Environmental Engineering Reference
In-Depth Information
Table 10.2
Target values for properties suitable for planting
Basis of decision
Unit
Target value
Remark
Water holding
ability
Effective water reten-
tion capacity
(l/m
3)
Above 100
pF1.5-3.8 range
Permeability
Coefficient of
permeability
(cm/s)
More than 10
−3
3-phase distribution
(solid, air, water)
(%)
Less than 30 solid
pF measurement
of 1.5
Above 25 air
Lightweight
Specific gravity under
wet conditions
(-)
Below 1.0
pF measurement
of 1.5
Fertilizer hold-
ing ability
CEC(Cation
Exchange Capacity)
(cmol/kg) Above 6
pF value indicates the strength in which the water in the soil is adsorbed by capillary force
used for planting derived from bark. In these results, the vegetation growing on a
base of fiber-solidified sludge is better than that growing on bark-derived compost
(Yamazaki et al.
2004
). In addition, if you consider the soil's physical characteris-
tics, the fiber-solidified soil, in comparison with normal commercial artificial light-
weight soils, has good water retention capacity, light weight and also holds nutrients
well, and is thus confirmed as a very promising greening base material.
Incidentally, the purpose of adding paper debris which is the special feature of
this method, is to aggregate the high water content muds such as construction sludge
without dewatering, and in doing so modify it into a transportable state. When the
modified soils are utilized as landfill material, the amount of paper debris added
is determined based on the water content ratio. However, in the case of producing
planting soils, if the amount of paper debris added is determined solely based on the
water content, the quality of the planting soil produced is not constant, because the
ratio of the amount of soil to the amount of paper debris in the planting soils is not
constant. Therefore, in order to produce planting soils of fixed quality regardless of
the water content of the original sludge, the appropriate ratio for the amount of soils
to the amount of paper debris was investigated (Yamazaki et al.
2008
).
The necessary performance criteria for planting soils are 'water holding ability',
'lightweight', 'permeability' and 'fertilizer holding ability'. Accordingly, target val-
ues which the planting soils should satisfy were set as shown in Table
10.2
.
Incidentally, when planting soils are produced in a factory, it is possible to reduce
the water content of the modified soils fully by solar drying or other methods. How-
ever, when construction sludge is recycled into planting soils at the construction
site, and subsequently used on site as the base for planting on slopes, it is difficult to
reduce the water content fully. Therefore, in this study, the planting soils were made
by two methods- a WET method and a DRY method. In the WET method, the water
content of the planting soils produced was adjusted to be 40 ± 5 %, and in the DRY
method, the water content of planting soils produced was adjusted to be 10 ± 5 %.
These planting soils were made by changing the additive amount of paper debris,
