Repeated Load Tests on Geocell Reinforced Sand Subgrades

In this research, results from a series of large scale dynamic model tests on geocell reinforced and unreinforced homogeneous sand beds are presented. The placement density of sand in all the tests was maintained at 70%. The loading was applied through a circular steel plate which replicates the load application from a passenger car. A single axle wheel load of 40 kN was assumed on the pavement surface of which 7 kN was calculated to be applied on the subgrade layer. The influence of the width and height of the geocell reinforcement on the cyclic behavior of the loading system was studied and the performance improvement in terms of traffic benefit ratios and cumulative plastic deformations/rutting was determined. A traffic benefit ratio was observed to be as high as 45 for the case of geocell size h/D=1, b/D=4 at 10% plate settlement. The cumulative permanent deformations were reduced by 8 fold for the same case against the unreinforced case at 5% plate settlement

Experimental Evaluation of Geojute Reinforced Sand Beds under Repetitive Loading

In this research, a series of large scale dynamic model tests were carried out on geojute and jute-geocell reinforced sand subgrade in controlled laboratory condition. The tests are conducted on geojute and jute-geocell (made from waste jute bags) reinforced and unreinforced sand subgrade under repeated loading to simulate traffic conditions. The placement density of sand in all the tests was maintained at 70% (stiffer subgrade) and 30% (weaker subgrade). A constant area of geojute and jute-geocell reinforcement was maintained throughout the test series. Cyclic behavior was investigated through varying the density, number of geojute layers and geojute arrangement. The influence of the width and height of the jute-geocell reinforcement on the cyclic behavior of the loading system was studied and performance improvement in terms of traffic benefit ratios and cumulative plastic deformation was determined. The loading was applied through a circular steel plate which replicates the load application from a passenger car replicating a single axle wheel load. A single axle wheel load was applied through a sophisticated double acting linear dynamic actuator which is attached to a 3.5m high reaction frame

Behavior of Embedded Footings Supported on Geogrid Cell Reinforced Foundation Beds

The results from laboratory model tests on an embedded circular footing supported on geogrid cell reinforced foundation beds are presented. The embedment depth of the footing (depth of placement of the footing with respect to the fill surface) was varied from zero to 0.6 times the footing width with foundation beds made of dry sand and saturated silty clay. The cellular mattress was prepared using a biaxial polymer geogrid, called a "Geogrid cell". The various parameters studied in this testing program include the depth of placement of cellular mattress below the footing base, width, and height of the cellular mattress. The load carrying capacity of the geogrid-cell reinforced sand beds have improved up to about 9.5 times with increase in the embedment depth of foundation as against 6.5 times for surface footings. In case of cellular reinforced soft clay beds, a fourfold increase in the performance of the surface footing is observed against unreinforced bed, and it increases up to 5.5 with the footing embedment depth. In case of sand beds, the increased performance of the footing is observed with increase in footing settlement. In case of clay beds a sharp decrease in performance improvement of the footing at around 15 % of the footing settlement is observed at all embedment depths. The effect of embedment depth of footing becomes marginal in case of sand beds when compared with clay beds at higher embedment depths. The sand bed was instrumented with earth pressure cells, and strain gages were mounted on a strip of geogrid that was placed below the cellular mattress. The earth pressure cells embedded in the subgrade soil show that with insertion of the cellular mattress, the footing pressure is distributed more uniformly over a wider area with footing embedment depth. The strain measurements also show a fairly uniform strain in geogrid strip under footing contact pressure

Use of Digital Image Correlation for the Evaluation of Flexural Fatigue Behavior of Asphalt Beams with Geosynthetic Interlayers

In this study, the flexural fatigue performance of two-layer asphalt beams with and without geosynthetic interlayers was evaluated with a digital image correlation (DIC) technique. A field scenario was simulated by considering an old, destressed pavement as the bottom layer with a compacted bituminous mix as an overlay. An appropriate tack coat and geosynthetic interlayer were at the interface. The digital images were recorded at a specific interval of load cycles during a repeated load four-point bending test. The displacement fields obtained from the digital images were analyzed so that the crack width, crack height, and tensile strains could be obtained and the crack initiation and propagation phenomena studied. The deformation data obtained from the DIC analysis were validated with the vertical deformations measured through linear variable differential transformers. The DIC results correlated very well with the measured data. The DIC data indicated that the tensile strains were as high as 4.75% at the crack tip in the control specimen compared with 1.42% in a polyester grid interlayered specimen at the failure of the corresponding specimens. With the inclusion of interlayers, the fatigue performance of the two-layer asphalt beam specimens improved by about 39, 12, and 1.7 times for Specimens I1, I2, and I3, respectively

Swell-shrink and strength behaviors of lime and cement stabilized expansive organic clays

Organic soils are mostly composed of decayed plant matter and weathered rock material. Often, these soils are known for their inferior engineering behavior including very high compressibility and low shear strength. In order to improve these properties, organic soils are, by and large, modified with calcium based stabilizers such as lime, cement and fly ash. However, transportation agencies in the United States have mentioned that the anticipated improvements were never achieved or the improvement obtained disappeared quickly with time. Therefore, a research study was initiated to understand the behavioral mechanisms of lime and cement stabilized organic soils. Eight natural expansive soils bearing different organic contents (varying between 2 and 6%) were selected for the present investigation. First, optimum dosages of lime and cement were determined for the selected soils. Then treated and untreated (control) specimens were prepared to study their physical and engineering behaviors of the soil specimens at varied curing periods. There is a drastic increase in unconfined compressive strength (UCS) of lime and cement treated specimens until 28. days of curing. Beyond which, a negligible improvement in UCS property was recorded for lime treated specimens and a slight decrease in UCS for cement treated soils was noticed. This reduction in strength for cement treated specimens could be attributed to the reduction in pH concentration with curing as well as the formation of inorganic calcium humic acid at this stage

Model studies of a circular footing supported on geocell-reinforced clay

The potential benefits of geocell reinforcement in soft clay foundations have been studied by a series of laboratory-scale static load tests on a rigid circular footing placed on a fill surface. Parameters of the test program include depth of placement of the geocell layer, width and height of the geocell layer, and influence of an additional layer of planar geogrid at the base of the geocell mattress. With the provision of geocell reinforcement, the load-carrying capacity of the soft clay foundation can be improved by a factor of up to 4.8 times that of the unreinforced soil. Heaving of the soil can be reduced substantially by providing geocell reinforcement of sufficient height and width. Further improvement in performance could be obtained with the provision of an additional layer of planar geogrid at the base of the geocell mattress

Utilization of Reclaimed Asphalt Pavements in Indian Low-Volume Roads

Utilization of reclaimed asphalt pavement (RAP) in the construction industry is gaining an advantage over conventional materials in terms of sustainable credits. However, the amount of production of RAP and its utilization has no comparison. The general practice is to replace a small fraction of virgin aggregates with RAP, usually restricted to a maximum of 30%, in base layers to promote RAP usage in the pavement industry. The present study focuses on the utilization of a high proportion of RAP (>50%>50%) substitution in virgin aggregates (VA) as a base material in low volume roads (LVR). Mixes containing 100∶0100∶0, 80∶2080∶20, and 60∶4060∶40 proportions of RAP∶VARAP∶VA stabilized with different dosages of fly ash were evaluated for maximum dry density (MDD), optimum moisture content (OMC), unconfined compressive strength (UCS), resilient modulus (MrMr) and California bearing ratio (CBR). It was observed that the 80∶2080∶20 RAP∶VARAP∶VA design mix with 40% fly ash meets the design requirements (UCS>1.7  MPaUCS>1.7  MPa and CBR>80%CBR>80%) specified by the Ministry of Rural Development (MoRD), Government of India, and was considered to be an optimum mix. An example is discussed to design an LVR with an optimum mix according to the Indian Roads Congress (IRC) and AASHTO methods. The results revealed that the fatigue and rutting strains are well within the permissible limits for the new mix. The new mix design proved economical, as there was a 50% reduction in base layer thickness compared with the conventional design mix. Read More: http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29MT.1943-5533.000137