Jonathan T.H. Wu

• University of Colorado

This article starts with an overview of reinforced soil retaining walls, in that the fundamental differences in design concepts between externally and internally stabilized reinforced soil walls were explained. Mechanically stabilized earth (MSE) walls belong to the former, whereas geosynthetic reinforced soil (GRS) walls belong to the latter. MSE...

This chapter discusses the engineering behavior and properties of geosynthetics that are relevant to the analysis and design of geosynthetic reinforced soil walls, including load‐ deformation behavior, creep and relaxation behavior, soil‐geosynthetic interface behavior, and hydraulic properties. It also discusses the advantages and disadvantages of...

This technical note presents a generic step-by-step design protocol based on consideration of bearing capacity of reinforced soil foundation (RSF) on a level ground. The technical note begins with a synopsis of notable studies on bearing capacity of geosynthetic reinforced soil (GRS) and a brief description of an analytical model for load-carrying...

A study was undertaken to investigate stress-deformation behavior of soil-geosynthetic composites (SGC) by finite element method of analysis. Five field-scale experiments conducted on representative SGC of different reinforcement stiffness/strength and reinforcement spacing were used to validate the analytical model. An elasto-plastic soil model, r...

Despite great promise of excellent performance characteristics of geosynthetic reinforced soil (GRS) bridge abutments under static loads, their response under earthquake loading remains a concern. In order to advance and implement this new technology, especially in seismically active regions, this study was undertaken to examine the performance of...

The response of GRS bridge abutments to earthquake loading remains a concern despite their great success under static loads. In order to advance and implement this new technology, especially in seismically active regions, the study described in this paper and the companion paper was undertaken to examine the performance of GRS bridge abutments unde...

In addition to self-weight and vertical surcharge, geosynthetic-reinforced soil (GRS) structures have recently been used as barriers to resist lateral forces from natural disasters, such as floods, tsunamis, rockfalls, debris flows, and avalanches. The stability of such structures subject to lateral loading is often evaluated using conventional ext...

In addition to vertical surcharges, geosynthetic-reinforced soil (GRS) structures have recently been used as barriers to resist lateral forces from natural disasters such as floods, tsunamis, rock falls, debris flows, and avalanches. The stability of such structures is often evaluated by conducting conventional external stability analyses with an a...

Professor Dov Leshchinsky is selected by the Transportation Infrastructure Geotechnology as the winner of the Fumio Tatsuoka Best Paper Award. The award is being presented for the first time since it was established. The Journal recognizes Prof. Leshchinsky’s groundbreaking research presented in the paper “Framework for Limit State Design of Geosyn...

The Federal Highway Administration (FHWA) has recently developed a new bridge abutment system, known as Geosynthetic-Reinforced Soil-Integrated Bridge System (GRS-IBS). The term “GRS” refers to a soil mass that is reinforced internally by closely spaced (reinforcement spacing not more than 0?3 m) horizontal layers of geosynthetic sheets. The design...

With this issue we launch a new journal, Transportation Infrastructure Geotechnology, a peer-reviewed scholarly journal focusing on advancement of geotechnology in transportation infrastructure.Transportation infrastructure, including bridges, retaining walls, roads, highways, railways, tunnels, seaports, airports, subways, canals, and pipelines, a...

There have been ongoing arguments whether heavy blocks and/or facing connection enhancement elements, such as pins, lips, or keys, are needed for facing stability of segmental reinforced soil walls with geosynthetic reinforcement. This study was undertaken to examine facing connection forces for vertical or near vertical segmental reinforced soil w...

The presence of geosynthetic reinforcement in soil mass has been shown to reduce the tendency of dilation of the soil when subject to shear stress, especially when the reinforcement is closely spaced. As tensile loads are induced in geosynthetic reinforcement, adjacent reinforcement layers tend to act as tensioned membranes that inhibit dilation of...

A majority of the applications to incorporate geosynthetics into pavements exist in low-volume asphalt roadways. This paper presents a state-of-the-art review of geosynthetics in pavements for low-volume asphalt roadways. Within that realm, the use of geosynthetics is grouped into three categories for the purpose of this review. The categories are...

In current design methods for reinforced soil walls, it has been tacitly assumed that reinforcement strength and reinforcement spacing play an equal role. This fundamental design assumption has led to the use of larger reinforcement spacing (0.3-1.0 m) in conjunction with stronger reinforcement to reduce construction time. Recent studies, however,...

This study investigated the composite behavior of a geosynthetic reinforced soil (GRS) mass. Many studies have been conducted on the behavior of GRS structures; however, the interactive behavior between the soil and geosynthetic reinforcement in a GRS mass has not been fully elucidated. Current design methods consider the reinforcement in a GRS str...

Geosynthetic-Reinforced Soil (GRS) mass, comprising soil and layers of geosynthetic reinforcement, is not a uniform mass. To examine the behavior of a GRS mass by a laboratory test, a sufficiently large-size specimen of soil and reinforcement is needed to produce a representative soil-geosynthetic composite. This paper presents a generic test, refe...

In current design methods for geosynthetic-reinforced soil (GRS) walls and abutments, there is a fundamental design assumption that the reinforcement strength and spacing play an equal role in the performance of a GRS wall/abutment, i.e., larger reinforcement spacing can be fully compensated by using proportionally stronger reinforcement and lead t...

An approximate solution method, referred to as the epsilon method, allows flow characteristics such as flow rate and exit gradient to be determined for seepage through a two-layer soil system. The finite element program SEEP was employed to analyze flow characteristics of an impervious dam with sheet pile on a layered soil. Extensive analyses were...

When an earth fill is subject to loading and subsequent unloading, it will bring about an increase in the lateral stress, provided that there is sufficient constraint to lateral deformation of the soil mass. The increase in lateral stress is commonly known as the "residual" or "lock-in" lateral stress. The residual stress resulted from compaction o...

Current design methods for Geosynthetic-Reinforced Soil (GRS) walls consider only the stresses and forces in the wall system. A GRS wall with modular block facing is inherently a fairly "flexible" wall system; hence it can be of critical importance to include the lateral movement of the wall in design. This paper presents an analytical model for es...

Two full-scale segmental facing Geosynthetic-Reinforced Soil (GRS) abutment walls, referred to as "the NCHRP test abutments", were constructed and load-tested at the Turner-Fairbank Highway Research Center in McLean, Virginia. The two experiments were conducted to (1) examine the behavior of segmental facing GRS abutment walls under increasing vert...

The long-term design strength of a geosynthetic reinforcement employed in current design methods is determined either by performing laboratory tests on the geosynthetic without considering soil-geosynthetic interaction or by imposing a very large safety factor to the tensile strength of the geosynthetic without any regard to the effect of backfill....

Presented are the results of five large-scale Geosynthetic Reinforcement Soil (GRS) experiments referred to as Mini Piers (MP). The MPs were constructed to evaluate the effect of reinforcement spacing and reinforcement strength on the performance of a GRS mass. The experiments were performed at the Federal Highway Administration (FHWA) Turner-Fairb...

Current design methods "borrowed" from the design concepts for externally stabilized retaining walls and adopted the Rankine or Coulomb earth pressure theories for design of segmental Geosynthetic-Reinforced Soil (GRS) walls. The earth pressure is used to determine the minimum reinforcement strength, minimum reinforcement length, and required conne...

Geosynthetic-reinforced soil GRS bridge-supporting abutments are similar in principle to GRS retaining walls, except that GRS abutments are typically subjected to a much higher area load, and that the loads are close to the wall face. The GRS abutment technology is relatively new, but it has great potential, and it has been gaining some popularity...

Compared to geosynthetic-reinforced soil (GRS) retaining walls, GRS abutment walls are generally subjected to much greater intensity surface loads that are fairly close to the wall face. A major issue with the design of GRS abutments is the allowable bearing pressure of the bridge sill on the abutments. The allowable bearing pressure of a bridge si...

This paper synthesizes the measured behavior and experiences gained from case histories of geosynthetic-reinforced soil (GRS) bridge-supporting structures with “flexible” facings. Only bridge-supporting structures with wrapped-face, modular block face, and rock face are included in the synthesis. The case histories were grouped into two categories:...

An innovative retaining wall system was adopted for the construction of a ramp connecting Interstate-25 and Interstate-70 in Colorado. The retaining wall system, known as the independent full-height facing IFF reinforced soil wall, has a full-height concrete facing panel in front of a soil mass that is reinforced with layers of tensile inclusion. T...

Field tests of segmental block-faced geosynthetic-reinforced soil (GRS) bridge abutments and piers have demonstrated excellent performance characteristics and very high load carrying capacity. One important feature of GRS abutment is that it can potentially eliminate the use of piling when situated over a weak foundation. This will not only reduce...

An extensive literature review was conducted to collect and synthesize information on geosynthetic-reinforced soil (GRS) walls that had been monitored for extended periods of time for assessment of their long-term performance characteristics. As a result, seven GRS retaining wall projects were selected. These projects typically had well-documented,...

A modified Soil-Geosynthetic Interactive Performance (SGIP) test apparatus for evaluating short- and long-term deformation behavior of soil-geosynthetic composites was developed. In the test, a specimen of soil-geosynthetic composite, with dimensions of 305 mm wide, 605 mm long, and 305 mm high, was subjected to a vertical sustained load under plan...

The feasibility of geosynthetic inclusion for reducing swelling of expansive soils was studied by performing laboratory soil-geosynthetic swell tests on an expansive soil. The test specimen measures 12x12x12 in., with a sheet of geosynthetic embedded horizontally at the midheight of the soil. To prepare the test specimen, the soil was first compact...

A study was undertaken to investigate the behavior of Geosynthetic Reinforced Soil (GRS) masses under various loading conditions and to develop a simplified analytical model for predicting deformation characteristics of a generic GRS mass. Significant emphasis was placed on the effect of preloading. To conduct the study, a revised laboratory test,...

A study was undertaken to investigate the effectiveness of the geosynthetic reinforcement in a skin-flow landslide repair method, known as the U.S. Forest Service deep-patch technique. A test apparatus, which can model a full-scale patched slope in the plane stain configuration, was devised and manufactured for the study. The test apparatus allows...

In this study, a finite element program was validated by comparing its analytical results with the results of a well-instrumented large-scale laboratory test conducted on a geosynthetic reinforced soil (GRS) retaining wall under well-controlled test conditions. The validated computer program was then used to investigate the effects of backfill type...

A quick and simple method of bridge substructure construction using geosynthetic reinforced soil (GRS) is illustrated. GRS is used to build abutments and pier foundations for simple bridges. It is a refinement of existing reinforced soil technology used during the last 20 years. The interaction of a closely spaced geosynthetic reinforced soil syste...

Pullout tests have been widely used to evaluate soil-reinforcement in- terface properties for the design and analysis of reinforced soil structures. However, there are difficultiesinterpretingpullout test resultsparticularlywhenextensiblemate- rials, such as geotextiles, are used as reinforcement. In this study, an analytical model (an"interface pu...

A simple laboratory performance test was devised for the assessment of long-term creep behavior of geosynthetic reinforcement due to soil-geosynthetic interaction. In the test, the geosynthetic reinforcement and the confining soil deformed in an interactive manner under a sustained surcharge that was applied to the soil over a long period of time....

A numerical model is developed to investigate long-term soil-geosyn- thetic interaction in typical geosynthetic-reinforced soil structures. The numerical model employsthe finite element methodwitha time marchingscheme whileincorpo- ratinga generalizedcreeplawforgeosyntheticsanda visco-plasticconstitutive lawfor soil.Toverifythenumericalmodel,two we...

A study was undertaken to investigate the bearing capacity of rectangular footings on geogrid-reinforced sand by performing laboratory model rests as well as finite-element analyses. The effects of the depth to the first layer of reinforcement, vertical spacing of reinforcement layers, number of reinforcement layers, and the size of reinforcement s...

A number of diverse methods are available for the design of geosynthetic-reinforced soil walls. The various methods yield widely varying results. This study involved reviewing six published design methods, comparing design concepts; comparing the results of designs for various wall heights and geometries using each of the methods, and comparing two...

It is well known that granular backfill can account for more than 50% of the total construction cost for typical geosynthetic-reinforced soil structures. It is therefore desirable to investigate the possibility of using low-quality onsite soil, which may be cohesive and near saturated, as backfill. A geosynthetic that possesses adequate drainage ca...

It had been reported, through observation of actual field installations, that the inclusion of tensile reinforcement in the approach fill behind bridge abutments can effectively reduce approach fill settlement, and hence reduce the “bump” that may otherwise be experienced at both ends of the bridge. This study was undertaken to investigate, by the...

An apparatus capable of measuring the strength and deformation properties of geotextiles under unconfined conditions and under the confinement of a membrane or a soil was developed. The appratus differed from conventional in-soil test apparatuses in that during the soil-confinement test the soil was allowed to deform with the geotextile while being...

A study was undertaken to investigate the effectiveness of using geosynthetic tensile reinforcements for strengthening two highway test embankments, 8·5 and 14·6 m in height, constructed over weak and highly pervious foundations. Both embankments were reinforced with geogrid mats placed near their base and were constructed in two stages. Field inst...

Existing test methods for measuring the load-extension properties, including the stiffness and the ultimate strength, of geotextiles as they are subjected to confining pressures are reviewed and critically evaluated. In addition, a new test method which surmounts the drawbacks of the existing methods is presented. The new method has three distinct...

Existing test methods for measuring the load-extension properties, including the stiffness and the ultimate strength, of geotextiles as they are subjected to confining pressures are reviewed and critically evaluated. In addition, a new test method which surmounts the drawbacks of the existing methods is presented. The new method has three distinct...

Description 26 papers help the reader with the selection, testing, design, and use of geosynthetics. The peer-reviewed volume: • Focuses on the many available geosynthetic material tests that are performed in isolation (index tests) • Contrasts these tests with soil/geosynthetic material tests (performance tests) • Determines if, and what type of,...

Non-woven geotextiles have been used worldwide as drainage and filteration materials. But the permeability of geotextile depending on surcharge has not been yet estimated clearly, so a testing apparatus has been developed to measure the permeability normal to geotextile specimen under confined conditions. We tried the permeability test of geotextil...

A testing apparatus has been developed to measure the hydraulic conductivities both normal to and in the plane of a geotextile specimen. For the in-plane flow condition, the system is also capable of measuring the hydraulic conductivity of the geotextile in the confinement of a soil under a specified confining pressure. This paper briefly describes...