Zongjian Wang

Dynamic and Static Combination Analysis Method of Slope Stability Analysis during Earthquake

The results of laboratory model tests for simulating the slope failure due to vibration, including unreinforced slope and the slope reinforced by using geotextile, show that the slope failure occurs when a cumulative plastic displacement exceeds a certain critical value. To overcome the defects of conventional stability analysis, which evaluates the slope characteristics only by its strength parameters, a numerical procedure considering the stiffness and deformation of materials and geosynthetics is proposed to evaluate the seismic slope stability. In the proposed procedure, the failure of slope is defined when the cumulative plastic displacement calculated by a dynamic response analysis using actual seismic wave exceeds the critical value of displacement estimated by a static stability analysis considering seismic coefficient. The proposed procedure is applied to the laboratory model tests and an actual failure of slope in earthquake. The case study shows the possibility that the proposed procedure gives the realistic evaluation of seismic slope stability.

Failure Mechanism of Strip Footing on Geotextile-Reinforced Soil

Several laboratory model tests were carried out on the bearing capacity of strip footings on reinforced soil foundation and reinforced slope. Compared with unreinforced cases, the deformation and failure of reinforced earth in different foundation conditions were monitored and analyzed. In order to visualize a failure mechanism when the ground reaches the state of limit equilibrium, a new numerical procedure was proposed. Assuming an elastic-perfectly plastic model, a smeared shear band approach and a modified initial stress method enable the proposed procedure to create an explicit collapse mode by the stress yield condition. On the basis of the development of failure mode and deformation of foundation, the bearing capacity of strip footings can be significantly increased by the inclusion of geotextile. And because the procedure considers the stiffness and deformation of the material, it may be applied to complex stability problems.

Analysis of Long-Term Deformation of Reinforced Retaining Wall Using Optical Fiber Sensor Geotextile

Geotextile have been widely used in the reinforced retaining wall, but it is not easy to measure the deformation of the wall during and after construction. To assess the deformation stability of the reinforced retaining wall, an optical fiber sensor was used in geotextile. Based on the measurement accuracy of strain for the sensor geotextile, an actual geotextile-reinforced retaining wall was studied using the fiber sensor geotextile. The experimental results were compared with the results from a numerical procedure, which employs the Mohr-Coulomb yield criterion and an initial stress method and determines the plastic displacement at collapse represented by the distribution of yield elements. The comparison shows that the numerical results have a good agreement with the corresponding measurement values. The result shows the possibility that the procedure gives the realistic evaluation of long-term deformation of reinforced retaining wall.

DEFORMATION OF A REINFORCED EARTH DOUBLE STRUCTURE WALL DUE TO AN EARTHQUAKE AND ITS REPAIRWORKS

平成 20 年 6 月 14 日に発生した岩手・宮城内陸地震 (マグニチュード 7.2)で,図-1に示す防災科学研究 所の強震観測網(Kik-net)の一関西 IWTH25 観測点で, 南北動1143gal,東西動1433gal,観測史上最大の上下動 3866gal,合成で 4.0G を超える最大加速度の強震記録が 得られた 。今回の地震により,補強土壁の変状が多 く確認されている 。本報告における補強土壁は図-1 の想定された断層面上に構築され,本震の震央から北西 約 4.5km の地点に位置する。当該箇所における補強土壁 の耐震設計は,中規模地震動を対象としていた。今回の 大地震は設計時の想定を大きく上回る地震動が,当補強 土壁に作用したものと推定される。地震時に補強土壁の 壁面が 170mm 程度前方へ変位し,一部の壁面材でひび割 れや角欠けが発生した。補強土壁と橋台のすり付け部に 隙間が生じて,変形吸収層の単粒度砕石が流出した。 地震後に実施した壁面変位の観測と2次元表面波探査 の結果から,ジオグリットにより補強された盛土体を含 めて,補強土壁は安定した状態であると判断された。し たがって,ジオグリットにより補強された盛土体はその ままで,損傷を受けた壁面材のみを取替えることで,補 修・復旧工事を行った。著しく変状した一般の補強土壁 を補修・復旧工事する場合は,壁面材を含めて,補強土 を全て撤去しなければいけないので,多額の工事費と工 期を必要とする。今回の補強土壁の補修・復旧工事は, 二重構造の特長を生かして,安全・経済的且つ短工期の 補修・復旧工事ができた。ここで、その補強土壁の変状 の状況と,補修・復旧工事の状況の報告を行う。