A Study on Methods for Judgment of Effectiveness of Grouting by Chemical Injections

为了设计砂质土层化学灌浆工艺，需要根据待稳定土的特点确定最合适的灌浆条件。为了找到理想的注浆条件，必须从定量和定性上了解土壤条件和注浆条件对土壤固结的影响。本试验主要研究凝胶时间、注入速度、覆盖层压力和土壤相对密度四个不同变量对化学浆液生长的影响。本研究的结果来自于200个室内试验的圆柱形沙样，其高度和直径分别保持在30cm不变，分别由Keisa 6号、7号和天然河砂制成。采用两种不同的化学路线，获得较短的获得时间（5秒）和较长的凝胶时间（5分钟），注射量由500cc/min改为2000cc/min。松散状态（Dr=35%）和致密状态（70%）试样的覆盖层压力变化范围为49kN/m^2 ~ 245.2kN/m^2。试验结果表明，在凝胶时间较短、注入速度较慢的情况下，容易发生破裂注浆。然而，当凝胶时间较长时，无论其他变量如何，都倾向于发生渗透注浆，在这种情况下，注浆形成接近球形的固结砂，这被认为是注浆的理想条件。对于胶凝时间较短的注浆，水力压裂往往发生在注入速率较低时，此时形成的固结砂形态不规则。当覆盖层压力较大时，有可能获得类似于渗透注浆的球形。但需要注意的是，当覆盖层压力较大时，固结土体积减小约为预估体积的15% ~ 20%。

In order to design chemical grouting process in sandy soil layrs, it is necessary to determine the most suitable grouting conditions depending on the characteristics of soils to be stabilized. For the purpose of finding ideal grouting conditions, one must know how soil conditions and injection conditions will affect the consolidation of soils quantitatively and qualitatively. This experiment focuses on the effect of four different variables, namely gel time, injection rate, overburden pressure and relative density of soils, on the growth of chemical grouts. The results presented in this study were drawn from 200 laboratory trials of cylindrical sand specimen whose height and diameter were held constant at 30cm respectively, which were prepared by Keisa No.6, No.7 and natural river sand. Two different types of chemical routs were used to get short get time (5 seconds) and long gel time (5 minutes) and injection rate was changed from 500cc/min to 2000cc/min. The overburden pressure was varied from 49kN/m^2 to 245.2kN/m^2 for the specimens of loose state (Dr=35%) an dense state (70% ).The results of this experiment indicate that fracture grouting tends to occur when the gel time is short and injection rate is relatively slow. However permeation grouting tends to occur irrespective of other variables when the gel time is long and in this condition the grout results in nearly spherical form of consolidated sand which is said to be a desired condition of grouting. For the cases of short gel time grouts, hykraulic fracturing tended to occur when the injection rate low and in this case irregular form of consolidated sand was obtained. When the overburden pressure is high, it is possible to obtain a spherical shape similar to permeation grouting. However it should be noted that when the overburden pressure is high, the volume of the consolidated soil is decreased about 15% to 20% of the estimated volume.