Accurate prediction of wall displacements induced by deep excavations is essential to guarantee stability and safety of the excavation as well as to prevent any harm and damage to the adjacent structures. This paper proposes and validates a set of equations for determining soil parameters of hardening soil model with small-strain stiffness (HS-small model) for medium dense sand in Ho Chi Minh City (HCMC), Vietnam. The study was based on back-analysis of diaphragm walls’ displacements from three well-documented excavation cases and data from twenty boreholes. Good agreements between finite element analysis (FEA) results and field observations were obtained by assuming the E50 stiffness value to 2500N (kPa) (N is the SPT value), the small-strain shear modulus, G0, to 7000ρN0.7 (kPa) and the shear strain at which the shear modulus is reduced to 70% of small-strain modulus, γ0.7, to 0.0002. The comparisons with field measurements indicated that HS-small model can better predict the diaphragm walls’ displacements than hardening soil model (HS model). Additionally, the field displacements of diaphragm walls in medium dense sand are in the range of 0.1–0.3%H (H is excavation depth).

Verification of soil parameters of hardening soil model with small-strain stiffness for deep excavations in medium dense sand in Ho Chi Minh City, Vietnam

Analysis of Shaft-Grouted Piles Using Load-Transfer Method

The paper focus on analyzing the influence of diaphragm wall on the bending moment and settlement of pile raft foundation. A case study in Ho Chi Minh City using pileraft foundation was used for studying process. The Finite element method (FEM) with the Hardening Soil model (HS) were employed to describe the behavior of soils. Behavior of pile-raft foundation was investigated by considering the available of diaphragm wall and the connection between diaphragm wall and raft. The results showed that the settlements of pile-raft foundation were decreased 12-20% and the moments of the raft were increased 17-20% when considering the influence of diaphragm wall. The connection between diaphragm wall and raft did not effect on the settlement and moment in middle area of pile-raft foundation.

Study on the Influence of Diaphragm Wall on the Behavior of Pile Raft Foundation

The concept of using Reinforced Earth (RE) walls for rail corridors is gaining popularity. As of now, very few nations have successfully adopted the RE walls for Railway infrastructure. These structures require good quality granular materials like sand for backfilling. However, due to the scarcity of good quality natural sand, research efforts are being made to look for cost effective alternatives to sand in backfill applications. The present study examines the possibilities of using the two sustainable materials, namely steel slag and construction and demolition waste (CDW), as backfills in RE walls subjected to harmonic train-induced load. In total, 63 separate full-scale numerical models of RE walls have been analyzed to understand the wall behavior with sustainable backfills subjected to different train speeds. The backfill materials were simulated with three different material models, namely, linear elastic, Mohr-Coulomb and Hardening Soil, for comparison. The results showed that the RE wall behavior is highly frequency-dependent. RE walls with steel slag and CDW backfills have shown 25% and 12% lesser deformations, respectively as compared to the sand backfill. Furthermore, reinforcement tensile forces in walls with sustainable backfills were found to be comparable to those of sand. The maximum deformation of the wall was observed when the fill materials were simulated with the Hardening Soil model. In overall, satisfactory performance of the RE wall was observed in the presence of sustainable backfill materials under Railway loading.

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Performance evaluation of reinforced earth walls with sustainable backfills subjected to railway loading

A combination between Diaphragm wall (D-wall) and Secant piles wall (SP-wall) in upgrading the depth of basement of a high-rise building project in Ho Chi Minh city was presented. In that, the SP-wall was installed next to the available D-wall designed for original depths of basements. FEM analysis by Plaxis 2D model was applied to perform the behavior of the combination. The results of the analysis including settlement of surface ground, horizontal wall displacement of D-wall and SP-wall were compared to field observation. The results of the comparison showed that the predicted results were got a good agreement with those values from observation and was on the safety side with little larger than those values from the observation.

Performance Analysis of a Combination Between D-Wall and Secant Pile Wall in Upgrading the Depth of Basement by Plaxis 2D: A Case Study in Ho Chi Minh City

The paper presented about an application of load transfer method in performance analysis of axially loaded pile in Ho Chi Minh City. The relationship between mobilized load and settlement at pile shaft and pile tip was described by exponential model. The simple iterative algorithm was applied to determine the behaviour of the pile. The analysis results were verified with a full scale static load test. A good agreement between predictions and measurements of load-settlement relationship at pile head and load distribution along depth was recorded. The settlements of pile were 10.3 and 13.4 mm for measurement and prediction at design load, respectively.

Performance Analysis of Axially Loaded Piles by Load Transfer Method: A Case Study in Ho Chi Minh City

It is noted that the settlement estimation using the D-box method (soil bag system) with a high thickness of the filling layer would have a high potential of risk, especially in the time-dependent calculation. Based on the requirements of solutions for the settlement problem of the ground-treated system in the Asia-Vietnam fertilizer factory (AVF factory), this research focuses on the settlement behavior of soil after 1year of operation with a lot of cracks and gaps in the current slab. This study used a new soil investigation with advanced laboratory tests and in situ plate load tests. In calculation, four cases of the strategy were investigated to predict the real behavior and the time-dependent settlement. The results show that the consolidation settlements of the D-box method were 112.62 cm, 205.28 cm, 219.57 cm, and 287.12 cm for case 1, case 2, case 3, and case 4, respectively. The settlement of the second year increased about 2% in comparison with the one of the first year, and this process performed that case 1 was suitable for the observed settlement behavior of D-box ground-treated system.

Thanh Hai Do

Papers

Performance Analysis of a Combination Between D-Wall and Secant Pile Wall in Upgrading the Depth of Basement by Plaxis 2D: A Case Study in Ho Chi Minh City

Performance Analysis of Axially Loaded Piles by Load Transfer Method: A Case Study in Ho Chi Minh City

A Study on Settlement Behavior Using D-Box Method: a Case Study in Vietnam