The definition should, therefore, be clarified. It is very often considered that a material whose TML can not be determined is the material which is not liable to liquefy. This definition is not correct as described in the next section. Thus, a method for judging whether the material may liquefy or not should be developed.
1.3 Liquefaction potential and transportable moisture limit
Three test procedures for determining TML are described in the BC Code. By the Flow Table Test and Penetration Test, flow moisture point (FMP), i.e., the moisture content at which liquefaction phenomenon take place under the specified acceleration and compaction condition, is measured and the TML is determined at 90 % of the FMP. In the case that the FMP for a material can be determined by the Flow Table Test or by the Penetration test under drained condition, it is appropriate to judge that the material may liquefy during voyage when it contains much moisture. It is, however, not appropriate to judge that a material is not liable to liquefy regardless of moisture content at shipment in the case that the FMP for the material was not able to be measured by these test. By Proctor/Fagerberg Test, TML is determined at the moisture content corresponding to degree of saturation 70 % under the specified compaction condition. By this test, in the case that the degree of saturation of a material reach to 70 %, TML can be determined even if the material is not liable to liquefy. On the other hand, in the case that the degree of saturation does not reach to 70 %, it is not appropriate to judge that the material is not liable to liquefy, because the condition of drainage from a sample is not specified in the test. This test, therefore, cannot be utilized for the judgment on the scope of application of the requirement. It can, therefore, be said that no test procedure for determining the application of the requirement is referred to in the BC Code. Taking these circumstances into consideration, we developed a new test procedure to enable the judgment on the scope of application of the requirement for various materials. Hereafter, "liquefaction potential" means the possibility of liquefaction during voyage.
2 Liquefaction phenomenon of solid bulk materials
A wet (partially saturated) granular material, represented by mineral concentrates, consists of solid particles and void consisting of water and air, in general. When the cyclic load is applied to such material, particles of the material may move microscopically and the volume of void may tend to decrease. In such case, if the void is filled with water and the water flow through the small void is resisted, the pressure of the water in void increases.
Shear strength of granular materials is maintained by friction and cohesion. Friction is expressed as the product of effective compressive force between particles and the friction coefficient. When pressure of water in void increases, effective compressive force between particles becomes decreases. Then, shear strength of the granular material becomes insignificant if cohesion is negligible, and the material may flow. Such phenomena is called "liquefaction".
When void of a material contains a certain proportion of air, air can go through the small void with small resistance and pressure of water in void does not increase significantly. This is the explanation why the liquefaction does not take place when the moisture content of the material is low.
In a material consisting of large particles, water can got through the big void with small resistance and pressure of water in void does not increase significantly. This is the explanation why the liquefaction does not take place when the material consists of large particles.
In a material consisting of very fine particles such as clay, its shear strength is mainly generated by cohesion which is not affected by cyclic loading. This is the explanation why the liquefaction does not take place when the material consists of very fine particles such as clay.
Liquefaction phenomena does not take place when one of the following conditions is satisfied:
(1) Cyclic load is not applied;
(2) The material has enough cohesion. In other words, the material consists of very fine particles;
(3) The material consists of large particles; or
(4) The moisture content of the material is low. In other words, the degree of saturation of the material is low.
