Cement grouting has been commonly used to solidify loose ground or to check ground-water leakage in the course of excavation or other types of construction work. In cement grouting, however, cement particles in the grout form a kind of so-called suspension; and the grout can penetrate neither into tiny seams of rock that are smaller than the cement particles, nor effectively into sand.
A means to be used successfully in such a case is chemical injection in which suitable chemicals that are originally in a prefectly liquid state are injected and made to coagulate after the injection to effect the purpose of solidification.
Heretofore, a combination of sodium silicate (Na₂SiO₃) and calcium chloride (CaCl₂) has been used for this purpose. But this method has a drawback concerning the procedure of injection. As the two chemicals react each other very rapidly, the solution of sodium silicate must be injected first, and, after cleaning the pipes and the pump free of the first chemical, the second chemical is to be injected. Thus, the injection of two chemicals must be carried out alternately, and this process not only is a troublesome operation but also has a drawback that the chemicals react each other and coagulate near the injection-pipe outlet to stop the passage of the second chemical, the deeper penetration of first chemical thus being not fully utilized.
Therefore, it is essential to inject both chemicals simultaneously through one injection pipe either by mixing them before pumping or by using two pumps. Moreover the time that shall pass after the two chemicals have been mixed together until they start to coagulate (coagulation time), should be able to be easily controlled to accord properly with the purpose of the work.
For instance, in case where a considerably large area or mass is to be solidified, the coagulation time should be maintained longer. On the other hand, for checking leakage of water, the chemicals should coagulate as quickly as other working conditions permit.
In order to develop higher strength of the solidified layers, a more concentrated solution of sodium silicate will be required. The viscosity of sodium silicate solution becomes higher at a great rate as the density increases, so it becomes more difficult to effect a satisfactory penetration in narrow voids. This has been another problem in injection of chemicals that consist mainly of sodium silicate. It is necessary to reduce the viscosity without affecting the strength and other properties of the chemicals. Various studies have been done in this respect.
Chemicals Proposed by the Authors:
As a mean to solve the above-mentioned problems, the author devised a method of using a combination of sodium silicate and sodium aluminate, adding, according to the necessity, a certain amount of NaOH in order to stabilize the reaction of these chemicals.
Sodium aluminate is an intermediate product in the process of manufacturing alumina. The proportion of its two components, Al₂O₃ and Na₂O, can be changed as is desired. In addition to this, the viscosity of this solution does not increase with the degree of its concentration at so great a rate as in case of sodium silicate (Fig. 1.).
Consequently, the mixture of sodium aluminate and sodium silicate solutions is far less viscous than sodium silicate alone. This is to say that the added sodium aluminate has a role of lowering viscosity while it itself acts as one component of the chemical reaction.
On the Coagulation Time:
The most influential factor in using these chemicals is the temperature of the solution. Fig. 9 shows the relation between the temperature and the coagulation time. The coagulation time flactuates also with the change in mixing proportion of these two chemical solutions as well as the proportion of the two components of each solution. In general, the coagulation time becomes sho

抄録全体を表示