Longer Piles Research Articles

The effectiveness of using the bearing capacity of piles in the formation of the pile field of the slab pile foundation of a 21-storey apartment building

This article is aimed at studying methods for optimizing the pile field in order to ensure the greatest use of the bearing capacity of piles, adopted in the project, considering the most unfavorable design combinations of forces. The object of the study is a multi-storey apartment building on a slab-pile foundation with a regular grid of piles, which clearly shows the imperfection of the calculation methods, due to the incomplete use of the bearing capacity of a significant number of piles, but the methods described in the article are also applicable to other buildings on slab-pile foundations, especially the difference between the original scheme and the optimized scheme will be clearly visible on the example with longer piles in less bearing soils, spread over the entire depth of the foundation. The purpose of this study is to study methods for optimizing a pile field, to study the methodology for using these methods on a specific example and compare them in terms of the parameters of using the bearing capacity of piles: the absolute and relative value of the minimum load on the pile, the absolute and relative value of the maximum load on the pile, the absolute and relative value average load per pile, as well as their comparison of economic efficiency. In the course of the article, numerical modeling was used, using the finite element method and analysis of the results of multivariate calculation. The result of this article is the application of pile field optimization methods to the multi-storey building on a slab-pile foundation, the evaluation of each of the methods and their comparison according to these indicators, as well as an understanding of the further development of this topic.

Improved Performance of Raft Foundation Using Detached Pile Columns in Loose Subsoil Conditions

Piles act as settlement reducers in case of connected piled‐raft foundation and hence decrease the settlements of the raft. The design concept of the connected piled‐raft foundations is to lessen the number of piles and utilize the bearing capacity of the system piled raft. Due to significant straining actions at the pile head‐raft connection, an alternative technique is proposed to disconnect the piles from the raft. A granular layer (cushion) beneath the raft is incorporated. The disconnection has a beneficial effect on reducing axial load compared to connected piles. For small piled rafts, nonconnected piled rafts show less stiffness than connected piled rafts, and the soil is highly stressed and shows greater raft settlement. In the case of the large piled raft, nonconnected piled rafts show greater settlement efficiency. Cushion stiffness was realized to be more substantial for a nonconnected piled raft with shorter piles than one with longer piles. The results show that the load transfer mechanism in a nonconnected piled raft is mainly governed by the thickness and stiffness of the cushion layer and by the stiffness of the subsoil.

Relationships between lateral and rotational load transfer stiffnesses and soil modulus for the elastic response of monopiles

Monopiles supporting offshore wind turbines are generally of relatively low slenderness ratio and are subjected to lateral loads that emanate from high above the seabed at an eccentricity that in most cases exceeds the embedded length of the pile. The rotational stiffness is a critical aspect of their design, owing to tight tolerances on the cumulative rotation that is permitted by industry guidelines. From a practical perspective, most design calculations for the lateral response are performed using load transfer analysis. However, the low slenderness ratio and high moment loading relative to the horizontal load have prompted closer scrutiny of the load transfer formulations that have been used historically in the offshore oil and gas industry, since these were calibrated from the response of much longer piles under very different loading conditions. Recent industry-led studies have led to new recommendations, including the addition of lateral and rotational springs at the pile base and rotational load transfer springs distributed down the pile shaft. As a first step to evaluate the initial stiffness of such springs, this paper presents results from three-dimensional finite element analyses of a homogenous elastic soil, with the aim of relating values of spring stiffness to the elastic shear modulus of the soil. Effects of non-uniform soil stiffness are discussed and the gradually increasing benefits of including the additional spring terms are quantified.

PILE SETTLEMENT INDUCED FROM SOIL MOVEMENT DUE TO BREAKDOWN OF RETAINING WALL

Very few studies measured the settlement of retaining wall supported piles foundation under a soil movement. This study explores the pile settlement induced from the sudden breakdown of a closely located retaining wall using a small-scale experimental model. Various factors affect the pile settlement, but the influence of the embedment ratio of the pile and collapsed height of the retaining wall is relatively more visible. The induced settlement decreases with pile embedment depth and increases with the collapsed height of the retaining wall. The pile settlement initially increases at a higher rate with an increase in the collapsed height to a certain extent, beyond which, becomes relatively less observable. Pile group settlement reduces with the increase in spacing and the number of piles in longer piles. However, opposite trends have been observed in piles with a smaller embedment ratio. The settlement reduces logarithmically with the increase in the distance between piles and the retaining wall. Pile groups with small embedment ratio are severely more affected by the breakdown of the retaining wall than the piles of a large embedment ratio. Pile groups placed parallel to the retaining wall are more affected than those placed orthogonally.

Effect of slab stiffness on the geotechnical performance of energy piled-raft foundation under thermo-mechanical loads

Several studies have examined the geotechnical behaviour of energy piles; however, the behaviour of piled-raft foundations containing thermal piles is not fully understood. Because piled-raft foundations are optimally designed to bear mechanical loading from the top structure, the energy piles induce extra stress and bending moments on the raft foundation (slab) from the thermal loads, which may cause structural failure. The present study evaluated the thermo-mechanical behaviour of the energy piled-raft foundations using 3D FEM to simulate the geometrical and mechanical parameters of the pile group with an emphasis on slab stiffness. The interaction between the adjacent piles in a group as well as the bending moment induced through the slab have been evaluated. The results showed that, under thermo-mechanical loads, the stiffness of the slab prevented the free expansion and contraction of the energy pile. Increasing in slab thickness from 0.2 to 0.5 m reduced the energy-pile displacement about 50%. It also was observed that a heating load induced more stress than a cooling load along the longer piles. Cooling mechanical loads caused negative skin friction in the longer piles. It was shown that the equivalent pier method is generally applicable for a group of energy piles.

Experimental Study of a Square Foundation with Connected and Non-Connected Piled Raft Foundation Under Eccentrically Loaded

In the recent years, non-connected piled raft foundation has been considered as an economical and practical deep foundation in the situation that high shear and concentrated loads may occur at the connection of the raft and pile head. This paper was presented an experimental study of a square foundation on the effects of parameters such as S/D, L/D and etc. in two cases of connected or non-connected piled raft system under the eccentrically loaded raft. The results was showed that square raft in the case of S/D = 3 and L/D = 8, the bearing capacity of the non-connected piles is more than that of the connected piles. The results of the experiments was showed pile length is more effective than the pile spacing in connected pile raft system. However by decreasing pile spacing, bearing capacity is increased in non-connected pile raft and pile spacing is more effective than the pile spacing in non-connected pile raft system. Comparison of bearing capacity and settlement indicated in the non-connected piled raft system, the longer piles not only has not much effect in increasing bearing capacity significantly, but also has lower effect on the reduction of the settlement. Also in non-connected piled raft system by increasing the pile spacing reduced BPI (bearing pile index) wile in connected piled raft system increased.

Sound absorption properties of acrylic carpets

Development of functional carpet structures is vital to improve sound quality of human life in transportation vehicles, residential and occupational environments. In this research, pile length and loop density parameters of acrylic carpets were studied to examine the effect on sound absorption properties. Carpet samples, with two different pile densities and four different pile lengths were produced for experimental purposes. Carpets with longer piles and dense loops result in the best sound absorption rates. Acrylic carpets produced with medium length piles and low density loops, yield better results at higher frequencies. Carpet samples with shorter piles and dense loops provide better sound absorption properties at low-to-mid frequencies. It has been observed that loop density and pile length parameters affect sound absorption properties at all frequency ranges. Anova analysis revealed that the combined effect of loop density and pile length parameters is evident in the mid and high frequency ranges.

Analysis of piled raft coefficient and load-settlement on sandy soil

A piled raft foundation is a combined foundation, which is developed to utilize the load-carrying capabilities of both raft and piles. To obtain an optimum piled raft design, it is important to properly evaluate and consider the load-sharing behavior between the raft and piles, which changes according to the settlement level of the piled raft. In this study, 27 three-dimensional finite element models were analyzed to investigate the piled raft coefficient with linear and nonlinear load-settlement behaviors. The length of piles was varied between 10, 15, and 20 m. The spacing between pile centers was varied between 3D, 5D, and 7D, and the pile diameter was kept constant. The number of piles and the distance between the exterior piles and the edge of the raft were maintained at 9 and 1 m, respectively. The sand conditions varied between dense, medium, and loose. The results indicated that the piled raft coefficient increases when the load-settlement curve is linear and decreases when the load-settlement curve is nonlinear. The influence of the incremental increase in pile length on the piled raft coefficient is more pronounced in short piles than in longer piles. The raft thickness has a negligible effect on the piled raft coefficient.

Centrifuge modelling of spudcan–pile interaction in soft clay

The installation and extraction of jack-up spudcans may induce significant stresses in the adjacent piles supporting the permanent jacket platforms at an offshore site. In the present study, centrifuge model tests were conducted to investigate the effects of spudcan movements on the lateral and axial behaviour of adjacent fixed-head piles embedded in soft clay. Parameters such as jack-up operation period, clearance between the spudcan and pile, and the embedment length of the pile are examined. The test results show that the most critical period for platform piles is at the end of spudcan installation, and the lateral pile behaviour is more severely affected than the axial pile behaviour. During spudcan installation, the induced bending moment on a pile located one-quarter spudcan diameter away from the spudcan edge is about 2·4 times that of a pile located one spudcan diameter away. For a deeply buried spudcan with penetration of over three-quarters spudcan diameter, the induced bending moment on longer piles is much smaller than that on shorter piles. The experimental findings provide further insights into the underlying mechanisms governing spudcan–pile interaction in soft clay under various configurations and conditions.

地下水揚水に伴う地盤沈下時のパイルドラフト敷設効果

The behavior of piled raft foundations on natural deposited soils subjected to ground subsidence due to dewatering is analyzed in this paper. A three-dimensional finite element model considering the soil-water coupled problem has been developed. In this analysis the piled raft and the soil are modeled as an elastic material and a two-phase elasto-plastic material, respectively. It can be deduced from the calculations that changes in axial forces and bending moments acting on the piles of piled raft foundations are lower than these corresponding to bearing pile foundations. This suggests that piled raft foundations are more effective for the reduction of negative skin frictions on piles. Piled rafts with longer piles can reduce the settlement due to dewatering in case that delayed consolidation does not occur. If the toes of piles locate in the layer which causes delayed consolidation, the settlement of piled rafts would be larger than that corresponding to raft foundations

Influence of Wear, Pile Height, and Cleaning Method on Removal of Mite Allergen from Carpet

Carpet is a major sink for house dust mite allergen. Vacuum extraction methods have been shown to reduce concentrations of such allergen in dust, but the influence of carpet construction and cleaning parameters on the efficiency of extraction is poorly understood. The objective of this study was to determine the effect of construction, degree of wear, and cleaning method on ease of removal of the primary allergen (Der f I) derived from the North American house-dust mite, Dermatophagoides Farinae. Carpets of different pile heights were seeded with house dust, some were then subjected to artificial wear, and all were then either dry vacuumed or wet extracted. The Der f I content of carpet cores was measured at each stage. As a result, the degree of wear and pile height were shown to be the two most important factors determining ease of Der f I removal from carpet. For worn carpet, dry vacuuming of short pile constructions was shown to be significantly more effective (p ≤ 0.05) than for longer pile height constructions, while removal of Der f I using either wet or dry vacuum extraction techniques was shown to be more efficient (> 61%) for unworn carpet than for worn carpet (< 30%). Only minor differences between types of cleaning method (wet vs. dry) were found. This study suggests that carpets differ greatly in their propensity to retain allergens, and that a consideration of carpet age, construction, and cleaning regime is important when advising the merits of different floor covering types, and on allergen avoidance techniques.