Sand compaction pile method (referred to as SCP method), one of the liquefaction countermeasure methods, has a long history, and its design, construction, and materials have been improved according to the needs of the times for more than half a century (Obayashi et al., 2015, Harada 2021). Sand and gravel are the most common filling materials used in the SCP method. However, due to the depletion of high-quality materials and environmental considerations, alternative materials such as steel slag, blast furnace slag, RC, and sand mixed with shells have been used. Meanwhile, in recent years, government policies such as the SDGs and the promotion of carbon neutrality have been implemented to curb global warming. In the civil engineering sector, decarbonizations initiatives are also required, and the selection of environmentally friendly materials and construction methods is considered important, and various civil engineering technologies have been developed using biomass materials that incorporate carbon. The authors therefore believe that SCP methods also need to develop new filling materials to meet the needs of the age of decarbonization. In this study, we focused on bamboo, which grows faster than other trees and is becoming a problem in neglected bamboo forests due to its fertility. The objective is to develop a new material for carbon sequestration in the ground by mixing bamboo chips with conventional filling material in the SCP method. The experimental results showed that the mixture of conventional filling material and bamboo chips is strong enough to replace the filling material in the SCP method.

Mechanically stabilized earth walls are often constructed on both sides of road embankments behind bridge abutments (back-to-back walls). In this case, both retaining walls were constructed close to each other. However, in general seismic designs, it is often assumed that the retaining wall exists only on one side of the embankment (hereinafter referred to as a single-sided wall), and the seismic behavior of back-to-back walls is not considered. Therefore, in this study, a series of 1/20 scale shaking table model tests were performed to verify the seismic behavior of back-to-back mechanically stabilized earth walls. The following important findings were obtained. As a conclusion, a good seismic performance was obtained for back-to-back mechanically stabilized earth walls with an aspect ratio which is not extremely large, while further investigation is needed in case of large aspect ratios.

The finite element (FE) software PLAXIS 3D is utilised to conduct a numerical analysis of the impacts of geocell reinforcement on the behaviour of flexible pavements subjected to cyclic loading conditions. The fidelity of the FE model was confirmed by comparing the findings from the numerical analyses to the existing experimental investigation reported in past literature. The impact of the geometrical parameters of the geocell (width, b, and height, h) on the overall performance of the pavement was explored and compared with the findings obtained from the unreinforced section. As primary parameters, the surface deformations, and the pressure at the subbase-subgrade interface were obtained. The study indicates that increasing the height of geocells in the pavement layer results in a substantial reduction in deformation values, with a notable range of 45% to 81%. In contrast, wider geocell widths appear to have the opposite effect, causing deformation values to rise by around 23% to 93%. Also, the study shows that the higher geocell heights resulted in lower pressure transfer to the underlying subgrade by approximately 45% to 81% compared to lower heights of geocell. It was observed from the study that the geocell with higher heights tend to contribute to reduced deformation, pressure distribution and improved pavement stability, while wider geocells might not provide the same level of benefit and could even lead to increased deformation and pressure distribution value. As compared to the unreinforced pavement, the vertical stress at the interface between the subbase and the subgrade was reduced by around 0.30 to 0.58 times for the geocell-reinforced pavement.

Geopier Rammed Aggregate Piers® (RAPs) are a ground improvement technology that creates a densified column of aggregate surrounded by a stiffened matrix soil. This paper describes the design and construction of RAPs at Te Kaha, a $683-million Multi-Use Arena under construction in Christchurch, New Zealand. CLL Projects are constructing 8331 RAPs including 1092 tension RAPs to depths between 5.5 to 12m to provide a ground improvement system supporting the arena.

Design considerations include estimation of soil densification in a wide range of soil conditions (sand, silty sand, silt and gravel), analysis of liquefaction triggering before and after ground improvement, numerical analysis to predict the bearing capacity and settlement of the foundations, and prediction of uplift capacity for tension RAPs. The design predictions and the actual results from verification testing are compared, including pre- and post- improvement CPTs and tension load tests. At Te Kaha the RAP installation resulted in a significant increase in penetration resistance of sandy soils between the RAP elements. The CPT results consistently underestimated the fines content of the soil. The tension load test results showed that the uplift capacity is dependent on the soil conditions at the tip of the tension RAP. If adequate confinement cannot be achieved at the base the tension RAP ‘unravels’ and the capacity is much lower than typical design methods would predict.

Road transportation is the most common and economical mode of transportation because of its easy accessibility. Hence, a stable road network plays a key role in the country’s development. However, we frequently observe a lot of failures in pavement such as cracking, rutting, heaving, and differential settlement of pavement panels. One of the major reasons for the above failures is lack of stability in embankments. Thus, selection of suitable embankment soil is very much essential. Due to increasing cost and demand, there is a lack of suitable soil. The selection of weak and problematic soils leads to a series of problems because of their low shear strength, low permeability, low bearing capacity, high swelling, high compressibility, etc. Further their behavior under dynamic loading conditions such as traffic, earthquake, and dynamic liquefaction is questionable. Expansive soil is a widely available problematic soil all over the earth. Hence stabilization of embankments is required with the usage of expansive soil. Currently, expansive soil is stabilized with cement, lime, fly ash, enzymes, slag, geosynthetics, polymers, industrial waste, etc. In this review, existing stabilization methods on expansive soil are described and the need for further research is discussed.