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Deformation characteristics of sedimentary rocks significantly changed with the water content during drying. In tunnel construction, extremely small displacements such as geological disposal, are a...

In addition to changes in the deformation characteristics of rock masses based on the water content, significant deformation occurs in sedimentary rocks from saturation to drying. In tunnel constru...

The stability of the tunnel face is a top priority in a tunnel construction. The estimation of the earth pressure acting in front of the face is essential for the stability evaluation of the face, and many model experiments have been conducted to understand the characteristics of face stability. On the other hand, there are many cases in which the stability of the tunnel face is evaluated by limiting analysis assuming a constant slip region by applying the loosening earth pressure derived by Terzaghi as a boundary condition, but the actual slip region is not always constant and expanded progressively accompanying by the collapse of the face. There are few past studies that have considered this phenomenon. In this study, a estimation method of the tunnel face pressure are developed in consideration of the progress of face collapse. The proposed method is a kind of limit equilibrium method. Assuming a slip line with two ellipses with the same center and different radii, the first-order linear differential equation of earth pressure in the tunnel face direction is calculated from the equilibrium for infinitesimal elements in the circumferential direction.

In recent years, the number of cases where tunnels are constructed in sedimentary rock layers has increased. It is essential to investigate the deformation characteristics of sedimentary rocks for predicting tunnel deformation. The mechanical properties of sedimentary rocks are widely varied due to moisture content. The rocks are dried by tunnel excavation and wetted by groundwater gushing or backfilling. It is necessary to grasp the changes of deformation characteristics of sedimentary rocks due to moisture changes. In this study, soaking tests were conducted on Neogene period Japanese tuff sampled at Utsunomiya, Japan. In the test, the cylindrical tuff specimens are air dried by over 240 hours at first. Then the tuff specimens are taken in pure water with measuring deformations in detail. There are no effective stress increases by soaking and only uniform matric suction are acted on the specimen without any restraints. The results demonstrated that strain tensor was reached to stable state for 2 - 3 days, and the value of the normal strain perpendicular to the bedding plane is greater than the other normal components and shear strains are also observed in both cases. Although the orientation of the maximum principal strain is in the near of the bedding orientation at the initial dry state, the orientation are suddenly rotated to the normal orientation of the bedding plane. It means that the principal orientation of anisotropy are rotated due to continuous moisture changes.

The authors introduce an experimental method that focuses on the flow-thermal relation and the visual observation of heat distribution around a cooling pipe in sand under the flow condition. This experiment aims to understand the effect of seepage flow on the heat transfer behavior of sand under cooling and freezing conditions due to a vertically buried heat exchanger pipe. This method combines a flow test, cooling or freezing processes, and the visual observations of temperature profiles with saturated Toyoura sand as the heat transfer medium. A vertical copper pipe inserted into the sand medium is used as the thermal exchanger, while an infrared thermograph is used to measure and visualize the surface-temperature profile of the specimen. The heat transfer distribution behavior is investigated by conducting a series of cooling and freezing experiments on the specimens with variation of the flow rate condition, initial condition, and pipe depth. The thermograph observation results show how water f...

Predicting the local size of a historic high-energy event from its boulders using numerical models is a challenging research topic. Modern high-energy events and their deposits are useful to validate these models; however, validating the accuracy of the results is difficult due to the scarcity of good datasets or the ambiguity of existing field data. Data on boulders transported by the 2011 Great East Japan tsunami at coastal sites (Settai, Taro, and Karakuwa) on the northeast coast of Japan were compiled. Pre-tsunami locations and settings and transport distances were found from evidence such as photographs, aerial images, and the testimony of survivors. The estimated weight of the boulders analyzed ranged from 11 to as much as 167 t, while the transport distance varied from a few to up to 600 m. Modeling results predicted that the minimum limit of maximum flow velocity of the tsunami at the pre-tsunami locations of the boulders varied from 4.2 to 6.8 m/s. The measured maximum flow depths at Settai (17–18 m) and Taro (14 m) were within the predicted range of flow depth when the Froude number = 1.0–1.5. Numerical model estimates for an older boulder (285 t) in Settai indicate that it was probably transported by a historical tsunami (1611 Keicho Sanriku event?) which may have been similar to or bigger than that of the 2011 event in the area. The maximum flow velocity could not have been less than 6.1 m/s, and if the boulder was transported to the present location by rolling, the flow velocity must have been within 7.5–23.7 m/s. Following systematic validation, the numerical modeling of boulder transport is proving promising for reconstructing the local magnitude of historical, high-energy events. Further improvements can be made with additional high quality field data from modern high-energy events.

This paper describes the petrological features and the ages of rock fractures filled mainly with carbonates at coastal outcrops of Yakushima Island, Japan. Microscopic observation and geochemical analysis were used to investigate the petrological features and the compositions of the fracture fillings. In addition, AMS 14C dating was also performed to estimate the ages of them. Microscopic study indicated that the fracture fillings contain not only cementing materials but also lithic fragments from host rock and bioclasts. SEM observation showed that the cements exhibit the characteristic textures of beachrocks. The cements were identified as Mg-calcite from XRD analysis. It was also observed from geochemical analysis that there were at least two stages of precipitation within the fractures. In addition, AMS 14C dating for seventeen samples of fracture fillings showed that the ages range from 2,460 to 5,130 years BP which is found to be younger than that of the uplifted coral at Yakushima Island (approximately 5,300–5,600 years BP). The results suggest that the fractures were solidified after the coral was uplifted.

Drying-induced deformations of porous materials are ubiquitous phenomena, but coupled behaviors of moisture content inside the material and deformation, which are difficult to express the behavior as a physical model. This is partly because multiple mechanisms governing drying-induced deformation are involved so that each mechanism may become dominant by respective situations. This article introduces various activities or efforts in some research fields, and retrieves common results in laboratory experiments and in field observations, mainly for sedimentary rocks. Through these processes, future works to be considered are elucidated.

In this study, an attempt has been made to investigate the deformation behaviour of Shirahama sandstone in drying process using small cylindrical samples. A series of comprehensive laboratory experiments was performed in different drying conditions under a no applied load. Saturated cylindrical samples were dried in a climatic chamber while deformation and evaporative water loss were being monitored. The results obtained are reported and further used in linear poroelastic relation in order to derive the matric suction evolution. In addition, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were used for evaluating their pore structure and explained its role on measured strain and estimated matric suction. The results show that virtually no volume change occurs in the samples until half of the saturated water content is evaporated. It also reveals that the maximum dimensional change capacity is independent of drying condition but evaporation rate and strain occurrences are shown to be affected significantly. In addition, the study of pore structure indicates that substantial strain magnitude and high matric suction occurrence are attributed to water loss from small pores in the clay matrix. Throughout the process, the samples displayed neither a likelihood nor tendency of damage or destruction. However, strain magnitude is observed to be higher for the sample saturated with concentrated sodium sulphate solution. The present study sheds light on essential elements in the studies of dimensional changes of clay bearing sandstone to assist in evaluating ground movement, deterioration, fluid flow and isolation properties of underground facilities.

Unsaturated hydraulic property (relation between the water retention curve and hydraulic conductivity function) of soft rock must be properly estimated for analyzing the saturated-unsaturated groundwater flow such as the flow around a tunnel, rock surface and so forth. In this study a practical technique for estimating the unsaturated hydraulic property of soft rock was developed on the basis of the Campbell model and Genetic Algorithm (GA). The major objectives of the present study are the following two; 1) investigation whether or not the Campbell model can be applied to soft rock for approximating the unsaturated hydraulic properties and 2) application of GA technique for estimating two parameters included in the Campbell model. These parameters were estimated through the inverse analysis of the transient change of evaporation rates from a surface of disk shaped specimen of Tertiary sedimentary rock which are sampled from the Rokkasho area, Aomori prefecture. Two transient evaporation experiments under different atmospheric conditions were proposed for the estimation. The Campbell's parameters of 13 soft rock specimens (5 sandstone and 8 tuff breccia specimens) were estimated through those types of experiments. As the results it was clearly found that the transient change of evaporation rates can be well fitted by the Campbell model except for the region of low saturation and this fact implies that the Campbell model can be applied to the soft rock. And also it was found that, the GA is a promising technique for parameters estimation in the inverse solution method. It can be concluded that the techniques are practically for estimating the unsaturated hydraulic properties of soft rock.

Volcanic breccia is a representative heterogeneous rock. As a preliminary study for determining its mechanical properties in laboratory and field experiments, its material properties and structural features were described. Three-dimensional clast-size distribution was also estimated for the study site using the theory of stereology. With this distribution determined, a numerical simulation was performed to investigate the relationship between the volumetric proportion of clasts in a sample and the areal proportion and maximum length of clasts on a lateral surface of the sample. The following observations were made: (1) coefficients of variation for volumetric proportion are dependent on the size of the sample, and became large when the size of the sample is small; (2) samples with a small coefficient of variation can be selected at any size if a restriction is placed on the ratio, Dmax/D0, of the maximum length of clasts to the size of the sample; and (3) the volumetric proportion of clasts in each sample can be estimated from the observed areal proportions within an error range that depends on the whole volumetric proportion.

ダブルコアチューブにより採取された比較的乱れの小さい自然状態の火山角礫岩を用いて圧密非排水試験を実施し, 力学的性質への礫含有率, 供試体寸法および最大礫径の影響を検討した. その結果, 礫含有率約40%以下の礫同士の接触が少ない状態において次のような結論を得た. 20%以上の礫の混入により内部摩擦角が若干大きくなる傾向にあるが, 礫混入の影響は比較的小さい. 弾性係数は礫含有率によって大きく変化せず, Reuss の理論式に沿った傾向を示す. 供試体寸法の影響は直径30cmまでの供試体では顕著に現われないが, 大きな供試体では内部摩擦角が若干低下する傾向にある. また供試体直径と最大礫径の比が1～3程度であっても力学的特性に大きな影響を与えない.

湿潤供試体や不均質な岩石などを対象として, 三軸圧縮試験において供試体の縦横ひずみを計測できるような局所ひずみの計測方法として, 熱収縮チューブ (HST) を利用した方法を提案した. またその検証実験を実施し, 合わせて三軸圧縮試験例を示した. さらに本手法とLDT (Local Deformation Transducer) を用いたひずみ計測を比較すると, 破壊時まで両者はほぼ一致した出力を示した. 本手法は簡便なひずみ計測方法として, 十分使用できるものと考えられる. 提案した手法は, 三軸セルからのゲージ取り出し口さえ準備すれば, 現有のセルをそのまま利用できる利点がある.

稲田花崗岩内の初期マイクロクラック分布について, 岩石薄片からのクラック抽出結果を画像解析することにより検討した. その結果, 薄片レベルにおいてクラックの空間的な分布は非常に不均質であることが明らかとなった. すなわち, 平均粒径が2mmである主構成鉱物が集合して平均間隔5-10mmのクラスター状に分布しているため, 岩石内で主に石英内に密集して分布している比較的長いクラックの分布もクラスター状となる. 稲田花崗岩の石目はクラック方向分布の最頻値の大きさによって特徴づけることができる. rift面を形成するクラックは長いものが多く粒間クラックが発達するが, 方向分布の散布度は小さい. grain面を形成するクラックにも比較的長いものが多いが, rift面を形成するクラックよりは本数が少なく, 散布度が大きい. それらに比べてhardway面を形成するクラックは短く, 本数も少ない. 一方, 各面におけるクラック長さの頻度分布は, 方向によらずほぼ同様の傾向を示す. また, 長さ別の方向分布は計測限界によらず相似形となる. 石切場におけるgrain面の方向とクラックの方向分布とは10-20°ほど異なり, クラック分布という観点から見ると稲田花崗岩は完全な直交異方性材料ではないと考えられる. また, このようにクラック分布が石目の主軸からずれていることが, 三軸圧縮試験時の最終的な破断面形成に大きな役割を果たしていると考えられる.

Changes in the pore pressure during CU (Consolidated-Undrained) cyclic loading triaxial tests on fully saturated specimens of four Miocene soft rocks, i.e. Ohya tuff, Yokohama siltstone, Kobe mudstone and sandstone are analyzed. As a result, three modes of failure, i.e. brittle, brittle-ductile and ductile can be recognized, and other characteristic stress levels e.g. crack initiation stress, plastic flow/gliding stress, dilation stress, etc. identified. The mobilization of the strength of these rocks in terms of cohesion and internal friction angle is then discussed. A procedure for the estimation of the rock cohesion strength is first introduced on the basis of the modified Griffith's failure criterion. The determination of the mobilized friction angle at any state of stress during the tests follows.

Consolidated-undrained, cyclic triaxial tests were performed on four saturated Miocene soft rocks of Japan namely Ohya tuff, Yokohama siltstone, Kobe mudstone and sandstone. Deformation behavior, pore pressure changes and strength mobilization as well as contraction/dilation characteristics of these rocks were studied with emphasis on the non-linearity, stress- and strain-dependence of their mechanical properties. A procedure was introduced to locate the yield point, estimate Young's modulus and study the deformation behavior of these soft rocks. Patterns of pore pressure changes and associated modes of failure were studied. Characteristic stress levels were found, based on which the “true” rock strength components were determined and their mobilization with respect to stress- and strain levels was analyzed. Volume change tendencies were inferred from pore pressure changes. The rate of such changes was related to the contraction/dilation behavior of soft rocks, from which the dilation angle was estimated and its stress- and strain-dependence was studied. The findings were applied to the FEM simulation of triaxial tests on-and of excavation in/on soft rocks.

A new type apparatus for shear-flow coupling test, named coupled shear-flow-visualization apparatus, was developed to investigate the hydromechanical behavior and the fracturing process of intact soft sedimentary rock. With this apparatus, it is possible to simultaneously carry out direct shear test and constant head flow test, and also to observe specimen surface during the experiment. Under controlled shear load, normal load, flow rate and shear displacement can be obtained as raw data. Moreover, fracture area and fracture apertures can be estimated using image-processing techniques. The shear and normal stress capacities of load cells are 4.08 MPa and 3.33 MPa, respectively. The measurable maximum permeability of apparatus is about 5.80×10 −3 cm/s under a hydraulic gradient of 40 cm/cm. According to the observation of visible fractures on specimen surface, the fractures were not completely propagated at the peak of shear stress. The developed testing method with image processing techniques enabled us to analyze the relationships between fracture flow rate, hydraulic aperture and two fracture apertures defined in this study.