Which four categories are there in Grading of grain gaps?
Draw for each a graph of grain size distribution!
Advantage of well-graded: the force is better distributed
uniformly graded = single size
What does Fuller’s curve describe, and what is the formula?
Empirical curve showing the optimal grain size distribution of aggregates
the exponent is only 0.5 for theoretical ideal consideration
Fuller curve in comparison to other Grading:
How can the uniformity (C_u) and gradation (C_c) coefficient be calculated?
What are the limitations?
d10 = Grain diameter at which 10% of the mass is finer
d60 = Grain diameter at which 60% of the mass is finer
well graded:
for sand: C_u >= 6 & 1 <= C_c <= 3
for gravel: C_u > 4 & 1 <= C_c <= 3
poorly graded: else
More suitable for coarser soils / not suitable for cohesive soils
How are the Porosity and void ratio defined? Limitations?
V_v = void Volume; V_t = total Volume; V_s = solid Volume
Porosity: n = V_v/V_t
void ratio: e = V_v/V_s
these are linearly dependent
only for non cohesive soil
How is the relative density (D_r) defined?
Categorize the soil from loose to dense according to D_r in percent!
relative density for given soil
D_r = (e_max - e)/(e_max - e_min) (e is void ratio)
e_min —> strong vibrations
e_max —> loose put in a container
(Soil Compaction) What is the formula for dry density (ϱ_d) in regard to the bulk density (ϱ) and the water content (w)?
bulk density: ϱ = M_t / V_t
dry density: ϱ_d = M_s / V_t
Water content: w = M_w / M_s
ϱ_d = ϱ / (1 + w)
For which kind of soil is the Proctor curve (Soil Compaction) suited? What is this curve for?
Draw the Proctor curve for two different rammer (2.5 and 4.5 kg)!
Proctor curve is suitable for COHESIVE soil, not so much for non-cohesive
Proctor curve quantifies how water content controls soil compactability under a defined energy input
Water acts as a lubricant between soil particles
Too little or too much water reduces achievable density
What are the Atterberg limits?
Define the Consistency Index I_c! How does it relate to the Maximum Shear Strength (τ_max)?
Atterberg limits define the water content boundaries at which a fine-grained soil changes its mechanical behavior
(plastic (w_P) and the liquid (w_L) limit are characterized by experiments; w is water content)
I_c = (w_L - w) / (w_L - w_P)
for 0.2≲I_c≲1.0 —>τ_max is proportional to I_c due to c:
(((Shrinkage limit: you dry the soil to a point, where drying it even more does not further decrease its volume)))
Estimation of the friction angle
Which term of the following formula is more important for cohesive and which for non-cohesive soil?
τ_max = c + p*tan(phi)
cohesive soil: τ_max is mostly controlled by the water content —> c is more important, which you get from I_c
non-cohesive soil: angle of friction (phi) is more important
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