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  1 Introduction 1.1 GENERAL Under the action of gravity, surface water and groundwater always tend toflow from higher to lower elevations. Surface water will flow over solid andthrough permeable formations, and its volume and velocity are a function of the available supply and the fluid head. Groundwater can move onlythrough a pervious material (fractured or fissured rock or soils withinterconnected open voids), so its flow characteristic is also a function of formation permeability. Groundwater elevation varies as the supply sourcevaries and can be raised or lowered locally by increasing or decreasing thelocal supply (naturally by precipitation or artificially by pumping a well orirrigating). In general, over a large surface area, groundwater surface is asubdued replica of ground surface.Many construction projects require the lowering of the natural landsurface to provide for foundations, basements, and other low level facilities.Other projects such as tunnels and shafts require underground constructionof long, open tubes. Whenever such excavations go below groundwatersurface, they disrupt the existing flow patterns by creating a zone of lowpressure potential. Groundwater begins to flow radially toward and into theexcavation. The situation is further aggravated by the fact that construction Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.  procedures generally enlarge existing fissures and voids and create new onesin the vicinity of the excavation.Contractors anticipate infiltration when the excavation is planned togo below groundwater level and generally make provisions for diverting theflow of water before it reaches the excavation or removing it before or afterit enters. Water problems during construction, which carry a cost penalty,occur when the provisions to handle groundwater prove ineffective. Waterproblems can range from nuisance value to actual retardation of theconstruction schedule to complete shutdown.Water problems may also occur after the completion of construction.Seepage that may have been tolerable during construction may becomeintolerable during facility operations. Post construction seepage mayincrease to intolerable levels due to termination of construction seepagecontrol procedures. Unanticipated water problems may occur because thestructural elements cause long-term modification of surface drainagepatterns or subsurface seepage patterns. Unusual amounts of precipitationmay raise normal ground water levels. Occasionally, shrinkage cracks in,and settlement of foundation elements may result in postconstructionseepage problems.The presence of unanticipated groundwater (either static or flowing)may lower the design value of bearing capacity. If higher values are used,based on dry conditions, water must be kept permanently from thefoundation area. The presence of water in basement areas may prevent useof such areas.The contractor has at his or her disposal many field procedures toprevent seepage or to control it after it reaches intolerable amounts. Some of these procedures are briefly discussed in Sec. 1.2. 1.2 MODIFICATION AND STABILIZATION ‘‘Modification’’ implies a minor change in the properties of soil or rock,while ‘‘stabilization’’ implies any change which renders the soil or rockadequate for changed strength or permeability properties (or both) requiredby field construction. Generally, all modification procedures result inincreased stability for granular materials and most cohesive soils, but notnecessarily for rock formations. These terms are used interchangeably in thistext.For granular (non-cohesive) materials, modification always consists of changing the volume of the soil voids, or replacing the void material, orboth. For cohesive materials, modification consists of mixing with stabilizersand preloading to eliminate or reduce future settlements. Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.  Decreasing the void volume of a soil mass, when done slowly enoughto avoid pore pressure build-up, results in increased shear strength, whichincreases bearing capacity and safety factor against plane failure. Replacingthe void fluid with a solid material will decrease the formation permeability,and may also add shear strength. (Under some special conditions, replacingpore water with a weak grout may decrease the formation shear strength).Field procedures to decrease the void volume include static anddynamic compaction, pile driving and the use of surface and deep vibratoryequipment. Explosives have also been used for this purpose.Ground water can be removed from a site by drainage ditches, bypumping from sumps, and by wellpoints and wells.Field methods to replace or modify the void fluid include grouting(both particulate and chemical), freezing, surface and deep mixing, jet pilingand slurry trenching. Compressed air may also be considered as a method of changing the void fluid from water to air.This past decade has also seen the development of biologicalstabilization methods, which add strength to a soil mass through thegrowth of roots. 1.3 SOIL AND ROCK SAMPLING Everything we build, at some point during its construction, rests on soil orrock. It is obvious that the soil or rock, for every specific case, must haveadequate properties to support whatever rests on it without structuralfailure or deleterious settlement.It is usually a straightforward design problem to determine the loads astructure’s foundation transmits to its supporting soil or rock. It is also arelatively straightforward problem to estimate the ability of the soil or rockto withstand the foundation loads. However, while the foundation loads canbe determined to a high degree of accuracy, the estimation of soil and rockproperties which determine bearing capacity is subject to many sources of error.While a full-scale field loading test, properly performed andinterpreted, will reliably define the foundation: soil interaction, such testsare generally not feasible. Thus, the way a soil or rock mass responds tobeing stressed is usually determined by previous experience in similarconditions, by extrapolating the results of small load tests or by usingspecific soil properties in various empirical formulae. These soil propertiesare sometimes inferred from previous experience, but more often reflect theresults of laboratory and field tests on soil and rock samples.Samples of soil from shallow depths can be obtained from holes orpits. In granular soils, holes and pits will cave unless the side slopes are less Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.  than 35 to 45 degrees. Therefore, taking samples in holes or pits becomeseconomically unfeasible below depths of several feet.In cohesive soils, walls of a pit may remain vertical for considerabledepth. However, below 5 to 6 feet personnel safety calls for bracing, makingdeep pits uneconomical.Samples scraped from the sides or bottom of holes and pits are‘‘disturbed’’. That is, whatever structure and stratification the soil may havehad in nature has been destroyed by the sampling operation.Hand augers of all kinds can be used to extract soil samples from holesup to 20 feet and more. Motor driven augers can go much deeper. All suchsamples are disturbed, and may even be mixed from different strata.The usual method for obtaining samples at significant depths belowthe surface is to push or drive a pipe or tube into undisturbed soil at thebottom of a drill hole. Of course, this process disturbs the soil, particularlywhen the pipe is heavy walled. Many different kinds and sizes of samplersare used, and the most common is shown in Figure 1.1. This sampler iscommonly called a split spoon. When used with the dimensions shown, andhammered into the soil by a free falling, 140 pound weight, dropping 30inches, this is the Standard Penetration Test (see ASTM Standard D.1586, F IGURE  1.1  Split spoon sampler. (Reprinted with permission from TheAnnual Book of ASTM Standards, copyright ASTM, 100 Bar Harbour Drive,West Conshohocken, PA, 19428.) Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.
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