Toshiyuki Mitachi

Development of a New Soil Tensile Strength Test Apparatus

This paper describes a newly developed apparatus for measuring the tensile strength of compacted and pre-consolidated saturated soft to medium clayey soils. This apparatus is simple to use to perform a soil tensile strength. Two types of tensile molds are described and results obtained from them are compared. Repeatability of test results is also verified. Effects of water content, dry density, proportions of particle size and amount of fines present in the soil are also examined. Tensile strength and unconfined compression test results are compared. It was found that the ratio of unconfined compression strength (qu) to tensile strength (qt) for statically compacted Kanto loam soil is around 12.5. In case of compacted Kanto loam, maximum value of qt and qu is obtained around 50~60% of water content for all the samples prepared at three different d ry densities (�d = 0.66, 0.68 and 0.7 g/cm 3 ). Both types of strength decrease on wet and dry sides of this maximum value. In case of mixtures of NSF clay, silt and sand in different proportions , it is observed that with the increase in the amount of finer particles, both qt and qu increase. But with the increase in the size of finer particles , reduction in the strengths is observed. In case of pre-consolidated saturated NSF clay, tensile and unconfined compression tests are performed. Saturated NSF clay samples are prepared under the preconsolidation stresses of 100, 200 and 300 kPa. The ratio of strength (qu/qt) obtained for this saturated NSF clay is around 6.

The Influence of Filter Strip Shape on Consolidated Undrained Triaxial Extension Test Results

A series of consolidated undrained triaxial extension tests was performed to investigate the influence of shape of filter strips on the required time of consolidation and undrained shear behavior of clay. Remolded saturated specimens of clay with five different filter strip shapes were consolidated isotropically in the triaxial apparatus and then sheared under undrained extension by decreasing axial stress, while lateral stress was maintained constant. Based on the test results, the filter strip with spiral slit is recommended for practical use in a consolidated undrained extension test because of fast consolidation and low tensile strength.

Factors Affecting Tensile Strength Measurement and Modified Tensile Strength Measuring Apparatus for Soil

In this paper tensile strength measuring apparatus developed by Tamrakar et al. (2005a,b) was used to measure the tensile strength of one dimensionally consolidated saturated NSF-clay and statically compacted unsaturated mixtures of NSF-clay, CFP-silt and Toyoura-sand. Tensile strength (qt) obtained from the tensile tests were compared with the unconfined compressive strength (qu). It was observed that the ratio qu/qt lied within the range of 2 to 3 for saturated NSF-clay and 4 to 16 for compacted mixtures. Effect of specimen thickness within the tensile mold, number of compaction layers and tensile pulling rates on the tensile strength were also examined. Comparing the specimen thickness within the tensile mold, it was found that the specimen having 5 cm thickness gave the minimum value. Also, tensile strength increased with the increase in the number of compaction layers. As in other shear strength, increment in the tensile strength was observed beyond tensile pulling rate of 0.34 mm/min. But below this pulling rate also, some increments were observed.

Correction Method of Settlement Values Obtained by Remote Control Plate Loading Test in Pneumatic Caisson Foundation Work

ニューマチックケーソン基礎では，施工時に平板載荷試験により基礎地盤の支持力特性を直接確認することが，大きな耐荷力の確保と高い信頼性を得る要因である。しかし，同試験は通常，高気圧の下で有人で行うことから短時間に完了する必要があり，現行試験法では荷重保持時間を短く設定せざるを得ない。筆者らが開発した遠隔操作平板載荷試験法は，平板載荷試験装置をケーソン掘削機に装着することにより遠隔操作による平板載荷試験を実現している。本試験法の特長は，厳しい高気圧下の作業を伴うことなく載荷条件の時間的自由度が拡がるため，基礎の設計荷重条件に応じた載荷ができることである。本論文は，本試験法のニューマチックケーソン基礎工事への適用を図る上で必要となる，地盤沈下量計測値の補正方法を提案し，数％以内の誤差で沈下量補正値を算出可能であることを示している。

Shear strength characteristics of undisturbed and remolded highly organic soils obtained from unconfined and triaxial test with suction measurements

不攪乱および練返し再構成の高有機質土について, サンプリングから室内試験に至るまでの作業過程をシミュレートするような一軸および三軸圧縮試験を実施した。まず不攪乱および再構成試料について異方圧密非排水せん断時のせん断特性の比較を行っている。つぎに異方圧密後応力解放し, サクションの測定から残留有効応力を知り, 不攪乱および再構成試料の残留有効応力と非排水強度の関係について調べている。再構成試料の非排水強度は不攪乱試料に比べて10%程度低下することが認められる。また, 有効せん断抵抗角は不攪乱・再構成試料に関わらず, また乱れの有無によらずほぼ一致することが確かめられた。一軸圧縮試験から得られた非排水強度は, 不攪乱および再構成試料に関わらず試験前の残留有効応力に支配されることが確認された。