 Welcome to advanced geotechnical engineering course, we are in module 5 which is on stability of slopes and this is lecture number 6 in stability of slopes and in this particular lecture we are going to concentrate on slope stabilization methods. In the previous lecture we have discussed about different slope stabilization techniques and in continuation of our discussion we will try to discuss about how lime piles or lime slurry injection can be helpful in enhancing the stability of a slope is a type of chemical hardening which we have mentioned in the previous lecture. Then the another method which is for in situ slope stabilization is soil nailing, so that we will try to discuss in detail and finally we will look into the method which is called as biotechnical stabilization or biotechnical slope stabilization which is gaining momentum in the recent past with a requirement of eco-friendly awareness. Before going into the typical slope stabilization techniques for natural slopes as we discussed there are two types of slopes, one is natural slope and other one is say manmade slopes and embankments fall in the manmade slopes category and in this particular slide the typical embankment failures are shown, the first figure on the left most left corner is the rotational failure of an embankment which is actually shown and this is possible when there is underlying clay is soft in nature then the direction of the movement is vertical and then outwards in this direction. So this is actually also called as a base failure which is actually happens if you are having a underlying soil which is soft in nature. Then the another failure of the typical embankment is that there is a displacement failure where embankment portion settles down with maximum settlement at the center and heaving on the both the sides. So this is typical nature for the soft material and where actually if it is a hard material is here nearby to the bottom surface then you can actually have settlement and a heave which is actually takes place on the both the directions. Suppose if there is an underlying layer is a soft clay seam beneath the soil surface and there is a possibility that a translatory failure can actually happen. To avoid these embankment failures one of the popular alternative is to stabilize the manmade slope or embankment slope by constructing a berm or in a combination of you know stabilizing with stone columns or so. So the effect of the berm on the slope stabilization if you look into is in this particular slide where an embankment which is subjected to a failure a base failure or rotational failure with a circular arc L1 with the center of arc O1 is shown here and which yields a say factor of safety FS1 then by the providing a berm the center of the arc shifts to O2 and the radius of the arc becomes say R2. So which yields a factor of safety FS2 which yields which is more than the FS1. So the provision of the berm helps in enhancing the stability of a slope. So the question is that you know the extent of the horizontal extent of the berm from the toe of the slope that is important and the height of the berm which is required need to be a set time. So sometimes what will happen is that it is not possible to extend the berm up to you know large distances in such situations one can actually resort to adopting you know the yesterday lecture the previous day lecture in the previous lecture we discussed about slope stabilization using stone columns that can be combined along with this are incorporated into it. So in the next slide what we are going to do is that the slope stabilization using stone columns which is particular method which is used for installing these rammed pierce or it also called as stone columns and in case there is a slope is existing and then the bund is required to be constructed on that the additional with the widening of the bund is required here then what we do is that we drive the sheet pile wall from the top. So this is in this particular slide a typical installation of stone column is shown here wherein the borehole which is actually made of required diameter and the stone charge is actually feed it. So there are two different types of feeding techniques one is called top feeding technique other one is called bottom feeding technique. In the top feeding technique once the borehole reaches to the certain depth then the charge is actually feed it in installments and then it is compacted by using the same are rammed by using this boiler. So this technique nowadays the availability of the vibrofloat sender helps to compact these stone charge efficiently and also helps in constructing the stone columns efficiently. So this is a particular technique where the slope stabilization of a existing embankments can be enhanced or an embankment to be constructed on a soft soil can be enhanced by using this particular technique. Now as we discussed that there is another technique which is called slope stabilization enhancement basically by using lime slurry injection or lime columns. Notice the lime and fly ash injection is also getting popular because of the abundant availability of the fly ash the appropriate combination of lime and fly ash are being used. So this slope stability can be improved by injection of lime slurry to increase the shear strength of clay and silty soils and it is not much successful with the sandy soils. The slope stability can be improved by injection of lime or lime fly ash in appropriate combinations in the form of slurry to increase the shear strength of the clay and silty soils and this is also sometimes is done in the form of lime columns or lime piles wherein similar to stone columns a drilled hole is filled with a lime of an appropriate type of material which is specified in the specified and this is actually done basically by a rotating disc auger penetrates into the depth of to a slip surface or sometimes beyond the slip surface and the stabilizing agent is injected into the resulting into the needed lime columns and one demerit of this method is that at least 80 days must be must elapse before columns of the stabilized soil can be subjected to loading but however the rate of increase of the strength over a period of time was found to be increasing because of the mobilization of the reactions which actually takes place with the presence of the lime. So this though this method actually has got at least the requirement of 80 days is required to before you know the stabilized soil is actually subjected to loading. So in this particular slide the installation of lime column or lime piles is actually shown here where a 0.5 meter to 0.8 meter diameter hole is actually made and they can be used up to 15 meter length according to Brahms 1991 and where the drilled hole is actually filled with the help of this lime column machine and is feeded and the lime is actually feeded and the lime columns are actually constructed and this is a typical you know slope stabilization by using injected lime slurry shown and nowadays with the availability of the portable rigs there is a possibility that it can be mounted easily on the slope surface and the injection is actually given along the slope surface. So this is particularly for you know wherever when we have highway railway embankments which are actually constructed you know with lime and posing problems because of the swelling and shrinking cycles and in such type of cases the adoption of this technique seems to be promising. However in the field the injection of the lime has to be done with an appropriate selecting the appropriate pressure and in appropriate quality of the lime. So this is a typical slope stabilization using lime piles which is actually shown here in this particular slide where you know the stabilization is actually adopted for a clay soil the approximate lime limit of treatment is actually shown here. So in this one then the portion is actually you know improved with by installing lime columns. So the increase in the soil shear strength due to lime columns can be expressed estimating the average shear strength along a potential failure or rupture surface in the soil. So this is actually obtained as C average is equal to Cu into 1 – A plus S column by A. So here what is actually Cu is the averaged cohesion. So Cu is the average undrained cohesion of the soil which is you know of the untreated and unstable soil and S column is the average shear strength of stabilized clay within lime piles and suppose if the columns are arranged in say square pattern and then let us say at S be the spacing of these lime piles then the soil in between which is that the gain instant that is average shear strength of stabilized clay within lime piles is treated as S column divided by A, A is nothing but the relative column area the column area which is nothing but pi D square divided by 4 square where it is nothing but pi D square by 4 is nothing but the area of the single lime pile divided by S square is nothing but the area some covered by this lime piles that S is the center to center spacing of lime columns or lime piles and D is the diameter of the lime column or lime pile. This S column is basically is a function of overburden pressure and relative stiffness of lime piles with respect to the surrounding unstable soil. So S column is found to be reported by Brahms 1991 as a function of overburden pressure and relative stiffness of lime piles with respect to the surrounding unstable soil. So with this once we get the average strength over a period of time let us say after elapsing certain time after the installation and this can be used for you know arriving at the enhanced effect on the increase in the stability of a slope. So lime treatment as a mix in place technique has been widely and successfully used around the world to improve weak soils and novel techniques using lime are now being developed and also to add to this you know some modern materials like nano materials and which may be helpful in enhancing the performance and this use of lime piles particularly if you are having a requirement of for the short term requirement which is not a long term stability of a slope but for a certain period of time and for stabilizing shallow slopes and use of lime piles seems to be very promising. And recent research has investigated the reaction mechanisms associated with the lime pile stabilization however with the current standard the further work is actually warranted in this direction to understand and quantify about the slope stabilization using lime piles. So then we actually have said that the another technique which is can be used for enhancing the stability of a slope or an excavation is by soil nailing technique and this is a technique which is gaining popularity for the past four decades and the soil nailing technique is a technique basically in which the slopes excavations are retaining walls are passively reinforced by insertion of relatively slender elements. These slender elements are nothing but normally steel reinforcement bars and they are passive anchors in which you know these nails are not prestested and they are actually soil nails which are called as soil nails and dowels and rock bolts and this technique also you know in a light way it is used in stabilizing the rock slopes also and these nails are actually placed along the slope surface again in the you know two different patterns one is the square pattern where with SH is the horizontal spacing between the nails and SV is the vertical spacing and the length of the nail which is actually to be penetrated into the ground to be inserted into the ground is recommended in the range of 0.5 to 0.7 h where h is the height of the slope to be treated and this technique is very useful particularly when we are actually using you know when suppose if you are having an abutment beneath the bridge and the road widening needs to be taken place and previously the abutment is with say natural slope and when you wanted to widen the road then there is a requirement of the steepening of the slope in such situation there is a need for enhancing this by using this you know the soil nailing technique. So in this particular slide this are the you know reinforcing bars typically shown and the different types of nails are there which we are going to discuss suppose if this is the potential failure surface and this is a portion which is called as a stable ground or this is say active ground or actual or potential landslide zone. So what will happen is that the relative movements mobilizes axial stiffness and resistance of dowel or soil nail and increase the normal stresses on the failure surface and basically it enables you know mechanism which actually enables the develops the resistance against the failure and the shear resistance of the dowel or a nail transfers demand to the underlying stata that is in the stable ground and increase in normal stress on failure surface increases the available resistance. So here increase in the normal stress at this particular portion enables to increase the resistance to the failure along the shear surface in addition to this is actually in addition to the resistance offered by the soil. So in the soil nailing technique basically they are passive anchors and they are inserted in the form of with their slender elements they normally steel reinforcing bars and these are done with a certain layout what is called as a nail layout and also their space that they are you know inclined at a certain inclination and they also been provided with certain facing which we are going to discuss. So here the slope stabilization using soil nailing technique wherein this is basically a top down construction technique wherein in fact this is actually very useful for temporary shoring purposes in underground excavations like suppose if you are actually excavating a certain ground in a soil slope area so excavate the level one and then the next method is to you know provide a short creating on the surface and then drive the nail or you know install the nail and then you know excavate further so like that one actually can do the installation of this nails from nail one, nail two, nail three, nail four, nail five, nail six from nail up to bottom of the other toe of the slope in this fashion and this is a typical you know installation of nail by using you know a specific rig which is actually used in the field is actually shown here. So the slope stabilization using soil nailing technique basically a top down construction technique and as we have discussed the nails are not pre-stressed they are basically called as passive elements which actually are used for stabilizing the slopes or excavation phases and the depending upon the requirement so there can be some cut element of the length of the nails also can be done but this is that 0.5 to 0.7 h the horizontal minimum required and this is the vertical spacing of these nails and along this slope surface the horizontal spacing will be there and this is the facing element which is required and there is at this portion where the nail is actually is bolted so that is where actually here the head of the nail will come into picture and the nails are actually inclined generally up to 15 to 20 degrees but however this depends upon the back slope inclination and also this depends upon the slope inclination for which this nailing technique is used. So various types of the soil nails in the sense that two popular types are driven nail and grout and nail in the grout and nail the after excavation the first holes are drilled in the wall or slope face and then in the nails are placed in the pre-drilled holes. Finally the drill hole is filled with cement grout so in this portion the entire length of the nail is actually filled with cement grout so the placement of this cement grout also helps in bonding the nail grout surface with the surrounding soil efficiently. So in the grout and nail after excavation the first holes are drilled in walls and slope face and then the nails are placed in pre-drilled holes at a particular inclination. Generally there are two types of placement of this grout and nails one is grouting one is gravity driven grouting wherein the grout is allowed to flow with natural gravity the other one is the pressure driven installation of the grout. So nowadays with the current research actually shows that the pressure driven grout found to be efficient because of the increased you know participation of the surrounding soil in mobilizing the soil nail grout resisting shear stress. The driven nails in this state the nails are mechanically driven into the wall during excavation and installation of this type of nail soil nailing is very fast the sense that the nails are placed at the nail bars are actually fired into the soil however it does not provide a good corrosion protection and this is generally used for temporary nailing for example wherein we need you know some immediate remediation measure and then these driven nails can be used very very effectively. And self-drilling soil nails in the sense that hollow bars are driven and grout is injected through the hollow bars simultaneously during drilling. So this method is faster than the grouted nailing and it exhibits more corrosion protection than the driven nails. Grouted soil nail basically here Z grouting is used to erode the ground basically the presence of water jets and air jets will allow the creation of a sort of erosion at the tip where this is done and for creating the hole into the install steel bars and the grout provides a corrosion protection from for the nail. The launched soil nails are bars are launched into the soil with very high speed that is what actually is called firing of the nails involving composite air and this method of installation very fast however it is difficult to control the length of the bars penetrating into the ground. So depending upon the soil resistance so launching soil nails the other one is the driven nails so that popular types of nails are grouted nails and driven nails and the as far as the type of installation of grout is concerned the jet grouted soil nail is another type and other one is called self drilling soil nail where hollow bars are driven and the grout is injected through the hollow bars simultaneously during drilling. So as we have discussed that there are two you know zones for the soil nail system wherein we have here active zone and then passive zone. So with the movements which are actually happening in the slope in the active zone the nail mobledges resistance in the form of tension as well as the shear and bending. So the slope which actually is you know reinforced with soil nailing resist tensile stresses shear stresses and bending moments imposed by the slope movements in the process what will happen is that the slope will get the enhanced stability and possibility of occurring or attaining steep slopes can be achieved can be obtained. So here it also depends upon the resistance offered or the bearing stress offered by the facing at the nail head that is this portion which is actually shown here. So and then the shear stresses which are actually mobilized at this area also you know corroborate for the functioning of this soil nail system. So this is in this slide the schematic distribution of tensile forces along soil nails are shown here and it is shown here the tension is mobilized along the nail length like this and almost 0 at the facing and 0 at the other end of the nail and this is the you know potential failure surface and this is the line of the maximum soil nail tensile forces and the force is supposed to be maximum distribution magnitude will be high here and as we go come to the top the mobilization of the nail in tensile forces will be less here but if the length is not adequate beyond the active zone area there is a possibility that the nail is actually subjected to a float failure. So in this one of the checks is to also to do a institute float test to ascertain the float capacity of these nails with that the nail capacity can be ascertain and another possibility is that the once the soil nails are installed and there is a can be clubbed with an instrumentation so with that the monitoring of this soil nail wall system can be or soil layered slope system can be achieved. So before looking into that the potential failure modes of a you know soil nail system can be seen there are basically two types one is called external failure and internal failure the external failure refers to the development of the potential failure surface essentially outside the soil nail ground mass. So and the failure can be in the form of sliding that means that entire soil nail block including the up to that means that up to which the length the nails were installed the sliding can take place and rotation are bearing particularly if the ground which is housing this particular structure say is not having adequate bearing capacity that bearing failure can occur or other forms of loss of over stability. So external failure basically refers to potential failure surface essentially outside the soil nail ground surface and the failure can be in the form of sliding rotation or bearing or other forms of overall or global stability. The internal failure refers to failures within the soil layer ground mass so that means that it can be you know breaking of the nails or breaking of the nail head and within the active zone basically the inter failures occurs within the active zone and passive zone basically occurs in the form of a pull out it takes place or in both of the two zones of the nail system. So internal failure can actually happen in active zone as well as in passive zone that is passive zone or the stable zone beneath the active zone so in both the or in both the zones of a soil nail system. So in the active zone basically the internal failure mode include the failure of the ground mass that means that the ground disintegrates and flows around the soil nails and the soil nail heads and the other thing is that bearing failure underneath the soil nail heads that means that if the facing is not having adequate you know load carrying capacity then there is a bearing failure can occur and the structural failure of the soil nail under combined actions of tension shear and bending that means that the structural failure of this so the adequate if the structural capacity of the soil nail is inadequate then the structural failure of the soil nail can occur under combined action of tension shear and bending and structural failure of the soil nail head are facing the bending or punching failure can actually occur or failure at the head reinforcement or facing reinforcement connection and surface failure between soil nail heads wash out erosion or local sliding failure there can be happen because of the when seeping of water the local failures can actually often erosion and local sliding failure in the passive zone basically the zone beneath behind the active zone the pull out failure at ground grout interface possibly this occurs at the top surface of the slope or wall and of the grout reinforcement remains basically should be considered. So in this particular slide what we have seen is that in the active zone the internal failure modes include failure of the ground mass basically and the bearing failure underneath the soil heads and the structural failure of the soil nail under combined actions of tension shear and bending and the structural failure of the soil nail head and the surface failure between soil nail heads and another in the passive zone what we said is that the pull out failure at the grout ground interface or grout reinforcement interface that means that if the reinforcement bar is pulled out of the grout surface that also can occur within the soil nail or a pull out failure can also occur between the grout and ground surface also. So two modes of failures can actually be possible when we are actually having a failure in the passive zone as far as the pull out failure is concerned. So here whatever we have discussed is shown pictorially this is the potential internal failure modes of a soil nail system wherein the failure of the ground of soil nails is actually shown here where the failure surface passing through the nails and ground flows around the soil nails so wherein you can see that this failure of the ground around the soil nails can be seen and in this soil nail head bearing failure where this portion of the nail got punched or failed this bearing failure on the soil nail head can also case one of the failures and the other one is that local failure between the soil nails that is the facing element failure basically here and this can actually cause because of the inadequate facing thickness and this is the local failure between the soil nails. The other one is that potential failure of the soil nails because of the rupture or breakage of the soil nails can take place with that what will happen is that the nail the slope surface moves this forward and then there is a possibility of the instability and the pull out failure of the ground grout interface that is ground and grout interface that is here which is can possible and grout or grout interface grout reinforcement interface. So these things will lead to again the slope to move outward and then undergo failure. Then we have bending or shear failure of soil nails suppose if the installed soil nails not having adequate bending and the resting against the shear then there is a possibility that along the potential failure surface there is a possibility of the bending and the shear can be observed which can lead to you know the failure. So with the locus of the maximum tensile force mobilization then matches with the failure surface at this location here. Similarly here for the potential internal failure modes of a soil nail system in a continuation and this is the structural failure of the and the connection failure at the soil nail head that means that nail and the soil head will can get detached and then the slope surface can actually you know can deform. So here this is the structural failure connection or failure of the facing where in you can see that the structural failure of the facing the facing is subjected to failure and here failure of the facing reinforcement connection which can actually is depicted here. So these are the typical internal failures of failure modes of a soil nail system. So in this particular slide a typical you know use of this technique for installing this usage of this technique for slope production in an underground excavation is shown here. What you see here is a short created surface and then the nails are actually placed here particularly with the presence of this buildings which are close to the slope surface and this seems to be very very viable and then is required because the protection of the slope is very important and to safeguard the existing structures also to facilitate the construction in the area of the interest. So here this is a typical example which is actually shown how the rays of the groundwater table and infiltration of the rain water creates seepage pressures within the slope and with this what will happen is that when the buildings are actually constructed close to the hill slopes and this type of slopes are prone for you know can cause instability failures and with the surrounding soil is the slope is actually made of slope then the adoption of a soil nailing technique for this is a viable option where in you know this technique ensures that the slope is actually is you know protected and then you know the safety can be ensured. So this is a typical application for this but however the effect of the raising groundwater table and the soil nail ground interaction need to be addressed so that the you know this can be attended properly. So the other application of this technique is to you know using for railway suppose if existing tracks and new tracks are to be laid then when it is in cutting need to be widened or steepened so in the process what actually happens is that for placing the new tracks and then the slopes can be protected by using this technique so here the different facings are used sometimes we are wire mesh fencing or you know gavion wall facing or there is you know these are the plates which are actually head and these are the nails so you can see that the nails are actually placed at a certain horizontal and vertical spacing covering the entire area so this ensures that the stability of a this particular slope and you know helps to you know creating additional space for laying new tracks and all. So this is a typical cross section of a drilled soil nail slope is shown here and where this is the facing and some geocomposite drains are used to facilitate the drainage of water rainwater and this is the close view of the nail head along with the nail bolting arrangement so this is the nail head nail bolting arrangement you know detail view is actually shown here. So this is you know how the construction of soil nailing is shown a typically preparation of the slope surface and mobile drilling equipment arrangement and driving of the nail and then installation of the steel bar and then grouting process this is shown basically to acquaint with the how the construction happens in the field. So now looking into you know the how you know the type of you know what should be the inclination and what should be the you know the length of the nail and what should be the facing how you know these actually affect on the you know slope stability parameters can be looking into it. So as we have discussed with that soil nailing technique particularly the passive inclusion technique and these are closely spaced along the horizontal surface and two patterns are possible one is square another one is staggered arrangement wherein two patterns are possible one is square arrangement where SH is the horizontal spacing SV is the vertical spacing and this is called as a staggered arrangement in which the nails are actually spreaded over the surface and with the mobilization of a slope movements in the active zone the forces tension shear and bending are actually mobilized in this nails and the resistance is actually developed to the way it is actually shown here. So when there is an increase in ground water table within the slope either due to rainfall water infiltration so there is a possibility that the forces in the nails get enhanced. So here in this particular slide the factor of safety of the nail inclination for different slope inclination shown here. So here two very steep slopes are considered one is 63.43 degrees which is nothing but two vertical one horizontal the other one is 79 degrees slope inclination which is 5 vertical one horizontal. So as can be seen that with a back slope of inclination of 0 that is the slope surface is horizontal you can see that as the nail inclination increases there is increase in factor of safety and then there is further decrease in the factor of safety. So this implies that there is a certain optimum inclination for which actually the factor of safety is high. So this analysis actually performed by incorporating nails and by using modified Bishop's method of slopes, the Bishop's method of slices and with this the factor of safety of a soil nail slope concept based on limit equilibrium approach could be obtained. So it can be seen that for a nail inclined at 10 degrees for a slope of inclination of 79 degrees it is found to be optimum and for a nail inclined at 25 degrees for a slope inclination of 60 degrees were found to be optimum you can see that further increase in the nail inclination lead to the decrease in factor of safety. So it must we must remember that the nail inclination need to be selected based on the slope configuration whether it is with the back slope inclination or with a slope inclination and in this particular slide two different thicknesses like four different thicknesses are actually considered with an increase in thickness of the facing the factor of safety was found to increase. So you can see that with an increase in thickness of the thickness of the facing then the nail the contribution of facing enhancing the stability of a slope can be seen. And if you with the variation of horizontal spacings let us say that for horizontal spacing of 1.3 meter 1.5 meter and when the vertical spacing is increased for example here with a vertical spacing of 1.5 meter so what you can see is that with an increase in vertical spacing there is a decrease in the factor of safety. So it can be seen that say for example with vertical spacing of say horizontal spacing of 2.1 meters and vertical spacing of 2.1 meters the factor with an increase in vertical spacing there is a decrease in the factor of safety which actually can be seen from this analysis. Similarly here the diameter of the nails basically we said that the reinforcing bars are used and these reinforcing bars are actually having different inclinations different inclinations as well as the different diameters. So particularly these reinforcing bars from 28, 38, 42 mm these are the normally available materials the torque state bars they are used and so as can be seen here with an increase in the diameter for example here this is for the nail diameter of 20 mm and 15 mm then increase in the factor of safety and this also found to the nail inclination also found to have the similar effect for a 60 degree slope inclination which is actually shown here. So in this particular slide the influence of pressure blouting on the slope stability is actually shown the reinforcing effects of pressure blouting on the slope stability. So here in this FEM analysis of a gravity grouted soil nails is actually shown here and this is the failure surface of the gravity grouted soil nail surface and this is again superimposed here and this is in this this is the pressure grouted soil nail surface. So this is after Kim et al 2013 where the developed slope failure surface for the gravity grouted and pressure grouted soil nails from the maximum plastic strain deformation plots. So these are actually failure surface were actually developed for the gravity grouted and pressure grouted soil nails from the maximum plastic strain distribution plots and the slope reinforced with pressure grouted soil nails exhibits expanded failure surface the failure surface was found to move towards the passive zone or a stable zone and compared to that of the gravity grouted reinforced slope and the grouting pressure may increase the stiffness of the reinforced slope system. So what is happening is that the grouting pressure influences in a big way in enhancing the stability of the slope because the surrounding soil is relatively compressed or compacted and offers higher resistance across each nail and that makes the pressure grouted soil nails for found to perform grouted soil nail stabilization technique were found to superior than the gravity grouted soil nail stabilization technique. So with this what we have understood is that the reinforcing effect of the pressure grouted soil nails are superior in enhancing the slope stability of a typical slope which is actually shown after Kim et al 2013. So this is you know adoption of the soil nailing technique for a water treatment plant in one of the sites in Kerala and wherein this is a slope of about 24 meters height and wherein at the top of the slope a 100 kilo Pascal's you know unit which actually imposes a load of 100 kilo Pascal's water tank was actually placed for supplying water by gravity method to the surrounding villages. So the soil is basically a laterate type of soil and which actually gets softened during you know the rains particularly the ingress of rain water. So it can be seen that the patches of water seepage can be seen here. So here in this you know a spacing of 1.5 meter by 1.5 meter is adopted for a typical you know nail lens and nail inclination is adopted and by this analysis was actually carried out by Taldren you know software which actually includes the effect of the soil nails in the modified method of bishops method of slices wherein the this is considered and the this particular site was actually you know done basically to increase the stability of a slope to carry the additional load of 100 kilo Pascal's at the top of the slope and to house the water tank at the top of the slope. So then another you know stabilization technique what we have discussed is called biotechnical slope stabilization technique and which is gaining popularity and wherein here a selected you know seats were placed along the slope and these the roots of these plants are penetrated into the ground and then the roots surrounding soil interaction were found to enhance the stability of a slope. So very recently also some of the live poles are actually used for enhancing the stability of a slope and wherein these are actually used for improving the stability one of the natural way of these using the technique of vegetation the vegetating the slope surface and enhancing the stability. So in this particular slide a typical you know live cuttings and a compacted fill is shown and mostly this is actually adopted for as well as for natural slopes or manmade slopes so this actually ensures the green effects surrounding the areas. Then in this you know this typical combination of you know in nowadays is combined with erosion control blankets these erosion control blankets are embedded with a materials like jute which is jute or a choir which are actually placed on the slope surface in a blanket form and they are actually also you know attached to the slope surface in the form of a pegging and then live facins were placed and planted which actually helps you know the combination of combined application actually wherein both you know erosion control blanket and live facins helps in maintaining the slope stable. So here these are actually adopted as also in the combination of even soil nailing or by using you know geocell on the slope surface where the erosion also can be controlled and as well as the live facins can be used for enhancing the stability of a slope. So in this particular slide what actually has been shown is you know a particular slope how it actually has been you know created by creating a steps and a small berms here along the berms these you know selected plants are actually placed and then after you know this is a typical vertebrate grass system after certain time it can be seen that you know these growth of this grass actually turns this entire area green and this is you know one of the promising area for the you know slope stabilization where the lot of work is actually also happening. So in this slope stabilization techniques you know particularly after having discussed the several causative factors of the slope failures what we have understood is that a different types of you know methods are there for enhancing stability of slopes like you know simple techniques of you remove of the you know materials from the head of the slope that is the you know replacement with you know heavier material with lighter materials or by benching the slope at the top portion that also can actually enhance the stability of a slope or we also said that the use of light materials like geofoam helps in enhancing the stability of a slope then we also discussed that you know there are methods like drainage techniques in this there is surface drainage techniques and subsurface drainage techniques and this is a prime and important technique where if the slope is actually some has efficient drainage system the stability of a slope can be enhanced. Nowadays you know the techniques of combining reinforcing the slope as well as you know facilitating the drainage these are actually called as hybrid way of stabilizing the slopes are in vogue and are being researched widely and then we also discussed about a typical technique of stabilizing the slope by using stone columns or gravel drains so they these stone columns or gravel drains work for you know as a dual function one is that to drain the you know also the these stone columns can also function as a gravel drains to drain the water and also they can increase the resistance against the slip and increase the amount of resistance in addition to the soil shear so they can actually have you know further effect in enhancing the stability of a slope as well in reinforcing the slope as well as as a facilitating as a drain is actually something called you know deep trench drains and another technique what we have discussed is that you know a type of technique by using chemical hardening where in the technique of you know using the lime and lime slurry injection or lime columns is one technique we have seen and in addition to that there are also some technique like use of ultra osmosis that means that by placing you know the electrically charges from positive charge and negative charge and this actually also helps in you know in improving the stability of a slope that means that the slope the water is actually drained by maintaining a electric potential between anode and cathode and that makes the you know the slope surface hardened and increases the shear strength of the soil and then we also discussed today in one of the techniques which is soil nailing technique where in this is an institute reinforcement technique which can be adopted for existing slopes natural are also man made slopes like highway railway embankments which are required to be protected or stability to be enhanced and this also technique can be adopted for you know existing slopes or slopes to be exposed for excavations as a shore protection system as a where in this is a type of shoring for the you know shoring technique for enhancing the stability of a you know a particular slope and this can be done both for the insular in the nails for this technique is done from top to bottom construction so nails are actually installed from top to bottom up to the top of the slope and the finally we have actually discussed regarding the biotechnical slope stabilization technique where in this technique allows to maintain the you know a selected facins or grass systems can provide stability of a slope in a better manner.