Sta­bil­i­ty of quar­ry sides

Quar­ries used for min­er­al extrac­tion are an inte­gral part of the min­ing indus­try, sup­ply­ing raw mate­ri­als for var­i­ous sec­tors of the econ­o­my. How­ev­er, the issue of quar­ry slope sta­bil­i­ty has become par­tic­u­lar­ly impor­tant today. Increas­ing atten­tion to occu­pa­tion­al safe­ty and envi­ron­men­tal pro­tec­tion cre­ates new chal­lenges for min­ing com­pa­nies in ensur­ing the sta­ble and safe oper­a­tion of deposits.

One of the most impor­tant con­di­tions for the safe­ty of pro­duc­tion process­es in open-pit min­ing is main­tain­ing the sta­ble con­di­tion of quar­ry slopes through­out the entire oper­a­tional life­time of the quar­ry, as well as pre­serv­ing the sta­bil­i­ty of bench­es and waste dumps.

The sta­bil­i­ty of quar­ry slopes is pri­mar­i­ly deter­mined by the cor­rect selec­tion of the slope angle. Its val­ue changes as the quar­ry deep­ens and reach­es its max­i­mum at the final stage of quar­ry devel­op­ment.

The main fac­tors affect­ing quar­ry slope sta­bil­i­ty and the val­ue of the slope angle include:

• phys­i­cal and mechan­i­cal prop­er­ties of rocks (strength, water-bear­ing capac­i­ty, grain size, bed­ding, frac­tur­ing, and oth­er dis­tur­bances with­in the slopes);
• hydro­ge­o­log­i­cal and cli­mat­ic con­di­tions; the shape of the quar­ry, its dimen­sions, and oper­a­tional life­time;
• exter­nal loads act­ing on the quar­ry slope.

Two types of forces act on board the quar­ry: shift­ing and hold­ing. The first includes exter­nal loads, the mass of rocks prone to shear, and hydro­dy­nam­ic pres­sure, and the sec­ond includes the forces of inter­nal adhe­sion and fric­tion of rocks. The ratio between these forces is called the sta­bil­i­ty coef­fi­cient of rocks and deter­mines the degree of their sta­bil­i­ty. The main con­di­tion for the ulti­mate equi­lib­ri­um of min­ing rocks is the equal­i­ty of the destruc­tive force of the sum of fric­tion and adhe­sion forces. In case of vio­la­tion of this con­di­tion, the destruc­tion of the sides may occur, expressed in var­i­ous forms depend­ing on the nature of the destruc­tive forces.

The con­di­tion of indi­vid­ual ledges also affects the sta­bil­i­ty of the sides of the quar­ry. The sta­bil­i­ty of ledges depends on the choice of slope angles, the height of the ledges, the width of the work­ing and safe­ty berms, the amount of exter­nal loads on the ledge, the method of reflect­ing the min­ing rock from the mas­sif and the choice of the safest loca­tion of the ledges in rela­tion to the ele­ments of the lay­er and the ser­vice life of indi­vid­ual ledges.

The ele­ments of the ledges must have the para­me­ters pro­vid­ed for by the project, accord­ing to which their sta­bil­i­ty and the safe­ty of the work­ers are ensured. Lim­it angles of slope of non-work­ing ledges are estab­lished by design or cal­cu­la­tion based on sur­vey­ing obser­va­tions, tak­ing into account the strength, crack­ing, water con­tent and oth­er phys­i­cal and mechan­i­cal prop­er­ties of min­ing rocks.

The sta­bil­i­ty of quar­ry slopes is of cru­cial impor­tance for deter­min­ing the incli­na­tion angles of work­ing and non-work­ing slopes, the shape and dimen­sions of the quar­ry, its oper­a­tional life­time, as well as meth­ods of waste dump for­ma­tion. This para­me­ter is com­mon­ly char­ac­ter­ized by the angle of repose, that is, the angle at which an exposed rock slope remains sta­ble with­out col­lapse. The val­ue of the angle of repose for dif­fer­ent rock types varies from 20° to 80° in accor­dance with the Stan­dards for Tech­no­log­i­cal Design of Non-Metal­lic Build­ing Mate­ri­als Indus­try Enter­pris­es and is pre­sent­ed in Table 1.

Table 1. Rec­om­mend­ed quar­ry slope angles for open-pit min­ing oper­a­tions

Char­ac­ter­is­tics of rocks by strength	The slope slope angle angle at at the the time when the work was com­plet­ed	For quar­ries up to 90 m deep	For quar­ries up to 180 m deep	For quar­ries up to 240 m deep	For quar­ries up to 300m deep
Strong and very strong rocks	75 and more	60–68	57–65	53–60	48–53
Quite strong, frac­tured rocks	65–75	60–60	48–57	43–53	42–48
Medi­um-strength, ven­ti­lat­ed or frac­tured rocks	55–65	43–50	41–48	39–45	36–43
Quite soft and soft rocks	40–55	30–43	28–41	26–39	24–36
Earth rocks	25–40	21–30	20–28

The height of a bench must not exceed the lim­it­ing val­ues spec­i­fied in the Occu­pa­tion­al Safe­ty Rules for the Devel­op­ment of Min­er­al Deposits by Open-Pit Min­ing, and must also not be greater than the max­i­mum dig­ging height of the exca­va­tor. The rec­om­mend­ed bench height for the extrac­tion of loose and hard (rock) mate­ri­als is pre­sent­ed in Table 2.

Table 2. Rec­om­mend­ed bench height for open-pit min­ing of min­er­al resources

Rock type	Rock name	Ledge height	Angle of the work­ing ledge	Angle of non-work­ing ledge	Angle of non-work­ing dou­ble ledge
Rocky (hard) rocks	Strong sand­stones, quartzites, lime­stones, igneous rocks for which are char­ac­ter­ized by indi­vid­u­als larg­er than 500 mm	15–20	to 80	70–75	65–70
	Strong sed­i­men­ta­ry and meta­mor­phic rocks, the cores of which are char­ac­ter­ized by rec­tan­gu­lar sep­a­ra­tions mea­sur­ing 300–500 mm and oblique sep­a­ra­tions greater than 500 mm	15–20	70–75	60–65	57–60
	Strong rocks of intense frac­tur­ing, which are char­ac­ter­ized by sep­a­ra­tions mea­sur­ing 100–300 mm.	15–20	65–70	55–60	52–57
Semi-rock and weath­ered rocks	Sand­stones, clay shales, mud­stones	15–20	to 80	55–60	52–57
	Weath­ered or inten­sive­ly frac­tured igneous and shale rocks	10–15	65–70	50–55	50–55
	Strong­ly weath­ered rocks	10–15	55–60	45–50	45–40
	Chlo­rite, sericite and talc-chlo­rite shale	10–15	50–55	40–45	40–45
Sed­i­men­ta­ry or com­plete­ly dis­in­te­grat­ed igneous and meta­mor­phic rocks	Clays of var­i­ous com­po­si­tion, com­plete­ly dis­in­te­grat­ed igneous rocks.	10	55–60	40–55	35–40
	Sand-grav­el mix­ture with­out clay	20–50	40–45	36–38	36
	Sand-grav­el mix­ture clay	10–50	35–55	40–45	35–40
	Soups and loams	10–20	30–50	20–25
	Sands	to 10	12–18	20–25

Anoth­er impor­tant ele­ment in the arrange­ment and man­age­ment of quar­ry oper­a­tions, which sig­nif­i­cant­ly affects slope sta­bil­i­ty and oper­a­tional effi­cien­cy, is the berm. A berm is a hor­i­zon­tal or gen­tly slop­ing plat­form on a work­ing or non-work­ing quar­ry wall that sep­a­rates adja­cent bench­es in height. Two main types are dis­tin­guished: safe­ty berms and trans­port berms.

A safe­ty berm is designed to improve slope sta­bil­i­ty and reduce the over­all slope angle of the quar­ry wall, as well as to pre­vent acci­den­tal falling of rock frag­ments onto low­er bench­es. The width of a safe­ty berm is approx­i­mate­ly 0.2 of the bench height, but not less than the width required to accom­mo­date equip­ment used for load­ing and trans­port­ing fall­en rock mate­r­i­al. The min­i­mum width of a peri­od­i­cal­ly mechan­i­cal­ly cleaned berm is 8 m.

A trans­port berm is intend­ed for the place­ment of trans­porta­tion routes that con­nect work­ing bench plat­forms with main haulage ramps. Its width is deter­mined depend­ing on the type of trans­port, traf­fic inten­si­ty, and oth­er oper­a­tional fac­tors.

In addi­tion, to ensure quar­ry slope sta­bil­i­ty, the fol­low­ing mea­sures are rec­om­mend­ed:

• sys­tem­at­i­cal­ly dewa­ter the rocks form­ing the quar­ry walls, pre­vent­ing their sat­u­ra­tion with sur­face and ground­wa­ter;
• avoid under­cut­ting rock lay­ers whose bed­ding planes dip toward the exca­vat­ed space; for this pur­pose, the quar­ry slope angle should be equal to or less than the dip angle of the stra­ta;
• use rein­force­ment meth­ods for bench sta­bil­i­ty, such as rock bolt­ing (anchor­ing), cemen­ta­tion of high­ly frac­tured rocks, and shot­cret­ing of slopes;
• avoid plac­ing heavy struc­tures on slopes that are prone to slid­ing; main­tain design para­me­ters of the quar­ry walls;
• in deep quar­ries, devel­op bench­es in such a way that, at the con­tact with rocks hav­ing reduced shear resis­tance, a safe­ty plat­form is left to local­ize poten­tial land­slides occur­ring in upper hori­zons;
• leave con­tin­u­ous pil­lars (intact blocks) of sta­ble rock to pre­vent slope fail­ure and land­slide process­es.

The engi­neer­ing and tech­ni­cal per­son­nel of a quar­ry, pri­mar­i­ly the ser­vices respon­si­ble for geo­log­i­cal and mine sur­vey­ing sup­port, are oblig­ed to sys­tem­at­i­cal­ly mon­i­tor the con­di­tion of the quar­ry slopes, both work­ing and non-work­ing bench­es, and to take time­ly mea­sures to pre­vent pos­si­ble fail­ures. To pre­vent slough­ing and col­lapse of bench­es dur­ing oper­a­tion, non-work­ing quar­ry walls in over­bur­den rocks are designed with a slope angle of 45°.

Dur­ing deposit devel­op­ment, in accor­dance with the min­ing oper­a­tions sched­ule, it is planned to unload the quar­ry walls in over­bur­den rocks by remov­ing mate­r­i­al, flat­ten­ing the slopes to a sta­ble angle, and rein­forc­ing them dur­ing recla­ma­tion through sow­ing peren­ni­al grass­es and plant­i­ng shrubs.

Thus, the sta­bil­i­ty of quar­ry slopes in min­er­al extrac­tion is an extreme­ly impor­tant aspect of envi­ron­men­tal pro­tec­tion. Address­ing chal­lenges relat­ed to ero­sion, land­scape trans­for­ma­tion, and pol­lu­tion requires an inte­grat­ed approach, includ­ing plan­ning and mon­i­tor­ing, as well as the use of advanced tech­nolo­gies in design and land recla­ma­tion of deposits.