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Design of heavily loaded foundations for tall buildings requires a realistic assessment of the design parameters. A comprehensive geotechnical investigation and in situ tests such as static cone penetrometer tests, pressure meter tests, and cross-hole seismic tests in addition to deep boreholes can provide the inputs for selection of the design pro...
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... may be used to transfer the loads to the piles with the intervening soils below the raft also contributing to the load transfer (see Fig. 3). As a result, it has potential costsaving and better control of differential settlement (Amornfa, et al, 2012) [13]. The contribution of the intervening soils could be substantial in stiff to hard clays and medium dense to dense sands. However, it may not be significant where the soils immediately below the raft are loose sands prone ...
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... Subsequently, the estimated effective shear modulus is used in the pseudo-static analysis of the combined system to obtain pile and soil stiffness using a continuum-based geotechnical model. The soil input parameters presented in Fig. 3 are of the Indo-Gangetic plains of India [7,65,67]. The soil input parameters as shown in Table 3 and Fig. 3 are obtained from the field investigation and laboratory testing [57,65]. ...
Due to the fast growth of the nuclear-powered industry, nuclear power plants (NPP) are being planned on soil sites, especially in active seismic zones. In such cases, a combined pile-raft foundation (CPRF) is considered a preferred choice for designers to support massive and stiff nuclear structures. As such, no study has been stated on the seismic design approach for NPP supported on the CPRF system. In the present study, an interactive iterative practical seismic design approach is proposed to estimate the dynamic response of a NPP resting on the CPRF considering continuum-based geotechnical and spring-supported structural models. The pseudo-static response of the continuum-based model is used to determine the soil-pile system stiffness for subsequent seismic analysis in a spring-supported structural model. A step-by-step algorithm is proposed to arrive at the final converged state of the combined system through an iterative procedure. A reasonably good agreement is achieved between the outcomes obtained from the suggested approach and the results of the experimental testing. The proposed approach is subsequently implemented on a typical NPP structure, and a good match is obtained with the results of the coupled time domain direct analysis, thus showing the reliability and practical applicability of the suggested approach. The suggested procedure can be used for the seismic analysis of NPP structures supported by the CPRF system.
... In terms of geotechnical engineering, alluvial soils, considered problematic and extensively studied by numerous researchers, exhibit distinct behavioral characteristics including weak bearing capacity, high void ratio, and low shear strength [1], [2]. In regions where weak soil layers such as alluvial soils, which are considered geological formations not yet fully formed, are present, there has been an increasing inclination towards deep foundations in planned constructions to ensure structural safety [3], [4], [5]. Pile foundations, which are a type of deep foundation, provide the opportunity for safe designs by transferring the superstructure load to soil layers with high bearing capacity, both under dynamic and static loads, thereby offering support to the superstructure [6]. ...
Alluvial soils are weak soils require precautions, which have disadvantageous engineering characteristics such as low shear strength and bearing capacity, high void ratio and settlement potential. Different foundation systems are preferred for structures built on these soils to transfer the load effects safely. Pile foundations as a deep foundation is classified depending on various parameters such as; material property, application method, load-bearing method. In this study, cylindrical and square concrete piles with different cross-sections and lateral areas placed in the alluvial soil. The natural alluvial soil taken from İzmir province, Balatcik location was placed in displacement-controlled pile model unit with a unit weight of ≈ 17 kN/m3. The manufactured concrete piles were driven into soil with Standard Proctor hammer. Tensile effects were applied at different time intervals to examine long-term and short-term behavior. As result of experiments, load-displacement (p-y) and displacement-time (y-t) graphs were drawn. When the displacement piles were examined under long-term tension, it was seen that the cylindrical piles displaced most. Square piles with same cross-sectional area with cylindrical piles made less displacement. All studies were modeled 1:1 as numerical and compared with experimental results. Studies showed that the experimental and numerical results for pile behavior were compatible.
The electric cone penetration test with pore water pressure measurement using piezocone, abbreviated as eCPTu or CPTu, is gaining popularity in India since the last 5–6 years. The geotechnical investigation activity in the country is now on the path to match up with international practices, and CPTu is one major step in this direction. An effective tool for site characterization, CPTu is being used to obtain various geotechnical parameters with high degree of reliability. The test lends economy in time and cost of investigation, and allows reliable in situ site characterization for robust geotechnical design and foundation optimization. The paper presents the authors’ experience with use of this technology as a useful tool for geotechnical investigation and site characterization. Four case studies are illustrated to demonstrate the use of the tests and the correlations that can be developed. In all the four projects, substantial savings was achieved in foundation costs by use of higher SBC values, higher pile capacities and elimination of need for ground improvement.
There has been a rapid development of the nuclear industry on account of climatic change caused by global warming. The most favorable rocky sites for nuclear power plants are exhausted worldwide, and now nuclear facilities are proposed on soil sites. In a soil site, a combined piled raft foundation (CPRF) system can provide the desired level of performance for a nuclear structure under seismic loading conditions. The combined system of the nuclear structure with the CPRF involves complex dynamic interactions between the pile, soil, raft, and the superstructure. In the existing literature, the dynamic behavior of the CPRF system supporting massive and stiff structures is not well studied and investigated. Due to the highly nonlinear dynamic characteristic of the CPRF system supporting massive and stiff reactor buildings, this paper adopts interface nonlinearities (separation and sliding) through the master and slave concept, concrete and reinforcement material nonlinearities through the concrete damage plasticity model for piles and superstructures, and an equivalent linear approach considering soil degradation and damping with Mohr–Coulomb post yielding hardening behavior for the soil. After the successful validation of the modeling approach with the results of the experimental testing, the different aspects of the CPRF of reactor building are investigated, such as amplification, pile and raft behavior, pile–raft coefficient, separation and sliding, contact pressure, nonlinearity in the piles, and the response of the superstructure. This study indicates that the peripheral piles of the CPRF system could prevent the separation of the raft from the soil. The numerical result shows that damage in the CPRF system occurs near the top portion of the pile. The presented procedure to develop the combined model for the seismic analysis in the time domain could help to formulate guidelines for safety-related nuclear structures resting on the CPRF system.
Raft foundation for a 35-storeyed residential tower in Noida bearing on alluvial soils was analyzed using PLAXIS 3D software to assess the pressures and settlement at foundation level. To develop realistic geotechnical parameters to input into the finite element model, the borehole data were supplemented with in-situ pressuremeter tests and cross-hole shear tests. Using the updated soil parameters, the soil–structure interaction analysis justified the use of raft foundation without the need for piles.
Alluvial soils can be defined as sediments that have not completed their geological formation have high void ratios, low bearing capacity, and low shear strength. To eliminate the unfavorable properties, various improvement methods can be applied, such as injection, compaction, and mixing. Polypropylene fibers, a kind of geosynthetic, are used to improve the geotechnical properties of soil. In this study, the shear strength characteristics of natural and polypropylene-reinforced alluvial soils were investigated. Firstly, the index properties were examined, the materials were classified, and an idealized soil profile was constituted. Afterward, direct shear experiments were conducted with loose and dense prepared, natural, and 0.5% and 1% polypropylene fiber–reinforced alluvial soils. To investigate the effect of density on shear strength, loose and dense samples were prepared at their liquid limits. The direct shear, test results showed that the dense prepared natural and polypropylene-reinforced samples had higher internal friction angles than did the loose samples. The density had a greater effect on the friction angles of the natural samples than the reinforced ones. The polypropylene fibers were prolonged at the predefined shear surface and increased the internal friction angle and shear resistance. The test results indicated that polypropylene fiber had a larger effect on the internal friction angle of coarse-grained (SC and SM-SC) alluvial soils. When the effect of PP fiber content on the internal friction angle of coarse-grained samples was examined, it was observed that 0.5% PP fiber additive caused a more significant increase than 1% PP fiber additive.
Recently, few nuclear facilities have been proposed on soil sites worldwide. Controlling the overall and differential settlement is a difficult task for a nuclear structure that rests on a soil site. Under these circumstances, a combined piled-raft foundation (CPRF) provides the required level of performance with a significant cost saving compared with a pile foundation. The combined system involves complexities in the interactions between the soil-pile-raft and superstructure system. The literature focuses on simulating the interactions between pile, soil, and raft. Until recently, the behavior of a CPRF that supported a heavy and massive structure had not been well studied and understood. A combined three-dimensional (3D) model of soil-pile-raft-superstructure systems will be developed in this study that considers the soil and interface nonlinearity along with the complex superstructure geometry. The modeling approach for the piled raft system will be validated using the standard benchmark problem and field case histories. Various aspects of a CPRF for a typical nuclear building (NB) will be investigated, such as the effect of the depth of soil medium, comparison of the behavior of the raft foundation, pile foundation, and CPRF, contact pressure distribution, pile behavior, soil behavior; and various performance indicators. The presented systematic procedure to configure the CPRF system could be useful in similar practical applications. This study indicated that the stiffening of the superstructure and sequential construction has a beneficial effect on the combined system. The findings of this study could be useful to frame the general guidelines for the economical design of CPRF systems.
