Foundation, Concrete and Earthquake Engineering

What is Moisture Movement in Building?

rajib_ce99@yahoo.com (RAJIB) — Wed, 01 Jan 2020 09:14:00 +0000

Materials used in building construction have pores, especially manufactured materials like cement or lime concrete, mortar, some types of stones, timbers, and bricks from clays. Such porous materials inherently absorb moisture from many sources and expend which is followed by shrinkage on drying. These moisture movements are of two types

• Reversible movements

• Irreversible movements

The reversible movements are those which have reverse movement on absorbing moisture and subsequent drying. Such movement is of cyclic nature which is due to change in inter-pore pressure controlled by moisture change. The degree of movement depends on porosity and molecular structure of a material.

rajib_ce99@yahoo.com (RAJIB) — Wed, 07 Aug 2019 06:52:00 +0000

Foundation

Foundations on Black Cotton Soil

Properties of Black Cotton Soil

Under-Reamed Piles: Safest Foundation Solution for Black Cotton soil

Pile foundation

Design Example of Pile Cap for Concentric Loading

Structural Capacity of Pile

Requirements of Bentonite in Boring of Pile Foundation

What is Batter Pile?

Why is Bentonite Required in Bored Piling Operation?

Earthquake

Buckling of Piles in Foundation on Liquefiable Soils

Earthquake Influence on Bearing Capacity of Foundation Soil

Generalize Recommendation To Design Earthquake Resistant Structure

What is Response Spectrum in Earthquake Analysis?

Earthquake Damage on Water Tanks

What is Pounding? Structural and Foundation Issues of Pounding

Expansive
soil

Behavior of Expansive Soil under Raft Foundation

How is Slab-On-Grade Foundation Repaired Distressed by Black Cotton Soil?

Low Cost Foundation Solution for Black Cotton Soil

Selection of Foundation and Structural System for Expansive Soil

Foundation
Failure

Symptoms of Foundation Failure

What are the Secondary Causes of Foundation Settlement?

Moisture Damage to Masonry Foundation of Lime Mortar

What are the Types of Foundation Settlement?

Dam
Failure

Failure of Dam

How do Soil Types of Dam's Foundation Influence Sliding?

Seismic Vulnerability of Tipaimukh Dam

Foundation design

What is the Significance of Modulus of Subgrade Reaction of Soil?

What should be the column spacing to have rigid foundation assumption?

Application Of Sand Drains

Contact Pressure Distribution Beneath Footing

Foundation Settlement due to Adjacent Dewatering

How to Determine A Foundation Whether to be Designed as Flexible or Rigid Body

Concrete Properties

Concrete Roof and Floor Surfaces

What is Cyclopean Concrete? What is Plums?

What is the Significance of Modulus Elasticity of Concrete?

Requirements for Shrinkage and Temperature Reinforcement for Concrete Member

Relation Between Compressive and Tensile Strength of Concrete

Quality of water in concrete Mix

Storage of Cement

ccccc

General Safety Guideline for Operation of Concrete Pump

rajib_ce99@yahoo.com (RAJIB) — Mon, 28 Mar 2016 17:52:00 +0000

Familiarization of pump & booms used in concrete work is very important prior to operation of pump without any supervision. Now what is safe operation of concrete pump?

Safe operation includes:

• Inspection of pump before leaving equipment yard,

• Driving safely to jobsite
• Operation of concrete pump safely after setting up in the jobsite
• Clean up of pump and driving it back safely to yard or drive to other pumping job.

Personal protective equipment:

Before entering jobsite, pump operator should have personal protective equipment stated below:

• Safety helmet

• Comfortable work cloth

• Safety glasses or goggles

• Gloves

• Heavy duty shoes

• Rubber gloves and boots (while cleaning)

• Breathing mask (when there have possibility of exposed to any types of dust).

It is important to ensure availability of all required tools related to pumping. Sometimes personal protective equipment are required like

• Hearing protection

• Steel-toe shoes

• Shirt having long sleeves

Before staring of engine, operator should check

• Engine oil

• Hydraulic oil

• Radiator water

• Yell of engine

All safety covers, grates, gauges, tires, outriggers should be inspected for proper operational safety. Appropriate clean out equipment for particular site should be ensure and pump operator should check adequate safety slings, chains or cables are available for particular system that may drop or fall.

Safety sling should be anchored to boom but not to pipeline. All clamps when required must be pinned including boom. The operator should go through operation manual of manufacture before operating any pumping equipment and if not understand any term or procedure, should contact with manufacturer. Only one selected person can guide pump operate for moving boom and should be predefined. The hand signals (14 safety signal), used in safety regulation should be learnt by all pump operators. The job site should be kept free of alcohol and drug.

Sometimes electrical wires may obstruct free movement of boom and American Concrete Pumping Association recommended to ensure a position of spotter who will be a dedicated person to guide operator to avoid accident. When voltage of electrical wires exceeds 350 kv and electrical wire is within 50 ft of concrete poring area, the spotter is essential.

When voltage is ≤350 kv the distance reduced to 20 ft. The spotter monitors boom movement and warn operator about possible accident. No amendment is valid for this rule form local, state or other requirement of national law.

It is expected to work on clean job area and should be kept clean. Never go into valve or water box; this will prevent serious injury. The water box should be kept covered while machine is in operation (ensure cover of box to remain in place). When the cover has to be removed, transmission should be cut off and accumulator bled should have zero pressure.

A professional concrete pump operator should have following qualification:

• Good driver-knowledge of pump operation

• Mechanically sound

• Good public relation skill

• Good judgment on safe operation of pump.

Why are Index Properties of Soil Required in Addition to Engineering Properties?

rajib_ce99@yahoo.com (RAJIB) — Sun, 06 Mar 2016 13:30:00 +0000

Engineering properties of soil that are frequently used in geotechnical engineering are:

a. Permeability

b. Compressibility

c. Shear strength

Permeability:

This is the property of soil that facilitates water to flow through them. The main importance of this property is to measure seepage discharge (either water or soil particles with it) throughout earth masses.

ConMatic IPC, automated soil consolidation system

Compressibility:

This is the property of soil which defines deformation of soil mass under compressive loads. This property is required to estimate settlement of foundation on soil.

Shear strength:

Shear strength defines capability of soil mass to counteract shear stress. This property helps us to determine following capabilities of soil

• Slope stability

• Bearing capacity

• Pressure on earth retaining structures.

Now what are index properties? –these are properties that are not determined in geotechnical engineering for primary purposes of foundation design and analysis but helps engineers to have idea about engineering properties.

The major index properties for coarse grained soils are

• Particle size

• Relative density

The major index properties for fine grained soil are consistency or atterberg’s limits.

Now we have defined engineering properties and index properties; why should we go for index properties? Engineering properties are the main properties with which (using one or more) we can design a foundation. Say with shear strength we can determine bearing capacity of foundation soil and with compressibility we can determine settlement criteria for loosely compacted cohesionless soil or time consuming consolidation of cohesive soils.

The consolidation tests required several days, again shear strength test required sophisticated instrument for both testing and collecting sample (undisturbed) from field. So engineering properties determination tests are laborious, time consuming and elaborate. Geotechnical engineers are often interested on index properties to gather rough knowledge about engineering properties. The simple tests that are conducted in lab or field (index properties) are called classification tests.

Here soil is indentified based on classification and often index properties offer good prediction of engineering properties. Even methods of testing engineering properties are also selected based on index properties; say draining and confining conditions during shear strength tests.

Soils having identical index properties are often found /assumed to have same engineering properties. But the correlations between two sets of properties are not perfect and reasonable factor safety should be employed if index properties are the basis of design. It is not recommended to design important and large structure only depending on index properties.

Requirements of Sheath for Micropile Encapsulation

rajib_ce99@yahoo.com (RAJIB) — Thu, 03 Mar 2016 12:16:00 +0000

We know sheath is used for encapsulation purposes; the encapsulation is required for aggressive exposure of micropile, especially when subjected to tension loading.

Sheath is essential part of corrosion protection process for unbounded length, later we will discuss about encapsulation of bond length. Sheath may be smooth or corrugated.

Smooth sheath can also be used as bond breaker as discussed in last post. When sleeves are used that may shrink with temperature change or sheaths of corrugated tube are used, separated bond breaker has to be used. We have discussed about requirements of bond breaker in last post.

Sheaths fabricated by following materials were found to have satisfactory performance:

A tube made of hot-melted extruded polyethylene comply ASTM D1248,Type III

A tube made of hot-melted extruded polyethylene comply PP210B55542-II,as per ASTM D4101

A corrugated tube satisfy requirements of encapsulation of bond length

These are the specifications according to which sheathing material is selected. The required properties for sheathing material are as following:

• Should have resistance against chemical attack; the aggressive environment, corrosion inhibition or grout are considered to produce chemical attack.

• Should have resistance against aging from UV-light

• Not harmful to any type of reinforcement

• Should have ability to withstand

 Impact

 Abrasion

 Bending while handling & installation

• Allow reinforcement enclosed by sheathing to elongate under stressing and testing.

Specification for Corrosion Inhibition and Bond Breaker for Micropile Foundation

rajib_ce99@yahoo.com (RAJIB) — Tue, 23 Feb 2016 07:58:00 +0000

We know corrosion is very important factor for subsurface construction and sometimes becomes governing factors in pile construction depending on ground condition. Dear reader we have already discussed about measures to be taken for corrosion protection of micropile.

Corrosion inhibition, if required, the compounds used for this purposes in free length and should be of organic say wax or grease.

The inhibiting compounds should have

Corrosion protection in micropile, Skyline Steel, Nucor Corporation

• Self-healing behavior

• Inhibiting additives

• Appropriate method for displacing polar moisture

• Nonreactive with

Prestressing steel
Anchor grout
Sheathing materials

• Chemically stable

• Can permanently retain its viscosity

When bond breaker is required, smooth plastic pipe or tube should be used for fabrication of it. The expected properties of pipe or tube are as follows:

• Should have resistance against chemical attack; the aggressive environment, corrosion inhibition or grout are considered to produce chemical attack.

• Should have resistance against aging from UV-light

• Not harmful to any type of reinforcement

• Should have ability to withstand

Impact
Abrasion
Bending while handling & installation

Regarding application of bond breaker, we can include, it allows elongation of prestressing steel while testing and also stressing. The tube or pipe discussed above should be made from polyethylene of medium-high density and should conform

• ASTM D1248

• AASHTO M252

Sometimes of polyvinyl chloride (PVC) tubes/pipes are uses which should comply with ASTM D1784, class 13463-B having wall thickness of at least 0.04 in or equivalent materials can be used.

Milling Methods for Concrete Removal to be Repaired

rajib_ce99@yahoo.com (RAJIB) — Mon, 15 Feb 2016 16:11:00 +0000

In concrete repair work usually damaged, deteriorated or defective portion have to be removed and in most cases damaged portions are hardly defined. Most recommendation state that deteriorated or damaged material must be removed completely.

It is very difficult to determine that all such portions are removed or excess amount are removed (i.e. some sound concrete is removed). A recommendation is to continuing removal until aggregate (coarse aggregate) particles are broken down under removal process instead of removal of cement matrix (which is relatively simpler than breaking down of aggregate).

But when low strength concrete is damaged, the aggregate may never fractured under demolition. Here we will learn about milling methods of concrete removal. This method is suitable for removing concrete from both vertical and horizontal surfaces; especially when specific amount from large concrete member.

The depth of removal may range from 3 mm to 100 mm approximately. This method usually produce sound concrete surface free from microcracks.

Usually scarifiers are used in these purposes. It is a cutting tool that uses rotary action with its mass of cutter bits. The rout cutting into concrete surface removes loose fragments of concrete like scaling from blasted surface. Weakened concrete (by any expansive agent) or previously cracked concrete can be successfully removed by this method.

Scarifiers of various sizes are available. Other advantages of this tool are:

Controlled removal of concrete to defined limit.
Simple in operation
Debris produced is relatively small which can be handled easily.
Both sound and deteriorated concrete containing wire mesh and ties (from formwork) can be removed.
Applicable for decks, slabs and for mass concrete.
Broom-mounted cutters can be used to remove concrete from ceiling and walls

Some limitations are as follows:

Concrete with reinforcement cannot removed
Removal rate becomes very low when applied to sound concrete
Noise, dust and vibration are produced
Concrete having microcracks can be damaged.

Effect of Accidental Inclusion of Sugar in Concrete

rajib_ce99@yahoo.com (RAJIB) — Fri, 05 Feb 2016 16:29:00 +0000

We know many impurities in water used in concrete mix produces different affect on concrete properties. Deleterious substances may also be included in concrete through aggregate (both fine and coarse aggregate). Here we will learn about effect of sugar in fresh concrete.

Though the title of this post is accidental application of sugar in concrete but in some important projects sugar is used intentionally for specific purposes. Sugar has retarding influence on concrete. Now consider about accidental inclusion; sugar mainly included due to use of sugar bags to transport aggregates to laboratory or when fresh concrete is transported by molasses bags.

This effect was discovered when investigation was conducted for very low strength of lab sample with proper mix design, careful sampling and curing procedures. The effects depend on quantity of sugar used/included and confusing results were found in previous tests.

It was found that careful application of sugar in small quantity resulted satisfactory retarding effect. The dose and retarding effects are as follows

Dosage: 0.05% of cement (measured by mass)

Retarding effect: about four hours

The probable cause of retardation is preventing action of sugar to form C-S-H. But actual rate of retardation depends on chemical composition of cementitious materials. Like other retarder, for this reason, performance of sugar as retarder should be ensured by different trail mixes (with actual cement that will be used in this job).

Sugar, thus, can be used in many untoward situation like when mixer or in some cases agitators become out of order and concrete cannot be placed due to site condition. The important fact is that it is an inexpensive retarder. Molasses was applied in construction of channel tunnel when residual concrete was required to be retarded due to difficulty in washing out underground.

Channel tunnel was constructed between Folkestone, Kent, England and Coquelles, Pas-de-Calais, France. The tunnel was opened on 6 May 1994. Construction began in 1988 and our reference was in 1990. A dose of (0.2-1) % of cement (by mass) will actually prevent total setting of cement.

Now we have to know about final strength of concrete on this application. When this retarder is applied in controlled manner, obviously, early strength becomes very low but after 7 days, the strength is increased by several percent relative to mix that are not retarded. The probable cause is hydrated cement gel becomes denser due to delayed setting.

Handling Precaution of Concrete Aggregate

rajib_ce99@yahoo.com (RAJIB) — Fri, 05 Feb 2016 04:10:00 +0000

We are very conscious about handling of concrete; in most cases don’t pay head to handling of aggregate. Handling of aggregate is also important to have designed gradation, to avoid foreign materials in aggregate and also to have ease of batching and economy of the same too.

Stockpiling and handling of coarser aggregate can lead to segregation. While tippling and discharging aggregate usually rolls down along slope. The large size aggregates have more weight and smaller size aggregates are relatively lighter. Thus large size particles remain in the bottom, the lighter particles remains at the top.

These results uniform grading at all layer; following size fraction should be spitted

 3/16” to 3/8”

 3/8” to ¾”

 3/4” to 1½” etc.

Splitting means stockpiling and handling separately; can be remixed during feeding into concrete mixer according to desired proportions. Even after this precaution segregation can be occurred but would be in narrow range within each fraction and even careful handling can reduce this segregation.

When aggregate particles to be handled are greater than 1½ in; there have every possibility to breakdown large aggregate particles. The precautions should be taken in this case are:

 Using rock ladders to lower aggregate into bins

 Not to drop from height.

In important and large projects, extra precaution to avoid breakage and segregation of aggregate is taken by providing rescreening just before feeding into bins. Thus excess of undesired undersize particles are eliminated.

Rescreening controls proportions of various sizes of aggregate effectively but with greater control more cost and complexity of batching operation are added.

Again a denser pack of aggregate leaves less space to take place finer cement particles; thus requirement of cement or cementitious materials are reduced and eventually economy is added against more cost of screening.

The uniformity of concrete also produces more workable mix facilitating placing. Again improper handling can cause contamination by deleterious substances and also by aggregate of low strength, less durable and undesired sizes. Sometimes aggregates are transported by contaminated container or sacks like sugar or salt etc. The affect of presence of salt in concrete has already been described in previous posts and in upcoming post we will learn about effect of adding sugar to concrete.

Pumping Difficulty of Light Weight Aggregate Concrete

rajib_ce99@yahoo.com (RAJIB) — Thu, 21 Jan 2016 15:22:00 +0000

Now-a-days pumping concrete to inaccessible distance is very common. Different specifications are established to make concrete workable and successfully used in concrete industry. We will not discuss here about normal-weight aggregate concrete, our concern is here application of light-weight aggregate in pumpable concrete.

The difficulties with using light-weight aggregate in concrete to be pumped are observed when surface of aggregate is not sealed as water demand of the mix increased greatly. When pressure is exerted by pump, the air voids in the aggregate get contracted. Water from the mix enters into the aggregate pores raising water demand.

The mix, in this case, becomes very dry and problem with pumpability arises. We know lightweight aggregate have voids filled with air which render low unit weight to them .

The remedy is to soak both coarse and fine aggregate for a period of two to three days. Alternatively vacuum saturation at dry rapid rate can be applied. The water absorbed in this way do not become a part of free water within the mix but affect in mix proportioning by mass. It was reported that light-weight concrete has successfully pumped vertically up to 1050 ft.

But saturation of aggregate in such way affects durability of concrete in respect of freezing-thawing exposure. The recommendation is this case is to protect concrete from exposure to such temperature. We know several insulation techniques are adopted in cold water concreting.

But when ambient temperature is very low dependence on waiting period is not enough to mitigate such problem. Special agent in addition to application of low absorbent aggregate may provide us a proper remedy for increment of water demand and freezing-thawing problems.

The agents stated above, when added to concrete mix, they enter into the pores around aggregate surface. When initial hydration of cement takes place the PH in the system is increased. With increased PH the viscosity of the agent also increased to form a high-viscous layer which isolates water from aggregate and absorption under pumping pressure is reduced.

How to Determine Water/Cement Ratio of Hardened Concrete?

rajib_ce99@yahoo.com (RAJIB) — Wed, 02 Dec 2015 14:27:00 +0000

We all are usually concerned about water/cement ratio of fresh concrete; here we will learn about water/cement ratio of hardened concrete. It should be kept in mind that we will determine water/cement ratio from hardened concrete sample but at the time of placing concrete mix i.e. fresh concrete.

This ratio is expressed as a function of cement content. We have already discussed about determination of cement content of hardened concrete. So if we can predict cement content with the determination of actual water content, the parameter can be determined.

Now question is how actual water can content in fresh concrete be determined from hardened concrete as majority portion of water is used for hydration (depending on maturity) and evaporation during placing and curing.

The water content during placing is expressed as a function of mass of water combined in the cement grains and volume of estimated capillary pores.

Capillary pores contain remaining water (say hydrated) of actual water content. Capillary water is also called non-evaporable water. This water is considered as 23 percent of mass of cement (obviously anhydrous, L.E. COPELAND and J.C. HAYES, 1983). For Type II cement this water content may even lower than 19 percent.

We can determine original water content in laboratory by igniting concrete sample under 10000C and determining drive out water (BS 1881: Part 124). But this method is not applicable for concrete sample containing blended cements (concrete society Report No.32).

Now consider the accuracy of this test method. Regarding this we can include the water/cement ratio determined may be of 10 % of actual water/cement ratio. There have also other methods like Reflected Light Fluorescence Microscopy.

Economical Strength for Prestressed Concrete

rajib_ce99@yahoo.com (RAJIB) — Sat, 12 Sep 2015 05:38:00 +0000

We know prestressed concrete need relatively high strength concrete. Now our question is-how much strength is economical? Generally it is found to be economical to produce 4 ksi to 5 ksi concrete for prestressed concrete. Though concrete strength should be unique for each job and should be considered individually, the mixes falls within this range are proved economical; i.e. there have some established reasons.

Strength ranging from 4 ksi to 6 ksi can be produced without excessive cement or labor. As an example, we can include that only 15% (Average) more cost is required to achieve a mix of 6 ksi strength relative to production of 3 ksi concrete; notice that at the cost of 15% more cost we can have 100% more strength which is very crucial for prestressed concrete and often of serious requirement in this type of construction.

When strength requirement exceeds 6 ksi, the cost involvement becomes excessive, this type of mix have to be designed carefully and extensive care in control of mixing and subsequent placing and curing are required which are never easy to introduce in field.

For 6 ksi concrete, the plant operations are required where quality of concrete production can be monitored and maintained with great accuracy. 6 ksi to 8 ksi strength are sometimes specified for both precast and prestressed concrete beams. More strength may sometimes be required but not a usual practice.

When strength of more than 5 ksi is the target, the water-cement ratio should not be more than 0.45 (by weight). To have ease of placement, 2 to 4 inch slump should be provided, otherwise specialized vibration, other than ordinary vibration is required.

For a concrete mix of water-cement ratio 0.45, to achieve 76mm slump, about eight bags cement/yd³ of concrete is required. Where utmost care is taken during vibration, half inch or no slump concrete can be designed for only 7 bags cement/yd³ of concrete.

We know excessive cement content in concrete is always associated with increased shrinkage. So a lower cement content is always desirable. In one word, proper vibration is essential and where possible appropriate admixtures should be employed to increase workability of mix.

Elements of Geotechnical Investigation of Shallow and Deep Foundation (IBC)

rajib_ce99@yahoo.com (RAJIB) — Sun, 30 Aug 2015 16:26:00 +0000

Geotechnical investigation is important for construction of building as owner or his authorized agent have to submit this document to building official during submission of approval requirement and for design suitable foundation system.

The geotechnical report should include at least following information:

a. A drawing of site showing location of bore holes for subsurface investigations.

b. An entire record of soil boring, log of penetration test and also soil samples should be provided in report which facilitates foundation engineer to determine variation in bearing capacity and settlement.

c. A complete record of soil profile.

d. In case of water table encountered in project site, the elevation of ground water table should be included. We have published post about determination of ground water level in our previous post.

e. Recommendations regarding

Foundation type
Design criteria which should include at least:

Bearing capacity of compacted or natural soil
Mitigation measures for expansive soils with authentic reference
Mitigation measures for liquefaction where liquefaction susceptibility soil and seismic activity are encountered.
Differential settlement
Variation of soil strength
Any possible influences of loads arrived from surrounding structures.

f. Desired total settlement and differentials settlement

g. Special provision for design and also for construction for foundation supported on soils having expansive nature when required.

h. Installed capacity of deep foundation.

i. Recommended spacing of foundation elements (say piles or piers) measure by center to center distance.

j. Installation procedure of deep foundation element

k. Driving criteria including drilling techniques, drilling fluids, sequences and also special measures for critical conditions

l. Reporting and inspection procedures which facilitates to determine imstalled capacity of foundation elements.

m. Requirements for load test; we will learn the topics as per IBC.

n. Durability aspects of foundation elements considering surrounding environment.

o. Group action of foundation elements; usually reducing while action, if applicable.

p. When shallow foundation is supported on compacted fill, the following specification should include

Site preparation prior test
Material
Test method (MDD, OMC)
Allowable thickness
Test method in filed
Frequency of testing and reference of dry density

q. Specification for controlled low-strength material; the specification required

Site preparation prior test
Material
Test method (MDD, OMC)
Allowable thickness
Test method in filed
Frequency of testing and reference of dry density

Plain Concrete and Masonry Unit Foundation IBC

rajib_ce99@yahoo.com (RAJIB) — Wed, 22 Jul 2015 06:36:00 +0000

Dear reader we have discussed many posts about shallow foundation; here our concern is plain concrete and masonry unit foundation. At first we will start with plain concrete; except light-frame structure, the edge thickness of such foundation supporting walls should not be equal or greater than 203 mm (8 inches) when supported on rock or soil.

When such footing support IBC occupancies group R-3, a reduction in edge thickness of up to 152 mm (6 inches) can be provided. But the footing should not be extended from both sides of supporting wall by a distance more than thickness of footing.

Dear reader we will discuss about plain concrete footing elaborately, here we have just included IBC provision.

Regarding dimension of masonry-unit foundation, we can include, as per IBC, that the mortar used in construction should comply with type M and Type S. Following table provides properties of different mortars according to ASTM C270. ASTM C270 is included here as IBC also referred to this standard.

The depth of footing should be equal or more than 2 times of projection beyond column, wall and pier. The width should be equal or more than 203 mm (8 inches) wider than wall supported by them.

Regarding offset, code recommended to provide a maximum of 38 mm (1.5 inches) for each course in foundation walls (stepped up) from footing. 38 mm is considered for laying single course when double courses are applied 76 mm is recommended.

Foundation Damage due to Fungus Rots

rajib_ce99@yahoo.com (RAJIB) — Fri, 19 Jun 2015 06:21:00 +0000

Dear reader, still there have many foundation constructed of wood. The main draw-back of timber foundations materials is deterioration under many biological and chemical action; sources are obviously from ambient environment.

Dear reader here we will learn about rotting and we have already discussed about insect attack on wood foundation. Dear reader we like to include a great palace that were founded over 13569 piles and these piles were all timber pile. You may be surprised to hear that this palace was built in 1648 and still it is standing quite good condition. Dear reader we are talking about Royal Palace of Amsterdam. So why are we discussing about rotting of timber foundations?

The palace was renovated in 2005 and left opened for visitor in 2009. But the renovation was only removing asbestos. We know health hazard associated with asbestos.

Timber is locally available foundation material in many regions of the world and historically this has been good and reliable material for constructing home and foundation. Still now it is more affordable material than steel or concrete.

As piling material, it is a popular choice but have low load bearing capacity than steel and concrete. Another consideration that should include in designing timber pile is rotting and subsequent insect attack.

Rotting is synonyms to decomposition which defines a process which break down organic substances into new simpler form. Now necessary supply of following elements is required to commence rotting:

a. Water

b. Oxygen

The royal palace of Amsterdam is still surviving today as these numerous piles remain below groundwater table. These piles have sufficient water but lack of dissolved oxygen.

Fungus grow vigorously using nutrient available in wood. But these have also a controlling factor; temperature. The temperature within (0-40)0C is essential for such growth. The wooden foundation elements must have not less than 20% water (in respect of their dry weight) to grow fungus with the wood.

Sometimes a foundation elements that is designed to have below ground water table, may suffer fungus rotting, as ground water is lowered with seasonal or other many man made changes in ambient environment. So if a foundation is suspected to subject water table fluctuation, the wood/timber has to be preserved by pressure treatments. With pile foundation, rafts are also subjected to rotting when water table drops below top of foundation.

We will learn about these preservation method in our upcoming posts

What is the Interference Effect in Closely Spaced Foundation?

rajib_ce99@yahoo.com (RAJIB) — Thu, 11 Jun 2015 16:26:00 +0000

We know raft foundation is adopted when bearing area required to support superstructure loading is equal or close to available floor area. But let’s consider-required bearing area is very close to available floor area and we want to avoid raft; what should be foundation design consideration?

This means there are very small gaps between footings or footings have to be placed in very close spacing. Sometimes footing may even touch each other. Now the question arises about interference effect. We will uncover the answer of the doubt about their structural behavior.

This effect of interaction between footings has been considered in many studies of researchers. They found a parameter that defines whether the interference should be considered seriously or not.

The parameter is angle of shearing resistance. When the value of angle of shearing resistance is low, the interference is too low to be considered negligible. In case of high values, this effect is significant. When a foundation surrounded in both sides by foundation, this effect is very significant.

Another parameter that influences interference effect is length to width ratio of foundation. When the length to width ratio tends to unity, this effect is found reduced.

In analyzing punching shear failure, interference effect needs not to be considered. For these reasons, it is recommended not to consider in design and analysis. However, a design professional should be careful about possibility of existence of them in special circumstances.

Why are Timber Piles Substituted by Concrete Piles?

rajib_ce99@yahoo.com (RAJIB) — Fri, 05 Jun 2015 17:36:00 +0000

Once timber piles were very popular as deep foundation; still they have importance in foundation construction and many building foundations are also supported by this type of deep foundation, especially light buildings. Now concrete pile is more popular and it becomes a versatile deep foundation element.

The main issue is durability and goes against timber pile, but the economy goes in favor of timber pile. Here we will discuss about a comparison between timber and concrete piles to explain why concrete piles are becoming popular day by day. These are:

a. The main problem with timber pile is durability and durability is also related to availability of water. For both concrete and timber, water is the vital issue about durability.

Except water-logged area, the water found around deep foundation is at or below ground water table. Concrete can be made waterproofed, porous, resistant against harmful chemical, in one word, concrete can be modified to have any degree of corrosion/deterioration protection. Thus durability of concrete piles is not a function of ground water table. Whereas the cut-off level of timber pile must be below ground water table.

Where ground water table means level of permanent ground water level as the level may vary due to seasonal change in ambient environment.

b. The concrete piles can be constructed to any size and shape and large size of these piles offer greater bearing capacity which limits number of piles in a pile group.

c. The embedment required for pile group, known as pile cap, becomes smaller in size as less piles requires for each group, which save concrete and reinforcement.

d. Any length of pile can be constructed with concrete. Pile length depends on bearing stratum and available skin friction. Now piles of more than 30 m length are very common.

e. Concrete piles can be applied in marine environment without having any treatment. The mix design is done carefully to have resistance against exposure to water, here also permanent exposure level to sea water is important as above these oxygen is available to emphasize corrosive environment.

f. Another important fact is connection with pile cap. Concrete piles usually cast monolithically with pile cap. The rigidity of connection is dependent on detailing of pile cap. We will learn these in our upcoming posts. Except pile cap, concrete pile can be corrected by grillage foundation.

In case of timber pile, the connection cannot be done perfectly.

Some advantage of timber piles cannot be ignored but considering durability, constructability and imperfection in connection they become less popular than concrete pile.

Requirements for Steel Grillage Foundation (IBC)

rajib_ce99@yahoo.com (RAJIB) — Tue, 02 Jun 2015 15:55:00 +0000

Dear reader in our previous post we have discussed about many types of foundation, but so far grillage foundation has not been discussed. Dear reader we will just discuss here about IBC requirements for steel grillage foundation. At first we like define grillage foundation in few words.

This foundation consists of sleeper with steel framework or some sleepers with some steel beams which will transfer loads to ground from support.

The sleepers should be made of wood, concrete or steel.

Generally they are used to support steel columns having heavy imposed load of superstructure on soil poor bearing capacity. This type of foundation is light and economical too; at the same time they can be placed at shallow depth.

To achieve attachments, grillage foundation should be constructed with sleeper support that transfers load (horizontal component) to sleepers. Sleeper supports are fixed rigidly to foundation beams.

International building code provided some requirements for steel grillage foundation; only steel grillage foundation is included in code, as follows:

-Grillage foundation of the structural steel shapes should be kept separate by using steel spacer approved by building officials.

-The spaces left between shapes as discussed above should be entirely filled with cement grout or concrete

-The encasement of concrete should not be less than 152 mm (6”) at bottom portion and no less than 102 mm (4”) at any points.

Water Proofing of Foundation Wall (IBC)

rajib_ce99@yahoo.com (RAJIB) — Mon, 25 May 2015 18:44:00 +0000

At first we will learn about ground water control according to IBC. Where it is found that ground water table is at equal or more than 152mm below lowest level of floor (bottom level), the floor and foundation wall as well need not to waterproofed i.e. damp proofing is enough according to recommended material and method of IBC.

When not found at desired elevation, proper control system can be adopted to lower ground water level according to following discussion:

Design of ground water control system to lower the water table should be based on standard and approved principles of civil engineering considering at least following:

• Permeability of soil

• Rate of entrance of water to designed drainage system

• Expected and maintained capacity of the pumps

• Head of operation of pumps

• Rated discharge capacity of disposal area In the ground water control system.

Again walls that will be treated or constructed should be of concrete/masonry; should be strong enough to withstand expected hydrostatic pressures, along with other lateral pressures/loads that are active in the walls.

Here hydrostatic pressure is considered as waterproofing term, when hydrostatic pressure condition dominate in the field and design of ground water control not include or not enough to lower expected elevation (as discussed above).

We know due to imperfection of concrete, formwork sealing and improper mixed or proportioned concrete, the surface of concrete member have some defects. We have discussed many posts about such imperfection of concrete work. However, our concern is here surface preparation; we are not discussing much about imperfection.

Before applying water proofing materials on surface of concrete walls, the imperfection like recesses or holes appeared after removal of formwork or any types of cracks (if not structural cracks) should sealed using bituminous materials or other accepted materials or method also can be used in this purposes.

In case of masonry walls, the exterior walls under ground level should be covered with plaster; may be of cement plaster or with other suitable material. The recommended thickness should be equal or more than 9.5 mm (3/8 inch) when mortar of Portland cement is used.

The plaster should used to masonry footing too. Now think about waterproofing, this should be used from top or above of maximum level of ground water table to bottom of wall. The IBC recommended to keep waterproofing more than 12” above of ground water table. The rest portion of wall should be damp proofed according to IBC as discussed in previous post.

Water proofing material (IBC)

Should consists of two ply hot mopped felts, equal or more than 6 mil polyvinyl chloride, polymer modified asphalt of 40 mil, 6 mil thick polyethylene or another approved materials or methods that is capable to bridge non-structural cracks. Sealing and lapping of joints in membrane should be provided according to installation instruction of manufactures.

Geologic and Geotechnical Investigation for Seismic Design of Foundation

rajib_ce99@yahoo.com (RAJIB) — Sun, 17 May 2015 14:11:00 +0000

Dear reader we have already discussed about seismic site classification and seismic design criteria according to international building code. We know seismic design categories are category A,B,C,D,E and F. At first we will learn about investigations required for foundations that support structures assigned to seismic design categories C to F.

The structures that are assigned to the seismic design category C, D, E and F according to section 1613, IBC 2009, geotechnical investigation should include determination of seismic and geologic hazards as follows:

1. Stability of slope of foundation is located in relevant site condition.

2. Liquefaction potential; dear reader we have discussed many posts about liquefaction hazard, analysis of hazard and some mitigation against this natural phenomenon.

3. Differential settlement

4. Displacement in surface due to lateral spreading or faulting.

Relation between faulting and occurrence of earthquake, fault geometry and paleoseismology have already discussed in previous posts.

These requirements are for seismic design category C to F; but when the structure is assigned to the category D to F, that is D, E or F, some additional geotechnical investigations are required; that is for category C only above four investigations are enough. But for category D,E and F more information is required which include

-Lateral earth pressure

-Soil strength reduction

-Recommended mitigation measure

We need to include following additional information to design a foundation supporting structures assigned to these categories:

1. Lateral pressure on retaining wall or foundation walls as a consequence of earthquake motion. There have many record of failure of earth retaining work during excavation and foundation construction work.

2. Liquefaction potential and strength loss of corresponding soils for

–PGA

–Magnitude

–Source characteristics

This parameter must be consistent with design seismic ground motions.

In calculation of peak ground acceleration (PGA), soil amplification factors are derived based on site specific studies. (Reference ASCE7, chap-21).

Alternatively PGA can be taken as S_DS/2.5,

where S_DS=Maximum considered seismic spectral response accelerations (for short period, ref: 1613.5.4 IBC-2009).

3. With assessment of liquefaction potential, consequences of liquefaction and subsequent strength loss should be included. Which includes:

–Differential settlement

–Lateral movement

–Lateral loading on foundation

–Reduction in bearing capacity of foundation soil

–Increased lateral pressure on earth retaining wall

–Floating potential of buried foundation element or structures.

4. At last, how to mitigate the consequences of above phenomenon? This discussion of measure to mitigate should include at least –Ground stabilization –Selection of proper foundation depth and types as well –Selection of proper structural system; the objective is to accommodate expected forces and subsequent displacement –Requirement of combination above measures and appropriate way to account in designing foundation and structures.

Controlled Low-Strength Material to Support Foundation (IBC)

rajib_ce99@yahoo.com (RAJIB) — Fri, 15 May 2015 01:21:00 +0000

Dear reader this is relatively new term in this blog, controlled low-strength material; this are used to establish structural fill/backfill of trench. In United States there have widespread use of it as foundation backfill. The special attention is for backfilling for utility and storm drainage on highway projects.

Dear reader our concern is here foundation backfill, we will have just introductory idea about controlled low-strength material. This will be expressed as CSLM for convenient of discussion.

This is produced by mixing cement, aggregate, fly ash and essentially water. So we can take it as concrete; the difference is very low strength which is at best 1200 psi and mostly less than that value. We know ordinary concrete have strength around 3000 psi.

Due to very low strength, we will not choose it as supporting material for building, bridges etc. rather we will go for backfilling as discussed earlier. The important parameter is it has greater flowability than normal concrete.

International building code provides us some geotechnical investigation required for using this materials as foundation backfilling material. Dear reader, yes, we are talking about shallow foundation and following are the requirements:

Specification to prepare site before placing controlled low strength material should be provided in geotechnical investigation.

Specification for CLSM

Field or laboratory test methods for determining bearing capacity, in other word compressive strength of CLSM

Test methods to approve CLSM in field

Frequency and number of in-situ tests, to determine acceptance according to Item 4 (above).

Structural Phenomena except Cracking in Black Cotton Soil

rajib_ce99@yahoo.com (RAJIB) — Wed, 13 May 2015 14:25:00 +0000

Other structural phenomena associated with black cotton soil except cracking are

•Gilgais

•Slickensides

•Structural sphenoid aggregate

•Self mulching in surface soils.

All of the phenomena stated above are also attributed to shrinkage and swelling of soil under moisture change; but actual mechanism is not understood clearly.

The soil movement under moisture variation is not found in only vertical or horizontal planes. This will produce sphenoid aggregate or wedge-shape aggregate and due to movement past each other, the peds becomes polished resulting slickensides.

The development of gilgais is the most interesting phenomena associated with black cotton soils. Gilgais is topographic phenomena where alternate depression and mounds occur at soil surface. The intermediate areas between them are called a shelf.

Many mechanism and many forms of gilgais were described considering uneven swelling & shrinkage of soil. The forms are

• Round or nomal

• Mehen hole

• Lattice

• Linear

• Tank

• Stony

The gilgais are formed by repeated swelling cycles of black cotton soil followed by subsequent shrinkage when moisture is lost. Soil becomes cracked and the cracks are filled with loose materials. When the soil mass swells under next rewetting cycle, the pressure in soil cannot be relieved by cracking which exerts forces sideway and results mounds.

The depressions hold water and make soil wetter and suffer more swelling and subsequent mounds and obviously more shrinkage under drying.

The cracks allow water to penetrate more deep into the soil mass leading more swelling and subsequent shrinkage. The increasing swelling and shrinkage results repeated depressions and mounds.

Thus regular heterogeneity occurs which made the mounds generally more alkaline than depression (shelf); but very few data is available for both shelf and mounds.

How is Specimen of Collapsible Soil Collected?

rajib_ce99@yahoo.com (RAJIB) — Tue, 12 May 2015 17:15:00 +0000

Dear reader we are discussing here only collapse test. We know it is very difficult to predict behavior of collapsible soil and our attempt is to collect specimen of collapsible soil such that it represent actual situation in the field. In this regard, undisturbed specimen is essentially required.

Dear reader we know collapsible soil may be from natural soil or filled material. If our site is situated on the ground that may have collapsible soil and the soil type is filled (uncontrolled) material; we can prepare specimen by compacted filled material to filed density and filed moisture content as well.

We have already learned about block sample; which is the best method to collect undisturbed specimens. Trimmed block sample can be collected alternatively extruded directly from sampler into confining ring.

Specimen requirement:

Specimen Dia=2.5” (6.4 cm)

Specimen height=1.0” (2.5 cm)

The trimming is done very quickly to minimize possibility of alter moisture content of soil specimen.

The water content, in most case, in collapsible soil is low and to keep in field condition trimming and storing should not be done in high humid environment. Trimming typically done in confining ring having thickness of specimen is equal to height of confining ring.

Fill and Grading of Foundation Site's Requirements in Flood Hazard Areas, IBC

rajib_ce99@yahoo.com (RAJIB) — Sat, 09 May 2015 13:36:00 +0000

All over the world there have many destruction related to natural disaster like flood. With the different flood control measures, we tried to control flood but in many cases we cannot control flood and we have establish areas under flood hazard based on flood hazard map with another supporting data.

The flood hazard map should include at least following-

• Flood boundary map

• Flood way map

• Flood insurance rate map

• Areas of special flood hazard

The federal emergency management agency provides this data and map as well.

In some cases, design flood elevations in flood hazard areas are not mentioned or sometimes floodway also not designated; in such cases building official have authority to ask to submit following data from applicant:

1. From sources like state, federal or other sources, acceptable design flood elevation or floodway data.

2. Submit the same according to accepted hydraulic/hydrologic engineering practices applicable to determine special flood hazard areas and registered professional should be employed in documenting this.

Flood hazard areas, established in these procedures, IBC provided some requirements to approve filling and establishing grading in these area. This code allows grading and filling only when:

a. Fill is provided, compacted and established slope to minimize slumping, shifting and erosion while rise & fall or subside of flood water; when required wave action is also encountered.

b. In floodways, proposed grading and filling, or any of them will not produce in any rise in flood level while design flood is appeared in flood hazard areas.

Now who is authorized to ensure this? As per code the demonstration should be approved by hydraulic and hydrologic analysis executed by registered design engineer/professional following standard and established engineering practice.

c. When structure is located in flood hazard areas and also action of high velocity wave is exist in respective areas, fills will be placed or conducted in such way that water and also waves toward foundation and structures are diverted effectively.

d. Dear reader in last part we have discussed about action to be taken when flood elevation or floodways are not designated. When design flood elevation are know, specified in flood hazard map but flood ways are not defined, the filling or grading can be done only when cumulative result of encroachment of propose flood hazard in combination of encroachment of expected and existing flood hazard area, will not rise design flood elevation by more than 1 foot anywhere around the fill.

Grading Around Building Foundation Site (IBC)

rajib_ce99@yahoo.com (RAJIB) — Wed, 06 May 2015 17:55:00 +0000

Dear reader we know surrounding condition of foundation also influences foundation performance. Dear reader here we will discuss about site grading requirements around foundation according to international building code.

There have specific guideline about slopes immediate adjacent to foundation; the ground should have slope away from foundation equal or more than 1 vertical to 20 horizontal i.e. a slope of five percent for a distance of minimum 10 feet which is measured normal to face of wall.

Now we have to consider about physical obstruction and boundary lines that prohibit measuring 10 feet distance discussed above. An approved method alternative to measuring perpendicular to foundation wall/ wall has to use; IBC suggested us to check 5% slope flowing water directing away from foundation.

In this purpose we can use swales; which should have minimum slope of 2 percent when they are observed within 10 feet of building foundation. When there have impervious surfaces around foundation within 10 ft of building foundation a minimum slope of 2% away from foundation is recommended in IBC.

But considering climatic condition or also of soil too, the ground slope away from foundation is permitted to reduce. The recommended slope is equal or more than 1 vertical to 48 horizontal i.e. 2% slope.

However any procedure used to determine ground level around the building foundation should consider additional settlement encountered for backfill.