Patil, Vikas Sahebrao (Flat No. 16, Navtarang Housing Society Opposite Aagakhan Palac, Pune-Nagar Road Pune 6, 411 00, IN)
This invention relates to a method for constructing retaining walls. This invention further relates to a method for constructing gravity type retaining walls with lofts.
BACKGROUND OF THE INVENTION:
5 Retaining walls are civil engineering structures required to support earth, loose stone and backfill and in' the construction of bridges, abutments, cross drainage works and the like. The retaining walls known in the art may be categorized as gravity wall, reinforced concrete cantilever retaining walls, counter fort walls, buttress wall and reinforced earth wall. .
l o Gravity walls are generally made of plain concrete or masonry. The actuating force is the earth pressure exerted by the backfill, whereas the stabilizing force is the weight of the wall itself. The requirement of stability is that this resultant must be within the middle third zone of the base of wall. The condition of resultant being within the middle third zone is operative for any cross-section of the wall as 1 5 well. This imperative condition assures that no tension is generated in the concrete/masonry that constitutes the bulk of the wall as also in the foundation. In addition the total weight of the wall should be such that the bearing capacity of the ground on which wall is erected is not exceeded and the base width should be such that the frictional resistance available between the base of the wall and 0 the ground should be reasonably more than the earth thrust generated by the backfill. Thus there should be sufficient stabilizing force available against overturning and sliding and no bearing capacity failure. Such walls are generally bulky and are not economical for heights above 1.4 m. Further Gravity walls do not bend.
5 Reinforced concrete walls generally have L or T shapes. For walls of such types the backfill exerts the earth pressure. The stability requirement for the base slab is again as gravity walls in the sense that the resultant of actuating force and stabilizing force should be within the middle third zone of the base-slab so that no tension is generated at the interface of the base-slab and the ground on which the wall stands. The stem of such walls deflects due to actuating earth pressure. The stem portion of such wall acts as cantilever and steel has to be provided in the stem or trunk portion of such wall in addition to foundation portion. Where there is a possibility of bending stress, steel has to be provided in such walls. The trunks of such walls are comparatively slim. The deflection that could be normally allowed for the stem of such walls is 1% of the height of the stem and considerable amount of steel as reinforcement is required for such walls. The thickness of base slab is also not fat and it also bends requiring steel reinforcement in that portion. In addition to the requirement of sufficient withstanding force against sliding at the base and no overshooting of bearing capacity at the Interface between base slab and ground, the requirement of no tension at the interface between base-slab of wall and foundation also hold for such type of walls. Such walls are used for 3 to 8 m height of retention.
In the counterfort walls, stem and the slab are tied together by counterforts. A counterfort is a transverse wall spaced at intervals, which ties the stem and the base-slab. In this case the counterfort is a compression member whereas the stem spans continuously on counterforts. Here again steel has to be provided in the stem and counterforts to cater for tension and compression respectively. Reinforcement is also required in the base-slab. The requirements for the stability are same as for cantilever walls but due to the fact that stem spans continuously over counterforts, such walls can withstand larger heights of unsupported earth slopes. Fir heights of 8 to 12 meters counterfort retaining walls would be less costly than the cantilever retaining walls. Buttress walls are similar to the counterfort wall. In buttress wall, the buttresses are provided similar to counterforts by the opposite side of retained material so that these act as compression struts. The stem slab spans continuously over the buttress and steel is required in stem slab, buttress and base slab. The requirements of stability are the same. Therefore, these walls, either counterfort, cantilever or buttress require higher grade of concrete, steel cage erection, proper cover to steel and in general require between quality of supervision.
The general principle of reinforced walls is that the actuating earth pressure on the stem of the retaining wall is resisted by a structural member embedded in the retained material and which goes under tension. The friction generated between earth fill and this member is necessary for the stability of such walls. The stem could be in panel form also. Reinforced earth wall cannot serve as load bearing walls. Further, they require specified machinery erection and the cost can slightly higher than the conventional retaining walls in addition to the requirements of suitable technical manpower. All these artifacts presuppose that backfilling is done after construction of the walls in part or while and therefore proper compaction could pose a problem.
In view of the shortcomings and costs involved in such walls, it was necessary to evolve retaining walls suitable for Indian conditions such that these walls are cost-effective, easy to construct could serve as load bearing members, would use conventional material, would not require higher technical skill, with ease of constuction and saving in time, would not require later backfilling and long- lasting. Necessity is the mother of invention.
OBJECTIONS OF THE INVENTION: It is therefore an objection of this invention to provide retaining walls, which are cost-effective and easy to construct. -A- It is a further objection of this invention to provide retaining walls, which can act as load-bearing members using conventional material.
Another objection to this invention is to provide retaining walls, which do not require higher technical skill.
Yet another objection to this invention is to provide retaining walls which would not require later backfilling and are long-lasting.
These and other objection and advantages of the invention will be apparent from the ensuring description, when read in conjunction with the accompanying drawings where Figure 1 shows the overall picture of construction of a wall by graviloft technology.
DESCRIPTION OF THE INVENTION: According to this invention is provided a method for constructing graviloft retaining walls.
According to this invention, and with reference to Figure 1, base slab/course IEIFGH made of plain cement concrete/rubble/masonry is constructed. This portion which is of plain cement concrete may have nominal reinforcement of steel. The portion IEIFGH serves as base slab cum leveling course. On this leveling course the total retaining wall ABCDEF1 along with loft S1 CMLDS is to be constructed. Novy part of the retaining wall JKEE1 is constructed by traditional methods. This portion of retaining wa|l js constituted by plan cement concrete, masonry or plain cement concrete with over sized stones. After this construction the earth is backfilled and suitably compact upto level LKl The height of retaining wall DE if not more, instead of constructing the portion JKEE1 , the complete portion SDEE1 could be constructed and the earth backfilled and compacted to the level DDL Therefore the portion of retaining wall SDEE1 could be constructed either in one lift or more than one lift depending upon the height of portion DE. If the height is more even more than two lifts could be arrange. However every time lift such as JKEE1 is constructed it should be backfilled by earth and earth suitably compacted. Therefore the construction of retaining wall and backfilling operations ar going on simultaneously. Their operations are therefore to be continued upto level of loft. When the retaining wall is constructed upto level SD. The loft S1 CMLDS is constructed. The loft is reinforced concrete slab provided with reinforcing bars, which are shown by dotted lines. After the loft has been formed the remaining portion of retraining wall ABCS1 is to be constructed if the height of ABCS1 is more this construction operation could be divided into two or more steps.
For eg. if the height is such that it is manageable in two lifts as per engineering norms. In that case the retaining wall PQCS1 is first constructed and the backfilling is done upto level QQ1. The backfilling earth is compacted to engineering norms. Now the final lift of the retaining wall ABPQ is constructed and earth backfilled upto level BB1 and this earth/soil suitably compact to engineering norms. This now leads to the complete retaining wall ABCMLDEFGHIE1A.
The actuating force on this wall is lateral earth force generated by the earth of height BC and shown as (1) and lateral earth force generated for height DG that is the remainder height shown as 1'. The summation of laterial earth force (1+1') is less than the lateral earth force generated for the total wall height BG. Thus the main actuating force is considerably reduced, because of the provision of loft at proper location having predetermined length, breadth and embedded tension reinforcement. This reduction of actuating force has been confirmed by the inventors in laboratory as well as in the field. The stabilizing force is the weight of retaining wall and the weight of earth supported by the loft shown as (2). generating counterbalancing moment, and the friction generated at the interface of the loft and backfill shown as (3). The stability requirements of these walls are same as for gravity walls and the loft design is as per engineering norms, but the provision of loft reduced the section of the wall thereby achieving economy of construction over the walls mentioned earlier.
The proposed technology has many merits over the traditionally constructed retaining walls. By tailoring the concept, without introducing any new material and without sacrificing the risk factor, it was made possible to achieve overall reduction in the cost of construction. The new concept has analytical base and extensive experimental findings to shore the proposal. In fact inventors have already given concept designs for such walls to different reputed authorities for carrying out field trials and such walls are already constructed in the field testifying the validity of approach. There are incidental advantages in this concept such as saving in excavation due to reduced width, saving in shuttering due to reduced section, ease of construction, saving in time, adaptability for any increase height in future, light structure leading to even settlement and between resistant to earthquakes.