トンネル覆工解析のための変位境界を用いた三次元連続体モデル

国立大学法人長岡技術科学大

Natural Para Rubber in Road Embankment Stabilization

This is the first study on “ribbed smoked sheets (RSS)” as a geogrid reinforcement in geotechnical engineering. An RSS is a kind of natural para rubber. RSS (grade 3) was designed as a biaxial geogrid with an aperture size of 20 mm × 20 mm and a spacing of 20 mm. The RSS was found to be a significant functional layer when applied to the subbase lateritic soil layer. The lateritic soil with an RSS reinforcing layer was greatly improved regarding the California bearing ratio (CBR). Numerical simulation using two-dimensional finite element software was used to determine the optimal number and positions of the RSS reinforcing layers in road embankment stabilization. The simulation data in terms of horizontal displacement of unreinforced road embankments was validated by the collected data from the actual construction site. The RSS reinforced layer was varied from one to three layers under 61 analysis conditions. The highest safety factor was obtained with two layers of RSS at 0.1H below the top of the road embankment and 0.4H below the first RSS layer, suggesting a suitable installation of the RSS reinforcing layer. The RSS is thus strongly recommended as a reinforcing material in low CBR lateritic soil for the road embankment

Evaluation of Interface Shear Strength Coefficient of Alternative Geogrid Made from Para Rubber Sheet

In this work, elastic natural rubber compound sheet (RCS) and ribbed smoked sheet grade 3 (RSS) were studied as alternative replacements for polymer geogrid for soil reinforcement. In order to investigate the reinforcing effectiveness in three distinct environments using the interface shear strength coefficient (Rin) by the large-scale direct shear test, the RSS and RCS geogrids were installed independently in sand, lateritic soil, and clay. Using either an RSS geogrid or RCS geogrid, the average Rin is progressively smaller in reinforced sand, lateritic soil, and clay, respectively. Higher tensile strength of reinforced materials using the RCS geogrid than those using the RSS geogrid is encouraged by the better elastic characteristics of the RCS geogrid. Thus, utilizing the RCS geogrid-reinforced materials can better increase the shear strength of coarse-grained soil such as sand and gravel

Feasibility study of using natural para rubber for reinforced embankment

This research developed a natural para rubber from rubber tree sap as a biodegradable-reinforced material in geogrid application with the purpose of membrane support, bearing capacity increment, and lateral restraint in embankment construction. Biaxial geogrids with an aperture size of 20 mm × 20 mm were prepared from the ribbed smoked sheet (RSS) made of the coagulated latex sheets, and rubber compound sheet (RCS) made of chemically modified RSS sheet to increase the rubber performance were investigated and compared. The performance of RSS and RCS was evaluated under the actual situation in a field test with an area of 4.5 m-length x 1 m-width with 0.5 m-depth. In each studied area of the reinforced zone, RSS and RCS were separately inserted at 250 and 450 mm from the base of a field test as the 1st and 2nd reinforcement layers, respectively. The load was applied to simulate the traffic load. The RSS- and RCS-reinforced zones in the field test were compared with the non-reinforced zone in terms of settlement and rut depth. The drastic settlement and rut depth were significantly detected in non-reinforced zones compared to the reinforced zones. Meanwhile, higher settlement and rut depth were observed at RSS-reinforced zones compared to the RCS-reinforced zones. The RCS geogrid in this research was successfully applied as a functional biodegradable-reinforced material for embankment construction

An efficient concrete plastic damage model for crack propagation in gravity dams during seismic action

PurposeConcrete gravity dams are important structures for flood control and hydraulic power generation, but they can be vulnerable to seismic activity due to ground movements that trigger crack propagation.Design/methodology/approachTo better understand the factors that affect the stability of concrete gravity dams against concrete fracture during earthquakes, a concrete plastic damage model has been utilized with two new expressions to simulate compressive and tensile damage variables.FindingsThe findings showed that the crack patterns were strongly influenced by the concrete’s strength. The simulation results led to the proposal of appropriate concrete properties aimed at minimizing damage. These findings, together with the proposed model, offer significant insights that can enhance the safety and stability of concrete gravity dam structures.Originality/valueThis study offers a comprehensive analysis of concrete behavior under varying grades and introduces simple and robust expressions for evaluating concrete parameters in plastic damage models. The versatility of these expressions enables accurate simulation of stress-strain curves for different grades, resulting in excellent agreement between model results and experimental findings. The simulation of the Koyna Dam case study demonstrates a similarity in crack patterns with previous simulations and field observations.</jats:sec