# Recent Case Histories of Carbon-Neutral Activity Using Ground Improvement Technology in Japan
## 2 The Classification and Historical Development of Ground Improvement Techniques  
When any type of infrastructure is constructed and soft soil is encountered, over an area, high levels of ground settlement and problems of stability failure and liquefaction are anticipated. Many types of ground improvement techniques have been developed and applied to many infrastructures as a countermeasure to these problems. Figure 1 shows the historical evolution of major ground improvement methods and the historical transactions in the field of geotechnical subjects in Japan [2]. Historically, a major geotechnical subject was the \"stability problem\" in the 1940s and the 1950s. It is not an exaggeration to say that the stability problem was the only issue that could be dealt with at that time due to insufficient development in geotechnical engineering and construction machinery. Replacement methods were frequently applied for stability problems, where the soft clayy soil stratum was entirely or partially excavated and replaced by sandy material prior to construction of the superstructure. After the development of consolidation theories in the 1940s, \"ground settlement\" became one of the main geotechnical subjects of discussion, together with the stability problem in the 1950s. In order to accelerate the consolidation process and to reduce the residual settlement, several improvement methods, which may be categorized into \"consolidation\", were developed in the 1950s and the 1960s. Among them, the sand drain method was first applied at Nagasaki Port in 1952, which was followed by several applications in the 1950s to the 1960s. In order for ground settlement and deformation control to be applied, several densification methods were developed in the 1950s and the 1960s. In 1956, the first type of sand compaction pile (SCP) machine with a hammering device was developed in Japan for the densification of sandy ground (Figure 2). After various developments in machinery, the SCP method with a vibro-hammer was developed in 1959. Following its successful application to marine clay deposits, the SCP method has been applied not only to sandy ground but also to clay ground in many marine as well as on-land construction projects [3]. After the Niigata Earthquake in 1964, the dynamic behavior and liquefaction of sandy soil became one of the key issues in the field of geotechnical engineering. A lot of research efforts have been carried out on the dynamic properties of soil and countermeasures for liquefaction since then. In the period of rapid economic growth in the 1970s, the introduction of soil admixture stabilization was desirable for a rapid strength gain and high stiffness. In the 1970s, the deep mixing method (DMM), one of the in situ soil admixture techniques, was developed and put into practice (Figure 3). Due to the rapid strength increase of the soil, the DMM has been frequently applied to improve many kinds of foundation in marine and on-land construction [4]. In the 1970s and the 1980s, soil and groundwater contamination became one of the most pressing social problems. Since then, the management of waste landfill and contaminated sites has been a serious concern for those working in the discipline of geotechnical and geo-environmental engineering. This required the development of new ground improvement techniques to construct impermeable barriers for disposal sites and the enhanced beneficial use of dredged soft soil, subsoil and industrial waste, and also of any by-products. Many soil admixture stabilization techniques, such as the liquefied soil method, the light-weight soil method [5] and the pneumatic flow mixing method (ref. [6]) were developed and put into practice in the 1990s and the 2000s.  
Figure 1: Historical evolution of major ground improvement methods and the historical transactions in the field of geotechnical subjects in Japan [2].  
Figure 3: Deep mixing machine in the 1970s.  
Figure 2: Sand compaction pile machine in the 1950s (courtesy of the Fudo Tetra Corporation).