Field study of the influence of various jet grouting parameters on soilcrete unconfined compressive strength and its diameter

Abstract

0. Natures and scopesSoilcrete mass is the result of jet grouting operation, which hasspecial characteristics such as high strength, low deformability andvery low permeability. Specifications of soilcrete columns that areachieved from the jet grouting procedures from the diameter andstrength aspect depend on jet grouting parameters such as groutpressure, lifting speed, number and diameter of nozzles and c/wratio and specifications of local soil. Due to the extensive range ofeffective parameters and dependency of conclusion to local soil, it isdecided to set some trial tests in constant local soil to achieve theoptimized jet grout parameters and c/w ratio. Therefore, this paperpresents new relations between soilcrete uniaxial compressionstrength and its diameter with lifting and rotating speed, c/w ratioand grout pressure. For this purpose, air pressure, air flow, waterpressure, water flow, number and diameter of nozzles and local soilspecifications are held constant, and then the grout pressure values,c/w ratio, lifting speed and rotating speed are changed, respectively,and UCS and diameter of the columns are recorded. According tothe numerical results obtained from experiments: (1) with increasein the grout pressure, UCS (MPa) of soil and diameter of soilcreteincreases logarithmically; (2) with increase in the c/w ratio, UCS(MPa) of soil and the diameter of soilcreteincreases logarithmically;(3) with increase in lifting and rotation speed, UCS (MPa) of soil anddiameter of soilcrete decrease logarithmically.1. IntroductionJet grouting is a very attractive method for various applicationsand has been effective in many instances. One of the mostimportant advantages of jet grouting is that different types of soilscan be used in such a method. Also, the strength and permeabilitycan be improved by means of this technique. This method is asuitable substitution for common injection methods, chemicalinjection, trenching (plastic concrete and grab), piling system,foundation and/or using compressed air with the freezing methodin tunnel building. In this method, the mixture of groutingpenetrates in pore spaces, joints, cracks and voids of rock and soilstructures and optimizes the physical and mechanical character-istics of these structures, thus the penetrateability and deform-ability of layers will become low and on the other hand thestrength of these layers will be increased [1]. The jet groutingmethod is frequently used as a mean for ground improvement,especially in shield tunneling, and also in all sorts of foundationtreatment in recent years [2,3].Generally, the most important parameters that affect jetgrouting designing are soil type, mixture influx between soiland grout, exiting jet energy from nozzle, grout flow rate, rotatingspeed and lifting speed [4]. The parameters that should beassigned in the single fluid system are: grout pressure, numberand dimensions of nozzles, cement/water ratio, rotating speedand lifting speed. In the double fluid system, in addition toparameters that have been mentioned in single fluid system, airpressure and its flow rate should be assigned as well. But in thetriple fluid system, the number and dimension of water and airnozzles should be assigned in addition to the seven parametersthat have been previously mentioned [5].In discussion of the effects of soil material properties on the jetgrouting process, many researchers have described the soil’sbehavior, using the various parameters. Nikbakhtan and Osanloo[1] have shown that by increasing the grout pressure and flow, theUCS (MPa) of soil increases logarithmically. Xanthakos et al. [5]and Covil et al. [4] showed that in soft grounds and also groundswith high cohesion, effective diameter of soilcrete will decreasewith increasing the standard penetration test ‘N’ values. Yoshitakeet al. [3] suggested a nozzle with 4mm diameter to prevent it ofbeing obstructed. Covil et al. [4] and Xanthakos et al. [5] has