• Computers and Concrete
• /
• 제18권2호
• /
• pp.235-266
• /
• 2016

A rock mass containing non-persistent joints can only fail if the joints propagate and coalesce through an intact rock bridge. Shear strength of rock mass containing non-persistent joints is highly affected by the both, mechanical behavior and geometrical configuration of non-persistent joints located in a rock mass. Existence of rock joints and rock bridges are the most important factors complicating mechanical responses of a rock mass to stress loading. The joint-bridge interaction and bridge failure dominates mechanical behavior of jointed rock masses and the stability of rock excavations. The purpose of this review paper is to present techniques, progresses and the likely future development directions in experimental and numerical modelling of a non-persistent joint failure behaviour. Such investigation is essential to study the fundamental failures occurring in a rock bridge, for assessing anticipated and actual performances of the structures built on or in rock masses. This paper is divided into two sections. In the first part, experimental investigations have been represented followed by a summarized numerical modelling. Experimental results showed failure mechanism of a rock bridge under different loading conditions. Also effects of the number of non-persistent joints, angle between joint and a rock bridge, lengths of the rock bridge and the joint were investigated on the rock bridge failure behaviour. Numerical simulation results are used to validate experimental outputs.

• Geomechanics and Engineering
• /
• 제18권5호
• /
• pp.545-554
• /
• 2019

The customary approach used in the blast vibration analysis is to derive empirical relations between the peak particle velocities of blast-induced waves and the scaled distance, and to develop patterns limiting the amounts of explosives. During the periods when excavations involving blasting were performed at sites far from residential areas and infrastructure works, this method based on empirical correlations could be effective in reducing vibrations. However, blasting procedures applied by the fast-moving mining and construction industries today can be very close to, in particular cities, residential areas, pipelines, geothermal sites, etc., and this reveals the need to minimize blast vibrations not only by limiting the use of explosives, but also employing new scientific and technological methods. The conventional methodology in minimizing blast vibrations involves the steps of i) measuring by seismograph peak particle velocity induced by blasting, ii) defining ground transmission constants between the blasting area and the target station, iii) finding out the empirical relation involving the propagation of seismic waves, and iv) employing this relation to identify highest amount of explosive that may safely be fired at a time for blasting. This paper addresses practical difficulties during the implementation of this conventional method, particularly the defects and errors in data evaluation and analysis; illustrates the disadvantages of the method; emphasizes essential considerations in case the method is implemented; and finally discusses methods that would fit better to the conditions and demands of the present time compared to the conventional method that intrinsically hosts the abovementioned disadvantages.

• Geomechanics and Engineering
• /
• 제16권6호
• /
• pp.635-642
• /
• 2018

Braced excavation systems are commonly required to ensure stability in construction of basements for shopping malls, underground transportation and other habitation facilities. For excavations in deposits of soft clays or residual soils, stiff retaining wall systems such as diaphragm walls are commonly adopted to restrain the ground movements and wall deflections in order to prevent damage to surrounding buildings and utilities. The ground surface settlement behind the excavation is closely associated with the magnitude of basal heave and the wall deflections and is also greatly influenced by the possible groundwater drawdown caused by potential wall leakage, flow from beneath the wall, flow from perched water and along the wall interface or poor panel connections due to the less satisfactory quality. This paper numerically investigates the influences of excavation geometries, the system stiffness, the soil properties and the groundwater drawdown on ground surface settlement and develops a simplified maximum surface settlement Logarithm Regression model for the maximum ground surface settlement estimation. The settlements estimated by this model compare favorably with a number of published and instrumented records.

• Geomechanics and Engineering
• /
• 제16권6호
• /
• pp.577-588
• /
• 2018

A major concern in deep excavation project in soft clay deposits is the potential for adjacent buildings to be damaged as a result of the associated excessive ground movements. In order to accurately determine the wall deflections using a numerical procedure such as the finite element method, it is critical to use the correct soil parameters such as the stiffness/strength properties. This can be carried out by performing an inverse analysis using the measured wall deflections. This paper firstly presents the results of extensive plane strain finite element analyses of braced diaphragm walls to examine the influence of various parameters such as the excavation geometry, soil properties and wall stiffness on the wall deflections. Based on these results, a multivariate adaptive regression splines (MARS) model was developed for inverse parameter identification of the soil relative stiffness ratio. A second MARS model was also developed for inverse parameter estimation of the wall system stiffness, to enable designers to determine the appropriate wall size during the preliminary design phase. Soil relative stiffness ratios and system stiffness values derived via these two different MARS models were found to compare favourably with a number of field and published records.

• 헤리티지:역사와 과학
• /
• 제33권
• /
• pp.68-92
• /
• 2000

This paper reconsiders the users of iron arrowheads from Mongchon Earthen Wall(夢村土城). Because the Mongchon Earthen Wall has been seen as a major dwelling fort of the Hansong Period(漢城時代 : 18 B.C.~475), Paekche(百濟), these iron arrowheads have been considered as artifacts of the Hansong Paekche with no systematic analysis since they were found in 1985. However, uncovering numerous Koguryo artifacts, the excavations in 1988 and 1989 showed that Koguryo(高句麗) army had occupied the Mongchon Earthen Wall after they had conquered Hansong Paekche. In this paper, focusing on the formal similarity between these arrowheads and those from other Koguryo sites, I attempt to reconsider the nature of arrowheads from the Mongchon Earthen Wall. Found from a small pit, all of these arrowheads (88 in number) seem to have been contemporaneous. While all are stemmed, they can be divided into nine types on the basis of the shape of body and point. Most types are equal or similar to Koguryo arrowheads of other regions, and especially type F and G have not been found in southern Korean Peninsula. Accordingly, it is suggested that the existing models be reconsidered, and that Koguryo army who had conquered Hansong Paekche used these arrowheads around mid-5th century AD. Although at this point it is difficult to determine the users of these arrowheads only by analyzing several formal attributes due to Korean archaeology's little understanding of the arrowheads of the Three Kingdoms Period(三國時代), I expect that application of natural scientific methods will contribute to a better understanding.

• Acta Via Serica
• /
• 제6권2호
• /
• pp.61-90
• /
• 2021

Recent excavations in Qinghai Province, China, have disclosed textiles and artworks from Tuyuhun-Tubo (Tibetan) tombs, dated to the 7^th-9^th centuries, that suggest artistic and cultural exchanges along an external southern branch of the main Silk Road, between Gansu and Sichuan Provinces, across the Qinghai-Tibetan plateau toward the Himalayas. Many similar textiles, possibly from this area, have appeared lately on the art market and ended in private collections. Although these textiles, dated to the early Tibetan period, follow a popular prototype established in Central Asia in the 6^th century, the technical features, colors, and other indigenous elements suggest that they were woven in workshops different from those established between Sogdiana and Gansu. The exhibition "Cultural Exchange Along the Silk Road - Masterpieces of the Tubo Period," organized by the Dunhuang Research Academy and the Pritzker Collaborative Art between July and October 2019 in Dunhuang, Gansu, was a groundbreaking event that gathered scholarly attention on early Tibetan material culture, but a relevant publication is still forthcoming. In my previous work, I briefly discussed a group of silk textiles, possibly from Qinghai or Sichuan, that I analyzed in 2014 in the China National Silk Museum in Hangzhou, Zhejiang. In light of the recent material excavated, published online, or displayed in Dunhuang, in this article, I reevaluate the data previously collected, and discuss in detail the technical and iconographic features of one of the fragments held in Hangzhou. Eventually, the piece was recognized as the ending part of a large panel, which is now in the Abegg Stiftung in Riggisberg, Switzerland.

• Structural Engineering and Mechanics
• /
• 제84권6호
• /
• pp.743-765
• /
• 2022

Near-surface excavations may cause the tilting and destruction of the adjacent superstructures in big cities. The stability of a huge excavation and its nearby superstructures was studied in this paper. Some test instruments monitored the deformation and loads at the designed location. Then the numerical models of the excavation were made in FLAC3D (a three-dimensional finite difference code) and Plaxis-3D (a three-dimensional finite element code). The effects of different supporting and reinforcement tools such as nails, piles, and shotcretes on the stability and bearing capacity of the foundation were analyzed through different numerical models. The numerically approximated results were compared with the corresponding in-field monitored results and reasonable compatibility was obtained. It was concluded that the displacement in excavation and the settlement of the nearby superstructure increases gradually as the depth of excavation rises. The effects of support and reinforcements were also observed and modeled in this study. The settlement of the structure gradually decreased as the supports were installed. These analyses showed that the pile significantly increased the bearing capacity and decreased the settlement of the superstructure. As a whole, the monitoring and numerical simulation results were in good consistency with one another in this practically important project.

• Earthquakes and Structures
• /
• 제22권3호
• /
• pp.277-287
• /
• 2022

The ancient underground cities are a collection of self-supporting spaces that have been manually excavated in the soil or rock in the past. Because these structures have a very high cultural value due to their age, the study of their stability under the influence of natural hazards, such as earthquakes, is very important. In this research, while introducing the underground city of Ouyi Nushabad located in the center of Iran as one of the largest man-made underground cities of the old world, the analysis of dynamic stability is performed. For this purpose, the dynamic stress-displacement analysis has been performed through numerical modeling using the finite element software PLAXIS. At this stage, by simulating the Khorgo earthquake as one of the large-scale earthquakes that occurred in Iran, with a magnitude of 6.9 on the Richter scale, dynamic analysis by time history method has been performed on three selected sections of underground spaces. This study shows that the maximum amount of horizontal and vertical dynamic displacement is 12.9 cm and 17.7 cm, respectively, which was obtained in section 2. The comparison of the results shows that by increasing the cross-sectional area of the excavation, especially the distance between the roof and the floor, in addition to increasing the amount of horizontal and vertical dynamic displacement, the obtained maximum acceleration is intensified compared to the mapping acceleration applied to the model floor. Therefore, preventive actions should be taken to stabilize the excavations in order to prevent damage caused by a possible earthquake.

• 수완나부미
• /
• 제7권1호
• /
• pp.157-186
• /
• 2015

Sittaung-Thanlwin region in Lower Myanmar is an ecological niche for human settlement. Evidences of human activities in the region are seen through various archaeological sites or settlements along the coastal area between the rivers Sittaung and Thanlwin (Salween). In Lower Myanmar, scholar, U Aung Myint, discovered one major site Kyaikkatha and other small scale sites, namely, Sittaung, Kawhtin, Kadaikgyi, Kadaikkalay, Katkadit, Kelatha (little Zothoke), Ayetthama, Winka, Zothoke (big Zothoke), Lagonbyi (Sampannago), Wagaru, Laming and Ye in present day Mon State. In 1980, U Aung Myint undertook an exploration program at Kyaikkatha. After the exploration, an excavation team conducted systematic digging at Kyaikkatha in March 1986. Excavation continued occasionally at Kyaikkatha throughout the years between 1995 and 2000. It is known that Kyaikkatha, the old city, reveals a kind of monumental civilization exposing four religious structures (a stupa and three monasteries). This essay looks into the distribution of features within Kyaikkatha and infers on its social, political, and religious organization. This essay is also about a new discovery of an early urban settlement located at the apex of the Gulf of Muttama (Martaban) where a lost city of Suvannahumi flourished in the ancient days. By means of aerial photographic observations, the site had been noticed recently, which was by followed some excavations. More systematic and detail surveying may be needed to know more about the site and its features for comparison to other similar settlements of through-out mainland South East Asia.

• Geomechanics and Engineering
• /
• 제37권6호
• /
• pp.629-641
• /
• 2024

The presence of excavations or cavities beneath the foundations of a building can have a significant impact on their stability and cause extensive damage. Traditional methods for calculating the bearing capacity and subsidence of foundations over cavities can be complex and time-consuming, particularly when dealing with conditions that vary. In such situations, machine learning (ML) and deep learning (DL) techniques provide effective alternatives. This study concentrates on constructing a prediction model based on the performance of ML and DL algorithms that can be applied in real-world settings. The efficacy of eight algorithms, including Regression Analysis, k-Nearest Neighbor, Decision Tree, Random Forest, Multivariate Regression Spline, Artificial Neural Network, and Deep Neural Network, was evaluated. Using a Python-assisted automation technique integrated with the PLAXIS 2D platform, a dataset containing 272 cases with eight input parameters and one target variable was generated. In general, the DL model performed better than the ML models, and all models, except the regression models, attained outstanding results with an R² greater than 0.90. These models can also be used as surrogate models in reliability analysis to evaluate failure risks and probabilities.