In the treatment of ground for its consolidation, there have heretofore been employed various methods. Examples of such methods include a method using cement milk and a method using sodium silicate and a hardening agent which hardens the sodium silicate. As the hardening agent, there is used, for example, at least one material selected from the group consisting of calcium chloride, sodium carbonate, sodium sulfate, sulfuric acid, copper sulfate, slaked lime, aluminum sulfate, construction-grade cement, bentonite, sodium aluminate, sodium bicarbonate, and sodium silicofluoride. In the method using sodium silicate and a hardening agent, however, the time (gelation time) in which the ground is consolidated is generally short and is extremely variable with a small change of blending ratio of sodium silicate with the hardening agent and therefore, since the gelation time can not be controlled sufficiently, the consolidation of ground by this method has been difficult.
In recent years, there have been developed various organic grouting agents of the type which have high ground-permeating capacities and by which gelation times are easily adjusted. Such organic grouting agents include those made of polyacrylamides, urea resins, polyacrylates, urethane resins and chromium lignin, for example. Use of these organic grouting agents has been banned in Japan since 1975 for fear that they may be toxic to human beings. This is because the organic grouting agents, when used in areas located near wells, underground water strata, rivers and brooks, lakes and swamps, or seas, may possibly effect humans, fishes and shell-fishes, etc. In Japan, the Ministry of Construction published "Provisional Guide Concerning Execution of Construction Works by Chemicals' Injection Process" in July, 1974. In this ministerial order, it is stipulated that "the chemicals acceptable for use in construction works shall be limited, for the time being, to water glass type liquid chemicals (liquid chemicals composed predominantly of sodium silicate) free from violently active compounds or fluorine compounds." Since then, only water glass type liquid chemicals have been used for the purpose.
Of the various methods available for works involving the use of these water glass type liquid chemicals, that which has gained widespread acceptance for actual use is the so-called LW process (Japanese Patent Publication No. 24122/1961) which makes use of a suspension type of water glass grouting agent composed of construction-grade cement and sodium silicate. To be specific, this grouting agent includes from 2.5 to 100 parts by weight of the principal component of water glass per part by weight of construction-grade cement. This LW process, however, has a disadvantage that the gelation time and the strength of treated soil are in a mutually contradicting relationship. As the ratio of cement is increased for the purpose of increasing the strength, the gelation time is shortened proportionally. In other words, the agent hardens itself before it penetrates to the desired depth in the soil, preventing smooth injection.
USPTO Backgrounds
USPTO Backgrounds