Lecture_4_-_Atterberg_Limits___USCS

Lecture_4_-_Atterberg_Limits___USCS - CHARACTERISTICS OF...

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Unformatted text preview: CHARACTERISTICS OF SOILS Physical characteristics Engineering characteristics PHYSICAL CHARACTERISTICS OF SOILS Grain size distribution Atterberg limits Compaction ATTERBERG LIMITS & THE UNIFIED SOIL CLASSIFICATION SYSTEM (USCS) Atterberg limits are consistency indices developed in the early ATTERBERG LIMITS 1900's by the Swedish soil scientist A. Atterberg for the ceramic industry. He defined several limits of consistency as follows: Upper limit of viscous flow Liquid limit (LL), which is the lower limit of viscous flow Sticky limit at which clay loses its adhesion to metal plate Cohesion limit at which grains cease to cohere to each other Plastic limit (PL), which is the lower limit of the plastic state Shrinkage limit (SL) that marks the lower limit of volume change The Atterberg limits are determined in the lab using the Casagrande liquid limit device. CASAGRANDE LIQUID LIMIT DEVICE PLASTICITY INDEX The plasticity index (PI) of soils can be calculated as follows: PI = LL PL The activity (A) is defined by Skempton (1953) as: A = PI/Clay fraction (%) ATTERBERG LIMITS 60 50 Plasticitry index 40 30 20 10 0 0 nic ys ga y cla r no lt c i & si st i pla andy w s Lo ys; cla M ium ed tic las p r ino ys cla nic ga U ne -li I= 0 L (L .9 8 ) A e -lin P = PI 0 L 3(L .7 0 2 ) CH OH or H M CL ML OL CL-ML ML Inorganic & organic silts and silty clays of low plasticity; rock flour, silty or clayey fine sand 20 40 60 80 100 Liquid limit THE UNIFIED SOIL CLASSIFICATION SYSTEM (USCS) THE USCS Coarse grained soils Yes Are 50% of particles > 0.075 mm? No Soil is fine-grained Soil is coarse-grained Gravel, 1st letter is G Yes Is gravel fraction > sand fraction? No Sand, 1st letter is S Is clay + silt fraction Yes Is clay fraction > silt fraction? Yes Plastic clayey fines, 2nd letter C No Non-plastic silty fines; 2nd letter M > 12%? Yes Yes < 5%? Between 5% & 12%? Yes Is clay fraction > silt fraction? No If 1st letter is G, CU > 4 & 1 < CC < 3, the soil is GW-GC, otherwise it is GP-GC If 1st letter is s CU > 6 & 1 < CC < 3, the soil is SW-SC, otherwise it is SP-SC If 1st letter is G, CU > 4 & 1 < CC < 3, the soil is GW-GM, otherwise it is GP-GM If 1st letter is s CU > 6 & 1 < CC < 3, the soil is SW-SM, otherwise it is SP-SM If 1st letter is G, CU > 4 & 1 < CC < 3, 2nd letter is W, otherwise it is P If 1st letter is S, CU > 6 & 1 < CC < 3, 2nd letter is W, otherwise it is P THE USCS Fine grained soils Yes Are 50% of particles < 0.075 mm? No Soil is coarse-grained Soil is fine-grained Yes Is LL( Oven - dried ) LL( Notdried ) < 0.75% ? No Is clay fraction > silt fraction? Organic soil, 1st letter is O Yes Clay, 1st letter is C No Silt, 1st letter is M Is LL >50%? Yes No High plasticity, 2nd letter is H; the soil is fat clay or elastic silt Low plasticity, 2nd letter is L; the soil is lean clay or silt ...
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This note was uploaded on 02/07/2008 for the course CE 337 taught by Professor Baladi during the Spring '08 term at Michigan State University.

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