The influence of delta formation mechanism on geotechnical property sequence of the late Pleistocene–Holocene sediments in the Mekong River Delta

Abstract

The aim of the study was to characterize a variety of microstructure development-levels and geotechnical property sequences of the late Pleistocene–Holocene deposits in the Mekong River delta (MRD), and the paper furthermore discusses the influences of delta formation mechanisms on them. The survey associated the geotechnical engineering and the sedimentary geology of the late Pleistocene–Holocene deposits at five sites and also undifferentiated Pleistocene sediments. A cross-section which was rebuilt in the delta progradation-direction and between the Mekong and Bassac rivers represents the stratigraphy. Each sedimentary unit was formed under a different delta formation mechanism and revealed a typical geotechnical property sequence. The mechanical behaviors of the sediment succession in the tide-dominated delta with significant fluvial-activity and material source tend to be more cohesionless soils and strengths than those in the tide- and wave-dominated delta and even the coast. The particular tendency of the mechanical behavior of the deposit succession can be reasonably estimated from the delta formation mechanism. The characteristics of the clay minerals from the Mekong River produced the argillaceous soil which does not have extremely high plasticity. The microstructure development-levels are low to very high indicating how to choose hydraulic conductivity value, k, for estimating overconsolidation ratio, OCR, by the piezocone penetration tests (CPTU). The OCR of sediments in the delta types strangely change with depth but none less than 1. The post-depositional processes significantly influenced the microstructure development, particularly the dehydrating and oxidizing processes.

Impacts of 25 years of groundwater extraction on subsidence in the Mekong delta, Vietnam

“…The model parameterized with an OCR of 1.63 provides the best match with the average InSAR-measured subsidence and was consequently used to calculate the reported results. This OCR value approaches the reported average OCR value of 1.6 reported for the MKD ( Hoang et al 2016 ) and HCMC ( Thoang and Giao 2015 ). The amount of the total InSAR-measured subsidence reproduced by the model, resulting from a cell-by-cell comparison, was ∼75% of the total measured subsidence for the best estimate model (respectively ∼50% and ∼95% for the most and least conservative model) (online supplementary S7 ).…”

“…Deformation behaviour is strongly determined by the overconsolidation ratio, but only limited data is available to constrain the OCRs for the MKD. Hoang et al ( 2016 ) determined OCRs ranging between 1.0 and 2.7 (average ∼1.6) for clayey deposits using cone penetration, incremental loading oedometer and constant rate of strain consolidation tests from five boreholes in the MKD. Thoang and Giao ( 2015 ) reported an OCR value of 1.6 for medium to stiff clays in HCMC province.…”

“…Based on these values, we established an initial OCR range of 1.2–2. As there is no known trend or consistency on how OCR changes with depth in the MKD ( Hoang et al 2016 ), a single OCR value was assigned to all model layers. A sensitivity analysis of modelled subsidence to OCR was used to further constrain the range of possible OCR values.…”

Peat layer accumulation and post‐burial deformation during the mid‐late Holocene in the Po coastal plain (Northern Italy)

“…Prominent successions of peat layers have been reported from several delta plains worldwide, including the Mississippi (Törnqvist et al, ), Rhine‐Meuse (van Asselen et al, ), Po (Amorosi, Bruno, Campo et al, ), Ebro (Somoza et al, ) and Mekong (Hoang, Lap, Oanh, & Takemura, ) deltas, among many others. Peat layers started to accumulate during the early Holocene, when the Late Pleistocene alluvial plains were progressively flooded in response to the post‐glacial sea‐level rise (Cohen, Gouw, & Holten, ; Törnqvist et al, ).…”

The Scientific and Practical Foundations for Sustainable Development and Climate Change Response in Mekong Delta, Vietnam

“…The high elevation delta plain is strongly influenced by river development, which is developed in swamps and inundated floodplains with elevation of 0.5m -1.5m and delim-ited by Late Pleistocene formation with elevations of 3m -5m in the Cambodian border. The high elevation delta plain extends through An Giang, Dong Thap, Can Tho, Hau Giang, Vinh Long, Long An, Tien Giang and Kien Giang provinces (Hoang et al, 2016). The low delta plain is strongly influenced by the wave and tidal regime and charaterizes by sand dune systems with the elevation of 3m -10m in height, which distribute parallelly to the shoreline in the direction of North East -South West, between the sand dunes is the lowlands with the elevation of 1.5m -2.5m in height (Oanh and Lap, 2008).…”