Geomechanics of Soft Ground Improvement by Perforated Piles: Review and Case Study

Civil Infrastructure built on soft and compressible soil is likely to collapse due to undrained shear failure or unacceptable settlement of supporting foundations. Incorporation of adequate ground improvement technique with the aim of upgrading the strength and stiffness of the weak soil is essential in such cases. Amongst various established methods adopted worldwide for improving soft ground, using perforated piles is a relatively emerging technique. Such piles not only transmit the structural load into the subsoil beneath in a manner similar to the conventional piles, but also assist in radial consolidation of soft soil due to perforated side walls. This paper presents a brief overview on the investigations carried out on this new technique. Also, a typical case study has been presented. As observed, the axial pile capacity progressively increased while settlement reduction took place, with accelerated radial consolidation.

Features of static pile load test

Pile foundations are commonly used in engineering practice to transfer the loads from heavy structures such as high-rise buildings to competent soil strata. In this manner, such complications as unfavorable geological conditions, compressible soil layers, and high levels of groundwater are avoided. Different types of piles are used in construction work. The specific type of pile used depends on the type of loading, the foundation soil, and the location of the groundwater table. The technical progress of large, bored piles and the continuous improvements of construction procedures and piling equipment today have created new possibilities. This paper describes a series of pile load tests that were performed in the capital city of Nur-Sultan, Kazakhstan. The control equipment, technological features are important for detailed information about the process of testing and the associated results make them more accurate and reliable. Keywords: pile, static test, load, equipment, soil

Using Nanomaterials in Stabilization of Soil for Oil Infrastructures

The design foundations of storage tanks for oil industry experiences significant problems due to the widespread occurrence of weak and compressible soil which resulted in foundation failure. In this study, soft soils were taken from two locations and mixed with three types of nanoparticles which were nano-alumina (nano Al2O3), nano-copper (nano CuO), and nano-magnesium (nano MgO). Nanomaterials were incorporated in small percentage (less than 1%) by dry weight of soil. The tested geotechnical characteristics included the water content, dry density, and the unconfined compressive strength. The results showed significant enhancements in the maximum dry density and unconfined compressive strength. The level of enhancement depended on the type of nanomaterials and the contents. Improved strength and hardening properties were shown with the utilization of nano CuO material in comparison to the soil samples with the other nanomaterials additions, with its optimum addition of 0.7% provided an increment rate of 662.7% while the optimum nano CuO which is about 1% showed a 532% increasing rate in the compressive strength of S1 soil. It was noted that the maximum dry density and unconfined compressive strength enhanced with the increase in the nanoparticles content until reaching a percentage in which the strength decreased. The optimum content of the nano MgO was 0.3% while the optimum nano Al2O3 content was about 0.3% for soil S1 and was about 0.1% for soil S2. The presence of nanomaterials in excessive contents caused agglomeration of particles which had negative influences on mechanical characteristics of the soils. Generally, the incorporation of finer particles like nanoparticles even with low amount would improve the geotechnical characteristics of soils with the consideration of the potential environmental benefits, these combined admixtures are intended to lower the cost and become a more sustainable and environmental alternative for soil stabilization

Ground Subsidence Triggered by the Overexploitation of Aquifers Affecting Urban Sites: The Case of Athens Coastal Zone along Faliro Bay (Greece)

Land subsidence in the coastal zone of the Neo Faliro, Moschato, and Kallithea municipalities, along the Faliro bay, has been recorded since the mid 1960’s. This phenomenon has caused damage to buildings, pavements, and roads. Aiming to identify the main causes of the observed ground deformations, data referring to the geological, geotechnical, and hydrogeological settings of the study area has been evaluated. Subsidence has been quantified by the use of space-born Synthetic Aperture Radar interferometry (InSAR) techniques. SVD (Singular Value Decomposition) and IPTA (Interferometric Point Target Analysis) techniques have been applied for the production of deformation maps, referring to the time period between 2002 and 2010. Furthermore, aiming to extend the study of the phenomenon further to the past, Persistent Scatterer Interferometry (PSI) data for the time period from 1992 to 2001 were also evaluated. Finally, the results of the InSAR analysis have been crosschecked with measurements acquired by a vertical geodetic control network as well as by ground truth data, referring to damage inventory of the site. The current research presents an interesting case study of an urban site affected for a long-lasting period by the activities of a neighboring industrial zone. The development of an extensive depression cone, mainly due to the overexploitation of the aquifers for industrial use, is the main cause of the land subsidence phenomenon, without excluding a component of motion due to the natural compaction of the compressible soil in the area of interest. The complexity of the geological, hydrogeological, and geotechnical conditions and the interaction of the numerous land use activities make this study far more interesting.

Diagnosing Subsidence Geohazard at Beijing Capital International Airport, from High-Resolution SAR Interferometry

Beijing Capital International Airport (BCIA) has suffered from uneven land subsidence since 1935, which affects the smoothness of airport runways and seriously threatens the safety of aircrafts. In this paper, a spaceborne interferometric synthetic aperture radar (InSAR) with high-resolution Cosmo-SkyMed SAR data was utilized at BCIA for the first time to diagnose the subsidence hazard. The results show that subsidence is progressing at BCIA at a maximum rate of 50 mm/year, which is mainly distributed in the northwest side of the airport. It was found that the Shunyi-Liangxiang fault directly traverses Runway2 and Runway3 and causes uneven subsidence, controlling the spatial subsidence pattern to some degree. Four driving factors of subsidence were investigated, namely: the over-exploitation of groundwater, active faults, compressible soil thickness, and aquifer types. For the future sustainable development of BCIA, the influence of Beijing new airport and Beijing Daxing International Airport (BDIA), was analyzed and predicted. It is necessary to take relevant measures to control the uneven subsidence during the initial operation of BDIA and conduct long-term monitoring to ensure the regular safe operation of BCIA. This case demonstrates a remote sensing method of diagnosing the subsidence hazard with high accuracy and non-contact, providing a reliable alternative for the geohazard diagnosis of key infrastructures in the future.

Field study of pile – prefabricated vertical drain (PVD) interaction in soft clay

Piles and prefabricated vertical drains (PVDs) are two well-established inclusions used by geotechnical practitioners when dealing with soft compressible foundations. Induced movements in highly compressible soil can adversely influence the pile response by inducing additional movements and stresses in the piles. Especially, undesirable soil–pile interaction often leads to the development of excess pore-water pressure during pile installation and negative skin friction caused by the settlement of compressible soil surrounding the piles. Additional drainage by PVDs prior to the installation of a pile could reduce excess pore-water pressure, lateral soil movement, and negative skin friction on the pile. In this paper, full-scale field testing on two trial embankments built on soft soil is reported and the relative behaviour of these two embankments is compared and discussed. Soft soil underneath both embankments was consolidated before one pile was installed at the centre of each embankment. The pore-water pressure, lateral soil movement, surface settlement, and associated strain at the pile shaft were recorded. The pile capacity was tested immediately and 3 h after pile installation. The monitoring and testing results indicated that preconsolidation with PVDs before piling can effectively reduce the excess pore-water pressure, lateral soil movement, and downdrag on the pile.

Analysis of methods for analytical calculation of foundation settlement in time

Currently, there exist three main methods for calculating foundation settlement: the method of linearly compressible layer (introduced by Prof. K. E. Egorov), the method of layer-by-layer summation (described in SP 22.13330.2016), and the method of one-dimension virgin compression (a special case of the equivalent layer method introduced by Prof. N. A. Tsytovich). All the above-mentioned methods for calculating foundation settlement are based on the linear dependence of deformations on stresses. The principal differences between these methods are in taking the account of natural soil stress from its own weight, the technique of assessing the compressible soil strata and evaluating the distribution of stress in depth from external pressure. In the practice of bases and foundations design, the layer-by-layer summation method is considered to be the most highly reputable and widely used. It should be noted that each method was initially developed to solve some specific problem. However, not every engineer at present knows the limits of a particular method application for calculating foundation deformation. The article presents calculations of the non-linear settlement development in the foundation performed by various methods. Comparison with actual deformations is made based on the results of long-term monitoring of foundation settlement of a well-known building in Saint Petersburg, and recommendations are offered regarding the applicability of the discussed methods.

Local Geology, Shear Strength Properties and Bearing Capacity of Coastal Plain Sands in Uyo Metropolis, Akwa-Ibom State, Southeastern Nigeria

The Bearing capacity of the soil within Uyo metropolis in South-Eastern State of Akwa Ibom was investigated in this study. The soil belongs to Coastal Plain Sand often called the Benin Formation in the geology of Niger Delta. Both Field and Laboratory methods were employed in the study. The field method consisted of Cone Penetration Test (CPT) with a 2.5 ton Dutch Guada cone penetrometer, and the Light weight penetrometer LRS 10. For the CPT, depth of investigation was refusal depth which varies from about 9.0 m to 20.0 m. The depth of investigation by the LRS 10 was not more than 6.0 m. The direct parameter the LRS 10 evaluates is the relative density. Soil sounding with the LRS 10 indicated for all the sites a ‘loose to medium’ consistency. No dense or very dense stratum was encountered. The Laboratory method employed was the Direct shear box tests This was used to determine the cohesive property and angle of shearing resistance of the soil, that is the C- ∅ property. The cohesion varies very widely; with a value ranging from a zero value to 54 kN/m2. The angle of shearing resistance ranges from 8º to 30.7º, with more than ninety percent falling below 28º, indicating a highly compressible soil that is prone to local shear failure. Ultimate bearing capacities are as low as 100.93 kN/m2 and as high as 571.1 kN/m2. Settlement associated with safe bearing pressure estimated from CPT data ranged from 0.35 cm to 3.89 cm. while that from laboratory gives lesser values, thereby making that from the field value conservative.