Science & STEM

ASTM Atterberg limits: Plasticity Index Quiz

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This quiz helps you practice the plasticity index under ASTM Atterberg limits, review key D4318 steps, and do quick PI math from LL and PL. Use it to spot weak areas before a lab or exam and build speed with soil data. For more hands-on practice, try our mineral identification test and instrument calibration test.

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1What is the formula for the plasticity index of a soil?
2In the context of Atterberg limits, what does LL stand for?
3In the context of Atterberg limits, what does PL stand for?
4Which ASTM standard covers the liquid limit and plastic limit test procedures?
5A soil with a high plasticity index indicates which characteristic?
6The liquid limit is the moisture content at which soil begins to behave as:
7Which instrument is used in the Casagrande method for determining the liquid limit?
8The plastic limit of a soil is expressed in terms of:
9A soil with a plasticity index less than 4% is classified as which type?
10According to the Unified Soil Classification System (USCS), a soil with LL=50% and PI=20% is labeled:
11Which Atterberg limit defines the boundary between the plastic and semisolid states of soil?
12Why is distilled or deionized water recommended for Atterberg limit tests?
13Calculate the plasticity index for a soil sample with a liquid limit of 55% and a plastic limit of 25%.
14Remolding a soil sample before the liquid limit test will typically ______ the measured liquid limit.
15Adding fine clay minerals to a soil generally ______ its plasticity index.
16What is the standard laboratory temperature range for conducting Atterberg limit tests?
17A soil sample has a liquid limit of 40% and a plasticity index of 20%. Under USCS classification, this soil is categorized as:
18The liquid limit test is most sensitive to which soil characteristic?
19An increase in laboratory temperature above 23°C generally will have what effect on the measured liquid limit?
20In the fall cone method for determining liquid limit, what is the standard mass of the cone used?
21The plasticity index is directly correlated with which soil behavior?
22How many blows are applied during a single liquid limit determination using the Casagrande cup?
23To achieve reliable liquid limit results, the moisture contents from two determinations should differ by no more than:
24In the plastic limit test, the soil is rolled into a thread before crumbling at approximately what diameter?
25When using a 120 g cone instead of the standard 80 g in the fall cone test, the liquid limit result should be corrected by multiplying by approximately:
26Under identical test conditions, which clay mineral typically exhibits the highest plasticity index?
Learning Goals

Study Outcomes

  1. Understand ASTM Plasticity Index Concepts -

    Grasp the fundamental principles of the plasticity index test under ASTM D4318, including the significance of liquid and plastic limits in soil behavior.

  2. Calculate Plasticity Index Using Formula -

    Apply the plasticity index formula (PI = LL − PL) to determine soil plasticity index values accurately from laboratory data.

  3. Analyze Liquid and Plastic Limit Data -

    Examine liquid limit and plastic limit test results to assess soil consistency and predict engineering performance.

  4. Interpret Soil Plasticity Index Charts -

    Use plasticity charts to classify soils based on plasticity index and liquid limit combinations for geotechnical design.

  5. Apply Standard ASTM D4318 Test Procedures -

    Follow step-by-step guidelines of the ASTM plasticity index test to prepare samples, perform measurements, and record results.

  6. Evaluate Soil Mechanics Skills Through the Quiz -

    Test your mastery of soil plasticity index concepts with targeted questions in the ASTM D4318 quiz and identify areas for improvement.

Study Guide

Cheat Sheet

  1. Liquid Limit (LL) Fundamentals -

    Understand the ASTM D4318 liquid limit test, which measures the water content at which soil transitions from plastic to liquid state. A handy mnemonic is "25 blows show how it flows," since 25 blows in the Casagrande cup marks the LL point. This value lays the foundation for accurate plasticity index calculation and is detailed in ASTM International standards.

  2. Plastic Limit (PL) Essentials -

    The plastic limit test identifies the water content at which soil crumbles into threads of about 3 mm diameter per ASTM D4318. Think "PL = Pliable Limit" to remember that you roll the soil until it breaks to find the PL. This measure, supported by the USDA Soil Mechanics Handbook, completes the inputs for the plasticity index test.

  3. Plasticity Index (PI) Calculation -

    The plasticity index formula (PI = LL - PL) quantifies the soil's range of plastic behavior for the ASTM plasticity index. For example, if LL = 50% and PL = 20%, then PI = 30%, indicating moderate plasticity. This simple PI calculation is universally applied in geotechnical engineering per ASTM D4318 and soil mechanics literature.

  4. Casagrande Plasticity Chart Interpretation -

    Plot LL versus PI on the Casagrande plasticity chart to classify soils into CL, ML, CH, or MH following USCS criteria. The A-line equation, PI = 0.73 (LL - 20), separates clays from silts and helps visualize soil plasticity index behavior. MIT OpenCourseWare and University of California guidelines both highlight this chart for ASTM D4318 quiz prep.

  5. Practical Applications in Design -

    Soil plasticity index is directly linked to shrink-swell potential and shear strength, informing foundation, pavement, and embankment design. High-PI soils (PI > 20%) demand mitigation measures to prevent structural damage, as noted by FHWA and in Terzaghi's Principles of Soil Mechanics. Mastering these real-world applications boosts your confidence for any ASTM D4318 quiz or field project.

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Updated Feb 18, 2026