the effect of matric suction changes on the behavior of Anchored excavations in expansive soil

Document Type : Original Research

Authors
M. Mansoori 1
A. labib 1
A. Akhtarpour 2
1 Ferdowsi University of Mashhad, Faculty of Engineering, Department of Civil Engineering
2 Ferdowsi University of Mashhad, Faculty of Engineering, Civil Engineering Department
A-10-11849-4
Abstract
Due to the increase in population and the increasing need for construction, the issues related to excavation and stability of the excavation have been given importance. The stability of excavations can be controlled and improved by various methods such as anchoring, retaining walls, shielding, etc. that in each project, according to the characteristics of that project and the type of factors threatening the stability of that excavation, one or more stabilization methods can be used. The excavation investigated in this research is stabilized by two pile-anchor and concrete pile methods. One of the factors leading to the instability of the excavation is the infiltration of water into the excavation. Water infiltration into the excavation can be due to various reasons such as rainfall, rise of the underground water level, pipe burst, etc.; Therefore, the possibility of water infiltration into the excavation should be checked in each excavation, and necessary measures should be taken in case of water infiltration. matric suction is defined as the difference between pore air pressure and pore water pressure, which plays a major role in the shear resistance behavior of unsaturated soils; Now, water infiltration reduces matric suction and as a result reduces shear resistance and increases soil volume in expansive soils. The excavation studied in this research has been exposed to factors that change matric suction such as pipe burst, absorption well and climate conditions. The boundary conditions of pipe bursting and absorption well are assumed for a period of one year; Also, the weather conditions have been obtained from the meteorological data of the two rainy months of Sarakhs city. Using sigma/W software and Couple analysis, the simultaneous effect of change in matric suction and change in stress and strain has been investigated. Also, the Penman-Monteith method has been used for the calculation of evaporation and transpiration to model the climate conditions. In this research, a comparison was made between different excavation stabilization situations (pile-anchor and pile method) under different conditions of matric suction (pipe burst, absorption well and weather conditions). Also, in this research, the effect of the location of the burst pipe and absorption well (distance from the excavation wall) on factors such as deformations, the moment created in the pile and the forces created in the anchors (behavior of the excavation) was investigated. Considering the destructive behavior of expansive soils in unsaturated conditions, the soil studied in this research is of expansive type. The characteristics of the modeled soil are related to the area of Sarakhs city. In order to consider the effect of soil swelling, the used elasticity modulus is related to the effective stress and as a result matric suction, which is called the swelling modulus. The results showed that the increase in moisture in the soil and as a result the decrease in matric suction in the swelling soil increases the force in the anchors and the bending moment in the pile. Also, the increase in the force of the anchors and the displacement created in the case of pipe bursting and absorption well modeling is much more than the conditions of the climate boundary effect for the two rainy months of the year. By increasing the distance of the absorption well and the bursting of the pipe from the excavation, the increase in the force created in the anchors decreases. climate conditions affect the upper 6 meters of the excavation, i.e. the active zone.

Keywords

Subjects

[1] A.P. Pratama, H.C. Hardyatmo, F. Faris, Parametric Study of the Effect of Ground Anchor on Deep Excavation Stability, in: J. Civ. Eng. Forum, 2020, pp. 19.
[2] R. Zhang, J. Zhao, G. Wang, Stability analysis of anchored soil slope based on finite element limit equilibrium method, Mathematical Problems in Engineering, 2016 (2016).
[3] C.S. Josefino, N. Guerra, A. Antão, Influence of the embedded length on the overall stability of single anchored retaining walls, Soils Rocks, 40 (2017) 133-145.
[4] K. Papadopoulou, A. Sofianos, Factors Affecting the Behaviour of Retaining Structures with Prestressed Anchorages Under 2D and 3D Conditions, Geotechnical and Geological Engineering, 34 (2016) 1877-1887.
[5] A. Johari, A. Kalantari, System reliability analysis of soldier-piled excavation in unsaturated soil by combining random finite element and sequential compounding methods, Bulletin of Engineering Geology and the Environment, 80 (2021) 2485-2507.
[6] D.G. Fredlund, H. Rahardjo, Soil mechanics for unsaturated soils, John Wiley & Sons, 1993.
[7] A. Gholampour, A. Johari, Reliability-based analysis of braced excavation in unsaturated soils considering conditional spatial variability, Computers and Geotechnics, 115 (2019) 103163.
[8] L. Ning, J.L. William, Unsaturated Soil Mechanics, 2004.
[9] G. Sivakumar Babu, D. Murthy, Reliability analysis of unsaturated soil slopes, Journal of geotechnical and geoenvironmental engineering, 131 (2005) 1423-1428.
[10] S.E. Cho, S.R. Lee, Instability of unsaturated soil slopes due to infiltration, Computers and geotechnics, 28 (2001) 185-208.
[11] C.P.K. Gallage, T. Uchimura, Effects of wetting and drying on the unsaturated shear strength of a silty sand under low suction, in: Unsaturated soils 2006, 2006, pp. 1247-1258.
[12] H. Rahardjo, A. Satyanaga, E.C. Leong, Unsaturated soil mechanics for slope stabilization, Geotech. Eng. J. SEAGS AGSSEA, 43 (2012) 48-58.
[13] a. Ali, s. Narges, e.f. Amin, r.k. Amir abas, Effect of matric suction on excavation stability in unsaturated soil, Journal of the Engineering Geological Society of Iran, 15 (1401) 1-17.
[14] C.-S. Tang, Q. Cheng, T. Leng, B. Shi, H. Zeng, H.I. Inyang, Effects of wetting-drying cycles and desiccation cracks on mechanical behavior of an unsaturated soil, Catena, 194 (2020) 104721.
[15] J.A. Blatz, N.J. Ferreira, J. Graham, Effects of near-surface environmental conditions on instability of an unsaturated soil slope, Canadian Geotechnical Journal, 41 (2004) 1111-1126.
[16] S. Qi, S.K. Vanapalli, Hydro-mechanical coupling effect on surficial layer stability of unsaturated expansive soil slopes, Computers and Geotechnics, 70 (2015) 68-82.
[17] A.N. Yazdi, A. Akhtarpour, M.M. Abdalhusein, M.S. Baradaran, Experimental Investigation of the Volume Change of a Swelling Clay and Its Improvement, Transportation Infrastructure Geotechnology, (2023) 1-24.
[18] balighi, Laboratory and numerical investigation of the swelling soil behavior using unsaturated triaxial test - case study: Khangiran Sarakhs, in: faculty of engineering Department of civil engineering, ferdowsi university of mashhad, mashhad, 1402.
[19] B.M. Das, Principles of geotechnical engineering, Cengage learning, 2021.
[20] M.T. Van Genuchten, A closed‐form equation for predicting the hydraulic conductivity of unsaturated soils, Soil science society of America journal, 44 (1980) 892-898.
[21] A. yazdi Laboratory investigation of expansive soil volume change and its improvement method based on unsaturated soil mechanics, in: faculty of engineering Department of civil engineering ferdowsi university of mashhad, 1400.
[22] W. Geostudio Sigma, Engineering Book for Stress-Deformation Modeling with Sigma/W, Geo-Slope International Ltd., Calgary, Alberta, Canada, (2012).
[23] P. Sabatini, D. Pass, R. Bachus, Geotechnical engineering circular no. 4: Ground anchors and anchored systems, in, 1999.
[24] GEO-SLOPE, Heat and Mass Transfer Modeling with GeoStudio, Geostudio Help, 2022.
[25] H.z. Zahra, B. Nasrin, R. Alireza, T.n. Meysam, B. Atefe, Spatial-temporal modeling of albedo in the area of Iran, Applied Research of Geographical Sciences, 17 (1396) 1-17.
Modares Civil Engineering journal
Volume 24, Issue 2
May and June 2024
Pages 139-156