**1. Introduction**

Recently, there have been many natural disasters due to climate change. In particular, slope failure in urban areas has caused loss of lives and of property [1]. The causes of slope failures around the world are intense rainfall, rapid snowmelt, water level changes in rivers or lakes at the foot of slopes, volcanic eruptions, and earthquakes [2]. In the type of slope failure, Soil slope mainly was occurred a deep circular failure and a shallow plane failure. The failure of the rock slope is caused by activity, overturning, and rockfall. In addition, there is debris flow and creep in soft ground [3].

The types of slope failure are determined by the composting materials and exterior conditions of slope. The shear strength of slope soil is decreased as time goes by, especially time-dependent deterioration of cut-slope would greatly happen after excavation. These cut-slopes are degraded in strength by time-deterioration phenomenon, and progressive slope failure is caused.

the slope displacements is easier then sensing the capillary force and water content of slope. Therefore, for this research, the slope displacements to progressive failure were calculated, then they were analyzed and applied to criteria of displacements

*Integrated Analysis Method for Stability Analysis and Maintenance of Cut-Slope in Urban*

*DOI: http://dx.doi.org/10.5772/intechopen.94252*

To link the slope stability analysis with the maintenance method based on the measured data, the displacement until the slope failure to the finite element model was analyzed and applied to the maintenance method. A flowchart of the integrated analysis method was presented and a case study was conducted. The slope stability analysis was performed by generating a finite element model and, the time-

dependent deterioration of slope was quantified by applying the SRF to the strength parameter of the soil. The FOS was calculated by the stress analysis method (SAM) of the finite element model, and the behavior up until slope failure was analyzed by nonlinear static analysis with *k*<sup>0</sup> condition. Each displacement of slope depth until failure is calculated from slope surface by finite element method (FEM). Accumulated displacement curve is derived each displacement from according to the strength reduction factor (SRF). It can draw the velocity curve and inverse-velocity curve. The three curves derived from FEM are applied to the slope maintenance method. The each displacement of slope depth is applied to the SPC method, and, it is the criterion of inclinometer for slope insides. In addition, it estimates the abnormal behavior of slope. Also, accumulated displacement curve of slope surface until the failure is used to make the mathematical failure model. Next, a mathematical failure model of the slope was predicted using a cumulative displacement curve. And the time of the slope failure was predicted using an inverse-velocity curve and, compared the formulation of Fukuzono [1] and the existing case of slope failure.

**2. Theoretical background for stability analysis and maintenance of**

The limit equilibrium method (LEM), a deterministic method, compares the shear stress and shear strength applied to assumed the failure surface of slope to present the FOS. However, because the limit equilibrium analysis provides only the minimum of FOS as the analytic result, it cannot present appropriate safety factor applicable to the analysis of progressive slope failure attributable to concurrent continuous displacement induced by a time-dependent deterioration of soil.

The finite element method can provide the measurement system for the maintenance of slope with proper analytic results. It also is an appropriate method to analyze the behavior of progressive slope failure [29]. The progressive slope failure has been examined through the finite element method. Zeinkiewicz, Humpheson and Lewis [8] had presented the strength reduction method that employed the SRF by which the safety factor was calculated as in the case of limit equilibrium analysis. Thereafter, Griffiths [10] had applied the strength reduction method to his analysis of progressive behavior of slope according to diverse soil conditions and geometries and verified the analytical method through comparative analyses with the chart (s)

The SAM is a combination of the advantages of simple limit equilibrium method (LEM) and of finite element method (FEM), the advanced method. The stress state in slope is analyzed through finite element analysis, and the FOS of virtual active surfaces of the limit equilibrium analysis are calculated. Thereafter, the minimum of FOS and critical section among active surfaces in the limit equilibrium analysis are calculated. In the finite element analysis, the model of the material constituting

**2.1 Finite element method (FEM) for slope stability analysis**

presented by Bishop and Morgenstern [30].

sensing.

**cut-slope**

**159**

A time-dependent deterioration of soil owing to external environmental change causes progressive slope failure and the traditional analysis of limit equilibrium stability has limitations for an appropriate analysis of the stability [4]. The analysis of progressive slope failure requires finite element analysis that is capable of analyzing the creation and progression of shearing zone [5–7]. The behavior of progressive slope failure can be evaluated through the finite element analysis. Besides, for the analysis of the slope stability, the calculation of safety factor is needed. Zeinkiewicz, et al. [8] have proposed the strength reduction method to calculate the safety factor through finite element analysis and the proposition was followed by many subsequent studies conducted by many researchers [9–11]. Recently, there has been many studies unsaturated slope stability analysis induced by rainfall infiltration [12–16]. In general, rainfall-induced slope failures are caused by increased pore pressure and seepage force during periods of intense rainfall [17, 18]. The factor of safety on the slope is calculated by the equilibrium equation of the force of the failure surface. The pore pressure acting as an active force on the failure surface is increased by seepage of rainfall, and the slope is collapsed when it is larger than the resistance force.

The slope behaviors and exterior environment should be measured continuously to maintain slope. The slope behavior is measured by inclinometer, electro-optical wave distance measuring instrument, groundwater level meter etc., also, the exterior environments, rainfall and temperature are measured by the weather station. The various management criteria of the sensors are developed based on mathematical or statistical methods; the slope reinforcement be done if the management criteria [19]. However, the developments of perfect safety factors and management criteria are very difficult from the analysis of measured data in slope.

In Korea, a lot of researches were done for cut-slope management near roadway [20–22]. The displacements of cut-slope were measured by tension wire, and the data were analyzed by the statistical process control (SPC) method. However, it confirm only the abnormal behaviors of slopes, the factor of safety (FOS) of slope cannot be calculated, therefore, the application of slope reinforcement methods are determined according to extra slope stability analysis.

Also, many studies had also been carried out to predict the time of the failure of slope through displacement velocity [1, 23–28]. The researchers have used the inverse-velocity obtained from measurements to predict the time of the slope failure and verified respective applications of the inverse-velocity through actual cases of the slope failure and experiments. However, in cases of slopes, the prediction of the time of the slope failure by using the inverse-velocity curve derived from such measurement is quite difficult because the behavioral aspects of such slope are diverse and the failure surface has to be assumed. So far, the slope stability analysis methods only estimate the FOS of slope and, maintenance methods based on the measured data do not provide clear management criteria. For these reasons, efficient maintenance and prevention of slope failure in urban areas have not been achieved. To solve this problem, the integrated analysis methods of slope stability analysis and maintenance for progressive slope failure due to time-dependent deterioration should be developed.

This study developed an integrated analysis method for stability analysis and maintenance of cut-slopes in urban. The integrated analysis method for this research treated cut-slope and the failure-inducing factor was considered the shear strength decrease (SRF) by time-dependent deterioration was considered as inducing factor of slope failure. The strength variation of soil slope happens continuously from the variation of weather conditions and infiltration of rainfall. Also, measuring *Integrated Analysis Method for Stability Analysis and Maintenance of Cut-Slope in Urban DOI: http://dx.doi.org/10.5772/intechopen.94252*

the slope displacements is easier then sensing the capillary force and water content of slope. Therefore, for this research, the slope displacements to progressive failure were calculated, then they were analyzed and applied to criteria of displacements sensing.

To link the slope stability analysis with the maintenance method based on the measured data, the displacement until the slope failure to the finite element model was analyzed and applied to the maintenance method. A flowchart of the integrated analysis method was presented and a case study was conducted. The slope stability analysis was performed by generating a finite element model and, the timedependent deterioration of slope was quantified by applying the SRF to the strength parameter of the soil. The FOS was calculated by the stress analysis method (SAM) of the finite element model, and the behavior up until slope failure was analyzed by nonlinear static analysis with *k*<sup>0</sup> condition. Each displacement of slope depth until failure is calculated from slope surface by finite element method (FEM). Accumulated displacement curve is derived each displacement from according to the strength reduction factor (SRF). It can draw the velocity curve and inverse-velocity curve. The three curves derived from FEM are applied to the slope maintenance method. The each displacement of slope depth is applied to the SPC method, and, it is the criterion of inclinometer for slope insides. In addition, it estimates the abnormal behavior of slope. Also, accumulated displacement curve of slope surface until the failure is used to make the mathematical failure model. Next, a mathematical failure model of the slope was predicted using a cumulative displacement curve. And the time of the slope failure was predicted using an inverse-velocity curve and, compared the formulation of Fukuzono [1] and the existing case of slope failure.
