Analysis of slope stability

Transcription

1 Engineering manual No. 8 Updated: 02/2016 Analyi of lope tability Program: Slope tability File: Demo_manual_08.gt In thi engineering manual, we are going to how you how to verify the lope tability for a critical circular and a polygonal lip urface (uing it optimization), and the difference between the method of analyi of lope tability. Aignment Perform a lope tability analyi for a deigned lope with a gravity wall. Thi i a permanent deign ituation. The required afety factor i SF = 1,50. There i no water in the lope. Scheme of the aignment Solution To olve thi problem, we will ue the GEO5 Slope tability program. In thi text, we will explain each tep in olving thi problem: Analyi No. 1: optimization of a circular lip urface (Bihop) Analyi No. 2: verification of lope tability for all method Analyi No. 3: optimization of a polygonal lip urface (Spencer) Analyi reult (concluion) 1

2 Inputting geometry and other parameter In the frame Setting click on Select and chooe option No. 1 Standard afety factor. Dialog window Setting lit Firtly, in the frame Interface input the coordinate range of the aignment. Depth of deepet interface point erve only to viualize the example it ha no influence on the analyi. Then model the interface of layer, or more preciely the terrain, uing thee coordinate: Adding interface point 2

3 Then define the parameter of oil and aign them to the profile. Table with the parameter of oil Soil (Soil claification) Unit weight 3 kn m Angle of internal friction ef Coheion of oil c ef kpa MG Gravelly ilt, firm conitency 19,0 29,0 8,0 S-F Sand with trace of fine, dene oil 17,5 31,5 0,0 MS Sandy ilt, tiff conitency, S 0, 8 18,0 26,5 16,0 r Note: In thi analyi, we are verifying the long-term lope tability. Therefore, we are olving thi tak with the effective parameter of lip trength of the oil (, c ef ef ). Foliation of the oil wore or different parameter of the oil in one direction - i not conidered in the aigned oil. Model the gravity wall a a Rigid Body with a unit weight of 23,0 kn m 3. The lip urface doe not pa through thi object becaue it i an area with a large trength (More info in HELP F1). The frame Aignment 3

4 In the next tep, define a trip urcharge, which we conider a permanent with it location on the terrain urface. Dialog window New urcharge Note: The urcharge i entered at 1 m of the width of the lope. The only exception i a concentrated urcharge, where the program calculate the effect of the load on the analyzed profile. For more information, ee HELP (F1). Skip the frame Embankment, Earth cut, Anchor, Reinforcement and Water. The frame Earthquake ha no influence on thi analyi, becaue the lope i not located in a eimically active area. Then, in the frame Stage etting, elect the deign ituation. In thi cae, we conider it a Permanent deign ituation. Frame Stage etting 4

5 Analyi 1 circular lip urface Now open up the frame Analyi, where the uer enter the initial lip urface uing the coordinate of the center (x, y) and it radiu or uing the moue directly on the dektop by clicking on the interface to enter three point through which the lip urface pae. Note: In coheive oil rotational lip urface occur mot often. Thee are modeled uing circular lip urface. Thi urface i ued to find the critical area of an analyzed lope. For non-coheive oil, an analyi uing a polygonal lip urface hould be alo performed in order to verify the lope tability (ee HELP F1). Now, elect Bihop a the analyi method and then et the type of the analyi to Optimization. Then perform the actual verification by clicking on Analyze. Frame Analyi Bihop optimization of circular lip urface Note: Optimization conit of finding the circular lip urface with the mallet tability the critical lip urface. The optimization of circular lip urface in the Slope tability program evaluate the entire lope, and i very reliable. Thi way even for different initial lip urface, we get the ame reult for critical lip urface. 5

6 The level of tability defined for the critical lip urface uing the Bihop evaluation method i atifactory: SF 1,82 SF 1,50 SATISFACTORY Analyi 2 comparion of different analyi method Now elect another analyi on the toolbar in the upper right corner of your Analyi frame in GEO5. Toolbar Analyi In the frame Analyi, change the analyi type to Standard and elect All method a the method. Then click on Analyze. Frame Analyi All method tandard type of analyi Note: Uing thi procedure, the lip urface made for all method correpond to the critical lip urface from the previou analyi tep uing the Bihop method. To get better reult the uer hould chooe the method and then perform an optimization of the lip urface. The value of the level of lope tability are: Bihop: SF 1,82 SF 1, 50 SATISFACTORY Felleniu / Petteron: SF 1,61 SF 1, 50 SATISFACTORY Spencer: SF 1,79 SF 1, 50 SATISFACTORY Janbu: SF 1,80 SF 1, 50 SATISFACTORY Morgentern-Price: SF 1,80 SF 1, 50 SATISFACTORY 6

7 Note: The election of the method of analyi depend on the experience of the uer. The mot popular method are the method of lice, from which the mot ued i the Bihop method. The Bihop method provide conervative reult. For reinforced or anchored lope other rigorou method (Janbu, Spencer and Morgentern-Price) are preferable. Thee more rigorou method meet all the condition of balance, and they decribe the real lope behavior better. It i not needed (nor correct) to analyze a lope with all the method of analyi. For example, the Swedih method Felleniu Petteron provide very conervative reult, o the afety factor could be unrealitically low a a reult. Becaue thi method i famou and in ome countrie required for lope tability analyi, it i a part of the GEO5 oftware. Analyi 3 polygonal lip urface In the lat tep we add another analyi and convert the original circular lip urface to a polygonal lip urface uing the Convert to polygon button. We inert a relevant number of egment. The frame Analyi converting to a polygonal lip urface Dialog window Convert to polygon A a method of analyi, elect Spencer, a an analyi type elect optimization, enter a polygonal lip urface and perform the analyi. 7

8 Frame Analyi Spencer optimization of a polygonal lip urface The value of the level of lope tability for the polygonal lip urface are: SF 1,53 SF 1,50 SATISFACTORY Note: Optimization of a polygonal lip urface i gradual and depend on the location of the initial lip urface. Thi mean that it i better to make everal analye with different initial lip urface and with a different number of ection. Optimization of polygonal lip urface can alo be affected by the local minimum of the factor of afety. Thi mean that the real critical urface need to be found. Sometime it i more efficient for the uer to enter the tarting polygonal lip urface in a imilar hape and place it a an optimized circular lip urface. 8

9 Local minimum polygonal and circular lip urface Note: We often get complaint from uer that the lip urface diappeared after the optimization. For non-coheive oil, where c ef 0 kpa the critical lip urface i the ame a the mot inclined line of lope urface. In thi cae, the uer hould change the parameter of the oil or enter retriction, in which the lip urface cannot pa. Concluion The lope tability after the optimization i: Bihop (circular - optimization): SF 1,82 SF 1, 50 SATISFACTORY Spencer (polygonal - optimization): SF 1,53 SF 1, 50 SATISFACTORY Thi deigned lope with a gravity wall atifie the tability requirement. 9