Guest
Chapter:
1. A project engineer receives a laboratory report with tests performed on central material testing laboratory,IOE,Pulchowk. The engineer suspects that one of measurement is in error. Are engineers suspicions correct? If so, which of se values is wrong and what should be it's correct value? `gamma`=unit weight of sample`=18.4 (KN)/M^3` `gamma_s`=unit weight of solid`=26.1 (KN)/M^3` `w`=water content`=40%` `e`=void ratio`=1.12` `S`=degree of saturation`=95%` [2072 Magh][8]
2.
Void ratio:
Void ratio is defined as the ratio of volume of voids to the volume of solid particles i.e,
`e=V_v/V_s`
`or, e=(V_w+V_a)/V_s`
Porosity:
Porosity denoted by n, is defined as the ratio of volume of voids to the total volume of soil. It is expressed in percentage.i.e,
`n=V_v/V*100`
`=(V_a+V_w)/(V_a+V_w+V_s)*100`
Degree of saturation:
Degree of saturation denoted by $S_r$ is defined as the ratio of volume of water to the total volume of voids in the soil mass. It is expressed in percentage.i.e,
`S_r=V_w/V_v*100`
Water content:
Water content or content of a soil mass, denoted by w, is defined as the ratio of weight of water to the weight of dry soil.i.e,
`w=W_w/W_s`
The weight used in the about expressions is the weight of water loss when the soil is heated to a temperature of 105 degree centigrade to 110 degree centigrade for such length of time that its weight is constant. In routing laboratory test, a period of 24 hours is considered enough for drying.
Bulk unit weight:
Bulk Unit Weight or mass unit weights denoted by `gamma_t` is defined as the weight of soil mass per unit volume of soil mass.i.e,
`gamma_t=W/V`
=`(W_s+W_w)/(V_s+V_w+V_a)`
Dry unit weight:
Dry Unit Weight denoted by `gamma_s` is defined as the ratio of weight of solid to volume of soil.i.e,
`gamma_s=W_s/V`
Unit weight of water:
It is the ratio of weight of water per unit volume of water.i.e,
`gamma_w=W_w/V_w`
Specific gravity of solids:
It is the ratio of Unit Weight of soil solid to Unit Weight of water at 4 degree centigrade.i.e,
`G=gamma_s/gamma_w`
`=W_s/(V_s*gamma_w)`
Specific gravityof water:
It is defined as the ratio of Unit Weight of water at any temperature to Unit Weight of water at 4 degree centigrade.i.e,
`G_t=gamma_w/gamma_0`
Where,`gamma_0` is the Unit Weight of water at 4 degree centigrade.
3. Define phase diagram. Draw phase diagram for saturated, partially saturated and dry soil. [2075 Bhadra][3]
4. By three phase soil system, show that degree of saturation `S_r` in terms of unit mass weight `gamma_m`, water content ratio `w` and specific gravity of soil `G` and unit weight of water `gamma_w` is given by: `S_r=w/((gamma_w*(1+w))/(gamma_m)-1/G)`
5. Name index test that are generally carried out to find index properties of soil. [2076 Baisakh][1]
6. Prove `gamma_t=(G+S_r*e)/(1+e)*gamma_w`
We know from above solution,
`gamma_t=(1+w)/(1+e)*G.gamma_w`..... (i)
Simalarly,we know,
`S_r*e=w*G`.... (ii)
Thus, `gamma_t=(G+S_r*e)/(1+e)*gamma_w`
Again,if the soil is saturate,then `S_r=1`,
So `gamma_t=gamma_(sat)` at `S_r=1`
Thus, `gamma_(sat)=(G+e)/(1+e)*gamma_w`
Again, if the soil is dry, then `S_r=0` and the bulk unit weight in this case becomes dry unit weight.
Thus, `gamma_d=G/(1+e)*gamma_w`
7. The moisture content of an undisturbed sample of clay belonging to a volcanic region is `265 %` under `100%` saturation. The specific gravity of solid is `2.5`and and dry Unit Weight is `3.3 (KN)/M^3`. Determine:
- saturated unit weight
- submerged unit weight
- void ratio
8. An embankment of `1,00,000 m^3` volume has to be constructed by compacting soil brought from excavation site. After compaction, dry unit weight of compacted soil (embankment) will be `16(KN)/M^3`. Also, bulk unit weight and water content of soil at excavation site are `12 (KN)/M^3` and `15%` respectively. Find volume and weight of soil to be excavated from excavation site. Take specific gravity of soil solid as `2.70`. [2073 Magh][5]
9. Explain phase diagram of soil.
Soil mass is defined as the uncemented aggregate of minerals grains and decayed organic matter with liquid and gas in the empty spaces between the solid particles. The space between the soil particles is known as voids and these voids may be filled with either air or water or both.
The soil will behave as a two phase system when its space is filled with air or water alone. A two phase diagram either represent a dry or a completely saturated soil. When all void space is filled with water the soil mass is fully saturated and exist in two phases as solid and water . Similarly, when the soil mass is completely filled up by air, the soil mass becomes dry soil and exist in two phases is solid and air.
Fig: saturated soil- Two phase diagram.
Fig: dry soil- two phase diagram
When the soil mass is partially filled up by water as well as air, it will behave as a three phase system.
The diagrammatic representation of the different phases in a soil mass is called the Phase diagram.
Fig: unsaturated soil: three phase diagram
10. A sample of wet silty clay has a mass of `126\ kg`. The following data were obtained from laboratory tests on sample:
Wet density,`rho_t=2.1 g/(cm^3)`
`G=2.7`
water content,`w=15%`
Determine:
- dry density
- porosity
- void ratio
- degree of saturation
`rho_d=1826.2 (kg)/m^3`
`n=32%`
`e=0.47`
`S_r=84.5%`
