Test 30 - Foundations on Expansive Soils and Swelling Control

Question 1 ప్రశ్న 1

A lightly loaded building is proposed on a clay deposit that swells when wetted and shrinks during drying. Which mechanism most directly explains the resulting foundation movement?

A Seasonal changes in concrete strength cause all movement without involving the soil. B Moisture changes alter the volume of susceptible clay minerals and the soil fabric, producing heave or shrinkage. C The soil can expand only if its grains are converted into sand. D Water absorption necessarily increases the soil's dry density without changing its volume.

Question 2 ప్రశ్న 2

A shallow foundation on expansive clay experiences upward movement after prolonged rainfall and downward movement during an extended dry period. Which engineering interpretation is correct?

A Both movements demonstrate immediate bearing-capacity shear failure. B The upward movement proves that the soil has no shrinkage potential. C The downward movement must be due only to corrosion of foundation reinforcement. D Wetting-induced swell and drying-induced shrinkage can create repeated differential movement and distress.

Question 3 ప్రశ్న 3

In assessing foundations on expansive soils, what is the most appropriate definition of the active zone?

A The depth interval within which moisture changes produce significant seasonal or environmental volume changes in the expansive soil. B The zone beneath a footing in which ultimate end-bearing failure has already occurred. C The entire soil profile down to bedrock, regardless of moisture variation. D The thickness of concrete placed between the foundation and finished floor level.

Question 4 ప్రశ్న 4

Which clay mineral is particularly associated with high swelling potential because of its mineral structure and affinity for water?

A Quartz. B Feldspar. C Smectite-group clay such as montmorillonite. D Fresh unweathered granite.

Question 5 ప్రశ్న 5

A site investigation in the Deccan region describes dark clayey ground as black cotton soil. Which statement is most defensible for foundation design?

A The colour alone proves that every such soil has identical swelling pressure. B Black cotton soils can exhibit troublesome swell-shrink behaviour, but the site's actual expansiveness and active-zone depth require investigation. C All black cotton soils behave as free-draining coarse sand. D No foundation treatment or assessment is needed once the soil is named black cotton soil.

Question 6 ప్రశ్న 6

A clay sample has liquid limit LL = 80% and plastic limit PL = 35%. What is its plasticity index PI, and what is the correct engineering interpretation?

A PI = 45 percentage points; this is an index of the soil's plastic consistency range, not a direct measurement of swelling pressure. B PI = 115 percentage points; it directly equals swelling pressure in kPa. C PI = 2.29; it is the coefficient of consolidation in m2/year. D PI = 35 percentage points; it is unaffected by the liquid limit.

Question 7 ప్రశ్న 7

Under IS 2720 (Part 40), which laboratory approach is used to determine the free swell index of a soil?

A Measure the standard penetration resistance at successive depths in a borehole. B Compress an undisturbed sample to failure in an unconfined compression apparatus. C Measure swelling pressure by forcing a saturated specimen to constant volume under a surcharge. D Compare the equilibrium sediment volumes of comparable dry soil portions in distilled water and kerosene.

Question 8 ప్రశ్న 8

In a free swell index test, the equilibrium soil-sediment volume in distilled water is 30 mL and that in kerosene is 20 mL. Using FSI = [(Vwater - Vkerosene)/Vkerosene] x 100, what is the free swell index?

A 33.3%. B 20.0%. C 50.0%. D 150.0%.

Question 9 ప్రశ్న 9

In an IS 2720 free swell index calculation, a sample has equilibrium sediment volume of 25 mL in kerosene. If the measured free swell index is 40%, what corresponding sediment volume in distilled water is implied by FSI = [(Vwater - Vkerosene)/Vkerosene] x 100?

A 15 mL. B 35 mL. C 40 mL. D 65 mL.

Question 10 ప్రశ్న 10

A clay specimen is dried gradually, and the relationship between water content and volume is monitored. Which description correctly identifies the shrinkage limit and its relevance to expansive-soil assessment?

A It is approximately the water content below which further drying produces little or no further reduction in the soil specimen volume. B It is the water content at which the soil first starts flowing like a liquid. C It is the pressure needed to prevent soil swelling during soaking. D It is identical to the field active-zone depth expressed as a percentage.

Question 11 ప్రశ్న 11

Which Indian soil-test provision most directly addresses laboratory measurement of swelling pressure, and what does that pressure represent in a constant-volume test?

A IS 2720 (Part 40); the percentage difference between water and kerosene sediment volumes. B IS 2720 (Part 5); the plasticity index obtained from liquid and plastic limits. C IS 2911 (Part 4); the force required to extract a pile in tension. D IS 2720 (Part 41); the applied pressure required to restrain the specimen's tendency to swell under the specified test conditions.

Question 12 ప్రశ్న 12

For a deliberately simplified uplift check, assume that a uniform net swelling pressure of 90 kPa acts upward over the full 2 m by 3 m plan area of a shallow foundation. The stabilizing downward permanent load is 450 kN, and all other effects are neglected. What are the upward soil force and the resulting unbalanced vertical force?

A 270 kN upward and 180 kN net downward. B 540 kN upward and 90 kN net upward. C 450 kN upward and zero net force. D 810 kN upward and 360 kN net upward.

Question 13 ప్రశ్న 13

A 1.50 m thick expansive clay layer is assumed to experience uniform vertical free-swell strain of 6% after wetting. Neglect confinement and lateral variation for this simplified estimate. What upward heave does the strain imply?

A 9 mm. B 60 mm. C 90 mm. D 150 mm.

Question 14 ప్రశ్న 14

Two supports 8 m apart experience upward heaves of 52 mm and 12 mm relative to a common stable datum. If relative vertical movement is represented by a straight-line profile, what is the magnitude of angular distortion between the supports?

A 1/200. B 1/100. C 1/400. D 1/800.

Question 15 ప్రశ్న 15

A lightly loaded slab rests directly on expansive clay near a large tree. Which explanation best accounts for possible seasonal differential movement even where the clay mineral composition is nearly uniform?

A Uniform mineralogy guarantees uniform soil suction and moisture at all points. B Tree roots necessarily eliminate all foundation heave by permanently strengthening the clay. C Only concrete creep can create differential movement in a site with one soil type. D Vegetation, drainage and exposure can create unequal moisture and suction changes beneath different parts of the slab.

Question 16 ప్రశ్న 16

A proposed building occupies expansive clay with a site-investigated active zone near the surface. Which under-reamed-pile concept is most appropriate for reducing foundation sensitivity to active-zone heave?

A Place every enlarged bulb within the most seasonally variable surface soil to maximize its heave exposure. B Omit structural connection between the pile and supported foundation so that uplift can be ignored. C Develop adequate load transfer and anchorage in relatively stable ground below the investigated active zone, while designing the shaft and cap for swelling-related actions. D Assume enlarged bulbs automatically prevent all future soil moisture change.

Question 17 ప్రశ్న 17

Which pairing correctly identifies the current Indian Standard specifically addressing the design and construction of under-reamed pile foundations, including their use in problematic soils?

A IS 2720 (Part 40):1977 — design and construction of under-reamed piles. B IS 2911 (Part 3):2021 — design and construction of under-reamed piles. C IS 2720 (Part 41):1977 — structural detailing of under-reamed pile caps. D IS 1498 — pile load testing and bulb construction procedures.

Question 18 ప్రశ్న 18

A suspended ground beam connects piles founded beneath expansive soil. Why may a deliberately maintained void or compressible void-forming system beneath the beam be specified?

A It provides space for anticipated soil heave so the swelling soil does not directly impose the full upward contact action on the beam. B It increases the expansive clay's free swell index without affecting the beam. C It transfers beam gravity loading to the seasonally active soil by continuous contact. D It eliminates the need to check any uplift forces on the pile shafts.

Question 19 ప్రశ్న 19

A structural detail requires clear separation beneath a suspended beam equal to the anticipated maximum heave of 60 mm plus a specified construction and performance allowance of 20 mm. A proposed detail provides 90 mm of maintained clearance. By how much does the provided clearance exceed the stated required value?

A 0 mm. B 20 mm. C 30 mm. D 10 mm.

Question 20 ప్రశ్న 20

A pumping-station site contains expansive clay, and poorly directed roof drainage discharges water next to one corner of the building. Which preventive measure most directly addresses the identified moisture-related cause of distress?

A Increase the clay's water entry at the affected corner to accelerate localized heave. B Provide reliable surface grading, roof-water collection and controlled discharge away from foundation-sensitive ground. C Remove all protective paving while keeping the roof-water outlet at the corner. D Assume drainage details cannot affect foundation movement in expansive soil.

Question 21 ప్రశ్న 21

An underground water-supply main develops a persistent leak close to one footing on an expansive-clay site. The adjacent footing starts moving upward relative to other supports. Which action addresses the likely geotechnical mechanism most appropriately?

A Ignore the leak because only seasonal rainfall can trigger expansive-soil swelling. B Increase the leaking flow rate to achieve uniform wetting without examining the soil. C Repair the leakage, assess the changed soil moisture and foundation movement, and implement compatible moisture and structural controls. D Replace the column steel reinforcement without investigating the changing groundwater or moisture condition.

Question 22 ప్రశ్న 22

For a lightly loaded pavement or floor slab above an identified shallow expansive clay layer, when is excavation and replacement with a suitably compacted nonexpansive material a defensible mitigation option?

A When investigation shows that the treated depth and extent are adequate for the movement mechanism, and replacement, compaction, water management and transitions are properly designed. B Whenever a thin surface layer is replaced, even if a much thicker active expansive layer remains untreated. C Only when no subsurface investigation has been performed. D Only if the replacement material is deliberately chosen to be more expansive than the original clay.

Question 23 ప్రశ్న 23

Lime stabilization is proposed for a highly plastic expansive clay, but the soil may contain appreciable soluble sulphates. Which specification approach is most technically justified?

A Assume a fixed lime content will always eliminate swelling in every clay, without laboratory evaluation. B Use only the soil colour to select the lime dosage and curing method. C Ignore sulphates because they cannot react with lime-treated clay. D Perform suitable mix-design and durability testing, including sulphate-related expansion risk, before adopting lime treatment and construction controls.

Question 24 ప్రశ్న 24

A foundation on expansive soil is subject to an assessed net upward swelling action of 360 kN. The permanent downward action available to resist uplift is 120 kN, and a connected under-reamed pile system has separately established ALLOWABLE additional anchorage resistance of 300 kN. Under this expressly simplified vertical force comparison, what is the required anchorage resistance and the outcome?

A Required resistance 360 kN; anchorage fails by 60 kN because permanent load must be ignored. B Required resistance 240 kN; allowable anchorage exceeds it by 60 kN under the stated check. C Required resistance 480 kN; anchorage fails by 180 kN. D Required resistance 120 kN; anchorage exceeds it by 180 kN.

Question 25 ప్రశ్న 25

A new water-treatment building is proposed on deep expansive clay with strongly variable seasonal moisture, and the structure contains rigid pipe connections sensitive to differential movement. Which foundation strategy is most defensible?

A Use shallow pads without a swelling investigation because the structural loads are relatively high. B Adopt a universal foundation depth from another project and ignore moisture variations. C Select a solution after evaluating swelling pressure, active-zone depth, groundwater, heave, structural loads and pipe tolerances; consider properly detailed deep foundations or ground treatment with moisture management. D Assume one large raft always eliminates differential heave even when active-zone movements remain unchecked.

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