Lowland Technology International

Horizontal Resistance Characteristics of Batter-Coupled Spiral Piles under Monotonic and Cyclic Loading

Takahiro Kurokawa — 2024-09-17

Spiral piles have high axial resistance and are used as foundations for small structures. On the other hand, spiral piles
have a lower bending rigidity than steel pipe piles of the same diameter, resulting in a problem of lower horizontal resistance.
The authors have focused on a two-pile coupled pile structure with spiral piles, which is also resistant to horizontal forces, and
have conducted research to understand its resistance characteristics. In this study, model tests were mainly
conducted on coupled piles with two spiral piles as batter piles to understand their horizontal resistance characteristics.
Monotonic loading tests on a dense dry sand showed that the use of spiral piles as batter piles provided higher elastic limit
spring rigidity and horizontal yield load than single piles or vertically-coupled piles. Furthermore, the highest elastic limit
spring rigidity was obtained when the angle of inclination of the batter pile was 45°. The durability of the batter piles under the
sand conditions of this study was demonstrated by cyclic loading tests at a load equivalent to the horizontal yield load.

Effect of Water-Cement Ratio and Liquidity Index on the Deep Mixing Method using Cement Slurry: A Case Study of Kaolin Clay Powder

Donzala David SOME — 2024-09-17

The liquidity index is a crucial factor in geotechnical engineering used to assess soil behavior under varying loading conditions. It provides valuable information about a soil's deformability when subjected to loads, which is vital for structural and foundation design. In the domain of soil-cement, especially within the deep mixing method (DMM), various factors influence the strength of cement-stabilized soft soils. These factors include water content, cement content, water-cement ratio (W/C), and soil consistency. Notably, a lower W/C ratio tends to result in higher unconfined compressive strength (). In the case of the Saga lowland, where soft cohesive soil with high compressibility and low strength is prevalent, the standard practice employs a W/C ratio of 1.0 with a cement content of 110 kg/m³ for most projects. However, this research introduces an innovative approach: utilizing a W/C ratio of 1.5 with the same cement content of 110 kg/m³, through laboratory experiments. It investigates the effects of the Liquidity Index (I_L), instead of soil sensitivity, and the water-cement ratio on the unconfined compressive strength of specimens prepared using commercial kaolin clay powder. These specimens are prepared with varying initial water content (), determined based on the liquid limit value (), to achieve different soil states. As a result, there is a slight reduction in strength, but it is more uniformly distributed. This approach is designed to bolster support for the existing infrastructure in the Saga lowland. The significance of this study in the field of DMM lies in advocating for an increased W/C ratio to ensure not only the quality of the mixture but, more importantly, the uniformity of strength within the columns. In this context, the optimal ratio depends on a soil candidate consistency parameter, such as its I_L.

Estimation Method for Disaster Immunity in a Flood Disaster

Ryo Nakano — 2024-09-17

In this study, disaster immunity—which in a broad sense means disaster prevention capability—was evaluated in cities in Saga Prefecture, Japan in regard to flood disasters because most of the prefecture is a lowland and is considered to be a high-risk disaster-prone area. A positive correlation was identified between the ratio of flood control costs and normal annual precipitation, demonstrating a greater degree of disaster immunity in high-rainfall areas compared with low-rainfall areas; therefore, the ratio of flood control costs to expenses for each local government to date was considered to represent the “current” disaster immunity. Literally “immunity” for precipitation was evaluated. In addition, “future” disaster immunity in consideration of the social and natural environmental changes, including the impacts of climate change, was estimated based on the ratio of flood control costs. As a result, cities in Saga Prefecture are considered to have relatively higher current and future disaster immunity compared with cities in other prefectures. In addition, estimations of current and future disaster immunity have become possible for flood disasters, and the evaluation method can easily be improved in consideration of other components and expanded for types of disasters such as landslide disasters.

Consideration of quality control standards through splitting tensile strength evaluation of plate-like improved soil

Mathiro Jose SINDETE — 2024-09-17

The Saga lowlands in Kyushu, Japan, face significant settlement issues in embankments due to the high compressibility, sensitivity, and low permeability of Hasuike and Ariake clays. To address these challenges, a combination of columnar and plate-like ground improvement techniques is used. However, natural disasters, such as earthquakes, have revealed the inadequacies of current quality control methods, leading to structural failures. This study aims to enhance quality control for plate-like improved soil constructed using slurry methods by organizing field data based on design standard tensile strength (σ_tk), field standard tensile strength (σ_tf), and lab standard tensile strength (σ_tl). It also investigates the relationship between unconfined compressive strength (qu) and splitting tensile strength (σt) through laboratory experiments. Hasuike clay was treated with varying binder dosages and a water-cement (W/C) ratio of 1, to evaluate the strength ratio (α) between qu and σt after 28 days of curing. Key findings show that setting σ_tl at 2.0 times σ_tf effectively minimizes the risk of falling below σ_tk, thereby enhancing soil performance. Laboratory results indicate that the strength ratio α for Hasuike clay varies with cement content, showing mean values between 0.12 and 0.15, with optimal combinations yielding values from 0.21 to 0.28, which is higher than the empirical standard of 0.1. Conversely, less favorable combinations with minimum values resulted in α values between 0.05 and 0.07, which should be carefully considered when designing plate-like improved soil. These results underscore a statistical and systematic approach to quality control in ground improvement projects to ensure the durability and stability of soil structures in challenging environments like the Saga lowlands.