Settlement Calculation Research Articles

Pile-Soil Stress Ratio and Settlement of Composite Foundation Bidirectionally Reinforced by Piles and Geosynthetics under Embankment Load

The settlement calculation of composite foundation bidirectionally reinforced by piles and geosynthetics is always a difficult problem. The key to its accuracy lies in the determination of pile-soil stress ratio. Based on the theory of double parameters of the elastic foundation plate, the horizontal geosynthetics of composite foundation are regarded as the elastic thin plate, and the vertical piles and surrounding soil are regarded as a series of springs with different stiffness. The deflection equation of horizontal geosynthetics considering its bending and pulling action is obtained according to the static equilibrium conditions. The equation is solved by using Bessel function of complex variable, and the corresponding deflection function of horizontal geosynthetics is deduced. Then, the calculation formula of pile-soil stress ratio and settlement of composite foundation is derived by considering the deformation coordination of pile and soil. The results of engineering case analysis show that the theoretical calculation results are in good agreement with the measured values, which indicates that the proposed method is feasible and the calculation accuracy is good. Finally, the influence of composite modulus of horizontal geosynthetics, tensile force of geosynthetics, and pile-soil stiffness ratio on pile-soil stress ratio and settlement is further analyzed. The results show that the pile-soil stress ratio increases with the increase of the composite modulus of the horizontal geosynthetics, the tensile force of geosynthetics, and the pile-soil stiffness ratio, and the settlement decreases with the increase of the composite modulus of the horizontal geosynthetics, the tensile force of geosynthetics, and the pile-soil stiffness ratio. When the flexural stiffness of the horizontal geosynthetics is small, the influence of the tensile action of the geosynthetics on the pile-soil stress ratio and settlement of the composite foundation cannot be ignored.

City planning of Hermanninranta – A combination of geotechnics, contamination, and climate change

The Hermanninranta area presents one of the most geotechnically challenging urban planning areas in the City of Helsinki. The area located on the shore of Vanhankaupunginlahti (Old City Bay) is approx. 50 ha in size. Most of the area is reclaimed from the sea and only Kyläsaari island is a natural formation. Land reclamation in the area was performed in various stages between the 1840s to the 1980s. Natural very soft clay layers encountered in the area extend to a depth of over 40 m below ground surface. Today, the proximity to the city centre makes Hermanninranta very attractive for residential and commercial construction. Thick fill containing contaminated soil, slag and ash on top of soft deep clay, are a challenging combination. Variable fills have caused the settlement of soft clays and the displacement of the embankment towards the bay. Changing current land use for residential purposes will require changing of current ground surface elevation to approximately 2 to 2,5 m upward. This will be an issue impacting geotechnical engineering. Rising sea level caused by global warming shall also be considered. Settlement calculations show that within the next hundred years almost half of the area will be under water in case of no pile slab or soil improvement. The draft city plan has been updated based on these geotechnical, environmental and climate change studies.

Consolidation settlement calculation and examination of the foundation settlements with finite elements method, example of Batman city Gültepe bridge

In this study, geological and geotechnical studies were carried out on the soil of a bridge built in 2015 in the Gültepe District of Batman City, located in southeastern Turkey, to perform the foundation settlement calculation. For this purpose, four foundation boreholes were drilled to determine the engineering parameters of the soil, and triaxial pressure and consolidation tests were carried out on the obtained samples. The consolidation settlement calculation was made in accordance with these parameters. Using the same data, numerical analysis was performed with PLAXIS V.8.2 (Finite Element Code for Soil and Rock Analyses), a two-dimensional finite element package program. The consolidation settlement value was calculated by performing dynamic analysis based on time in the computer software. The settlement value was determined to be 1.70 cm after the analysis, and it was evaluated by correlating with the consolidation settlement analysis results made according to Bowles (1988). Consolidation settlement calculations and finite element package program analyses gave similar results. We observed liquefaction risk and settlements in the structures with shallow foundations in the residential zone near the study area since the soils in the study area consist of silty sand of 5-10 meters and have groundwater. The Bored Pile technique, which is one of the soil improvement methods, was applied and discussed in order to determine the geological problems in the study field.

Improving the pressuremeter approach for settlement calculation under high-speed railway embankments

Consolidation settlement under embankment is often calculated using the oedometric approach. However, engineers tend to conduct these calculations in clays based on in situ test results including the pressuremeter measurements. The pressuremeter method is based on Menard's rheological coefficient, enabling to shift from the pressuremeter modulus to the oedometric one. This relationship has demonstrated some prominent success when estimating consolidation settlements within a defined stress domain. This paper addresses improvements in this method for settlement calculation in overconsolidated terrain. For this purpose, the authors suggest two expressions for the rheological coefficient based on back-calculation together with a linear and nonlinear multiple regression. The results indicate that using the rheological coefficients proposed in this study gives settlements approximating the measured ones compared to the rheological coefficients reported in the literature. The authors have also established an adjusting coefficient to be introduced as part of the common pressuremeter settlement expression for approximating the measured values on-site.

Effect of Grouting Reinforcement on Settlement of Existing Tunnels: Case Study of a New Crossing Underpass

In the construction of the new shield tunnels crossing existing tunnels, grouting rings are often installed in the existing tunnels for protection. To study the effect of grouting rings on the settlement of existing tunnels, the variations of soil properties and relevant parameters before and after the grouting are analyzed. By considering the effect of the grouting ring on the reduction of the stress and the reinforcement of the surrounding foundation soil, the stress reduction model of the heterogeneous soil layer and the model of the tunnel settlement calculation are proposed. The formula for the reduction of the stress after passing through the grouting ring is deduced. Moreover, by comprehensively taking the influences of the shield excavation and grouting ring into account, the formula for calculating the vertical displacement of the existing tunnel caused by the excavation of the new tunnel is derived. Further, the impacts of the length and the thickness of the grouting ring on the settlement of the existing tunnel are studied. The results of the theoretical calculation method proposed herein are well consistent with the data computed by the finite element model, and both follow a relatively similar change trend. According to the obtained results, installing the grouting ring on the existing tunnel can effectively reduce the tunnel settlement. Finally, the results demonstrate that increasing the length and the thickness of the grouting ring can strengthen the protection of the existing tunnel, but the effect gradually decreases.

A Theoretical Calculation Method of Ground Settlement Based on a Groundwater Seepage and Drainage Model in Tunnel Engineering

Seepage is ubiquitous during tunneling in areas with high groundwater tables. The ground settlement trough on a single tunnel is well described by Peck’s formula, but it cannot reflect the settlement caused by seepage. In this paper, assuming that the groundwater inside and outside the tunnel is a one-dimensional steady-state seepage condition, the groundwater seepage and drainage model of the tunnel was established. Based on the model and the principle of groundwater dynamics, the seepage flow calculation formula was derived, and the dewatering funnel curve equation of the groundwater level surface of a tunnel aquifer was obtained. A case study of a tunnel project in Gansu Province was carried out, and the influence of seepage on the effective stress of the stratum around the tunnel and the calculation of ground settlement caused by seepage were analyzed. The results show that seepage makes the effective stress of the upper soil layer of the tunnel increase, which leads to an increase in ground deformation; when the groundwater level of the tunnel is greatly lowered, the seepage has a significant influence on the vertical deformation of the stratum.

Calculation of Shallow Foundation Settlement Taking into Account Lateral Expansion of Soil

Nowadays the prediction of the settlement of shallow foundation is almost carried out by using the result of the oedometer test, in which the lateral expansion of soil mass is excluded. Geotechnical engineering software, such as Plaxis, Geostudio, Flac, Midas-GTS-NX, etc, are capable of solving most geotechnical problems, taking into account the lateral expansion of soil mass. The comparison between the result procured when using the classically analytical method and the result obtained with the help of the geotechnical engineering software show us an enormous divergence. It can be explained by the difference in approaches of solving the question between numerical method and analytical method, in which the effect of lateral expansion of soil mass is neglected. Therefore, the authors suggest a method to improve the prediction of settlement basing on the studies of Russian scientists in the 1960s, taking into account the effect of lateral expansion of soil mass below the shallow foundation. The result of the article can be considered to predict the long-term, short-term settlement as well as the settlement at any moment of soil consolidation with the acceptable difference when comparing with the results given from the nowaday geotechnical engineering software.

Research on creep characteristics of sand with different fine content

The storage yard in port terminal project is generally is formed by backfilling. If the backfill contains high content of fine particle, on the one hand, it will cause difficulty in foundation treatment, on the other hand, excessive settlement will occur during the operation period, which will affecting the normal operation of the project. In this paper, through experimental research on the creep settlement of sandy soils with different fine content, the relevant parameters of sandy soils with different fine-grained contents and different types of finegrained soils are obtained, and through the analysis and fitting of commonly used rheological element models, the settlement calculation parameters of sandy soil with different fine contents are obtained.

A practical method of calculation of bearing capacity and settlement of large- diameter post-grouting piles

A practical method of calculation of bearing capacity and settlement of large- diameter post-grouting piles

Settlement prediction for footings based on stress history from V-S measurements

A settlement prediction method based on shear wave velocity measurements and soil nonlinearity was recently developed and verified by means of centrifuge tests. However, the method was only applicable to heavily overconsolidated soil deposits under enlarged yield surfaces. In this study, the settlement evaluation method was refined to consider the stress history of the sublayer, based on an overconsolidation ratio evaluation technique, and thereby incorporate irrecoverable plastic deformation in the settlement calculation. A relationship between the small-strain shear modulus and overconsolidation ratio, which can be determined from laboratory tests, was adopted to describe the stress history of the subsurface. Based on the overconsolidation ratio determined, the value of an empirical coefficient that reflects the effect of plastic deformation over the elastic region is determined by comparing the overconsolidation ratio with the stress increment transmitted by the surface design load. The refined method that incorporate this empirical coefficient was successfully validated by means of centrifuge tests, even under normally consolidated loading conditions.

An Improved Nonlinear Settlement Calculation Method for Soft Clay considering Structural Characteristics

The settlement calculation model for soft clay foundation is established based on Hooke’s law and the Duncan-Chang model. By introducing the concept of damage ratio, the method for determining the deformation modulus of soil before and after damage under load is presented, and a nonlinear settlement calculation method which considers the structural characteristics of soft clay is proposed. In the end, a practical engineering example is analyzed with the proposed method and some current methods for soft clay settlement calculation. The results indicated that the proposed method is feasible and applicable in practical engineering.

The Weight of Cities: Urbanization Effects on Earth's Subsurface

AbstractAcross the world, people increasingly choose to live in cities. By 2050, 70% of Earth's population will live in large urban areas. Upon considering a large city, questions arise such as, how much does that weigh? What are its effects on the landscape? Does it cause measurable subsidence? Here I calculate the weight of San Francisco Bay region urbanization, where 7.75 million people live at, or near the coast. It is difficult to account for everything that is in a city. I assume that most of the weight is buildings and their contents, which allows the use of base outline and height data to approximate their mass, which is cumulatively 1.6·1012 kg. I build a series of finite element models to study effects of pressure exerted by the weight distribution. Within the elastic realm, I look at compression, flexure, isostatic compensation, stress change, dilatation, and fluid flow changes. Within the nonlinear realm I show example calculations of primary and secondary settlement of soils under load. The combined modeled subsidence from building loads is at least 5–80 mm, with the largest contributions coming from nonlinear settlement and creep in soils. A general result is closing of pore space and redirection of pore fluids. While the calculated subsidence of the Bay Area is relatively small compared with other sources of elevation change such as pumping and recharge of aquifers, all sources of subsidence are concerning given an expected 200–300 mm sea level rise at San Francisco by the year 2050.

Calculation model of overburden subsidence in mined-out area based on Brillouin optical time-domain reflectometer technology

With the increase of the coal consumption, the gob scale has become significantly large, increasing the risk of subsidence. Using Brillouin optical time-domain reflectometer (BOTDR) technology, this paper studied the deformation and failure state of overburden above the gob. An overburden subsidence calculation model considering rock mechanical parameters based on the BOTDR was established. In addition, the influence of damage distribution parameters and rock particle contact parameters on the subsidence calculation model was discussed, and the spatial and temporal distribution rule of overburden subsidence was obtained. Taking Zhang Huaizhu working face in Zhangzhuang Coal Mine as an example, this paper verified the accuracy of the subsidence calculation model. The research results show that: The damage distribution parameters have little effect on the overburden subsidence calculation model. The subsidence maximum change caused by the tangential inclination of the particle contact surface in the bulking zone is 0.016 times the height of the bulking zone, while the subsidence maximum change caused by the friction coefficient is 0.046 times the height of the bulking zone. The overburden subsidence of Zhangzhuang Coal Mine has gradually been stabilized after deforming for one and a half year. The ground subsidence in the gob has a negative exponential relationship with time during research period. Compared the result of the subsidence calculation model proposed in this paper with the field monitoring value, it was found that the ground subsidence tendencies are basically the same, and the relative error is less than 8%. It indicates that the subsidence calculation model is reliable in calculating the overburden subsidence in the gob.

Engineering Properties of Norwegian Peat for Calculation of Settlements

Engineering Properties of Norwegian Peat for Calculation of Settlements

Improved approach of super-long pile group considering multiple interaction under axial load

This work presents an improved approach to consider the effect of any intermediate piles between the two piles in pile groups. Based on the thin ring shear model of concentric cylinder and elastic theory, a multi-pile analysis model under axial load is proposed with full consideration of the mutual reinforcing effect between super-long piles. A theoretical derivation of interaction coefficient and the deformation of super-long pile groups which simultaneously consider the reinforcing effect and the existence of other piles in pile groups was carried out. Example analysis shows that the analytical solution agrees well with the experimental results. In this work, the error between the calculated result of the presented model and the measured value is 25% less than that in the traditional model. The multi-pile model fully analyzes the interaction mode between multiple piles and considers the mutual reinforcing effect among the piles, which makes up for the deficiency in traditional settlement calculation of pile groups. Consequently, the model proposed can accurately reflect the working characteristics of super-long pile groups in actual engineering.

Load-displacement behaviour of tapered piles: Theoretical modelling and analysis

This paper presents a simplified analytical approach for evaluating the load-displacement response of single tapered pile and pile groups under static axial compressive loads. The response of the tapered pile shaft is considered elastically in the initial stage, whereas the increase in stresses due to slippage along the pile-soil interface is obtained from a developed undrained cylindrical cavity expansion solution based on the K0-based anisotropic modified Cam-clay (K0-AMCC) model. An effective iterative computer program is developed to calculate the load-displacement behaviour of a single tapered pile. Regarding the response analysis of tapered pile groups, a finite-difference method is employed to calculate the interaction between tapered pile shaft, and the linear elastic model to simulate the interaction developed at the pile base. A reduction coefficient is introduced into the analysis of pile shaft interaction to clarify the reinforcing effect between tapered piles. Therefore, the settlement calculation methods of pile groups are proposed for different pile cap stiffness. The calculation methods of single tapered pile and pile groups are validated using two 3D Finite Element (FE) programs, and the comparison results show that reasonable predictions can be made using the method proposed in this paper. Parametric studies are conducted to investigate the effects of taper angle, soil anisotropy, pile spacing, and pile number on the load-displacement behaviour of single tapered pile and tapered pile groups.

Analysis of deformation characteristics of layered ground under uniform load

For the layered ground in a large area, the deformation under uniform load is analyzed numerically. Considering the work property of the concrete plane, the uneven settlement is strictly restrained using different foundation. In the process of settlement calculation, according to the linear interpolation of multiple borehole elevations, the geological profiles with different soil layer thickness are formed, and the influence of compressed soil layer thickness on the total settlement and uneven settlement is fully considered.

Stochastic method for prediction of subsidence due to the underground coal mining integrated with GIS, a case study in Serbia

The problem of subsidence and damages on buildings above mining works is an inevitable consequence of underground coal mining in large mining basins. Significant development of various methods for prediction of the displacement parameters of the undermined terrain took place in the period from the middle of the last to the beginning of this century. In this paper, a new mathematical model of the stochastic Pataric-Stojanovic method for the predictive subsidence calculation is developed. A case study, as an example for the practical application of the proposed stochastic method, is given for the underground coal mine “Rembas”- Resavica, Serbia. An original MITSOUKO program package, supported by spatial analyses in the Geographic Information System (GIS), was developed for the predictive subsidence calculation based on the stochastic method proposed by the authors Pataric and Stojanovic. The comparative analysis of predicted and measured subsidence values confirms the possibility of using this stochastic method for predictive subsidence calculation in practice, which is a necessity of modern mining.

PERANCANGAN EFEKTIVITAS PERBAIKAN TANAH DENGAN MENGGUNAKAN METODE PREFABRICATED VERTICAL DRAIN

As a country that surrounded by active volcanoes, Indonesia has a very diverse clay soil content. However, in reality, clay soil is an unfavorable condition for construction activities because of its low-level of stability. Therefore, when the clay soil receives a static load on it, the soil will slowly have a settlement due to the dissipation of pore water. This settlement usually occurs over a very long period of time, thus, it is necessary to do the soil improvement using Prefabricated Vertical Drain (PVD) combined with preloading in order to shorten the time of soil consolidation so that the consolidation process becomes faster. Soil settlement analysis is calculated using two soil parameters derived from the NSPT correlation data and laboratory test data to determine the most efficient soil parameters. Furthermore, a theoretical soil improvement analysis was carried out by comparing Baron's theory and Hansbo's theory and using the Settle3D analysis program. The analysis results show that the calculation of consolidation settlement using soil parameters from laboratory test results has the closest value to the actual results in the field with a efficiency of 91%. Meanwhile, for soil improvement, the most effective PVD design was chosen using the Hansbo theory with a triangular installation pattern and a spacing of 150 cm combined with a gradual embankment.

Probabilistic Settlement Analysis of Strip Footing on Spatially Random Soil

The prediction of settlement in a traditional design approach usually uses a deterministic value of modulus of elasticity (E), which is estimated as an average value by testing the soil at selected locations. However, these deterministic properties of soil may not represent the actual properties of soil and site condition. Due to numerous sources of uncertainty, the properties of soil mass are spatially varying and anisotropic in the natural field condition. In this study, a random finite element method (RFEM) is used to evaluate the reliability of settlement of the strip footing on spatially random soil. Modulus of elasticity is the only considered random parameter. For this purpose, 2000 spatially random realizations of E-field are generated using Monte Carlo Simulation. Each of these realizations of heterogeneous soil profile is passed to FEM to analyze the settlement of footing. The final settlement results measured in all these realizations are then statistically evaluated and compared. The results of analysis show that the mean and standard deviation of the footing settlement are increased with increasing spatial correlation length. The large value of isotropic correlation length led to an increase in the mean settlement value by more than 25% as compared with the deterministic settlement calculations. Also, it is concluded that the rate of increase of settlements for anisotropic correlation length is lower than the one under isotropic condition.