Soft Soil Improvement Research Articles

The Effect of Soaking on CBR Values in Soft Soils Stabilized with Stone Ash and Sand

Constructing in the soft soil is necessary to improve. The improvement of soft soil by mixing natural materials, namely stone ash and sand, reduces the impact of environmental damage when using chemical additives. Variations of materials mixture were 0%, 5%, 10%, 15%, and 20%. To determine the strength of the soil that has been mixed with natural materials, a test called the California Bearing Ratio (CBR) is carried out. The CBR laboratory test illustrates the conditions that will occur in the field. This CBR test was carried out using soaked and un-soaked methods. For testing by soaking, mixed variations of 0% and 5% obtained a low CBR value. The highest was 10% mixed variation and decreased to 15% and 20%. The CBR test without soaking had the highest CBR value at 5% mixture variation and the lowest at 0%. Adding a mixture variation above 5% causes the CBR value to decrease slowly. The results of the tests show that soaking the soil makes the soil condition saturated with water so that the resulting CBR value becomes very low.

Improvement of soft clay soil with a combination of pre-gelatinized corn starch and nanoparticle agro waste: A multi-objective grey wolf optimizer approach

The present study aimed to assess the potential of a bio-inspired algorithm, multi-objective grey wolf optimization algorithm (MOGWO), to optimize the strength properties (California bearing ratio (CBR) and unconfined compressive strength (UCS)) of an expansive subgrade soil. This optimization process involves the use of two additives, namely a bio-polymer, pregelatinized corn starch (PGCS), and a nanoparticle agro waste, rice husk ash (RHA), blended with the soil in different mix ratios determined by a 32 factorial experimental design. The CBR samples were cured for 7 days, while the UCS samples were cured for 1, 7, and 28 days. To optimize the expansive subgrade soil strength, regression models were developed using PGCS and RHA as predictors for CBR and UCS, serving as fitness functions in the slightly modified MOGWO optimization technique. Next, the optimization analysis produced non-dominated solutions. The results obtained from the laboratory experiments and optimization analysis revealed that there was significant improvement in the UCS and CBR of the soil. These improvements can be attributed to the pozzolanic reaction between the soil-RHA matrix, the formation of intercalated and exfoliated nanocomposites, and the hydrophilic interaction of PGCS. By applying the slightly modified MOGWO technique, the study achieved optimal enhancements in UCS (710.3 kN/m2) and CBR (24.2%) when the expansive subgrade soil was mixed with 0.2637% PGCS and 12.2413% RHA. The results demonstrate the potential of the MOGWO technique in improving the properties of expansive subgrade soil.

Analysis of Soil Improvement Through PVD and Vacuum Preloading with Several Equivalent Permeability Methods

Vacuum preloading combined with prefabricated vertical drain (PVD) is one of the common soft soil improvement methods. Soft soils often pose significant problems in construction projects due to their low shear strength and high compressibility, leading to settlement issues and potential structural instability. The PVD combined with vacuum preloading method addresses these problems by accelerating the consolidation process and minimizing settlement during service period. The acceleration occurs due to the presence of PVD, allowing dissipation of excess pore water in horizontal direction towards the PVD. Thereafter, the water in the PVD is drained to the surface. When modelled in 2D, PVD behaves as a continuous drain in the plane strain direction, causing the flow conditions to deviate from the actual conditions. To address this issue, equivalent soil permeability values is required, allowing the 2D model to produce results closely resembling the actual conditions. This research explores the improvement of PVD vacuum preloading through three equivalent permeability approaches. Utilizing field monitoring data, which includes settlement measurements from settlement plates, changes in pore water pressure recorded by piezometers, and lateral deformation data captured by inclinometers, the study evaluates the effectiveness of these approaches. Comparative analyses with field monitoring data reveal that Indraratna equivalent permeability method has the best fit. The integration of PVD and vacuum preloading, coupled with the refinement of equivalent permeability methodologies, offers a promising solution for addressing soft soil problems in geotechnical engineering. This research contributes to the practical application of these methods in construction projects, emphasizing their potential to enhance soil stabilization and reduce settlement-related risks.

Feasibility of recycled concrete aggregate stabilized with one-part geopolymers as semi-rigid inclusion columns

Recycled concrete aggregate (RCA) is a voluminous solid waste material derived from the construction sector and is typically stockpiled in landfills. In recent years, the ground improvement industry has grappled with challenges stemming from the depletion of natural quarry materials, resulting in a skyrocketing of their prices and increased project costs. This research investigated the feasibility of using RCA stabilized by one-part geopolymers to produce an innovative semi-rigid inclusion column system for ground improvement of soft soils. Na2SiO3-anhydrous was used as a sole solid activator for the activation of fly ash (FA), slag (S) or a binary precursor (FA+S) in the stabilization of RCA. The unconfined compressive strength (UCS) and microstructure of the stabilized mixtures have been examined with respect to different binder formulations and curing conditions. The permanent deformation characteristics of mixtures under cyclic loading were evaluated through repeated load triaxial (RLT) tests to replicate the moving wheel loads imposed on the semi-rigid inclusion columns. In addition, the cost and environmental impacts of the optimum mixtures suggested in this research were studied. The test results indicated that stabilizing RCA with as low as 5% one-part alkali-activated FA, S or (FA+S) met the minimum strength requirement (1.034 MPa) for ground improvement work. Compared with standalone FA and S geopolymer stabilized RCA mixtures, (FA+S) geopolymer stabilized RCA mixtures were identified as preferred industrial formulations due to their prolonged setting time for ease of mixing and handling when used in stone column applications. It was found that curing temperature and duration played a pivotal role in the strength gain of the mixtures. The RLT test results demonstrated that implementing the optimum RCA + 5%(FA+S) mixture as identified in this study for semi-rigid inclusion columns, led to a reduction in permanent strain values by approximately 90% compared to conventional unbound stone columns. The comparison between the optimum mixture highlighted in this study with other stabilization methods showed that the semi-rigid inclusion columns had great potential to enable large-scale production, cost and emission reduction in future ground improvement projects.

Cyclic performance of geosynthetic-encased granular pile with tire chips and aggregates mixture in soft soil – A model study

The performance of encased granular piles subjected to heavy cyclic loading presents a significant concern in the current context. Meanwhile, global waste tire management poses a major challenge because it has a detrimental effect on the environment. To address both difficulties, this research utilizes recycled tire chips derived from end-of-life tires (ELTs) and substituting traditional aggregates in granular pile construction. This study summarizes laboratory model tests investigating the performance of geosynthetic encased granular piles designed for soft soil improvement under vertical cyclic loading. The composition of the granular pile comprised (25 % tire chips + 75 % aggregates). Various cyclic loading parameters were scrutinized, including the selection of encasement material and the best configuration for granular piles, cyclic loading frequency (f), cyclic loading amplitude (qca), length-to-diameter (L/D) ratios, granular pile end conditions, and strength of surrounding soft soil. The novel feature of this research is the evaluation of the cyclic induced settlement (Sc) – excess pore water pressure (Pexc) coupled performance for all considered factors and its effects on the encased granular piles improved soft ground under vertical cyclic loading. Key findings include ordinary granular piles (OGP) illustrated optimal performance when subjected to lower frequency and amplitude loading, smaller L/D ratios, and end bearing conditions. The provision of Combi-grid encasement notably improved the cyclic performance of granular piles by substantially reducing the cyclic induced settlement (Sc) on improved soft beds across all examined factors. This research also discusses the increased cyclic stress on the surrounding soft soil initiated excess pore water pressure (Pexc) development and is reduced to a greater extent with the help of Combi-grid encasement across all test cases.

Performance of Nickel Slag as a Stabilization Material for Soft Soil

The chemical soil stabilization method is an effort to improve soil bearing capacity according to soil work specifications in construction. The use of conventional stabilization materials, such as cement and lime, is considered environmentally unfriendly. Utilizing by-products from the mining industry becomes an alternative that can be developed in soil improvement efforts. This research aims to examine the influence of nickel slag on the enhancement of soil bearing capacity as observed through its unconfined compressive strength value. In this study, the concentration of added nickel slag as a stabilization material is 3%, 6%, 9%, and 12% by dry soil weight. The test specimens used are cylinders with a diameter of 5 cm and a height of 10 cm. Unconfined compressive strength testing is conducted after the specimens are cured for 14 days. The results of this study indicate that the clay soil used is classified as organic clay with high plasticity based on the USCS classification, with an unconfined compressive strength value of 0.2 kg/cm2. The addition of nickel slag with concentrations of 3%, 6%, 9%, and 12% results in respective increases in unconfined compressive strength by 46%, 50%, 68%, and 47%. These findings demonstrate that the optimum nickel slag content of 6% provides the maximum unconfined compressive strength. Therefore, it can be concluded that nickel slag, as a source of silica, has the potential to be used as an alternative material in soft soil improvement.

Research and evaluate the potential of rice husk ash and rice straw ash for soil improvement in Vietnam

Rice husk ash and rice straw ash are common agricultural wastes in developing countries. Currently, utilizing these wastes in the construction sector such as soil improvement and cement concrete production is a trend in many areas around the world. In Vietnam, with a rice production of more than 40 million tons/year, millions of tons of rice husk ash and straw ash can be generated. This is an abundant and a cheap material source. This article will research and evaluate the potential of rice husk ash and straw ash for soft soil improvement in Vietnam. Research results show that straw ash and rice husk ash are materials having high pozzolan activity. Various studies in the world and some studies in Vietnam showed that rice husk ash and straw ash not only improve some physical and mechanical properties of soil but can also partially replace the amount of binder. Vietnam has different types of soft soil and construction activities are increasing, so the demand for improving soft soil is also increasing. In which, improving soil with cement binder is one of the most popular methods. Therefore, rice husk ash and rice straw ash have great potential to combine with cement in improving soft soil in Vietnam. Utilizing these wastes not only helps reduce the negative impact their causes on the environment but also helps improve construction quality and reduce construction costs.

Parametric Study on The Bearing Capacity of Down-hole Dynamic Compaction

The DDC method is well known as Down-Hole Dynamic Compaction, an effective ground treatment method. DDC combines dynamic compaction and soil replacement methods to enhance bearing capacity, reduce settlement, minimize the potential for collapse, and mitigate liquefaction. DDC has been commonly used to stabilize collapsible soil, DDC basically forms a column inside the soil stratum which is similar to a stone column except DDC materials are put in sequence and then compacted by using DDC hammer, this is known as the self-tamping method. DDC is considered as a suitable method for soft soil improvement. This study modeled DDC as reinforcement for runway area which is predominantly soft soil in the study location. DDC is modeled with various dimension and spacing to assess its impact on bearing capacity and settlement, thereby simplifying the selection of suitable dimension during installation. The results show that the stress induced by external loads on Down-hole Dynamic Compaction (DDC) rises in correlation with the spacing between DDC installations. The peak stress was documented on a DDC unit with a 1-meter diameter positioned at a distance of 2.5 meters from the other DDC units, measuring 83.9 kN/m2. The highest stress level was recorded in the soil surrounding a DDC unit with a 1.5-meter diameter, which was positioned 3 meters away from other DDC units, measuring 157.89 kN/m2. The highest bearing capacity was achieved when a DDC with a diameter of 1.5 meters was positioned at a distance of 3 meters, resulting in a bearing capacity value of 1407.32 kN/m2.

Soft Soil Improvement with Encased Granular Piles Composed of Aggregates and Tire Chips Mixture: Experimental and Numerical Studies

Soft Soil Improvement with Encased Granular Piles Composed of Aggregates and Tire Chips Mixture: Experimental and Numerical Studies

Numerical Analysis of Soft Soil Improvement using Pile at Airport Construction Project

Construction on the soft ground poses an excellent challenge for geotechnical engineers. Several engineering problems such as bearing capacity failure and differential settlement could occur either during or after the construction phase due to high compressibility and low shear strength. Nowadays, a number of soil improvement techniques are available to solve such problems. However, each method has its advantages and disadvantages. In this study, soil improvement analysis using pile were performed with three variations depths so called 12 m, 18 m, and 24 m from the ground level. A finite element simulation has been performed using PLAXIS 2D. The pile has been modeled as plate and Mohr-Coulomb model was used for soil model. The results show that the deeper the pile, the settlement will be decreasing. Moreover, the axial force and bending moment of the pile obtained from the output of PLAXIS 2D were also presented to assess the performance of the soil improvement technique.

Research on experimental evaluation horizontal coefficient of consolidation Ch on CPTu dissipation test to determine permeability parameters in the field to improvement of soil soft.

In the solution of soft soil improvement by preloading method combined with prefabricated, the horizontal consolidation coefficient Ch is a very important parameter to help predict the settlement speed of soft soil. But when designing the coefficient of horizontal consolidation, it is often assumed that the coefficient of vertical consolidation is quite large. This can lead to settlement over time that will fluctuate in a rather large range of values. In this paper, research and evaluation of the horizontal consolidation coefficient Ch by dissipation test on piezocone penetration device with pore water pressure measurement has been mentioned to determine the permeability parameters in-situ for the soft soil improvement at the projects.

Calculation for soft soil improvement by vacuum consolidation method combined with PVDs

This paper presents a method of soft soil improvement by vacuum consolidation method combined with PVDs. One of the effective methods of soft soil improvement compared to the traditional preloading method, which consumes a lot of embankment materials, Extending construction time, and also causes the risk of slope instability due to the height of the embankment. The method of soft soil improvement by vacuum is a method of creating negative pressure in groundwater by vacuum pump and that negative pressure is maintained by an airtight geo-membrane system, thus increasing the effective pressureof soil by reducing excess pore water pressure while the total pressure remains unchanged. When using the vacuum compression method combined with PVDs, the surrounding soil tends to move into the vacuum area, thus minimizing the risk of slope instability. And the time to apply vacuum pressure is much faster than preloading method to create equivalent pressure. Specific application for the soil improvement of a factory in Cai Mep industrial zone will show the effectiveness of this method.

Improvement of soft soil for road construction on the north brebes tegal ring road project

The Brebes-Tegal North Ring Road is a primary arterial road located in the Central Java North Coast (Pantura) corridor that crosses Brebes Regency (12,385 km) and Tegal City (4,715 km), this road was built with the aim of breaking up the traffic congestion that occurred in the City Center of Brebes and Tegal City. In 2010, the construction of the Brebes-Tegal North Ring Road began. However, in 2013 development activities temporarily stopped due to a number of problems, one of which was the condition of the soil at some of the construction sites in the form of swamps and ponds resulting in low soil carrying capacity which affected the construction of roads on it. This condition starts from STA. 8+800 to STA. 17+377 from the direction of Brebes to Tegal. therefore, in December 2019 the project was resumed with a design change to improve the subgrade so that it could withstand the burden of road construction and passing traffic. Soil improvement is carried out using geotextiles, PVD and PHD in the selected soil embankment work process so as to increase the CBR value of the subgrade for the better (higher CBR). In addition, in bridge construction work it is necessary to use pile slabs to prevent high pile failures.

Instrumentation and Data Interpretation in Transportation Geotechnics

AbstractTransportation networks on the eastern coast of Australia are often built on or traverse coastal flood plains and marine clays with unfavourable soil conditions. In the past two decades, a significant number of laboratory investigations were carried out in soft soil improvement using Prefabricated Vertical Drains (PVDs) combined with vacuum-assisted surcharge preloading. In addition, significant research efforts were made to reduce the maintenance costs of railway tracks and increase their longevity by using synthetic inclusions such as geocomposites, geogrids and shock mats. These research outcomes were implemented and validated in practice through several field investigations along the eastern coast of Australia. This paper demonstrates the significance of instrumentation and data interpretation in geotechnical field investigations through 6 case histories. Field trials including Port of Brisbane Land Reclamation, Ballina Bypass Upgrade and Sandgate Rail Separation Projects were presented highlighting innovative ways of monitoring the performance of PVDs with vacuum and non-vacuum surcharge preloading. Also, railway track design improvements using geosynthetic and shock mats were discussed through Bulli and Singleton trial track case studies. Further, the heavy haul track testing facility at Russell Vale, New South Wales, was discussed as an alternative for expensive and time-consuming field trials.

In situ digital testing method for quality assessment of soft soil improvement with polyurethane

This study purposes an in situ testing method on quality assessment of soil improvement. Factual drilling data includes the spatial distribution and in situ strength of untreated and treated soil along three different drillholes measured by on-site drilling monitoring method. These factual drilling data can characterize the degree of soil improvement by penetration injection with permeable polyurethane. Result from on-site drilling monitoring shows that the linear zones represent constant drilling speeds shown in the plot of drill bit advancement vs. net drilling time, which indicates the spatial distributions of soil profile. The soil profile at the study site is composed of four layers, which includes fill, untreated silty clay, treated silty clay, and mucky soil. The results of soil profile are verified by the parallel site loggings. The constant drilling speeds profile the coring-resistant strength of drilled soils. By comparing with the untreated silty clay, the constant drilling speeds of the treated silty clay have been decreased by 13.0–62.8%. Two drilling-speed-based indices of 61.2% and 65.6% are proposed to assess the decreased average drilling speed and the increased in situ strength of treated silty clay. Laboratory tests, i.e. uniaxial compressive strength (UCS) test, have been performed with core sample to investigate and characterize in situ strength by comparing that with drilling speeds. Results show that the average predicted strengths of treated silty clay are 2.4–6.9 times higher than the average measured strength of untreated silty clay. The UCS-based indices of 374.5% and 344.2% verified the quality assessment (QA) results by this new in situ method. This method provides a cost-effective tool for quality assessment of soil improvement by utilizing the digital drilling data.

Selection of single machine learning model for designing compressive strength of stabilized soil containing lime, cement and bitumen

The unconfined compressive strength (Qu) is one of the most important criteria of stabilized soil to design in order to evaluate the effective of soft soil improvement. The unconfined compressive strength of stabilized soil is strongly affected by numerous factors such as the soil properties, the binder content, etc. Machine Learning (ML) approach can take into account these factors to predict the unconfined compressive strength (Qu) with high performance and reliability. The aim of this paper is to select a single ML model to design Qu of stabilized soil containing some chemical stabilizer agents such as lime, cement and bitumen. In order to build the single ML model, a database is created based on the literature investigation. The database contains 200 data samples, 12 input variables (Liquid limit, Plastic limit, Plasticity index, Linear shrinkage, Clay content, Sand content, Gravel content, Optimum water content, Density of stabilized soil, Lime content, Cement content, Bitumen content) and the output variable Qu. The performance and reliability of ML model are evaluated by the popular validation technique Monte Carlo simulation with aided of three criteria metrics including coefficient of determination R2, Root Mean Square Error (RMSE) and Mean Square Error (MAE). ML model based on Gradient Boosting algorithm is selected as highest performance and highest reliability ML model for designing Qu of stabilized soil. Explanation of feature effects on the unconfined compressive strength Qu of stabilized soil is carried out by Permutation importance, Partial Dependence Plot (PDP 2D) in two dimensions and SHapley Additive exPlanations (SHAP) local value. The ML model proposed in this investigation is single and useful for professional engineers with using the mapping Maximal dry density-Linear shrinkage created by PDP 2D.

Improvement of Soft Clay Soil Using Stone Columns

Improvement of Soft Clay Soil Using Stone Columns

A Comparative Case Study on Drainage Consolidation Improvement of Soft Soil under Vacuum Preloading and Surcharge Preloading

Based on an improvement project of soft soil ground in Zhuhai City on the Pearl River Delta, a comparative study on vacuum preloading and surcharge preloading was performed. The ground and stratified settlements, excess pore water pressure, and the degrees of consolidation of soft soil are analyzed, along with the horizontal displacement and soil strength. The results show that surcharge preloading results in smaller secondary consolidation settlements than vacuum preloading. Primary consolidation settlement quickly increases with increasing excess pore water pressure of less than −40 kPa in vacuum preloading, while also increasing between 20 kPa and 25 kPa in surcharge preloading. The sharp increase in the strata permeability coefficient will induce the increase in strata consolidation degree and has little effect on the ground consolidation degree. The surcharge preloading can be given priority to reduce the settlement foundation in the service stage.

Prediction of the settlement associated with construction on soft clay improved using rigid inclusions considering the installation effect

One of the most common methods in soil improvement of soft soils is using rigid inclusions (RI) that enhance the stiffness of the soil surrounding and beneath the inclusions. This paper aims to develop simple and user-friendly charts to estimate the settlement improvement factor (N) that correlates the settlement values without soil improvement to the settlement values after improvement, considering the installation effect of the rigid inclusions in soft clay formations. The cavity expansion method is used to model the installation process of the rigid inclusions. A parametric study is carried out using numerical modelling to predict the variation in the improvement factor with the variation of the treated soil stiffness and geometry of the RI system. The analyses are performed using a verified numerical model for a case study of a zone loading test performed at New Mansoura city in Egypt, employing the finite element software (PLAXIS 3D). The cavity expansion approach is first utilized for an axisymmetric model by imposing a prescribed displacement equivalent to the inclusion radius to simulate the construction effect of the rigid inclusion. From the axisymmetric model, the enhancement in the deformation modulus and the over consolidation ratio of the soft clay, resulting from the construction of the rigid inclusions, are determined. In the second stage of the analysis, the improved soil parameters are then implemented in the 3D finite element model, in which the external stresses due to superstructure are applied over the improved soil. The settlement associated with loading both the improved and unimproved soils is then compared for each studied condition in the parametric study to determine the improvement factor (N). The performed analyses clearly showed the high effect of the rigid inclusions in reducing the settlement associated with the construction on the improved soft clay. The achieved improvement factor varies between 2.88 to 58.10, with an average value of about 12.00. Based on the conducted parametric study, design charts are developed to provide a simple tool for predicting the settlement values associated with construction on improved soft clay formations with rigid inclusions under different conditions.

In situ long-term improvement of large-scale lacustrine soft soil using laboratory and field data: a case study from a copper mine in China

In situ long-term improvement of large-scale lacustrine soft soil using laboratory and field data: a case study from a copper mine in China