column service load and known allowable bearing pressure. Always use SERVICE loads (not factored) with q_a.
What each part means
A_req = required footing area (m²); P = service column load (kN); q_a = allowable soil bearing pressure (kPa = kN/m²). Dividing kN by kN/m² gives m² — units check out!
Q_u = Q_p + Q_s
Mnemonic
BALUT: Tip + Skin = Total (Q_u = Q_p + Q_s)
When to use
Always when finding total pile capacity. Both terms must be included — omitting either one is a critical error.
What each part means
Q_u = ultimate pile capacity (kN); Q_p = point/end-bearing capacity at pile tip (kN); Q_s = skin friction capacity along pile shaft (kN). Both components resist the applied load.
Q_p = 9 · c_u · A_p (clay, deep pile)
Mnemonic
NINE cats UNDER the Area Plate (N_c* = 9, c_u = undrained shear, A_p = tip area)
When to use
End-bearing capacity of a DEEP pile in CLAY only. For shallow footings in clay, use N_c = 5.14 (Terzaghi) or 5.7 — NOT 9.
What each part means
9 = bearing capacity factor N_c* for deep piles in clay; c_u = undrained shear strength (kPa); A_p = cross-sectional area of pile tip = π/4 · D² (m²). Result in kN.
Q_s = α · c_u · (π · D) · L (clay, α-method)
Mnemonic
Alpha gecko on a cylinder: α × undrained × Perimeter × Length
When to use
Skin friction capacity of a pile in CLAY using the total-stress α-method. Used when c_u is known. α decreases as c_u increases (stiff clay = lower adhesion).
What each part means
α = adhesion factor (0.5–1.0, dimensionless); c_u = undrained shear strength (kPa); π·D = pile perimeter (m); L = embedded pile length (m). Q_s in kN.
f_s = K · σ'_v · tan(δ) (sand, β-method)
Mnemonic
KST — Kanina Siyang Tangis (K × Stress × Tangent)
When to use
Skin friction in SAND using the effective-stress β-method. Requires knowledge of K and δ. Average σ'_v may be used for uniform profiles.
What each part means
K = lateral earth pressure coefficient (0.5–2.0 depending on pile type); σ'_v = effective vertical stress at depth considered (kPa); δ = pile-soil friction angle (degrees). f_s = unit skin friction (kPa). Total Q_s = f_s × π·D·L.
Q_group = η · n · Q_single
Mnemonic
Gilas team: η × n × individual jump = group jump
When to use
Pile group analysis. Always apply η — never assume η = 1 unless specifically stated. Also compute block failure for clay soils.
What each part means
η = group efficiency factor (≤ 1.0); n = total number of piles in group; Q_single = ultimate capacity of one pile (kN). Check also against block failure capacity; the lower governs.
Q_a = Q_u / FS (FS = 2.5 to 3.0 for piles)
Mnemonic
Two-point-five to three, divide Q_u — that's the allowable for you!
When to use
Converting ultimate capacity to allowable capacity for design. FS = 2.5 when pile load test data available; FS = 3.0 when relying on formula alone.
What each part means
Q_a = allowable pile capacity (kN); Q_u = ultimate capacity (kN); FS = factor of safety, typically 2.5 (with pile load test) to 3.0 (without test).
A_p = π/4 · D² and Perimeter = π · D
Mnemonic
TIPS: Tip area = π/4·D² (circle); Skin perimeter = π·D (circumference)
When to use
Every pile capacity problem. A_p goes with Q_p; π·D goes with Q_s. Swapping these areas is the #1 numerical error in pile problems.
What each part means
A_p = cross-sectional tip area (m²) for end-bearing calculation; π·D = circumference/perimeter (m) for skin friction calculation; D = pile diameter (m). These are different — never swap them.
Quick recall chains
Steps to Compute Ultimate Pile Capacity in Clay
Recall test
Without looking, state the 6 steps to find Q_a for a pile in clay. Start with: 'First, find the tip area...'
Memory chain
Think of BALUT preparation: (1) Find the egg's cross-section (A_p). (2) Calculate how hard the tip pushes in (Q_p = 9c_u A_p). (3) Measure the egg circumference (perimeter = πD). (4) Smear adhesion sauce (alpha gecko) over the surface (Q_s = α·c_u·πDL). (5) Total the egg's holding power (Q_u = tip + skin). (6) Divide by safety (Q_a = Q_u/FS). Balut: prepare, push, measure, smear, total, divide!
Items to remember
- Step 1: Compute A_p = π/4 · D²
- Step 2: Compute Q_p = 9 · c_u · A_p
- Step 3: Compute perimeter = π · D
- Step 4: Compute Q_s = α · c_u · (π·D) · L
- Step 5: Add Q_u = Q_p + Q_s
- Step 6: Divide Q_a = Q_u / FS
Shallow Foundation Types (in order of increasing area coverage)
Recall test
Name the 4 types of shallow foundations in order from smallest to largest coverage. What is the switching criterion for a mat foundation?
Memory chain
FIESTA TABLE progression: Solo plate (isolated) → Shared plate for two (combined) → Two plates with a bamboo stick connecting them (strap) → One giant bilao for everyone (mat). As the party gets bigger, the plates get combined until everyone eats from one giant tray!
Items to remember
- Isolated (spread) footing — one column, one footing
- Combined footing — two columns, one footing
- Strap footing — two footings connected by a beam
- Mat/Raft — one slab under entire structure
Common Pitfalls in Foundation Problems (Board Exam Danger Points)
Recall test
List all 5 common pitfalls in foundation problems. Which one involves soil dragging down on the pile?
Memory chain
Remember the mnemonic '9-TIPS-η-DRAG-BLOCK': 9 goes deep (N_c*=9 for piles). TIPS reminds you which area goes where. η (eta) is always ≤ 1 for groups. DRAG = downdrag/negative skin friction adds load. BLOCK = block failure check for clay groups. String it: Nine Tips Eta Drags the Block!
Items to remember
- N_c* = 9 for deep piles, NOT for shallow footings
- Skin friction uses perimeter (πDL), end bearing uses tip area (πD²/4)
- Pile group capacity requires efficiency factor η ≤ 1
- Negative skin friction ADDS to the load, reduces net capacity
- Always check block failure for pile groups in clay
Factors Affecting α (Adhesion Factor) in Clay
Recall test
If c_u = 120 kPa (stiff clay), would you expect α to be closer to 0.5 or 1.0? Why?
Memory chain
ALPHA is SHY around STIFF people: Stiff clay (high c_u) → α is small (shy = 0.5). Soft clay (low c_u) → α is bold (opens up to 1.0). Alpha is half to whole — just like a shy student becoming confident when the class is easier.
Items to remember
- α ranges from 0.5 to 1.0
- Higher c_u (stiff clay) → lower α
- Lower c_u (soft clay) → higher α (up to 1.0)
- α is determined empirically from pile load tests
Sequence to Size a Square Spread Footing
Recall test
A column carries P = 850 kN on soil with q_a = 180 kPa. Find B for a square footing.
Memory chain
APO ko — BANIG math: Get the load (P), get the soil's limit (q_a), invoke APO ko formula (A = P/q_a), unfold the square banig (B = √A), trim to practical size, then double-check the mat won't tear (settlement + structural checks).
Items to remember
- Get service load P (kN)
- Get allowable bearing pressure q_a (kPa)
- Compute required area: A = P / q_a
- Compute side length: B = √A
- Round up to nearest practical size (e.g., 0.05 m increments)
- Check settlement and structural design (shear/flexure)
Diagrams
Foundations Chapter — Complete Concept Map
A hierarchical mind map covering all major concepts in Foundations: shallow vs. deep types, formulas, key numbers, pile group checks, and common pitfalls. Use this as a navigation map before and after studying each concept.
Foundation Selection and Pile Capacity Calculation Flowchart
A comprehensive decision flowchart for foundation selection and pile capacity calculation. Shows the complete problem-solving path: from soil assessment → shallow vs. deep selection → footing sizing or pile capacity → group checks → negative skin friction. Use this as your exam problem-solving roadmap.
Step-by-Step Pile Capacity in Clay — Board Exam Solution Path
A linear flowchart showing the exact step-by-step solution for pile capacity in clay, from given data to allowable capacity. Includes the group capacity extension. Follow this path on every board exam pile problem to avoid missing steps.
Distribution of Foundation Problem Types in PRC Board Exams
A pie chart showing the approximate distribution of foundation problem types in PRC Civil Engineer board examinations. Pile capacity (single and group) accounts for 55% of foundation problems — prioritize pile calculations. Footing sizing is second at 25%.
Skin Friction: Positive vs. Negative — State Transition Diagram
A state diagram showing the transition from normal skin friction (resists load = positive) to negative skin friction (adds load = negative). The trigger is consolidating fill causing soil settlement faster than pile settlement. Use this to remember when and how negative skin friction occurs and its effect on pile design.