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Modelling inundation settlement and loading collapse settlement using RMYSF
Published in Mohd Jamaludin Noor, Soil Settlement and the Concept of Effective Stress and Shear Strength Interaction, 2020
The effective stress concept was introduced by Terzaghi (1943) and it has been the most important concept in soil mechanics. The concept characterises soil settlement based on the increase in the effective stress. This is based on the quote by Terzaghi (1943) which said, “All the measurable effects of a change in stress, such as compression, distortion, and a change in shearing resistance, are exclusively due to changes in effective stress σ′1, σ′2 and σ′3.” The concept has been very successful in describing the settlement behaviour of saturated soils. The expression for effective stress s′ is as in Equation 5.1, where σ is the total stress and uw is the pore water pressure.
Effective stress
Published in Longtan Shao, Xiaoxia Guo, Shiyi Liu, Guofeng Zheng, Effective Stress and Equilibrium Equation for Soil Mechanics, 2017
Longtan Shao, Xiaoxia Guo, Shiyi Liu, Guofeng Zheng
Terzaghi’s effective stress principle is very important for saturated soil mechanics, of which the application is very successful. Similarly, it is always desirable to search for an effective stress principle that is feasible for unsaturated soils. It can be well known from the derivation of effective stress equation that the strength and deformation of unsaturated soils are controlled by effective stress, as the effect of pore pressure can be ignored. Since the strength and deformation of a soil are those of skeleton and determined by skeleton stress, a uniform effective stress principle that is applicable for a soil in both saturated and unsaturated states may be stated as: Effective stress is the soil skeleton stress induced by all the external forces, excluding pore fluid pressure;The relationship between the effective stress, the total stress and pore fluid pressure satisfies σ′ = σt − ua + Se(ua − uw). This is the effective stress equation for a soil in both saturated and unsaturated states;The shear strength and deformation are determined by effective stress when the effect of pore fluid pressure on the shear strength and deformation can be neglected.
Introduction to the analysis and design of excavations
Published in Chang-Yu Ou, Deep Excavation, 2014
Effective stress is one of the most important principles in soil mechanics. Though the stress can be distinguished into effective stress and total stress, only the former influences the characteristics of consolidation and strength of soils. The total stress does not. Thus, this chapter uses considerable space to explicate the drained and undrained strengths of soils on the basis of the principle of effective stress. Many concepts about soil strength to be introduced in this chapter, though not included in the general textbooks on soil mechanics, have been applied in engineering practice for years. Readers are advised to study the part introducing the relations between effective stress and drained and undrained strength.
Decomposing and mapping different scales of land subsidence over Shanghai with X- and C-Band SAR data stacks
Published in International Journal of Digital Earth, 2022
Ru Wang, Mengshi Yang, Tianliang Yang, Jinxin Lin, Mingsheng Liao
Differing from the large-scale deformation, the medium-scale deformation in Shanghai is more related to major construction activities that are often accompanied by displacements in a relatively small area up to a square kilometre. In recent years, numerous engineering constructions have become a significant factor affecting the development of land subsidence, especially in the suburbs, which warrants further investigation (Xu et al. 2016). It mainly has a significant impact on the shallow soft soil layer. The surface subsidence of the construction is caused primarily by the early dewatering of the foundation pit and the various later loads of urban buildings, activities, and infrastructures. In dewatering of the foundation pit, the pore water stress is dissipated with the water in the pores of the soil discharging. The effective stress of the soil will increase, resulting in the consolidation and compression of the soil layer, which is reflected as ground settlement or deformation on a macroscale. It is why the formation of the relatively small ground subsidence funnel is related to nearby engineering activities.
Laboratory modeling of siphon drainage combined with surcharge loading consolidation for soft ground treatment
Published in Marine Georesources & Geotechnology, 2018
Hongyue Sun, Gang Wu, Xu Liang, Xin Yan, Dongfei Wang, Zhenlei Wei
Due to the equal vertical strain assumption, the initial average pore pressure is u0 and is calculated using formula (7). The pore pressure is 0 kPa when r = rd, so the initial pore pressure near the plastic drain plate reaches 0 kPa and the initial pore pressure far from the plastic drain plate is greater than u0, which can be calculated by formula (4). Compared with the calculations of formula (4), siphon drainage combined with surcharge loading is different from the sand-drained ground method because the sand-drained ground method can only dissipate excess pore pressure (Figure 9). However, siphon drainage combined with surcharge loading can dissipate excess pore pressure and also dewater groundwater. Thus, the effective stress of soil located on the hydraulic level increases and the thickness of saturation decreases, which can accelerate soil consolidation and settlement. The pore pressure of sand-drained ground eventually stabilizes on the soil surface, while siphon drainage combined with loading can dewater the hydraulic head below the soil surface (Figure 9). Moreover, the descent rate of pore pressure in the case of siphon drainage combined with surcharge loading at the initial stage is faster than that of the sand-drained ground consolidation (Figure 9).
Development of subgrade Mr constitutive models based on physical soil properties
Published in Road Materials and Pavement Design, 2018
Ayan Mehrotra, Murad Abu-Farsakh, Kevin Gaspard
It is well known that effective stress controls the strength and deformation characteristics of soils. Therefore, an accurate representation of the Mr value for unsaturated soils must incorporate the effect of matric suction. This effect has previously been accounted for in a similar relationship between Go (small-strain shear modulus) and matric suction (Sawangsuriya, Edil, & Bosscher, 2008). An efficient methodology to determine Mr, while accounting for the effects of moisture variation and matric suction for unsaturated soils, without performing repeated load triaxial (RLT) tests, would be a valuable tool for practitioners. Previous studies (Nazzal & Mohammad, 2010; Yau & Von Quintus, 2002) have demonstrated the ability to capture the effect of moisture variation on the Mr value in constitutive models. Studies have also shown that Mr can be evaluated utilising stress-state constitutive models with simple laboratory testing (Drumm, Boateng-Poku, & Johnson Pierce, 1990; George, 2004; Hall & Thompson, 1994; Puppala, 2008). These studies predicted the regression coefficients for the Mr constitutive models based on simple soil physical properties, which allowed them to evaluate Mr without performing RLT tests but were still able to incorporate the stress state. However, these studies did not utilise Mr constitutive models that include matric suction, which is necessary to capture the stress state of unsaturated soils. Previous studies have also demonstrated that calibration of prediction models based on local soil types is necessary.