The compressive strengths of a rock measured in the air dry, absolutely dry, and water saturated sta

The main physical properties of wood are:

Density. Refers to a unit volume.

The weight of the wood. The weight and volume of wood are affected by the moisture content.

Effect. The drying weight of the wood specimen and its volume when saturated with moisture. The ratio of the volume after drying to the volume at the time of furnace drying is called the basic density, respectively.

Absolute dry density and furnace dry density. The ratio of the weight of the wood after air drying to the volume after air drying is called the air dry density of the wood. Wood density varies with the tree species.

The air-dry density of most woods is around gram cm3. Dense wood generally has higher mechanical strength.

Moisture content of wood. Refers to the percentage of water weight in the wood to the weight of the dried wood.

The water in wood can be divided into two parts, one part exists in the cell wall of wood cells, which is called adsorbed water; The other part is found between the cell cavity and the intercellular space and is called free water (free water). When the adsorbed water reaches saturation and there is no free water, it is called the fiber saturation point. The fiber saturation point of wood varies depending on the species, ranging from 23 to 33.

When the moisture content is greater than the fiber saturation point, the effect of moisture on the properties of the wood is very small. When the moisture content decreases from the fiber saturation point, the physical and mechanical properties of the wood change accordingly. Wood absorbs or evaporates moisture in the atmosphere, relative humidity with the surrounding air.

The constant moisture content that is adapted to the temperature is called the equilibrium moisture content. The equilibrium moisture content of wood varies with region, season and climate and is about 10 18.

Expansion. When wood absorbs water, it expands in volume and shrinks when it loses moisture. The dry shrinkage rate of wood from the fiber saturation point to the furnace dry is about 3 6 in the radial direction and 6 12 in the radial direction.

The difference in the dry shrinkage rate in the radial and chordal directions is the main cause of cracks and warpage in wood.

Mechanical properties of wood:

Wood has very good mechanical properties, but wood is organic anisotropic.

The mechanical properties of the material, the direction of the grain and the direction of the horizontal grain are very different. Grained tensile and compressive strength of wood.

Both are higher, but the tensile and compressive strength of the transverse grain are lower. Timber strength also varies depending on the tree species and is subject to timber defects and loads.

The effects of action time, moisture content and temperature are the most important among the wood defects and load action time. Due to the different size and position of the knots, and the different force properties (tension or compression), the strength of knotted wood can be reduced by 30 60 compared with knotless wood. The long-term strength of the timber is almost half of the instantaneous strength under long-term load.

The softening coefficient kb of the material is equal to the compressive strength (fb) of the material in the saturated state of water absorption divided by the compressive strength (fg) of the material in the dry state. The softening coefficient of this question kb=168mpa 178mpa=. larger, can be used for underwater engineering.

Very good rocks, of course it could be used.

d(1+pushout, d= 1+, so the dry weight is percolation m3

n Chant Yuye Segment 1- d (gs water) =

m d n water =

Hail bend d(1+

d Source trail stuffiness (1+.)

n 1-d gs water.

m d state brigade n water.

Answer]: A Ti Lu's show: According to the magnitude of the rock softening coefficient, it can be discussed early to distinguish the strength of the softening of the rock, according to the general classification criterion greater than the weak, otherwise it is strong. It can be seen that the answers to B and D are contradictory.

Answer]: A softening coefficient refers to the ratio of the ultimate compressive strength of saturated rock to the ultimate compressive strength of dry rock. It is calculated as follows:

Absolute high trace k = f f. where k is the softening coefficient of the material; f is the compressive strength of the material in the water-saturated state, mpa; f is the compressive strength of the material in the dry state, mpa. then the softening coefficient of the rock is k=2

1/3. 2 = 。When kr, the state of mind is to soften the rock, and when kr, it is not to soften the rock.

Specimen cross-sectional area 50 4; Average ultimate load (179 + 182 + 174 + 178 + 189 + 185) 6=

Class 181160.

A: This limestone block has a strength grade of m90.

Answer]: A full bridge only and uniaxial bridge widening resistance pressure sensitive brightness strength greater than 60MPa belongs to hard rock.

Answer] :d the basic quality index bq of rock mass, it should be calculated according to the megapascal value of the quantitative index rc of the grading factor and the only change kv, as follows:

bq＝100＋3rc＋250kv

When using the above-mentioned common model Huai formula, the following provisions should be observed:

When RC 90kV 30, the BQ value should be calculated by substituting RC 90kV 30 and kV;

When kv, the bq value should be calculated by substituting kv and rc.

In this problem, rc 60mpa, kv, and 90kv 30 57 60, so take rc 57.

Sodan Mountain Friends are available: BQ 100 3 57 250.

As can be seen from Table 1-1-8, the basic quality level of the rock mass is .

Table 1-1-8 Basic quality classification of rock mass.