Presented by: Civil Engineering Academy

Transcription

1 Presented by: Civil Engineering Academy

2 Soil Classification Presented by: Civil Engineering Academy

3 Is an aggregate of loose mineral and organic particles. Exhibits strong and permanent cohesive forces between the mineral particles.

4 Coarse grained soil Gravel Sand Fine grained soil Silt Clay

5 Coarse grained Soil Sieve test: soil is passed through a set of consecutively smaller openings. Fine grained Soil Hydrometer test: Relates speed of particle falling out of suspensions to its diameter and density.

6

7 Hazen uniformity coefficient (Cu) Cu = D 60 /D 10 Eq CERM D 10 = effective grain size means 10 % finer of particle size D 60 = means 60 % finer of the particle by weight Coefficient of Gradation (Cz) Cz = D 302 / (D 10 x D 60 ) Eq CERM D 30 = 30 % of particles are fine

8 From the given data, solve for Cu and Cz. Sieve Diameter % passing Number (mm) # # # # # # # # Characteristics of # 40 fraction LL 35 PL 20 D 60 = is between 64 & 54 Cu = D 60 / D 10 54% = 2mm diameter 64% = diameter D 60 = D 60 = mm For D 10 : mm = 9% mm = 17% D 10 = D 10 = Cu = D 60 / D 10 = 2.228/0.162 = For Cz: Cz = D 302 / D 60 x D 10 D 30 = between 34 & mm = 22% mm = 34% D 30 = D 30 = 0.7 Cz = (0.7) 2 / (2.228)(0.162) = 0.14

9 AASHTO and Unified are the two primary soil classification systems to be familiar with. CERM Table 35.1 shows all the organizations currently involved in classifying soils. Both are based on the following factors. Sieve analysis. The sample s particle size distribution. Liquid limit (LL). The water content corresponding to the transition between the plastic and liquid state. A liquid limit of 100 means that the moisture weighs as much as the dry soil. Plastic limit (PL). The range of moisture content over which the soil is between a semisolid and plastic state. Plasticity index (PI). The range of moisture content over which the soil is plastic.

10 AASHTO = American Association of State Highway Transportation Officials Using the test data, proceed from left to right in the chart. The correct group will be found by process of elimination. The first group from the left consistent with the test data is the correct classification. The A-7 group is subdivided into A-7-5 or A-7-6, depending on the plastic limit. For plastic limit PL = LL - PI less than 30, the classification is A-7-6. For plastic limit PL = LL PI greater than or equal to 30, it is A-7-5. NP means nonplastic.

11

12 Group Index (comparing soils within a group) I g = (F ) (0.2 +(0.005(LL-40 ))) (F ) (PI- 10) Eq. 35.3, CERM Where: F 200 = percentage of soil passing #200 sieve LL = Liquid Limit PI = Plasticity Index (LL PL Eq , CERM) PL = Plasticity Limit For I g = 0, good subgrade I g > 20 poor subgrade material I g < 0, assume Ig = 0

13 Sieve Diameter % passing Number # # # # # # # # Characteristics of # 40 fraction LL 35 PL 20 From the given data, classify this soil using the AASHTO Method. Solution Refer to Table 35.4 % passing # 10 = 92% > 50 % passing # 40 = 53% > 30 % passing # 200 = 17% < 35 LL = 35 PI = LL - PL = 15 From this data, soil is classified as A-2-6 Solve for Group index G 1 = (F ) (0.2 +(0.005( LL- 40))) (F ) (PI - 10) G 1 = (17-35) (0.2 +(0.005(35-40))) (17-15) (15-10) G 1 = -3.05, thus = 0 The soil is classified as A-2-6(0), silty or clayey gravel and sand

14 USCS = Unified Soil Classification System

15 Soils are classified into USCS groups that are designated by a group symbol and a corresponding group name. Particle Size Fraction X X Modifier Coarse Grained Fine Grained Primary Modifiers Primary Modifiers G = Gravel S = Sand W well graded, fairly clean C significant amount of clay P poorly graded, fairly clean M significant amount of Silt M - inorganic silts C - inorganic clay O - organic silt and clay L = low compressibility (LL less than 50) H = high compressibility (LI = 50 or greater)

16 Sieve Diameter % passing Number (mm) # # # # # # # # Characteristics of # 40 fraction LL 35 PL 20 From the given data, identify soil this is using the USCS Method. Solution Refer to Table 35.5 %coarse = = 83% %sand = = 70%, 70/83 = 84.3% of coarse aggregate % passing # 200 = 17% < 35 LL = 35 PI = LL - PL = 15 >12 From LL an PI, we can see that point is above A- line, thus soil classification is SC, clayey sand Note: The Equation of the A-line is PI=0.73(LL-20) *write this in your CERM!

17 CERM Ex. 35.1

18 Six-Min Problems - Geotech Prob. 2 (CERM Eq. 35.1) (CERM Eq. 35.2)

19 Six-Min Problems Prob. 2 (continued)

20 Six-Min Problems Prob. 2 (continued)

21 Six-Min Problems - Geotech Prob. 23

22 Six-Min Problems - Geotech Prob. 23 (Continued)

23 Important factors. They can all look slightly different but they always provide the most important information: Blow count or SPT or N: SPT is the Standard Penetration Test, amount of blows to go through 6 inches of soil (total of 18 in). You discount the first number and count the last to. So, a means 10 blows that s it s N value. A high blow count means stronger soils. Water Table: where they hit the water table during drilling sometimes they show where a design water table is or static water head. Type of soil, depth, etc. are all other good pieces of information.

24 More soil classification practice problems! Next topic: Soil Properties