Ground Improvement Research Articles

Mechanical and hydraulic characteristics of unvegetated or vegetated loess soils amended with xanthan gum

With the development of western and central China, the increasing construction of transportation infrastructures (e.g., roads, railways, etc.) has been producing a large number of man-made slopes in loess regions. Biopolymer as an eco-friendly stabilizing material, has a great potential to amend soils for the purpose of ground improvement and slope stabilization, with its application in vegetated soils particularly at the initial growing stage to support vegetation growth as well as offer reinforcement to unprotected soils being reported recently. In the current study, the contribution of xanthan gum (XG) to both mechanical and hydraulic behaviors of the unvegetated and vegetated loess soils subjected to climatic wetting–drying cycles under the impacts of degree of compaction and biopolymer content are explored, whilst the effectiveness of the two XG-based soil reinforcing methods (with and without vegetation) are compared. Results indicate that XG treatment improved the water-retention capacity of loess soils to an extent that even the degradation of water retention upon initial wetting–drying cycles could be mitigated particularly at higher degrees of compaction. The strengthened shear resistance of loess soils was observed, mainly attributed to the increased soil cohesion, whilst the friction angle remained almost constant. The unvegetated loess soils basically had an increased cohesion proportional to the XG content up to 1.00% of the dry soil mass, whilst the vegetated soils had the highest soil cohesion at a fixed XG content of 0.50% which corresponded to the mostly promoted vegetation growth. Although a dense soil structure inhibited the seed germination and growth of sprouts and roots, it contributed to the overall shear strength of the vegetated soils similar to its effect on the unvegetated soils. XG amendment outperformed planting vegetation at enhancing soil shear strength at a degree of compaction of 95% (comparable to those adopted for design of highway subgrade), whilst providing XG in combination with vegetation was able to result in a more sizable strength increment over the summation of gains in strength by utilizing XG and vegetation separately, suggesting the considerable potential of XG in assisting vegetated soils for ecological slope stabilization. The results obtained from the current research support the broader usage of biopolymers (either used alone or in combination with vegetation) as reliable geotechnical engineering materials in practical implementations.

Effect of Ground Improvement on Settlement Problems of Lignite Spoil Heaps Using Numerical Modelling

Effect of Ground Improvement on Settlement Problems of Lignite Spoil Heaps Using Numerical Modelling

Numerical analysis of microbially induced calcite precipitation and enzyme induced calcite precipitation in calcareous sand: Multi-process and biochemical reactions

Microbially induced calcite precipitation (MICP) and Enzyme induced calcite precipitation (EICP) techniques were implemented to reinforce the large-scale calcareous sand in this study. Then a coupled numerical model to predict the biochemical reactions and hydraulic characteristics of MICP and EICP reaction was proposed and verified by physical experiments. Results showed that: This model could describe the variations of bacteria, calcium, calcite, permeability over time reasonably. It is necessary to consider the influence of the calculation domain scale when simulating the convection-diffusion-reaction in the multi-process of MICP and EICP reactions. The numerical and experimental values of calcite content are 0.841 g/cm3 and 0.861 g/cm3 for MICP-reinforced sand, 0.263 g/cm3 and 0.227 g/cm3 for EICP-reinforced sand after 192 h of reaction. The reaction rate krea is an important parameter to control the calcite content. Accordingly, the permeability coefficient of MICP and EICP reinforced calcareous sand decreases by 32% and 18%. Due to the influence of substance transportation and calcite precipitation, the calcite shows a trend of decreasing firstly and then increasing with the enhancing of the initial permeability coefficient in biochemical reactions. The optimal injecting ratio q11: q12 in this study is 100:300 mL/min. The process for the application of MICP and EICP coupled numerical model is also recommended, which provides reference for engineering projects in ground improvement.

Field-Scale EICP Biocemented Columns for Ground Improvement

Field-Scale EICP Biocemented Columns for Ground Improvement

Revisiting mixing uniformity effect on strength of cement-based stabilized soft clay

Despite the fact that mixing uniformity (i.e. the consistency of binder distribution) significantly influence the quality of ground improvement during in situ soil mixing projects, its quantitative evaluation was rarely concerned due to the difficulty of measurement from an engineering perspective. A methodology was proposed to quantitatively evaluate the mixing uniformity of stabilized soil using handheld X-fluorescence spectrometry (XRF), which is helpful to elucidate the significance of mixing uniformity on strength. In other words, the calcium content was monitored to ascertain the distribution of cement within the matrix, and a quantitative index was subsequently established. It was observed that an increase in mixing uniformity resulted in a transition in the behavior of the stabilized clay from a plastic to a brittle failure mode, and from a localized failure to a global shear failure under unconfined compression. Subsequent observation of the destruction process revealed that cracks were more readily formed in the low cement zones and then bypass the high cement zones. Furthermore, the effect of mixing uniformity on strength is likely to be amplified with prolonged curing periods. The enhancement of uniformity would increase the volume of the high binder zones, thereby enhancing the overall high-strength performance. The proposed methodology is capable of characterizing the discreteness between the tracked element's measured and theoretical contents, thusing avoiding the uncertainty associated with other indirect indicators. The convenience of the portable handheld XRF apparatus was confirmed, as it can be readily deployed in situ or ex situ to track calcium content within the stabilized mass after borehole sampling.

An approach for strength development assessment of cement-stabilized soils with various sand and fine contents

Cement stabilization is a well-established ground improvement technique. However, there have been limited investigations aimed at the effect of heterogeneous soil types with varying amounts of coarse-grained (sand) and fine-grained (silt and clay) substances, on the strength enhancement of cement-stabilized soils. In this cement stabilization research study, sand (S) and clayey silt (F) were mixed together to have a variety between coarse- and fine-grained fractions at 100, 75, 50, 25, and 0 % by dry weight, designated as the ratio of S:F=100:0, 75:25, 50:50, 25:75, and 0:100, respectively. The water content was prepared at the range of 1.25–2.50 optimal water content to simulate field applications. The strength enhancement of cement-stabilized soils was influenced by the fine content, water content, and cement content. The soil–water to cement ratio (s-w/c) was effectively incorporate the impact of both water and cement contents on the strength enhancement, for a given a specific fine content. The generalized correlation between unconfined compressive strength, qu and s-w/c could be represented as a power function: qu = M/(s-w/c)N. In this equation, M and N are constants that are primarily influenced by the fine content. The shear strength ratio versus fine content chart was proposed as a means to assess the effect of fine content on the strength of cement-stabilized soil with varying s-w/c. A stepwise approach for assessing the strength enhancement of cement stabilization in soil based on physical characteristics (i.e., plasticity index and fine content) was proposed and validated. The robustness of the proposed approach was realized by the low mean absolute percent error, (MAPE<7.0 %) and high coefficient of determination (R2 > 0.95) for measured and predicted strengths comparison. This technique serves as a valuable tool for mix design, specifically in relation to clay mineral and fine content. It supports in making engineering decision regarding the appropriate amount of water and cement needed to achieve strength requirements throughout the requisite curing period, while minimizing the number of repetitions needed.

Modeling of rigid inclusion ground improvements in large-scale geotechnical simulations

Abstract The methods for modeling rigid inclusion ground improvements are well documented in the literature, yet their application to large-scale geotechnical simulations remains underanalyzed. Due to the large number of discretization elements/nodes used in such simulation, certain simplifications are necessary. This paper presents methods for modeling rigid inclusion ground improvements in large-scale geotechnical simulations. The methodologies involve modeling the inclusions using continuum elements, beam elements or replacing them with an equivalent medium through homogenization techniques. The advantages and drawbacks of each method are discussed, particularly regarding their applicability to analyses covering significant areas. In the second part of the paper, a case study of the foundation of the conduit pipe in the dam of Szalejów Górny dry antiflood reservoir in Poland is simulated using two of the considered methods. The obtained results are compared and discussed.

Sustainable ground improvement of soft clay using eggshell lime and rice husk ash

Stabilization of clay using lime or cement is conventionally accepted practice. Although it is effective, they impose several implications on the environment. Hence, it is high time that an alternate sustainable binder needs to be investigated. Eggshell, a waste from food industry, is an alternate source for calcite and can be considered to produce eggshell lime (EL). Also, rice husk ash (RHA), an agricultural waste product, is a silica rich source which is a pozzolanic material. In the current study, the efficiency of both the materials in stabilizing the soft soil is investigated and the results suggests that the plasticity and the strength characteristics of soft clay can be significantly improved by the addition of EL. After adding optimum concentration of 3 % EL, the liquid limit decreased from 74 % to 53 %, plastic limit increased from 27 % to 46 % and shrinkage limit increased from 8 % to 44 %. On increasing the EL content, the swelling got reduced from 88 % of virgin clay to 17 % in case of 3 % EL and finally to zero with 5 % of EL. Also, the addition of combination of EL and RHA to the soft clay has improved the strength characteristics significantly. As the curing days increased, slight variation was only seen in the plasticity characteristics which may be due to rapidity of cation exchange. But strength characteristics increased suggesting the occurrence of pozzolanic reactions and formation of gel. The 28th day strength of the clay treated with 3 % EL increased to as high as 757 kPa. The strength characteristics showed that as we increase the percentages of EL and RHA combination, the strength would increase tremendously much better than the treatment with eggshell lime alone. This is because of the supply of CaO and SiO2 sources. For 5 % of EL and 15 % of RHA, the 1 day curing strength was near to 500 kPa. With less concentration of eggshell lime and RHA, the treated soil was appearing to be more porous in SEM while when the binder concentration was increased, the pores were filled and presence of C-S-H gel was also detected. XRD test results also showed the presence of C-S-H gel.

Optimum Design of Granular Pile Anchor System for Ground Improvement on Expansive and Shrinking Soil

Optimum Design of Granular Pile Anchor System for Ground Improvement on Expansive and Shrinking Soil

Creep Versus Consolidation in Tunnelling through Squeezing Ground—Part B: Transferability of Experience

This paper investigates potential differences between creep and consolidation in mechanised tunnelling through squeezing ground, placing focus on the practical question of using experiences gained from existing tunnels about the required thrust force as a reference for tunnels of different diameter or adjacent tunnels. The investigations focus on two aspects. First, the effect of the tunnel diameter on the risk of shield jamming is examined. The paper demonstrates that larger-diameter tunnels are more favourable in poor-quality ground, while the opposite holds in better-quality ground, as well as in the case of pronouncedly time-dependent ground behaviour due to consolidation or creep. Second, the effect of a tunnel on the required thrust force in a neighbouring tunnel built later is examined. The paper shows that this interaction effect is particularly important in water-bearing ground of low permeability, where the drainage action of the first tunnel induces pore pressure relief and ground consolidation in an extensive area, leading to a remarkable reduction of the thrust force in the second tunnel. Conversely, in the case of creep the interaction is negligible even under extremely squeezing conditions, due to the fundamentally different nature of the purely mechanical rheological processes from coupled hydromechanical processes. The presented investigations into the transferability of experiences are valuable for tunnelling practice, in cases of twin tunnels as well as in situations where a smaller-diameter tunnel is constructed prior to the main tunnel (e.g. a pilot tunnel for exploration, advance drainage or ground improvement), or also the opposite (e.g. upgrade of a road tunnel by later construction of a safety tunnel with a smaller diameter).

Assessing foundation characteristics at the war dam site, lake tana basin, Ethiopia: A geophysical and geotechnical perspective

An integrated geophysical and geotechnical study evaluated the foundation conditions at the War dam site in northwest Ethiopia. This investigation included the classification of rock quality, shallow seismic refraction, and magnetic approaches. The dam's location comprises quaternary soil deposits and rhyolite rock units that have undergone varied weathering and fracturing. The shallow seismic refraction method distinguishes three layers of p-wave velocities that are less than 1.5 km per second with a depth range of 2–6 m, 1.5–2.5 km per second at a depth range of 15–20 m, and 2.5–3.5 km per second ranging from 20 to 40 m, respectively. Magnetic data were used to identify lineaments, and the RQD value acquired from boreholes ranged from extremely poor to excellent. Lineaments were recognized using the tilt angle approach. The results of the permeability tests demonstrated that the rock mass that serves as the dam's foundation had characteristics that are resistant to low permeability. The maximum and minimum lugeon values obtained from the testing were 9Lu and 0.81Lu, respectively. There are weak zones at and below the surface of the dam site, according to the overall findings acquired from seismic refraction, magnetic, and discontinuity surveying. These results were obtained from monitoring the dam site. These significant structures are directed towards a SW-NE, NE-SW, NNW-SSE, and SSW-NNE orientation. The study assessed the geological suitability of a proposed dam site using seismic refraction and magnetic survey methods. Significant geological variations were observed, particularly in the right abutment and valley floor, indicating the need for targeted grouting. The findings suggest that while the site is generally suitable for dam construction, specific areas require further ground improvement to ensure stability.

Secondary consolidation simulation of peat with vertical drains under time-dependent loading

Preloading with vertical drains is an effective ground improvement technique used to accelerate the consolidation process. Generally, embankments are constructed over a period, by increasing the fill height with time. Hence, it is not always realistic to analyse embankments as a single ramp loading or an instantaneous loading. Although many studies have been conducted to calculate the settlement variation under time-dependent loading, those methods are complex in practical applications and do not consider the secondary consolidation settlement, which is important for very soft organic soils. In this study, the original Barron consolidation theory is applied to calculate the variation of settlement, pore water pressure and degree of consolidation due to incremental step loading of embankments, constructed on compressible soft organic soil, stabilised with vertical drains (gravel compaction piles, sand compaction piles and prefabricated vertical drains). The settlement predictions are compared with the actual settlement monitoring data obtained during the construction of road embankments, and pore pressure variation is compared with the results obtained from a case study reported in the literature. The comparisons show that the results obtained from the proposed method match very well with the actual field measurements.

Fruit and vegetable waste used as bacterial growth media for the biocementation of two geomaterials

This paper investigates the feasibility of using randomly collected fruit and vegetable (FV) waste as a cheap growing medium of bacteria for biocementation applications. Biocementation has been proposed in the literature as an environmentally-friendly ground improvement method to increase the stability of geomaterials, prevent erosion and encapsulate waste, but currently suffers from the high costs involved, such as bacteria cultivation costs. After analysis of FV waste of varied composition in terms of sugar and protein content, diluted FV waste was used to grow ureolytic (S. pasteurii, and B.licheniformis) and also an autochthonous heterotrophic carbonic anhydase (CA)-producing B.licheniformis strain, whose growth in FV media had not been attempted before. Bacterial growth and enzymatic activity in FV were of appropriate levels, although reduced compared to commercial media. Namely, the CA-producing B.licheniformis had a maximum OD600 of 1.799 and a CA activity of 0.817 U/mL in FV media. For the ureolytic pathway, B. licheniformis reached a maximum OD600 of 0.986 and a maximum urease activity of 0.675 mM urea/min, and S. pasteurii a maximum OD600 = 0.999 and a maximum urease activity of 0.756 mM urea/min. Biocementation of a clay and locomotive ash, a geomaterial specific to UK railway embankments, using precultured bacteria in FV was then proven, based on recorded unconfined compressive strengths of 1–3 MPa and calcite content increases of up to 4.02 and 8.62 % for the clay and ash respectively. Scanning Electron Microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), attested the formation of bioprecipitates with characteristic morphologies and elementary composition of calcite crystals. These findings suggest the potential of employing FV to biocement these problematic geomaterials and are of wider relevance for environmental and geoenvironmental applications involving bioaugmentation. Such applications that require substrates in very large quantities can help tackle the management of the very voluminous fruit and vegetable waste produced worldwide.

A two‐stage combined filtration‐consolidation model for slurry ground treated by vacuum preloading

AbstractThe vacuum preloading technique is extensively employed for ground improvement, particularly for slurry ground characterized by high‐water content and low strength. Such ground frequently exhibits a delay in pore water pressure dissipation when treated with prefabricated vertical drains. To clarify the drainage and consolidation behaviour of high‐water content slurry ground under vacuum preloading, this study proposed a two‐stage combined model that integrates both filtration and consolidation processes. Initially, an axisymmetric filtration model was used to describe the formation of the soil column through the radial migration and compaction of the particles. The end‐of‐filtration radial distributions of void ratio, permeability coefficient, and effective pressure served as initial conditions for the consolidation stage analysis. This stage was depicted using a large strain consolidation model based on the free strain condition. The results showed the necessity of incorporating the filtration stage to capture the overall drainage mechanism and characteristics of slurry ground with vacuum preloading treatment.

Discussion of “Numerical Study of the Effect of Ground Improvement on Basal Heave Stability for Deep Excavations in Normally Consolidated Clays”

Discussion of “Numerical Study of the Effect of Ground Improvement on Basal Heave Stability for Deep Excavations in Normally Consolidated Clays”

Discussion of “Numerical Study of the Effect of Ground Improvement on Basal Heave Stability for Deep Excavations in Normally Consolidated Clays”

Discussion of “Numerical Study of the Effect of Ground Improvement on Basal Heave Stability for Deep Excavations in Normally Consolidated Clays”

Closure to “Numerical Study of the Effect of Ground Improvement on Basal Heave Stability for Deep Excavations in Normally Consolidated Clays”

Closure to “Numerical Study of the Effect of Ground Improvement on Basal Heave Stability for Deep Excavations in Normally Consolidated Clays”

Influence of biocementation treatment extent on dynamic system performance: A centrifuge liquefaction study

Previous centrifuge experiments have shown Microbially Induced Calcite Precipitation (MICP) is a viable ground improvement technique to mitigate liquefaction. However, in these past experiments the entire sample in the model container was MICP treated. This study is an investigation of the effect of treatment extent on the system seismic performance by varying the depth of improvement, while maintaining the same cross-sectional area. Specifically, MICP treated zones (10 cm × 10 cm in model scale in plan view) were varied in depth to 100%, 75%, and 37% of the liquefiable sand layer depth. As a comparison, two additional models were constructed, an untreated and fully treated model. The treated models were initially prepared to a relative density of less than 40% and MICP treatment applied until a change of shear wave velocity (Vs) of 300 m/s was measured. All models were instrumented with accelerometers and pore pressure transducers to capture the dynamic responses during the same sequence of eight shaking events. Cone penetration resistance was measured to verify the uniformity of the untreated zones in the models and track the evolution of penetration resistances at three different times during the shaking sequence. Vs was measured after each shaking event to assess the cementation integrity of the MICP treated zones. Linear potentiometer and pre- and post-surface measurements were obtained to track seismic-induced settlements. Pore pressure generation and settlements were reduced in the MICP treated zones compared to untreated zones, showing the increased liquefaction resistance and system performance of MICP. Amplification of the strong ground motions in the models with treatment through the full liquefiable layer lead to significant degradation of the MICP. While a base isolation effect was observed in the models not treated to the full depth of the liquefiable layer, reducing seismic demands to the MICP treated zoned, and leading to minimal changes in cementation integrity. These findings suggest that there may be a benefit to not improving the entire liquefiable depth for maintaining cementation integrity of MICPtreated soils.

SOIL STRUCTURE INTERACTION AND STRUCTURAL RESPONSE USING DYNAMIC TEST SYSTEM

Reducing the accessibility of real building sites has contributed to an expansion in the usage of smaller areas, in which the bearing limit of the fundamental sediments is exceedingly limited. The conventional strategy would be to get a deep and exclusive base for these weak stores. There is a necessity to create real-world provisions that have made ground improvement a significant exploration area. The settlement of shallow foundations and bearing capacity as a cost-effective foundation system. The foundation beds are laid on the thin soil in low-lying, poorly-drained soil. The resulting improved granulated layer decreases the settlements by providing a better pressure distribution and strengthening the performance to bear the underlying weak soil’s load. To support shallow foundations, the use of reinforced soils has received considerable attention during the past 35 years. Various researchers have expanded knowledge of strengthened soil’s support possible benefits on bearing capacity, shallow base settlement, and failure mechanisms. Several empirical and experimental experiments have been shown to test the bearing ability of strengthened soil footings.

Vibro stone column ground improvement practice in the United Kingdom

Vibro stone-column (VSC) techniques have been applied in the United Kingdom (UK) since the late 1950s–early 1960s, where they are one of the most commonly adopted ground improvement techniques. While there have been significant advances in VSC equipment development and also in the monitoring of the installation process for the VSC technique over the past 50 years, the design of VSC remains largely empirical and has changed very little since the 1970s. Publication of well-documented case histories and of instrumented field trials has also been limited over the past 25 years in the UK, in a VSC ground improvement market, which is predominantly commerce driven, based on the cheapest price. This has inherent implications for further advancement of design and innovation through funded full-scale field-based research. Current state-of-the-art of VSC in UK ground improvement is reviewed in the above context, together with comments on future challenges.