PREGLED HAZARDA PROUZROČENOGA SLIJEGANJEM POVRŠINE U DELTI PEKALONGAN, SREDIŠNJA JAVA: UVID IZ PODZEMLJA

Land subsidence is a global threat to coastal areas worldwide, including the North Java coastal area. Of many areas experiencing land subsidence in North Java, the rate of land subsidence in Pekalongan has matched the high subsidence rates usually found in big cities. The rate of land subsidence in Pekalongan far exceeds the sea-level rise, resulting in a looming threat of land loss. The devastating impacts of land subsidence are the manifestation of its subsurface movement. Therefore, it is essential to understand the subsurface to elucidate the mechanism of land subsidence. Previous studies on land subsidence in Pekalongan are mainly related to subsidence rate monitoring and have not elaborated on the subsurface condition. This paper reviews the Pekalongan subsurface geology based on available literature to provide insight into the land subsidence problem. The results revealed that the land subsidence occurs in the recent alluvial plain of Pekalongan, consisting of a 30-70 m thick compressible deposit. Possible mechanisms of land subsidence arise from natural compaction, over-exploitation of confined groundwater, and increased built areas. As the seismicity of the study area is low, tectonic influence on land subsidence is considered negligible. It is expected that the offshore, nearshore, and swamp deposits are still naturally compacting. As the surface water supply is minimal, over-exploitation of groundwater resources from the deltaic and Damar Formation aquifers occurs. In the end, future research direction is proposed to reduce the impacts of the subsidence hazard.Slijeganje površine tla prijetnja je svim obalnim područjima, pa tako i obali sjeverne Jave. Niz područja u tome prostoru podložno je takvu slijeganju. Iznos toga spuštanja posebno je izražen u velikim gradovima područja Pekalongan. Taj iznos daleko nadilazi porast morske razine rezultirajući gubitkom kopna. Vrlo velik učinak takvih površinskih spuštanja odražava se također i u dubini. Zato je nužno razumjeti ispodpovršinske pojave kako bi se objasnilo samo spuštanje površine. Prethodna istraživanja tih pojava u Pekalonganu uglavnom su bila usmjerena na praćenje iznosa spuštanja, bez uvida u dubinske odnose. Ovdje je prikazana dubinska geologija istraživanoga područja, pregledom dostupne literature. Rezultati su pokazali kako se spuštanje događa u recentnoj aluvijalnoj ravnici Pekalongana, koja obuhvaća tlo debljine 30 – 70 m. Jedan od mogućih uzroka spuštanja jest prirodno zbijanje, zatim pretjerana eksploatacija podzemnih voda te prevelika izgrađenost. Seizmičnost je prostora mala, stoga je i utjecaj tektonike na taj proces zanemariv. Nadalje, morski, priobalni i močvarni talozi podložni su recentnom, prirodnom zbijanju. Kako je pritok svježe, meteorske vode minimalan, dolazi do pretjerane eksploatacije vodonosnika formacije Damar u delti. Predložena su buduća tematska istraživanja kojima bi se smanjio utjecaj opasnosti proizišlih iz slijeganja

Tropical Volcanic Residual Soil

In West Lampung, Sumatra, Indonesia, tropical volcanic residual soils are formed from weathering of volcanic breccias in hydrothermal alteration areas with a thickness of up to 20 m. This soil has the characteristics of clayey silt, low to high plasticity, brownish-red color, has the potential to swelling, easily eroded, and slide when it is saturated, and contains the minerals kaolinite, halloysite, illite, dickite, nacrite, montmorillonite, despujolsite, hematite, and magnetite. The results showed that this soil can cause corrosion of steel and is widely used by the community as a medium for growing plants and vegetables and as a foundation for infrastructure (for example, houses). The volcanic residual soil of the research area had Low Rare Earth Element (LREE) potential and specific uses. The soil with characteristic low plasticity has Liquid Limit (LL) brine value 50%, was more ideal for the primary forest

PRAĆENJE JEZGRE I ISPITIVANJE STATIČKIM PRODIRANJEM U ANALIZI NOSIVOSTI KVARTERNOGA DEPOZITA I NJEGOVA POVEZANOST S RASPODJELOM FACIJESA NA JUŽNOM BALIJU

Area development deals with optimal land use and the reduction of the risk of geological disasters. The coastal area of South Bali is prone to land settlement hazards. In order to mitigate the risk, it is important to understand the depositional environment of the area related to its bearing capacity and geological hazard risks. The aim of this research is to understand the subsurface depositional environment and quantifying its bearing capacity. Quantitative modeling was carried out to obtain the sediment-bearing capacity of the Pendungan area in Bali, Indonesia. The methods used in this research were the observation of borehole cores, the identification of the cone penetration test (CPTu) curves pattern, the sediment index property test, the soil strength laboratory, and bearing capacity analysis. Based on lithologic association, the CPTu curve pattern, and grain size analysis, there are three facies developing in the study area with different bearing capacity values. Generally, beach ridge sand has a higher bearing capacity (N-SPT value of 8 – 52) for shallow foundation than fluvial clay. Meanwhile, floodplain facies has the lowest bearing capacity (N-SPT value of 2 – 20).U razvoju područja važno je optimalno korištenje zemljišta i smanjenje rizika od geoloških katastrofa. Obalno područje Južnoga Balija podložno je opasnostima. Za smanjenje rizika važno je poznavati okoliš taloženja područja povezano s njegovom nosivošću i geološkim rizikom. Cilj je ovoga istraživanja ispitati podzemno taloženje i kvantificirati njegovu nosivost. Kvantitativno modeliranje provedeno je kako bi se dobio kapacitet taloženja u području Pendungan, Bali, Indonezija. Metode korištene u ovome istraživanju bile su promatranje jezgara bušotina, identifikacija uzorka krivulja ispitivanja statičkim prodiranjem (CPTu), ispitivanje svojstva indeksa sedimenata, ispitivanje čvrstoće tla i analiza nosivosti. Na temelju litološke povezanosti, uzorka krivulje CPTu-a i analize veličine zrna, u području ispitivanja izdvajaju se tri facijesa s različitim vrijednostima nosivosti. Općenito, pijesak na grebenu plaže ima veću nosivost plitkih temelja (N-SPT vrijednost od 8 do 52) od fluvijalne gline, dok poplavni facijes ima najnižu nosivost (N-SPT vrijednost 2 do 20)

Towards sustainable land subsidence mitigation in Semarang and Demak, Central Java: Analysis using DPSIR Framework

The Semarang-Demak plain has experienced intense human intervention over the last 40 years, thereby causing land subsidence. This study aims to assess long-term conditions in the study area using the drivers-pressures- state-impacts-response (DPSIR) framework to mitigate land subsidence. Methods include analysis of land subsidence, socioeconomic, surface, and subsurface data, as well as spatial analysis. Results show that rapid population growth and economic activities are major driving forces, manifesting as pressures exerted from overexploitation of groundwater, increasing building and infrastructure loads, and decreasing non-built areas. Groundwater overexploitation reduced the artesian pressure in the 1980s, forming depression cones of the groundwater level from 5 to 30 m below mean sea level. From 1984 to the present, the constructed areas have increased more than tenfold, with Semarang City possessing the most densely built area. Based on our findings, we propose responses consisting of surface water utilization, spatial building regulation, and rigorous groundwater and land subsidence monitoring. Moreover, we encourage the strengthening of law enforcement and inter-sectoral management to ensure the successful land subsidence mitigation

The review of the geological disaster of Bandung Basin subsurface: perspective from geological approach

The basin area is at risk of geological disaster. The Bandung Basin is a crucial part of the country’s political, economic, and social. The Indonesian Disaster Risk Index show average value of 153.85 in 2015–2020 indicates that this region is extremely susceptible to natural disasters because may disaster event happened in this location. The Bandung Basin Region is a crucial economic and political hub for Indonesia. However, its natural environment and the region’s importance as a national strategic sector are at odds with one another. Geological subsurface conditions and vulnerability content must be understood to provide an overall picture of the situation in this location. The main goal of this research is to summarize how underground conditions affect natural disasters, which is the main factor of this event. Earthquakes, landslides, and liquefaction are only a few geological disasters strongly linked to conditions below ground. Due to the Holocene sedimentary layer, the stability of the basin is threatened. All these things happen naturally: liquefaction, subsidence caused by an intercalated sand layer, and structural failure by settlement. Considering the area’s capacity and population growth, more research related to mitigation and laboratory analysis is needed to decide if this area needs to be turned into a strategic city