# Time-Series Prediction of Long-Term Sustainability of Grounds Improved by Chemical Grouting
###### Abstract  
In the field of geotechnical engineering, the problems of liquefaction and land subsidence are of major concern. In order to mitigate or prevent damage from liquefaction, the chemical injection method is actively used as one of the countermeasures for ground improvement. However, a complete understanding of the long-term sustainability of improved grounds is still unavailable due to a lack of knowledge of the influencing parameters. Thus, the chances of chemical injection accidents cannot be ruled out. In this study, the compressive strength of improved grounds by the granulated blast furnace slag (GBFS), one of the grouting materials used in the chemical injection method, was evaluated and used for a time-series prediction of long-term sustainability. The objective of this study was to evaluate the accuracy and validity of the prediction method by comparing the prediction results with the test results. The study was conducted for three different models, namely, the autoregressive integrated moving average (ARIMA) model, the state-space representation (SSR) model, and the machine learning predictive (MLP) model. The MLP model produced the most reliable results for the prediction of long-term data when the input information was sufficient. However, when the input data were scarce, the SSR model produced more reliable results overall. Meanwhile, the ARIMA model generated the highest degree of errors, although it produced the best results compared to the other models depending on the criteria. It is advised that studies should be continued in order to identify the parameters that can affect the long-term sustainability of improved grounds and to simulate various other models to determine the best model to be used in all situations. However, this study can be used as a reference for the selection of the best prediction model for similar patterned input data, in which remarkable changes are observed only at the beginning and become negligible at the end. s 2023 13 133  
[PERSON] and [PERSON] [10] proposed the installation of sand compaction piles for a better seismic response of the liquefiable sand deposits. [PERSON] et al. [11] studied the simulation of liquefaction itself so that future designs can be more effectively designed. Meanwhile, the chemical injection has also been actively used as a ground improvement method to combat these adverse effects. The method can increase ground stability by reducing ground permeability and increasing ground strength [12,13]. [PERSON] [12] reported that chemical injection is an effective method to prevent ground settlement caused by groundwater drainage. Moreover, this method is environmentally friendly as it produces very little industrial waste for almost all types of soils, with very little construction noise or vibrations. In addition to ground stabilization, the chemical injection method has also been used in support anchoring, strata sealing, reducing and diversifying groundwater flow and water ingress, and creating a load-bearing ring during tunneling operations [12]. Despite all these advantages and its popularity in the civil engineering field, there are unfortunately still many unknowns left to be discovered in relation to this method. For example, to confirm the efficiency of this method for ground improvement, reliance must be placed on post-investigations of the improved soil by uniaxial compressive strength tests, because direct visualization technology is still in its infancy. Moreover, depending on the soil type, compression test samples are prone to disturbances during their extraction, which often results in inaccurate interpretations. A literature review on the subject shows that many studies on the long-term curing of the uniaxial compressive strength of the granulated blast-furnace slag (GBFS) used for soil improvement have used an initial start-up strength for 28 days. [PERSON] et al. [14], [PERSON] et al.