RAD­HI­CA DE SIL­VA

rad­hi­ca.sookraj@guardian.co.tt

Soil ero­sion dur­ing trop­i­cal down­pours has been oc­cur­ring in T&T for decades, but with­in re­cent times, mas­sive land­slides have been de­vel­op­ing at an alarm­ing rate, in ar­eas nev­er be­fore seen.

Last week­end fol­low­ing sev­er­al days of rain­fall, sev­er­al com­mu­ni­ties were cut off due to land­slides. Ac­cess to San­gre Grande from Ma­yaro is no longer pos­si­ble with the col­lapse of the Man­zanil­la Road.

Mass slip­pages in Mamoral Bras­so, Flana­gin Town and Tabaquite left vil­lagers ma­rooned.

In Au­gust, Skin­ner Trace in Siparia be­gan slid­ing down, cap­siz­ing a house, dig­ging drains across the street, top­pling elec­tri­cal lines, and even­tu­al­ly pulling down the SS Erin Road.

In Lengua, St Croix and St Julien over 25 hous­es have col­lapsed with­in five years, dis­plac­ing dozens of peo­ple. At var­i­ous parts of Clax­ton Bay in­clud­ing Hill­top Road, Macaulay Road and Belle View, over 15 hous­es have fall­en and fam­i­lies have been forced to live with­out ba­sic ameni­ties like garbage dis­pos­al and pipe-borne wa­ter.

In the south­west­ern penin­su­lar, the South­ern Main Road has caved in mul­ti­ple places while in east Trinidad, Guayagua­yare Road, Man­zanil­la Main Road, and Rio Claro/Guayagua­yare Road have all been un­der­mined with slip­pages.

This has caused spec­u­la­tion whether the drilling of hy­dro­car­bons had weak­ened the is­land's soil struc­ture.

In Pe­nal along Scotts Road, Rivero Trace, Rock Road, Good­man Trace and Sam­my Trace, quar­ry­ing and ad-hoc de­vel­op­ment have been blamed for mak­ing the soil vul­ner­a­ble to ero­sion.

Yet still, ge­ol­o­gists, in­clud­ing Prime Min­is­ter Dr Kei­th Row­ley, spec­u­lat­ed that in­tense rain­fall and cli­mate change were re­spon­si­ble for the re­cent slip­pages, par­tic­u­lar­ly in south Trinidad, where the soil is made up most­ly of clay.

 Due to the ex­tent of dam­age in cer­tain ar­eas, Gov­ern­ment last week al­lo­cat­ed $100 mil­lion for ur­gent land­slides and road re­in­state­ment works through­out the coun­try.

In an at­tempt to un­cov­er the rea­sons for these ma­jor land slip­pages, Guardian Me­dia sought an­swers from ex­perts in­clud­ing a civ­il en­gi­neer, a geo­sci­en­tist and a ge­ot­ech­ni­cal con­sul­tant who are all fa­mil­iar with the caus­es of land­slips in T&T.

 And as the Gov­ern­ment pre­pares to em­bark on road re­ha­bil­i­ta­tion across the coun­try in the new year, these ex­perts have al­so pro­vid­ed rec­om­men­da­tions for the fu­ture as it re­lates to build­ing codes and main­te­nance of ex­ist­ing in­fra­struc­ture.

A vehicle manoeuvres over one of the seven landslides along the Penal Rock Road, Moruga, earlier this month.

KRISTIAN DE SILVA

Hy­dro­car­bon drilling and soil degra­da­tion–Is there a link?

The idea that drilling of hy­dro­car­bons has weak­ened the soil struc­ture has been de­bunked by promi­nent geo­sci­en­tist Xavier Moo­nan, who has done ex­ten­sive re­search on T&T's soils.

Moo­nan said Trinidad does not have a lime­stone struc­ture, so drilling of hy­dro­car­bons does not trig­ger land­slips.

"Be­neath most of the places that cur­rent­ly have land­slips are thou­sands of feet of sand and clay lay­ers. The ex­trac­tion of hy­dro­car­bon does not play a ma­jor role in the slip­page," he said.

How­ev­er, he ad­mit­ted that open pit quar­ry­ing can weak­en the walls of rock on the sides of the quar­ry but on­ly in the im­me­di­ate vicin­i­ty.

"Slip­page is dri­ven by over­bur­dens on the weight of the over­ly­ing rock lay­ers, build­ings, roads, road traf­fic and the sat­u­ra­tion of wa­ter in the rock. As the wa­ter sat­u­ra­tion in­creas­es, the over­all weight of the over­bur­den in­creas­es. The wa­ter al­so aids in lu­bri­cat­ing faults and frac­tures which then be­gin to move or slip," Moo­nan ex­plained.

He not­ed that quar­ry­ing usu­al­ly in­volves trucks car­ry­ing heavy loads of ma­te­r­i­al on par­tic­u­lar roads very fre­quent­ly.

But Moo­nan said poor drainage along roads was al­so a con­trib­u­to­ry fac­tor for land­slide de­vel­op­ment.

"The land may al­so slip if the in­fra­struc­ture is built on un­sta­ble clays. Al­so, if the in­fra­struc­ture is built on ridges or along ac­tive faults, across nat­ur­al wa­ter­ways with­out de­sign­ing al­ter­na­tive or by­pass routes for the wa­ter­ways," he ex­plained.

Moo­nan added that slip­page is dri­ven by grav­i­ty.

"What aids slip­page and the rate of slip­page is the weight of the over­ly­ing rock and the sat­u­ra­tion of wa­ter. The more sat­u­rat­ed the soil the greater it be­gins to be­have like a liq­uid," he added.

Moo­nan agreed with Prime Min­is­ter Dr Row­ley who said ar­eas in south Trinidad that are more prone to land­slides cor­re­late to ar­eas with very clay-rich soils.

"The clays re­tain the wa­ter, in some cas­es, they swell up­on re­ac­tion with wa­ter and be­come un­sta­ble," Moo­nan said. He agreed that the main fac­tor that geo­me­chan­i­cal­ly weak­ens the soil is the high sat­u­ra­tion of wa­ter.

Residents of Sahai Trace, St Croix Road, Princes Town, protest to highlight a landslide in their area in January.

RISHI RAGOONATH

Il­le­gal quar­ry­ing and poor drainage

Il­le­gal quar­ry­ing, back­fill­ing of drains and di­ver­sion of wa­ter cours­es have al­so been blamed for mas­sive land­slides in re­cent times. At var­i­ous parts of Pe­nal and Bar­rack­pore, in­clud­ing Sam­my Trace, Rivero Trace, Moolchan Trace and Pe­nal Rock Road, landown­ers have been quar­ry­ing to sell back­fill.

Chair­man of the Pe­nal/Debe Re­gion­al Cor­po­ra­tion Dr Allen Sam­my said that land­slips have oc­curred in these ar­eas be­cause peo­ple have quar­ried pri­vate land, back­filled prop­er­ties, clogged drains and even back­filled riv­er banks.

"Some have ap­plied for per­mis­sions to quar­ry and oth­ers have not. There is a de­mand for back­fill. More peo­ple are in­ter­est­ed in liv­ing in Pe­nal and look­ing for suit­able land," Sam­my said. When soil sta­bil­i­ty is un­der­mined, land­slides oc­cur trig­ger­ing prop­er­ty loss.

Dur­ing a re­cent En­gi­neer­ing Sem­i­nar ti­tled "Fix­ing It Right–Our Roads, Bridges and Drainage In­fra­struc­ture, ge­ot­ech­ni­cal con­sul­tant Adesh Sur­ju­nath; Rakesh Ram­nath, Pres­i­dent of Con­struc­tion Man­age­ment In­sti­tute of T&T and civ­il en­gi­neer Dr Don Samuel ex­plored the caus­es of land­slides in T&T.

Su­ru­j­nath said over­sat­u­rat­ed soils were large­ly re­spon­si­ble for re­cent slip­pages.

"Soils are be­com­ing sat­u­rat­ed from sur­face wa­ter runoff due to rain­fall. This is com­pound­ed by the re­moval of veg­e­ta­tion due to quar­ry­ing, land de­vel­op­ment and oth­er such ac­tiv­i­ties," he added.

Ex­plain­ing soil com­po­si­tion, Su­ru­j­nath said soils in cen­tral and south­ern Trinidad, tend to be fine-grained, high­ly plas­tic, and some­times ex­pan­sive clay.

 "Slopes and em­bank­ments that com­prise this type of clay soil lose strength and be­come less sta­ble when sat­u­rat­ed, thus lead­ing to slope move­ments," he ex­plained

He not­ed that north­ern Trinidad com­pris­es main­ly gran­u­lar soils, that is soils that con­tain pre­dom­i­nant­ly grav­el and sand-sized par­ti­cles.  

Why did the Man­zanil­la road col­lapse?

Mean­while, civ­il en­gi­neer Dr Don Samuel said the re­cent col­lapse of the Man­zanil­la-Ma­yaro Road oc­curred be­cause of no road­side drainage. He said the in­flux of stormwa­ter un­der­mined the road struc­ture.

"We need to fol­low the ad­vice of our ge­ot­ech­ni­cal con­sul­tants and en­gi­neers to as­sist with ro­bust de­sign so­lu­tions. For ex­am­ple, re­tain­ing walls are used to pre­vent land­slips, but the ge­ot­ech­ni­cal en­gi­neer knows which type of re­tain­ing wall is ap­pro­pri­ate for the type of soil fail­ure giv­en that the soil de­sign pa­ra­me­ters have been ex­tract­ed from test­ing," he said.

"As with all in­fra­struc­tur­al re­pairs in this coun­try, we need to go back to first prin­ci­ples which pro­vide sim­ple but ef­fec­tive tech­ni­cal so­lu­tions."

The home of Safeena Mohammed which was destroyed by a landslide at St Croix Road, Princes Town, recently.

KRISTIAN DE SILVA

Lack of main­te­nance

Re­cent­ly, Prime Min­is­ter Dr Row­ley ad­mit­ted that main­te­nance of road in­fra­struc­ture had been ne­glect­ed over the past few years. Cli­mate change and in­tense rain­fall ex­ac­er­bat­ed by poor main­te­nance led to the col­lapse of many road­ways.

Dr Samuel agrees that poor main­te­nance is a cru­cial fac­tor that must be ad­dressed.

"The longer the na­tion waits to as­sess, eval­u­ate and re­pair se­vere­ly di­lap­i­dat­ed roads, the more ur­gent the is­sue be­comes. We are now see­ing pho­tographs of roads with ma­jor de­pres­sions which pro­vide clear ev­i­dence of the sit­u­a­tion but what we do not re­al­ize is that roads which have mi­nor de­pres­sions are just the start of the jour­ney to­wards a di­lap­i­dat­ed road," Dr Samuel said.

"Roads are not sup­posed to have mi­nor de­pres­sion. When rain falls, pud­dles of wa­ter col­lect on the roads. Wa­ter col­lect­ing in these mi­nor de­pres­sions can lead to un­safe roads."

Dr Samuel said the fix­ing roads of roads must start in the dry sea­son of 2023. He pro­pos­es new meth­ods for road re­pairs, a na­tion­al drainage study and ef­fi­cient main­te­nance of in­fra­struc­ture to safe­guard the coun­try from dev­as­tat­ing land­slides.

To be con­tin­ued