Conference Agenda

This paper presents a probabilistic back analysis for a geosynthetic reinforced soil slope (GRSS) at Yeager airport considering the uncertainty of statistical parameters of random varia-bles based on the Bayesian network. The response surface method was used to develop the in-put-out relationship between the random variables and the safety factor of the GRSS. The Mar-kov chain Monte Carlo (MCMC) simulation was used to update the statistical parameters of random variables. The results show that the soften soil strength of soil-rock interface is the main reason of failure of the reinforced soil slope at Yeager airport.

The deformation and magnitude of the coefficient of earth pressure at locations in a Geo-synthetic Reinforced Soil – Integrated Bridge System subjected to self-weight and external vertical and horizontal loads was investigated using Plaxis 2D. The soil mass was found to move outward at all locations under all loading conditions. The application of the external loads increased the outward movement over the full height of the wall. The magnitude of the coefficient of earth pressure varied significantly. Over the middle two-thirds of the wall height the coefficient was close to the active value or between the active and at rest values. At the top and bottom of the wall it was closer to the at rest value. Directly beneath the bank seat the application of the external loads significantly increased the magnitude of the coefficient to higher than the at rest condition.

Polyester (PET) materials have become more common as reinforcement solution in rein-forced soil walls (RSW). It has been shown that strength and stiffness of geosynthetics products, including PET strap reinforcements, is load-, time-, and temperature-dependent. Furthermore, the mechanical response of these materials is influenced by in-soil condi-tions. The present study describes visco-elastic and visco-plastic constitutive formulations used to model PET strap reinforcement layers in thermos-mechanical finite element mod-els. The models are demonstrated using an idealized 15-meter high RSW with concrete facing panels, including loading due to a road at the top of the structure. Reinforcement model parameters were calibrated using laboratory measured creep master curves. Anal-yses include temperature boundary conditions representing a Mediterranean climate for a 1-year period following end of construction. Calculated stress and strain values were in accordance with values found in the literature. The results of this study are a precursor for the long-term modelling of RSWs under operational conditions subjected to changing at-mospheric boundary conditions.

Plaxis 2D was used to investigate the deformational response of a geosynthetic reinforced soil – integral bridge system with different geogrid arrangements. Vertical and alternating horizontal loads were applied at the top of the wall. Three geogrid arrangements were investigated, the first had primary and secondary geogrid layers. The second had primary geogrid layers only and the third had also primary geogrid but with greater vertical spacing between the layers in the lower part of the wall. The direction of the horizontal load great-ly influenced the response, with smaller deformations, that were independent of geogrid arrangement, occurring when the load was applied towards the abutment. When the horizontal load was applied away from the abutment, longer geogrid lengths resulted in smaller wall deformations. Closely spaced geogrid layers, directly under the bankseat were found to slightly reduce vertical displacements of the bankseat but did not significantly change the horizontal displacement of the wall facing.

The paper refers to the design and construction of the largest reinforced soil walls project in Cyprus. The overall project includes reinforced soil wall (RSW) and true bridge abutment structures for the perimeter highway in Lefkosia, the Germasoyeias - Akrountas – Dierona - Arakapa road in Akrounta, the northern bypass of Geroskipou in municipal boundaries Paphos Konia, the Limassol - Saittas Motorway. The project, with a total of 22 RSW with 23,471 m2 of wall facing, is considered the largest reinforced soil walls application in the country. The RSW were designed and built using the MacRes system, developed by Maccaferri, consisting with precast concrete panel facing elements and ParaWeb polymeric geostrip reinforcements. All Cyprus is a seismic area, with peak ground acceleration varying from region to region in the range 0.15 - 0.25 g. The paper reports the design procedure for the RSW, both in static and seismic conditions. Construction details are introduced and illustrated by photos and sketches.

<p>The use of reinforcement geosynthetics to prevent localized collapses such as cavities is common today. Numerous experimental and numerical studies allow a precise understanding of the geosynthetics behavior related to these applications. Within the REGIC (Reinforcement using Intelligent Geosynthetics over Natural or Anthropic Cavities) research project, an innovative solution has been developed and patented by the Afitexinov company.</p>

<p>The designing of the reinforcement geosynthetic at maximum potential diameter of the cavity often leads to very stiff geosynthetics. But when cavity rises up slowly, it is important to be able to detect and monitor the soils deformations and a high stiffness geosynthetic may often not allow relievable measurements. An innovative geosynthetic is based on a double stiffness reinforcement geosynthetic equipped with adequate optical fibers has been developed. The first “low” stiffness at lower strain allows detecting low deformations of the soil; after this stage, the second “high” stiffness insures the stability and structure maximum settlements requirement. This two-stages reinforcement system intends to widen the possibility of detection and monitoring of rising up cavities, bringing an increased safety of the reinforcing solution.</p>

<p>To validate this solution, both laboratory and full-scale experimentations have been performed.</p>

<p>Sinkholes were experimentally simulated under treated soil layers, reinforced or not by geotextiles. After the cavity occurred, the platform was loaded until its rupture. A dedicated instrumentation was used to measure the soil and the geosynthetic displacement, the load transfer and the deformation of the geotextile. Laboratory tests were performed to characterize the treated soil and the interface between the soil and the geosynthetic.</p>

<p>All these results allowed calibrating numerical simulation, validating the efficiency of the double stiffness reinforcement geosynthetic equipped with adequate optical fibers to detect cavities and prevent accident.</p>

<p>The comprehension of rainwater infiltration effect into Geosynthetic Mechanically Stabi-lized Earth (GMSE) walls is required to precisely predict the mobilized tensile loads in de-sign analyses. A laboratory-testing device that simulate a geosynthetic-reinforced layer was used to assess the water infiltration effects in tensile loads mobilized by the rein-forcement. The experimental device allows applying a controlled infiltration rate over a re-inforced layer and capture the mechanical response from backfill soil to geosynthetic dur-ing infiltration. Water content profile, horizontal pressure variations, reinforcement tensile load and strain were provided by the monitoring program. The results demonstrated that the infiltration led to reinforcement strains and loads up to 15% of the ultimate tensile load. In addition, the rates of increases were found to be directly related to the average matric suction of the reinforced-layer. </p>

Mechanically stability earth (MSE) walls have been widely used as bridge abutments due to the advantages of reducing both the construction space saving and the bridge span. This paper presents a case study of an MSE wall with embedded bridge-supporting piles in Anhui, China. Instead of using traditional isolation casing, innovative geogrid treatments were taken to by-pass the piles embedded in the MSE wall. The facing deformations, including both lateral dis-placements and settlement, were monitored for eight months after the completion of con-struction using a machine vision monitoring system. Monitoring data indicated that both the lateral displacements and settlements of the wall facing increased with time until six months after construction. The rainfall resulted in a small increase of the lateral deformations. In the horizontal direction of facing, both the lateral displacements and settlements at different ele-vations had an obvious increase from the wing wall to the road centerline. Overall, the defor-mation of the wall facing was stable and far less than the design limit value, indicating that the MSE wall with embedded bridge-supporting piles showed good service performances after construction.

<p>To investigate the geogrid reinforcement mechanisms in the reinforced soil retaining walls, discrete element modeling has been carried out based on the model tests under strip foot-ing loads. The mechanical and deformation behavior of the reinforced soil retaining wall was analyzed at a mesoscopic scale during construction and under strip footing loads. With increasing heights of the retaining wall during the construction period, the strains of geogrids increased. Before applying the footing loads, the contact forces in the retaining wall showed a realistic distribution under gravity and the geogrid strains of lower layers were slightly larger than those of the upper layers. With increasing loads of the strip foot-ing, the vertical settlement of the footing increased gradually. The horizontal deformation of the upper part of the wall facing was larger than the lower part. With increasing footing loads, the strains of geogrids increased, but the increment of geogrid strains was relatively small under the loading conditions in this study. The discrete element modeling results in this study visualize the load transfer between geogrid and soil and quantify the defor-mation behavior of geogrids in the reinforced soil retaining wall during construction and under strip footing loads.</p>

<p>Design guidelines for reinforced soil and for soil nailing or rock anchors are often combined due to similar principles (<em>Ref. 1&amp;2</em>) however hybrid solutions combining some form of nail or anchor with a reinforced soil system lack a clear design approach and are seldom constructed due to the specialist nature of the different geotechnical fields involved.</p>

<p>These solutions are particularly applicable in cut areas where there is insufficient space for a full reinforced soil solution or where constructing the solution would necessitate the excavation and reinstatement of large volumes of material unnecessarily. Additionally, this hybrid system offer clear aesthetic advantages to the more utilitarian nail and anchor heads and enable the installation of vertical faces with a wide range of aesthetic finishes.</p>

<p>The failure of a historical dry laid masonry gravity wall on a main road in Hereford provided difficulties for the local authority in maintaining traffic access along the existing road with a guaranteed level of stability whilst enabling the retaining wall to be reconstructed with minimal visual impact and upgrading the original vehicular restraint system to meet more exacting modern standards.   </p>

<p>This paper will look at the design, construction and detailing of the solution proposed to the client’s Engineer WSP by Huesker and Dywidag as well as exploring similar historical solutions to highlight the variety of face finishes achievable and demonstrating the clear advantages hybrid solutions offer to geotechnical asset owners. The paper will also review the limited design advice available for such hybrid solutions and make recommendations for the expansion of existing design codes to specifically address the use of hybrid anchored and reinforced soil solutions.</p>

<p><em>Ref. 1, BS 8006 Part 1 Code of practice for strengthened/reinforced soils and other fills </em></p>

<p><em>Ref. 2 BS8006 Part 2 Code of practice for strengthened/reinforced soils Part 2: Soil nail design</em></p>