B.6 Correlation of various properties of treated soil

B.6.1 Field strength and laboratory strength

Different mixing and different curing conditions cause the difference between field and laboratory mixed soils. The laboratory test procedures are different in Europe and Japan as mentioned in Clause 5. In each of the regions, different mixing tools are used and this makes it difficult to compare the field strength and the laboratory strength in a general manner. However, if the same mixing tools are used under a standardised quality control system, it is possible to compare field- and laboratory-treated soil, based on accumulated experience.

According to Swedish dry mixing experience in soft plastic clays, the ratio of field strength and laboratory- mixed sample strength is in the range 0,2 to 0,5. In granular soils, the ratio of field and laboratory-mixed sample strength is likely to be significantly higher. In granular soils, the fines content largely determines the ratio.

For the CDM method (Cement Deep Mixing Method) – the most common wet mixing method in Japan – the CDM association has established the quality control procedure and the minimum blade rotation number. The typical dry mixing method – the DJM method (Dry Jet Mixing Method) – employs the mixing tool manufactured by the same manufacturer. Japanese experience from accumulated data by CDM and DJM on land are summarised in Figure B.3 and for CDM works in Figure B.4.

Relation between strength results of field and laboratory tests for on-land constructions

Key

  • 1 Field strength quf, MPa
  • 2 Laboratory strength qul, MPa
Figure B.3 — Relation between strength results of field and laboratory tests for on-land constructions [19]
Relation between strength results of field and laboratory tests for marine constructions

Key

1 Unconfined compressive strength of in-situ treated soil, quf, MPa
2 Unconfined compressive strength of laboratory treated soil, qul, MPa
3 Clay
4 Sand		 } 5 Daikoku pier
6 Clay Hatskaichi port
7 Silty clay
8 Sandy silt		 } 9 Kanda port
10 Chiba port
11 Kitakyushu port
Figure B.4 — Relation between strength results of field and laboratory tests for marine constructions [5]

B.6.2 Correlation between mechanical characteristics and unconfined compressive strength

Values of bending strength, tensile strength, modulus of elasticity and permeability are often required in the design. These characteristics may be obtained from core samples of in-situ treated soil after the construction. In the design stage, however, these values should be assumed appropriately on the basis of a reliable database. For the Japanese wet mixing method, abundant data exist and are compiled by the Coastal Development Institute of Technology, Japan [5].

EN 14679:2005 Execution of special geotechnical works — Deep mixing