Spatial Variability of Subsurface Soil Conditions Causing Roadway Settlements

Settlement of problematic soils constituting the roadway subgrade may result in pavement distress and structural failure, requiring periodic pavement patching and resurfacing. Many of these problems occur as a result of the settlement of soft cohesive and organic soils. Due to the extent of roadway projects and the limited frequency of boring locations, spatial variability of subsurface soil conditions, and sometimes due to an inadequate extent of exploration, these problematic soils may not be identified suitably during subsurface explorations. An extensive subsurface exploration program was implemented for detailed characterization of subsurface conditions for a relatively short section of an existing roadway experiencing continuing settlements. This paper presents some of the exploration results, assesses the spatial variability of the subsurface soil conditions, and comments on the effect of spatial variability of subsurface conditions on the roadway\u27s performance

The Jovian ionospheric conductivity derived from a broadband precipitated electron distribution

The Pedersen ionospheric conductivity and conductance at Jupiter are computed assuming a broadband precipitating-electron flux and compared to values obtained when assuming a mono-energetic precipitating-electron flux. Among other results, it is found that the ratio between the broadband and the mono-energetic conductances depends on the electron mean energy of the precipitating-electron population. For a mono-energetic distribution, an optimal energy exists, around 30-40 keV, for which the conductance arising from the precipitation is maximal. If the mean electron energy is well below this optimal energy, the conductance calculated for a broadband distribution is enhanced compared to the mono-energetic case because part of the electron energy distribution reaches this optimal level. The conductance is also underestimated for a mono-energetic electron precipitation well above the optimal value. The opposite trend is observed around the optimal energy as most of the electrons of the broadband distribution have either lower or higher energies, while all electrons of the mono-energetic distribution have an energy close to the optimum

AWAKE, the advanced proton driven plasma wakefield acceleration experiment at CERN

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world׳s first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long (rms ~12 cm) proton bunch in the plasma. These experiments are planned for the end of 2016. Later, in 2017/2018, low energy (~15 MeV) electrons will be externally injected into the sample wakefields and be accelerated beyond 1 GeV. The main goals of the experiment will be summarized. A summary of the AWAKE design and construction status will be presented

Path to AWAKE : evolution of the concept

This paper describes the conceptual steps in reaching the design of the AWAKE experiment currently under construction at CERN. We start with an introduction to plasma wakefield acceleration and the motivation for using proton drivers. We then describe the self-modulation instability - a key to an early realization of the concept. This is then followed by the historical development of the experimental design, where the critical issues that arose and their solutions are described. We conclude with the design of the experiment as it is being realized at CERN and some words on the future outlook. A summary of the AWAKE design and construction status as presented in this conference is given in Gschwendtner et al. [1]

Analysis of Vertical Column Support Systems for Stabilization of Roadway Subgrade Settlements

Every year, patching and resurfacing projects are undertaken to repair pavement distress and structural failure due to problematic subgrade soils. These conditions seriously impact roadway function and safety and create substantial costs to remediate the problems caused by subgrade settlement. Many of the subgrade settlement issues occur as a result of very soft to soft cohesive soils, very loose to loose granular soils, saturated soils, and/or organic soils, all of which yield low strength and subgrade support characteristics. The settlement problem can usually be addressed by using conventional remediation methods or by using vertical column support methods.Conventional methods to remediate subgrade settlements caused by problem soils include removal of weak soils and replacement with new suitable engineered fill, near-surface chemical stabilization such as lime or cement, or preloading/surcharging with or without wick drains. However, when problem soils are relatively deep, or long term settlement tolerances are low, these conventional methods can sometimes prove ineffective or too costly. New technologies and extended application of old technologies has led to some relatively limited use of vertical column support methods for the remediation of roadway subgrade settlements. A specific search was performed to identify other research studies performed on the use of vertical column support systems for the remediation of existing roadways exhibiting subgrade settlements, however, no other similar research studies were located. Some previous research studies on the use of vertical column support systems used to support embankments for new roadways, road widening, and bridge approaches were reviewed, although these research projects were not for the remediation of existing roadway settlements. The use of vertical support columns can be employed either as a deep foundation system or as a ground improvement technique.Vertical column support systems create relatively stiff column elements which allow for reduced loads on the surrounding weaker soils and improved support of the overlying roadway systems. Vertical column composition varies greatly and includes concrete, grout, stone/aggregate, sand, or soil-cement inclusions within the existing soil matrix. Some methods not only create strong vertical column elements at the locations they are installed but also improve the surrounding weak soils through a number of differing techniques. As a result, the current vertical column support methods can generally be grouped into two distinct subsets: ground improvement and deep foundations. Examining the available vertical column support methods and identifying the cost effective methods which provide increased subgrade support and decreased settlements will assist transportation agencies by improving roadway safety, reducing future pavement rehabilitation projects, lowering repair costs, as well as lowering the overall cost to the road users and society as a whole