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Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents an experimental investigation revealing the effects of key design parameters on the behavior of disconnected piled raft (DPR) system. Large-scale model tests are conducted on instrumented foundations by varying the pile spacing, pile length, and the cushion thickness. From the test results, the load capacity improvement (LCI) factor of 3 × 3 DPR is found to increase with increasing pile spacing and length and decreasing cushion thickness. Interestingly, this factor is found to be higher at lower settlement of the raft irrespective of the length and spacing of the piles. The maximum axial load in a pile is found to occur 0.25 m below the pile head due to the generation of negative skin friction in the shallow depth. A significant downward shift of the neutral axis of the pile is observed with increasing cushion thickness resulting a higher difference between the pile head load and maximum axial load. The average load proportions of the piles and the raft in a DPR system are found 31% and 69%, respectively, when the raft settlement reaches 10% of its width. Based on the quantitative impact of these design parameters, recommendations are also provided regarding the design of the DPR system. [ABSTRACT FROM AUTHOR]

The disconnected piled raft foundation (DCPRF) is one of the newly introduced foundations for specialization in geotechnical engineering, which significantly reduces the moment and stress on the pile head. In addition, this type of foundation is an ideal choice in areas with seismic activity due to the presence of cushion material between the raft and the piles. This work aims to present a numerical model in PLAXIS 3D software for connected piled raft and disconnected piled raft foundations under the influence of seismic loads and investigate the effect of pore water pressure on the disconnected foundation compared to the connected foundation. The study will depend on the earthquake that struck Iraq in November 2017 in the Halabja region. Strength was 7.3 on the Richter scale with PGA (0.1g). The results of changing pore water pressure showed the variation of pore water pressure. In the case of a DCPRF, the porewater pressure and excess porewater pressure in the soil are much greater than in the case of a CPRF. The increase in the porewater pressure is due to the weight of the building and the weight of the additional cushion layer on the soil. The mechanism for transferring the load in the case of a DCPRF is carried out by raft, then to the cushion, and then to the soil and piles. The load transferred to the soil in the case of DCPRF is more than that transferred to the soil in the CPRF system.

Failure of an excavation support structure will inevitably result in stress state changes and ground settlements behind the wall, affecting the serviceability of adjacent structures. Such excavation-induced effects on existing piled rafts received little attention in the literature. This paper aims to investigate the load-settlement behaviour of existing disconnected piled rafts (DPR) with unequal pile lengths that were arranged beneath the cushion in various practical configurations. The DPRs were subjected to a passive loading triggered by an adjacent rigid retaining wall movement. ABAQUS was utilized to carry out the three-dimensional finite element analyses. The numerical approach was validated by experimental studies on DPRs with 2 × 2 long and short rigid piles close to a rotating retaining wall. The results show that the arrangement of the group's long and short piles has a significant impact on the overall settlement and tilting of the raft. An increased number of long piles close to the wall helps to recede the additional foundation settlement caused by the wall movement. The stiffness of the foundation soil effects the load-settlement response as well. The stiffer the subsoil, the greater the proportion of the applied working load carried by the soil prior to wall movement and the larger the amount released as the wall movement progresses. The vertical loading history prior to wall movement significantly affects the foundation settlement behaviour, with wall movement causing the 3 × 3 piled raft's settlement to increase by up to 21.7% for a working load increase from 180 to 900 kPa. [ABSTRACT FROM AUTHOR]

Practicing geoengineers and researchers generally consider the load sharing behavior in multi-type pile composite foundation as an important design aspect. On the other hand, due to urbanization, such foundation system in cities will inevitably appear next to supported excavation. This paper discusses the result from relatively largescale indoor experiment conducted to investigate the load sharing behavior of loaded long-short CFG pile composite foundation behind a neighboring rigid retaining wall undergoing rotation around the bottom. It was found that with progression of wall movement, the hidden load from soil displacement was borne by the piles with marked reduction in soil load sharing. At the end of wall rotation, the percentage of long piles’ head load increment needed to arrive at a new static equilibrium was about 12.57~32.22% while the end bearing increased by more than 97%. The consequences on the short piles, however, were manifested with an increasing pile head (13.42%) and toe (28.9%) load for the pile far from the wall whereas the closest one experienced a certain increment up to 15×10-4rad wall rotation and finally the head load and end bearing decreased to 8.28% and 12.63%, respectively. The 3D numerical back analysis conducted using FE software ABAQUS yielded the pile – soil stress ratio lower than the value obtained from the experiment but provided great insight into pile settlement characteristics during wall rotation. [ABSTRACT FROM AUTHOR]

This paper presents a comparative experimental study highlighting the differences in load transfer mechanism between the connected and disconnected piled raft systems. Scaled physical model tests are performed on instrumented foundations embedded in sand under vertical load. Results suggests that the connected piled raft (CPR) shows higher settlement efficiency than disconnected piled raft (DPR) system. The thickness of the cushion layer in DPR is found to play crucial role in defining the load transfer mechanism that is different from the CPR. Unlike CPR, the maximum axial load on pile in DPR does not occur at the pile head but at a depth equals to 10 times the pile diameter below from the pile top due to the generation of negative skin friction in the upper part of the pile. In DPR, the raft takes the majority of load initially and then the pile load proportion increases gradually which is exact opposite to the CPR phenomenon. A progressive reduction in the axial load on the pile in DPR is observed with increasing cushion thickness. The piles in CPR basically act by reducing the raft stiffness, whereas, in DPR, settlement-reducing disconnected piles act primarily as soil reinforcement by enhancing the raft stiffness. [ABSTRACT FROM AUTHOR]

This paper presents the results of 1g model tests performed on instrumented model foundations, i.e., unpiled raft, single piled raft, single disconnected piled raft (DPR) and 3 × 3 DPR in sand under vertical load by using different granular materials and thickness of the granular cushion layer to investigate the effects of granular cushion on the performance of DPR system. The Settlement Efficiency (η) of the DPR which is nonlinear in nature is found to increase as the cushion thickness decreases and the mean particle size (d50) of the cushion material increases. A cushion thickness of two times the pile diameter and cushion material having d50 more than or, equals to 2 mm might serve as the suitable cushion material for the optimum performance of 3 × 3 DPR. The neutral axis and the zone of occurrence of maximum axial load of the pile in DPR are found to move downward with increasing cushion thickness. The piles in DPR are found to carry 35% of the total superstructure load within the settlement range considered in the study. [ABSTRACT FROM AUTHOR]

A disconnected piled raft (DPR) foundation has been introduced as an effective pile design to reduce the vertical loading experienced by the pile. The characterization of DPRs has focused on the load transfer mechanism, foundation and soil settlement, bearing capacity, load distribution, and bending moment of the piles. DPR piles can act to increase the bearing capacity of the ground, and DPRs can reduce settlement while securing the bearing capacity. In this study, centrifuge model tests are performed to simulate the static behavior of DPRs under actual stress conditions. The behaviors of the DPR foundation for axial load, axial load distribution among the piles, and bending moment are compared to those of the connected piled raft foundation to understand the complex behaviors of DPRs. The centrifuge test results show that DPRs help reduce the pile axial load and bending moment during vertical loading. In addition, DPRs show smaller vertical settlement than shallow foundations. Therefore, we confirm that DPRs can be applied in foundation design as settlement reducers. [ABSTRACT FROM AUTHOR]

To control the problems of high stresses and applied moments in the piled raft foundations disconnected piled were used and the piles considered as reinforcement to the soil rather than as structural members, the gap (separation layer) between the piles and the raft can be filled with stabilized granular material which distributes the stresses below the raft and decreases the concentration stresses at the pile heads. Fifteen model tests were performed using three precast concrete pile models embedded within soft clayey soil of undrained shear strength 30kPa. Flexi-Force sensors were used fixed on piles head and the surrounding soil to measure the sharing load transmitted to piles and the surrounding soil. Geogrid and geocell materials were used in different depths and in multilayers to reinforce the separation layer and increase its stiffness. The results show that when reinforcing the separation layer with geogrid at different depths, an increase in depth over the top of the piles reduced the bearing pressure. When used, geocell reinforcement significantly increases in load carrying capacity, and a significant reduction in footing settlement occurs.