scholarly journals Landslide Failure Mechanisms of Dispersive Soil Slopes in Seasonally Frozen Regions

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Lixiang Wang ◽  
Xiaoming Yuan ◽  
Miao Wang
Keyword(s):  
Soil Structure ◽  
Theoretical Calculations ◽  
Substantial Reduction ◽  
Soil Mass ◽  
Soil Slope ◽  
Soil Layers ◽  
Landslide Occurrence ◽  
Soil Instability ◽  
Seasonally Frozen Regions ◽  
Dispersive Soil

Hydraulic projects with dispersive soil in seasonally frozen regions are susceptible to landslide failures. The mechanism of such landslide failures has not been fully understood thus far; therefore, it was investigated in this study by using on-site surveys, laboratory tests, and theoretical calculations. The results showed that the landslides of dispersive soil in seasonally frozen regions could be categorized as shallow-seated landslides and deep-seated landslides. The preconditions for landslide occurrence were soil mass looseness and cracks, caused by freeze-thawing. The degradation of dispersive soil led to a rapid influx of water into the soil. The reason for shallow-seated landslides was that the numerous sodium ions present in the soil mass dissolved in water and damaged the soil structure, resulting in a substantial reduction in shear strength. The reason for deep-seated landslides, however, was the erosion due to rainfall infiltration after the shallow-seated landslides caused tensile cracks at the top of the slope, leading to soil instability. Landslide failures occurred when the dispersing soil slope underwent freeze-thawing and saturated soaking. The sliding surface was initiated at the top of the slope and gradually progressed to the bottom along the interface between the soil layers.

scholarly journals Effect of Transmitting Boundary on Soil – Slope - Foundation Interaction

2020 ◽  
Vol 9 (4) ◽  
pp. 3130-3136
Keyword(s):  
Soil Structure ◽  
Equivalent Plastic Strain ◽  
Seismic Energy ◽  
Soil Mass ◽  
Soil Structure Interaction ◽  
Seismic Load ◽  
Soil Slope ◽  
Transmitting Boundary ◽  
Input Motion ◽  
Transmitting Boundaries

In recent years, extensive research has been performed when the foundation is placed on the crest of slope. Besides of so many researches less number of researches has been done for foundation is placed on slope considering Soil-Structure Interaction (SSI) effect. Construction on slopes poses more challenges especially under seismic load due to an earthquake in addition to the forces of sliding slope itself. The failure of slope not only affects any structure but also has damaging consequences on the environment in general. Therefore, transmitting boundaries should be adequate to absorb the seismic energy at the boundaries. In this paper, effect of transmitting boundary on soil-slope-foundation interaction (SSFI) is studied. Two cases have analysed for SSFI when foundation is placed at various position on the crest and slope itself. El-Centro earthquake (1940) with three different PGA viz. 0.25g, 0.5g and 1g is applied as input motion for both the cases. It is observed that the foundation placed near the slope is more susceptible to damage. Responses of slope (acceleration and displacement) have also been observed at three different nodal points on slope. Results show that the amplification in soil mass leads to settlement of foundation. Shear stress and equivalent plastic strain distribution for SSFI is discussed for different load conditions. It is found that the slope-foundation system shows the local and global failure. Further Post earthquake peak settlement for foundation is plotted and it shows the true behavior of soil.

scholarly journals Depletion of soil carbon and aggregation after strong warming of a subarctic Andosol under forest and grassland cover

SOIL ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 115-129 ◽  
Author(s):  
Christopher Poeplau ◽  
Páll Sigurðsson ◽  
Bjarni D. Sigurdsson
Keyword(s):  
Soil Structure ◽  
Terrestrial Ecosystems ◽  
Soil Mass ◽  
Soil Warming ◽  
Aggregate Breakdown ◽  
Northern Latitudes ◽  
Mass Proportion ◽  
Fraction Distribution ◽  
Soil Responses ◽  
Or Modelling

Abstract. The net loss of soil organic carbon (SOC) from terrestrial ecosystems is a likely consequence of global warming and may affect key soil functions. The strongest changes in temperature are expected to occur at high northern latitudes, with forest and tundra as prevailing land cover types. However, specific soil responses to warming in different ecosystems are currently understudied. In this study, we used a natural geothermal soil warming gradient (0–17.5 ∘C warming intensity) in an Icelandic spruce forest on Andosol to assess changes in the SOC content between 0 and 10 cm (topsoil) and between 20 and 30 cm (subsoil) after 10 years of soil warming. Five different SOC fractions were isolated, and their redistribution and the amount of stable aggregates were assessed to link SOC to changes in the soil structure. The results were compared to an adjacent, previously investigated warmed grassland. Soil warming depleted the SOC content in the forest soil by −2.7 g kg−1 ∘C−1 (−3.6 % ∘C−1) in the topsoil and −1.6 g kg−1 ∘C−1 (−4.5 % ∘C−1) in the subsoil. The distribution of SOC in different fractions was significantly altered, with particulate organic matter and SOC in sand and stable aggregates being relatively depleted and SOC attached to silt and clay being relatively enriched in warmed soils. The major reason for this shift was aggregate breakdown: the topsoil aggregate mass proportion was reduced from 60.7±2.2 % in the unwarmed reference to 28.9±4.6 % in the most warmed soil. Across both depths, the loss of one unit of SOC caused a depletion of 4.5 units of aggregated soil, which strongly affected the bulk density (an R2 value of 0.91 and p<0.001 when correlated with SOC, and an R2 value of 0.51 and p<0.001 when correlated with soil mass in stable aggregates). The proportion of water-extractable carbon increased with decreasing aggregation, which might indicate an indirect protective effect of aggregates larger than 63 µm on SOC. Topsoil changes in the total SOC content and fraction distribution were more pronounced in the forest than in the adjacent warmed grassland soils, due to higher and more labile initial SOC. However, no ecosystem effect was observed on the warming response of the subsoil SOC content and fraction distribution. Thus, whole profile differences across ecosystems might be small. Changes in the soil structure upon warming should be studied more deeply and taken into consideration when interpreting or modelling biotic responses to warming.

scholarly journals Strong warming of subarctic forest soil deteriorated soil structure via carbon loss – Indications from organic matter fractionation

2019 ◽  
Author(s):  
Christopher Poeplau ◽  
Páll Sigurðsson ◽  
Bjarni D. Sigurðsson
Keyword(s):  
Organic Matter ◽  
Forest Soil ◽  
Soil Structure ◽  
Terrestrial Ecosystems ◽  
Soil Mass ◽  
Soil Warming ◽  
Ecosystem Responses ◽  
Structure Changes ◽  
Northern Latitudes ◽  
Fraction Distribution

Abstract. Net loss of soil organic carbon (SOC) from terrestrial ecosystems is a likely consequence of global warming and this may affect key soil functions. Strongest changes in temperature are expected to occur at high northern latitudes, with boreal forest and tundra as prevailing land-cover types. However, specific ecosystem responses to warming are understudied. We used a natural geothermal soil warming gradient in an Icelandic spruce forest (0–17.5 °C warming intensity) to assess changes in SOC content in 0–10 cm (topsoil) and 20–30 cm (subsoil) after 10 years of soil warming. Five different SOC fractions were isolated and the amount of stable aggregates (63–2000 µm) was assessed to link SOC to soil structure changes. Results were compared to an adjacent, previously investigated warmed grassland. Soil warming had depleted SOC in the forest soil by −2.7 g kg−1 °C−1 (−3.6 % °C−1) in the topsoil and −1.6 g kg−1 °C−1 (−4.5 % °C−1) in the subsoil. Distribution of SOC in different fractions was significantly altered, with particulate organic matter and SOC in sand and stable aggregates being relatively depleted and SOC attached to silt and clay being relatively enriched in warmed soils. The major reason for this shift was aggregate break-down: topsoil aggregate mass proportion was reduced from 60.7 ± 2.2 % in the unwarmed reference to 28.9 ± 4.6 % in the most warmed soil. Across both depths, loss of one unit SOC caused a depletion of 4.5 units aggregated soil, which strongly affected bulk density (R2 = 0.91 when correlated to SOC and R2 = 0.51 when correlated to soil mass in stable aggregates). The proportion of water extractable carbon increased with decreasing aggregation, indicating an indirect SOC protective effect of aggregates > 63 µm. Topsoil changes in total SOC and fraction distribution were more pronounced in the forest than in the adjacent warmed grassland soils, due to higher and more labile initial SOC. However, no ecosystem effect was observed in the response of subsoil SOC and fraction distribution. Whole profile differences across ecosystems might thus be small. Changes in soil structure upon warming should be studied more deeply and taken into consideration when interpreting or modelling biotic responses to warming.

scholarly journals Multiband Software Defined Radar for Soil Discontinuities Detection

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
S. Costanzo ◽  
F. Spadafora ◽  
O. H. Moreno ◽  
F. Scarcella ◽  
G. Di Massa
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Soil Structure ◽  
Frequency Division Multiplexing ◽  
Frequency Division ◽  
Soil Layers ◽  
Validation Test

A multiband Software Defined Radar based on orthogonal frequency-division multiplexing technique is proposed in this work for an accurate soil discontinuities detection, taking into account also the dispersive behavior of media. A multilayer soil structure is assumed as a validation test to demonstrate the effectiveness of the proposed approach, by accurately retrieving the unknown thicknesses and permittivities of the soil layers.

Effects of Soil-Structure Interaction on the Response of a Structure With Tuned Mass Dampers

2015 ◽  
Author(s):  
Chong-Shien Tsai ◽  
Hui-Chen Chen
Keyword(s):  
Soil Structure ◽  
Damping Ratio ◽  
Excitation Frequency ◽  
Soil Structure Interaction ◽  
Entire System ◽  
Mass Ratio ◽  
Tuned Mass Dampers ◽  
Soil Layers ◽  
Structure Interaction ◽  
Multiple Tuned Mass Dampers

This paper aims at examining the effects of soil-structure interaction (SSI) on the response of a structure which is equipped with multiple tuned mass dampers (MTMD) and founded on multiple soil layers overlying bedrock. Closed-form solutions have been obtained for the entire system, which consists of a shear beam type superstructure, multiple tuned mass dampers, and multiple soil layers overlying bedrock, while subjected to ground motion. The proposed formulations simplify the problem in terms of well-known frequency ratios, mechanical impedance and mass ratio, which can take into account the effects of SSI, mass ratio of the MTMD at each excitation frequency and damping ratio in the entire system. These formulations are capable of explicitly interpreting the major dynamic behavior of a structure equipped with multiple tuned mass dampers and interacting with the multiple soil layers overlying bed rock. The SSI effects on the dynamic response of a tuned-mass-damped structure as a result of multiple soil layers overlying bedrock were extensively investigated through a series of parametric studies.

scholarly journals Urban Train Soil-Structure Interaction Modeling and Analysis

2019 ◽  
Author(s):  
Danial Mohammadzadeh S. ◽  
Nader Karballaeezadeh ◽  
Morteza Mohemmi ◽  
Amir Mosavi ◽  
Annamária R. Várkonyi-Kóczy
Keyword(s):  
Soil Structure ◽  
Smart Cities ◽  
Free Field ◽  
Bending Moment ◽  
Soil Mass ◽  
Two Dimensional ◽  
Finite Element Program ◽  
Modeling And Analysis ◽  
Dimensional Modeling ◽  
Interaction Modeling

Design and advancement of the durable urban train infrastructures are of utmost importance for reliable mobility in the smart cities of the future. Given the importance of urban train lines, tunnels, and subway stations, these structures should be meticulously analyzed. In this research, two-dimensional modeling and analysis of the soil-structure mass of the Alan Dasht station of Mashhad Urban Train are studied. The two-dimensional modeling was conducted using Hashash&rsquo;s method and displacement interaction. After calculating the free-field resonance and side distortion of the soil mass, this resonance was entered into PLAXIS finite element program, and finally, stress and displacement contours together with the bending moment, shear force and axial force curves of the structure were obtained.

scholarly journals ON APPLICATION OF COMBINED PILE-RAFT FOUNDATIONS FOR ROAD STRUCTURES

2020 ◽  
Author(s):  
Steffen Leppla ◽  
Arnoldas Norkus
Keyword(s):  
Soil Structure ◽  
Soft Soil ◽  
Structure Design ◽  
Bridge Engineering ◽  
Soil Structure Interaction ◽  
Design Solution ◽  
Natural Soil ◽  
Soil Layers ◽  
Structure Interaction ◽  
Raft Foundations

Roads and road infrastructure systems are designed to satisfy ultimate and serviceability conditions under long-term actions caused by transport loadings and environmental effects. Selected design solutions must be safe and rational in terms of construction and maintenance costs. In cases when weak or soft soil layers of natural soil profiles are shallow and/or the traffic loads are very large, the Combined Pile-Raft Foundation (CPRF) is the economical road and railway structure design solution. Application of CPRF is cheaper geotechnical solution comparing with soil change or usual piled foundation alternatives. The development of this system is based on the analysis of relevant mechanical properties of soil layers and the evaluation of the soil-structure interaction. The soil-structure interaction is of highest importance allowing proper evaluation of load bearing resistance and deformation transmitted by raft and piles to soil layers. The soil and foundation system usually is subjected by loadings, resulting elastic-plastic resistance range. Therefore, relevant nonlinear physical laws due to the stress levels are used. The paper purpose is summarizing the experience of application of Combined Pile-Raft Foundations used in road and railway construction and bridge engineering.

scholarly journals The Effect of Mass, Depth, and Properties of the Soil Below the Raft Foundation on the Seismic Performance of R.C. Plane Frames

2019 ◽  
Vol 9 (5) ◽  
pp. 4685-4688
Author(s):  
J. A. Alomari
Keyword(s):  
Modal Analysis ◽  
Modulus Of Elasticity ◽  
Soil Structure ◽  
Soil Mass ◽  
Seismic Excitation ◽  
Soil Structure Interaction ◽  
Foundation Soil ◽  
Structure Interaction ◽  
Raft Foundation ◽  
Soil Modulus

Soil structure interaction has been the subject of numerous studies. The foundation soil has a definite effect on the performance of structures during seismic excitation. Recent studies show that the effect of soil-structure interaction SSI may be detrimental to the structure during seismic excitation. In this study, the effect of consideration of the soil below foundation and its depth, and the soil modulus of elasticity on the response of structures is investigated. The number of mode shapes considered has an effect on the accuracy of the values of structure response. A structural model consisting of an 8-story reinforced concrete frame resting on raft foundation, and including the soil below the raft is analyzed. The frame is analyzed using SAP2000 software, and time history and modal analysis are carried out with varying values of both soil depth and soil modulus of elasticity. The soil below the foundation is connected to the raft elements by gap links. Gap element links are compression–only members with appropriate stiffness, which are active only in compression. Modal analysis results show that the periods of vibration decrease as the modulus of elasticity of the soil increases. Periods of vibration of the frame without the soil mass consideration are less than those when the soil mass below the raft is considered, and they increase with increased depth of foundation to a certain limit. The structures response in the form of columns shear forces and story displacements are also evaluated under the variable parameters considered.

scholarly journals Can cocoa agroforestry restore degraded soil structure following conversion from forest to agricultural use?

2020 ◽  
Vol 94 (6) ◽  
pp. 2261-2276
Author(s):  
Danny Dwi Saputra ◽  
Rika Ratna Sari ◽  
Kurniatun Hairiah ◽  
James M. Roshetko ◽  
Didik Suprayogo ◽  
...  
Keyword(s):  
Root Length ◽  
Soil Structure ◽  
Fine Root ◽  
Aggregate Stability ◽  
Agricultural Systems ◽  
Degraded Soil ◽  
Soil Layers ◽  
Soil Aggregate Stability ◽  
Fine Root Length ◽  
Cocoa Agroforestry

AbstractAlternating degradation and restoration phases of soil quality, as is common in crop-fallow systems, can be avoided if the restorative elements of trees and forests can be integrated into productive agroforestry systems. However, evidence for the hypothesis of ‘internal restoration’ in agroforestry is patchy and the effectiveness may depend on local context. We investigated to what extent cocoa (Theobroma cacao, L.) agroforestry can recover soil structure and infiltration in comparison to monoculture systems across the Konaweha Watershed, Southeast Sulawesi. We compared soil organic carbon, fine root length and weight, soil aggregate stability, macroporosity and infiltration from three soil layers at five land use systems: i.e. degraded forests, 9–14 years old of complex-cocoa agroforestry, simple-cocoa agroforestry, monoculture cocoa and 1–4 years old annual food crops, all with three replications. In general, roots were concentrated in the upper 40 cm of soil depth, contained of 70% and 86% of total fine root length and weight. Compared to simple agroforestry and cocoa monoculture, complex agroforestry had greater root length and weight in the topsoil, even though it attained only half the values found in degraded forests. Higher root density was positively correlated to soil organic carbon. In upper soil layers, complex agroforestry had slightly higher soil aggregate stability compared to other agricultural systems. However, no significant difference was found in deeper layers. Complex agroforestry had higher soil macroporosity than other agricultural systems, but not sufficient to mimic forests. Degraded forests had two times faster steady-state soil infiltration than agricultural systems tested (13.2 cm h−1 and 6 cm h−1, respectively), relevant during peak rainfall events. Compared to other agricultural systems, complex agroforestry improves soil structure of degraded soil resulting from forest conversion. However, a considerable gap remains with forest soil conditions.

Sign in / Sign up

Export Citation Format

Share Document