Table.1 Physical properties of soil materials

Maebaru	Asagiri
Soil particle density(g/cm $ ^{3} $ )	2.721	2.370
Initial water content (%)	34.89	76.9
Fine particle content Fc(%)	72.17	74.06
Maximum particle diameter (mm)	4.75	9.5
Uniformity coefficient Uc	-	-
Curvature coefficient Uc $ ^{-} $	-	-
Plasticity index Ip	38.54	N.P
Ignition loss (%)	7.7	25.7
Core index (kN/m $ ^{2} $ )	984.53	-

silt and clay. In particular, the earth materials from Maebaru City contains much silt and clay, and its cone index at the natural water content is $ 984.5 \, kN/m^{2} $ ; so it is type 3 construction-generated soil. On the other hand, the construction-generated soil from Asagiri was a muddy soil for which it was not possible to obtain a cone value. It is a volcanic ash clay with an ignition loss of 25.7% and high organic content.

### 2.3 Test conditions

Table 2 shows the conditions for preparing the test specimens for the unconfined compression tests. For the mechanical property investigation, test specimens prepared under specific conditions were used, and unconfined compression tests were carried out. To prepare the test specimens, the soil material was adjusted to a specific water content, and then the hardener was added. Here, the percentage hardener added is the mass percentage of the soil material. After curing in air for the specific curing period (0, 7, 28 days), the unconfined compression tests were carried out. The method of preparation of the test specimens for unconfined compression tests was to compact by tamping each layer five times with the same energy $ \left(\mathrm{E}_{\mathrm{c}}=50\left(\mathrm{kJ}/\mathrm{m}^{3}\right)\right) $ in a mould with 5 cm diameter and 10 cm height, for a total of four layers. On the other hand, for the Ministry of the Environment Notification No. 46 test, the same material was used as in the mechanical tests, and the concentration of leachate was measured on an assay solution prepared based on the preprocessing procedures of the Ministry of the Environment Notification No. 46 in a spectrophotometer (ICP plasma emission spectrometer).

Table.2 Specimens preparation conditions for unconfined compression tests

Soil material	Hardener	Water content (%)
Type	Percentage added(%)
Maebaru	Bassante A	10	40
Bassante B
Blast furnace slag type B	15
Asagini	Bassante A	20	80
Bassante B
Blast furnace slag type B

### 3. TEST RESULTS AND DISCUSSION

### 3.1 Unconfined compression test results

In order to quantitatively and clearly show the amount of increase in strength associated with the addition of the hardener, Figs. 3 and 4 show the relationship between the unconfined compressive strength $ q_{u} $ for each hardener content and the strength increase ratio $ R = q_{u}/q_{i} $ normalized using $ q_{i} $ at 0% hardener content against percentage hardener content. Here, the black line in the figures indicates unimproved soil (R = 1.0). For Maebaru, it can be seen that the after-improvement strength is about the same as for slag cement type B obtained from a blast furnace. On the other hand, after curing for about 28 days, it can be seen that for both bassanites there is an improvement effect of a factor of 2 to 6 compared with the case where hardener is not added. This indicates that in soil improved with bassanite, the strength increase associated with curing is not as large as the increase with cement. On the other hand, in the high-organic-content soil from Asagiri, it can be seen that the improvement effect is of a factor of 0.7 to 3, which is smaller compared with Maebaru. However, with slag cement type B obtained from blast furnace, which showed a large improvement effect with Maebaru soil, the improvement factor was 1 to 2 even after curing. Therefore, there was almost no effect. On the other hand, with bassanite, the strength increased with increase in the number of days of curing, and an improvement factor of about 3 was obtained. Therefore, the strength improvement