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The following are collection reviews from the MCS team members for your reference. Shall there be any query in regards to the review(s), kindly contact the team member(s) for clarification.

Piles – Part 3. Vertical (Tension) Bored Pile

posted Sep 15, 2021, 5:28 AM by jeffery jim   [ updated Sep 15, 2021, 6:52 AM ]

Piles (deep foundation) are normally designed to distribute load(s) from superstructure and its burden, stress and loading to ground in order to maintain its state of equilibrium which retains its stability through fixity with minimal or acceptable settlement that may not be detrimental to the structure. In such state of design, piles are designed to be in constant state of compression if there is no consideration on lateral force which may induce moment for rotation and/or shear off pile at the plastic hinge point. That is how piles are typically designed.

2. Nevertheless, in certain cases, piles are not designed to be under constant compression but to perform under tension and it is called tension pile. Such application is unusual and can only be found in special projects and applications. The design is usually related to buoyancy and/or water hydrostatic/pore pressure (may varies depending on ground water table/level) as the main force which causes uplifting apart from extreme moment rotation (from lateral forces too), wind or cyclone event, and seismic activity. In some instances, this can cause by less known natural phenomenon of swelling for certain types of expansive clays or clayey soils. Similarly, certain types of calcareous soil (sandy, although most of the cases would involve downdrag or negative skin friction) that will result the same apart from short piles on certain weathered rock. Therefore, it is important to understand the soil pedology or at least guided by soil taxonomy in order to include a calculated risk involving the site, planning for site investigation, and the structure which will be constructed.

3. In some common practices, certain configurations of piles are required to be functional as assigned, compression and/or tension based on assumed (and/or accidental) load direction as well as the setting with incline angle (raked pile) as a system or part of a system within a group of piles which provides stiffness to the design. The imperative consideration for a tension pile design is to always ensure it is workable in cyclic loads (compression and tension scenarios) which more often create design problem or complication if it is constructed without proper planning or simulation based on fieldtest during the site investigation phase.

4. Tension pile are primarily utilized in marine and oil & gas industry. Vertical tension piles are usually installed at dockyard which remain at rest when flooded with water and perform as demanded when vessel is placed as turned as drydock. Hydrostatic pressure and uplift happen when this infrastructure turns to a drydock without vessels as counterweight and produce compressive downward in putting up with load and propagate it to bearing. Likewise, some other applications would be raking piles as a measure to balance the lateral forces coming from fender piles for a typical harbour or jetty foundation during berthing of large vessels. Raking piles with both compression and tension members are introduced on superstructure which are exposed to slip and slide as well as rotation/bending especially those constructed on undulating surface or steep slope by enforcing stiffness to the ground. The ultimate application for tension pile would be the anchoring or the mooring system for oil rig platform at the ocean depending on the platform type.

5. For tension pile requirements in standard specifications, we shall take into account all relevant British and European standards as reference in the next few paragraphs discussing about design principles and literature. There are three main references which we shall use as guide rules in this discussion as this will guide the design of bored pile which is a replacement pile.
i. BS EN 1997 Part 1, Geotechnical Design (General Rules, Design Assisted by Fieldtesting) for both (1994 and 2004) and Malaysia Annex MS EN 1997:2012
ii. BS EN 1536, Execution of Special Geotechnical Works – Bored Pile (2000 and 2010)
iii. BS 8004, Code of Practice for Foundation (1985 and 2015)

6. Let us review the significant changes made in BS 8004 Code of Practice for Foundation based on two revisions; 1986 and 2015. BS 8004:2015 revision is still in place although BS EN 1997 or Eurocode 7 take precedence in modern design criteria. The profound changes made in BS 8004: 2015 is the integration of BS EN 1997-1 into the latest revision and hence, the former should be read in conjunction with the latter.

6A. Literature BS 8004 (1985 vs. 2015)
There is no detail on bored pile reinforcement except for execution works in BS 8004:1985 while BS 8004:2015 made recommendation to refer to BS EN 1536 as guideline as it provides larger coverage for execution works. Literature on tension pile is also limited as BS 8004:1985 make recommendation to design by considering all possible loadings to the surrounding ground and the reinforcement in the pile should be adequate to carry the tensile stress and considerations for cyclic loads. Additional recommendation made for bored pile where reinforcements should be carried down for the full length of the piles (which is mentioned in BS E 1536:2000 as well) and into the enlarged base if the tensile force is substantial. BS 8004:2015 makes reference to BS EN 1997 Part 1 for information on tensile resistance.

6B. BS EN 1997 Part 1 (1994 & 2004)
BS 8004:2015 improvises the previous revision by stipulating the sole reference for design to be made based on BS EN 1997:1994 Part 1. In this general rule section, the basic consideration of normal pile should be designed and cater tensile force acting on group of pile based on values derived for water pressure (upward and downward forces) and shear resistance at the boundary of the block of soil especially for cyclic condition as discussed earlier. No detailed reinforcement consideration is made, except that it is to be derived from calculation as suggested.

6C. BS EN 1536:2010
BS 8004:2015 redirects designer to BS EN 1536:2010 on materials and products for construction, execution works and tolerances as well as supervision and monitoring works. There are considerable small references made for design considerations with normative references to other parts of the Eurocode mainly BS EN 1991 and other parts which is/are relevant to the structure or application. Reinforcements was discussed but on superficial level with minimum percentage of longitudinal reinforcement area size ratio to nominal bored pile cross section area size, and some bar bending standard requirements on minimum spacing, reinforcement lapping length and maximum nominal size of aggregates for concrete and et cetera.

7. One design criterium which requires extra consideration when performing design analyses on software is the partial safety factors which are different in Eurocode when compared to our local Annex, MS EN 1997 Part 1. The tensile resistance partial safety factor based on BS EN 1997:2000 where γs;t can be as low as 1.40. However, MS EN 1997:2012 strictly enforced the partial safety factor to be 2.20 and as usual, it renders the commitment of the committee to promote higher safety factor just like other geotechnical applications. A short discussion with other professionals indicates a much higher safety of factor since in certain circumstances, pile under tension may permits momentarily robustness into serviceable limit state and fail in a shorter period of time or under low cycles in comparison to compression pile if design is not carefully considered.

8. Literature from specifications do not explicitly mention exact values and parameters as it only covers concepts for considerations. Hence, designers would have to reflect on their own solution which is site-specific. There are numerous studies have been conducted which can be good bases of consideration when planning for a bored pile for tension pile application.

9. Let us consider the design shape and for the ease of understanding, the barrette shapes shall be eliminated from this discussion and focus on bored piles with circular cross-section. Further to that, in order to extend high skin friction, steel casing shall not be included into the permanent design and shall be only use as temporary casing on stratum with loose soil and removed upon casting. The use of chisel is allowed and therefore the base of the shaft will not affect much settlement under cyclic load mainly under compression apart from using flight auger and drilling bucket. Enlarged base bored pile would be great to resist uplift however due to availability of such technology and smaller diameter bored pile (less than 1.5m), this will also be eliminated from the design criteria. These are some of the assumptions we are using when making recommendation.

10. Reinforcement is essential in this case where it supposed to be designed in order to cater the tensile capacity within the bored pile and other component such as the steel plate and components of the substructure member. Apart from increased steel reinforcements in comparison to conventional compression pile, it is crucial to ensure the spacing for reinforcement is design with ample spacing and pitch for both helicoidal, hoops and main reinforcements; unlike its conventional counterpart, the compression vertical pile. It is recommended to have larger bored pile with at least two to three percent for reinforcement/pile area size ratio. If the steel surface ratio is too low and insufficient to resist tensile force, steel tube as permanent casing should be considered when soil friction resistance is fairly high with proper rock socket (if it is not highly weathered rock or else further and comprehensive considerations should be made). High tensile capacity can be achieved if socketing zone and length is embedded on rock with high shear strength. The preferred length of rock socket is quite arbitrary and high safety factor should be made for chalk and marl type of rock.

11. For general consideration and comparison on skin friction value, the β value is important as it guides the theoretical outcome of possible skin friction based on McClelland (1974) formula. When the effective stress and perimeter surface area of the pile remains the same or constant, there will be almost significant change when the β value for compression pile is 0.15 to 0.35, while tension pile is only 0.10 to 0.25. This clearly renders the possible intention on why Malaysia Annex MS EN 1997 prescribes partial safety factor of 2.20 for tension pile when BS EN 1997 allows 1.40 - as a safety precaution to cover designers from erroneous calculation derived from overestimating the actual skin friction.

12. I hope this short note will give you some perspectives on tension vertical bored pile that maybe quite foreign to some of you in construction. Design considerations can be derived from site investigation and test pile. These may guide you in preliminary design and then refined design as the result from a test pile will allow you for some contingencies in capacity and to comply to design philosophy as per BS EN 1990 and BS EN 1997 Part 3 which highlights the concept on design assisted by testing.

Stormwater Drainage: A Runoff Conveyance System Design

posted Sep 10, 2021, 3:50 AM by jeffery jim   [ updated Sep 10, 2021, 4:51 AM ]

Another inquiry was made today in regards to stormwater drainage design and its conveyance system. In the previous short note on drainage, I spoke briefly about stormwater drainage and its function. Let us recap on the previous short note where the drainage system that we usually have are meant to mitigate risk coming from flash flood and hence, design usually considers a period of 180 minutes.

2. To many people, drainage system looks like the easiest part of civil engineering and most of the time this particular branch of engineering is taken for granted. In actual fact, drainage and its conveyance system is not as easy as most think especially when it involves large development or in town planning for a proposed large township. Similar goes to drainage involving agricultural canal and development at elevated or undulating areas. Further explanation of differences shall be based on experience involving in all of these kinds of projects.

3. Unlike structural design which require only a single software for design, drainage design need more than just stormwater design software. The most cumbersome and strenuous part of stormwater design and hydrological engineering is in deriving and generating unique data which changes from one region to another or worst, its temporal and spatial variability within a large site. The design starts based on LiDAR and remote sensing in determining the topographical and geological features based on proformas before placing entry into GIS software for geostatistical analyses in order to see water spatial movement and flow intensity map. Subsequently waterbodies, water shedding areas, aquifers and subsurface water drainage are considered for hydrological cycle. These values are then checked to gauged water level for validation process and tested during hydrological modelling. Once model is tested for its accuracy in hydraulic modelling software, it shall be the base for modelling and simulation as calibrated model. Only with a calibrated model, a proper peak discharge can be considered based on probable maximum precipitation.

4. Probable maximum precipitation may need a lot of statistical analyses by using Gumbel’s Distribution or L-Moment Ratio Diagram in order to generate an accurate rainfall frequency model for ungauged site. Besides this, one can refer to IDF parameters from guideline from nearest weather station when designing for rainstorm from IDF relationship in order to keep life easier unless requested by the client. From these, we can generate both Intensity Depth Frequency or IDF and Depth Duration Frequency (DDF). There are software out there with pre-build database for several weather station however the accuracy of the region precipitation and micro climate may not suit the actual site condition. Therefore, customization is required by overwriting or reprogramming the duration for longer hour precipitation which requires the change of hydrograph block duration. The peak storm should also include the consideration for areal reduction factor for larger catchment area (which is more than 100km2) and climate change factor (based on projected value provided in the guideline or climatology analyses). After all parameters were derived, Q value can be generated based on rainfall duration and Peak Q value can be established for pre-construction. The model is then modified based on post construction surface condition and the introduction of drainage conveyance system in order to generate Peak Q value for post construction. When both values are compared based on maximum of 50 years or 100 years ARI, the value of post construction should be smaller than pre-construction.

5. Else, remodelling is required by making changes in town planning level or by introducing more stormwater structural mitigation facilities or even reroute before reaching the confluence point or the discharge point in order to avoid sudden surge of torrent at estuary or at floodplain which are common areas with dense population. Toward the end of this modelling process, the best outcome from drainage size and length as well as on-site detention facilities will be adopted for drainage design. It is quite tedious as the whole large area is divided to smaller parcels or catchment areas based on specific development condition and criteria.

6. For smaller areas when it is less critical, it is sufficient to use Rational Method instead of SWMM or SCS method which need a lot of consideration involving many parameters and considerations for time of consideration. Peak Q value is generated by multiplying coefficient, intensity and area of development.

7. For agricultural drainage or conveyance canal, the most important criteria are similar to the processes I have mentioned earlier with exception where net water demand and gross demand with certain level efficiency shall be provided depending on the irrigation stage; pre-saturation or normal stage. The only additional structural facility available in this kind of project is the water gate in order to control the water on main season and off-season.

8. There are various types of drain design which can be use depending on the site condition and the required volume of conveyance with at least one foot of freeboard. Nevertheless, the introduction of interceptor drain may need specific consideration if it involves overflowing runoff from adjacent land especially from high hills. It is sufficient to allow for high intensity rainfall based on Rational Method for interceptor drains but it is best to use Hydrograph as this method will include critical parameters especially on overland slope gradient and flow length. Other drain design which require due care and consideration would be the horizontal drain and subsoil drainage. These should allow for subsurface drainage and geological mapping to ensure these types of drain is free from aquifer or is not part of waterbodies which may take time to discharge and desaturate. Instant desaturation can trigger loss of mass and sudden settlement and changes in slope equilibrium.

9. Culvert construction is another design which needs a lot of geotechnical considerations and have to be constructed on stabilized soil and preferably have a very low settlement when tested with plate bearing test. This is essential as small differential settlement can trigger tension crack on subgrade on top of the culvert and destroy the integrity of the subgrade after water infiltration This will cause the road to undergo degradation and leads to rutting or sudden depression on machine direction. It would be best to have the (concrete surround) culvert sitting on treated soil via geotextile. The crux to this practice is to ensure uniformity of level when soil starts to consolidate over time under heavy traffic loading.

10. I hope this short note will give you some insights on stormwater drainage design and the complexity of modelling which involves GIS, geology, geotechnic, geohydrology, hydrology and other soil pedology in deriving an accurate calibrated model. As a comparison, structural engineering is less strenuous with one design software, probably hundreds of hours in drafting and months of headache when integrating MEP into structural drawings. That may not be the case in a turnkey project when all in-house consultants are on BIM (AutoCAD suite) and sharing information across the server.

Site Investigation - Elementary or Supplementary to Pile Design?

posted Sep 8, 2021, 8:09 AM by jeffery jim   [ updated Sep 8, 2021, 8:33 AM ]

In previous short note on pile application and positioning, the main concern about piling and the effect on nearby properties, we have seen literature point to no specific values when it comes to safe distance for piling point from triggering damages to properties. All literature prescribe this to be tackled during site investigation and most of the time, this issue is often overseen or remain negligible to many designers.

2. Many structural engineers and contractors usually oblige with the cost envelope indicated or dictated for a project. In many cases, site investigation is a process which is deemed as supplementary to many as it only provides geologist's recommendation for pile type or furnish engineer with time and depth of possible ground in order to have proper ground treatment work for infrastructures.

3. This is wrong and horrendously despicable as this will lead to negligence and abusing the opportunity provided to have a comprehensive understanding of the site condition. Before a site investigation is conducted, design engineers should conduct site reconnaissance and desktop study in order to determine preliminary considerations before planning of a proper site investigation or exploration. Many engineers will use GIS software typically Google Earth for a mere peep on the site location and some to the extend of reviewing river and elevations. These are not able to substantiate proper planning of the exploration. The basemap for a preliminary stage should be based on digital elevation map which is widely available before making adjustment if the area is known to be involved with new developments nearby. GIS application like ArcGIS will help with some statistical analyses on terrain feature which is far more extensive that what Google Earth could offer.

4. The other relevant maps to be considered at areas which deemed critical would be the geological map and soil map. Soil Map may not be necessary since soil family is relatively similar if it sits on similar elevation or topography unless it sits on certain geological formation and era. Soil use report is another good source of understanding and often being used by many environmental consultants when generating their EIA report. Sadly, these kind of sources are usually obsolete and no longer in place due to socio-economic changes which taken place and certain changes in land husbandry within the region. Provision should be made with contamination that could take place making certain zone into brownfield and not as reported 40 years ago as greenfield.

5. BS 5930 Code of Practice for Site Investigation is a great manual, however this code speaks the fundamental of things and key concepts when talking about planning and execution of proper and comprehensive investigation. The interpretation of report from the work should be done by multidisciplinary engineer (preferably geotechnical engineer and a geologist) when it comes to irregularity of readings, arbitrariness of records; and temporal and spatial variability from soil/rock test and geological mapping. This goes back to geostatistics fundamental of random sampling with high volume of sampling for correlation or krigging, or perhaps purposive method. The research or investigation should be planned based on criteria and sampling method should be accurate. In this case, seasoned engineers and geologists will be useful when using purposive method based on localized experience and knowledge. This eliminate biases from total randomness to proximity with minimal or sparse outliers.

6. Most typical site investigation reports we come across in local projects involves soil/rock properties from field tests and sunken borehole logs (including limited groundwater level monitoring) apart from limited chemical tests. It is quite rare to have a report which includes geological mapping unless slope failure occurred during the construction phase which involves seismic hotspots and fault lines. It is even rare to see the use of various geological instruments to determine site condition such as the use of Electrical Resistivity Tomography to reconfirm readings from boreholes except for certain special projects (landfill and water dam in my previous projects).

7. There are so many test to be conducted and I will not be discussing about these testings as I have discussed about some of it in my past short notes or unless if there are specific follow-up inquiries about these test at site. I have rendered the actual practices of how site investigation have been treated as supplementary record during design instead of taking precedence to the whole design process especially the foundation which is the primary structural member in providing stability.

8. In order for a structure to be designed with sufficient loading capacity and efficient load propagation to bearing, the pile should designed based on the site condition. Boreholes should be located between 10 to 15m for critical water retaining structure and 30m for ordinary structure depending on imposed load category, partial safety factor and reliability differentiation. For infrastructure, boreholes may not be essential (it can be substantiate with Macintosh Probe, Trial Pit, Vane Test, Plate Test, etc.) except for locality with superstructures especially regions with possible geological deposit less than 30m depth and with seismic PGA value of 0.05G (add on microzoning test if lack of data or other geophysics testings).

9. Retrofitting of structure and introduction of new piles may need more reconsideration in planning which is similar to adjacent property damage protection studies. This involves a lot of parameters and conditions throughout different phases which may fluctuate momentarily, temporarily or periodically many parameters involving water and soil.

10. Once more, it is important for all engineers to revisit and reconsider processes in site investigation. This should take precedence above all and as the key reference in practicing value engineering. Incomplete data only points toward a direction where nothing can be validated and to substantiate the design. Worst, GIGOLO - Garbage in, Garbage Out, Laugh Out(loud).

Piles - Part 2. Application and Positioning

posted Sep 7, 2021, 6:29 AM by jeffery jim

Piles as we have learned previously is an engineering application which involves loads and stresses propagation from structure to substructure and subsequently to the ground. Today, an inquiry was made in regards to the safe distance of piling works to the nearest building.

It is a simple question but it is rather complex to be precise and can cause serious engineering, legal and economic implications if it is done the wrong way. As known to many, adjacent properties mainly structures can settle or crack and most of the time vibration is the main culprit. I would like to highlight that vibration is not the main concern as I will discuss in thematic paragraphs.

2. We often get a lot of feedback and concern when piling works is too close to adjacent properties or facilities. Standard specifications did not dictate any distance nor method in facilitate piling works with the site condition and this particular concern. In British standard (BS 8004), this is vaguely mentioned as part of survey and reconnaissance work on adjacent property. The European Standard (BS EN 1997) made reference to execution of geotechnical works on various types of piles (BS EN 12699, 12794 and 14199) prescribe similar considerations as per British Standard. American Concrete Institute (ACI 543) did not mention anything in regards to such requirement at all. In Malaysia context, the two standards which can be used bases for this and the compliance without defaulting Section 14 of Contract Form PWD203/203A. This particular section only highlights that damages to properties and other liabilities are to be handled by contractor and client shall be kept indemnified from all legal action(s) and demand(s) shall there be any damage to property or properties surrounding the site during the construction. Standard Specification for Building Works (SSBW) 2005 highlights the risks and possibilities from piling works and property damages. SSBW 2014 prescribes this issues to be mitigated or explained in method statement as part of the construction management or Project Quality Plan. Nevertheless, SSBW 2014 unnecessarily includes consultant and client into the picture as they are called to approved the method statement.

3. The question remains how far is too far and how close is too close? It is all very much depending on the ability of design engineers to interpret the site condition during the design stage and mobilize the right method to suit the proximity of surrounding structures and cost as well as ground condition. As recommended by earlier literature, all pile design should be robust and perform safely based on geological setting and geotechnical consideration. For developers or turnkey contractor, this can be mitigated by integrating the piling design as part of methodological construction method to resolve problems which may arise from damages succumbed by nearby properties.

4. To many, the simplistic approach for this problem is by introducing micropile or injection method for displacement piles. Injection pile is a great method which can reduce the vibration up to twenty times and can maintain pretty low cost as per conservative pile driving method with exception of space constrain and existing platform condition to operate. Micropile and bored pile on the other hand can be ridiculously expensive and time consuming. Then again, it is subject to financial ability of a client after conducting cost benefit analysis of a particular foundation design.

5.There are many other methods which can be considered however ground condition at the surrounding parallel to the properties should be first considered. One of the most common methods would be from the site investigation borehole log. Nevertheless, the limitation of a borehole log is its accuracy when we making interpolation of strata based on triangulation method as each borehole is only accurate and reliable for 10 meters. This is an issue when it comes to chaotic soil or geological condition.Trial pit methods is limited by the depth of the trench based on the excavator boom reach. The best method would be Electrical resistivity tomography (ERT) by placing a single line parallel to the structure or property intended for protection. This test should be done with additional info in regards to the property's structure and foundation design. With the probe from ERT in placed, the section can reach up to 50 depth and soil condition can be determined.

6. The reason why ERT should be used as part of supplementary test to boreholes is to check the resistivity of material underground. This will give clear indication of the position and depth of materials and saturation level based on correlation. The importance of establishing saturation condition and underground material is to generate possible direction of (vibration) Reyleigh wave, S wave and P wave and annotation it produced in circular or cylindrical condition. The other outcome which ERT provides would be the possible localized water saturation zone and aquifers. From soil taxonomy and pedology, infiltration rate can be projected which is essential when we are using various damping methods. This generates condition or phases which may cause settlement due to water saturation or even loss of mass as an outcome due to soil bulking factor.

7. Geological and geotechnical report from ERT will suggest the best way forward to mitigate issue in regards to property damage. There are standalone methods and some are combination of several methods. In-fill trench is one of the simplest method which works in a way which will halt vibration from Reyleigh wave and weaken P and S wave which travel in cylindrical or circular manner respectively. Nevertheless, the suitability is depending on cost for infill material. Water is the cheapest however may subject to pore pressure, infiltration and retention rate as well as other geotechnical issues on global stability - depending on resting or active phase/condition. If water is used, it is recommended that this only functional if it is more than 8 meter away from piling point and amplitude can be reduced by almost 0.8 by ratio if piling point is 12 to 16 meters away. Subsurface or ground water movement can be hazardous if the soil saturation changes and this lead to disequilibrium and settlement to nearby property especially if sits on shallow foundation. Differential settlement can cause damages to public and private infrastructures.

8. Another method is combination of piling method which employs the use of micropile and injection pile up to two or 3 grid lines at the edge of the project perimeter or boundary which will act as buffer before continuing other grids with hydraulic driven piles. It is similar to infill method with exception that this soldier pile-like application is used to suppress the annotation of vibration waves. It is surprising that smaller pile can triggers extraordinary vibration. Smaller pile is said to contribute to excessive vibration in comparison to its larger size counterpart as the result of resistance at the shaft and/or the shoe or toe. Hence, depth of soldier pile is subject to distance and suppression capacity based on soil condition.

9. One way which contractor or developer can consider as a confirmatory method of piling method selection is the use of geophones and other geo instruments. This test method is viable and recommended during the site investigation stage in order to find the right way forward in preserving and protecting nearby structure. Test has to be done at the earlier stage of the design or else, telltale sign will accommodate you with lawsuits and demands once the surrounding property or properties is/are damaged.

10. There is no straight answer and recommendation made by any standard specification as this question remains quite subjective. This depends highly on the soil condition as redundantly mentioned in all specifications and require geologist, geotechnical engineer and structural engineer considerations.

Piles - Part 1. Introduction

posted Sep 6, 2021, 8:14 AM by jeffery jim

A request came in this afternoon from a friend and also a fellow consulting engineer to discuss about piles and geotechnic application. The inquiry is quite complicated and I will divide this question into parts so that there is continuity in this discussion which involves a very long article and revolves around various literature. Therefore, I will start with introduction to those who are quite new or not so familiar with piles and deep foundation.

2. Pile is generally a design option involving deep foundation and comes in various types, shapes and dimensions. There is no single pile system which is superior than the rest. Like most engineers, one have to consider design requirements as well as financial limits. Engineering is an empirical process which combines functionality, safety and cost efficiency. Without these criteria, any construction will not need engineer as overdesign will always lead to very high safety factor.

3. Foundation is essential as it is meant to transfer loads, bearings and/or stresses from the superstructure to the substructure and subsequently to the ground. For shallow foundation, these burdens are usually transfer directly to the ground surface and the ability or strength of the soil is called soil bearing capacity. This is sufficient when the overall load is low or small or the structure itself is not critical from other stresses. For larger loads (hereafter considered as a combination of building loads, stresses and bearings) may need to be considered for larger building, larger load or functions with higher performance during the construction period due to temporary staging or platform. When loads propagate from the top and require higher bearing capacity, shallow foundation may no longer be be economic or engineeringly sound. This requires a combination of skin friction from the soil and end bearing from hard soil or rock.

4. When deep foundation is the choice for a particular design, the specific type, size and dimension shall be determined. Deep foundation on pile is a slender structure with stilt-like shape penetrate deep into the ground. Due to its shape which is slender, this structural member is considered quite vulnerable if placed under extreme condition and/or under constant duress. Pile will have to react to vertical load most of the time and usually is considered and designed to be able to resist lateral load as well. Lateral load is vital as part of the design criteria as both the building and ground are dynamic in nature. Buildings sway when react to wind load as well as a reaction to its natural frequency. Ground on the other hand is constantly on the move when induced by seismic or earthquake, or even in a continuous progression when sitting on geologically unsteady materials such as colluvium. The other forces which which may not be considered in design would be the accidental load and hydrostatic pressure. This is something designers may consider or written off when considering on the safety factor and/or when deriving partial safety factor for each cases.

5. The pile must have adequate reinforcement bars and desired compressive strength for the concrete. Piles are usually categorized based on its capacity to carry load and classified in three groups based on SIRIM or Malaysia Standard. M Class which complies with MS standard and British/Euro Standard, J Class which complies with the older JKR standard, and the commonly available S class which is usually used for commercial purpose in most residential construction by developers. S class piles have reduced reinforcement percentage which does not mean it is inferior but maybe require additional considerations for certain engineering works. The main concern probably be when this class of pile is exposed to extreme lateral load and in certain soil type which may lead to possible failure when developing plastic hinge at certain length of the driven shaft.

6. As known to many, the vertical or axial load is the main concern when taking up load. The criteria of a pile depends on the type of pile mobilized and type of construction. Generically, pile are considered to have sufficient capacity when it is able to withstand double working (axial/vertical) load and certain degree of lateral force depending on geotechnical or structural application. For certain geotechnical applications; the slip, slide or rotation criterium may need to extend up to 3.0 for factor of safety. Hence, it is open to discussion or consideration depending on literature adopted by the engineer himself. Test shall be conducted to reaffirm the design considerations are appropriate and it is workable until twice the working load. The termination criteria for piles varies depending on the pile used. Driven pile are guided by its set criteria which is derived from Hiley Formula. Bored pile depth dictates by total length of the shaft and surface area which provides sufficient friction surface as load resistance, and the socket length depending on the end bearing and the capacity to clean the end of the shaft after completing boring works.

7. There are several tests to be conducted but it is common to have test piles at area of concern or perhaps more when there is sudden or drastic change to geological or geotechnical consideration apart from statistically representation of (two percent) whole foundation capacity. Static Load Test (STL) and Dynamic Load Test (DLT) are test conducted on the conditioned pile. STL can be in many forms such as Maintained Load Test or Bi-Directional Static Load Test (BDSLT). DLT in the other hand is usually done via Pile Dynamics Analyzer (PDA) for high strain. These tests have their own benefits and DLT is usually a confirmatory test on the load capacity aside from checking pile's structural integrity. When talking about STL, it is preferable to conduct BDSLT where this test usually compliment PDA's integrity test with its earlier checking through sonic logging test. Ultrasonic pulses are introduced and integrity or defects can be determined through time of arrival from pulse generated in sections of piles. BDSLT may cost as much as MLT but it is time saving test and extremely low in risk.

8. MLT will ensure the pile have to ability to settled in certain depth when working loads are introduced. Residual settlement will confirm the pile's ability to be in elastic condition or perhaps requires further probe on elastic shortening shall the residual settlement indicate lack of movement after load is discharged. If test indicates any failure, test pile is usually abandoned and a new pile test location nearby is suggested. If test indicates failure of a pile on a working pile, remedy shall be made by enlargement or increasing in numbers of piles as part of a group pile. Failure in test requires engineer to return to the drawing board and redesign their piles and reconsider other options.

9. When the test pile failed, it can be due to many factors from design, ignorance, site investigation, exploration and test, construction method, other disturbances and/or combination of these factors. The most common problem is due to the inability to derive the soil strata and its capacity. This is the case when no additional or complementary boreholes nearby is allowed for in the construction cost. Soil profile changes every ten feet or three meter, while geological condition can change slightly within this span of distance. Worst, when engineers are not competent to predetermine the inter-bedding of a geological formation especially at vicinity which have chaotic soil dispersion mainly in alluvial region and close to water bodies.

10. The second most common problem is the independence in execution handed to third party laboratory when conducting exploration. This is usually the problem faced when the design engineer have no prior knowledge or failed to conduct desktop study for due diligence purposes when assigning borehole location(s). The chosen location may not be statistically representative and the failure of laboratory to explore deeper. Usually, the termination depth required is after five consecutive flights of N>50 soil or five consecutive successful rock coring. I personally will require at least six consecutive layers of soil N>50 or five consecutive rock coring if the Rock Quality Designation (RQD) may achieve 30% at certain stratum or six layers if none achieved RQD>30%. Recovery ratio is another indicator which I persistently get updated during the exploration process.

11. Pile failure during the driving process may happen when pile was driven into floater or perhaps it is due to QAQC issues where not fully cured concrete pile or broken pile (during pitching) is used. The wrong shoe can also cause issues when driving test pile.

12. One of the important questions is about selection the pile shape and its resistance when exposed to lateral load. Well, there are a lot of literature about this issue but then again, square pile have a multiplier of 1.2 and H piles, 1.5 when compare to a round pile of similar properties. Is this something we may need to consider when selecting a pile type? Yes, if you want to have a rigid design when applying for high ductility structure in seismically active region, square and/or H piles is/are best. Naturally, H piles is the preferred choice for many Japanese engineers when introducing raking piles for their building. In seismic area and/or when colluvium is a concern for smaller building, I recommend the use of round pile as I have discussed with a fellow friend and a doctorate holder. The reason behind the selection of shallow foundation with short round pile and smaller circumference would allow the raft foundation to swift based on the ground movement. It is almost like contiguous pile system where movement is permissible and desired without introducing much lateral stress which may end up with broken pile due to plastic hinge. Similar goes with bridge design, it is very much depending on semi-integral or fully integral bridge design.

13. I hope this short note will give you some insights about piles. In coming days or weeks, I will write more on piles with interesting coverage. You can comment below if you need a specific coverage on certain issue involving piles or deep foundation.

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Unsuitable Material for Earthwork in Road Construction

posted Sep 6, 2021, 8:13 AM by jeffery jim

Understanding unsuitable material is important as it is the prerequisite for works involving soil bearing or strength. I am fond about this issue as one of my friends who stuck in IT department for Pan Borneo project finally got a job as a Pan Borneo project engineer because he answered this accurately during his interview. Hence, it is a very important topic when it comes to road construction.

2. In most constructions, the criteria is rarely obliged or ignorantly overseen and thus, lead to poor subgrade formation in most road projects. Most civil engineers know how to differentiate good soil and unsuitable to a certain degree. Most understood that soil should be free from filth, peat, log, roots and other perishable matters as well as dead logs and stumps which is quite visible to the eye during the formation of subgrade and typically embankments.

3. Those who are in QAQC understand the essential values that soil must have through laboratory testing where soil properties are determined through Sieve Analysis for constituent grading, and Atterberg Limit when it comes to liquid and plasticity limits and index. These two test will highlight the classification of the soil name and type and refined based on the A-line based on Plasticity Chart and Soil Standard Classification.

4. The other test would be the laboratory CBR test for determine soil strength based on penetration value for design purposes of the pavement. Besides that, many have not take prerogative action to further check the volumetric change which not supposed to swell more than three percent.

5. Two other tests which rarely taken place in a lot of road projects are the test to check for organic matter content through loss of weight by ignition as well as the clay content as sieving is only done until wet sieve with aperture size of 63 micron which partially grade silt. Here, assumptions are made for silt and clay which can be very menacing for quality control.

6. Another way to determine unsuitable material before tests are conducted would be the blows required to penetrate one foot of stratum using the Macintosh Probe. A typical unsuitable material will take less than 40 blows for a foot of penetration. For embankment fills, the criteria changed based on height of the proposed fill level and may be a minimum of 150 blows, depending on the geotechnical consulting engineer's instruction.

7. There are more to be specific when it comes to unsuitable material and here is where many have overlooked. Soil should not be mixed or from worn down argillaceous rocks. The strategy here is to understand what is defined as argillaceous or part of argillites or worst, melange where the matrix have no indication of good bonding among constituents.

8. There are some bases which a civil engineer or QAQC engineer can use to determine melange or argillites at site. Melange is visible based on the profile of a section of open cut or a trial pit as shown in the annexed photos. This kind of soil is not suitable for earth filling and should be carted away and disposed unless exemption is given as counterbalance or counterweight or filler for less critical undulating toes.

9. The reason why melange or argillites is not suitable as filling material is due to its behavior which easily dissolved under constant water exposure or saturation. There are Garinono, Ayer and Wario Formation in parts of Sabah, this kind of argillaceous material have given JKR Sabah a lot of problems during and post construction. In some other formations like this Crocker Formation, melange can be spotted in localized clusters. This area have interbedding and intertwining geological features of older Oligocene to early Miocene and Quartenary Alluvium.

10. As a civil engineer, one should be good enough to establish unsuitable material at site and order the removal from site from any use primarily for earth fill. Quantity surveyor should also understand that this material is not suitable and reflect it clearly in the bills of quantities.

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May be an image of outdoors

Bigger Drain - Good Against Flood?

posted Sep 6, 2021, 8:11 AM by jeffery jim

Many simpletons have this idea of mitigating flood but flood was never in the plan when it comes to best management practices or BMP in stormwater management. The key issue and derivation of design is based on practices to avoid flash flood from occurring which may cause property and life loss.

2. In order to understand how drains and other hydraulic structures are designed to accomodate the Stormwater Management Manual or Manual Saliran Mesra Alam or MSMA, one have to understand the main objective of stormwater management itself. The main objective is to mitigate sudden torrential runoff and rise of water level within 3 hours of heavy precipitation and expecting the runoff to recede within 6 hours.

3. The hydrograph concept will guide the water retention and dispersal by comparing flow value during pre-development and post development. The concept is similar to fighting COVID-19 where we try to flatten the curve from sudden surge which will incapacitate the hospital with influx of patients in short span of time when it is possible to stretch it through engineering means by manipulating hydraulic structures or other non-structural approaches. Non-structural approaches usually are in administration and by mean of enforcement, where as structural approaches involve civil engineering via hydraulic manipulation concept.

4. Stormwater management is not similar to flood estimation. These are two different concepts and referred to two different Hydrological Procedures and Manual produced by the Drainage and Irrigation Department. Both will use hydrograph but the storm duration time for observation and modelling is different.

5. Over-engineered structural methods is costly and may not be economical apart from taking too much space and be hindrance to local development. This approach may solve issues when it comes to abnormal rainfall intensity which sees triple or quadruple in volume. With BMP, the mitigation will be balanced in sense of economics as well as risk and vulnerability.
6. Although MSMA is a manual which provides suggestions to remedy issues related to flash flood, more solutions can be developed from creativity of the hydraulic engineer.

7. I was challenged to provide hydraulic retention for a high rise condominium in a small plot of land. The manual only speaks about concept and somehow, I came up with the best solution for both developer and DID Sabah. Instead of building weir and swale and typical pipes and culverts as a mean to retain water during storm event, I did modified my basement parking as water storage area without endangering residents and their vehicles. Although the typical intensity of a 50 Years ARI would be around 124mm at Kota Kinabalu, my design have no problem catering up to 250mm of rain.

8. In order to move forward, proponents of stormwater management should be more creative and learn the fundamental ideas before even trying to use all means and procedures highlighted by the DID. This is the only way forward. As for the countrymen who are generally simpletons, I hope such explanation will educate them on why certain designs are not up to the standard as they initially thought. It is hard to fight flood but we are ready to tackle flash flood.

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Road Construction: Why road get damaged?

posted Sep 6, 2021, 8:10 AM by jeffery jim

My dad forwarded photos, a video and comments in our family group about a road which is badly damaged. Just like everyone else, there is certainly a genuine concern about safety as road users. Although my dad is not a civil engineer, he have some good ideas and reasoning which may deem valid to justify possible causes that triggers defects if not aggravating the road in a long run.

2. Construction of road is relatively easy by principle and concept where the thickness of each material can be calculated easily based on the CBR value for subgrade which essentially be the value for load bearing capacity. Another parameter which is vital would be the traffic volume in order to ensure the road would last as planned.

3. Throughout the road alignment, site investigations are conducted with miscellaneous type of test in order to ensure the existing bearing capacity is sufficient or else, treatments shall be provided through stabilization, replacement or reinforcement. Apart from bearing capacity, the soil material is scrutinized to ensure that material is suitable and not of argillaceous in nature which can be broken down easily due to its weak matrix condition. Similar goes with unsuitable material which fits other definitions. These are predetermined throughout the process in periodical stages where soil properties are determined every 1,500 m3 of soil extracted from borrow pit.

4. After subgrade is treated and compacted, it requires one validation check. Earlier all QA and QC test have taken place by conducting Field Density Test when compacting a flight of 300mm for every 500m2 minimum as well as monitoring the movement via deep settlement gauge. Before confirmatory instruction is provided to proceed with subsequent layers, subgrade level shall be first tested for its in-situ CBR value, and then surveyed and dipping are conducted. Once this is done, proof rolling test (of 50 tonne load) by utilizing a 70 tonne tonne truck with load shall make it way in five to six different paths in traffic direction in order to check if there is rutting or settlement to the existing subgrade. After passing this test, only subbase can be placed to required thickness in specified flight thickness.

5. In many cases, most road constructions skipped this proof rolling test. It is a test that requires specific truck with such capacity or a retrofitted truck that can achieve the specification. Without conducting this kind of test, the subgrade bearing capacity is in doubt even though in-situ CBR indicate otherwise.

6. There are more than just a single test to determine the durability and robustness of a constructed road. The said proof rolling test is the best foolproof test which can be deployed as final confirmatory test as part of QAQC but not the overall engineering works.

7. Engineering works may lead to many other issues when designers are not competent. Yes, most designers maybe professional engineers themselves but not many are learned geologist and geotechnical engineers. This is the main issue for substandard road design in our country. The inability to have proper design which lead to ineffective construction method and under/over costing of road construction.

8. Road construction is actually a very complex process where it requires and goes beyond engineers of all disciplines. They need to be a team of inter-discipline and learned professionals. The failure to integrate hydraulic and hydrology as well as environmental scientist will result in catastrophic water issues throughout the project duration. This have been the issue that cause many inconvenience to dwellers surrounding the project site.

9. Water is known as the main problem that can cause aggravation during construction for ongoing materials and work-in-progress if not planned according or protected thoroughly. Temporary water diversion and dewatering also caused environmental degradation although it maybe temporary or momentary. Coupled with lack of due diligence conducted prior to construction, issues will continue as hindrances or worst, hazards to third parties especially road users.

10. This is a short note about basic shortcomings during road construction. There are more but it would take many chapters to cover.

May be an image of one or more people, people standing and road

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May be an image of one or more people, people standing and outdoors

Is it debris flow?

posted Sep 6, 2021, 8:07 AM by jeffery jim

A friend of mine showed me an article by Prof Emeritus Dr. Ibrahim Komoo in one English newspaper and I found the original article as attached below. In the English article, it was mentioned that the event at Mount Jerai is considered as debris flow where as in the Malay article, it was not mentioned as so.

Earlier, I told my friend that I am not in agreement with Prof Emeritus with the terminology of debris flow to describe that catastrophe. The issue here is the technicality behind the rheology and mechanics which differentiate debris flow and other terminologies. What happened at Mount Jerai is actually debris flood.

Prof Emeritus explained things in the simplest form and the mechanics and science behind the calamity where as my post is a summary of chain of events. So let me sum up in point form for ease of understanding.

1. Sulfuric acid used in mining and rock extraction may seep into the ground. Acid rock which forms most of the granite and quartz at Mount Jerai and also may be the cause to acid drain/rock drainage. Another possibility of chemical contamination is probably due to enzymes used for road and embankment stabilization.

2. This may cause depletion of aluminum ion within the soil since Ferrasols soil have good water dispersion. With depletion of aluminum ion, the cohesion binding began to reduce and subsequently may lead to instability and no longer in equilibrium state. For Ferrasols, the highly clay soil depends highly on cohesion value instead of friction angle in order to be stable against induced external forces such as hydraulics and etc. At this stage, disposition of soils in a further distance than usual is called debris flow with some water content and usually depending on the topography, mainly gully or rill for its direction. At certain steep slope, the sudden move or drop like rock fall is known as debris avalanche.

3. The erosivity of rainfall is as important as other external forces and play an important role in metamorphism. This also depends on soil's aggregate stability in order to deter flaking or breaking down due to rain drop splash. Soil erodibility is another parameter which need to be considered as it has different kind of variability in regions since highly dependent on the organic content and soil rheology to determine its classification based on HSG.

4. The final sedimentation yield based on USLE depends on runoff volume and peak discharge apart from regional topography such as slope length and so on. Imagine 283mm precipitation and runoff Qpeak and volume.

5. Clay is different than silt and sand where it requires proper wet basin and proper settlement distance in a basin. Not known to many, the occurrence of free clay in runoff and in contact with Mount Jerai lime outcrop lead to another significant issues, which is flocculation. This binds clay and settled similar to sediments.

6. Flocculated clay, when mixed with alluvial sand at water bodies will actually clog waterways and will lead to the building up of natural dammed lake. Antecedent rain of more than 20mm in a cyclic of wetting and drying manner for many days will lead to changes of pore pressure and variance of ground water in certain rocks. Changes of cross section profile also generate different level of energy or power throughout the river. This will aggravate the situation and may also increase the accumulation of more debris and increase the capacity of the dammed lake.

7. Continuous antecedent rains have increased the water volume and overtime, the dammed lake is breached and the water gushes down together with most of the larger debris during the initial sequence of the event. The immense power of the water will start to disperse and come to everyone's surprise as torrent of deadly flood. The tremendous amount of water and rapid velocity is called debris flood.

I hope this will explain the reason why I posted earlier on the possible issues from pedology perspective. I am more interested with main issue and probes like many forensic engineer rather than to identify the transportation mechanism.
Apart from that, this also verify and justify why I am not in agreement with writer(s) who transcribed Prof Emeritus' use of debris flow as terminology to explain the disaster. It supposed to be debris flood by definition.

May be an image of text that says "abtu, Rencana Aliran puing bagai 'tsunami' di daratan, hadir tanpa amaran Emeritus irkal airter Pengunjung perlu dinasihati supaya menjauhi alur sungai apabila hujan lebat berlaku kawasan pergunungan tanah diangkut ngdiT risiko jadian Hayun, Yan memberi mengurangkan asa-hadapan. epada berkaasa langkah aperk dinmhi maca)"

Kampung Kopungit Landslide: A Simple Desktop Study

posted Sep 6, 2021, 8:05 AM by jeffery jim

It is a mellow and rainy afternoon. It is pretty much a good time to have a good read but then, I came across an update about landslide at Kampung Kopungit, Kota Kinabalu, Sabah. I did a study similar geotechnical reconnaissance work previously but it is on a large structure belong to Telekom Malaysia.

2. Kopungit hill is a known to many Kota Kinabalu residents as an exciting hill which provide easy tracking where the trail is rather friendly and also challenging. Geologically, this hill a mix of a few types of topography - swamp at the foot of the hill and surrounded by moderate and high hills with slope of more than 25 degree. This village is home to many villagers in a highly concentrated and dense population where houses are build too close to each other regardless of the terrain.

3. The landslide triggered in between two types of soil association which is the Lokan Soil and Dalit Soil at a higher elevation. The main soil unit for both soils is the Acrisols with dispersion of Cambisols at the ridge where water tanks are sitting. The main concern of Acrisols type of soil is its nature which is usually porous by nature until it is stripped down and form hard surface crust. This clayey type of soil forms impermeable surface which allows water runoff on the surface. Nevertheless, consistent rain and the formation of rills on the slope disposition the soil from the top to the lower section part of the slope.

4. Water runoff plays important role in devastating event such as landslide when soil constituents start to form additional overburden on slope areas which have been in equilibrium due to the cohesiveness of the clay and certainly some angle of friction resistance derived from larger and coarser aggregates with alluvial related origin. This disposition leads to disequilibrium and certainly periodic water saturation at lower elevation does not help; instead, adding pore pressure at the whole equation of the geotechnical calculation. Hence, the slope is no longer stable and triggers landslide as a mechanism to shed the overburden until a shallower stratum can remain in equilibrium. Sliding occurred and soil moves; and dwellers and properties will experience the wrath of mother nature.

5. A short desktop investigation shows that this event is not an event which occurred suddenly and compulsively. Landslide is the outcome of progressive loss of bonding in soil matrix. For the past two years, satellite images shows that there are progressing soil erosion surrounding the affected area as per attached photos. There are also clear indicators where temporary remedial works were on place where tarpaulin is used to cover the slope before permanent slope stability restoration works can progress.

6. Tarpaulin is a great remedial but it is momentary and should not be placed on the slope surface without further engineering considerations. In many cases, half covered slope is worse than status quo as water saturation at the toe of the slope will weaken the overall slope stability and introduce the trigger point. This can be avoided if proper drainage and water diversion as well as tension cracks at the ridge is remedied. The tension crack might not be visible in this particular case but it is developed in between weakened soil and stable soil which sits directly under the water tank structure with pile foundation.

7. These geotechnical issues aggravated by site condition where most slopes have close to 90 percent gradient which is almost 1:1 in ratio for horizontal and vertical. The soil erosion possibility increases by hundreds of folds from a flat soil to undulating hill and grievously hazardous at this kind of steep and high slope.

8. The other condition which many may not be clear here during design consideration or site valuation is the overburden introduced by vehicles and residential at these slope. Apart from overburden, what is significant and consequential condition would be the pore pressure buildup at certain areas which is an impermeable layers under the houses and road. Water infiltration rate which is not uniform and therefore leads to difference which is not considered when modelling the geotechnical condition based on drained and/or undrained conditions of a triaxial shear test.

9. One of the method which is not introduced here is the utilization of gabions as counterweights at the toe slope with proper interceptor and horizontal drains as a temporary measure before the construction of proper retaining wall.

10. The use of rubble wall as permanent solution is not advisable since TM building which is nearby gone through such slope failure from the use such engineering feature. Unknown or undetermined finite element modelling may not able to consider all complex stress conditions of this particular slope and hence, design criteria involving overturning and sliding should be increased to 10.0 for factor of safety.

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