321.2 Geotechnical Guidelines - Revision history

Hoskir: updated per RR4256

2026-10-26T16:04:51Z

updated per RR4256

Hoskir: /* 321.2.4.2 Walls */ updated per RR4244

2026-10-26T15:16:12Z

321.2.4.2 Walls: updated per RR4244

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	:c. Need Qu's for design of the rock socket.		:c. Need Qu's for design of the rock socket.

	===321.2.4.2 Walls===		===321.2.4.2 Walls===

	1. MSE (Mechanically Stabilized Earth)		1. MSE (Mechanically Stabilized Earth)
			: a. Sample about every 200' with shelby tubes. Two sample holes per wall minimum. Try to sample where the wall is the highest.
	:a. Sample about every 200' with shelby tubes. Two sample holes per wall minimum. Try to sample where the wall is the highest.		: b. Take undisturbed soil samples to at least 10 ft. below footing elevation for Qu, Direct Shear, and Atterberg limits. Need to find internal angle of friction for retained and foundation material. If retained material is fill, get internal angle of friction from soil survey. If sand is encountered, take samples for gradations and atterberg limits as appropriate (seismic).
			: c. If soil is too rocky to use shelby tube, penetrate every 2 1/2' at least 10 feet below footing elevation. Take Atterberg samples, moisture samples, and pocket penetrometer readings.
	:b. Take undisturbed soil samples to at least 10 ft. below footing elevation for Qu, Direct Shear, and Atterberg limits. Need to find internal angle of friction for retained and foundation material. If retained material is fill, get internal angle of friction from soil survey. If sand is encountered, take samples for gradations and atterberg limits as appropriate (seismic).		: d. If foundation material is too soft to use shelby tubes or osterberg sampler, run S.P.T. at 2.5 ft. intervals for at least 10 ft. below footing elevation. If still soft, go to 5 ft. increment. May use cantilever wall on piling. Rock bit or core at least 5 ft. of good rock or shale.
			: e. If rock is encountered above footing elevation or before you sample 10' below bottom of wall, core a minimum of 5 ft. below bottom of wall for MSE wall and 10' minimum below bottom of wall for cantilever wall.
	:c. If soil is too rocky to use shelby tube, penetrate every 2 1/2' at least 10 feet below footing elevation. Take Atterberg samples, moisture samples, and pocket penetrometer readings.		: f. Auger holes are usually laid out at about every 25'. If you are in uniform soil and rock is more than 5 ft. below the footing elevation, you can skip every other hole. Auger about 10' below bottom of wall or a little deeper if you suspect rock is close.
			: g. Settlement Limits
	:d. If foundation material is too soft to use shelby tubes or osterberg sampler, run S.P.T. at 2.5 ft. intervals for at least 10 ft. below footing elevation. If still soft, go to 5 ft. increment. May use cantilever wall on piling. Rock bit or core at least 5 ft. of good rock or shale.		:: For Settlement analysis, see [[321.1_Design_of_Earth_Slopes#321.1.3_Serviceability\|EPG 321.1.3 Serviceability]], LRFD BDS 11.10.4.1 and FHWA-HIF-24-002 FHWA EC 011; section 4.4.7 and section 2.4.3 table 3.
			:: Total Settlement - If the wall contains or supports a structure such as a bridge abutment, then limit the total settlement to 1-inch. If the wall DOES NOT contain or support a structure (e.g., wall supporting a roadway), then 2 inches of total settlement is allowed.
	:e. If rock is encountered above footing elevation or before you sample 10' below bottom of wall, core a minimum of 5 ft. below bottom of wall for MSE wall and 10' minimum below bottom of wall for cantilever wall.		:: If total settlement is greater than the maximum limit, recommendations for ground improvements shall be provided.
			:: Differential settlement along the face of the wall shall be evaluated in accordance with LRFD BDS 11.10.4.1. Slip joints in the MSE wall structure may be used to address isolated differential settlement issues. When widespread differential settlements is anticipated, provide ground improvement techniques and other recommendations.
	:f. Auger holes are usually laid out about every 25'. If you are in uniform soil and rock is more than 5 ft. below the footing elevation, you can skip every other hole. Auger about 10' below bottom of wall or a little deeper if you suspect rock is close.		:: Differential settlement along the length of the wall and from front to back of the wall shall be evaluated. If required, the limits of settlement remediation should be provided (ie how many feet in front of the wall and within the final designed reinforcement strap length or other length in the reinforcement zone).

	2. Cantilever Walls or Spread Footings		2. Cantilever Walls or Spread Footings
			: a. Do similar to MSE wall except if rock is near footing elevation and wall may be set on rock, take 10 ft. of core (depending on wall height, 5' of good rock may be adequate) and if shale, run Qu's.
	:a. Do similar to MSE wall except if rock is near footing elevation and wall may be set on rock, take 10 ft. of core (depending on wall height, 5' of good rock may be adequate) and if shale, run Qu's.

	3. Sound Walls		3. Sound Walls
			: a. Use S.P.T. and 3" shelby tubes to sample a hole about every 200 ft. of wall length.
	:a. Use S.P.T. and 3" shelby tubes to sample a hole about every 200 ft. of wall length.		: b. Push 3" shelby tube 2.5 feet followed by the split spoon sampler.
			: c. Run S.P.T. and shelby tube on the first 5 ft. interval below bottom of wall. Take Qus (for determination of nominal bearing resistance and resistance factor), Atterberg samples, moisture samples, pocket penetrometer readings and torvane readings.
	:b. Push 3" shelby tube 2.5 feet followed by the split spoon sampler.		: d. Continue to run S.P.T. at 2.5 intervals for at least 20 ft. below bottom of wall. Take Atterberg samples, moisture samples, and pocket penetrometer readings.
			: e. Amount of Rock Core.
	:c. Run S.P.T. and shelby tube on the first 5 ft. interval below bottom of wall. Take Qus (for determination of ~~allowable~~ bearing), Atterberg samples, moisture samples, pocket penetrometer readings and torvane readings.		:: i. If rock is encountered within 5 to 10' below bottom of wall, core 5'.
			:: ii. If rock is less than 5' from bottom of wall, core 10'.
	:d. Continue to run S.P.T. at 2.5 intervals for at least 20 ft. below bottom of wall. Take Atterberg samples, moisture samples, and pocket penetrometer readings.		: f. Augering
			:: i. Locations same as MSE walls.
	:e. Amount of Rock Core.		:: ii. Auger 25' below bottom of wall.

	::i. If rock is encountered within 5 to 10' below bottom of wall, core 5'.

	::ii. If rock is less than 5' from bottom of wall, core 10'.

	:f. Augering

	::i. Locations same as MSE walls.

	::ii. Auger 25' below bottom of wall.

	===321.2.4.3 Box Culverts===		===321.2.4.3 Box Culverts===

Hoskir: /* 321.2.3.5 Practical Considerations */ updated per RR4244

2026-10-26T15:14:24Z

321.2.3.5 Practical Considerations: updated per RR4244

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	'''2. Construction Problems.''' In most cases, investigative techniques are clear cut and the scope of the investigation may be less detailed when only one type of foundation is feasible. However, the scope of investigation should be influenced by considerations of the possible consequences of a change in foundation type during construction. If spread footings on rock are anticipated but no rock is found at one column, then a pile driver must be brought in. If there is no bid item for that type of work, then the price must be negotiated. The contractor will likely ask for an additional working day and claim severe impact costs, etc. For these reasons, more thorough work (at least in numbers of borings) are needed where spread footings are anticipated than for most other foundation types. Of course, being shallow, the borings should be completed more quickly. The reverse circumstance is less critical. If piles are planned and a suitable bearing stratum for footings is found on one bent, it is a simple matter to form and pour the footing while under running the piles at that location. This also has implications with respect to the scope of the foundation investigation. There is often little risk in omitting holes when piles are the logical foundation type and subsurface conditions appear uniform.		'''2. Construction Problems.''' In most cases, investigative techniques are clear cut and the scope of the investigation may be less detailed when only one type of foundation is feasible. However, the scope of investigation should be influenced by considerations of the possible consequences of a change in foundation type during construction. If spread footings on rock are anticipated but no rock is found at one column, then a pile driver must be brought in. If there is no bid item for that type of work, then the price must be negotiated. The contractor will likely ask for an additional working day and claim severe impact costs, etc. For these reasons, more thorough work (at least in numbers of borings) are needed where spread footings are anticipated than for most other foundation types. Of course, being shallow, the borings should be completed more quickly. The reverse circumstance is less critical. If piles are planned and a suitable bearing stratum for footings is found on one bent, it is a simple matter to form and pour the footing while under running the piles at that location. This also has implications with respect to the scope of the foundation investigation. There is often little risk in omitting holes when piles are the logical foundation type and subsurface conditions appear uniform.

	'''3. Footings on Hard Rock.''' For most simple structures, spread footings on hard rock will be of some practical minimum size so that unit loads will usually be 10 tsf or less and almost never in excess of 20 tsf. This is one reason why strength tests on hard rock are usually rather pointless and judgments on hard rock ~~allowable~~ bearing ~~capacities~~ are subjective, sometimes involving building code tables, RQD, and other empirical means. Keep in mind that the discontinuities of rock (bedding planes, joints, etc.) and, in particular, any loss while coring represent the real bearing limitations of that rock. You must rely on the driller's judgment as to why you didn't recover core. If the drill stem dropped quickly with little or no resistance, you have a void, a clay seam, or other soft material.		'''3. Footings on Hard Rock.''' For most simple structures, spread footings on hard rock will be of some practical minimum size so that unit loads will usually be 10 tsf or less and almost never in excess of 20 tsf. This is one reason why strength tests on hard rock are usually rather pointless and judgments on hard rock nominal bearing resistances are subjective, sometimes involving building code tables, RQD, and other empirical means. Keep in mind that the discontinuities of rock (bedding planes, joints, etc.) and, in particular, any loss while coring represent the real bearing limitations of that rock. You must rely on the driller's judgment as to why you didn't recover core. If the drill stem dropped quickly with little or no resistance, you have a void, a clay seam, or other soft material. Footings on soft rocks such as clay shales, claystones and even some sandstones and siltstones are another matter. Here the normal bearing resistances may be within a much lower range, requiring substantial enlargement of footings. In such cases, fairly detailed test data (SPT, Qu, and even pocket penetrometer data) may be needed to make judgments about allowable footing loads.
	Footings on soft rocks such as clay shales, claystones and even some sandstones and siltstones are another matter. Here the normal ~~allowable bearings~~ may be within a much lower range, requiring substantial enlargement of footings. In such cases, fairly detailed test data (SPT, Qu, and even pocket penetrometer data) may be needed to make judgments about allowable footing loads.

	===321.2.3.6 Philosophy ===		===321.2.3.6 Philosophy ===

Hoskir: /* 321.3.3.4 Division of Responsibility */ fixed typo

2026-10-26T15:12:38Z

321.3.3.4 Division of Responsibility: fixed typo

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	:: Amount of settlement estimates have been found to be fairly accurate. Actual rates of settlement are usually, but not always faster, than predicted. If a predicted time of settlement appears critical, office calculations are checked by doing field permeability tests and back figuring coefficients of consolidation. Usually, field perms will indicate much faster drainage, but sometimes agree very well with predictions based on laboratory tests. Before using vertical sand drains or any very expensive solution, field permeability testing should be done.		:: Amount of settlement estimates have been found to be fairly accurate. Actual rates of settlement are usually, but not always faster, than predicted. If a predicted time of settlement appears critical, office calculations are checked by doing field permeability tests and back figuring coefficients of consolidation. Usually, field perms will indicate much faster drainage, but sometimes agree very well with predictions based on laboratory tests. Before using vertical sand drains or any very expensive solution, field permeability testing should be done.

	===321.3.3.4 Division of Responsibility ===		===321.2.3.4 Division of Responsibility ===

	'''1. The Bridge Unit or district prepares a sounding layout with a suggested boring plan. '''		'''1. The Bridge Unit or district prepares a sounding layout with a suggested boring plan. '''

Hoskir: /* 321.3.3.4 Division of Responsibility */ updated per RR4244

2026-10-26T15:08:33Z

321.3.3.4 Division of Responsibility: updated per RR4244

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	'''5. Bridges.''' The Bridge Unit will design the foundation units in almost all cases but may ask for design assistance in certain instances. It is the geotech's responsibility to furnish data inputs of the type and quantity required to design those foundation types which are technically and economically feasible at each site. This infers that the geotech must have the capability and knowledge, and must have developed the information necessary to design the foundation if requested to do so. Keep in mind that a foundation cannot be designed in isolation. You can design an individual pile or footing but you must also know column and bent loads, group or cluster effects, embankment "drag loads", etc. and understand the interactions of the resulting stresses.		'''5. Bridges.''' The Bridge Unit will design the foundation units in almost all cases but may ask for design assistance in certain instances. It is the geotech's responsibility to furnish data inputs of the type and quantity required to design those foundation types which are technically and economically feasible at each site. This infers that the geotech must have the capability and knowledge, and must have developed the information necessary to design the foundation if requested to do so. Keep in mind that a foundation cannot be designed in isolation. You can design an individual pile or footing but you must also know column and bent loads, group or cluster effects, embankment "drag loads", etc. and understand the interactions of the resulting stresses.

	'''6. ~~Allowable~~ Bearing.''' "~~Allowable~~ bearing" is not an intrinsic soil property but rather is a value based upon intrinsic soil properties as influenced by a specific arrangement of specific types, dimensions, and loadings of foundation units and the resulting distributions of stresses. It is not to be confused with "presumptive bearing values" or any specific measure of soil strength. While in most instances the distinction may seem academic, it can be a critical distinction. Examples: (1) A single square footing will have a different "~~allowable~~ bearing" than a strip footing or a rectangular footing and that of either type may be adversely affected by the proximity of another bearing unit. (2) Similarly, the capacity of a single friction pile or a single earth anchor may be reduced by the proximity of similar units. In any case, "~~allowable~~ bearing" is influenced not only by the factor of safety against failure (the usual criterion) but also by considerations of allowable deformations in the structure. The underlying reason why higher factors of safety against bearing failure are utilized than for other failure modes is to limit deformation. Keeping unit loads near the unconfined compressive strength (not in excess of about 1.2 Qu) keeps loads at or below the preconsolidation value of the soil.		'''6. Nominal Bearing resistance.''' "Nominal bearing resistance" is not an intrinsic soil property but rather is a value based upon intrinsic soil properties as influenced by a specific arrangement of specific types, dimensions, and loadings of foundation units and the resulting distributions of stresses. It is not to be confused with "presumptive bearing values" or any specific measure of soil strength. While in most instances the distinction may seem academic, it can be a critical distinction. Examples: (1) A single square footing will have a different "nominal bearing resistance" than a strip footing or a rectangular footing and that of either type may be adversely affected by the proximity of another bearing unit. (2) Similarly, the capacity of a single friction pile or a single earth anchor may be reduced by the proximity of similar units. In any case, "nominal bearing resistance" is influenced not only by the factor of safety against failure (the usual criterion) but also by considerations of allowable deformations in the structure. The underlying reason why higher factors of safety against bearing failure are utilized than for other failure modes is to limit deformation. Keeping unit loads near the unconfined compressive strength (not in excess of about 1.2 Qu) keeps loads at or below the preconsolidation value of the soil.

	===321.2.3.5 Practical Considerations ===		===321.2.3.5 Practical Considerations ===

Hoskir: /* 321.2.3.3 General Procedures */ updated per RR4244

2026-10-26T15:03:53Z

321.2.3.3 General Procedures: updated per RR4244

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	The first step after receipt of a request from the Bridge Unit or district is a file search for soil survey reports, preliminary bridge reports, and foundation reports for adjacent structures. A packet of information, which includes plans, correspondence, and prior reports is assembled for field use. Next, the district is consulted for advice as to field conditions, problems with utilities, crops, landowners, etc. If site access conditions are especially bad, someone from the [http://sharepoint/systemdelivery/CM/geotechnical/default.aspx Geotechnical Section] may visit the site to determine what equipment may be needed and how the site can be reached. As noted previously, either the Bridge Unit or the district's boring plan may be modified as appropriate given site conditions and constraints. Some of the considerations here include:		The first step after receipt of a request from the Bridge Unit or district is a file search for soil survey reports, preliminary bridge reports, and foundation reports for adjacent structures. A packet of information, which includes plans, correspondence, and prior reports is assembled for field use. Next, the district is consulted for advice as to field conditions, problems with utilities, crops, landowners, etc. If site access conditions are especially bad, someone from the [http://sharepoint/systemdelivery/CM/geotechnical/default.aspx Geotechnical Section] may visit the site to determine what equipment may be needed and how the site can be reached. As noted previously, either the Bridge Unit or the district's boring plan may be modified as appropriate given site conditions and constraints. Some of the considerations here include:
			: '''1. General knowledge of conditions in the physiographic or geologic area where the work is to be done.''' This strongly influences the kind of investigation which should be performed and how detailed it should be. For example, in the Springfield area, residual clay over heavily pinnacled rock is likely and the most important thing is to map the rock surface irregularities with a lot of auger borings to rock so that point bearing pile lengths can be determined. In the bootheel area, auger borings are virtually worthless and standard penetration test borings for design of friction piles are most important.
	:'''1. General knowledge of conditions in the physiographic or geologic area where the work is to be done.''' This strongly influences the kind of investigation which should be performed and how detailed it should be. For example, in the Springfield area, residual clay over heavily pinnacled rock is likely and the most important thing is to map the rock surface irregularities with a lot of auger borings to rock so that point bearing pile lengths can be determined. In the bootheel area, auger borings are virtually worthless and standard penetration test borings for design of friction piles are most important.		: '''2. Site access conditions are a very practical consideration.''' It may just not be feasible to drill a hole in the middle of an urban interstate highway and it may be extremely difficult and/or expensive to drill one in the middle of a river. That is where judgments must be made about how necessary that particular boring is: can conditions be reasonably extrapolated from offset borings, would geophysical methods work as well, etc.? In many cases, the borings can be omitted with little risk. In other situations, considerable expense and trouble may be justified to get on location. This may involve a different type of equipment, hiring a bulldozer, mobilizing the portable barge, or temporarily blocking a lane of roadway. The most extreme access problems involve major river or lake crossings where barges, tugs, and support services must be provided by contract.
			: '''3. The third consideration involves foundation conditions actually encountered as the investigation progresses.''' This is a principal reason why all MoDOT foundation investigations are supervised in the field by trained personnel. If conditions encountered are different than anticipated, it is expected that the scope of the investigation will be adjusted as necessary to fit actual conditions.
	:'''2. Site access conditions are a very practical consideration.''' It may just not be feasible to drill a hole in the middle of an urban interstate highway and it may be extremely difficult and/or expensive to drill one in the middle of a river. That is where judgments must be made about how necessary that particular boring is: can conditions be reasonably extrapolated from offset borings, would geophysical methods work as well, etc.? In many cases, the borings can be omitted with little risk. In other situations, considerable expense and trouble may be justified to get on location. This may involve a different type of equipment, hiring a bulldozer, mobilizing the portable barge, or temporarily blocking a lane of roadway. The most extreme access problems involve major river or lake crossings where barges, tugs, and support services must be provided by contract.		: '''4. As previously noted, the Geotechnical Section rarely makes recommendations for specific foundation types.''' The basic aim is to furnish the Bridge Unit with the information needed to develop designs for foundation types practical for a particular site. Several rules of thumb are helpful in deciding what is practical. For example:
			:: '''a. Spread footings'''
	:'''3. The third consideration involves foundation conditions actually encountered as the investigation progresses.''' This is a principal reason why all MoDOT foundation investigations are supervised in the field by trained personnel. If conditions encountered are different than anticipated, it is expected that the scope of the investigation will be adjusted as necessary to fit actual conditions.

	:'''4. As previously noted, the Geotechnical Section rarely makes recommendations for specific foundation types.''' The basic aim is to furnish the Bridge Unit with the information needed to develop designs for foundation types practical for a particular site. Several rules of thumb are helpful in deciding what is practical. For example:

	::'''a. Spread footings'''

	::Spread footings for bridges will not be considered unless foundation material has an unconfined compressive strength of 3 tsf or more, and such material is within a fairly shallow depth. If firm material is 10 feet or more below final grade line, then piles will be used.		::Spread footings for bridges will not be considered unless foundation material has an unconfined compressive strength of 3 tsf or more, and such material is within a fairly shallow depth. If firm material is 10 feet or more below final grade line, then piles will be used.
			:: '''b. Deep Foundations '''
	::'''b. Deep Foundations '''		:: MoDOT guidelines used to estimate how far to carry standard penetration tests for design of friction piles are 30 continuous feet of bearing strata with an N60 value of 20 or greater. It is normal practice to drill half again as deep, or at least 100 ft. in any case, to check depth to rock for a point-bearing option. Point bearing is usually a feasible option almost everywhere in the state except in the southeast lowlands or "bootheel" area where sands extend to depths of several thousand feet. Even here, however, a careful check must be made for the possible presence of soft clay layers within and just below the range of probable friction pile penetration.
			:: '''c. Culverts with Floor Slab Omitted '''
	::MoDOT guidelines used to estimate how far to carry standard penetration tests for design of friction piles are 30 continuous feet of bearing strata with an N60 value of 20 or greater. It is normal practice to drill half again as deep, or at least 100 ft. in any case, to check depth to rock for a point-bearing option. Point bearing is usually a feasible option almost everywhere in the state except in the southeast lowlands or "bootheel" area where sands extend to depths of several thousand feet. Even here, however, a careful check must be made for the possible presence of soft clay layers within and just below the range of probable friction pile penetration.		:: Large box culverts may be built more economically if a floor slab can be omitted. The Bridge Unit feels this is generally feasible if rock is within five feet of flowline. So, where rock may be shallow, an attempt is made to drill auger holes every 25 ft. or so along each proposed wall. An attempt is made to judge the durability of the rock based on inspection of exposures and cores and knowledge of past performance of particular formations. The rock should have an RQD equal to or greater than 75 and should not be thin bedded. If rock is deeper, only a few auger borings to verify this fact may be sufficient.
			:: '''d. Culverts with Compressible Foundations '''
	::'''c. Culverts with Floor Slab Omitted '''		:: Culverts, if built over compressible foundations, may require special investigations based on undisturbed sampling to determine need for camber to compensate for settlement and to assess the danger of joints opening due to spreading caused by settlement. In some areas of the state where this is a particular problem, structural collars are sometimes recommended around joints to control spreading and faulting and piping of silty soils into opened joints.
			:: '''e. Retaining Structures '''
	::Large box culverts may be built more economically if a floor slab can be omitted. The Bridge Unit feels this is generally feasible if rock is within five feet of flowline. So, where rock may be shallow, an attempt is made to drill auger holes every 25 ft. or so along each proposed wall. An attempt is made to judge the durability of the rock based on inspection of exposures and cores and knowledge of past performance of particular formations. The rock should have an RQD equal to or greater than 75 and should not be thin bedded. If rock is deeper, only a few auger borings to verify this fact may be sufficient.		:: Analysis and design of retaining walls should be performed as per guidance in [[751.24_Retaining_Walls\|EPG 751.24]] and FHWA GEC 011. For retaining structures, information is obtained for determination of nominal bearing resistance, resistance factor and angles of internal friction of the materials to be retained and the foundation material. The latter can be done by correlation to Plasticity Index (PI) for walls of low height (using the average correlation less one standard deviation), [[321.2_Geotechnical_Guidelines#321.2.10.5_Correlations_of_Strength_Characteristics\|EPG 321.2.10.5]], and by drained shear testing for higher and more critical structures. In some cases, it may be necessary to obtain undisturbed samples for testing in order to evaluate overall stability of the slope of which the wall will be a component. Evaluation of external stability including bearing resistance, sliding and global or overall stability is a Geotechnical Section responsibility and should be completed as per AASHTO LRFD Section 11 and FHWA GEC 011. If inadequate global stability is likely, possible solutions are evaluated - such as lowering the base of the wall, increasing the width to height ratio and excavation and replacement with rock fill, etc.
			:: '''f. Spill and Channel Slopes '''
	::'''d. Culverts with Compressible Foundations '''		:: The Geotechnical Section attempts to furnish overall guidance on prudent slope selection. This was done first by development of criteria, based on soil type and geologic origin, which is used by the district geologist in making project slope recommendations. Secondly, a review is made, often by specific request of the Bridge Unit, of the adequacy of embankment stability in the vicinity of the bridge ends, particularly at stream crossings. Geotechnical recommendations may affect bridge length, the fill end slopes, and erosion control measures for the channel banks. Often, for example, evidence will be found of channel bank failures which reflect a need for bank stabilization or bridge lengthening.
			:: '''g. Special Investigations '''
	::Culverts, if built over compressible foundations, may require special investigations based on undisturbed sampling to determine need for camber to compensate for settlement and to assess the danger of joints opening due to spreading caused by settlement. In some areas of the state where this is a particular problem, structural collars are sometimes recommended around joints to control spreading and faulting and piping of silty soils into opened joints.		:: These investigations were discussed in Section I where it was noted that, while normally initiated by the district as part of the soil survey, a problem may not be identified until final bridge soundings are being done. Undisturbed foundation sampling is done or supervised by a geologist, engineer, or senior technician. Large diameter samples are strongly preferred, often of 5 in. diameter, although 3 in. diameter samples are also commonly taken. In very soft soils, piston samplers are used in lieu of the normal Shelby tubes. Continuous undisturbed sampling is preferred, with frequent use of a 5 in. sampler, then a 3 in. sampler, followed by pushing a split spoon for inspection before cleaning the hole and restarting the cycle. MoDOT practice differs from that of many agencies in that soil samples are routinely extruded in the field. This permits thorough inspection and logging, obtaining field moisture and Atterberg Limits Classification samples, and preliminary field testing with the Torvane and Pocket Penetrometer. Most important, it permits the technical supervisor to develop a good feel for the problem as the investigation progresses. Samples are selected and designated at this time for certain types of testing, wrapped in foil, and sealed in wax in cartons for transport back to the lab. [[image:321.2.3.3.jpg\|right\|275px\|thumb\|<center>'''Direct Shear Testing'''</center>]]For a typical problem involving an embankment settlement and stability problem, the lab testing program will include moisture contents, Atterberg limits, consolidation tests, unconfined compression, and drained, direct shear tests, all supplemented by Torvane and Pocket Penetrometer tests. Stability analyses are performed using a computer program, either circle analysis (Bishop), block and wedge (Spenser), or both as may be most appropriate for particular circumstances. Total strengths are used to assess the initial or rapid construction case. Effective stress analyses are used to assess fully consolidated conditions as well as intermediate degrees of consolidation. This data can be interpreted to assess the need for controls on rate of construction.
			:: Amount of settlement estimates have been found to be fairly accurate. Actual rates of settlement are usually, but not always faster, than predicted. If a predicted time of settlement appears critical, office calculations are checked by doing field permeability tests and back figuring coefficients of consolidation. Usually, field perms will indicate much faster drainage, but sometimes agree very well with predictions based on laboratory tests. Before using vertical sand drains or any very expensive solution, field permeability testing should be done.
	::'''e. Retaining Structures '''

	::For retaining structures, information is obtained for determination of ~~allowable footing~~ bearing ~~pressures~~ and angles of internal friction of the materials to be retained and the foundation material. The latter is done by correlation to Plasticity Index (PI) for walls of low height (using the average correlation less one standard deviation), ~~Appendix F~~, and by drained shear testing for higher and more critical structures. In some cases, it may be necessary to obtain undisturbed samples for testing in order to evaluate overall stability of the slope of which the wall will be a component. ~~By agreement with the Bridge Unit~~, ~~evaluation of~~ global or overall stability is a Geotechnical Section responsibility. If inadequate global stability is likely, possible solutions are evaluated - such as lowering the base of the wall, increasing the width to height ratio and excavation and replacement with rock fill, etc.

	::'''f. Spill and Channel Slopes '''

	::The Geotechnical Section attempts to furnish overall guidance on prudent slope selection. This was done first by development of criteria, based on soil type and geologic origin, which is used by the district geologist in making project slope recommendations. Secondly, a review is made, often by specific request of the Bridge Unit, of the adequacy of embankment stability in the vicinity of the bridge ends, particularly at stream crossings. Geotechnical recommendations may affect bridge length, the fill end slopes, and erosion control measures for the channel banks. Often, for example, evidence will be found of channel bank failures which reflect a need for bank stabilization or bridge lengthening.

	::'''g. Special Investigations '''

	::These investigations were discussed in Section I where it was noted that, while normally initiated by the district as part of the soil survey, a problem may not be identified until final bridge soundings are being done. Undisturbed foundation sampling is done or supervised by a geologist, engineer, or senior technician. Large diameter samples are strongly preferred, often of 5 in. diameter, although 3 in. diameter samples are also commonly taken. In very soft soils, piston samplers are used in lieu of the normal Shelby tubes. Continuous undisturbed sampling is preferred, with frequent use of a 5 in. sampler, then a 3 in. sampler, followed by pushing a split spoon for inspection before cleaning the hole and restarting the cycle. MoDOT practice differs from that of many agencies in that soil samples are routinely extruded in the field. This permits thorough inspection and logging, obtaining field moisture and Atterberg Limits Classification samples, and preliminary field testing with the Torvane and Pocket Penetrometer. Most important, it permits the technical supervisor to develop a good feel for the problem as the investigation progresses. Samples are selected and designated at this time for certain types of testing, wrapped in foil, and sealed in wax in cartons for transport back to the lab. [[image:321.2.3.3.jpg\|right\|275px\|thumb\|<center>'''Direct Shear Testing'''</center>]]For a typical problem involving an embankment settlement and stability problem, the lab testing program will include moisture contents, Atterberg limits, consolidation tests, unconfined compression, and drained, direct shear tests, all supplemented by Torvane and Pocket Penetrometer tests. Stability analyses are performed using a computer program, either circle analysis (Bishop), block and wedge (Spenser), or both as may be most appropriate for particular circumstances. Total strengths are used to assess the initial or rapid construction case. Effective stress analyses are used to assess fully consolidated conditions as well as intermediate degrees of consolidation. This data can be interpreted to assess the need for controls on rate of construction.

	::Amount of settlement estimates have been found to be fairly accurate. Actual rates of settlement are usually, but not always faster, than predicted. If a predicted time of settlement appears critical, office calculations are checked by doing field permeability tests and back figuring coefficients of consolidation. Usually, field perms will indicate much faster drainage, but sometimes agree very well with predictions based on laboratory tests. Before using vertical sand drains or any very expensive solution, field permeability testing should be done.

	===321.3.3.4 Division of Responsibility ===		===321.3.3.4 Division of Responsibility ===

Hoskir: /* 321.2.1.2 Types of Reports */ undo RR4175 rev not ready yet

2026-05-06T16:05:31Z

321.2.1.2 Types of Reports: undo RR4175 rev not ready yet

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	'''2. The preliminary bridge foundation report,''' which is submitted by the district as an adjunct to the soil survey report, is usually furnished to the Bridge Unit for their guidance in preparing preliminary bridge layouts and to the Materials Engineering Unit for guidance in conducting a more detailed foundation investigation. (Preliminary borings for such reports may be omitted where access problems are especially difficult.)		'''2. The preliminary bridge foundation report,''' which is submitted by the district as an adjunct to the soil survey report, is usually furnished to the Bridge Unit for their guidance in preparing preliminary bridge layouts and to the Materials Engineering Unit for guidance in conducting a more detailed foundation investigation. (Preliminary borings for such reports may be omitted where access problems are especially difficult.)

	'''3. The final foundation investigation report''' ~~will provide the requested properties~~ from ~~Form A of~~ the Bridge ~~Division Request for Soil Properties~~ in ~~accordance with EPG Sections 320, 321, 700 and other applicable sections. The report will also provide seismic properties as requested on Form B~~. The Bridge ~~Division~~ or District ~~will provide the~~ preliminary ~~structure~~ layout and ~~location of each foundation location~~. ~~The Geotechnical Section~~ will ~~determine~~ boring locations ~~and sampling frequency based on guidance in, EPG 321~~.~~2 Geotechnical Guidelines~~, ~~and specific site conditions~~. The Geotechnical Section ~~may make~~ recommendations for specific foundation types ~~if site conditions require special considerations~~. The ~~intent~~ is to ~~provide~~ the Bridge ~~Division~~ or District with the information needed to develop designs for ~~the~~ foundation types practical for a particular site. Rules of thumb as to what is practical have been developed jointly by the Geotechnical Section and the Bridge ~~Division~~. These are discussed in ~~the applicable sections within the EPG~~.		'''3. The final foundation investigation report''' for structures starts with a formal request from either the Bridge Unit or District following procedures in FS-25 of the Materials Manual. The Bridge Unit or District provides a preliminary layout and a suggested boring plan. This boring plan typically will call for a core and/or standard penetration boring at every other bent with auger borings at the remaining column locations. By prior agreement, it is understood that this suggested boring plan is only a guide which will be modified as deemed necessary. The Geotechnical Section only rarely makes recommendations for specific foundation types. The basic aim is to furnish the Bridge Unit or District with the information needed to develop designs for those foundation types practical for a particular site. Rules of thumb as to what is practical have been developed jointly by the Geotechnical Section and the Bridge Unit. These are discussed elsewhere in this document.

	===321.2.1.3 "Special Investigations" ===		===321.2.1.3 "Special Investigations" ===

Hoskir: /* 321.2.1.2 Types of Reports */ updated per RR4175

2026-05-06T15:57:58Z

321.2.1.2 Types of Reports: updated per RR4175

← Older revision		Revision as of 10:57, 6 May 2026
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	'''2. The preliminary bridge foundation report,''' which is submitted by the district as an adjunct to the soil survey report, is usually furnished to the Bridge Unit for their guidance in preparing preliminary bridge layouts and to the Materials Engineering Unit for guidance in conducting a more detailed foundation investigation. (Preliminary borings for such reports may be omitted where access problems are especially difficult.)		'''2. The preliminary bridge foundation report,''' which is submitted by the district as an adjunct to the soil survey report, is usually furnished to the Bridge Unit for their guidance in preparing preliminary bridge layouts and to the Materials Engineering Unit for guidance in conducting a more detailed foundation investigation. (Preliminary borings for such reports may be omitted where access problems are especially difficult.)

	'''3. The final foundation investigation report''' ~~for structures starts with a formal request~~ from ~~either~~ the Bridge ~~Unit or District following procedures~~ in ~~FS-25 of the Materials Manual~~. The Bridge ~~Unit~~ or District ~~provides a~~ preliminary layout and ~~a suggested boring plan~~. ~~This boring plan typically~~ will ~~call for a core and/or standard penetration~~ boring ~~at every other bent with auger borings at the remaining column~~ locations. ~~By prior agreement~~, ~~it is understood that this suggested boring plan is only a guide which will be modified as deemed necessary~~. The Geotechnical Section ~~only rarely makes~~ recommendations for specific foundation types. The ~~basic aim~~ is to ~~furnish~~ the Bridge ~~Unit~~ or District with the information needed to develop designs for ~~those~~ foundation types practical for a particular site. Rules of thumb as to what is practical have been developed jointly by the Geotechnical Section and the Bridge ~~Unit~~. These are discussed ~~elsewhere~~ in ~~this document~~.		'''3. The final foundation investigation report''' will provide the requested properties from Form A of the Bridge Division Request for Soil Properties in accordance with EPG Sections 320, 321, 700 and other applicable sections. The report will also provide seismic properties as requested on Form B. The Bridge Division or District will provide the preliminary structure layout and location of each foundation location. The Geotechnical Section will determine boring locations and sampling frequency based on guidance in, EPG 321.2 Geotechnical Guidelines, and specific site conditions. The Geotechnical Section may make recommendations for specific foundation types if site conditions require special considerations. The intent is to provide the Bridge Division or District with the information needed to develop designs for the foundation types practical for a particular site. Rules of thumb as to what is practical have been developed jointly by the Geotechnical Section and the Bridge Division. These are discussed in the applicable sections within the EPG.

	===321.2.1.3 "Special Investigations" ===		===321.2.1.3 "Special Investigations" ===

Hoskir: updated link

2025-04-17T18:53:53Z

updated link

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	* [http://epg.modot.org/documents/321_Fill_Slope_Guide.pdf Fill Slope Guide]		* [http://epg.modot.org/documents/321_Fill_Slope_Guide.pdf Fill Slope Guide]
	* [http://epg.modot.org/documents/321_Geophysical_Methods_FHWA_1998.pdf Geophysical Methods FHWA 1998]		* [http://epg.modot.org/documents/321_Geophysical_Methods_FHWA_1998.pdf Geophysical Methods FHWA 1998]
			* [https://highways.fhwa.dot.gov/sites/fhwa.dot.gov/files/FHWA-NHI-16-072.pdf Geotechnical Site Characterization]
	* [http://epg.modot.org/documents/321_Modified_State_Plane.pdf Modified State Plane]		* [http://epg.modot.org/documents/321_Modified_State_Plane.pdf Modified State Plane]
	* [http://epg.modot.org/documents/321_MoDOT_Field_Log_Protocol.pdf MoDOT Field Log Protocol]		* [http://epg.modot.org/documents/321_MoDOT_Field_Log_Protocol.pdf MoDOT Field Log Protocol]
	* [http://epg.modot.org/documents/321_p-y_Curve_Criteria.pdf P-Y Curve Criteria]		* [http://epg.modot.org/documents/321_p-y_Curve_Criteria.pdf P-Y Curve Criteria]
	* [http://epg.modot.org/documents/321_Seismic_Procedure.pdf Seismic Procedure]		* [http://epg.modot.org/documents/321_Seismic_Procedure.pdf Seismic Procedure]
	* [[media:321 Soil and Rock Properties FHWA 2002.pdf \|Soil and Rock Properties, FHWA 2002]]
	* [http://epg.modot.org/documents/321_Soil_Profile_Type.pdf Soil Profile Type]		* [http://epg.modot.org/documents/321_Soil_Profile_Type.pdf Soil Profile Type]
	* [[media:Split Spoon Test in Shale.doc\|Split Spoon Test in Shale]]		* [[media:Split Spoon Test in Shale.doc\|Split Spoon Test in Shale]]

Hoskir: fixed spelling error

2025-04-17T18:01:38Z

fixed spelling error

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	<div style="float: right; margin-top: 5px; margin-left: 15px; width:320px; font-size: 95%; background-color: #f8f9fa; padding: 0.3em; border: 1px solid #a2a9b1; text-align:left;">		<div style="float: right; margin-top: 5px; margin-left: 15px; width:320px; font-size: 95%; background-color: #f8f9fa; padding: 0.3em; border: 1px solid #a2a9b1; text-align:left;">
	'''<u><center>~~Sdditional~~ Resources</center></u>'''		'''<u><center>Additional Resources</center></u>'''
	* [[media:I 64.pdf\|Design Skin Friction and End-bearing of Drilled Shafts in Shale, I-64 Project]]		* [[media:I 64.pdf\|Design Skin Friction and End-bearing of Drilled Shafts in Shale, I-64 Project]]
	* [http://epg.modot.org/documents/321_Field_Guide.pdf Field Guide]		* [http://epg.modot.org/documents/321_Field_Guide.pdf Field Guide]