LOADS OF SEWER MANHOLES WITHIN MINING AREA

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1 Jounal of Sustainable Mining e-issn p-issn JOURNAL HOMEPAGE jsm.gig.eu The online vesion of the Jounal of Sustainable Mining is the pimay, efeence vesion of the jounal Zięba M. (24). Loads of sewe manholes within mining aea. Jounal of Sustainable Mining, 3(4), doi:.7424/jsm437 ORIGINAL PAPER Received: 2 Octobe 24 Revised: 3 Novembe 24 Published online: 29 Decembe 24 LOADS OF SEWER MANHOLES WITHIN MINING AREA Magdalena Zięba * Depatment of Suface Stuctues Potection, Cental Mining Institute (Katowice, Pol) * Coesponding autho: mieba@gig.eu, tel.: , fax: ASTRACT Pupose Methods Results Pactical implications Oiginality/ value The pupose of this pape is to pesent the method of taking into account additional extenal hoiontal loads acting on sewe manholes within mining aeas, caused by the impact of hoiontal stains on the subsuface soil laye. The detemination of the dependencies of the changes in the coss-sections of flexible manholes ise pipes (with diffeent cicumfeential stiffness) on the values of hoiontal soil stains, based on laboatoy tests. The esults include fomulas fo detemining the values of extenal hoiontal loads acting on sewe manholes within mining aeas, in paticula flexible manholes made of themoplastics. The esults will be used fo the assessment of conditions in which sewe manholes can be used within mining aeas will be beneficial when consideing the following: design, potection assessment of esistance to hoiontal stains. The pesented method is an oiginal concept. It enables the detemination of additional extenal hoiontal loads acting on sewe manholes within mining aeas, in paticula the flexible manholes made of themoplastics. It also enables the detemination of dependencies of changes in the coss-sections of ises of flexible sewe manholes (with diffeent cicumfeential stiffness) on the hoiontal soil stains. Keywods sewe manholes, loads, mining aea. INTRODUCTION The impact of mining defomations in subsuface soil laye on the stuctue of sewe manholes is manifested mainly by the inteaction of hoiontal stains. This inteaction may esult in the beaing capacity of the components of manholes being exceeded, causing them to fail as well as leading to changes in the shape of coss-sections fom the flexible (defomable) objects. In the case of modula manholes made of plastics, pefabicated concete o einfoced-concete elements, the inteaction can also cause angula deviations of such elements even a loss of tightness. The evaluation of the conditions in which the sewe manholes can be used within mining aeas consists of detemining the foundation depth fo the expected values of hoiontal stains in subsuface soil laye as well as the type condition of the soil. In ode to detemine this depth, it is necessay to know the values of the extenal hoiontal loads. These values constitute the basis fo the calculation of bending moments axial foces acting on the walls of such objects, aftewads, they ae compaed with thei beaing capacity. These loads ae also used fo detemining the values of the elative defomation of the flexible manhole coss-section, which is compaed to the pemissible defomation (Kalis, 2). This pape focuses on the impact of hoiontal stains in subsuface soil laye caused by undegound mining on the walls of, both flexible igid, sewe manholes. It was assumed that the level of goundwate is does not each the bottom of the manhole. The exemplay esults of peliminay laboatoy tests concening the impact of hoiontal soil stains on models of flexible ises of sewe manholes made of plastics with diffeent cicumfeential stiffness have been pesented. As in the case of pipelines (Mokos, 998), the coss-section defomability of the ise of a sewe manhole means its susceptibility to change of shape unde the impact of unevenly distibuted extenal hoiontal foces. This change affects the values distibution of extenal loads which ae induced by soil. An impotant paamete, which chaacteies the flexibility of sewe manholes made of plastics, is the cicumfeential stiffness of the manhole ise pipes, detemined based on test esults (Rydaowski & Walcak, 2). These ise pipes ae chaacteied by the following stiffness classes: 2, 4, 8 as well as 2 6 kn/m 2. Cental Mining Institute 24

2 Jounal of Sustainable Mining (24) 3(4), IMPACT OF HORIZONTAL SOIL STRAINS ON THE WALLS OF SEWER MANHOLES 2.. The initial state of loads of flexible igid manholes It is assumed that the distibution of extenal hoiontal loads on sewe manholes with a cicula coss-section is even befoe mining defomations in subsuface soil laye occu thei value inceases along with the foundation depth of the manhole (Fig. a Fig. b). In the case of sewe manholes made of plastics, a slight unevenness of loads on thei cicumfeences can occu. This is caused by the uneven compacting of the non-cohesive soil layes of backfill. The stesses in the soil laye at a depth of amount to (Wiłun, 23) σ γ q n q () σ σ ξ σ ξ (γ q n q) (2) whee: σ vetical stess of soil, σ hoiontal stess of soil at the main diection x (Fig. 2), σ hoiontal stess of soil at the main diection y (Fig. 2), ξ at est soil pessue coefficient, unit weight of soil, foundation depth of the analysed coss-section of the manhole, q n suface weight, q useful load of suchage ove the analysed coss-section of the manhole. a) q n+q b) ξ o(+q n+q) A = Fig.. Distibution of loads along with the foundation depth of the manhole a, distibution of loads on the cicumfeence of the manhole b Extenal hoiontal loads on sewe manholes lead to the ceation of cicumfeential compessive foces in thei walls. Themoplastics ae mateials with viscoplastic popeties thus, they ceep unde loads. The walls of manholes defom thus, the diamete of manhole ise pipes educes slightly. The soil, aound the manholes, loosens which leads to an active limit state. The lateal soil pessue coefficient educes to the limit value ξ (Petoff, 994) which is assumed in static calculations instead of the at est soil pessue coefficient ξ. In such cases, 2% of load unevenness at the cicumfeence of such objects is assumed Loads of flexible igid manholes Depending on the position of the exploitation edge, the impact of hoiontal soil stains aound the walls of a sewe manhole can be sepaated into thee stages: hoiontal soil loosening, compacting loosening again. A Rigid manholes loosening of the subsuface soil laye Loosening of the subsuface soil laye esults in the eduction of extenal hoiontal loads on objects buied within it, both in a paallel pependicula diection to the exploitation edge. At the same time, the hoiontal loads on the walls of objects ae unevenly distibuted it contibutes to changes in axial foces bending moments. In contast to flexible objects, defomation of the coss-section of igid manholes is so small that it has no impact on the values distibution of the uneven loads acting on them (Mokos, 998). Duing the hoiontal loosening of the subsuface laye of non-cohesive soil fo the hoiontal stains of 2 3 mm/m, an active limit state occus. The hoiontal stesses acting in a pependicula diection to the exploitation edge (x-axis, Fig. 2) ae detemined accoding to the following fomula σ ξ σ (3) Changes in hoiontal stesses ae as follows: Δσ σ ξ σ σ (ξ ξ ) (4) σ Δσ (ξ ξ )σ Then σ ξσ σ ξσ σ ξ (ξ ξ ) σ (6) thus, the diffeence of hoiontal stesses Δσ, acting on the walls of igid manholes at the soil loosening stage, assuming that σ > σ as well as min σ max σ, amounts to Δσ σ max σ min σ σ whee: ξ active soil pessue coefficient, Poisson s atio. (ξ ξ) ( ) σ Rigid manholes compacting of the subsuface soil laye Compacting of the subsuface soil laye esults in an incease in the values of the extenal hoiontal loads on igid manholes buied in it. In exteme cases, the pessue value can each the value of passive pessue in non-cohesive soils with defomations of 3 35 mm/m. In the immediate vicinity of the walls of the igid manholes, thee is a significant concentation of hoiontal soil stains which esults in a spatial defomation state spatial stess state within that aea, howeve slight changes in the values of vetical stesses ae ignoed. Changes in hoiontal stesses σ σ duing soil compacting, taking into account the concentation of hoiontal stains ε defined with the coefficient k (Kwiatek, 998), can be detemined based on the following dependences 2Gε 2Gkε σ (8) 2Gε σ σ (σ ξσ) (9) (5) (7)

3 36 Jounal of Sustainable Mining (24) 3(4), whee: hoiontal soil stains, G the modulus of tansvese elasticity of soil. Then σ ξσ σ ξσ 2Gε () taking into account that min σ max σ, the diffeence of hoiontal stesses Δσ acting on the walls of the igid manholes at the soil compacting stage amounts to 2Gε k Δσ σmax σmin σ σ () Flexible manholes loosening of the subsuface soil laye In cases whee an active limit state has not occued yet as a esult of ceeping plastics, loosening of the subsuface soil laye esults in the eduction of extenal hoiontal loads on flexible manholes. Simultaneously, thee is an uneven distibution of hoiontal loads at the cicumfeence of such objects it esults in the defomation of thei coss-section (the axis in a pependicula diection to the exploitation edge inceases). Due to the flexibility of coss-sections of the manholes, thee is a less unevenness of thei hoiontal loads in elation to igid objects. Moeove, the changes in soil stains ae smalle in the immediate vicinity of flexible manholes than in the vicinity of igid objects whee disode occus. An active limit state in the aea of the soil adjacent to the flexible object occus late than in the aea of the soil which is distant fom this object. The complete defomation of the coss-section of a flexible manhole 2s depends on the cicumfeential stiffness of the ise pipe the values of hoiontal soil stains at the soil laye loosening stage this can be detemined using the following fomula 2 s α d αε d (2) whee: α the incement of the elative defomation of the ise coss-section of the flexible manhole, caused by soil loosening, α the coefficient of the elative defomation of the ise coss-section of the flexible manhole fo soil loosening, d the aveage diamete of the manhole coss-section. The coefficient of elative defomation of the object s coss-section has been implemented based on the scientific wok (Kalis, 2) which is a deivative of the function () descibing the dependence between the incement of defomation of the object s coss-section the hoiontal stains of the subsuface soil laye caused by mining exploitations, afte such stains d ( ) (3) d In the case of the linea function, the coefficient is a constant detemined by the atio of the incement of elative defomation of the objects coss-section to the incement of stains which induce it (4) The value of the coefficient depends on the cicumfeential stiffness of the object, as well as the popeties compacting of the non-cohesive soil which constitutes its backfill can also depend on the foundation depth of the object. The values of the coefficient can be detemined based on the dependencies (obtained duing expeimental tests) of the defomation of coss-sections of manhole ise pipes with diffeent cicumfeential stiffness on the values of hoiontal soil stains. Assuming that the hoiontal stesses σ σ ae e- spectively σ σmin σ σmax, thei values can be detemined by the fomula (Kwiatek, 998): σ ξσ Δσ (5) σ ξ σ Δσ (6) then in such a case, the diffeence in the hoiontal stesses is σ σ σ σ Δσ α ε 3 ss Em (7) whee: E m the elasticity modulus of the mateial of which the manhole is made, s s thickness of the manhole wall, aveage adius of the manhole coss-section. The values of the hoiontal stesses, which ae educed duing the loosening of the soil laye, cannot be lowe than the value of the pessue occuing duing the active σ limit state ξ σ. Thus, the diffeence in the hoiontal stesses Δσ, acting on the walls of flexible manholes at the soil loosening stage, is σ σξ ξ Δσ (8) σ Flexible manholes compacting of the subsuface soil laye Soil compacting leads to significant unevenness in the distibution of extenal hoiontal loads on the manhole. In the case of a flexible manhole, its coss-section defoms thus, this unevenness is educed in compaison with a igid manhole. The wall of the flexible object moves back in a pependicula diection to the exploitation edge unde the pessue of soil. In such cases, the value of the hoiontal stain of soil in the aea adjacent to the manhole is lowe in compaison with a igid object. It can also be lowe than the values of hoiontal stains, caused by mining exploitation in the soil laye outside of the impact fom the object placed in it. The value of pessue is also lowe. In the paallel diection to the exploitation edge, defomation of the object s coss-section causes an additional defomation passive soil pessue in the vicinity of the manhole walls. Compacting of the subsuface soil laye causes much geate changes in loads thei geate unevenness at the cicumfeence of flexible manholes than occus duing loosening. Theefoe, the impact of hoiontal soil compacting on the stuctues of flexible sewe manholes has the most advese effect. Figue 2 shows the distibution values of loads at the cicumfeence of a flexible sewe manhole fo

4 Jounal of Sustainable Mining (24) 3(4), hoiontal soil compacting, using a modified Molin model (Janson, 23; Kalis 2). It is assumed that the axis of the cicula coss-section of a flexible object is educed by the value 2s both in a paallel diection (y-axis) a pependicula diection (x-axis) to the exploitation edge (Kalis, 2) s α d α ε d (9) 2 whee Δα is an incement of elative defomation of the object s coss-section caused by hoiontal compacting of the soil laye, Δα α ε. s y = = s, o max = Δ = + A A + = x diection at which kieunek diałania hoiontal soil poiomych odkstałceń s Δ stains act Δ guntu Δ s o max = Fig. 2. Distibution of loads at the cicumfeence of a flexible manhole at the stage of soil compacting The value of hoiontal stesses acting in a diection pependicula to the exploitation edge can be epesented by the geneal fomula σ ξ σ (2) Δσ In a diection paallel to the exploitation edge, the value of hoiontal stesses also inceases. Additionally, as a esult of the defomation of the flexible manhole coss-section, passive soil pessue occus. The exteme hoiontal stesses acting on the walls of the ise pipe of a flexible manhole in this diection can be pesented by the geneal fomula σ ξσ Δσ omax (2) whee σ omax is the exteme passive soil pessue in the y-axis. The value of passive soil pessue is popotional to the value of displacement of the flexible object s wall depends on the type condition of soil, chaacteied by the ' secant modulus of hoiontal soil eaction E s. Analogously, as fo the flexible pipes, it is assumed that the passive soil pessue has paabolic distibution (Janson, 23) with the maximum value in the diection paallel to the exploitation edge equal to s ' ' ' σo max α α ε () In the assumed distibution of hoiontal loads, soil pessue value σ is the sum of the at est soil pessue chaac-, teied by the lateal eath pessue coefficient, the stesses esulting fom the compaction of the soil laye in a pependicula diection to the exploitation edge the passive soil pessue caused by displacement of the object s walls with a paabolic distibution ' Eε ' σ ξσ Δσ a α ε ξσ a α 2 ε (23) whee: a the coefficient esulting fom the distibution of passive soil pessue, a =,5, E modulus of soil elasticity. The diffeence of hoiontal stesses σ acting on the walls of flexible manholes at the soil compacting stage, assuming that Δσ σ then σ σmin σ Δσ ε σmax σ, is α 2 3 ' ss Δσ α a Em E 2 3 ' ss σ ξσ α a Em E 2 ' E a E (24) 3. LAORATORY TESTS CONCERNING THE IMPACT OF MINING EXPLOITATION ON MANHOLES PLACED IN THE SUSURFACE SOIL LAYER ε s ε (25) (26) Only peliminay laboatoy tests consisting of detemining the dependence of changes in the deflection of cicula coss-sections of flexible manhole models on the hoiontal stains of the suounding non-cohesive soil laye cicumfeential stiffness of such models have been caied out so fa (Kalis, 2; Zięba & Kalis, 22). Equipment which enables the simulation of the impact of hoiontal soil stains on the lateal loads of undegound pipelines (Kalis, 2) sewe manholes was used in ode to cay out peliminay laboatoy tests. The changes in the diamete of the coss-section of the flexible manhole model in the diection whee the stains ae induced wee measued. The pupose of these measuements was to detemine the impact of the hoiontal compacted soil (as the most advese stage of the impact of mining exploitations on these objects) on the changes in the shape of the coss-section of flexible object models tested. Examples of esults fom two expeiments (Zięba & Kalis, 22), which wee caied out on flexible object models made of plastics with vaious cicumfeential stiffness, ae pesented below. The elative defomation α of the model s coss-section was detemined fom the dependence (3), in the case of linea dependence of defomation of the flexible object coss- -section on the hoiontal stains of soil laye, the coefficient was detemined fom the dependence (4). The gaph (Fig. 3) pesents the obtained test dependencies of the elative defomation of the coss-section of flexible

5 38 Jounal of Sustainable Mining (24) 3(4), manhole models on the hoiontal stains induced in compacted non-cohesive soil. The pictues (Photo Photo 2) pesent the condition of the coss-sections of flexible manhole models befoe afte the laboatoy tests. Wględna Relative defomacja defomation pekoju of coss-section popecnego of modelu the flexible obiektu object podatnego model, α, %,8,6,4,2,,8,6,4,2,, 2,5 5, 7,5, 2,5 5, Hoiontal Poiome odkstałcenie soil stain guntu [mm/m] [mm/m] Fig. 3. Dependence of elative defomation of coss-sections of manhole models made of polypopylene polyvinyl chloide on the hoiontal soil stains PP SN,5 Photo. Model of manhole made of polypopylene befoe (left) afte (ight) laboatoy tests PVC SN8 Photo 2. Model of manhole made of polyvinyl chloide befoe (left) afte (ight) laboatoy tests Expeiment no. was pefomed on the sample of a pipe made of polypopylene (PP) with the following paametes: aveage extenal diamete d = 57.5 mm, wall thickness s s = 2.5 mm cicumfeential stiffness SN.5 kn/m 2. The value of coefficient of elative defomation of the tested sample coss-section obtained in these stains anges fom 2.5 to mm/m was α =.85. Expeiment no. 2 was pefomed on a sample of a pipe made of polyvinyl chloide (PVC) with the following paametes: aveage extenal diamete d = 2 mm, wall thickness s s = 6. mm cicumfeential stiffness SN 8 kn/m 2. The value of the coefficient of elative defomation of the tested sample coss-section obtained in the stains anges fom to 2.5 mm/m was α =.. 4. SUMMARY AND CONCLUSIONS The impact of undegound mining exploitation on sewe manholes placed in the subsuface soil laye is manifested mainly by the inteaction of hoiontal soil stains on manhole walls. These stains cause changes in the values distibution of extenal hoiontal loads. In compaison with igid manholes, the unevenness of the distibution of such loads is lowe fo flexible objects, howeve this is, in tun, the cause of the defomation which takes place in thei coss- -sections. Hoiontal soil stains can lead to failues in the stuctue of manholes as well as a loss of tightness in the joints of elements. The evaluation of possibilities conditions in which sewe manholes can be used within mining aeas consists of the detemination of the foundation depth fo the expected values of hoiontal stains of the subsuface soil laye, as well as the type condition of soil. In ode to detemine this foundation depth, it is necessay to know the values of extenal hoiontal loads. In ode to descibe the distibution values of hoiontal loads of flexible objects, it is necessay to know the dependencies of the coss-section defomation of such objects on the values of hoiontal soil stains with diffeent cicumfeential stiffness foundation conditions. The foundation depth of stad poduced sewe manholes, geneally, should be limited, especially fo categoy III IV mining aeas o additional einfocement to thei bottom pats should be applied. ased on the esults obtained fom laboatoy tests concening the detemination of expeimental dependencies of deflection of cicula coss-sections of flexible manhole models made of polypopylene (PE) polyvinyl chloide (PVC) on the values of the hoiontal stains of the suounding soil diffeent cicumfeential stiffness of such objects in the condition of compacted non-cohesive soil, it was stated that: defomation of the flexible manhole coss-section depends, not only on the value of hoiontal soil stains caused by mining exploitation, but also on the cicumfeential stiffness of the ise pipe of this object the lowe the value of cicumfeential stiffness, the highe the value of the coefficient of elative defomation of coss-section α is, the initial compaction of non-cohesive soil (which constitutes its backfill) plays an essential ole in placing a sewe manhole. In addition, it detemines an even load pope coopeation of such objects with the suounding soil, including the esistance of these objects to the settlement caused by dynamic loads deiving fom taffic. Along with an incease in the value of the soil concentation coefficient, geate defomation of the flexible object coss-section takes place. Moeove, the foundation depth of the flexible object in the subsuface soil laye is also impotant, as well as the value of vetical stesses. Consequently the value of pessue fom the backfill on the object s walls depends on this foundation depth. Acknowledgements Souce of funding: the pape pesents the exemplay esults of laboatoy tests caied out as a pat of the statutoy eseach of the Cental Mining Institute (Compute symbol of the statutoy at the Cental Mining Institute: 82-32). Financing ody: Ministy of Science Highe Education.

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