What is the difference between setting time of cement and concrete?

In laboratory setting time of cement is determined by standard Vicat apparatus. The initial setting time as well final setting time of cement is a indication of quality of cement. Now we will learn what the both setting times are.

a. Initial setting time:

This is the time when cement starts to stiffen remarkably

b. Final setting time:

This is the time when cement that get hardened to limit that it take some load.
Thus setting time of cement indicates the hydration of cement is in either normal or not satisfactory. In our regular construction process with cement it is desired that initial setting time should not be too small and final setting time should not be too large.

To determine the both setting time both Gillmore needle and Vicat needle arrangement are used. The most common method is Vicat needle test. The specification of setting time of Portland Cement according to ASTM C150 are:

Test Method	Set Type	Time Specification
Vicat	Initial	≥ 45 minutes
	Final	≤ 375 minutes
Gillmore	Initial	≥ 60 minutes
	Final	≤ 600 minutes

Setting time of cement may be affected by:

1. Fineness of cement

2. Water-cement ratio

3. Chemical content(like gypsum)

Now what are the difference between concrete and cement?

There have wide difference between setting time of both. Though cement with some aggregate with presence of water produce a concrete mass, the setting time of cement is not the same that of concrete. In construction industry it is more important to know the setting time of concrete than that of cement. In concrete mix design sometimes some admixture or additives are used which may change widely the setting time of concrete. In ready mix concrete industry it is very common to use retarding admixture to delay the setting time until the concrete is reached to the placement site. The setting time of concrete is dependent on: 

a. Water/cement ratio

b. Temperature condition

c. Type of cement 

d. Admixture

Even curing methods According to ASTM C 403 the setting time of concrete is determined by pentrometer test.

How can Concrete be Made Pumpable?

Are you astonished? Why should concrete be pumped?

Now-a-days ready mix concrete is an essential part of concreting process. This plant or truck mixed concrete is transported to the site to place followed by other operations of concreting. In the project where concrete have to lift long vertical distance, it is the simplest way to pump it. The application suitable pump can lift concrete several hundred feet. To pump concrete mass it is required to make concrete pumpable.

Pumpable concrete has the properties not to be segregated or bleeded with the right selection of constituent materials to bind all material, that consist concrete, under pressure. The requirements of mix are:

1. Under pumping pressure do not get segregated or bleeded.

2. When concrete mix flows through the bends, it should have ability to deform.

3. The concrete mix must assist redial movement of adequate grout to provide and maintain initially provided lubricating film on the pipe line.
 
To reach these properties special cares are taken. These steps are:

a. The size of fines in the proportions should be less than 0.25 mm (approximately less than 300 microns). The fines are cement and other fine particles like sand. 
 

b. In the mix proportions 350-400 kg/cum fine particles are essential.

c. Concrete of slump 75 mm towards collapse range provides pumpability properties in concrete.

d. The pipe line should have diameter of >(3-4)times of the maximum aggregate size.  

What are Steel Formworks? How are They Used for Large Concrete Works?

Concreting works need form works to place concrete in required shape without leaking valuable water and cement to have excellent finishing surface as well as desire strength properties. Steel form works are strong, durable and can be used for several times with advantage of installation and dismantling with in small time. We will not discuss advantages of steel form works. In this post we will try to have overall idea of steel form works. 

These form works are fabricated in panels having thin steel plates which is stiffened by steel angles along all edges or as designed or strength requirement.

Sometimes diagonal flat bar are used to provide additional strength and stiffness. There have some arrangement like clamps, bolts to have make panels to work together. Horizontal or vertical centering of steel or timber facilitates the shuttering to keep in alignment and make the form work serviceable. The panels may of different shape and size. Usually a slab or wall panels are of (60 cmX60cm)-(60cmX120cm).

In case of curved shaped or circular structures like chimneys, columns, tanks etc, steel form work are essential to give the required shapes.

Steel form works are used in large construction works where several reuses of form works are required. In precast concreting process, these forms are used advantageously for repetitive casting operation.

Though they are relatively costly form works i.e. they require higher initial cost, they can be used more than a order of 100 times and economy is achieved for medium to large construction projects.

How can Concrete be Made more Impermeable?

A concrete mass consists of well graded aggregate having compacted well and of which segregation, bleeding and any sources of air voids are avoided successfully, is impermeable. This is more or less known to all engineers. In this post we will discuss about some compounds that render impermeable property to concrete.

These compounds are found as both liquid and powder form. Compounds like talc, chalk, fuller’s earth are used successfully in concrete industry to fill/eliminate the unexpected voids in concrete which makes concrete permeable.Thus concrete becomes water proof.

Some compounds applied in concrete like aluminum sulfate, calcium chlorides, alkaline silicates etc, chemically reacts with concrete and produce a water proof mass of concrete.

Many prepared water proofing compounds are now available in the market. The most common compounds are Impermo, Pudlo, Permo, Sika etc. The application guidelines of water proofing compounds are printed in the package. The manufacturers provide amount of water proofing compounds per bag of cement and application method of them. The amount of water proofing compounds may be vary depending on the exposure condition of concrete. Normally 1 Kg of water proofing agent is added to 1 bag cement to produce a water proof concrete or mortar.

How can Hand Mixing of Concrete be Performed?

It is very interesting to know that a set of bad ingredient cannot produce a good concrete but a set of good ingredient cannot ensure a good concrete if intensive care is not taken. So to produce a good concrete it is required to know the good practice of concreting following the standard rules. Each stage of concreting process is important. Of the various stages of concreting, mixing, particularly hand mixing is discussed here.

To manufacture a concrete of uniform strength and durability properties, it should have uniformity. This uniformity is ensured by proper mixing of concrete. Mixing ensure a concrete mass of uniform color, consistency that produce a homogeneous mass of concrete. Mixing can be performed by two methods:

1. Hand mixing

2. Machine mixing
Impervious brick or concrete floor is required as platform to mix all ingredients of concrete. The platform should be large enough to mix a concrete mix of one bag cement. At first according to the mix ratio the quantity of the coarse aggregate and fine aggregate are calculated. These two types of aggregate are spread in alternate layers. The cement are poured on top of them and in dry condition they are mixed by shovel. The mixture is turned over repeatedly to achieve a mixture of uniform color. When color becomes uniform, the mixer is spread in a thickness of around 200 cm. Now a water can having arrangement of sprinkling like rose-head are used to sprinkling the water. It should be noticed that water should be sprinkled not poured to avoid washout of green cement water. With sprinkling of water the turning over process is continued till a homogeneous and uniform concrete is found. It should be noticed that amount of water is determined from water/cement ratio as defined in mix design. Of this amount of water small amount of water is left not used. The rest water is added at the ending of mixing to just reach the required workability.
The most important things that I have forgotten to discuss is the feasibility of hand mixing. Hand mixing is exercised in small and less important concreting work. This is due to the probability of having inefficient and not uniform mix. A 10% excess cement is used sometimes to avoid inferior concrete that are supposed to produce by this method.

Why should Concrete be Remixed after Discharging from Mixer?

Concrete mixing machines are used for both reinforced concrete and mass concrete with some advantages like efficiency and sometimes economical in case of large volume concreting work. There have various mixers with variable efficiency in the concrete industry. In normal concreting work batch mixer is the right choice for concrete technicians. The batch mixer are of different types like pan type and drum type mixer.

Whatever the mixer, the discharging techniques of mixed concrete are important to avoid segregation. We know concrete is a mixer of cementing material and inert materials like coarse and fine aggregates which is to be bonded by the cementing materials like cement or lime in the presence of water with or without application of concrete admixture to render special properties or to ease placement and transportation work of concrete. Of which coarse aggregates, the heavier components of concrete, are supposed to segregate from the relatively lighter mix of cement and sand. When concrete is discharged from mixer, the heavy coarse aggregate falls first and then the matrix of cement and sand comes out resulting a little segregation. In some non-tilting drum concrete mixer have lever operated chute to facilitate the discharge without segregation.

But whatever precautions are taken, it is noticed that segregation cannot be avoided. So to have workable and efficient concrete mix, a little remixing is required after discharge of concrete from mixer on the platform upon which mixed concrete are accumulated prior transporting to the placement site.

 

How can Bleeding of Concrete be Reduced?

Bleeding is nothing but a segregation of concrete where some quantity of water is reached to surface creating some channels towards surface. Sometimes some amount of cement also comes out to the surface with the water. This phenomenon is observed in badly proportioned and inadequately mixed concrete or a mix having wetness of higher degree. Normally thin structural member like slabs show extensive bleeding. The bleeding channels described above produce a permeable concrete structure.

More or less every engineer is known about bleeding. In this post we discuss how to reduce bleeding. The ways we can reduce bleeding are:

a. Proper proportioning of concrete mix can reduce bleeding.

b. A complete and uniform mixing of concrete also can reduce bleeding.

c. We have already known about the bleeding channel. If we can increase the traveling length of water to be bleeded, the bleeding can be reduced considerably. For this purpose we can use finely divided pozzolanic materials.

d. An introduction of air-entrainment by using air entraining agent can reduce bleeding phenomenon. 

e. The use of finer cement can reduce bleeding.

f. Application of cement of alkali-content can also reduced.

g. By using of a rich mix rather than lean mix can reduce bleeding.

Controlled vibration can reduce bleeding. When bleeding is appeared in the fresh and plastic concrete, revibration of concrete in controlled way can overcome detrimental impact of bleeding. 

How can Maintenance of Concrete Mixing Machine be Done?

Mixing of concrete is very important as a through and proper mixing produce a uniform concrete of homogeneous mass. It is desired to produce a mix of uniform consistency and color to have good workable concrete to facilitate placing and compaction work followed by mixing process. Now-a-days almost all concrete are mixed with concrete mixing machine for either reinforced concrete or mass concrete of large volume. Machine mixing is the most efficient method of mixing and in regard to economy it also provides economy to concrete production when a large scale concrete production is required. The time consumption for mixing concrete is also a fact to be considered.

Many types of mixer are available in concrete industry and their suitability is different depending on purpose to be served. Whatever the type it is very important to keep mixing running throughout the concreting work up to desired construction joint concreting are achieved. Thus nonstop concreting operation is very important in concrete industry. This purpose can only be achieved if concrete mixture is well maintained.

The mixer should be placed at the construction site on a leveled and firm platform. The blades with drum must always be cleaned after concreting operation. The skip must have proper support like sand bag cushion and should operate carefully. In case of not use, it should be noticed that the drum does not catch rain water or other source of water. In this regard; the drum can be kept covered or can be kept tilted position. 

Black Cotton Soils and Their Swelling Pressure

In India black cotton soils are found in the regions of Western Madhya Pradesh, Deccan plateau, Andhra Pradesh, some portion of Gujarat, Uttar Pradesh, Maharashtra and Karnataka covering more than 20% landmass of her. Here the soils that swell are named, as defined above, black cotton soil. Generally montmorillonite, the giant mineral portion of black cotton soils, becomes weathered to form less active particles of clay group like kaolinite and illite. But this process needs heavy weathering from rainfall. This active montmorillonite, when becomes saturated with water from a unsaturated state, it gets swelled and if reverse condition are occurred it gets shrunk. 

Geotechnical engineers are concerned with the magnitude of swelling pressure under desire environmental changes.

Swelling pressure:

Swelling pressure of soil is the maximum stress (Force/Area) that is required to keep the volume, supposed to be subject to swell, unchanged. This is a index that indicates how much trouble will exert an expansive soil. Usually a swelling pressure <20 kpa is not considered to be result much problem to foundation.ffff

The potential of a soil to swell is a function of loading condition and the water content expected to under foundation. The swell pressure and swell potential of black cotton soil can be examined by the ASTM (ASTM D 4546-90)Standard test procedure. This is the test method of cohesive soils for one dimensional or swells potential. If the soil sample are disturbed during sampling, the soil are compacted to achieved field water content and density as well with standard compaction mould like proctor. 

How can Water Table of Foundation Soil be Lowered?

There have many difficulties in foundation construction where water table is above the bottom level of foundation. To provide stability of foundation materials and to avoid difficulties in foundation construction, the only way is to lowering water table. The purpose is achieved by draining water to safe distance into galleries or ditches or pumping out from wells or sumps. This process is called gravity drainage as the gravity generates the force to flow the water to the designed drain.

This flow of water exerts a seepage pressure which forces the grains too with the water to the outlet. If there have silt or fine grained sand, finer constituents, they are washed out from the mix grained soil materials. They may clog drains, can result erosion tunnels or settlement to the drained soil. So this migration should be prevented. This purpose can be accomplished by using a filter that covers the drained materials with coarse materials of granular texture. The filter does not prevent the flow of water but the fine particle gets blocked by the small void of filter. 

For satisfactory result from the filter, particle-size distribution curve of it should be suitably related to the soil materials to be filtered.

To mathematically depict the relation, filter ration R are used as follows:

In addition to 50% and 15% sizes related requirements described by above expressions, the particle size distribution curve of filter material must have a smooth shape without sharp breaks and have to be parallel to the soil that have to be protected.

SI. NO.	Grading of filter material	R50	R50
1	Uniform where Cu ≤ 4	5-10	-----
2	Subrounded particles i.e. Nonuniform	12 -58	12-40
3	Angular Particles i.e. Nonuniform too	9-30	6-18
The particle size distribution curve of filter material must have a smooth shape without sharp breaks and have to be parallel to the soil that have to be protected.

Foundation Settlement Due to Vibration

Generally vibration occurs in foundation when pile driving and blasting operation are done. This may be a part of construction operation of surrounding under construction buildings or for the new structure, that’s soil settlement are considered in design. The both operations are performed as a concept of compacting loose sand and subsidence is expected for new building but not expected for existing neighbor building if any.

As an example in a loose deposit of cohesionless soil 100 piles of 50 ft length were driven for same purpose of compaction. The result were occupied ground area settled 6 in. It was noticed that the settlement gradually decrease apart from pile driving area as an example at 50 ft apart the settlement was recorded only 1/8 in. So foundation engineers should be conscious about pile driving in such loose sand to avoid damage to surrounding structure. Sometimes other construction options are to be chosen leaving such vibration type foundation treatment.

Another source of vibration is arrived from machine foundation. It is very important to design machine foundation to have a period that has safe difference from the period of

adjacent soil to avoid possible resonance. Normally foundation weight is increased to absorb vibrations and distinguish period of both soil and foundation. There have a thumb rule of providing 2.5 times weight to foundation than that of machine to be supported.

Now, which type of soils suffers more due to vibration?
he cohesive soil suffers less impact from vibration. But alarming increment of relative density of cohessoinless soils are observed in this regard. This condition becomes worse to sands under water table or sand that is relatively dry. But sands above water table sometimes show sufficient cohesion not to re-arrange grain structure.

Erection Safety of Pile Rig

We all are concern with piling operation, investigating damaged pile, pile cap design and casting and other operation followed by them. But we are little concern with safety against piling hazard. In this post, we discuss erection of pile rig.

The frames of pile rigs must be checked safe structurally for expected dead, operational load and wind loads. If engineer in charge doubts structural strength, relevant test should be conducted to ensure any failure during operation or idle time. Every pile driving and operational equipments should be inspected and certified as safe. 

In case of large project where two or more rigs are working at a time, a separation of distance more than longest leg of two rigs should be kept. 

Concrete beds, firm timber sills or any other secure foundations should be used as support of pile drivers. Sometimes pile drivers are guyed to withstand storm, wind, earthquake or other lateral impact. Normally three guys are required to have a least resistance to such impact. This safety measures are equally applicable to the rigs that are not even in use.

How can bearing capacity of shallow foundation be determined from permissible settlement?

This post concerned with plate bearing test. At first we have to know what plate bearing test. By this field test ultimate bearing capacity of soil and its settlement under designed load can be determined. In this test a steel plate is loaded at foundation level and settlement respective to load increment are recorded. The loads are gradually increased until the steel plate sinks at rapid rate. The ultimate bearing capacity of soil at foundation level is determined by the load at which plate sinks rapidly divided by area of steel plate. As we know, safe bearing capacity is a fraction of ultimate bearing capacity. This fraction is call factor of safety.

A plot, known as load-settlement curve, on logarithmic scales (log-log plot) are done with load intensity as ordinates and settlement values as recorded in test as abscissa. In the plot two straight lines are found. The yield value or yield point is determined from intersection of two lines. This yield point is important in this discussion.

Now question is how to use this value. We realized, so far, in this discussion that safe bearing capacity is closely related to settlement of footing. The above load settlement curve provides ultimate bearing capacity and hence safe bearing.

The load intensity corresponding to yield point is the ultimate bearing capacity. From which using factor of safety 2-3 the safe bearing capacity is determined. This is safe bearing capacity for settlement.

The actual safe bearing capacity should smaller of following two:

a. Safe bearing capacity from settlement as derived from load-settlement curve.

b. Safe bearing capacity on the basis of shear failure

Piles in Tension in Pile Group

Generally the number of pile is determined by the axial load divided by capacity of each pile considering both end bearing and skin friction. But actual situation is there have always some reactions from lateral forces like earthquake and wind forces to piles as axial force, moment and shear force. The axial force is treated as usual. But the moment makes the differences in design and anchorage properties of both in pile and caps. In case of moment in pile cap, total reaction on each pile can be found by the expression below:

Where, P=sum of reactions that are resulted from axial and moment

∑V= total vertical loads on foundation

n= number of piles in pile group

∑M=this is the sum of moments that have discussed above. The moment is not about center of gravity of cap but about center of gravity of pile group.

d= distance from the respective piles to the center of gravity of pile group.

If the p is positive there is no question of uplift and necessary anchorage. But if p is negative and piles in group are not anchored to pile caps the only a part of piles in pile group are in compression up to neutral axis. As the rest piles are not anchored to pile cap, these piles become ineffective as neither compression nor tension reactions are developed in them. The worse situation is, as some portion of piles in group is ineffective the compression reaction on the active piles is increased.

Thus it can be concluded that if piles in group are capable to withstand tension and sufficient anchorage to cap ia available the loads of each pile is calculated by the expression above.

What is Retempering of Concrete?

In concrete industry retempering is a common and confusing term. Retempering is remixing of concrete mass which is observed undue stiffening and loss of workability due to delay in placing concrete after mixing. Now question is why to delay as we know very tiny setting time of cement. Placing of concrete can be delayed due to concrete delivery from mixing plant to

-construction site of lengthy tunnels

-road construction work where long haul is required.

-manual transpor-tation of concrete in hilly region

This partially set concrete or undue stiffened concrete is sometimes rejected by engineer in charge. But from economical consideration concrete is costly material and from environmental consideration wastage of natural aggregate is occurred. So it is important to justify actually this stiffened concrete is workable and not harm desire strength and durability properties.

As defined above, retempering need some clarification like:

-addition of water

-addition of cement

i.e. sometimes additional water and cement are required to achieve desire property.

But many specifications, provided in the codes all over the world, do not allow retempering. Say I.S. Code did not allow remixing of partially hardened mortar/concrete. It requires renewed mixing with or without use of additional cement, water or aggregate.   

An observation on properties of retempered concrete shows that a very wet mix having delay of one hour gains a strength increment of 2-15% when retempering is applied. But further delay renders a decrease in strength.

Some research shows that retempering with additional water that is required to have desire slump i.e. maintaining water/cement ration as per design may be allowed.

Thus it can be concluded that if initial workability and the workability derived from retempering of concrete with addition of water is same, the strength loss is small. 

Raft Foundation Construction Method

Raft foundation is reinforced concrete Slab which founds the entire supporting member of structure like column, shear wall etc. Foundation construction of this type is required where made up ground, expansive clay soil or marshy site are chosen to found a heavy structure.

Raft foundation slab generally covers entire contact area of structure like a floor and foundation slab projects 30 cm to 45 cm distance from outer wall/basement wall of the structure towards all sides.  But  when  property line merges with basement wall, the projections are sometimes avoided.

If the bearing area exceeds the above defined area, the projection may be changed and depending on the eccentricity due to lateral load moment and unsymmetrical axial loads on column and shear wall the symmetry of projection may be changed. The excavation is done around the area defined above to designed depth and necessary protections are taken to excavation related hazard and to give safety to neighbor buildings.

The excavated area is well consolidated and if required necessary treatment is applied to soil to achieve desired bearing capacity depending on soil investigation data. The consolidated and treated surface is the base upon which raft slab will cast. In case of inverted foundation beams (both main and secondary beams) as discussed in previous post, the beams are cast after the slab with necessary precaution to provide construction joints. Further continuation is commenced after the proper curing of the raft slab and beams.

Pile Cap Analysis and Design Program from S.E Software

Pile Cap Analysis and Design is a design program that facilitates a foundation engineer to design to design and analysis a cap for Pile group. This is a windows-based and interactive design program of which professional version allows one to arrange piles in positions that align piles accurately or nearly close to provide center of resistance to center load in same axis to avoid eccentricity. This facilitates engineers to read the new position of pile coordinates from this program and to supply piles and pile caps layout to the contractor. This facility followed by the designing the cap at the same time. One can delete and/or add and even he can temporarily disable the influence of any pile in a cap. Manual calculation to input coordinates is not required as the arrangement of piles are pre-programmed. Caps for upto 16 piles in group having various sizes, shape and of different materials like steel, concrete or timber of any capacity can be handled and designed. Just provide number of piles and the pile cap edge with piles in standard layout are drawn. The dropdown menus provide facility to change spacing, concrete strength, edge distance, covering, grout strength, reinforcement, column size and many other relevant parameters.

Besides providing number of piles and layout, it can be calculated the number of piles and necessary alignment from provided axial loads. A cap can be designed for calculated reaction or for maximum capacity of pile. There have either option of entering cap thickness and then check it or calculation of required thickness for pre-defined or pre-programmed alignment/arrangement of piles. Once user has created drawing of pile groups and position of columns and cap edge, he can enter the design loads and the cap can be checked for service condition.

What is Piling? What is Point of Refusal?

Piling is portion of system of foundation that is pushed into just under the cap into the earth to provide support to the superstructure above. Piling is used in relatively weak shallow strata of the earth where loads from superstructure are transferred through piles to deeper stronger strata. It is often used as foundation repair solution for existing distressed building where foundation sinking, cracking and warping in different structural member are visible, alarming the dwellers of structural failure. The names that are used regarding piles depending on types and uses of them in Geotechnical engineers are :

a. Segmented piling

b. Push piling

c. Pile blocks

d. Steel piling 

e. Concrete piling

f. Double piling

There have other name like grouted pile and drilled pile and different languages and regions of the world also named piles in hundred ways.

In case of piling in sandy soils, friction developed around surface of the piles developed main capacity to the piles. In case of piling in clay soil, the capacity of piles are expected to develop from both wall friction between soil and pile surface and capacity that developed at the tip of pile (end bearing) in a more stable or competent stratum.

Pile Point of Refusal:

This is a point at which level piling operation can no longer be continued into the earth without lifting or breaking the structure above. A lighter structure, as it has less weight, it reaches point of refusal at a relatively shallow depth. A heavy structure, as it is relatively heavier, it attains its refusal point at relatively deeper point so that it reach hard strata or rocks or it have combined or isolated action of   skin friction enough to support heavier loads. It should be noticed that a point of refusal in wet condition is not the same as it in dry condition.

Expansive Soil Instability of Foundation and Solutions to Avoid Foundation Repair in California

In residential building having relatively lighter structures expansive clay soils cause adverse impact on foundation resulting instability of foundation and foundation repair in this state is very common which involves a lots of money i.e., financial loss to the home owners. So home foundation problem, home foundation settlement or home foundation repair are very common terms in this state to both home owners and foundation repair contractors. Various contractors have made colorful pages in the web seeking quotes and tempting the home owners to inspect their foundations for free.

In the previous posts regarding black cotton soil as well as expansive soils it was discussed many times how expansive soil results failure or settlement to foundations. In this post we discuss possible solution more accurately simple and low cost solution for foundation problems of this type.

Solution for foundation problem:

In many places of the world, the home owners consider soil investigation for their small homes is not important. But the main fact is that expansive soil is harmful to the lighter structures having shallow foundation. The established and skill soil investigation firms should be chosen for this purpose. The soil investigation data assist foundation engineers to predict size and depth of foundation (if possible) avoiding top expansive layer if there any. If foundation have to found on expansive soil i.e., there is no way to avoid it, the investigation report provides information to design the foundation to withstand adverse effect of existing expansive soil. This also helps tp provide future maintenance facility if there have any problem.

For structures that are already affected by expansive soils, some foundation solutions are used to strengthen foundation to support foundation and to restrict further movement. This purpose can be served by various methods of underpinning and reinforcing the foundation walls. Underpinning prevents sliding and vertical movement and the later one are used to withstand lateral pressure.

The structures that exist on expansive soil and not yet suffer any adverse effects of expansive soil, soil maintenance is the cheapest and important solution to keep foundation safe. Soil maintenance includes providing and keeping constant and uniform moisture level in the soil. Maintaining uniform and continuous moisture to the soil prevent shrinkage and swelling of such soil. To avoid differential or localized or isolated saturation of soil proper drainage facilities should provide.

Problem with Pier and Beam Foundation in Texas

Expansive and reactive clay soils generate main foundation problems to lighter residential buildings in all over the world. United States are not an exception in this regard. In Texas, Virginia, California and some portion of Colorado, in United States, this problem is considered the main foundation problem and the home owners kept always busy to find the perfect foundation repair contractor to fix and repair their sweet home.

Texas foundation, foundation settlement

More than 90% of the older homes in Texas were built with pier and beam foundations. Heavy rainfall is very common in Texas especially in northern and eastern portion of Texas State. The excessive rainfall associates the foundation problems in pier and beam houses.

The foundation problems include development of cracks in walls and jamming of doors and windows. More over the older homes have no proper drainage to drain water and results accumulation of water or seepage of water towards vertical and lateral directions. The condition becomes worse where expansive clay soil exist beneath building which is very common in Texas. Expansive soil gets expanded with the presence of water and results the piers to heave. When  the clay soil under a pier gets saturated, this pier sunk as soil lacks its ability to support this pier.

Besides this major foundation problem sometimes termite damage, warped beams, decomposed wood in different structural members also make busy home owners to get repaired their foundations.

Black Cotton Soil

The property of volumetric changes with the change of atmospheric conditions makes black cotton soil dangerous to be founded buildings. It swells excessively when wet and shrinks excessively when dry resulting terrible cracks in soil without any warning. It has a great affinity to water. This tendency of soil is on account of the presence of fine clay particles. Cracks are formed due to movement of the ground on account of alternate swelling and shrinkage. The cracks thus formed are sometimes 15 to 20 cm wide and 2.5 to 4 m deep. The summary for all posts on black cotton soil are listed below:

Foundation design tips on black cotton soil

Foundations on Black Cotton Soil

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Tips for Foundation Engineers to Found on Black Cotton Soil

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Low Cost Foundation Solution for Black Cotton Soil

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Precautions to be Taken for Choosing Shallow Foundation on Black Cotton Soil

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Application of Jute Geotextile to Black Cotton Soil: A Railway Track Subgrade Improvement Technique

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Merits and Demerits of Black cotton soil

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Micropile: The Most Common Foundation Solution in Texas

The most common foundation problem are settlement of foundation and basement leak which is visible and sometimes leads to total foundation damage. The foundation repair is very critical, expensive and time consuming task. Sometimes it is almost impossible to repair a particular foundation. So it is very important to select a right foundation or foundation system.

Pile or pile group is a deep foundation that carry load to firm strata beneath foundation. But when a firm stratum lays at a relatively shallow depth but shallow foundation at this depth is not economical and for foundation repair task like retrofitting and underpinning structure micropile technique are adopted.

Micropile is a reinforced replacement pile that is installed by drilling followed by grouting. Typically micropile is designed to be small diameter having dia of less than 300 mm. It can be designed to act like conventional pile to withstand lateral and axial loading or it can be grouped to have combined soil and pile bearing action to support designed loading.

Micropile can be designed as a group of micropiles that the loads directly or closely spaced grids of micropiles of to reinforce the soil mass internally. In the later case they together with the soil form a reinforced composite that supports entire designed loads. In the first case the reinforcement in pile resist almost entire loads. In this post we discuss the fist methods of micropiling of directly loaded.

These piles can be designed as a substitute of conventional piles of medium to large dia to transfer load to relatively stable or firm strata. The loads that come from either axial or lateral sources are supported geotechnically by grout for each pile and structurally by reinforcement in pile. At least 90 percent projects of foundation construction and foundation repair in Texas involve this type of micropiles.