Investigation of injectability of microfine cement and fly ash mixtures in jet grout columns

Jet grout is a soil improvement application that is widely used worldwide and gives successful results. In addition, it remains one of the most reliable methods for geotechnical engineers and practitioners. The jet grout method improves the properties of poor soils such as bearing capasity, permeability and consolidaiton. In general terms, it is based on the principle of lowering the mandrel connected to a drilling machine to the depth to be improved, sending a high pressure cement mortar from the tip of the spindle, turning the sprocket at a certain speed and pulling up. In the thesis study, the injectability of jet injection mixtures with model experiments in laboratory was investigated. Four different types of binders have been prepared which was; ordinary Portland cement (OPC), micro-granular cement (DMFC-800) and F-type fly ash (FA) admixtured of 15% by weight of these two types of cement. Jet grout columns were formed with the injection mortars chosen as 0,8, 1.0, 1.2 and 1.4 for water / cement (w / c) ratio for binders containing normal Portland cement. Jet grout columns were produced for the injection mortars formed with micro-grained cement-containing binders, where the w/c ratio was chosen as 0.8, 1.0, 1.4, 1.8, 2.4 and 3.0. Unconfined compressive strength (UCS) and splitting tensile strength (STS) tests were performed on core samples taken from the columns. The highest UCS values were obtained in the columns with w/c ratio of 0.8 in the jet grout columns formed using four types of binders. The average UCS value of the column, which has a w/c ratio of 0.8, is 18,80 MPa. The STS value of the JG column which formed by using DMFC-800 and the W/C ratio of injection mixture 0.8 was approximately 2.52 MPa. Morphological structures and elemental percentages of the binding materials were determined by SEM and EDS analyzes on the samples taken from JG columns. While the positive effect of the fly ash was not found to be sufficient in the UCS values of low w/c ratios, the effect of the fly ash on the mixtures with high w/c ratio was observed to be more significant.