Basement

3 cellar 3 Basement 1 Quick revision 1. 1 Problems arising from root cellar pull a. jibe mode. b. Surface and drop anchor piddle promise c. Lateral stability of cellar mining. d. stability of adjoining building. 1. 2 Ground urine system control dewate evade a. break Sump Pumping b. wellpoint form. c. Sh get out-Bored Well System d. Deep-Bored Well System 1. 3 Basement slam a. Open excavation b. Sheet agglomerate coffer Supported with raking struts Supported with struts and walings Supported with landed estate anchors Ground support and demonstrate water control for deep excavation truncated off striaings c. hack fixed diaphrage d. Mixed in place ring e. Ground treatment f. tirade pneumatic caisson g. Diaphrage sea surround 1/11 3 cellar 2. Cut-off palisadeings 2. 1 thin out grouted pessary A series of touching cosmopolitan beams or tugs ar impelled into the do of import to the required perspicaciousness. A grout nip pipe is fixed to the web t he naval division and this is connected to a group substance at the ground. As the sections are retreat the void created is change with cement grout to form the thin membrane. This is a non-structural rampart and services only as a cut-off paries. It is uitable sub footing of silt, sand and gravel. 2. 2 Thin grouted pessary (Source R. Chudley) Mixed-in-place wall A pickle churn drill is drilled into the ground. usurpation grout is pumped through the labor kelly bar during the drilling operation. When the required depth is r individuallyed, the auger rotation is reversed and move while grout snap continues. The grout is thus mixed with the existing injury to form a mixed-in-place weed. The above mathematical do is repeated with the scores being tramp against each other until the whole wall is make. Mixed-in-place skunk (Source Jufri & Wellmen) /11 3 root cellar 2. 3 Ground treatment The study disadvantage of pumping is ca using settlement of border ground. In urban areas, settlement would just affect the stability of adjacent properties. In this situation, grouting method roll in the hay be utilize to control ground water. The basic method is to inject the priming coat or judder with fluids which, on setting, seal or sl alter the permeability of the material. There are different types of grouts. The choice of grouts, the pattern and spacing of the guessing pipes will depend upon the particle sizes of the soil or the size of fissures in the rock.Cement Grouting (Source R. Chudley) 2. 3. 1 Cement grouting Cement grout is fitting for injecting into coarse materials which bewilder a highschool permeability. This method not only support form an impermeable barrier to ground water but also change integrity loose soils which prevents from collapsing during excavation. It is usual to commence grouting with a batch of thin grout and hence to increase the viscosity of the grout as the process continues, by cut the water-cement ratio . The grout used may be self-possessed of neat cement grout, or a mixture of cement and 3/11 3 wine cellar sand in the ratio of 1 4.The adding of sand stifles the court of material but it also reduces the workability. On the other hand, pulverized fuel ash (PFA) may be used to commute part of the cement (up to 50%) to reduce the cost of the material. The spherical particle manikin of PFA improves the flow quality of the grout without reducing its strength. 2. 3. 2 Bentonite grouting Bentonite grouting is used in ground conditions where the particles of the soil are too delicate for cement grouting. While bentonite grout adds bittie strength to the soil, it has a high foe to water flow and in that locationfore produces an glorious barrier.Bentonite is produced from montmorillionite clay, which has thixotropic properties when it coagulates it forms a gel, and if mixed with certain additives, such as Portland cement or water-soluble silicates, the barrier formed will be permanent. 2. 3. 3 Chemical grouting There are deuce main processes of chemical grouting one-shot and 2 shot. In the two-shot process, pipes are driven into the ground at around 600 mm centres, and the first chemical, normally sodium silicate, is injected. This is followed straightaway by the injection of the second chemical, atomic number 20 chloride.The reaction between the two chemicals is immediate, resulting in a tough, insoluble silica-gel. The process gives large strength to the soil and not bad(p)ly reduces its permeability. Two-shot process for chemical grouting 4/11 3 root cellar The two-shot process has been largely superseded by the one-shot process, which consists of mixing together prior to injection two chemicals whose gel time screwing be sufficiently delayed to forgo full penetration of the soil onwards gel occurs. The extent of the delay drop be accurately controlled by alter the proportions of the two chemicals.The extra time usable for placing this g rout allows wider spacing of the boreholes. 4. 2. 6 orotund cofferdam Steel sheet pile cofferdams may be arranged in circular shape in plan. Circular cofferdams may be supported with ring walings. The walings are subject to tangential make and act as a continual arch. Thus transverse struts are not required. Large diameter circular cofferdams may be formed of cover full point wall and reinforced with ring cover beam. The advantage of this method is that it proposes a stool excavation un-hampered by struts. However, the method is certified to circular shape.Circular cofferdam support with ring walings Basement tress of IFC 5/11 3 basement 5 midriff Walls Diaphragm walling describes the kink of continuous concrete walls into the ground. The process, sometimes called the slurry chuck method, involves the excavation of a narrow infringe to the required depth which supported with bentonite slurry. The trench is thus filled with concrete to form the wall. fixion of chec k wall 5. 1 Advantages of using diaphragm walls for basement construction 1. The process of constructing the wall is relatively quiet and has little vibration. . The wall can be constructed to a great depth. 3. The wall admits temporary ground supports during excavation hence expensive bracework is eliminated or minimized. 4. The wall provides a good water cut-off no dewatering is required and hence has little set up on adjacent structure. 5. The wall serves twain as external wall for the basement and the knowledgeability for the superstructure. 6. For deep basement, diaphragm walling is much economical than using steel pelt cofferdam. 6/11 3 basement 5. 2 Method of construction of concrete diaphragm wall 1. A allowance trench, 1 to 1. m deep and with a width gibe to the wall burdensomeness plus 300 mm is excavated. 2. The trench is lined on both sides with cl mm thick in-situ concrete. (The linings provide a guide for the grab and protect the slide by of the excavation from collapse. ) 3. The wall is separate into to bloodsheds. The width of each decorate is intimately 4. 5 to 7 m. The sequence of construction for the panels is in an alternatively way. That is, an intermediate panel is excavated after panels on its both sides have been seethe. 4. The trench is then filled with bentonite slurry from a large storage tank ahead excavation.Excavation is through with(p) by a grab. During excavation, it is primary(prenominal) to maintain the slurry level at about(predicate) 0. 5 m below the top of the trench. (The function of the bentonite is to prevent the ingress of water and soil into the trench. ) Excavation is continued until the open is reached. 5. Stop end pipes of diameter equal the wall thickness are fixed at both ends of the panel. A sustenance cage is pass uped through the bentonite and panel is cast with tremie concrete. The displaced bentonite is recovered, agonistical to remove the soil particles and then stored for succee ding(a) use. 6.When the concrete has set, the await end pipes are removed. Semi-circular sockets are formed which provide key for the adjacent panels. 7. promote panels of the diaphragm wall are then formed in a uniform manner until the wall is completed. 5. 3 formed cover Diaphragm Walls Diaphragm walls can also be formed with formed concrete panels. The construction sequence is 1. A perimeter trench, lined on both sides with concrete walls, is prepared. 7/11 3 basement 2. The trench is filled with bentonite slurry and excavated with a grab. During excavation, the slurry level is maintained at about 0. m below the top of the trench. Excavation is continued until the founding is reached. 3. Cement grout is introduced to the bottom of the trench with a spreader. The displaced bentonite is recovered, strained to remove the soil particles and then stored for future use. 4. Precast posts or panels are inserted into the trench to form the wall 5. When the grout has set, it seals t he joints of the precast panels effectively, and the diaphragm wall is formed. Precast concrete Diaphragm Wall Precast Concrete Diaphragm Wall (Source R. Holmes) (Source R. Holmes) 8/11 3 basement 6 spend pile wallSince the wall of a basement must be watertight, if a pass pile wall is used as a basement wall, the piles of the wall will be constructed to overlap with each other. This type of wall is also called sec pile wall. The overlapping is about one hundred twenty to 200 mm. It is cut by a hydraulic actuated type fitted with a cutting ring at the lower end. The cutting must be done within one or two days after the concrete has been cast to prevent it become to hard. second pile wall Alternatively, the piles of the wall are cast contiguous. Boreholes are drill at the joints of the piles which cut the edges of the piles. The boreholes are then filled ith bentonite-cement grout to seal the joints. Secant pile wall (Source R. Chudley) 9/11 3 basement 7 top- rout Basement bec omeion It is to construct the basement in the downward direction to the last(a) levels of the basement. The sequence of work is as follows1. Construct the permanent basement wall using diaphragm wall or pass piles wall. 2. Construct bored piles with temporary steel casings as the founding of the basement. The cut-off level of the piles is at the final basement level. 3. Place steel columns wrong the steel casings of the bore piles from the foundation level up to the ground level. . Backfill the shafts with amyloid material to hold the steel columns. 5. Construct the ground floor slab supported on the steel columns and the diaphragm walls. (This slab provides a running(a) platform for superstructure construction and acts as the askant support for the basement excavation. ) Access commencement in this slab shall be provided for further excavation. 6. bring out beneath the ground floor slab down to next basement floor soffit. 7. Cut the steel casing, remove the gravel and le t out the steel column. 8. Cast the second basement slab. The slab is connected to the columns with shear studs and connected the diaphragm wall with dowels) 9. Repeat the process for the accompanying basement floors until down to the final basement slab. The top-down method provides the following main advantages1. Superstructure can be constructed at the corresponding time as the basement construction takes place and therefore the overall construction time is reduced. 2. Temporary and permanent plant are combined and therefore there is no need for extensive steel temporary kit and caboodle. 3. Stiff rigid walls allow an almost watertight construction and basement construction to great depth.These stiff walls provide at the same time a limitation to ground movement. 10/11 3 basement Steel casing infilled with granular material Steel column on top of bored pile Reference Control of groundwater for temporary works (1986), S. H. Somerville, CIRCA verbalism Technology (1987), R. C hudley, Longman Building Construction Handbook (1992), R. Chudley, Newnes Introduction to well-behaved applied science Construction (1985), R. Holmes, College of Estate Management Civil Engineering Construction IV (1991), S. A. R. Jufri & R. J. Wellmen, Hong Kong polytechnic 11/11