- 1 The Materials Used To Protect Foundations From Moisture Are Referred To As Either Damp Proofing Or Waterproofing 1 (61.89 KiB) Viewed 19 times
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Feudis / 65 (a) INTIMEWNO (d) FICURE 2.51 Seeps in the construction of a proprieury pressure-injected, bottom driven concrete pile footing, a) A charge of a very low- concrete mix is inserted into the bottom of the steel drive tube at the surface of the ground and compacted into a ligplug with repeated blows of a drop hammer. (b) As the drop hammer drives the sealing plug into the ground, the drive tube is pulled by the friction between the plug and the tube. (When the desired depth is reached the tube is held and a bulb of Cecis formed by adding small charges of concrete and driving the concrete out into the soil with the drop hammer. The bulb provides an increased hearing area for the pile and strengthens the bearing stratum by compaction. (d. The shaft is formed of additional compared Concrete as the cube is withdrawn. Charges of concrete are dropped into the tube from a special bucket supported the leads of the driving equipment Courtesy of Franki Foundation Company
66 / Chapter 2 Foundations Seismic Base Isolation The rubber Layers deform in shear It may be required for any of several In areas where strong earthquakes are to allow the rectangular isolator to reasons. The existing foundations common, buildings are sometimes become a parallelogram in cross sec- may never have been adequate to placed on base isolators. When signifi- between the ground and the build tion in response to relative motion carry their loads, leading to exces sive settlement of the building over cant ground movement occurs, the base isolators flexor yield to absorba ing. A lead core deforms enough to time. A change in building use or significant portion of this movement: allow this motion to occur, provides additions to the building may over- as a result, the building and its sub damping action, and keeps the layers loud the existing foundation. New of the sandwich aligned. construction near a building may dis structure move significantly less than turb the soil around its foundations they would otherwise, reducing the or require that its foundations be forces acting on the structure and UNDERPINNING lessening the potential for damage. carried deeper. Whatever the cause, A frequently used type of base isola underpinning is a highly specialized Underpinning is the process of task that is seldom the same for any tor is a multilayered sandwich of rub- bet and steel plates (Figure 2.52). strengthening and stabilizing the two buildings. Three different alter- foundations of an existing building. natives are available when foundation Deplacement of building -Base Bolo -Calubase plate -Leadcore -Multiple layers of steel plates and rubber -Isolator base plate Motion af ground FIGURE 2.5 Base isolation
Underpinning 67 Capacity needs to be increased: The or the soditelf can be strengthened foundations may be enlarged: new, by grouting or by chemical treat- deep foundations can be inserted ment. Figures 2:53 and 254 illustrate under shallow ones to carry the load in diagramatic form some selected to a deeper, stronger stratum of soil concepts of underpinning - Nude Medlem Jacky SECTION 4. ELEVATION SECTION FIGURE 2:53 Two methods of supporting a building while carrying out underpinning week beneath is foundation, each shown in both elevation and section. (a) Trenches are dug beneath the existing foundation intervals, leaving the majority of the foundation supported by the soil. When portions of the foundations have been completed in the wrenches, wing one of the types of underpinning shown in Figure 254, another set of reaches is dug between them and the remainder of the foundation is completed. The foundations of an entire wall can be exposed at once by seedling, in which the wall is apparsed temporarily on needle beame threaded through holes cut in the wall. After underpinning has been accomplished, the jacks and needle beams are removed and the wrench is backfilled SCHON CSECRON A ELEVATION 2 MON FIGURE 4.54 Three types of underpinning. (a) A new foundation wall and footing are constructed beach the existing foundation. (b) New piles or caisses are constructed eacher side of the existing foundation. (c) Minipiles are inserted through the existing Foundation. Minipiles de su generally require excavation or temporary support of the building
68 Chapter 2 Foundations RETAINING WALLS as the height of the wall, the character of the wall or undermining of the wall of the soil behind the wall the presence by flowing groundwater (Figure 2.55), A raining wall holds soil back to cre- or absence of groundwater behind the Careful engincering design and ste ate an abrupt change in the eleva- wall. any structures whose foundations supervision are crucial to the success of tion of the ground. A retaining wall apply pressure to the soil behind the retaining wall. must resist the pressure of the earth wall, and the character of the soil be There are many ways of building that bears against it on the uphill neath the use of the wall, which mest retaining walls. For walls less than side. Retaining walls may be made of support the footing that keeps the wall 3 feet (900 mm) in height, simple, masonry, preservative treated wood, in place. The rate of structural fail unreinforced walls of various types coated or galvanized steel, precast ure in retaining walls is high relative are often appropriate (Figure 2.56). concrete, or most commonly, Nitecast to the rate of failure in other types of For taller walls, and ones subjected concrete. structures. Failure may occur through to unusual loadings or groundwater, The structural design of a retaining fracture of the wall, overturning of the the type most frequently employed wall must take into account such factors wall due to soil failure, lateral sliding today is the cantilevered concrete Water table M . OVERTURNING SLIDING UNDERMINING FIGURE 2.55 Three Failure mechanisms in retaining walls. The high water cable shown in these illustrations creates pressure against the walls that contributes to their failure. The undermining failure is directly auributable to groundwater running beneath the base of the wall carrying soil with it. MARCH SYONE GRAVITY WALL VERTICAL TIMER HORIZONTAL TIMBER CAT.EVERED WALL WALL WITH DEADMEN FIGURE 2.36 Three types of simple remaining walls, usually used for heights not exceeding 3 feet (900 mm). The deadmen in the horizontal timber wall are timbers embedded in the soil behind the wall and connected to it with timbers inserted into the wall at right angles. The timbers, which should be pressure treated with a wood preservative, are held together with very large spikes or with steel reinforcing bars driven into drilled holes. The crushed-stone drainage reach behind each wall is important as a means of relieving water pressure against the wall to prevent wall failure. With proper engineering design, any of these types of construction can also be used for taller retaining walls
Retaining was -Crushed some drastase layer FIGURE 1.57 Cantilevered recaining walks of coace and concrete masonry The footing is shaped to resise sliding and over and drainage behind the wall reduces the likelihood of undermining. The per of steel reinforcing herokee ines) is designed to resise dhe tessile forces in the wall -Weep boles Perforated drainage pipe Key to pre sliding REINTORCED CONCRETE REINFORCED CONCRETE MASONRY FIGURE 3.58 A segmental retaining will consisting of specially made coace blocks designed to insestock and prevents. The wall leans back against the strains, this reduces the amount of the wall me Train animalasi matleagலை the lateral push of the world VERSA-LOK Praining in TROL
70 / Chapter 2 Foundations retaining wall, two examples of walls that need no steel reinforcing glass fibers, which stabilize the soil in which are shown in Figure 2.57. (Figure 2.58). much the same manner as the roots The shape and reinforcing of a Farth famong Figure 2:59) is of plants Gabons are another form of cantilevered wall can be custom de an economical alternative to conven earth retention in which corrosion-re- signed to suit almost any situation. tional raining walls in many situ sistant wire baskets are filled with cob Proprietary systems of interlocking tions. Soll is compacted in thin layers ble or boulder-sized rocks and then concrete blocks are also used to cach containing strips or meshes of stacked to form retaining walls, slope construct sloping segmental retaining galvanised steel, polymer fiets or protection, and similar structures. FICURE 2-59 Two examples of each reinforcing. The embankment in the top section was placed by alternating thin layers of earch with lovers of synthetic mesh fabric. The retaining wall in the kwer section is made of precast concrete panels fastened to long gahanized steel straps that run back into the soil
Rewining Walls / 71 GEOTEXTILES Geotextiles are flexible fabrics made of chemically inert Tooftop terraces, where it maintains free passage for the plastics that are highly resistant to deterioration in the drainage of water above a waterproof membrane. soil. They are used for a variety of purposes relating to Synthetic filter fabrics are wrapped over and around site de clopment and the foundations of buildings. As subterranean crushed stone drainage layers such as the described in the accompanying text, in earth reinforcement one frequently used around a foundation drain. In this or soil forn a plastic mesh fabric or grid is used position, they keep the stone and pipe from gradually to support an earth embankment or retaining wall. The becoming clogged with fine soil particles carried by the same type of mesh may be utilized in layers to stabilize groundwater. Similar fabrics are used at grade during con- engineered fill beneath a shallow footing (Figure A), or struction, acting as temporary barriers to filter soil out to stabilize marginal soils under driveways, roads, and air- of water that runs off a construction site, thus preventing port runways, acting very much as the roots of plants do contamination of lakes, streams, or stormwater systems. in preventing the movement of soil particles. Special geotextiles are manufactured to stake down Another geotextile that is introduced later in this on freshly cut slopes to prevent soil erosion and encour- chapter is drainage matting, an open matrix of plastic fila- age revegetation; some of these are designed to decay and ments with a feltlike filter fabric laminated onto one side disappear into the soil as plants take over the function of to keep soil particles from entering the matrix. In addi- slope stabilization. Another type of geotextile is used for tion to providing free drainage around foundation walls, weed control in landscaped beds, where it allows rainwa- drainage matting is often used beneath the soil in the bot- ter to penetrate the soil but blocks sunlight, preventing toms of planter boxes and under heavy paving tiles on weeds from sprouting Colum bota Sol rentang gids