Liquefaction was one of the primary causes of severe ground deformation during the 2018 Palu earthquake, particularly in the Petobo area, where large-scale flow liquefaction resulted in extensive ground displacement. Despite extensive field investigations, laboratory-based residual shear strength data for Petobo soil had not been available to explain the exceptional mobility of the flowslide. This study investigated the stress-strain response and post-liquefaction residual strength of Petobo silty sand with variable fines content using monotonic consolidated undrained (CU) triaxial tests. Reconstituted specimens were prepared using the moist tamping method with fines contents of approximately 9% and 26.4% and tested under three levels of initial mean effective stress. The results showed that specimens with higher fines content generated excess pore water pressure more rapidly and exhibited stronger contractive behavior at small strains. At large strains, however, both fines contents mobilized comparable residual strength levels, expressed as normalized residual strength ratios (qres/p’0) ranging from 0.79 to 0.94. These findings indicate that while fines content influenced early-stage contractive behavior and pore-pressure generation, its effect on post-liquefaction residual strength under very loose density conditions was limited. The residual shear resistance was primarily governed by the loose sand fabric and the effective stress level at the stabilized post-peak condition. This study provides the first laboratory-based residual shear strength data for Petobo silty sand, offering essential parameters for back-analysis, numerical modeling, and liquefaction hazard assessment related to flow-type deformation in Palu and similar alluvial environments.

Introduction. Designing for geotechnical stability in tropical zones presents a unique set of challenges due to the climatic, geological, and environmental factors prevalent in these regions. It requires a comprehensive understanding of the local soil conditions, climatic factors, and environmental challenges. Materials and methods. Tropical regions often experience heavy rainfall, leading to increased erosion and soil instability. The erosion can weaken soil structures, leading to slope failures, landslides, and foundation instability. Areas with geologically disturbed areas such as clay shale, colluvium, and deformed rock due to relic active tectonic activity are attributed to unexpected failure during construction. While area with problematic soil such as the soft soil zone exhibits large long-term compression and low bearing capacity challenges.Results. Designing to accommodate the challenges of geologically disturbed areas and problematic soil is crucial to prevent structural damage. Tropical regions also often have high groundwater tables due to frequent rainfall and low evaporation rates. This can pose challenges for geotechnical and structural design as structures may be subjected to buoyancy forces and soil liquefaction during seismic events. Tropical ground requires careful consideration of material properties and behaviour, environmental conditions, and potential hazards. Engineers can solve the difficulties that come with these problematic grounds in tropical areas and guarantee the safety, stability, and sustainability of infrastructure projects by applying suitable geotechnical engineering techniques and mitigating measures.Conclusions. Case studies about problematic tropical soil and solutions.

Recently, construction on shores, flood plains, swamps, and similar areas with soft soil deposits cannot be avoided.Soft soil has low bearing capacity and high compressibility.Peats are soft soil that was formed by the weathering of plants.Consequently, the organic content found in peats was 75% or higher.High organic content causes many uncertainties in the construction of peat.Padang Pariaman Toll Road Project is constructed on top of a soil embankment.The height of the embankment was 3 m to 6 m above the existing ground.Peat and soft soil were found in the area up to 11 m depth.Selected soil improvement was rigid inclusion and high-strength geotextile.Inclusions utilized are concrete mortar columns with a diameter of 420 mm.The spacing between each column was 1.6 m.Load Transfer Platform (LTP) was placed above the columns.High-strength geotextile was inserted inside the LTP.A settlement profiler was installed to monitor the settlement of embankment.Finite Element Models (FEM) were developed with several scenarios of LTP thickness and geotextile tensile strength.This paper presents the results of full-scale monitoring on construction sites compared with finite element analysis.Slope stability of the reinforced embankment complies with the minimum criteria in Indonesia.Total vertical settlement observed on field was only 2% relative to the total thickness of peat and soft soil.Results are confirmed on both finite element model and field monitoring.The addition of high tensile geotextile reinforcement above rigid inclusion columns to support embankment on peat in the Padang Pariaman Toll Road Project has been proven to be feasible and successful.

A bibliometric analysis spanning from 2002 to 2022 examines the landscape of seismic hazard and risk assessment research, critical for disaster preparedness in earthquake-prone regions. The study uncovers a substantial increase in related studies, notably surging around 2006. Leading contributors hail from China, the United States, Italy, and the United Kingdom, underlining the global significance of the subject. Common terms in scholarly articles include “seismic hazard”, “seismic risk”, “earthquake”, “vulnerability”, “GIS” (Geographic Information System), and “liquefaction”. While seismic hazards remain the primary focus, a growing interest in risk assessment, particularly for induced phenomena like landslides and liquefaction, is noted. Researchers predominantly assess vulnerability across various structural elements, reflecting a holistic approach to understanding and mitigating the impact of earthquakes on infrastructure and communities. In summary, the bibliometric analysis provides a comprehensive overview of seismic hazard and risk assessment research, highlighting field growth, key research areas, and an increasing focus on risk assessment in response to natural phenomena. The findings offer valuable insights for both academics and practitioners invested in the field’s future development.

In accomplishing Sustainable Development Goals (SDGs), the construction of roads played a substantial role in achieving economic equity. However, landslides due to problematic soil would hinder its construction process. Thus, it is essential to understand the mechanism of slope movement to reduce landslide problems. A landslide that happened during the construction of the Semarang-Bawen toll road was analyzed in this research. The landslide was known to fail between the interface of the tuff breccia overburden and the problematic clay shale soil. This research proposed the direct shear test to determine the interface shearing behavior. Before the test, the overburden was differentiated as various sand and weathered clay shale ratios. After the overburden soils were compacted, a multistage interface direct shear test was conducted with three different loadings. Water was added to the overburden layer to model the infiltration at the interface by increasing the water content. From the test, results such as the interface cohesion, friction angle, and average stress ratio were obtained. Overall, the interface shear strength decreased as the water content increased. The decreasing value was due to the wetting at the interface. Thus, it would moisten the interface and disrupt the structure of both the top and bottom layers of the sample. In conclusion, the interface direct shear test was able to describe the shear behavior at the clay shale interface. It also indicated that water had a considerable role in triggering interface landslides for two different soil layers.

When operating in tropical climates with clay shale formations, the construction industry faces obstacles. Due to changes in moisture content, tropical clay shale has unique geotechnical characteristics such as high plasticity, limited permeability, and vulnerability to cycles of swelling and shrinking. Furthermore, expanding clay minerals can cause ground movement, which could harm infrastructure. The cohesive structure of the soil makes excavation and earthmoving operations in tropical clay shale even more challenging, making it challenging to create solid slopes and stop erosion. Increased runoff and sedimentation at construction sites may affect project deadlines and environmental sustainability. These problems are made worse by the unpredictable nature of tropical weather, which includes high temperatures and lots of rainfall, calling for the use of adaptable building materials and techniques. The paper will conclude by highlighting several case studies that tropical clay shale presents for civil projects. A comprehensive strategy that includes environmental management and geotechnical engineering is needed to address these issues. To construct suited to tropical clay shale environment, research, and innovation in these fields are essential to understand more about the behaviour of clay shale.

Embankment construction in a very soft clay layer for transportation projects is common in many areas in Indonesia.One of them is the construction of a new double-track connecting Purwekerto and Kroya in Central Java.However, the challenge of this project was the existing track that must continue to operate while the new embankment was constructed.The project requirement was to limit the impact of the new tracks during construction on the stability and settlement of the existing railway embankment.Therefore, deep soil mixing (DSM) ground improvement technique with grid spacing was selected to increase the bearing capacity of the existing soil and reduce the settlement of the embankment.Numerical simulations using a 2D finite element program were performed to evaluate the performance of the deep soil mixing method in terms of factor of safety and settlements.The results showed that the stability of the embankment during static and seismic conditions satisfies the requirements.The settlements caused by the construction of the new embankment were remained within the allowable settlement during the construction and operational conditions.The deep soil mixing has successfully improved the stability of the embankment and limited the deformation of the existing railway track constructed on soft ground conditions; hence the train continued to operate during the construction.

Earth-fill dams are commonly constructed by composing different geomaterials to optimally utilize local natural resources. In Indonesia, random fill materials are frequently used as a major composition in dam construction. The term random fill material originated from its broad range of grain size. Grain size distribution influences shear strength characteristics of geomaterials. There are 2 shear strength equations to model the behavior of fill material, i.e., linear Mohr-Coulomb and non-linear power curve. Two series of large scale in situ direct shear tests were performed at Keureuto Dam, Indonesia. Sieve analysis tests were performed accordingly. The random fill material was composed of cobbles, gravel, and less than 25% of sand. The stress-displacement characteristics of random fill material indicated that plastic deformation occurred at shear strain of 1% to 4%. The shear failure was reached in shear displacements of 60 – 90 mm, equivalent to shear strain of 8% – 12 %. Stress-strain relationships showed a dilative behavior indicating the random fill was in a relatively dense form. The dilatancy tends to decrease as the normal stress increases. The linear Mohr-Coulomb failure criteria and non-linear power curve equation are suggested to characterize the shear strength of the random fill material. To obtain a realistic value of the non-cohesive strength parameter of granular material, the Mohr-Coulomb approach should be intercepted at zero. A relationship between secant friction angles for different normal stresses is presented. This angle tends to decrease at higher normal stresses.

Settlement is a common geotechnical problem occurs in soft soils. The replacement method is the easiest way to improve this problematic soil. This technique is carried out by removing the unwanted part of the soil and replacing it with a more suitable material or soil. This study focuses on using Lightweight Expanded Clay Aggregate (LECA) as a construction material to replace normal sand and aggregate in filling work. LECA is one of the best alternatives that can be used to improve soil properties because it is lightweight, strong and environ-mentally friendly. However, there are no specific guidelines for the LECA replacement in filling work. Therefore, this study was conducted to develop the construction procedures and LECA replacement requirements for geotechnical application in Malaysia. LECA aggregates have been used as a filling material to solve the settlement problem at Masjid At-Taqwa, Teluk Intan, Perak, Malaysia. LECA samples were collected from different location at different compaction levels for inspection of physical properties and quality of compaction examination. The level of compaction effort performed on LECA replacement represents by the number of passes. The relationship in compaction conditions related to LECA replacement is determined by two graphs namely LECA Compaction Effort and Targeted Compaction Level. The compaction quality of LECA aggregate filling work can be checked using Lightweight Deflectometer (LWD). The maximum desired density can be determined in advance. With reference to the LECA Compaction Effort plot established in this study, the number of passes that need to be performed during the placement work can be planned according to the desired compact density. Whereas, the compaction level, R% can be predicted based on the Target Compaction Level plot. An LWD test should then be carried out to ensure that the compacted density reaches the required level.

A large-scale in situ direct shear test was developed to evaluate the shear strength behavior of random fill material for dam construction in Indonesia. A 70 × 70 × 30 cm large square soil inside a shear box was fabricated in situ. The testing mechanism followed a stress-controlled procedure. The term of random fill material is commonly used for dam construction to the major composition of earth-fill dams in Indonesia. The shear strength characteristic of random fill material may vary depending on the actual particle size distribution. In this paper, in situ shear strength testing on random fill was conducted in Keureuto Dam, Indonesia. The random fill material was majorly composed of coarse material: gravel and sand. A total of 4 samples were tested in situ with a variety of vertical stresses. The testing results showed that plastic deformation started to occur between shear strain of 1–2

A series of tests on horizontally loaded short pile in sand, with varying lengths and diameters has been performed. The purpose of the work is to determine an analytical description of reducing the scale effect, which can then be used for the transposition of the model test results to prototype. Coefficient of dimensional factor is introduced to eliminate the two-dimensional effect on pile analysis. It was found out that the coefficient of dimensional factor has a minimal effect towards the stress level. It was then used to reduce the scale effect in predicting the prototype behaviour. The prediction of moment carrying capacity between model and prototype using this coefficient, gives differences between model and prototype moment values ranging between 8% and 16% depending on soil density and embedment length.

Yogyakarta Province is located close to two active seismic sources, Opak Fault which crosses the province area and the South Java subduction source which is located at the south of Java island. The province is located at the southern part of Java island. Based on the Indonesian earthquake database, from 1984 to 2015 at least seven earthquakes struck this province. The 2006 earthquake with 6.2 Mw magnitude was the largest earthquake to hit this area, causing approximately 88,249 buildings to be totally destroyed and 98,343 buildings to collapse. Most of the destroyed and collapsed buildings were constructed based on the old version of the seismic design code. Improvements in earthquake research have already been conducted in this area and the latest research was conducted at 2016. According to the New Indonesian seismic code 2019, improvements in seismic acceleration for building design need to be adjusted in this area. This paper described the seismic microzonation of Yogyakarta Province based on the New Indonesian seismic maps and 2019 seismic code in terms of the Risk-targeted Maximum Considered Earthquake. The analysis was performed by conducting a combination of three seismic hazard analysis, namely probabilistic, deterministic and Risk-targeted Ground Motion. Based on the Risk-targeted Maximum Considered Earthquake data calculated and its distribution in this area, an area with a maximum 10 km radius from the Opak Fault trace was detected as the largest acceleration area. This area can be used as an indicator of a dangerous area of the province when subject to earthquake ground motion.

Calculation of surface spectral acceleration (SA) is one of the important steps in seismic design.The SA value can be obtained from bedrock spectral acceleration and multiplied by the site factor.According to ASCE/SEI 07-16, for short-period spectral acceleration (0.2 sec / SS) greater than 1g and long-period (1 sec / S1) greater than 0.2g, Site-Specific Propagation Analysis (SSA) shall be used for site factor calculation.SSA can be performed using three different data, bedrock elevation, dynamic soil profile, and acceleration time histories.The site factor can be calculated by comparing the surface to bedrock spectral acceleration obtained from SSA.This paper describes the development of the site factor at the alluvial area (soft soil area) in Semarang city, Indonesia.The site factor was calculated at 23 boring positions.Microtremor tests were conducted in this area to predict the soil dynamic profile.Five different acceleration time histories having magnitude from 6.5 Mw to 6.8 Mw and epicenter distance less than 10 km were collected for SSA.The average FPGA and Fa values developed at 23 boring positions using SSA in this area were almost equal compared to the same site factor developed using the 2019 Indonesian Seismic Code.However, the average Fv calculated using SSA is lower than the same site factor calculated based on 2019 Code.

This research focuses on soft clay improvement by using Kenaf textile as a natural geotextile reinforcement. A series of small-scale laboratory tests were conducted to study the impact of the geotextile reinforcement depth, d, the vertical spacing between reinforcement, S and the number of reinforcement layers, N on the bearing capacity of the soil model. The test results were verified using the numerical simulation by PLAXIS 2D. In this study, the influence factors included four different d/B ratios of 0.25, 0.5, 0.75 and 1.0; three different S/B ratios of 0.25, 0.5 and 0.75, and a different number of reinforcement layers, N from 1 to 4 were investigated where B is the footing width. The results clearly showed that the bearing capacity of rigid footings was significantly improved with the Kenaf geotextile layers in the kaolin. The measured and predicted bearing capacity results were in good agreement. The optimum d/B ratio and S/B ratio, which resulted in the maximum ultimate bearing capacity of the Kenaf-reinforced model ground were about 0.25 and 0.25, respectively. The optimum N was 3, i.e., the bearing capacity insignificantly improved even with N > 3.

Cases of landslides on clay shale slopes have been an intriguing study in Indonesia. Most of the slopes failed due to the weathering of the clay shale rock. As studies focused on the properties of clay shale, several FEM analyses indicated a unique translational type of failure between the interface of clay shale and its overburden. However, the modeling of the interface in a case study was still limited. This study aims to evaluate a landslide using a thin-soil interface model using FEM software. The model used two conditions, extreme groundwater level conditions. There were several iterations of the shear strength parameters of the interface layer conducted. Results indicated that the thin-soil interface could portray the interface condition at the landslide. Compared to laboratory interface results, the interface would fail at a high degree of saturation due to water infiltration at the surface. Also, granular overburden with high permeability had a higher chance of failure than cohesive overburden. From the results, this study opened the path to incorporating the interface layer in clay shale slope analysis. However, further studies are needed using the thin-soil interface model in other clay shale landslide cases to synthesize its repeatability.

Calculation of site coefficient and design response spectral acceleration are two important steps in the seismic design of buildings. According to Indonesian Seismic Code 2019, two information requirements for site coefficient calculations are the site soil class and Risk-targeted Maximum Considered Earthquake (MCER-SS for short and MCER-S1 for long period) spectral acceleration. Three different hard/SC, medium/SD and soft/SE are typically site soil classes used for building designs. Two different site coefficients (Fa for MCER-SS and Fv for MCER-S1 spectral acceleration) are used for surface and design response spectral acceleration calculations. The Indonesian Seismic Code provides two (Fa and Fv) tables for calculating site coefficients. If the MCER-SS or MCER-S1 values developed for a specific site are not exactly equal to the values in Fa or Fv tables, the site coefficients can then be predicted using straight-line interpolation between the two closest Fa or Fv values within the tables. When the straight-line interpolation is adjusted for Fa or Fv calculation, different results were observed in comparison to the values developed using website-based software (prepared by Ministry of Public Works and Human Settlements). This study evaluates site coefficients and design response spectral acceleration predictions in Semarang City, Indonesia, according to straight-line interpolation method and website software calculations. The study was conducted at 203 soil boring positions in the study area. The site soil classes were predicted using average standard penetration test values (N-SPT) of the topmost 30 m soil deposit layer (N30). Three different site soil classes were observed in the study area. On average, the largest differences between the two analysis (linear interpolation and website) methods in the site coefficient values and design response spectral acceleration calculation were observed for the SD and SE classes. However, for the SC site soil class, the difference was small, with their values approximately similar.

This research aims at investigating and modeling the axial bearing capacity degradation of a bored pile on clay shale due to the bored pile installation processes. Clay shale sample models were prepared to simulate the wetting and drying cycles through weathering process between 0 to 6 hours. All samples were tested in which every 1 hour of the weathering process representing 1 cycle of wetting and drying. The direct shear laboratory tests were performed to obtain the peak and residual shear strength parameters of the interface between the bored pile and clay shale. The peak and residual shear strength parameters were obtained after 6 hours of the weathering process. The residual shear strength parameters were measured by applying with and without stress release. This investigation showed that the shear strength degradation at peak, residual without stress release, and residual with stress release respectively reached 87-62%, 28-20%, and 25-14% after 1 to 6 hours of weathering process. This result is very useful for predicting the bored pile skin friction in clay shale soils.

Clay shale has been a problematic soil due to its weathering characteristic. Weathering is the degradation of shear strength due to exposure to water and air. As the depth of soil increases, the weathering effect would decrease, leading to different weathering grades. On a slope, the different weathering grades would lead to an interface slope failure. Until now, laboratory methods on finding the interface shear strength between the weathering grades seldom been investigated. This research will propose a method and give an evaluation of the results. An interface direct shear test has been conducted until its residual state between an undisturbed clay shale and weathering clay shale. The weathering condition of the bottom clay shale is achieved by soaking and drying the bottom of the sample using a two-days wetting-drying cycle. Results showed scattered values with different behavior for the soaked and unsoaked conditions for increasing weathering days. The soaked condition resulted in an increasing cohesion, increasing average stress ratio, and decreasing friction angle. The unsoaked condition resulted in decreasing cohesion, increasing friction angle, and increasing average stress ratio. Previous research shows that, the residual shear stress should have decreased as the weathering days increases. The cause for the contrary results is due to soil swelling and the absence of a separator when weathering the bottom clay shale. In conclusion, the test conducted is not quite suitable to understand the interface shearing behavior of weathering clay shale. Thus, a modification is suggested for future research according to the identified causes.

The evolution in developed countries has taken a role in global warming and natural disasters such as flash flood, El-Nino, earthquake and groundwater contamination. The underground storage tank leakage problems and spillage of hydrocarbon liquid leading to the contamination of non-aqueous phase liquids (NAPLs) into the groundwater could reduce the quality of groundwater. This chapter is intended to investigate the behaviour and the pattern of NAPL migrations in double-porosity soil under vibration and intact conditions. The experimental model is developed by using kaolin soil type S300 and toluene as NAPLs. The kaolin soil was mixed with 25% of moisture content to produce kaolin granules in the soil column and vibrate under 0.98 Hz of frequency within 60 seconds. As a result, both specimen liquids completely migrated to the bottom of soil column: sample 1 has higher permeability compared to sample 2. This is due to the fracture in double-porosity soil under vibration effect and loosened the soil structure in sample 1 compared to good intact soil sample 2 with stronger and compact soil structure. In conclusion, this study proves that the dangerous hydrocarbon NAPL migration in fractured double-porosity soil has very harmful effect on the environment and groundwater resources.