Soil Modulus Research Articles

Research on the equivalent stiffness of bucket foundations for offshore wind power

Natural frequencies and foundation displacements are vital for the safe operation of offshore wind turbines because of their dependence on the equivalent stiffness of foundations. To investigate this dependency, a finite element method based on substructures is proposed for wide and shallow bucket foundations (aspect ratios of 0.25–1). The equivalent stiffness coefficient (ki) is defined to analyze the influences of the relative skirt flexibility, foundation size, and soil parameters on the equivalent stiffness. The results highlight the predominant impacts of the relative skirt flexibility and aspect ratio on the equivalent stiffness coefficients of bucket foundations. Conversely, certain factors, such as bucket diameter, skirt thickness, and soil modulus, have minimal influences on the equivalent stiffness coefficients. The significance of the Poisson's ratio of the soil is particularly notable, especially concerning the vertical stiffness coefficients. Based on finite element calculations, an empirical formula for bucket foundation equivalent stiffness is proposed and effectively utilized for predicting natural frequencies and evaluating foundation displacements.

Lignin-Improved Soil Research Progress

As a byproduct of biomass, lignin demonstrates significant potential and application value in the field of soil improvement. Historically, lignin has been utilized to enhance the strength, modulus, and water stability of soils, although its effects and mechanisms on various soil types, such as silt, require further investigation. Research indicates that the efficacy of lignin amendments is influenced by its source, type, and method of application, while environmental factors like soil moisture content, curing conditions, and curing duration also significantly affect the outcomes. Consequently, optimizing the use of lignin, exploring its micro-mechanisms of interaction with soil, and developing efficient lignin amendment strategies are crucial for future research. Additionally, the successful application in engineering projects demonstrates the practicality and eco-friendliness of lignin soil amendment technologies, offering new perspectives for the green and sustainable development of soil engineering.

Prediction of Damping Ratio and Shear Modulus of Saturated Clay Soil under Rotating Machine

Developing countries' industrial growth necessitates innovative machine foundation design and resilient infrastructure. Meanwhile, soil properties play a significant role in the satisfactory design of machine foundations. The paper presents an experimental work to determine accurately the damping ratio and shear modulus by equations. The paper studies the effect of different parameters (embedded depth of foundation, shape of footing, and changing operating frequency of machine) on the damping ratio and shear modulus of saturated clay soil. Moreover, mathematical expressions are derived from statistical analysis to predict the damping ratio for rectangular and circular footing on saturated clay. The physical model results reveal that the damping ratio inside the soil will be increased with an increase in the depth of the point inside the soil for all cases. The damping ratio tends to decrease with an increase in operating frequency. The maximum damping ratio has occurred below a rectangular foundation with a 16.6 Hz operating frequency in saturated clay. The damping ratio is a function of many factors, such as embedment depth, degree of saturation, shape of foundation, and operation frequency of the machine.

Research on correlation between dynamic resilient modulus and CBR of coarse-grained chlorine saline soil

A large area of coarse-grained saline soil is distributed in saline soil areas, and chlorine saline soil with a high salt content is a typical representative. The dynamic resilient modulus was accurately predicted using the California-bearing ratio (CBR) value to determine the relationship between the dynamic resilient modulus of coarse-grained chloride saline soil and its CBR value. Indoor dynamic triaxial tests and CBR tests were conducted to investigate the evolution of the dynamic resilient modulus (MR) and CBR of coarse-grained chlorine saline soil under the influence of the stress level, water content, and salt content. The test results showed that the dynamic resilient modulus increased with an increase in the confining pressure and bulk stress and decreased as the deviator stress increased; however, the CBR increased with an increase in the corresponding unit pressure. The higher the salt and water contents, the more obvious the influence of stress on the dynamic resilient modulus and CBR value. Under the same stress level, the decrease in the dynamic resilient modulus and CBR gradually increased with increasing salt and moisture content, and the effect of salt tended to be more significant than that of water. Based on the correlation between the dynamic resilient modulus and CBR revealed by the experiment, a more widely applicable model was selected from the existing theoretical models related to CBR for the regression analysis of the test data, and a prediction model of the dynamic resilient modulus based on the CBR value was proposed (MR = 21.06CBR0.52). This prediction model had a high correlation coefficient (R2 = 0.893) and could effectively predict the dynamic resilient modulus of coarse-grained chlorine saline soil using CBR values. The results provide a simple and reliable method for determining the design parameters of a coarse-grained saline soil subgrade.

Estimation of Model Parameters on Resilient Modulus of Coarse-grained Soils as Subgrades Using Geotechnical Properties

Estimation of Model Parameters on Resilient Modulus of Coarse-grained Soils as Subgrades Using Geotechnical Properties

Characterizing the dynamic resilient modulus of subgrade soil treated by BT-SAP subjected to freeze-thaw cycles

Freeze-thaw (FT) cycles are regarded as a damage effect to the dynamic resilient modulus (MR) of subgrade soil in seasonal frozen regions and improving the resistance on freeze-thaw cycles must be concerned urgently. For this purpose, the bentonite superabsorbent polymer (BT-SAP) was developed as an available admixture to relieve the attenuation of MR of subgrade soil under FT cycles. In order to evaluate the improvement of resistance on FT cycles, a series of dynamic triaxial tests were conducted after various FT cycles. The main influences on MR were investigated including the numbers of freeze-thaw cycles, BT-SAP contents, deviator stress and confining stress. The experimental results indicate that the BT-SAP can delay the attenuation trend of MR that means the resistance on freeze-thaw cycles have been promoted. The ensuing discoveries are that with the increment of BT-SAP content, the sensitivity of the subgrade soil to FT cycles is gradually reduced. Nevertheless, results reveal that a proper content of BT-SAP is recommended as 0.5%, where if the BT-SAP content exceeds 0.5%, the improvement effect of resistance on FT cycles decreases. Moreover, the improved effect caused by BT-SAP can produce a coupling enhancement combining with confining stress, and it also can offset the softening effect due to the deviator stress. For better application and practicability, the high-accuracy empirical model for predicting MR is established and validated. Finally, based on the soil freezing temperature, unfrozen moisture content and moisture distribution characteristics, the mechanism of BT-SAP reducing the freeze-thaw cycle sensitivity is analyzed. The conclusions mentioned above show that employing BT-SAP material is acceptable and significant to improve resistance on freeze-thaw of subgrade soil.

Mechanism and Application of Soilbags Filled with Excavated Soil in Soft Soil Subgrade Treatment

This research addresses the characteristics of soft soil subgrades treated by soilbags filled with excavated clayey soil. We evaluated of the strength and deformation modulus of soilbags containing excavated soil using unconfined compression tests. In addition, the drainage consolidation characteristics of soilbag-treated subgrades were investigated via model consolidation tests. Furthermore, a practical application included the construction of a 100 m-long rural road subgrade with these soilbags. The field test and numerical simulation results included the surface settlement and pore water pressure during and after construction to validate the effectiveness of the soilbag treatment for soft soil subgrade. The results show that the soilbags significantly enhanced both the strength and deformation modulus of the soft soil, which met the design requirements after the soilbag treatment. The drainage attributes of the soilbag treatment were also found to support the consolidation process of the soft soil subgrade effectively. Notably, the pore water pressure diminished rapidly during the construction interval, which is beneficial to reducing the post-construction settlement. The settlement uniformity of the subgrade is good verification of the superiority of the soilbag-treated subgrades.

Importance of higher modes for dynamic soil structure interaction of monopile‐supported offshore wind turbines

AbstractOffshore wind turbines (OWTs) have emerged as one of the most sustainable and renewable sources of energy. The size of OWTs has been increasing, which creates more challenges in the design of foundations due to the potential higher‐mode effects involved in the dynamic soil‐structure interaction (DSSI) response. Several foundation modeling techniques are available for calculating the OWT fundamental frequency; however, their capability to predict the higher modes by considering real geometric configurations is unclear. The main aim of this study is to perform a rigorous modal analysis of the NREL 5MW reference OWT to investigate the higher mode effects using the 3D finite element method. A detailed parametric analysis is also performed to study the effects of soil inhomogeneity, initial soil modulus, and the monopile dimensions (diameter, thickness, and embedded pile depth) on higher modes' natural frequencies and effective mass participation ratios. The study shows that dynamic soil‐structure interaction has a significant role in modal response and the simplified foundation models are not accurate enough. Given the significant contribution from higher modes, they should not be simply ignored in the OWT design, particularly in earthquake‐prone zones.

Emerging technologies and advanced analyses for non-invasive near-surface site characterization

The in-situ small-strain shear modulus of soil and rock materials is a parameter of paramount importance in geotechnical modeling. It can be derived from non-invasive geophysical surveys, which provide the possibility of testing the subsurface in its natural and undisturbed condition by inferring the velocity of propagation of shear waves. In addition, for soil dynamics and earthquake engineering applications, the small-strain damping ratio plays a relevant role, yet its estimation is still challenging, lacking consolidated approaches for its in-situ evaluation. Recent advancements in instrumentation, such as distributed acoustic sensing (DAS), combined with advanced analysis methodologies for the interpretation of seismic wave propagation (e.g., machine learning and full waveform inversion), open new frontiers in site characterization. This paper presents and compares some advanced applications of measuring 1D and 2D variations in shear wave velocity and attenuation in-situ with reference to a specific case history.

Mechanical response and numerical simulation of liquid soil abutment backfill

The application of a new liquid soil material and the treatment effect of backfilling an underpass tunnel in an airport are studied. The deformation and mechanical properties of liquid soil and conventional soil under load are comprehensively compared and analyzed via a numerical simulation with finite element software. The effects of the buried depth of overlying fill, tunnel height, and traffic load on the backfilling of liquid soil abutment are analyzed. The research results show that under the action of load, the overall deformation and stress distribution of the liquid soil and conventional soil show similar laws. However, liquid soil backfilling has great advantages over conventional soil backfilling in all aspects. Liquid soil backfilling can reduce the deformation and the compressive stress at the corner of the backfilling area by approximately 13% and 15%, respectively. The overburden buried depth has a great impact on the subgrade deformation. In the actual construction, the overburden buried depth should be 1.5 m. Overburden depth has a greater impact on the vertical deformation of the road, the self-weight of the overburden will act as an additional load on the overall roadbed, compared to conventional soil backfill, the overburden depth of 2.0 m conventional soil backfill overall deformation of the overburden depth is about equal to the overburden depth of 1.5 m liquid soil backfill, the use of liquid soil backfill is equivalent to the overburden fill to reduce the additional load of 0.5 m. The height of the box culvert has a greater impact on the stress, but this change is not linear, the actual construction in the case of meeting the specific requirements of use, should try to control in the vicinity of 8.4 m, and at the same time the use of liquid soil backfill can reduce the compressive stress of about 14%. The compressive stress increases first and then decreases with the increase in liquid soil modulus. The liquid soil modulus should be controlled to 180 MPa. Moreover, liquid soil backfilling can reduce the compressive stress in the backfilling area by approximately 25%. The trapezoidal slope of the backfill area is proportional to the deformation amount. Although an obvious correlation with compressive stress exists, the regularity is not strong. Thus, the trapezoidal slope should be set to 1:1 during construction. Traffic load slightly affects the overall deformation and compressive stress of the road. However, the distribution trend of deformation and stress changes obviously under the action of aircraft load. In the actual design, only one load form of aircraft load should be considered.

Effect of complex climatic and wheel load conditions on resilient modulus of unsaturated subgrade soil

Resilient modulus (Mr) is a fundamental mechanical property vital for assessing the resistance of pavement structures to cyclic vertical loads. It has played a pivotal role in pavement design and has been instrumental in predicting pavement responses and fatigue life. The Mr of subgrade soil is affected by a multitude of factors, including stress, moisture, and temperature conditions, all of which interact to define the response of the soil. This research investigated the effect of complex climatic conditions on Mr with a particular focus on areas experiencing significant seasonal changes in snowy cold regions like Hokkaido, Japan. Previous studies have proposed predictive models for Mr, incorporating the concept of matric suction, to account for moisture conditions. However, these models have rarely considered suction hysteresis in the soil–water characteristic curve (SWCC) or the effects of wheel loading on frost-susceptible subgrade soil during different seasons. In this study, a series of Mr tests were conducted on two types of subgrade soil under various climatic and wheel loading conditions. The test results promise to enhance our understanding of the complex interplay of climatic and stress conditions on Mr of standard sand and frost susceptible subgrade soil along different drying and wetting paths, particularly in regions with significant seasonal variations.

A new mathematical model for the estimation of shear modulus for unsaturated compacted soils

Small-strain shear modulus ( G) is an essential parameter for many geotechnical analyses. Most of shallow foundations are constructed in an unsaturated soil and the shear modulus of the unsaturated soil fluctuates because of the precipitation, evaporation, and rising of ground water table. In this paper, a new mathematical model is proposed for the estimation of the shear modulus function, Gunsat, which defines the relationship between small-strain modulus of unsaturated soil and matric suction. In the proposed model, the soil-water characteristic curve in the form of the degree of saturation is used as the input information. There are additional two parameters named n and C, which can be calibrated with the experimental data, are adopted in the proposed model. The estimated results show good agreement with the experimental data from literature. The proposed method can be used to track the tendency of Gunsat and minimize the data points from the laboratory tests.

Constrained modulus of fine-grained soils from in situ-based correlations and comparison with laboratory tests

The Constrained Modulus of soil is an important parameter to quantify compressibility of soils and calculate consolidation settlements, especially for clays. It is often expressed in terms of 1D constrained modulus, M or its inverse coefficient of volume change, mv. One method that has been suggested to assess M is from Cone Penetration Testing (CPTU) measurements through various correlations. Although, this is sometimes difficult, because of uncertainties regarding the appropriate stress, σ’v0, which are highly affected by the groundwater and bulk density γ, of soils. The usual method to measure M (or mv) is from oedometer tests in laboratory. Correlating in situ tests with laboratory tests results is crucial to increase the quality of soils strengths and stiffness information for design. However, most of the times it is a challenging process, which involves many uncertainties from different soils’ tests. This paper will look at comparison of CPTU derived M to oedometer tests taking into consideration various types of soils mostly from well-documented testbed sites where high quality in situ (CPTU for all sites and SDMT where available) and oedometer tests are carried out. The importance of CPTU measurements and site-specific correlations with laboratory tests to establish unique soil type coefficients for use in equations to derive CPTU-based M will be highlighted.

Resilient moduli characterization of cement-treated silt

The performance of a flexible pavement depends on the resilient modulus (MR) of subgrade soil. Thus, MR is a key design parameter for mechanistic-empirical pavement design of flexible pavements. Generally, the resilient modulus is determined by conducting repeated load triaxial (RLT) tests in the laboratory and has been used to characterize the subgrade soil behavior under repeated traffic loading conditions. The use of cement to stabilize natural subgrade soils is widely accepted by transportation agencies. Several research studies were conducted on the resilient behavior of cementtreated soils. However, limited research studies have been conducted on the resilient behavior of cement-treated silty soil. Therefore, the current research study assessed the resilient moduli properties of cement-treated silt. Cement-stabilized soil specimens were statically compacted and cured in a humid room for a stipulated curing period before conducting RLT tests. RLT tests were conducted on cement-treated specimens at different cement dosages and curing periods to study the effect of the cement dosage and curing time on the resilient modulus. Test results indicated that a significant improvement in performance was observed after cement treatment. The untreated soil specimens exhibited stresssoftening behavior with an increase in deviator stress, whereas the cement-treated specimens exhibited stress-hardening behavior. The resilient modulus was increased with an increase in cement dosage. Regression analyses were conducted on RLT test results using three-parameter universal model and model parameters were determined. It was observed that the three-parameter universal model exhibited an excellent fit with experimental data.

Temperature-dependent elastic shear modulus of a saturated lateritic clay

The thermo-mechanical behaviour of saturated clays and sands has been studied by many researchers, considering that it is useful in many geotechnical problems, such as the analysis of energy foundations and the effects of climate change on earth structures. Despite the fact that temperature is known to affect the yielding and volume change behaviour of soils, the effects of temperature on the elastic shear modulus (G0) of soils are rarely studied. In this study, a temperaturecontrolled oedometer equipped with bender elements was developed. It was used to investigate the effects of temperature on G0 of a compacted lateritic clay at saturated conditions. The G0 was measured at 5 and 40°C during loading and unloading in the stress range of 30 to 400 kPa. Four tests were conducted in which two different initial densities (95% and 85% of maximum dry density (MDD) were considered. The results will be interpreted and discussed with reference to the elastoplastic modelling of thermo-mechanical soil behaviour.

Relation between liquefaction resistance and shear modulus of crushable volcanic soils

Pumice-rich soils originating from volcanic eruptions are deposited in various parts of the world, such as in the central region of North Island, NZ. The pumice sand components of these natural pumiceous (NP) soils are known to be crushable and lightweight, resulting in a significant difference in their cyclic resistance ratio (CRR) and small-strain shear modulus (Gmax) when compared to hard-grained (quartz) sands. In this paper, the results of a number of cyclic triaxial and bender element tests performed on reconstituted specimens of three types of NP sands having different pumice contents (PC), as well as on quartz-type Toyoura sand specimens, are discussed. Then, the concept of modified cyclic yield strain, εay,m, which relates the CRR of the specimen to its Gmax, is used. The results indicate that εay,m appears to be dependent only on the soil type, and independent of the confining pressure applied and the relative density of the specimen. All NP sand specimens show higher εay,m when compared to Toyoura sand because of their higher CRR and lower Gmax, with values of εay,m increasing as the PC of the specimen increases. Based on the results obtained, an empirical chart is developed to estimate the CRR of NP sands from their shear wave velocity (Vs) values under field conditions.

Calibration and limitations of a fixed-partly fixed resonant column apparatus

The small-strain shear modulus of soils and rocks is an important input parameter in geotechnical analyses. Its estimation using the resonant column apparatus relies on accurate knowledge of the rotational inertia of the apparatus’s active end. Due to the complex geometry of the active end, its inertia is typically found from a calibration exercise. In this study a range of aluminium calibration bars and steel masses were used to compare two different calibration exercises presented in the literature. The resulting values of active end inertia are shown to be highly method-dependent. The method of compensating for the drive connection stiffness by finding the apparatus resonant frequency is found to introduce errors at low stiffness. The combined use of calibration bars and masses reduces scatter but yields poor results for stiff bars. An alternative approach to mitigate both of these problems is suggested. Active end inertia is found to be constant using this alternative approach. While effects of base inertia and reaction mass inertia are found to be small for this apparatus, compliance of the drive system is shown to significantly reduce resonant frequencies at high stiffnesses which increases the apparent active end inertia. This reduction in resonant frequency is modelled and used to derive frequency correction factors, which reduce errors in shear modulus to within acceptable limits when using the constant value of active end inertia. This demonstrates the potential for increasing the limit of sample stiffness where sufficient calibration data are available.

Improved correlation of soil modulus with SPT N values

Improved correlation of soil modulus with SPT <i>N</i> values

One‐Dimensional‐Convolutional Neural Network (1D‐CNN) Based Reliability Analysis of Foundation Over Cavity Incorporating the Effect of Simulated Noise

This paper presents a thorough reliability assessment of cavity foundation systems involving the generation of 272 datasets using Plaxis 2D automation. The parameters were systematically varied across feasible ranges, and Sobol‐based sensitivity analysis identified the negligible influence of the soil modulus of elasticity (E) on subsequent reliability analyses. A robust 1D‐CNN surrogate model was developed to predict the critical foundation responses by integrating Gaussian white noise to simulate real‐world uncertainties. A log transformation with 1,000 bootstrap samples was chosen for resampling non‐normally distributed data. This study employed a novel approach utilising 1D‐CNN regressor models for bearing capacity (BC) prediction, achieving promising results with R2 values of 0.953 and 0.945 for BC in the training and testing phases, respectively. Bootstrapping resampling facilitates reliability analysis preparation and ensures robustness in handling complex data. Simulated noise varied with specific variance (p) from 0.01 to 0.5, allowing the examination of model efficacy under varying noise levels. Both the Monte Carlo Simulation (MCS) and first‐order reliability method (FORM) were employed, revealing a reliability index (β) of 2.046 for FORM and 2.066 for MCS. This indicates a 0.976% increase in β and a 75% increase in the probability of failure transitioning from FORM to MCS, underscoring the model’s sensitivity to analytical methods.

Influence of fibres on the resilient modulus and expansion of clayey subgrade soils

ABSTRACT Expansive clayey soils at the subgrade level of roads and highways in different cities can affect the performance and durability of pavements. This increases the need for maintenance and conservation work, leading to higher operating costs. Traditionally, clayey soils are stabilised by adding lime or cement. However, the handling and use of these materials are restricted in some Latin American countries due to illegal drug production, and obtaining high-quality materials from distant sources can be impractical. The goal of this study is to determine the effectiveness of incorporating fibres in improving the performance of expansive clayey subgrade soils. To achieve this goal, resilient modulus tests and measurements of compacted soil expansion were performed. Two types of fibres were selected for this study: natural Ichu fibre, which is common in the Peruvian Andes, and polypropylene fibre. The soil used was a high-plasticity clay from the city of Pucallpa, to which varying percentages of fibres were incorporated (0.25%, 0.5% and 1%). The samples were prepared with a gyratory compactor to achieve their maximum dry density as obtained with the standard compaction effort. The results indicated that the incorporation of fibres improved the value of the resilient modulus while significantly reducing soil swelling.