Settlement Of Soft Soil Research Articles

Probability analysis of vertical drainage improvement for soft soil settlement prediction using a Bayesian back analysis framework and the simplified Hypothesis B method

Probability analysis of vertical drainage improvement for soft soil settlement prediction using a Bayesian back analysis framework and the simplified Hypothesis B method

Consolidation analysis for soft soil with non‐Darcian flow considering variable discharge capacity of prefabricated vertical drain

AbstractGround improvement is a complex issue, and accurately predicting the consolidation and settlement of soft soil with prefabricated vertical drain (PVD) presents a significant challenge. Recent laboratory and field tests have highlighted the influence of the variable discharge capacity of PVD and the non‐Darcian flow behavior of soft soil on consolidation. However, existing theories have not yet considered these two factors simultaneously. To address this gap, a numerical solution for consolidation analysis incorporating non‐Darcian flow and variable discharge capacity of PVD was developed and applied in a test area. The results of this study demonstrate the significant impact of both non‐Darcian flow and variable discharge capacity on the consolidation rate. A comprehensive comparison between the findings of this numerical solution, the degenerate solution, and monitored data reveals clear differences. Notably, the non‐Darcian exponent (s) and discharge capacity parameters (A3) were found to exert a greater influence on consolidation behavior compared to other factors. These findings provide valuable guidance for the design and implementation of following airport ground improvement strategies.

Numerical Analysis of a Dual-Layer Geosynthetic-Encased Stone Column Installed in Soft Soil

Stone columns are being used to reduce soft soil settlement and increase load-carrying capacity. Since there is inadequate lateral support from the local native soil, soft soil undergoes excessive settlement under vertical loading. This issue is effectively resolved by suitably encasing stone column material by geosynthetic with significant axial stiffness, which provides the required additional confinement reported in the literature. In the current study, an effort has been made to examine the load settlement behaviour of the dual-layered geosynthetic-encased stone column (DL-GESC) under vertical loading. In order to simulate the behaviour of stone column-reinforced soft soil, a FEM analysis was performed using PLAXIS-3D and three-dimensional (3D) models made utilising the unit cell idealisation technique for a single column. The stone column diameter, spacing to diameter (s/d) ratio, and encasement layers were varied to determine their influence on load-settling behaviour. The vertical load-carrying capacity of the ground was significantly improved when an additional layer of geosynthetic encasement was inserted into the stone column as compared to SL-GESC. Improvement of 15–25% was observed for the analysis of a single column installed in soft clay, according to the result obtained. Improvement ratios have been discussed in detail for various encasement conditions.

Avoid construction failure by controlling settlement with a geosynthetic enchased geofoam granular column

Soils with low bearing capacity (soft soils) can cause the collapse of overlying structures. Before the superstructure is built, the soft soil needs to be improved first. Effective methods to improve soft soils include applying vertical drain techniques or using geofoam materials. With vertical drains, such as PVD or sand drains, the soft soil settlement can be controlled, while geofoam can be used as a top layer material on soft soil. The purpose of this research is to investigate the performance of Sand Geofoam Granule Columns (SGGCs) as a vertical drain. These SGGCs consist of sand-geofoam as the core and geotextile as the wrapper and filter. Variation in diameter and spacing of SGGCs is investigated in large-scale model consolidation equipment in laboratories. The result of the study is that the optimal performance of SGGC is at a diameter of 4.85 cm with 3D spacing. Soft soil improvement with SGGC as a vertical drain can accelerate consolidation time and improve soil bearing capacity.

Study on Microstructure and Silting Characteristics of Soft Soil: A Case Study of Nansha District, Guangzhou

With the development of society and economy, land subsidence in soft soil areas has become a prominent geological disaster in our country’s coastal area. Land subsidence has the characteristics of irreversibility, wide influence range, long aging, etc., and these characteristics are closely related to the characteristics of soft soil, such as physical and mechanical parameters, microstructure characteristics, etc. The Nansha District of Guangzhou was taken as the study area in this paper. Through the collection of preliminary data, two-dimensional scanning electron microscopy, and three-dimensional Computed Tomography (CT), the micro-structure characteristics of soft soil are expounded and its plugging characteristics are further analyzed. The results show that the study area’s soft soil has a honeycomb, granular, and flocculent structure. From the perspective of pore scale distribution, the number of macropores and ultramicro pores is small, and the continuity is poor. In most small and medium pores, namely the aggregate and granular pores. The siltation of soft soil is closely related to the microstructure of soil and can be treated according to the effect of siltation characteristics on the consolidation settlement of soft soil. The research results of this paper can provide targeted prevention and control suggestions for the soft land subsidence disaster in the Nansha area, and also provide a reference for other similar research.

Lightweight geo-bead fill to prevent soft ground deposit failure

As a foundation for transportation infrastructure, soft ground has limited bearing capacity and high compression. To prevent embankment failure, lightweight material is suggested. In the construction of road embankments, EPS can be regarded as an environmentally sustainable lightweight fill material. The study's goal is to create a formula for GB (Geo-bead) concrete mixing as a lightweight fill ingredient. Several tests are performed on the material specimens, including bulk density, interface shear strength, unconfined compression, and a SEM of the composite material. The tests were designed to determine the physical and mechanical qualities using GB percentages (20%, 30%, and 40%). Composite material has a lower density than compacted sand. The friction angle falls between the adhesion of GB-GB and GB-cemented sand. A ductile failure pattern develops because the bond between cement paste and GB is less than that between cement sand. The composite material's CBR passed embankment specifications. In the case of an embankment on soft soil, the 2D FEM analysis expressed settlement by compacted sand and lightweight fill material. Lightweight geo bead backfill decreases soft soil settlement, preventing failure.

Improvement of consolidation properties of clay soil using fine-grained construction and demolition waste

As urbanization spreads rapidly, more structures are being built, and more construction and demolition waste (CDW) is produced, occupying about 36–40% of the total solid waste generation in the world; hence, CDW has become a burden nowadays. Moreover, the construction of low-rise buildings on weak soil is always challenging and costly due to the soil's high compressibility and low bearing capacity. Sand or other granular materials are commonly used to improve the compressibility behavior and associated settlement, drainage, and shear strength of weak soil. The massive use of natural sand for construction purposes of different civil engineering structures have lessened their reserves in recent times, increasing their price and destroying the balance in the environment. Among the several methods of improving soil, this research uses fine-grained CDW to improve the geotechnical behavior of weak soil under study. The main objective of this research is to observe the changes in soil properties after mixing with CDW. Recycled waste mortar powder has been selected as CDW mixed in different percentages in the soil. In addition, CDW powder was inserted into soil mass as a circular powder column in triangular and square grid patterns as an alternative to the sand column. CDW in the soil samples improved consolidation settlement, and reduced settlement time and compression index. Increments in the pre-consolidation pressure, consolidation rate, and permeability of the clay-CDW mixtures were also remarkable. Soil improvement through reusing CDW is a sustainable way to solve problems in solid waste management and the soft soil settlement issue under a shallow foundation, ultimately reducing the environmental footprints, saving natural resources, and supporting the circular economy concept.

Evaluation of Asaoka and Hyperbolic Methods for Settlement Prediction of Vacuum Preloading Combined with Prefabricated Vertical Drains in Soft Ground Treatment

This study evaluated the use of the Asaoka and hyperbolic methods to estimate the ultimate settlement of soft ground treated by vacuum preloading combined with prefabricated vertical drains. For this aim, a large-scale physical laboratory model was constructed. The model was a reinforced-tempered glass box containing a soil mass with dimensions of 2.0 × 1.0 × 1.2 m (length × width × depth). Physical models of this scale for the same purpose are rare in the literature. The soil was taken from a typical coastal region in Dinh Vu Hai Phong, Vietnam. The surface settlement near and between the two drains was measured right after the vacuum preloading started. Important properties of the soil were tested to evaluate the effectiveness of the treatment method. The measured settlement was used in the Asaoka and hyperbolic methods to predict the potential ultimate settlement. The results showed the superiority of the vacuum consolidation approach in improving fundamental engineering properties of soft soil. Furthermore, the ultimate settlement predicted by both methods showed a good agreement with the measured value, proving that the Asaoka and hyperbolic methods are suitable for the estimation of the ultimate settlement of soft soil treated with vacuum consolidation.

Observations from Ground Improvement Using Vacuum Consolidation Method

In the modern world of Civil Engineering, challenges arise during the various phases of construction, starting from the project development phase to the completion of the project. One of the main factors to be considered before commencing any infrastructure project is the foundation of where it is to be built. Without a strong foundation, it's not possible to proceed further to subsequent stages and in some cases, significant improvements may be required before starting the construction process. Although there are several different available methods for soil improvement in Civil Engineering, preloading using vacuum pressure with prefabricated vertical drains (Vacuum Consolidation Method) is one of the commonly applied techniques. Nowadays, it is widely used in countries having soft soil settlement problems. This paper presents the observations made from a soil improvement project using VCM including the site conditions and methodologies adopted during the process. The field data related to parameters such as pore pressure, settlement and shear strength improvement in natural soft clay have been presented and discussed. The degree of consolidation in the field has been back-calculated from settlement data and compared with values obtained from the 1-D consolidation equation. Field investigation tests, such as borehole tests and field vane shear tests, were performed before and after the soil improvement and it was found that the soft soil properties can be enhanced using vacuum consolidation without the use of any surcharge loading as well.

Micropore Structure and Fractal Characteristics of Clays Due to Freeze-Thaw and Compression Based on Mercury Intrusion Porosimetry

The artificial ground freezing method has been widely used in shield end reinforcement and connecting channel reinforcement of urban subway tunnel in water-rich soft soil. Accurate quantification of micropore change and redistribution due to freeze-thaw is important to understand frost heave and thaw settlement of soft soils including mucky clay and silty clay. This paper presents Mercury Intrusion Porosimetry (MIP) data for mucky clay and silty clay specimens before and after freeze-thaw and compression. MIP tests were conducted on the soil samples of undisturbed soil, frozen-thawed soil, compressed soil and compressed frozen-thawed soil. The pores of clays were divided into five groups according to the diameter, including 1) macro pore, 2) medium pore, 3) small pore, 4) micro pore, 5) ultramicro pore. Micro pores and ultramicro pores account for more than 80% of clays’ total pore volume and pore surface area. The pore distribution characteristics of mucky clay and silty clay were studied, and the pore volume and pore surface area distributions’ capacity dimension was estimated. The particle contact, pore changes of clays due to freeze-thaw and compression were analyzed quantitatively. Total pore volume and pore surface area of clays increased due to freeze-thaw, and decreased due to compression correspondingly. The distribution of clays’ pore volume and pore surface area have statistical self similarity, and it is effective to quantify the microstructure changes of clays due to freeze-thaw and compression by estimating capacity dimension, which can provide a new way to reveal the internal micro-pore change of clays due to freeze-thaw and compression quantitatively.

Random Field Reliability Analysis for Time-Dependent Behaviour of Soft Soils Considering Spatial Variability of Elastic Visco-Plastic Parameters

• K-L expansion method was adopted to generate random field with different spatial correlation lengths • A critical spatial correlation length existed for predicting time-dependent settlement of soft soils • A single random variable analysis is not always the most conservative analysis in predicting settlement of soft soils • It is essential to perform random field analysis to reduce the risk of the design to be applied in construction. Low embankment strategy is one of the effective methods to control time-dependent settlement of soft soils in infrastructure construction projects. Spatial variability of soil characteristics is a crucial factor, affecting the reliability of predictions of the long-term settlement in soft soils. In this paper, the time-dependent behaviour of soft soils is analysed incorporating spatial variability of elastic visco-plastic model parameters. Standard Gaussian random fields for correlated elastic-plastic model parameter ( λ / V ) and the initial creep coefficient ( ψ 0 / V ) are generated adopting Karhunen-Loeve expansion method based on the spectral decomposition of correlation function into eigenvalues and eigenfunctions. Then the generated random fields are incorporated in the proposed non-linear elastic visco-plastic (EVP) creep model. The impacts of spatially variable elastic visco-plastic model parameters (i.e. ψ 0 / V and λ / V ) on long-term settlement predictions are evaluated through random field analysis (RF) with different spatial correlation lengths, and results are then compared to a single random variable (SRV) analysis. The probability of failure (PF) is calculated adopting RF and SRV analysis to determine the critical spatial correlation length, resulted in a maximum probability of failure. This study can be employed by design engineers to determine the critical spatial correlation length for safe design in the absence of adequate data to determine the exact spatial correlation length. The results also confirm that SRV analysis is not always the most conservative analysis in predicting time-dependent settlement of soft soils; and it is essential to perform RF analysis considering the spatial correlation length to reduce the risk and increase the reliability of the design to be applied in construction.

Research on HC-LSSVM Model for Soft Soil Settlement Prediction Based on Homotopy Continuation Method

Prediction of soft soil settlement is an important research topic in the field of civil engineering, and the least square support vector machine is one of the commonly used prediction methods at present. Nonetheless, the existing LSSVM models have problems of low search efficiency in the search process and lack of global optimal solution in the search results. In order to solve this problem, based on the leave-one-out cross-validation method, the homotopy continuation method was used to optimize the LSSVM model parameters, and then the HC-LSSVM model was constructed with the goal of minimizing the sum of squares of the prediction error of the full sample retention one. Finally, the rationality and correctness of the model are verified by engineering application. The results show that the HC-LSSVM model constructed in this study can accurately predict the settlement of soft ground, which is superior to the common LSSVM model and solves the problem that the parameters of LSSVM model cannot be solved optimally. The research results provide a new method for prediction of soft soil settlement.

EXPERIMENTAL STUDY ON GROUND IMPROVEMENT WITH STONE COLUMNS

Ground improvement is an important requirement in today’s construction industry as land reclamation is becoming increasingly popular. Stone column method is one of the efficient and economical method and it is one of the soil stabilizing method that is used to increase the bearing capacity and decrease the settlement of soft soils. In this research paper the bearing capacity, settlement of stone columns and encased stone columns were analysed using a scaled model. Gunny bags are used as geo textile for stone column encasement. The results shown significant improvement in bearing capacity of soil using stone column, the efficiency of stone column is increased when encased with geotextile.

A new simplified method for calculating short-term and long-term consolidation settlements of multi-layered soils considering creep limit

The long-term consolidation settlement of soft soils under infrastructures is seriously concerned in coastal areas. In practice, soft soil ground is usually composed of multiple layers with different properties, and the effect of soil creep is nonnegligible. However, in conventional consolidation analysis, creep is seldom included during the “primary” consolidation. With conventional creep model, creep strain will reach infinity with time, which is unreasonable in the long-term view. In this study, a new simplified method based on Hypothesis B is presented to calculate both short-term and long-term consolidation settlements of multi-layered soils exhibiting non-linear creep. There are three main characteristics for this new simplified method: (a) the consolidation analysis for multi-layered soil is conducted using spectral method; (b) a nonlinear creep function with creep limit is incorporated to calculate both short-term and long-term creep settlements; (c) the “primary” consolidation and creep are calculated independently and combined with an empirical parameter α together with the consolidation degree U for correcting the creep settlement. Finite element analysis with a self-developed Elastic Visco-Plastic (EVP) constitutive model considering creep limit was also carried out. Verifications by field cases and finite element simulation demonstrate the efficiency and accuracy of the new simplified method in calculating the long-term settlements of soft soil ground under varied engineering conditions. Influences of major parameters selection in the calculation of the new simplified method are also discussed.

Study on the disturbance and recompression settlement of soft soil induced by foundation pit excavation

Study on the disturbance and recompression settlement of soft soil induced by foundation pit excavation

Diffused arching in embankments supported by non-compliant columns with capping beams

A column-supporting system for embankments on soft soils is analyzed using the Finite Element Method. The numerical problem has boundary conditions similar to that of a trap-door, but, contrary to the classical trap-door studies, the focus in this paper is on the load transfer to the supporting columns measured by the system efficacy, and on the critical embankment height that prevents differential settlements on the embankment surface. The stress state simulated in the embankment rapidly evolves in the first stages of the soft soil settlement, measured by millimeters, but the changes to the elastic–plastic stress field developed are marginal in the subsequent stages of settlement simulated up to 10 cm. The displacement field in low embankments with a height comparable to the column spacing is dominated by the failure mechanism with shear bands reaching the embankment crown, causing differential settlements on the embankment surface. In higher embankments, the failure mechanism is confined to the lower portion of the fill, and no differential settlements were detected on the embankment surface. It was suggested that a hypothetical diffused soil arch formed above the failure mechanism, with a shape approximately following the principal stress trajectories. This conjecture was made based on the presence of elevated stress along the symmetry plane of the embankment-column periodic cell. Numbers related to system efficacy and critical height are reported for a limited set of model parameters, but the qualitative outcome of the study is likely applicable to a wider variety of embankments.

Settlement of soft soil treated with group of floating bottom ash columns

Settlement of soft soil treated with group of floating bottom ash columns

Experimental Study on Bearing Capacity of Alkaline Activated Granular Asphalt Concrete Columns on Soft Soils

In civil engineering, alternative materials showed rapid progress. Asphalt derived from Buton Island in Indonesia, also known as Asbuton, was located in the limestone bedrock. A large deposit of Asbuton could guarantee the supply of alternative construction materials. In that regard, Asbuton performance as an alternative material to several subjects needs to be analyzed. Therefore, this study was conducted to analyze Asbuton’s behavior as a filler in a floating column model as a soft soil improvement concept. Asbuton added to sand and gravel mixture as filler and waterglass as a binder. CBR samples were tested to acquire the optimum composition with varied curing days namely 0, 3, and 7 days, following ASTM D-1883, followed by a compressive column model test which was based on ASTM D-2166. Finally, the column applied to the soft soil layer to be tested in a loading test, and the results are then compared for each composition. The results showed that the granular material's composition including Asbuton, the waterglass content, and the curing period significantly affect the engineering properties of the artificial column. The results revealed that the granular column with Asbuton with the addition of waterglass could increase soil’s load capacity and reduce the settlement of soft soils. Doi: 10.28991/cej-2020-03091623 Full Text: PDF

Effect of GGC (Geoform Granule Column) on Acceleration of Settlement in Soft Soil

Soft soils has low bearing capacity and high compressibility which is potentially damage the structure laid above it. An effort is taken to use EPS beads to form GGC will accelerate of consolidation process. The purpose of study to investigate the influence of density and diameters of GGC against strength and settlement. Triaxial test are conducted to identify the shear strength parameter after consolidation test were done. The equivalence value of permeability (kve) is calculated using the Chai Method (2001) by considering smear effect. Test results showed that the settlement of soft soil in 90 degree consolidation reached in short period of time upon for smallest density and largest diameter of GCC.

The Effectiveness of Vacuum Consolidation to Soft Soil Settlement

The main issue of building constructions on soft soils is not a uniform settlement of soft ground, which has a slow process that effected construction failures and rising maintenance expenses. For many decades, to the improvement of ground soil stability, then applied using prefabricated vertical drain (PVD). Along the development of science and technologies, which followed by improvement of the soil stability method, that is called as Vacuum Consolidation Method (VCM). The objectives of this study are to determine how the effectiveness of vacuum consolidation with various patterns to soft soil settlement of constructions, and to find the right spacing of PVD installation due to un-uniform settlement of soft soils. The analysis of this study compared the numbers and rates of settlements in preloading, PVD, and VCM with various patterns, and to get a uniform settlement by two scenarios analysis, which are various spacing with single suction pressure (scenario 1) and single spacing with various suction pressures. Based on the result of analysis which showed the settlement of VCM in both patterns are 2.247 m in 105 days (square pattern) and 2.252 m in 90 days (triangular pattern). It means with a triangular pattern has 70.2 more effective than others in the rate of the settlement period. It also showed the VCM has larger than others in volume settlements. The results of 2 scenarios analysis showed that the implementation of scenario one was difficult due to various spacing, while scenario two can be implemented because numbers of settlements depend on suction pressure of the vacuum.