Weak Ground Research Articles

İNŞAAT MÜHENDİSLİĞİNDE ZAYIF ZEMİNLER VE ZEMİN İYİLEŞTİRME YÖNTEMLERİ

In this article, focuses on weak soils and soil all previous studies on weak soils and soil improvements in civil engineering.  For this purpose all academic studies conducted  in the past were scanned, relevant ones were compiled  and it was tried to understand how to determine the most appropriate and most efficient method in improvement. The weakest feature of the soils reveals itself in its bearing capacity. İt is understood from the increase of academic studies publıshed in resent years that different additives are added to these weak soıls under laboratory conditions and there is a search improving the geotechnical parameters of this soıls. It has been understood that the addition of fly ash to a weak and clayey ground and keeping this ground in the appropriate curing time is an effective method for soil improvement since it increases the bearing capacity of the weak ground, and this additive material can give the highest strength by keeping it for the most appropriate curing time. In addition, it has been revealed by experimental studies that the addition of different additives (cement, polymer, garbage water) in appropriate proportions on a sandy or silty weak ground increases the strength of the soil and its resistance to fluidity. Likewise, subjecting a weak ground to consolidation by compressing it with the optimum water content by the compaction method will result in a decrease in the void ratio and naturally increase in the bearing power. The results obtained as a result of all these experimental applications should be evaluated among the soil improvement methods. For this reason based on the soıl improvement methods in all this studies, a remerkable and aplıcable comon starting poınt was trıed to be determined under the tıtle of this article and the methods in the literature studies were associated with the suggestıon from this article.

A special support design for a large-span tunnel crossing an active fault (T9 Tunnel, Ankara–Sivas High-Speed Railway Project, Turkey)

Throughout construction process of a tunnel in an active tectonic region, it may be impossible to avoid active faults. Active faults create two adverse effects on the tunnels which are sudden fault displacement and weak ground conditions in fault zone. If a tunnel crossed by an active fault, the tunnel might be damaged by sudden movement of the fault. However, the main goal is to localize this damage without complete loss of tunnel. In this study, a special design developed for a wide span tunnel cut by an active fault is presented and the performance of the design is verified by numerical analyses. T9 tunnel was constructed within the scope of Ankara–Sivas High-Speed Train Project, Turkey, and the special design at the intersection of T9 tunnel with the Akdagmadeni active fault is the main subject of this study. T9 tunnel predominantly passes through agglomerate, basalt, marble and gneiss units and the tunnel route crosses the Akdagmadeni fault at around Km: 327 + 915. At this location, major deformations occurred in the tunnel and the tunnel excavation had to stop for a certain period. After the re-design phase, a special tunnel support system for this location were developed and proposed design was analyzed with numerical analyses. In addition, the possible displacement of the Akdagmadeni fault was estimated and the inner lining was re-designed considering the seismic parameters (i.e. peak ground acceleration and maximum displacement during a large earthquake). Consequently, in the present study, the effects of active fault crossing on the tunnel were explained and a special inner lining design was proposed to localize the possible damages, which are originated from the sudden displacement of the active fault.

Underground mine stream crossing assessment: A multi-disciplinary approach

Underground mine designs typically try to avoid extraction beneath streams and rivers of any significant size, especially when the overburden rock thickness between the stream bed and the mine is thin. Potential issues with mining beneath streams include excessive groundwater inflow to the mine, weak ground (roof, floor, and pillar) conditions, horizontal stress effects, as well as stream loss and other potential adverse environmental effects. However, there are times when crossing beneath a stream or river is necessary to move into a new area of mineral reserve without creating additional mine access points from the ground surface. Often, stream crossings are completed without thorough assessment, potentially resulting in increased costs, decreased safety, and, in some cases, failure to advance the mine. Selection of the most favorable location(s) to cross the stream must account for numerous factors and the associated assessment often requires a multi-disciplinary approach. Stream crossing investigations often require geological, hydrogeological, geotechnical, and geophysical expertise. Phases of stream crossing investigations include desktop evaluation of maps and aerial photography, stream bed observations, drilling, detailed rock core logging, downhole geophysical surveying, hydraulic conductivity testing (packer testing), geotechnical laboratory testing, assessment, and reporting. The deliverables from a stream crossing assessment typically include geological, geotechnical, and hydrogeological characterization of potential stream crossing locations, classification of favorable and unfavorable crossing locations, recommendations for entry design and pillar sizing, and recommendations for if, and how, to conduct pre-grouting activities. Examples of technical aspects of data collection and assessment are provided based on decades of industry experience conducting stream crossing assessments in various underground mining scenarios.

Weak Ground Truth Determination of Continuous Human-Rated Data

The article presents a novel weak ground truth (WGT) determination procedure on continuous human-rated data. The notion of WGT is essential in cases where there is no direct empirical evidence for an observed construct and human annotations provide the most reliable means for determining the ground truth. The core idea behind the proposed procedure is to transform the ratings to reduce rater bias, maximize inter-rater agreement, and improve WGT. The procedure was evaluated on two behavioral datasets containing continuous annotations of several expressive dimensions. The results show that the procedure improves the size of WGT data by removing the disagreement originating from rater-specific distortions, such as rater mean and scaling bias. The entropy of residuals decreases after WGT optimization, meaning that more relevant information is retained. The average improvement of WGT data size is between 10.1 and 20.9 percentage points, depending on the respective dimension. However, in cases where the rater bias is small, the procedure does not substantially modify WGT. This indicates that the proposed optimization only removes rater biases derived from rater-specific distortions, while retaining and improving valid WGT. The proposed procedure is generalizable on any type and size of continuous or discrete numerical data where multiple raters are involved.

Transform-domain noise synthesis and normal moveout-stack deconvolution approach to ground roll attenuation

Ground roll is coherent noise in land seismic data that contaminates seismic reflections. Therefore, it is essential to find efficient ways that remove this noise and still preserve reflections. To this end, we have developed a signal and noise separation framework that uses a hyperbolic moveout assumption on reflections, coupled with the synthesis of coherent ground roll. This framework yields a least-squares problem, which we solve using a sparsity-promoting program that gives coefficients capable of modeling the signal and noise. Subtraction of the predicted noise from the observed data produces data with amplitude-preserved reflections. We develop this technique on synthetic and field data contaminated by weak and strong ground roll noise. Compared to conventional Fourier filtering techniques, our method accurately removes the ground roll while preserving the amplitude of the signal.

Google Earth Imageries for Validating Groundwater Recharge Zone in Basaltic region

Abstract A majority of the existing groundwater potential studies in the literature lack adequate validation. In developing countries, it is attributed to many reasons including- poor/limited data on water yield, sparse spatial and temporal data on wells, lack of data protocol/sharing, a weak ground water governance structure such as disparate agencies, lack of registration/georeferencing of irrigation wells. A rapid, simple and replicable approach is proposed to overcome these difficulties using Google Earth imageries for visual interpretation, interwined with cadastral data and telecommunication for a representative block located in basaltic region of Maharashtra, India. Each of 1684 irrigation well in the study area was enumerated, its irrigation area estimated and verified through available records, field visits, telecommunication with well owners and georeferenced to link with land parcel identification number and build well information system. Functional and defunct wells were distinguished using deacadel timeline data. Nine major biophysical and environmental factors namely geomorphology, soil, land use land cover, slope, lineament density, drainage density, topographical wetness index, curvature and aspect were analyzed to asses the groundwater recharge potential (GWP). The GWP zones were verified using the georeferenced enumeration data on wells, their density and area irrigated per unit well. The number of wells, functional well density followed an order high < moderate < moderate to poor < poor to nil, i.e. highest density (0.034/ha) in high potential zone and lowest density (0/ha) in poor to nil potential zone. Number of defunct wells also exhibited linear correspondence with least share (51%) in ‘high’ potential zone and higher share (76%) in ‘moderate to poor’ potential zone. It is concluded that Google Earth imageries provide direct and conclusive well enumeration, its irrigated area and therby accurate means of evaluating GWP zonation. It has immense potential for use in many countries where historical data are inadequate to assist groundwater management/governance.

Identifying Different Classes of Seismic Noise Signals Using Unsupervised Learning

AbstractProper classification of nontectonic seismic signals is critical for detecting microearthquakes and developing an improved understanding of ongoing weak ground motions. We use unsupervised machine learning to label five classes of nonstationary seismic noise common in continuous waveforms. Temporal and spectral features describing the data are clustered to identify separable types of emergent and impulsive waveforms. The trained clustering model is used to classify every 1 s of continuous seismic records from a dense seismic array with 10–30 m station spacing. We show that dominate noise signals can be highly localized and vary on length scales of hundreds of meters. The methodology demonstrates the complexity of weak ground motions and improves the standard of analyzing seismic waveforms with a low signal‐to‐noise ratio. Application of this technique will improve the ability to detect genuine microseismic events in noisy environments where seismic sensors record earthquake‐like signals originating from nontectonic sources.

Characteristics of spatial variability of shear wave velocity on seismic response of slopes

The soil shear wave velocity has long been recognized as an effective parameter in the assessment of the seismic response of slopes. However, most seismic analyses have been carried out by deterministic models considering just a single realization of soil shear wave velocity. In other words, only a small number of researchers have explored the spatial variability effects of soil shear wave velocity on the seismic response of slopes. This paper investigates this phenomenon stochastically, and the auto-correlation matrix decomposition method based on Monte Carlo Simulation was applied to generate the stationary random fields in order to simulate the spatial variability of soil shear wave velocity. This framework includes interpreting the coefficient of the soil shear modulus variation and auto-correlation length effected on maximum horizontal equivalent acceleration. The results showed that the spatial variation of shear wave velocity might have a significant effect on the dynamic response of the sliding mass if slopes were subjected to weak ground motions. By contrast, it could have a significant effect on maximum horizontal equivalent acceleration induced in slopes subjected to intense ground motions.

Hybrid predictor for ground-motion intensity with machine learning and conventional ground motion prediction equation

The use of strongly biased data generally leads to large distortions in a trained machine learning model. We face this problem when constructing a predictor for earthquake-generated ground-motion intensity with machine learning. The machine learning predictor constructed in this study has an underestimation problem for strong motions, although the data fit on relatively weak ground motions is good. This underestimation problem is caused by the strong bias in available ground-motion records; there are few records of strong motions in the dataset. Therefore, we propose a hybrid approach of machine learning and conventional ground-motion prediction equation. This study demonstrates that this hybrid approach machine learning technology and physical model reduces the underestimation of strong motions and leads to better prediction than either of the individual approaches applied alone.

The critical forces in the weak ground under the influence of technogenic relief

The initial critical force that the ground is exposed to from the weight of a structure is one of the main characteristics of the “structure-ground environment” system. A significant part of grounds are classified as weak, and the strain modulus value does not exceed 5 MPa. These soils have a weak load-carrying capacity and they are significantly deformed by the weight of the structures and the static load of technogenic relief. The theory and methodology of determining the initial critical force and its maximal action depth for various two-dimensional technogenic land forms, the force diagrams of which are described by trapezes and triangles of various types, are considered. The models grounds considered herein are a homogeneous elastic half-space or horizontally layered strata on the surface of a homogeneous elastic half-space. The nomograms of the relations of the initial critical force and its maximum depth of action to the ground’s physical and mechanical properties are attained. The identified relations are quasi-linear and the value of the initial critical force increases with an increase in the ground’s physical and mechanical parameters. The presented nomograms significantly simplify the calculation of the initial critical force in the ground.

Critical issues for the ground control of shallow roadways in weak ground: a case study

The roadways located in weak ground experience strong and cyclic dynamic loading induced by the thick coal seam extraction, which caused costly support and delay of normal production. This paper discusses the critical issues and support strategy for such roadways through a case study on a roof collapsed roadway which was excavated in a coal stratum at a depth of 120 m in Shanxi Province, China. A 2-m-high void between the concrete support and the exposed roof strata was left untreated due to poor roadway construction. The roadway collapse reached up to approximately 6 m in the roof strata, which was attributed to the large untreated void as well as the highly fractured rock mass. A combination support method of the void filling, the fracture grouting, and rock bolting was proposed to rebuild and reinforce the roadway. The deformation of the roadway was effectively controlled, and the maximum roof displacement reached 135 mm. The failure mechanism of the roadway was numerically investigated using discontinuous deformation analysis (DDA) based on specific geological conditions. The numerical findings suggested that the void above the roadway could significantly impact on the stability of the overlying strata.

Shaking table tests on V-shaped RC columns at the weak ground storey of a building

This paper presents experimental and numerical investigations of the seismic behaviour of V-shaped reinforced-concrete (RC) columns at the weak ground storey of a building. Two half-scaled RC columns were tested to failure by a simulated ground acceleration time history using a shaking table. The test setup was designed to simulate the sliding mechanism of the column specimens, termed the double-curvature mechanism, which is expected to occur in a soft-storey building. The seismic responses of the specimens were evaluated and compared with each other in terms of general performance, hysteresis response and failure modes. Thereafter, a fibre-element model, verified by the test data, was used to conduct a parametric study on the effects of axial load ratio and longitudinal reinforcement arrangement on the seismic performance of irregularly shaped columns.

Modification of the data-driven period/height relationship for buildings located in seismic-prone regions such as Quito (Ecuador)

The fundamental period of structures is a parameter used in structure under design and for evaluating existing structures. Data-driven methods using ambient vibrations have become popular, particularly for the adjustment of empirical relationships applied to building classes. This study presents the results of a survey of ambient vibrations performed in 146 reinforced concrete buildings in the center of Quito (Ecuador). Classical functional forms giving period (T) for height (H) or number of floors (N) are derived and compared with the relationships available in the Ecuadorian seismic design provisions. We highlight variations in the empirical relationships according to soil conditions, but above all according to the date of construction and the historic seismic sequence to which the buildings have been exposed. The cumulative damage effect is finally confirmed by repeating ambient vibration measurements after the 2016 Mw 7.8 Pedernales earthquake located in the subduction zone, about 175 km from Quito. Even with such a long epicentral distance, leading to low macroseismic intensity (IEMS98 = IV), the seismic ground motion of between 0.017 and 0.081 g recorded in Quito reduced the resonant frequency of the buildings tested by between 2 and 13%. This confirms the effect of cumulative damage in reinforced concrete buildings located in seismic zones, even for weak ground motions, and the variability of empirical T/H relationships associated with damage.

Regional Air Pollution Process in Winter over the Yangtze River Delta and Its Influence on Typical Northern Cities

In this study, we analyzed several pollution episodes that occurred in the autumn and winter of 2018-2019 using multiple methods including the hierarchical clustering analysis, backward trajectory, and potential source contribution analysis based on monitored air quality and meteorological data. Bengbu, being a representative city to the north of the Yangtze River Delta (YRD) region and located in a heavily polluted area during these two pollution processes, is the focus of this work. The results indicated that the northern part of the YRD region is affected because of unfavorable meteorological conditions such as weak ground pressure, high humidity, low temperature, low wind speeds, and regional transport. The regional pollution processes over the YRD region in the autumn and winter seasons exhibit characteristics of wide influence and long duration with mainly two types of pollution:regional transport and intra-regional accumulation. During the two selected pollution episodes, the average PM2.5 concentration in the northern YRD region reached 131.6 μg·m-3 and 115.4 μg·m-3, respectively. The former type had a shorter duration but exhibited rapid accumulation of pollutants in a short period of time with greater pollution intensity, wider pollution range, and deeper pollution intrusion. Qualitative and quantitative analysis of the potential sources of PM2.5 based on PSCF and CWT showed that the PM2.5 concentration during EP1 was due to transport from cities such as Linyi, Xuzhou, Suqian, and Lianyungang to the pollution trajectory. The CWT value generally exceeded 80 with the highest value near 200. In contrast, EP2 was affected by the neighboring cities such as Suqian, Suzhou, and Xuzhou, and the CWT value was over 60 with the highest approaching 160, indicating that the interaction among cities in the study area is significant. This study shows that cross-regional air pollution control strategies are particularly important for alleviating the pollution situation in the northern part of the YRD region.

Publicity, Propaganda and Press: All India Muslim League in Propagation of Demand for Pakistan

The evolution and growth of press in the Subcontinent revolutionized the flow of information and propagation of political activities. All-India Muslim League went through the process of reorganization in the late 1930's and the new political resolve needed more publicity and propaganda to expand further among the masses. League handled the need of the hour by starting its party-owned newspapers while the provincial Leagues and some of the League organs launched their newspapers to publicize policy and program of the party. The major share in the press came from the Leaguers and pro League newspapers from all over India. The last phase of the freedom movement witnessed the emergence of a more radical and outspoken press in support of the demand for Pakistan. Overseas publicity and press remained weak ground for League due it financial constraints. The Middle East zone was omnipresent in League's activities due to its Islamist stance.England publicity wing started working quite late but it remained successful in making a mark over the minds of the public. The American front was neglected and only a few appearances were available to propagate League and its demand for Pakistan.

Selected safety issues in designing engineering structures

The article discusses the safety requirements specified in pertinent standards and recommendations for designing civil engineering objects, with particular emphasis on earth structures intended for vehicle traffic. The focus was on the following issues: the essence of reliability and durability of the structure and ensuring safety at the stage of designing vehicle traffic embankments with a slope supported with the use of a retaining wall and embankments placed on a substrate characterized by insufficient bearing capacity. The procedure for designing traffic embankments on weak ground, reinforcing weak ground and designing retaining structures (on the example of a reinforced soil massif) was carried out in accordance with the calculations pertaining to the field of geo-engineering, applying general analytical dependencies.

Steel tubular friction damper and vibration reduction effects of double-layer reticulated shells

A steel tubular friction damper (STFD) is proposed for vibration reduction in large-span spatial structures. The effects of the amplitude of the applied displacement, the pre-tightening force of the high-strength bolts, and the material of the friction plates on the hysteretic behaviour of the STFD are analysed experimentally. The single-cycle energy consumption increases and the equivalent stiffness decreases with increasing displacement amplitude. In addition, the single-cycle energy consumption and equivalent stiffness of the STFD increase with increasing pre-tightening force. Both the single-cycle energy consumption and the equivalent stiffness of the STFD with aluminium alloy or brass friction plates are larger than that of the STFD with steel friction plates. Then, a mechanical model of the STFD is established for further numerical analysis. Several structural members in a 40-m-span double-layer reticulated shell are replaced with STFDs to provide vibration reduction. Optimal arrangement of STFDs is studied based on additional modal damping ratio. The effects of the replacement rate, earthquake intensity and various ground motions on the vibration reduction effect are investigated via numerical analyses. The reduction ratio first increases and then decreases with increasing replacement rate, and the best performance is observed at a replacement rate of 10%. The vibration reduction effect of the STFDs is more obvious for strong ground motions than for weak ground motions. Under various ground motions, the vibration reduction effect of the STFDs is better for the two ordinary ground motions than for the four long-period ground motions selected herein.

Study of the influence of face pressure on surface settlements by shield tunneling

In the mechanized excavation of subway tunnels, the shield tunnel boring machine (TBM) has been developed in recent decades for managing the instability of the excavation profile in complicated geotechnical conditions in urban areas. The paper presents a 3D simulation procedure for the detailed description of TBM (via the finite element code Abaqus) and quantifies the influence of TBM face pressure on ground surface settlements. The model is used to calculate ground surface settlements for different values of TBM face pressure. An additional aspect of the investigation is the determination of the critical value of TBM face pressure, which controls face instability in very weak ground. During the advancement of shield tunnel boring machines, the face-stabilizing pressure is one of the most important factors of critical. In tunneling by shield tunnel boring machines, high face pressure often leads to surface upheaval, whereas low face pressure leads to sudden collapse of the face and ultimately settlement of the surface. For the model condition, the maximum value was quantity 250 kPa and the minimum value obtained quantity 150 KPa.

Problems Encountered during a Railway Tunnel Excavation in Squeezing and Swelling Materials and Possible Engineering Measures: A Case Study from Turkey

The T3 railway tunnel—under construction within the scope of the Bursa-Yenişehir high-speed train project—is located in northwestern Turkey and has a length of 1250 m. The tunnel is being constructed entirely in silty clay/clayey silt, sand, and clay units, and it is designed in accordance with the principles of weak ground tunneling described by the new Austrian tunneling method (NATM). When the tunnel excavations began in 2013, during and after portal excavations, a failure occurred at the entrance of the tunnel; thus, a revision of the support systems became mandatory. While the excavation works proceeded after the revision phase, a collapse occurred again at the tunnel face where the overburden thickness was low. This study presents the mechanisms of the collapse that took place at the portal location and in the middle of the tunnel. The proposed tunnel support systems and their numerical analyses are also discussed, because the case is interesting for the tunnel community and will inform future tunnel construction work. For this reason, the relationship between portal excavation and tunnel excavation stability is described. Consequently, tunnels excavated through weak ground conditions are considered, and the importance of considering the face stability of tunnels in tunneling studies is underlined.

The Influence of Surface Topography on the Weak Ground Shaking in Kathmandu Valley during the 2015 Gorkha Earthquake, Nepal.

It remains elusive why there was only weak and limited ground shaking in Kathmandu valley during the 25 April 2015 Mw 7.8 Gorkha, Nepal, earthquake. Our spectral element numerical simulations show that, during this earthquake, surface topography restricted the propagation of seismic energy into the valley. The mountains diverted the incoming seismic wave mostly to the eastern and western margins of the valley. As a result, we find de-amplification of peak ground displacement in most of the valley interior. Modeling of alternative earthquake scenarios of the same magnitude occurring at different locations shows that these will affect the Kathmandu valley much more strongly, up to 2–3 times more, than the 2015 Gorkha earthquake did. This indicates that surface topography contributed to the reduced seismic shaking for this specific earthquake and lessened the earthquake impact within the valley.