My Thoughts

Geotechnical Lab Tool — ASTM D4318 / IS-2720-5

Atterberg Limits

Liquid Limit (LL) · Plastic Limit (PL) · Plasticity Index (PI) · Toughness Index (TI)
Flow curve · USCS classification · Consistency & Liquidity indices

Sample ID

Date

Project name

Location / depth

Tested by

Natural MC (%)

Liquid Limit — Casagrande Cup Method

ASTM D4318 §8 / IS-2720-5 · Blows should bracket 25

#	Container	No. of blows	Wet + con (g)	Dry + con (g)	Container (g)	Dry soil (g)	Moisture (g)	WC (%)	±2% check

Liquid Limit (LL)

--

% at 25 blows

Flow Index (I_f)

--

Δw / Δlog N

R² fit quality

--

≥ 0.90 good

No. of dets.

0

min. 3 req.

ASTM D4318 §8: Minimum 3 determinations spanning the 25-blow point; blow counts should bracket 25 (some below, some above). Water content w = (moisture / dry soil) × 100. Flow curve: WC (linear) vs. blows (log₁₀ scale). LL = WC interpolated at 25 blows from best-fit line. Flow Index I_f = |slope| = (w₁ − w₂) / log₁₀(N₂ / N₁) = rate of change of WC per log-cycle of blows. Acceptance: Adjacent determinations ≤ 2% WC apart.

Plastic Limit — Thread Rolling Method

ASTM D4318 §9 / IS-2720-5 · 3.2 mm diameter thread

#	Container	Wet + con (g)	Dry + con (g)	Container (g)	Dry soil (g)	Moisture (g)	WC (%)

Plastic Limit (PL)

--

% average

Std deviation

--

accept. ≤ 1%

Range (max–min)

--

accept. ≤ 2%

ASTM D4318 §9: Roll soil to a 3.2 mm thread at ~90 strokes/min. PL = average WC of ≥ 3 successful determinations where thread crumbles at 3.2 mm. If soil crumbles before reaching 3.2 mm, that WC is the PL. If it does not crumble at 3.2 mm, soil is non-plastic (NP). Acceptance: individual values within 2% of mean (std dev ≤ ~1%).

Index Properties

derived values

LL (%)

--

PL (%)

--

PI (%)

--

I_f

--

TI = PI/I_f

--

--

Enter data to classify plasticity.

Toughness Index TI = PI / I_f (Skempton 1953). TI < 1: crumbly at PL. TI 1–3: typical. TI > 3: tough at PL.
Plasticity: NP (PI=0) · Slight (<2) · Low (2–7) · Medium (7–17) · High (>17).

USCS Classification

ASTM D2487 · Casagrande chart

--

Plot LL vs PI to determine group symbol.

A-line: PI = 0.73(LL − 20). Above A-line → Clay (C). Below → Silt/Organic (M/O). U-line (upper bound): PI = 0.9(LL − 8). LL ≥ 50 → High plasticity (H). LL < 50 → Low (L). CL-ML zone: 4 ≤ PI ≤ 7, LL < 25.

Consistency & State

Atterberg limits diagram

Shrinkage Limit SL (%):

Shrinkage
Limit (SL)

--

%

Plastic
Limit (PL)

--

%

Liquid
Limit (LL)

--

%

Plasticity
Index (PI)

--

LL − PL

Natural
MC (w)

--

% field value

Consistency
Index (CI)

--

(LL − w) / PI

Liquidity
Index (LI)

--

(w − PL) / PI

Activity
(A)

PI / clay%

needs clay fraction

CI = (LL − w) / PI  ·  LI = (w − PL) / PI.
LI < 0: stiff / brittle  ·  0–0.5: stiff  ·  0.5–1: soft / plastic  ·  LI > 1: liquid state.
CI + LI = 1. Enter Natural MC in the project panel above to compute CI and LI.

Data Management

sample loading · export

Standards: ASTM D4318-17e1 — Liquid Limit, Plastic Limit, and Plasticity Index of Soils. IS-2720 (Part 5):1985 — Determination of Liquid and Plastic Limit. USCS classification per ASTM D2487. Flow Index I_f = Δw / Δlog₁₀N (slope of semi-log regression). Toughness Index TI = PI / I_f (Skempton 1953). Consistency Index CI = (LL − w) / PI. Liquidity Index LI = (w − PL) / PI.